Patent Application
20220204857
The present invention relates to a dispersant, a dispersed material, a resin composition, a mixture slurry, an electrode film, and a non-aqueous electrolyte secondary battery.
Generally, it is known that, when inks and the like are produced, it is difficult to stably disperse pigments at a high concentration, which causes various problems in the production process and the product itself. For example, a dispersed material containing a pigment composed of fine particles often exhibits high viscosity, which not only makes it difficult to remove and transport a product from a dispersing machine, but also causes gelation during storage in the bad case, and it is difficult to use it. Furthermore, poor conditions such as decreased gloss and poor leveling occur on the surface of a colored object.
Thus, a dispersant is generally used to maintain a good dispersion state. The dispersant has a structure including a part that adsorbs to a pigment and a part that has a high affinity for a dispersion medium, and the performance of the dispersant is determined by the balance of these two functional parts.
Generally, when the surface of a pigment is strongly hydrophobic, an adsorption mechanism using a hydrophilic and hydrophobic interaction according to the surface of the pigment is used in order to adsorb a dispersant to the pigment, and when there is a functional group on the surface of the pigment, an adsorption mechanism using an acid/base on the surface is used.
In addition, as a method of producing a film electrode of a lithium ion battery, a method of forming a mixture slurry containing a conductive material, an active material and a dispersant into a film is known.
Since the capacity of a lithium ion secondary battery largely depends on a positive electrode active material and a negative electrode active material, which are main materials, various materials therefor have been actively researched, but the charging capacities of the active materials that have been put into practical use have all reached a value close to the theoretical value thereof, and improvements therein have neared their limit. Therefore, since the capacity can be simply increased if the amount of an active material filled into a battery is increased, there have been attempts to reduce the amount of a conductive material or a binder added that does not directly contribute to the capacity.
Regarding this, a conductive material has a function of forming a conductive path inside the battery and preventing disconnection of the conductive path due to expansion and contraction of the active material by connecting active material particles, and in order to maintain the performance with a small amount of addition, it is effective to form an efficient conductive network using nanocarbons having a large specific surface area, specifically carbon nanotubes (CNT). However, since a nanocarbon having a large specific surface area has a strong cohesive force, there is a problem that it is difficult to favorably disperse it in a mixture slurry or an electrode.
For example, regarding the dispersion of carbon black and carbon nanotubes (hereinafter referred to as a CNT), Patent Literature 1 and 2 disclose a method of producing a dispersed material using a polymer dispersant such as a polyvinyl alcohol (hereinafter referred to as a PVA) or polyvinylpyrrolidone (hereinafter referred to as a PVP). However, polymer dispersants such as PVA and PVP exhibit an effect in polar solvents such as N-methyl-2-pyrrolidone and water, but do not exhibit an effect of dispersion in other dispersion mediums.
On the other hand, Patent Literature 3 discloses an electrode binder composition of a non-aqueous electrolyte solution type battery containing a polymer having a large number of repeating units derived from a monomer containing a nitrile group and having a weight average molecular weight of 500,000 to 2,000,000. According to Patent Literature 3, it is reported that a binding force improves as the polymer has an increasing molecular weight, and it is possible to increase the lifespan of the battery.
[Patent Literature 1]
Japanese Patent Laid-Open No. 2014-193986
[Patent Literature 2]
Japanese Patent Laid-Open No. 2003-157846
[Patent Literature 3]
PCT International Publication No. WO 2012/091001
Since the above PVA and PVP are generally highly hydrophilic and have a property of being soluble in water, when used as a dispersant for carbon black, problems such as a decrease in water resistance of the coating film occur when a dispersed material is used as a coating film. For example, when a carbon dispersed material using PVA or PVP is used as a dispersed material for a lithium ion battery, problems such as deterioration in battery performance due to moisture absorption occur.
In addition, while PVA and PVP are highly hydrophilic and can secure dispersibility in water and hydrophilic solvents such as N-methylpyrrolidone (NMP), their solubility in other solvents is low, and it is difficult to deploy them in hydrophobic solvents. In addition, due to high hydrophilicity of PVA and PVP, the wettability with respect to pigments that are not highly hydrophilic is not sufficient, and the dispersion time tends to be relatively long in order to produce a stable dispersed material.
An objective of the present invention is to provide a dispersant which enables the production of a dispersed material having excellent dispersibility and storage stability even when the dispersant is used in a small amount as compared with conventional dispersants, a dispersed material having excellent dispersibility and storage stability, an electrode film having excellent adhesiveness and electrical conductivity, and a non-aqueous electrolyte secondary battery having excellent rate properties and cycle properties.
A first dispersant of the present embodiment is a polymer containing 40 to 100% by mass of a (meth)acrylonitrile-derived unit and having a weight average molecular weight of 5,000 to 400,000.
One embodiment of the first dispersant is a polymer containing less than 100% by mass of the (meth)acrylonitrile-derived unit and further containing a unit derived from one or more monomers selected from the group consisting of an active hydrogen group-containing monomer, a basic monomer, and a (meth)acrylic acid alkyl ester.
A second dispersant of the present embodiment is a polymer containing a (meth)acrylonitrile-derived unit and a unit derived from one or more monomers selected from the group consisting of an active hydrogen group-containing monomer, a basic monomer, and a (meth)acrylic acid alkyl ester,
the polymer containing 40 to 99% by mass of an acrylonitrile-derived unit and having a weight average molecular weight of 5,000 to 400,000, and
the acrylonitrile-derived unit having a cyclic structure.
A third dispersant of the present embodiment is a polymer containing an acrylonitrile-derived unit and a (meth)acrylic acid-derived unit,
the polymer containing 40 to 99% by mass of the acrylonitrile-derived unit and 1 to 40% by mass of a (meth)acrylic acid-derived unit, and having a weight average molecular weight of 5,000 to 400,000, and the dispersant having a cyclic structure from the acrylonitrile-derived unit and the (meth)acrylic acid-derived unit.
A dispersed material of the present embodiment contains a dispersion medium, the dispersant, and an object to be dispersed.
In one embodiment of the dispersed material, the object to be dispersed is one or more selected from the group consisting of a coloring agent and cellulose fibers.
In one embodiment of the dispersed material, the object to be dispersed is a conductive material.
A resin composition of the present embodiment contains the dispersed material and a binder resin.
A mixture slurry of the present embodiment contains the resin composition dispersed material and an active material.
An electrode film of the present embodiment is obtained by forming the mixture slurry into a film.
A non-aqueous electrolyte secondary battery of the present embodiment includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and at least one of the positive electrode and the negative electrode includes the electrode film.
According to the present invention, there are provided a dispersant which enables production of a dispersed material having excellent dispersibility and storage stability even when the dispersant is used in a small amount as compared with conventional dispersants, a dispersed material having excellent dispersibility and storage stability, an electrode film having excellent adhesiveness and electrical conductivity, and a non-aqueous electrolyte secondary battery having excellent rate properties and cycle properties.
First, the terms in this specification are defined.
The monomer is an ethylenically unsaturated group-containing monomer.
The polymer includes a homopolymer and a copolymer unless otherwise specified.
The monomer unit is a structural unit derived from the monomer contained in the polymer.
The proportion of the monomer units in the copolymer is based on the total amount (100% by mass) of the monomer units constituting the copolymer.
The term (meth)acrylonitrile is a general term for acrylonitrile and methacrylonitrile, and the same applies to (meth)acrylic acid and the like.
In this specification, “to” indicating a numerical range includes a lower limit value and an upper limit value thereof unless otherwise specified.
A dispersant of the present embodiment is a polymer containing 40 to 100% by mass of a (meth)acrylonitrile-derived unit and having a weight average molecular weight of 5,000 to 400,000.
This dispersant contains 40% by mass or more of a (meth)acrylonitrile-derived unit. The strong polarization of non-hydrogen bonding cyano groups and the carbon chain of the dispersed resin main chain can improve adsorption to an object to be dispersed and the affinity for a dispersion medium, and allows the object to be dispersed to be stably present in the dispersion medium. In addition, the weight average molecular weight of the dispersant is 5,000 to 400,000, and when the dispersant has an appropriate weight average molecular weight, adsorption to the object to be dispersed and the affinity for the dispersion medium are improved, and the stability of the dispersed material is excellent.
The dispersant of the present invention is preferably used in applications, such as for example, offset inks, gravure inks, resist inks for color filters, inkjet inks, paints, conductive materials, and colored resin compositions. The dispersant of the present invention prevents reaggregation of the object to be dispersed and has excellent fluidity, and thus good dispersion stability is obtained.
This dispersant may be a monopolymer composed of (meth)acrylonitrile-derived units, or may be a copolymer having other monomer units. The monomer constituting other monomer units is preferably an active hydrogen group-containing monomer (a), a basic monomer (b), or (meth)acrylic acid alkyl ester (c).
The active hydrogen group-containing monomer (a) is, as an active hydrogen group, for example, a hydroxy group-containing monomer (a1), a carboxyl group-containing monomer (a2), a primary amino group-containing monomer (a3), a secondary amino group-containing monomer (a4), or a mercapto group-containing monomer (a5). Here, the “primary amino group” is a —NH2 (amino group), and the “secondary amino group” is a group in which one hydrogen atom on a primary amino group is replaced with an organic residue such as an alkyl group. In addition, “—C(═O)—O—C(═O)—” (referred to as an “acid anhydride group” in this specification) which is a group having a structure in which two carboxyl groups are dehydrated and condensed, is also included in the active hydrogen group in this specification because it forms a carboxyl group by hydrolysis. However, a primary amino group and a secondary amino group in an acid amide are not included in the active hydrogen groups in this specification.
Examples of hydroxy group-containing monomers (a1) include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, glycerol mono(meth)acrylate, 4-hydroxyvinylbenzene, 2-hydroxy-3-phenoxypropyl acrylate and a caprolactone adduct of these monomers (the number of moles added is 1 to 5).
Examples of carboxyl group-containing monomers (a2) include unsaturated fatty acids such as (meth)acrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, and citraconic acid, and carboxyl group-containing (meth)acrylates such as 2-(meth)acryloyloxyethyl phthalate, 2-(meth)acryloyloxypropyl phthalate, 2-(meth)acryloyloxyethyl hexahydrophthalate, 2-(meth)acryloyloxypropyl hexahydrophthalate, ethylene oxide modified succinic acid (meth)acrylate, and 3-carboxyethyl (meth)acrylate. In addition, examples of carboxyl group-containing monomers (a2) include acid anhydride group-containing monomers such as maleic anhydride, itaconic anhydride, and citraconic anhydride obtained by dehydration condensation of carboxyl group-containing monomers, and monofunctional alcohol adducts of the acid anhydride-containing monomer.
Examples of primary amino group-containing monomers (a3) include aminomethyl (meth)acrylate, aminoethyl (meth)acrylate, allylamine hydrochloride, allylamine dihydrogen phosphate, 2-isopropenylaniline, 3-vinylaniline, and 4-vinylaniline.
Examples of secondary amino group-containing monomers (a4) include t-butylaminoethyl (meth)acrylate.
Examples of mercapto group-containing monomers (a5) include 2-(mercaptoacetoxy)ethyl acrylate, and allyl mercaptan.
The active hydrogen group-containing monomers (a) may be used alone or two or more thereof may be used in combination.
Among the active hydrogen group-containing monomers (a), in consideration of ease of availability of raw materials, ease of handling, affinity with a dispersion medium to be described below, and the like, the hydroxy group-containing monomer (a1) or the carboxyl group-containing monomer (a2) is preferable. Among the hydroxy group-containing monomers (a1), hydroxyalkyl (meth)acrylates are preferable, hydroxyethyl (meth)acrylate is more preferable, and hydroxyethyl acrylate is still more preferable. In addition, as the carboxyl group-containing monomer (a2), unsaturated fatty acids are preferable, (meth)acrylic acid is more preferable, and acrylic acid is still more preferable.
The basic monomer (b) is a monomer having a basic group. Examples of basic groups include a tertiary amino group, an amide group, a pyridine ring, and a maleimide group. Here, monomers having a primary amino group and monomers having a secondary amino group may be included in the basic monomers, but in the present invention, they are treated as active hydrogen group-containing monomers and are not included in the basic monomers.
Examples of basic monomers (b) include dialkylaminoalkyl (meth)acrylates such as dimethylaminoethyl (meth)acrylate, and dimethylaminopropyl (meth)acrylate; N-substituted (meth)acrylamides such as (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-isopropyl (meth)acrylamide, and acryloyl morpholine; heterocyclic aromatic amine-containing vinyl monomers such as 1-vinylpyridine, 4-vinylpyridine, and 1-vinylimidazole; N-(alkylaminoalkyl) (meth)acrylamides such as N-(dimethylaminoethyl) (meth)acrylamide, and N-(dimethylaminopropyl)acrylamide; and N,N-alkyl (meth)acrylamides such as N,N-dimethyl (meth)acrylamide and N,N-diethyl (meth)acrylamide.
The basic monomers (b) may be used alone or two or more thereof may be used in combination.
Among the basic monomers (b), in consideration of ease of availability of raw materials, ease of handling, and affinity with a dispersion medium to be described below, dimethylaminoethyl (meth)acrylate or dimethylaminopropyl (meth)acrylate is preferable, and dimethylaminoethyl acrylate is more preferable.
The (meth)acrylic acid alkyl ester (c) is a monomer having a structure represented by (R1)2C═C—CO—O—R2 (where, R1's are a hydrogen atom or a methyl group, and at least one is a hydrogen atom, and R2 is an alkyl group that may have a substituent).
Here, those containing an active hydrogen group or a basic group as a substituent for an alkyl group are treated as the active hydrogen group-containing monomer (a) or the basic monomer (b), and are not included in the (meth)acrylic acid alkyl ester (c).
Examples of (meth)acrylic acid alkyl esters (c) include chain-like alkyl group-containing (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate;
branched alkyl group-containing (meth)acrylic acid esters such as 2-ethylhexyl (meth)acrylate, (meth)isostearyl acrylate;
cyclic alkyl group-containing (meth)acrylic acid esters such as cyclohexyl (meth)acrylate, isobornyl (meth)acrylate;
aromatic ring substituted alkyl group-containing (meth)acrylic acid alkyl esters such as benzyl (meth)acrylate, phenoxyethyl (meth)acrylate;
(meth)acrylic acid alkyl esters in which a fluoro group is substituted such as trifluoroethyl (meth)acrylate and tetrafluoropropyl (meth)acrylate;
epoxy group-containing (meth)acrylic acid alkyl esters such as glycidyl (meth)acrylate, and (3-ethyl oxetane-3-yl)methyl (meth)acrylate and heterocyclic (meth)acrylates such as tetrahydrofurfuryl (meth)acrylate and 3-methyloxetanyl (meth)acrylate;
silyl ether group-containing (meth)acrylic acid alkyl esters such as 3-methacryloxypropylmethyldimethoxysilane;
alkyloxy group-containing (meth)acrylic acid alkyl esters such as 2-methoxyethyl (meth)acrylate, and (meth)polyethylene glycol monomethyl ether acrylate; and
cyclic polymerizable monomers such as 2-(allyloxymethyl)methyl acrylate.
The (meth)acrylic acid alkyl esters (c) may be used alone or two or more thereof may be used in combination.
Among the (meth)acrylic acid alkyl esters (c), in consideration of ease of availability of raw materials, ease of handling, and affinity with a dispersion medium to be described below, ethyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, or (meth)lauryl acrylate is preferable, and 2-ethylhexyl acrylate or lauryl acrylate is more preferable.
When this dispersant is a polymer containing a (meth)acrylonitrile-derived unit and a unit derived from one or more monomers selected from the group consisting of the active hydrogen group-containing monomer (a), the basic monomer (b), and the (meth)acrylic acid alkyl ester (c), the proportion of the unit of the (meth)acrylonitrile-derived monomer is preferably 40 to 99% by mass, more preferably 55 to 99% by mass, still more preferably 65 to 99% by mass, and particularly preferably 75 to 99% by mass.
In addition, the proportion of the unit derived from the active hydrogen group-containing monomer (a), the basic monomer (b), and the (meth)acrylic acid alkyl ester (c) is preferably 1 to 40% by mass, more preferably 1 to 35% by mass, and still more preferably 1 to 30% by mass.
A total amount of the proportion of the unit of the (meth)acrylonitrile-derived monomer and the proportion of the unit derived from the active hydrogen group-containing monomer (a), the basic monomer (b), and the (meth)acrylic acid alkyl ester (c) is preferably 80% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, and most preferably 98% by mass or more.
With inclusion in these ranges, the affinity between the object to be dispersed and the dispersion medium is further improved and the dispersibility is further improved.
This dispersant may further include other monomer units. Examples of monomers constituting other monomer units include styrenes such as styrene and α-methylstyrene;
vinyl ethers such as ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, and isobutyl vinyl ether;
vinyl fatty acids such as vinyl acetate and vinyl propionate; and
N-substituted maleimides such as N-phenylmaleimide and N-cyclohexylmaleimide.
The dispersant of the present invention can disperse various objects to be dispersed such as a conductive material, a coloring agent, and cellulose fibers.
A method of producing a dispersant is not particularly limited, and examples thereof include a solution polymerization method, a suspension polymerization method, a bulk polymerization method, an emulsification polymerization method, and precipitation polymerization, and a solution polymerization method or a precipitation polymerization method is preferable. Examples of polymerization reaction systems include addition polymerization such as ion polymerization, free radical polymerization, and living radical polymerization, and free radical polymerization or living radical polymerization is preferable. In addition, examples of radical polymerization initiators include peroxide and azo-based initiators. A molecular weight adjusting agent such as a chain transfer agent can be used when a dispersant is polymerized.
Examples of chain transfer agents include alkyl mercaptans such as octyl mercaptan, nonyl mercaptan, decyl mercaptan, dodecyl mercaptan, and 3-mercapto-1,2-propanediol, thioglycolic acid esters such as octyl thioglycolate, nonyl thioglycolate, and 2-ethylhexyl thioglycolate, and 2,4-diphenyl-4-methyl-1-pentene, 1-methyl-4-isopropylidene-1-cyclohexene, α-pinene, and β-pinene. In particular, 3-mercapto-1,2-propanediol, thioglycolic acid esters, 2,4-diphenyl-4-methyl-1-pentene, 1-methyl-4-isopropylidene-1-cyclohexene, α-pinene, β-pinene or the like is preferable because the obtained polymer has a low odor.
The amount of the chain transfer agent used with respect to 100 parts by mass of all monomers is preferably 0.01 to 4% by mass and more preferably 0.1 to 2% by mass. When the amount of the chain transfer agent is within the above range, the molecular weight of the dispersant of the present invention can be adjusted to be within an appropriate molecular weight range.
The weight average molecular weight of the dispersant is 5,000 or more and 400,000 or less and preferably 5,000 or more and 200,000 or less in terms of a polystyrene conversion value. When the dispersant has an appropriate weight average molecular weight, adsorption to the object to be dispersed and the affinity for the dispersion medium is improved, and the stability of the dispersed material is further improved.
Among these, in order to prevent precipitation of the dispersed material and improve the strength of the coating film, the weight average molecular weight is preferably 50,000 or more and preferably 200,000 or less, and more preferably 150,000 or less.
In addition, in order to improve the fluidity and processability of the dispersed material, the weight average molecular weight is preferably 5,000 or more, more preferably 6,000 or more, and still more preferably 7,000 or more, and preferably 100,000 or less, more preferably 75,000 or less, and still more preferably 50,000 or less.
In this dispersant, the acrylonitrile-derived unit may form a cyclic structure. When the acrylonitrile-derived unit has a cyclic structure, the dispersibility and the storage stability are further improved. When the polymer obtained by the polymerization method is treated with an alkali, the acrylonitrile-derived unit changes to a cyclic structure such as a hydrogenated naphthyridine ring. The dispersibility of this dispersant is further improved by the presence of the cyclic structure. Here, the alkaline treatment may be performed at an arbitrary timing after the copolymer is synthesized, and when heating is performed, the structure easily changes to a ring structure. In order for the acrylonitrile-derived unit to form a cyclic structure, the acrylonitrile-derived unit needs to have at least two consecutive partial structures, and preferably has three or more consecutive partial structures. A polymer having two or more consecutive partial structures is easily obtained when it contains 55% by mass or more of the acrylonitrile-derived unit and more easily obtained when it contains 65% by mass or more of the acrylonitrile-derived unit, for example, when a random polymer is polymerized by addition polymerization such as free radical polymerization. In addition, it can also be obtained by polymerizing a block polymer by addition polymerization such as ion polymerization or living radical polymerization.
In addition, when this dispersant has a (meth)acrylic acid-derived unit, the (meth)acrylic acid unit may form a cyclic structure.
When it has a (meth)acrylic acid unit, since a glutarimide ring may be formed as a cyclic structure together with the acrylonitrile-derived unit by an alkaline treatment, a ring structure such as a hydrogenated naphthyridine ring and a glutarimide ring exist together. Thereby, the dispersion stability is further improved. When this dispersant is a polymer having a (meth)acrylic acid unit that forms a cyclic structure, the amount of (meth)acrylic acid units based on all monomer units of the copolymer is preferably 1 to 40% by mass, more preferably 1 to 35% by mass, and still more preferably 1 to 30% by mass. In addition, the amount of acrylonitrile-derived units based on all monomer units of the copolymer is preferably 40 to 99% by mass, more preferably 55 to 99% by mass, still more preferably 65 to 99% by mass, and particularly preferably 75 to 99% by mass. In order to form the glutarimide ring, at least the acrylonitrile-derived unit and the acrylic acid unit need to have adjacent partial structures.
The dispersed material of the present embodiment contains a dispersion medium, the above dispersant, and an object to be dispersed. When this dispersed material contains this dispersant, a dispersed material having excellent dispersibility and storage stability of the object to be dispersed is obtained.
This dispersed material contains at least a dispersion medium, a dispersant, and an object to be dispersed, and may further contain other components as necessary. Hereinafter, components that can be contained in the dispersed material will be described, but since the dispersant is as described above, description thereof here will be omitted.
The object to be dispersed is particles dispersed in the dispersion medium, and may be appropriately selected depending on applications of the dispersed material. Examples of objects to be dispersed include coloring agents such as an organic pigment, a conductive material, an insulating material, and fibers. Here, needless to say, the object to be dispersed is not limited thereto.
Examples of coloring agents include various organic pigments and inorganic pigments used for inks and the like. Examples of pigments include soluble azo pigments, insoluble azo pigments, phthalocyanine pigments, quinacridone pigments, isoindolinone pigments, isoindoline pigments, perylene pigments, perinone pigments, dioxazine pigments, anthraquinone pigments, dianthraquinonyl pigments, anthrapyrimidine pigments, anthanthrone pigments, indanthrone pigments, flavanthrone pigments, pyranthrone pigments, and diketopyrrolopyrrole pigments. Hereinafter, specific examples shown with color index numbers include Pigment Black 7, Pigment Blue 6, 15, 15:1, 15:3, 15:4, 15:6, 60, Pigment Green 7, 36, Pigment Red 9, 48, 49, 52, 53, 57, 97, 122, 144, 146, 149, 166, 168, 177, 178, 179, 185, 206, 207, 209, 220, 221, 238, 242, 254, 255, Pigment Violet 19, 23, 29, 30, 37, 40, 50, Pigment Yellow 12, 13, 14, 17, 20, 24, 74, 83, 86, 93, 94, 95, 109, 110, 117, 120, 125, 128, 137, 138, 139, 147, 148, 150, 151, 154, 155, 166, 168, 180, 185, and Pigment Orange 13, 36, 37, 38, 43, 51, 55, 59, 61, 64, 71, and 74.
When the object to be dispersed is a coloring agent, applications of the dispersed material include, for example, offset inks, gravure inks, resist inks for color filters, inkjet inks, paints, and a resin composition for molding.
Examples of insulating materials include metal oxides such as titanium dioxide, iron oxide, antimony trioxide, zinc oxide, and silica, cadmium sulfide, calcium carbonate, barium carbonate, barium sulfate, clay, talc, and chrome yellow.
When the object to be dispersed is an insulating material, applications of the dispersed material include, for example, an insulating film for an electronic circuit.
Examples of fibers include organic fibers such as aromatic polyamide (aramid) fibers, acrylic fibers, cellulose fibers, and phenol resin fibers, and metal fibers such as steel fibers, copper fibers, alumina fibers, and zinc fibers; inorganic fibers such as glass fibers, rock wool, ceramic fibers, biodegradable fibers, biosoluble fibers, and wallastonite fibers; and carbon fibers. Among these, cellulose fibers are preferable.
When the object to be dispersed is a fiber, applications of the dispersed material include applications that take advantage of a high heat resistance, a low coefficient of linear expansion, a high elastic modulus, a high strength, and high transparency that the fiber has, for example, adhesives, various paints, packaging materials, gas barrier materials, electronic members, molded products, and structures.
When the object to be dispersed is a conductive material, applications of the dispersed material include, for example, a power storage device, an antistatic material, an electronic component, a transparent electrode (ITO film) substitute, and an electromagnetic wave shield. Examples of power storage devices include an electrode for a non-aqueous electrolyte secondary battery, an electrode for an electric double layer capacitor, and an electrode for a non-aqueous electrolyte capacitor. In this case, the conductive material is preferably a carbon material. Examples of antistatic materials include IC trays of plastic and rubber products and molded products of electronic component materials. Hereinafter, a dispersed material in which the object to be dispersed is a conductive material may be referred to as a conductive dispersed material.
Examples of conductive materials include metal powders such as gold, silver, bronze, silver-plated copper powder, silver-copper composite powder, silver-copper alloys, amorphous copper, nickel, chromium, palladium, rhodium, ruthenium, indium, silicon, aluminum, tungsten, molybdenum, and platinum, inorganic powders coated with these metals, powders of metal oxides such as silver oxide, indium oxide, tin oxide, zinc oxide, and ruthenium oxide, inorganic powders coated with these metal oxides, and carbon materials such as carbon black, graphite, carbon nanotubes and carbon nanofibers. These conductive materials may be used alone or two or more thereof may be used in combination. Among these conductive materials, in consideration of the adsorption performance of the dispersant, carbon black is preferable, and carbon nanotubes and carbon nanofibers are more preferable.
Examples of carbon blacks include acetylene black, furnace black, hollow carbon black, channel black, thermal black, and ketjen black. In addition, carbon black may be neutral, acidic, or basic, and oxidized carbon black or graphitized carbon black may be used.
As the carbon black, various types of commercially available acetylene black, furnace black, hollow carbon black, channel black, thermal black, and ketjen black can be used. In addition, carbon black subjected to an oxidation treatment and carbon black subjected to a graphitization treatment, which are generally performed, can be used.
Carbon nanotubes have a shape in which flat graphite is wound into a cylindrical shape. The carbon nanotubes may be a mixture of single-walled carbon nanotubes. Single-walled carbon nanotubes have a structure in which one layer of graphite is wound. Multi-walled carbon nanotubes have a structure in which two or three or more layers of graphite are wound. In addition, the side wall of the carbon nanotubes does not have a graphite structure. For example, a carbon nanotube having a side wall having an amorphous structure can be used as the carbon nanotubes.
Carbon nanotubes (CNT) include flat graphite wound in a cylindrical shape, single-walled carbon nanotubes, and multi-walled carbon nanotubes, and these may be mixed. Single-walled carbon nanotubes have a structure in which one layer of graphite is wound. Multi-walled carbon nanotubes have a structure in which two or three or more layers of graphite are wound. In addition, the side wall of the carbon nanotube does not have to have a graphite structure. In addition, for example, a carbon nanotube having a side wall having an amorphous structure is also a carbon nanotube in this specification.
The shape of carbon nanotubes is not limited. Examples of such a shape include various shapes including a needle shape, a cylindrical tube shape, a fishbone shape (fishbone or cup stacked shape), a playing card shape (platelet) and a coil shape. In the present embodiment, among these, the shape of carbon nanotubes is preferably a needle shape or a cylindrical tube shape. The carbon nanotubes may have a single shape or a combination of two or more shapes.
Examples of forms of carbon nanotubes include graphite whisker, filamentous carbon, graphite fibers, ultra-fine carbon tubes, carbon tubes, carbon fibrils, carbon microtubes and carbon nanofibers. The carbon nanotubes may have a single form or a combination of two or more forms.
When the conductive material is a carbon material, the BET specific surface area thereof is preferably 20 to 1,000 m2/g and more preferably 150 to 800 m2/g. The average outer diameter of the carbon nanotubes is preferably 1 to 30 nm and more preferably 1 to 20 nm. Here, the average outer diameter is first captured by observing a conductive material under a transmission electron microscope. Next, in the observation image, any 300 pieces of conductive material are selected and the particle size and outer diameter thereof are measured. Next, regarding the number average of the outer diameter, the average particle size (nm) and the average outer diameter (nm) of the conductive material are calculated.
When the conductive material is a carbon nanotube, the carbon purity is represented by a content (% by mass) of carbon atoms in the conductive material. The carbon purity with respect to 100% by mass of the conductive material is preferably 90% by mass, more preferably 95% by mass or more, and still more preferably 98% by mass or more.
The volume resistivity of the conductive material is preferably 1.0×10−3 to 1.0×10−1 Ω·cm and more preferably 1.0×10−3 to 1.0×10−2 Ω·cm. The volume resistivity of the conductive material can be measured using a powder resistivity measuring device (commercially available from Mitsubishi Chemical Analytech Co., Ltd.: Loresta GP powder resistivity measurement system MCP-PD-51).
The content of the dispersant with respect to 100 parts by mass of the object to be dispersed is preferably 1 to 60 parts by mass and more preferably 3 to 50 parts by mass.
The content of the object to be dispersed based on the non-volatile content of the dispersed material is preferably 0.5 to 30% by mass and more preferably 1 to 20% by mass.
Examples of dispersion mediums include water, a water-soluble solvent, and a water-insoluble solvent, and these may be used alone or a mixed solvent of two or more thereof may be used. Regarding the water-soluble solvent, alcohol-based solvents (methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, benzyl alcohol, etc.), polyhydric alcohol-based solvents (ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, etc.), polyhydric alcohol ether-based solvents (ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether, diethylene glycol monoethyl ether, diethylene glycol monobutyl ether, polypropylene glycol monomethyl ether, polypylene glycol monoethyl ether, polypylene glycol monobutyl ether, ethylene glycol monomethyl ether acetate, triethylene glycol monomethyl ether, triethylene glycol monoethyl ether, triethylene glycol monobutyl ether, ethylene glycol monophenyl ether, polypylene glycol monophenyl ether, etc.), amine-based solvents (ethanolamine, diethanolamine, triethanolamine, N-methyl diethanolamine, N-ethyl diethanolamine, morpholine, N-ethylmorpholine, ethylenediamine, diethylene diamine, triethylene tetramine, tetraethylene pentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethyl propylenediamine, etc.), amide-based solvents (N-methyl-2-pyrrolidone (NMP), N-ethyl-2-pyrrolidone (NEP), N,N-dimethylformamide, N,N-dimethylacetamide, N,N-diethylacetamide, N-methylcaprolactam, etc.), heterocyclic solvents (cyclohexylpyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone, γ-butyrolactone, etc.), sulfoxide-solvents (dimethyl sulfoxide, etc.), sulfone-based solvents (hexamethylphosphorotriamide, sulfolane, etc.), lower ketone-based solvents (acetone, methyl ethyl ketone, etc.), and additionally, tetrahydrofuran, urea, acetonitrile and the like can be used. Among these, water or an amide-based organic solvent is more preferable, and among amide-based organic solvents, N-methyl-2-pyrrolidone and N-ethyl-2-pyrrolidone are particularly preferable.
In addition, examples of water-insoluble solvents include ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; ether-based dispersion mediums such as tetrahydrofuran; aromatic compounds such as toluene, xylene, and mesitylene; nitrogen atom-containing compounds including amide-based dispersion media such as dimethylformamide and dimethylacetamide; sulfur atom-containing compounds including sulfoxide-based dispersion media such as dimethyl sulfoxide; and esters such as ethyl acetate, butyl acetate, propylene glycol monomethyl ether acetate, and γ-butyrolactone.
When this dispersed material is used for a non-aqueous electrolyte secondary battery, water or a water-soluble solvent is preferable, and water or NMP is particularly preferable.
(meth)acrylonitrile-derived unit, the active hydrogen group-containing monomer (a): among units containing the hydroxy group-containing monomer (a1), the carboxyl group-containing monomer (a2), the primary amino group-containing monomer (a3), the secondary amino group-containing monomer (a4), and the mercapto group-containing monomer (a5), and the basic monomer (b) and the (meth)acrylic acid alkyl ester (c),
when the dispersion medium is water, the amount of the (meth)acrylonitrile-derived unit is preferably 99% by mass or less, a polymer containing a unit derived from one or more monomers selected from the group consisting of (a), (b), and (c) is preferable, and a polymer containing (a) is more preferable. In addition, (a) is more preferably one or more monomers selected from the group consisting of (a1), (a2), (a3), and (a4), particularly preferably (a2), and (a) containing the (meth)acrylic acid unit is most preferable. In the case of a polymer containing more than 99% by mass and 100% or less of the (meth)acrylonitrile-derived unit, since the hydrophilicity of the polymer becomes very low, the polymer becomes insoluble and it becomes difficult for it to act as a dispersant when the dispersion medium is water. In addition, if the hydrophilicity becomes high as the polymer is completely and easily dissolved in water, the affinity with the dispersion medium becomes too high, and it becomes difficult for the polymer to act on the object to be dispersed.
When the dispersion medium is a water-soluble solvent, the amount of the (meth)acrylonitrile-derived unit is preferably 100% by mass or less, and a unit derived from one or more monomers selected from the group consisting of (a), (b) and (c) may be contained. Among (a), (b) and (c), it is preferable to include any or both of (a) and (b), and it is more preferable to include (a). (a) is more preferably one or more monomers selected from the group consisting of (a1), (a3), and (a4), particularly preferably (a1), and most preferably one containing 2-hydroxyethyl (meth)acrylate or the like. In addition, when this dispersant has a cyclic structure, the affinity for the water-soluble solvent may be appropriately lowered, the balance of the affinity between the object to be dispersed and the dispersion medium may be improved, and the dispersibility may be improved.
When the dispersion medium is a water-insoluble solvent, the amount of the (meth)acrylonitrile-derived unit is preferably 100% by mass or less, and a unit derived from one or more monomers selected from the group consisting of (a), (b), and (c) may be contained. Among (a), (b) and (c), it is preferable to contain (c).
In any case of the dispersion medium, when a monomer having an appropriate solvent affinity as described above according to the polarity of the dispersion medium is contained in an amount in the above preferable range, the balance of the affinity between the object to be dispersed and the dispersion medium is improved, and the dispersibility is improved. There is a concern that the dispersibility will decrease if any of the affinities for the object to be dispersed and the dispersion medium is too high or too low.
The dispersed material of the present invention may contain an inorganic base, an inorganic metal salt, or an organic base. Thereby, the dispersion stability of the object to be dispersed over time is further improved. As the inorganic base and the inorganic metal salt, a compound having at least one of an alkali metal and an alkaline earth metal is preferable. Examples of inorganic bases and inorganic metal salts include chlorides, hydroxides, carbonates, nitrates, sulfates, phosphates, tungstates, vanadates, molybdates, niobates, and borates of alkali metals and alkaline earth metals. Among these, chlorides, hydroxides, and carbonates of alkali metals and alkaline earth metals are preferable because it can easily supply cations. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include calcium hydroxide and magnesium hydroxide.
Examples of alkali metal carbonates include lithium carbonate, lithium hydrogen carbonate, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, and potassium hydrogen carbonate.
Examples of alkaline earth metal carbonates include calcium carbonate and magnesium carbonate. Among these, lithium hydroxide, sodium hydroxide, lithium carbonate, and sodium carbonate are more preferable. Here, the metal contained in the inorganic base and inorganic metal salt of the present invention may be a transition metal.
Examples of organic bases include primary, secondary and tertiary alkylamines which may be substituted with 1 to 40 carbon atoms and other compounds containing a basic nitrogen atom.
Examples of primary alkylamines that may be substituted with 1 to 40 carbon atoms include propylamine, butylamine, isobutylamine, octylamine, 2-ethylhexylamine, laurylamine, stearylamine, oleylamine, 2-aminoethanol, 3-aminopropanol, 3-ethoxypropylamine, and 3-lauryloxypropylamine.
Examples of secondary alkylamines that may be substituted with 1 to 40 carbon atoms include dibutylamine, diisobutylamine, N-methylhexylamine, dioctylamine, distearylamine, and 2-methylaminoethanol.
Examples of tertiary alkylamines that may be substituted with 1 to 40 carbon atoms include triethylamine, tributylamine, N,N-dimethylbutylamine,
N,N-diisopropylethylamine, dimethyloctylamine, tri-n-butylamine, dimethylbenzylamine, trioctylamine, dimethyldecylamine, dimethyllaurylamine, dimethylmyristylamine, dimethylpalmitylamine, dimethylstearylamine, dilaurylmonomethylamine, triethanolamine, and 2-(dimethylamino)ethanol.
Among these, primary, secondary or tertiaryalkylamines that may be substituted with 1 to 30 carbon atoms are preferable, and primary, secondary or tertiaryalkylamines that may be substituted with 1 to 20 carbon atoms are more preferable.
Examples of other compounds containing a basic nitrogen atom include 1,8-diazabicyclo[5.4.0]undecene-7 (DBU), 1,5-diazabicyclo[4.3.0]nonene-5 (DBN), 1,4-diazabicyclo[2.2.2]octane (DABCO), imidazole, and 1-methylimidazole.
A total amount of the inorganic base, inorganic metal salt, and organic base added with respect to 100 parts by mass of the dispersant is preferably 1 to 100 parts by mass and more preferably 1 to 50 parts by mass. When an appropriate amount is added, the dispersibility is further improved.
In the dispersed material of the present invention, as necessary, for example, other additives such as a wetting penetrating agent, an antioxidant, a preservative, a fungicide, a leveling agent, and an antifoaming agent, can be appropriately added as long as the objective of the present invention is not impaired, and can be added at an arbitrary timing such as before production of the dispersed material, during dispersion, and after dispersion.
The dispersed material of the present invention is preferably produced by, for example, finely dispersing the object to be dispersed, the dispersant, and the dispersion medium using a dispersing device according to a dispersion treatment. Here, in the dispersion treatment, the timing at which the material to be used is added can be arbitrarily adjusted, and a multi-step treatment can be performed twice or more.
Examples of dispersing devices include a kneader, a 2-roll mill, a 3-roll mill, a planetary mixer, a ball mill, a horizontal sand mill, a vertical sand mill, an annual bead mill, an attritor, and a high-pressure homogenizer.
The dispersibility of the conductive material dispersed material can be evaluated by a complex modulus of elasticity and a phase angle according to dynamic viscoelasticity measurement. The complex modulus of elasticity of the conductive material dispersed material is smaller as the dispersibility of the dispersed material is better and the viscosity is lower. In addition, the phase angle is a phase shift of the response stress wave when the strain applied to the conductive material dispersed material is a sine wave, and in the case of a pure elastic component, since the strain becomes a sine wave with the same phase as the applied strain, the phase angle becomes 0°. On the other hand, in the case of a pure viscous component, the response stress wave is advanced by 90°. In a general viscoelastic sample, a sine wave having a phase angle of larger than 0° and smaller than 90° is obtained, and if the dispersibility of the conductive material dispersed material is good, the phase angle approaches 90°, which is an angle of the pure viscous component.
The complex modulus of elasticity of the conductive material dispersed material is preferably less than 20 Pa, more preferably 10 Pa or less, and particularly preferably 5 Pa or less. In addition, the phase angle of the conductive material dispersed material of the present embodiment is preferably 19° or more, more preferably 30° or more, and particularly preferably 45° or more, and preferably 90° or less, more preferably 85° or less, and particularly preferably 80° or less.
The resin composition of the present embodiment contains the above conductive dispersed material and a binder resin. Since this resin composition contains this dispersed material, it becomes a resin composition having excellent dispersibility and storage stability of the conductive material.
This resin composition contains at least a dispersion medium, a dispersant, a conductive material, and a binder resin, and as necessary, may further contain other components. Since components that can be contained in the dispersed material are as described above, the binder resin will be described below.
The binder resin is a resin for bonding substances. Examples of binder resins include polymers or copolymers containing ethylene, propylene, vinyl chloride, vinyl acetate, vinyl alcohol, maleic acid, acrylic acid, acrylic acid ester, methacrylic acid, methacrylic acid ester, acrylonitrile, styrene, vinyl butyral, vinyl acetal, vinylpyrrolidone, or the like as structural units; polyurethane resins, polyester resins, phenol resins, epoxy resins, phenoxy resins, urea resins, melamine resins, alkyd resins, acrylic resins, formaldehyde resins, silicone resins, and fluororesins; cellulose resins such as carboxymethyl cellulose; rubbers such as styrene butadiene rubber and fluorine rubber; and conductive resins such as polyaniline and polyacetylene. In addition, modified products and mixtures of these resins and copolymers may be used. Among these, when used as a binder resin for a positive electrode, in consideration of resistance, it is preferable to use a polymer compound having a fluorine atom in the molecule, for example, polyvinylidene fluoride (PVDF), polyvinyl fluoride, or tetrafluoroethylene. In addition, when used as a binder resin for a negative electrode, carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), or polyacrylic acid having good adhesiveness is preferable.
The weight average molecular weight of the binder resin is preferably 10,000 to 2,000,000, more preferably 100,000 to 1,000,000, and particularly preferably 200,000 to 1,000,000.
The content of the binder resin based on the non-volatile content of the resin composition is preferably 0.5 to 30% by mass, more preferably 0.5 to 25% by mass, and still more preferably 0.5 to 25% by mass.
The mixture slurry of the present embodiment contains the above fat composition and an active material, and is made into a slurry in order to improve the uniformity and the processability.
The active material is a material that serves as the basis of a battery reaction. Active materials are divided into positive electrode active materials and negative electrode active materials according to electromotive force.
As the positive electrode active material, for example, metal compounds such as metal oxides and metal sulfides that can be doped or intercalated with lithium ions can be used. Examples thereof include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides with lithium, and inorganic compounds such as transition metal sulfide. Specific examples thereof include transition metal oxide powders such as MnO, V2O5, V6O13, and TiO2, composite oxide powders of lithium and transition metals such as lithium nickelate, lithium cobalt oxide, lithium manganate, and nickel manganese lithium cobalt oxide which have a layered structure, and lithium manganite having a spinel structure, a lithium iron phosphate material which is a phosphoric acid compound having an olivine structure, and transition metal sulfide powders such as TiS2 and FeS. These positive electrode active materials may be used alone or a plurality thereof may be used in combination.
The negative electrode active material is not particularly limited as long as it can be doped or intercalated with lithium ions. Examples thereof include metal Li, and alloys such as tin alloys, silicon alloys, and lead alloys which are alloys thereof, metal oxides such as LiXFe2O3, LiXFe3O4, LiXWO2 (x is a number of 0<x<1), lithium titanate, lithium vanadium, and lithium siliconate, conductive polymers such as polyacetylene and poly-p-phenylene, artificial graphite such as highly graphitized carbon material or carbonaceous powder such as natural graphite, and carbon-based materials such as resin-baked carbon materials. These negative electrode active materials may be used alone or a plurality thereof may be used in combination.
The amount of the conductive material in the mixture slurry with respect to 100% by mass of the active material is preferably 0.01 to 10% by mass, preferably 0.02 to 5% by mass, and preferably 0.03 to 3% by mass.
The amount of the binder resin in the mixture slurry with respect to 100% by mass of the active material is preferably 0.5 to 30% by mass, more preferably 1 to 25% by mass, and particularly preferably 2 to 20% by mass.
The amount of the non-volatile content of the mixture slurry with respect to 100% by mass of the mixture slurry is preferably 30 to 90% by mass, more preferably 30 to 85% by mass, and more preferably 40 to 80% by mass.
The mixture slurry can be produced by various conventionally known methods. For example, a production method of adding an active material to a conductive material and a production method of adding an active material to a conductive material dispersed material and then adding a binder resin may be exemplified.
In order to obtain a mixture slurry, it is preferable to add an active material to a conductive material and then perform a treatment for dispersion. A dispersing device used for performing such a treatment is not particularly limited. For the mixture slurry, a mixture slurry can be obtained using the dispersion device described in the conductive material dispersed material.
An electrode film (F) of the present embodiment is formed by forming the mixture slurry into a film. For example, a mixture slurry is applied and dried on a current collector, and thus a coating film in which an electrode mixture layer is formed is obtained.
The material and shape of the current collector used for the electrode film are not particularly limited, and those suitable for various secondary batteries can be appropriately selected. For example, examples of materials of current collectors include metals such as aluminum, copper, nickel, titanium, and stainless steel, and alloys. In addition, regarding the shape, a foil on a flat plate is generally used, but a current collector with a roughened surface, a current collector having a perforated foil shape, and a current collector having a mesh shape can be used.
A method of applying a mixture slurry on the current collector is not particularly limited, and known methods can be used. Specific examples thereof include a die coating method, a dip coating method, a roll coating method, a doctor coating method, a knife coating method, a spray coating method, a gravure coating method, a screen printing method and an electrostatic coating method, and regarding the drying method, standing drying, a fan dryer, a warm air dryer, an infrared heater, a far infrared heater, and the like can be used, but the drying method is not particularly limited thereto.
In addition, after coating, rolling may be performed using a planographic press, a calendar roll or the like. The thickness of the electrode mixture layer is generally 1 μm or more and 500 μm or less and preferably 10 μm or more and 300 μm or less.
The non-aqueous electrolyte secondary battery of the present embodiment includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and at least one of the positive electrode and the negative electrode includes the electrode film.
The electrode preferably includes a current collector and the electrode film. The electrode film is preferably formed on the current collector. A method of forming an electrode film on the current collector is as described above.
Regarding the positive electrode, those obtained by applying and drying a mixture slurry containing a positive electrode active material on a current collector to produce an electrode film can be used.
Regarding the negative electrode, those obtained by applying and drying a mixture slurry containing a negative electrode active material on a current collector to produce an electrode film can be used.
Regarding the electrolyte, various conventionally known electrolytes in which ions can move can be used. Examples thereof include those containing lithium salts such as LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiCF3SO3, Li(CF3SO2)2N, LiC4F9SO3, Li(CF3SO2)3C, LiI, LiBr, LiCl, LiAlCl, LiHF2, LiSCN, and LiBPh4 (where, Ph is a phenyl group), but the present invention is not limited thereto. The electrolyte is preferably dissolved in a non-aqueous solvent and used as an electrolyte solution.
The non-aqueous solvent is not particularly limited, and examples thereof include carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; lactones such as γ-butyrolactone, γ-valerolactone, and γ-octanoic lactone; glymes such as tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,2-methoxyethane, 1,2-ethoxyethane, and 1,2-dibutoxyethane; esters such as methylformate, methylacetate, and methylpropionate; sulfoxides such as dimethyl sulfoxide and sulfolane; and nitriles such as acetonitrile. These solvents may be used alone or two or more thereof may be used in combination.
The non-aqueous electrolyte secondary battery of the present embodiment preferably contains a separator. Examples of separators include a polyethylene non-woven fabric, a polypropylene non-woven fabric, a polyamide non-woven fabric and those obtained by subjecting them to a hydrophilic treatment, but the present invention is not particularly limited thereto.
The structure of the non-aqueous electrolyte secondary battery of the present embodiment is not particularly limited, but is generally composed of a positive electrode and a negative electrode, and a separator provided as necessary, and various shapes such as a paper shape, a cylindrical shape, a button shape, and a laminate shape can be used according to the purpose of use.
While the present invention will be described below in more detail, the present invention is not limited to these examples. In the examples, “carbon nanotube” may be abbreviated as “CNT.” Here, “% by mass” is described as “%.” The formulation amounts in the tables are % by mass.
The dispersant of the present invention, the molecular weight of the binder resin, and evaluation of various physical properties of the dispersed material using the dispersant of the present invention are as follows.
The weight average molecular weight (Mw) was measured by a gel permeation chromatographic (GPC) device including an RI detector.
For the device, HLC-8320GPC (commercially available from Tosoh Corporation) was used, and three separation columns were connected in series, “TSK-GELSUPERAW-4000,” “AW-3000,” and “AW-2500” (commercially available from Tosoh Corporation) were used as fillers in order, and the measurement was performed at an oven temperature of 40° C. using an N,N-dimethylformamide solution containing 30 mM trimethylamine and 10 mM LiBr as an eluent at a flow rate of 0.6 ml/min. The sample was prepared in a solvent including the above eluent at a concentration of 1 wt %, and 20 microliters thereof was injected. The molecular weight was a polystyrene conversion value.
In order to measure the viscosity, using a B type viscometer (“BL” commercially available from Toki Sangyo Co., Ltd.), at a dispersed material temperature of 25° C., the dispersed material was sufficiently stirred with a spatula, and then immediately rotated at a B type viscometer rotor rotation speed of 60 rpm. The rotor used for measurement was a No. 1 rotor when the viscosity was less than 100 mPa·s, a No. 2 rotor when the viscosity was 100 or more and less than 500 mPa·s, a No. 3 rotor when the viscosity was 500 or more and less than 2,000 mPa·s, and a No. 4 rotor when the viscosity was 2,000 or more and less than 10,000 mPa·s. When the viscosity was lower, the dispersibility was better, and when the viscosity was higher, the dispersibility was poorer. If the obtained dispersed material was clearly separated or precipitated, it was regarded as having poor dispersibility.
Determination criteria for those other than cellulose fibers are as follows.
⊙+: less than 30 mPa·s (good)
⊙: less than 50 mPa·s (good)
◯: 50 or more and less than 1.000 mPa·s (usable)
Δ: 1,000 or more and less than 10,000 mPa·s (unusable)
x: 10,000 mPa·s or more, precipitated or separated (poor)
Determination criteria for cellulose fibers are as follows.
⊙: less than 500 mPa·s (good)
◯: 500 or more and less than 10,000 mPa·s (usable)
x: 10,000 mPa·s or more, precipitated or separated (poor)
In order to evaluate the storage stability, the viscosity after the dispersed material was left at 50° C. for 7 days and stored was measured. For the measuring method, the same method for the initial viscosity was used for measurement. The evaluation criteria are as follows.
⊙: No change in viscosity (a rate of change was less than 3%) (good)
◯: The viscosity was slightly changed (a rate of change was 3% or more and less than 10%) (usable)
Δ: The viscosity was changed (a rate of change was 10% or more) (unusable)
x: The solution was gelled, precipitated, or separated (poor)
100 parts of acetonitrile was put into a reaction container including a gas inlet pipe, a thermometer, a condenser, and a stirrer, and the inside was purged with nitrogen gas. The inside of the reaction container was heated to 70° C. and a mixture containing 50.0 parts of acrylonitrile, 25.0 parts of acrylic acid, 25.0 parts of styrene and 5.0 parts of 2,2′-azobis(2,4-dimethylvaleronitrile) (V-65, commercially available from NOF Corporation) was added dropwise over 3 hours, and a polymerization reaction was performed. After dropwise addition was completed, the reaction was additionally performed at 70° C. for 1 hour, and 0.5 parts of perbutyl 0 was then added, and the reaction was additionally continued at 70° C. for 1 hour. Then, the non-volatile content was measured, and it was confirmed that the conversion ratio exceeded 98%, and the dispersion medium was completely removed by concentration under a reduced pressure to obtain a dispersant (A-1α). The weight average molecular weight (Mw) of the dispersant (A-1α) was 15,000.
A fabrication of dispersants (A-2α) to (A-13α) were produced in the same manner as in Production Example 1α except that monomers used were changed according to Table 1. The weight average molecular weights (Mw) of the dispersants were as shown in Table 1α. Here, in synthesis of the dispersant, the chain transfer agent was added, the amount of the polymerization initiator was adjusted, and reaction conditions and the like were appropriately changed to prepare the Mw.
50 parts of the dispersant (A-3α) obtained in Production Example 3a was added to 198 parts of purified water, and the mixture was stirred with a disper to prepare a slurry. Next, 2.0 parts of a 1 N sodium hydroxide aqueous solution was added dropwise at 25° C., and the mixture was stirred with a disper for 2 hours while heating in a water bath. In IR measurement (device: FT/IR-410, commercially available from JASCO Corporation), it was confirmed that the intensity of the peak derived from the cyano group was reduced to 80% or less and it was confirmed that the cyclic structure was formed. Next, washing with purified water was performed, and filtering and drying were performed to obtain a dispersant (A-14α) having a hydrogenated naphthyridine ring and a glutarimide ring. Here, the weight average molecular weight (Mw) was 14,000.
A dispersant (A-15α) having a hydrogenated naphthyridine ring was obtained in the same manner as in Production Example 13α except that the dispersant used was changed from (A-3α) to (A-6α). Here, the weight average molecular weight (Mw) was 14,000.
According to the compositions shown in Table 2-1α and Table 2-2α, carbon black as a conductive material, a dispersant, an additive, and a dispersion medium were put into a glass bottle, sufficiently mixed and dissolved, or mixed, and then dispersed with a paint conditioner using 1.25 mmφ zirconia beads as media for 2 hours to obtain carbon black dispersed materials. As shown in Table 2-1α and Table 2-2α, the dispersed material 1α to dispersed material 35α using the dispersant of the present invention all had low viscosity and good storage stability.
According to the compositions shown in Table 3a, an object to be dispersed, a dispersant, an additive, and a dispersion medium were put into a glass bottle and sufficiently mixed, dissolved, or mixed, and various objects to be dispersed were then added, and the mixture was dispersed with a paint conditioner using 0.5 mmφ zirconia beads as media for 2 hours to obtain dispersed materials. As shown in Table 3α, the dispersed material 26α to dispersed material 32α using the dispersant of the present invention all had low viscosity and good storage stability.
The dispersed materials 1α to 35α prepared in Examples 1α to 35α, and binder resins were blended with dispersed materials so that the non-volatile content and the carbon concentration in the non-volatile content were as shown in Table 4, and thereby carbon dispersed materials were prepared. Using a bar coater, the dispersed material prepared using the bar coater was applied to the surface of a PET film having a thickness of 100 μm, and drying was then performed at 130° C. for 30 minutes to form a coating film having a thickness of 5 μm. The surface resistance value of the coating film was measured using a resistivity meter (product name “Hiresta,” commercially available from Mitsubishi Chemical Analytech Co., Ltd.). The results are shown in Table 4α.
⊙: less than 1.0×104 Ω/cm2 (good)
◯: 1.0×104 or more and less than 1.0×107 Ω/cm2 (usable)
Δ: 1.0×107 or more and less than 1.0×1010 Ω/cm2 (usable)
x: 1.0×1010 Ω/cm2 or more, precipitated or separated (poor)
Water resistance: coated plates obtained in Examples 43α to 77α or comparative examples were immersed in warm water at 25° C. for 2 hours, and then pulled up, water droplets on the surface were wiped off, and the state of the coating film was then visually evaluated. The results are shown in Table 4α.
Determination Criteria
⊙: There was no change in the coating film.
◯: Whitening was observed on the coated surface, but the state returned to its original state after being left for 24 hours.
x: The coating film was significantly whitened, and easily peeled off simply with light rubbing.
Based on the above results, when the dispersant of the present invention was used, it was possible to produce a dispersed material having excellent dispersion efficiency and excellent dispersibility, fluidity, and storage stability. In particular, when the dispersion medium was water or a hydrophilic solvent such as NMP, a dispersant containing an active hydrogen group-containing monomer or a basic monomer was preferable, and dispersants containing (meth)acrylic acid alkyl ester were excellent for solvents such as butyl acetate, MEK, and PGMAc.
In addition, in Comparative Example 7α in Table 2α, the conventional dispersant had a certain degree of dispersibility when the amount used increased, but the dispersibility was reduced when the amount used decreased. On the other hand, the dispersant of the present invention had good dispersibility even if the amount used was reduced.
In addition, using the dispersant of the present invention, it was possible to produce a dispersed material having good dispersibility and excellent fluidity and storage stability not only for a conductive material but also for an object to be dispersed other than the conductive material.
When the dispersant of the present invention was used for a power storage device, an electrode having excellent electrical conductivity and good water resistance was obtained.
The dispersant of the present invention, the molecular weight of the binder resin, and evaluation of various physical properties of the dispersed material using the dispersant of the present invention are as follows.
The measurement of the weight average molecular weight (Mw), the measurement of the viscosity of the dispersed material, and the evaluation of the stability of the dispersed material were performed according to the same methods and criteria as in Example group α.
100 parts of acetonitrile was put into a reaction container including a gas inlet pipe, a thermometer, a condenser, and a stirrer, and the inside was purged with nitrogen gas. The inside of the reaction container was heated to 70° C. and a mixture containing 55.0 parts of acrylonitrile, 25.0 parts of acrylic acid, 20.0 parts of styrene, 0.5 parts of 3-mercapto-1,2-propanediol and 0.4 parts of 2,2′-azobis(2,4-dimethylvaleronitrile) (V-65, commercially available from FUJIFILM Wako Pure Chemical Corporation) was added dropwise into the reaction container over 3 hours, and a polymerization reaction was performed. After dropwise addition was completed, the reaction was performed at 70° C. for 1 hour, and 0.1 parts of V-65 was then added, and the reaction was additionally continued at 70° C. for 1 hour to obtain a desired product as a precipitate. Then, the non-volatile content was measured and it was confirmed that the conversion ratio exceeded 98%. The product was filtered off under a reduced pressure and washed with 100 parts of acetonitrile, and the solvent was completely removed by performing drying under a reduced pressure to obtain a polymer (A-1β). The weight average molecular weight (Mw) of the polymer (A-1β) was 75,000.
Dispersants (A-2β) to (A-15β) were produced in the same manner as in Production Example 1β except that monomers and chain transfer agents used were changed according to Table 1β. The weight average molecular weights (Mw) of the dispersants were as shown in Table 1β. Here, in synthesis of the dispersant, the chain transfer agent was added, the amount of the polymerization initiator was adjusted, and reaction conditions and the like were appropriately changed to prepare the Mw.
50 parts of the dispersant (A-4β) obtained in Production Example 3β was added to 198 parts of purified water, and the mixture was stirred with a disper to prepare a slurry. Next, 2.0 parts of a 1 N sodium hydroxide aqueous solution was added dropwise at 25° C., and the mixture was stirred with a disper for 2 hours while heating in a water bath. In IR measurement (device: FT/IR-410, commercially available from JASCO Corporation), it was confirmed that the intensity of the peak derived from the cyano group was reduced to 80% or less of the initial value and it was confirmed that the cyclic structure was formed. Next, washing with purified water was performed, and filtering and drying were performed to obtain a dispersant (A-16(3). Here, the weight average molecular weight (Mw) was 74,000.
A dispersant (A-17β) having a hydrogenated naphthyridine ring was obtained in the same manner as in Production Example 16β except that the dispersant used was changed from (A-4β) to (A-10β). Here, the weight average molecular weight (Mw) was 74,000.
According to the compositions shown in Table 2-1β and Table 2-2β, carbon black as a conductive material, a dispersant, an additive, and a dispersion medium were put into a glass bottle, sufficiently mixed and dissolved, or mixed, and then dispersed with a paint conditioner using 1.25 mmφ zirconia beads as media for 2 hours to obtain carbon black dispersed materials.
As shown in Table 2-1β and Table 2-2β, the dispersed material 1β to dispersed material 45β using the dispersant of the present invention all had excellent dispersibility so that they had low viscosity and good storage stability.
According to the compositions shown in Table 3β, an object to be dispersed, a dispersant, an additive, and a dispersion medium were put into a glass bottle and sufficiently mixed and dissolved, or mixed, and then dispersed with a paint conditioner using 0.5 mmφ zirconia beads as media for 2 hours to obtain dispersed materials.
As shown in Table 3β, the dispersed material 46β to dispersed material 52β using the dispersant of the present invention all had excellent dispersibility so that they had low viscosity and good storage stability.
The dispersed materials 1β to 45β and binder resins were blended with dispersed materials so that the non-volatile content and the carbon concentration in the non-volatile content were as shown in Table 4β, and thereby carbon dispersed materials were prepared. Using a bar coater, the dispersed material prepared using the bar coater was applied to the surface of a PET film having a thickness of 100 μm, and drying was then performed at 130° C. for 30 minutes to produce a test film having a coating film having a thickness of 5 μm.
The surface resistance value of the coating film of the obtained test film was measured using a resistivity meter (product name “Hiresta”, commercially available from Mitsubishi Chemical Analytech Co., Ltd.). The results are shown in Table 4.
⊙: less than 1.0×104 Ω/cm2 (very good)
◯: 1.0×104 or more and less than 1.0×107 Ω/cm2 (good)
Δ: 1.0×107 or more and less than 1.0×1010 Ω/cm2 (poor)
x: 1.0×1010 Ω/cm2 or more, precipitated or separated (very poor)
The obtained test film was immersed in warm water at 25° C. for 2 hours, and then pulled up, water droplets on the surface were wiped off, and the state of the coating film was then visually evaluated. The results are shown in Table 4β.
Determination Criteria
⊙: There was no change in the coating film (very good)
◯: Whitening was observed on the coating film, but the surface was returned to its original state after being left for 24 hours (good)
x: The coating film was significantly whitened, but the state was not returned to its original state even after being left for 24 hours (poor)
Based on the above results, when the dispersant of the present invention was used, it was possible to produce a dispersed material having excellent dispersion efficiency and excellent dispersibility and storage stability. In particular, when the dispersion medium was water or a hydrophilic solvent such as NMP, a dispersant containing an active hydrogen group-containing monomer unit or a basic monomer unit was preferable, and dispersants containing a (meth)acrylic acid alkyl ester unit were excellent for solvents such as butyl acetate, MEK, and PGMAc.
In addition, in Comparative Example 7β in Table 2-2β, the conventional dispersant had a certain degree of dispersibility when the amount used increased, but the dispersibility was reduced when the amount used decreased. On the other hand, the dispersant of the present invention had good dispersibility even if the amount used was reduced.
In addition, using the dispersant of the present invention, it was possible to produce a dispersed material having good dispersibility and excellent fluidity and storage stability not only for a conductive material but also for an object to be dispersed other than the conductive material.
When the dispersant of the present invention was used for a power storage device, an electrode having excellent electrical conductivity and good water resistance was obtained.
According to the composition and dispersion time shown in Table 5β, 0.8 parts of a dispersant, 0.2 parts of an additive, and 97 parts of a dispersion medium were put into a glass bottle (M-225, commercially available from Hakuyo Glass Co., Ltd.), and sufficiently mixed and dissolved, or mixed and 2 parts of CNT as a conductive material was then added thereto, and dispersed with a paint conditioner using zirconia beads (with a bead diameter of 0.5 mmφ) as media to obtain a CNT dispersed material (CNT dispersed material 1β). As shown in Table 5β, the CNT dispersed material 1β had low viscosity and good storage stability.
According to the compositions and dispersion times shown in Table 5β, CNT dispersed materials (CNT dispersed materials 2β to 26β, and comparative CNT dispersed materials 11β to 4β) were obtained in the same manner as in Example 100β. As shown in Table 5β, the CNT dispersed materials (CNT dispersed materials 2β to 26β) of the present invention all had low viscosity and good storage stability.
The viscosity value was measured according to the method of evaluating the stability of the dispersed material except that the determination criteria were changed as follows.
Determination Criteria
⊙: less than 500 mPa·s (very good)
◯: 500 or more and less than 2,000 mPa·s (good)
Δ: 2,000 or more and less than 10,000 mPa·s (poor)
x: 10,000 mPa·s or more, precipitated or separated (very poor)
The storage stability was evaluated according to the method of evaluating the stability of the dispersed material except that the determination criteria were changed as follows.
Determination Criteria
└: Equivalent to the initial value (very good)
◯: No problem (good)
Δ: The viscosity increased but the material did not gel (poor)
x: Gelled (very poor)
The CNT dispersed material (CNT dispersed material 1β), CMC, and water were put into a plastic container having a volume of 150 cm3, and then stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation) to obtain a CNT-containing resin composition 1β. Then, an active material was added thereto, and the mixture was stirred at 2,000 rpm for 150 seconds using the rotation/revolution mixer. In addition, SBR was then added thereto, and the mixture was stirred at 2,000 rpm for 30 seconds using the rotation/revolution mixer to obtain a negative electrode mixture composition 1β. The non-volatile content of the negative electrode mixture composition 1β was 48% by mass. The non-volatile content ratio of the active material:CNT:CMC:SBR in the negative electrode mixture composition was 97:0.5:1:1.5.
Artificial graphite: CGB-20 (commercially available from Nippon Graphite Industries, Co., Ltd.), a non-volatile content of 100%
CMC: carboxymethyl cellulose #1190 (commercially available from Daicel FineChem Co., Ltd.), a non-volatile content of 100%
SBR: styrene butadiene rubber TRD2001 (commercially available from JSR), a non-volatile content of 48%
CNT-containing resin compositions 2β to 14β and comparative CNT-containing resin compositions 1β and 2β, negative electrode mixture compositions 2β to 14β and negative electrode comparative mixture compositions 1β and 2β were obtained in the same method as in Example 124β except that the type of the CNT dispersed material was changed.
The CNT dispersed material (CNT dispersed material 15β) and NMP in which 8% by mass PVDF was dissolved were put into a plastic container having a volume of 150 cm, and the mixture was then stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation) to obtain a CNT-containing resin composition 15β. Then, an active material was added thereto and the mixture was stirred at 2,000 rpm for 150 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation). In addition, NMP was then added thereto and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation) to obtain a positive electrode mixture composition 1β. The non-volatile content of the positive electrode mixture composition 13 was 75% by mass. The non-volatile content ratio of the active material:CNT:PVDF in the positive electrode mixture composition was 98.5:0.5:1.
NMC (nickel manganese lithium cobalt oxide): HED (registered trademark) NCM-111 1100 (commercially available from BASF TODA Battery Materials LLC), a non-volatile content of 100%
PVDF: polyvinylidene fluoride Solef #5130 (commercially available from Solvey), a non-volatile content of 100%
CNT-containing resin compositions 16β to 26β, comparative CNT-containing resin compositions 3β and 4β, positive electrode mixture compositions 2β to 12β and positive electrode comparative mixture compositions 1β and 2β were obtained in the same method as in Example 138β except that the type of the CNT dispersed material was changed.
The negative electrode mixture composition shown in Table 8β was applied to a copper foil having a thickness of 20 μm using an applicator, and the coating film was then dried in an electric oven at 120° C.±5° C. for 25 minutes to produce an electrode film with a mixture layer. Then, the electrode film was rolled by a roll press (3t hydraulic roll press, commercially available from Thank Metal Co., Ltd.). Here, the basis weight per unit of the mixture layer was 10 mg/cm2, and the density of the mixture layer after rolling was 1.6 g/cc.
The surface resistivity (Ω/□) of the mixture layer of the obtained negative electrode was measured using Loresta GP, MCP-T610 (commercially available from Mitsubishi Chemical Analytech Co., Ltd.). After the measurement, the thickness of the mixture layer was multiplied to obtain a volume resistivity (Ω·cm) of the negative electrode. For the thickness of the mixture layer, using a film thickness meter (DIGIMICRO MH-15M, commercially available from NIKON), the film thickness of the copper foil was subtracted from the average value measured at 3 points in the electrode to obtain a volume resistivity (Ω·cm) of the negative electrode. The electrical conductivity of the negative electrode was evaluated as ⊙ (very good) when the volume resistivity (Ω·cm) of the electrode was less than 0.3, ◯ (good) when the volume resistivity (Ω·cm) was 0.3 or more and less than 0.5, and x (poor) when the volume resistivity (Ω·cm) was 0.5 or more.
(Method of Evaluating Adhesiveness of Negative Electrode) The obtained negative electrode was cut into two 90 mm×20 mm rectangles with the coating direction as the major axis. The peeling strength was measured using a desktop tensile tester (Strograph E3, commercially available from Toyo Seiki Co., Ltd.), and evaluated according to the 180 degree peeling test method. Specifically, a double-sided tape with a size of 100 mm×30 mm (No. 5000NS, commercially available from Nitoms Inc.) was attached to a stainless steel plate, and the side of the mixture layer of the produced negative electrode was brought into close contact with one surface of the double-sided tape to prepare a test sample. Next, the test sample was vertically fixed so that the short sides of the rectangle were on the top and bottom, the end of the copper foil was peeled off while pulling it from the bottom to the top at a certain speed (50 mm/min), and the average value of stress at this time was used as the peeling strength. The adhesiveness of the electrode was evaluated as ⊙ (very good) when the peeling strength was 0.5 N/cm or more, ◯ (good) when the peeling strength was 0.1 N/cm or more and less than 0.5 N/cm, and x (poor) when the peeling strength was less than 0.1 N/cm.
The positive electrode mixture composition shown in Table 8β was applied to an aluminum foil having a thickness of 20 μm using an applicator, and then dried in an electric oven at 120° C.±5° C. for 25 minutes to produce an electrode film with a mixture layer. Then, the electrode film was rolled by a roll press (3t hydraulic roll press, commercially available from Thank Metal Co., Ltd.). Here, the basis weight per unit of the mixture layer was 20 mg/cm2, and the density of the mixture layer after rolling was 3.1 g/cc.
The electrical conductivity of the obtained positive electrode was evaluated according to the same method as in the negative electrode except that an aluminum foil was used in place of the copper foil. The electrical conductivity of the positive electrode was evaluated as ⊙ (very good) when the volume resistivity (Ω·cm) of the electrode was less than 10, ◯ (good) when the volume resistivity (Ω·cm) was 10 or more and less than 20, and x (poor) when the volume resistivity (Ω·cm) was 20 or more.
The adhesiveness of the obtained positive electrode was evaluated according to the same method as in the negative electrode except that an aluminum foil was used in place of the copper foil. The adhesiveness (N/cm) of the electrode was evaluated as ⊙ (very good) when the peeling strength was 1 N/cm or more, ◯ (good) when the peeling strength was 0.5 N/cm or more and less than 1 N/cm, and x (poor) when the peeling strength was less than 0.5 N/cm.
As shown in Table 8β, the negative electrode and the positive electrode using the CNT dispersed material of the present invention all had good electrical conductivity and adhesiveness.
93 parts by mass of the positive electrode active material (HED (registered trademark) NCM-111 1100, commercially available from BASF TODA Battery Materials LLC.), 4 parts by mass of acetylene black (Denka Black (registered trademark) HS100, commercially available from Denka Co., Ltd.), and 3 parts by mass of PVDF (Kureha KF polymer W #1300, commercially available from Kureha Battery Materials Japan Co., Ltd.) were put into a plastic container having a volume of 150 ml, and then mixed with a spatula until powder was uniform. Then, 20.5 parts by mass of NMP was added thereto and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation). Then, the mixture in the plastic container was mixed with a spatula until it was uniform, and stirred at 2,000 rpm for 30 seconds using the rotation/revolution mixer. In addition, 14.6 parts by mass of NMP was then added thereto, and the mixture was stirred at 2,000 rpm for 30 seconds using the rotation/revolution mixer. Finally, the sample was stirred at 3,000 rpm for 10 minutes using a high-speed stirrer to obtain a standard positive electrode mixture composition.
The above standard positive electrode mixture composition was applied to an aluminum foil having a thickness of 20 μm as a current collector using an applicator and then dried in an electric oven at 120° C.±5° C. for 25 minutes, and the basis weight per unit area of the electrode was adjusted to 20 mg/cm2. In addition, the sample was rolled by a roll press (3t hydraulic roll press, commercially available from Thank Metal Co., Ltd.) to produce a standard positive electrode having a mixture layer density of 3.1 g/cm3.
Acetylene black (Denka Black (registered trademark) HS100, commercially available from Denka Co., Ltd.), CMC, and water were put into a plastic container having a volume of 150 ml, and then stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation). In addition, artificial graphite (CGB-20 (commercially available from Nippon Graphite Industries, Co., Ltd.)) as an active material was added, and the mixture was stirred at 2,000 rpm for 150 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation). Subsequently, SBR (TRD2001 (commercially available from JSR)) was added thereto, and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation) to obtain a standard negative electrode mixture composition. The non-volatile content of the standard negative electrode mixture composition was 48% by mass. The non-volatile content ratio of the active material:conductive material:CMC:SBR in the standard negative electrode mixture composition was 97:0.5:1:1.5.
The above standard negative electrode mixture composition was applied to a copper foil having a thickness of 20 μm as a current collector using an applicator and then dried in an electric oven at 80° C.±5° C. for 25 minutes, and the basis weight per unit area of the electrode was adjusted to 10 mg/cm2. In addition, the sample was rolled by a roll press (3t hydraulic roll press, commercially available from Thank Metal Co., Ltd.) to produce a standard negative electrode having a mixture layer density of 1.6 g/cm3.
The negative electrode and the positive electrode shown in Table 9β were punched out into 50 mm×45 mm and 45 mm×40 mm, respectively, and a separator (porous polypropylene film) inserted therebetween was inserted into an aluminum laminate bag and dried in an electric oven at 70° C. for 1 hour. Then, 2 mL of an electrolyte solution (a non-aqueous electrolyte solution obtained by preparing a mixed solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate at a ratio of 1:1:1 (volume ratio), additionally adding 1 part by mass of vinylene carbonate with respect to 100 parts by mass as an additive, and then dissolving LiPF6 at a concentration of 1 M) was injected into a glove box filled with argon gas, and the aluminum laminate was then sealed to produce non-aqueous electrolyte secondary batteries 1β to 26β and comparative non-aqueous electrolyte secondary batteries 1β to 4β.
The obtained non-aqueous electrolyte secondary battery was installed in a thermostatic chamber at 25° C. and charging and discharging measurement was performed using a charging and discharging device (SM-8 commercially available from Hokuto Denko Corporation). Constant current and constant voltage charging (a cut-off current of 1 mA (0.02 C)) was performed at a charging current of 10 mA (0.2 C) and a charge final voltage of 4.3 V, and constant current discharging was then performed at a discharging current of 10 mA (0.2 C) and a discharge final voltage of 3 V. This operation was repeated three times and constant current and constant voltage charging (a cut-off current 1 mA (0.02 C)) was then performed at a charging current of 10 mA (0.2 C) and a charge final voltage of 4.3 V, constant current discharging was performed at a discharging current of 0.2 C and 3 C until the discharge final voltage reached 3.0 V, and each discharge capacity was determined. The rate properties can be expressed as a ratio of the 0.2 C discharge capacity and the 3 C discharge capacity according to the following Formula 1.
Rate properties=3C discharge capacity/3rd 0.2 C discharge capacity×100% (Formula 1)
For the rate properties, those having rate properties of 80% or more were evaluated as ⊙ (very good), those having rate properties of 60% or more and less than 80% were evaluated as ◯ (good), and those having rate properties of less than 60% were evaluated as x (poor).
The obtained non-aqueous electrolyte secondary battery was installed in a thermostatic chamber at 25° C. and charging and discharging measurement was performed using a charging and discharging device (SM-8 commercially available from Hokuto Denko Corporation). Constant current and constant voltage charging (a cut-off current of 2.5 mA (0.05 C)) was performed at a charging current of 25 mA (0.5 C) and a charge final voltage of 4.3 V, and constant current discharging was then performed at a discharging current of 25 mA (0.5 C) and a discharge final voltage of 3 V. This operation was repeated 200 times. The cycle properties can be expressed as a ratio of the 3rd 0.5 C discharge capacity and the 200th 0.5 C discharge capacity at 25° C. according to the following Formula 2.
Cycle properties=3rd 0.5 C discharge capacity/200th 0.5 C discharge capacity×100(%) (Formula 2)
For the cycle properties, those having cycle properties of 85% or more were evaluated as ⊙ (very good), those having cycle properties of 80% or more and less than 85% were evaluated as ◯ (good), and those having cycle properties of less than 80% were evaluated as x (poor).
In the above examples using the dispersed material of the present invention, non-aqueous electrolyte secondary batteries having better cycle properties than those of comparative examples were obtained. It was thought that a non-aqueous electrolyte secondary battery having better cycle properties than those of comparative examples was obtained due to strong polarization of the acrylonitrile-derived unit and the cyclic structure. Therefore, it can be clearly understood that the present invention can provide a non-aqueous electrolyte secondary battery having cycle properties that cannot be realized with a conventional conductive material dispersed material.
The dispersant of the present invention, the molecular weight of the binder resin, and evaluation of various physical properties of the dispersed material using the dispersant of the present invention are as follows.
The measurement of the weight average molecular weight (Mw) was performed according to the same method and criteria as in Example group α.
In order to measure the viscosity value, using a B type viscometer (“BL,” commercially available from Toki Sangyo Co., Ltd.), at a dispersion solution temperature of 25° C., the dispersion solution was sufficiently stirred with a spatula and then immediately rotated at a B type viscometer rotor rotation speed of 60 rpm. The rotor used for measurement was a No. 1 rotor when the viscosity value was less than 100 mPa·s, a No. 2 rotor when the viscosity value was 100 or more and less than 500 mPa·s, a No. 3 rotor when the viscosity value was 500 or more and less than 2,000 mPa·s, and a No. 4 rotor when the viscosity value was 2,000 or more and less than 10,000 mPa·s. When the viscosity was lower, the dispersibility was better, and when the viscosity was higher, the dispersibility was poorer. If the obtained dispersed material was clearly separated or precipitated, it was regarded as having poor dispersibility.
Determination Criteria
⊙: less than 500 mPa·s (very good)
◯: 500 or more and less than 2,000 mPa·s (good)
Δ: 2,000 or more and less than 10,000 mPa·s (fair)
x: 10,000 mPa·s or more, precipitated or separated (poor)
The storage stability was evaluated based on the change in liquid properties after the dispersed material was left and stored at 50° C. for 7 days. The change in liquid properties was determined based on the ease of stirring when stirring was performed with a spatula, ⊙: no problem (good), ◯: the viscosity increased but the material did not gel (fair), and x: gelled (very poor).
The negative electrode mixture slurry was applied to a copper foil using an applicator so that the basis weight per unit of the electrode was 10 mg/cm2 and the coating film was then dried in an electric oven at 120° C.±5° C. for 25 minutes. Then, the surface resistivity (Ω/□) of the dried coating film was measured using Loresta GP, MCP-T610 (commercially available from Mitsubishi Chemical Analytech Co., Ltd.). After the measurement, the volume resistivity (Ω·cm) of an electrode film for a negative electrode was obtained by multiplying the thickness of the electrode mixture layer formed on the copper foil. The thickness of the electrode mixture layer was obtained by subtracting the film thickness of the copper foil from the average value measured at 3 points in the electrode film using a film thickness meter (DIGIMICRO MH-15M, commercially available from NIKON) to obtain a volume resistivity (Ω·cm) of the electrode film. The electrical conductivity of the electrode film was evaluated as ⊙ (very good) when the volume resistivity (Ω·cm) of the electrode film was less than 0.3, ◯ (good) when the volume resistivity (Ω·cm) was 0.3 or more and less than 0.5, and x (poor) when the volume resistivity (Ω·cm) was 0.5 or more.
The negative electrode mixture slurry was applied to a copper foil using an applicator so that the basis weight per unit of the electrode was 10 mg/cm2 and the coating film was then dried in an electric oven at 120° C.±5° C. for 25 minutes. Then, the film was cut into two 90 mm×20 mm rectangles with the coating direction as the major axis. The peeling strength was measured using a desktop tensile tester (Strograph E3, commercially available from Toyo Seiki Co., Ltd.), and evaluated according to the 180 degree peeling test method. Specifically, a double-sided tape with a size of 100 mm×30 mm (No. 5000NS, commercially available from Nitoms Inc.) was attached to a stainless steel plate, the produced battery electrode mixture layer was brought into close contact with the other surface of the double-sided tape, peeling off was performed while pulling from the bottom to the top at a certain speed (50 mm/min), and the average value of stress at this time was used as the peeling strength. The adhesiveness (N/cm) of the electrode film was evaluated as ⊙ (very good) for 0.5 or more, ◯ (good) for 0.1 or more and less than 0.5, and x (poor) for less than 0.1.
The positive electrode mixture slurry was applied to an aluminum foil using an applicator so that the basis weight per unit of the electrode was 20 mg/cm2 and the coating film was then dried in an electric oven at 120° C.±5° C. for 25 minutes. Then, the surface resistivity (Ω/□) of the dried coating film was measured using Loresta GP, MCP-T610 (commercially available from Mitsubishi Chemical Analytech Co., Ltd.). After the measurement, the volume resistivity (Ω·cm) of an electrode film for a positive electrode was obtained by multiplying the thickness of the electrode mixture layer formed on the aluminum foil. For the thickness of the electrode mixture layer, using a film thickness meter (DIGIMICRO MH-15M, commercially available from NIKON), the film thickness of the aluminum foil was subtracted from the average value measured at 3 points in the electrode film to obtain a volume resistivity (Ω·cm) of the electrode film. The electrical conductivity of the electrode film was evaluated as ⊙ (very good) when the volume resistivity (Ω·cm) of the electrode film was less than 10, ◯ (good) when the volume resistivity (Ω·cm) was 10 or more and less than 20, and x (poor) when the volume resistivity (Ω·cm) was 20 or more.
The positive electrode mixture slurry was applied to an aluminum foil using an applicator so that the basis weight per unit of the electrode was 20 mg/cm2 and the coating film was then dried in an electric oven at 120° C.±5° C. for 25 minutes. Then, the film was cut into two 90 mm×20 mm rectangles with the coating direction as the major axis. The peeling strength was measured using a desktop tensile tester (Strograph E3, commercially available from Toyo Seiki Co., Ltd.), and evaluated according to the 180 degree peeling test method. Specifically, a double-sided tape with a size of 100 mm×30 mm (No. 5000NS, commercially available from Nitoms Inc.) was attached to a stainless steel plate, and the produced battery electrode mixture layer was brought into close contact with the other surface of the double-sided tape, peeling off was performed while pulling from the bottom to the top at a certain speed (50 mm/min), and the average value of stress at this time was used as the peeling strength. The adhesiveness (N/cm) of the electrode film was evaluated as ⊙ (very good) for 1 or more, ◯ (good) for 0.5 or more and less than 1, and x (poor) for less than 0.5.
The non-aqueous electrolyte secondary battery was installed in a thermostatic chamber at 25° C. and charging and discharging measurement was performed using a charging and discharging device (SM-8 commercially available from Hokuto Denko Corporation). Constant current and constant voltage charging (a cut-off current of 1 mA (0.02 C)) was performed at a charging current of 10 mA (0.2 C) and a charge final voltage of 4.3 V, and constant current discharging was then performed at a discharging current of 10 mA (0.2 C) and a discharge final voltage of 3 V. This operation was repeated three times and constant current and constant voltage charging (a cut-off current 1 mA (0.02 C)) was then performed at a charging current of 10 mA (0.2 C) and a charge final voltage of 4.3 V, constant current discharging was performed at a discharging current of 0.2 C and 3 C until the discharge final voltage reached 3.0 V, and each discharge capacity was determined. The rate properties can be expressed as a ratio of the 0.2 C discharge capacity and the 3 C discharge capacity according to the following Formula 1.
Rate properties=3C discharge capacity/3rd 0.2 C discharge capacity×100% (Formula 1)
For the rate properties, those having rate properties of 80% or more were evaluated as ⊙ (very good), those having rate properties of 60% or more and less than 80% were evaluated as ◯ (good), and those having rate properties of less than 60% were evaluated as x (poor).
The non-aqueous electrolyte secondary battery was installed in a thermostatic chamber at 25° C. and charging and discharging measurement was performed using a charging and discharging device (SM-8 commercially available from Hokuto Denko Corporation). Constant current and constant voltage charging (a cut-off current of 2.5 mA (0.05 C)) was performed at a charging current of 25 mA (0.5 C) and a charge final voltage of 4.3 V, and constant current discharging was then performed at a discharging current of 25 mA (0.5 C) and a discharge final voltage of 3 V. This operation was repeated 200 times. The cycle properties can be expressed as a ratio of the 3rd 0.5 C discharge capacity and the 200th 0.5 C discharge capacity at 25° C. according to the following Formula 2.
Cycle properties=3rd 0.5 C discharge capacity/200th 0.5 C discharge capacity×100(%) (Formula 2)
For the cycle properties, those having cycle properties of 85% or more were evaluated as ⊙ (very good), those having cycle properties of 80% or more and less than 85% were evaluated as ◯ (good), and those having cycle properties of less than 80% were evaluated as − (poor).
100 parts of acetonitrile was put into a reaction container including a gas inlet pipe, a thermometer, a condenser, and a stirrer, and the inside was purged with nitrogen gas. The inside of the reaction container was heated to 70° C., and a mixture containing 50.0 parts of acrylonitrile, 25.0 parts of acrylic acid, 25.0 parts of styrene and 5.0 parts of 2,2′-azobis(2,4-dimethylvaleronitrile) (V-65, commercially available from NOF Corporation) was added dropwise over 3 hours, and a polymerization reaction was performed. After dropwise addition was completed, the reaction was additionally performed at 70° C. for 1 hour, and 0.5 parts of V-65 was then added, and the reaction was additionally continued at 70° C. for 1 hour. Then, the non-volatile content was measured, and it was confirmed that the conversion ratio exceeded 98%, and the dispersion medium was completely removed by concentration under a reduced pressure to obtain a dispersant (A-1γ). The weight average molecular weight (Mw) of the dispersant (A-1γ) was 15,000.
Dispersants (A-2γ) to (A-10γ) were produced in the same manner as in Production Example 1γ except that monomers used were changed according to Table 1γ. The weight average molecular weights (Mw) of the dispersants were as shown in Table 1γ.
50 parts of the dispersant (A-3γ) obtained in Production Example 3γ was added to 198 parts of purified water, and the mixture was stirred with a disper to prepare a slurry. Next, 2.0 parts of a 1 N sodium hydroxide aqueous solution was added dropwise at 25° C., and the mixture was stirred with a disper for 2 hours while heating in a water bath. In IR measurement (device: FT/IR-410, commercially available from JASCO Corporation), it was confirmed that the intensity of the peak derived from the cyano group was reduced to 80% or less and it was confirmed that the cyclic structure was formed. Next, washing with purified water was performed, and filtering and drying were performed to obtain a dispersant (A-11γ) having a hydrogenated naphthyridine ring and a glutarimide ring. Here, the weight average molecular weight (Mw) was 14,000.
A dispersant (A-12γ) having a hydrogenated naphthyridine ring was obtained in the same manner as in Production Example 13γ except that the dispersant used was changed from (A-3) to (A-6γ). Here, the weight average molecular weight (Mw) was 14,000.
93 parts by mass of the positive electrode active material (HED (registered trademark) NCM-111 1100, commercially available from BASF TODA Battery Materials LLC), 4 parts by mass of acetylene black (Denka Black (registered trademark) HS100, commercially available from Denka Co., Ltd.), and 3 parts by mass of PVDF (Kureha KF polymer W #1300, commercially available from Kureha Battery Materials Japan Co., Ltd.) were put into a plastic container having a volume of 150 cm3 and then mixed with a spatula until powder was uniform. Then, 20.5 parts by mass of NMP was added thereto and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation). Then, the mixture in the plastic container was mixed with a spatula until it was uniform, and stirred at 2,000 rpm for 30 seconds using the rotation/revolution mixer. In addition, 14.6 parts by mass of NMP was then added thereto, and the mixture was stirred at 2,000 rpm for 30 seconds using the rotation/revolution mixer. Finally, the sample was stirred at 3,000 rpm for 10 minutes using a high-speed stirrer to obtain a standard positive electrode mixture slurry.
The above standard positive electrode mixture slurry was applied to an aluminum foil having a thickness of 20 μm as a current collector using an applicator and then dried in an electric oven at 120° C.±5° C. for 25 minutes and the basis weight per unit area of the electrode was adjusted to 20 mg/cm2. In addition, the sample was rolled by a roll press (3t hydraulic roll press, commercially available from Thank Metal Co., Ltd.) to produce a positive electrode having a mixture layer density of 3.1 g/cm3.
According to the compositions and dispersion times shown in Table 2γ, a dispersant, an additive, and a dispersion medium were put into a glass bottle (M-225, commercially available from Hakuyo Glass Co., Ltd.) and sufficiently mixed and dissolved, or mixed and an conductive material was then added thereto, and the mixture was dispersed with a paint conditioner using zirconia beads (with a bead diameter of 0.5 mmφ) as media to obtain conductive material dispersed materials (dispersed material 1γ to dispersed material 23γ, and comparative dispersed materials 1γ to 5γ). As shown in Table 2γ, the conductive material dispersed materials (dispersed material 1γ to dispersed material 23γ) of the present invention all had low viscosity and good storage stability.
The conductive material dispersed material (dispersed material 1γ), CMC, and water were put into a plastic container having a volume of 150 cm3 and the mixture was then stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation) to obtain a conductivity-containing resin composition 1. Then, an active material was added thereto, and the mixture was stirred at 2,000 rpm for 150 seconds using the rotation/revolution mixer. In addition, SBR was then added thereto, and the mixture was stirred at 2,000 rpm for 30 seconds using the rotation/revolution mixer to obtain a negative electrode mixture slurry 1. The non-volatile content of the negative electrode mixture slurry 1γ was 48% by mass. The non-volatile content ratio of the active material:conductive material:CMC:SBR in the negative electrode mixture slurry was 97:0.5:1:1.5.
Conductive material-containing resin compositions 2γ to 18γ, 21γ, and 22γ, comparative conductive material-containing resin compositions 1γ, 3γ to 5γ, negative electrode mixture slurries 2γ to 18γ, 21γ, and 22γ and negative electrode comparative mixture slurries 1γ, and 3γ to 5γ were obtained in the same method as in Example 24γ except that the type of the conductive material dispersed material was changed. As shown in Table 3γ, the electrode films using the conductive material dispersed material of the present invention all had good electrical conductivity and adhesiveness.
The conductive material dispersed material (dispersed material 19γ) and NMP in which 8% by mass PVDF was dissolved were put into a plastic container having a volume of 150 cm and then stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation) to obtain a conductive material-containing resin composition 19γ. Then, an active material was added thereto, and the mixture was stirred at 2,000 rpm for 150 seconds using the rotation/revolution mixer. In addition, NMP was then added thereto, and the mixture was stirred at 2,000 rpm for 30 seconds using the rotation/revolution mixer to obtain a positive electrode mixture slurry 19γ. The non-volatile content of the positive electrode mixture slurry 19γ was 75% by mass. The non-volatile content ratio of the active material:conductive material:PVDF in the positive electrode mixture slurry was 98.5:0.5:1.
Conductive material-containing resin compositions 20γ and 23γ, a comparative conductive material-containing resin composition 2γ, positive electrode mixture slurries 20γ and 23γ and a positive electrode comparative mixture slurry 2γ were obtained in the same method as in Example 44γ except that the type of the conductive material dispersed material was changed. As shown in Table 4γ, the electrode films using the conductive material dispersed material of the present invention all had good electrical conductivity and adhesiveness.
The mixture slurry shown in Table 5γ was applied to a metal foil using an applicator and the coating film was then dried in an electric oven at 120° C.±5° C. for 25 minutes to produce an electrode film. Then, the electrode film was rolled by a roll press (3t hydraulic roll press, commercially available from Thank Metal Co., Ltd.). When the positive electrode mixture slurry was applied, an aluminum foil was used as the metal foil, application was performed so that the basis weight per unit of the electrode was 20 mg/cm2, and rolling was performed so that the density of the dried electrode film was 3.1 g/cc. When the negative electrode mixture slurry was applied, a copper foil was used as the metal foil, application was performed so that the basis weight per unit of the electrode was 10 mg/cm2, and rolling was performed so that the density of the dried electrode film was 1.6 g/cc.
The negative electrode and the positive electrode shown in Table 6γ were punched out into 50 mm×45 mm and 45 mm×40 mm, respectively, and a separator (porous polypropylene film) inserted therebetween was inserted into an aluminum laminate bag and dried in an electric oven at 70° C. for 1 hour. Then, 2 mL of an electrolyte solution (a non-aqueous electrolyte solution obtained by preparing a mixed solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate at a ratio of 1:1:1 (volume ratio), additionally adding 1 part by mass of VC (vinylene carbonate) with respect to 100 parts by mass as an additive, and then dissolving LiPF6 at a concentration of 1 M) was injected into a glove box filled with argon gas, and the aluminum laminate was then sealed to produce non-aqueous electrolyte secondary batteries 1γ to 23γ, and comparative non-aqueous electrolyte secondary batteries 1γ to 4γ.
In the above examples, the dispersant was a copolymer containing a (meth)acrylonitrile-derived unit, and one or more monomer units selected from the group consisting of an active hydrogen group-containing monomer, a basic monomer, and a (meth)acrylic acid alkyl ester, and in the copolymer, a conductive material dispersed material containing 40 to 99% by mass of the (meth)acrylonitrile-derived unit and having a weight average molecular weight of 5,000 to 50,000 was used. In the examples, non-aqueous electrolyte secondary batteries having better cycle properties than those of comparative examples were obtained. In particular, in the conductive material dispersed material containing 75% by mass of the (meth)acrylonitrile-derived unit and having a weight average molecular weight of 5,000 to 50,000, since the acrylonitrile-derived unit had a cyclic structure, non-aqueous electrolyte secondary batteries having better cycle properties than those of comparative examples were obtained. Therefore, it can be clearly understood that the present invention can provide a non-aqueous electrolyte secondary battery having cycle properties that cannot be realized with a conventional conductive material dispersed material.
The weight average molecular weight (Mw) and the number average molecular weight (Mn) were measured by a gel permeation chromatographic (GPC) device including an RI detector, and based on the obtained Mw and Mn, the molecular weight distribution (Mw/Mn) and the proportion of components having a molecular weight of 1,000 or less were calculated. For the device, HLC-8320GPC (commercially available from Tosoh Corporation) was used, and three separation columns were connected in series, “TSK-GELSUPER AW-4000,” “AW-3000,” and “AW-2500” (commercially available from Tosoh Corporation) were used as fillers in order, and the measurement was performed at an oven temperature of 40° C. using an N,N-dimethylformamide solution containing 30 mM trimethylamine and 10 mM LiBr as an eluent at a flow rate of 0.6 ml/min. The sample was prepared in a solvent including the above eluent at a concentration of 1 wt %, and 20 microliters thereof was injected. The molecular weight was a polystyrene conversion value.
The infrared spectroscopic analysis of the dispersant was performed using an infrared spectrophotometer (Nicolet iS5 FT-IR spectrometer, commercially available from Thermo Fisher Scientific). In addition, in the case of the conductive material dispersed material, the conductive material was separated by centrifugation, and the separated supernatant was dried with hot air at 100° C. to prepare a measurement sample.
Measurement of the viscosity of the conductive material dispersed material, and evaluation of the stability of the dispersed material; evaluation of the electrical conductivity and evaluation of the adhesiveness of the electrode film using the positive electrode mixture slurry; and evaluation of rate properties and evaluation of cycle properties of the non-aqueous electrolyte secondary battery were performed according to the same method and criteria as in Example group γ.
For the complex modulus of elasticity and the phase angle of the conductive material dispersed material, dynamic viscoelasticity measurement was performed in a distortion rate range from 0.01% to 5% using a rheometer (RheoStress1 rotary rheometer, commercially available from Thermo Fisher) with a 2° cone having a diameter of 60 mm, at 25° C. and a frequency of 1 Hz, for evaluation. If the obtained complex modulus of elasticity was smaller, the dispersibility was better, and if the obtained complex modulus of elasticity was higher, the dispersibility was poorer. In addition, if the obtained phase angle was larger, the dispersibility was better, and if the obtained phase angle was smaller, the dispersibility was poorer.
Determination Criteria for Complex Modulus of Elasticity
⊙: less than 5 Pa (very good)
◯: 5 Pa or more and less than 20 Pa (fair)
x: 20 Pa or more (poor)
xx: 100 Pa or more (very poor)
Determination Criteria for Phase Angle
⊙: 45° or more (very good)
◯: 30° or more and less than 450 (good)
Δ: 190 or more and less than 30° (fair)
x: less than 19° (poor)
100 parts of acetonitrile was put into a reaction container including a gas inlet pipe, a thermometer, a condenser, and a stirrer, and the inside was purged with nitrogen gas. The inside of the reaction container was heated to 70° C. and a mixture containing 100.0 parts of acrylonitrile, 4.0 parts of 3-mercapto-1,2-propanediol and 1.0 part of 2,2′-azobis(2,4-dimethylvaleronitrile) (V-65, commercially available from NOF Corporation) was added dropwise over 3 hours, and a polymerization reaction was performed. After dropwise addition was completed, the reaction was additionally performed at 70° C. for 1 hour and 0.5 parts of V-65 was then added, and the reaction was additionally continued at 70° C. for 1 hour to obtain a desired product as a precipitate. Then, the non-volatile content was measured and it was confirmed that the conversion ratio exceeded 95%. The product was filtered off under a reduced pressure and washed with 100 parts of acetonitrile, and the solvent was then completely removed by performing drying under a reduced pressure to obtain a dispersant (C-1δ). The weight average molecular weight (Mw) of the dispersant (C-1δ) was 5,000, the molecular weight distribution (Mw/Mn) was 1.8, and the proportion of components having a molecular weight of 1,000 or less was 3.5%.
Dispersants (C-2δ) to (C-5δ) were produced in the same manner as in Production Example 1δ except that monomers used were changed according to Table 1δ. The weight average molecular weights (Mw) of the dispersants were as shown in Table 16.
50 parts of the dispersant (C-2δ) obtained in Production Example 2δ was added to 198 parts of purified water, and the mixture was stirred with a disper to prepare a slurry. Next, 2.0 parts of a 1 N sodium hydroxide aqueous solution was added dropwise at 25° C., and the mixture was stirred with a disper for 2 hours while heating in a water bath. In IR measurement (device: FT/IR-410, commercially available from JASCO Corporation), it was confirmed that the intensity of the peak derived from the cyano group was reduced to 80% or less and it was conformed that the cyclic structure was formed (
The molecular weight distributions (Mw/Mn) of the dispersant (C-1δ) to the dispersant (C-6δ) were all in a range of 1.0 to 3.0. In addition, the proportions of the components having a molecular weight of less than 1,000 were all 4% or less.
According to the compositions and dispersion times shown in Table 2δ, a dispersant, an additive, and a dispersion medium were put into a glass bottle (M-225, commercially available from Hakuyo Glass Co., Ltd.) and sufficiently mixed and dissolved or mixed and a conductive material was then added thereto and the mixture was dispersed with a paint conditioner using zirconia beads (with a bead diameter of 0.5 mmφ) as media to obtain conductive material dispersed materials (dispersed material 1δ to dispersed material 9δ, and comparative dispersed materials 1δ to 3δ). As shown in Table 2δ, the conductive material dispersed materials (dispersed material 1δ to dispersed material 9δ) of the present invention all had low viscosity and good storage stability.
The materials shown in Table 2δ are abbreviated as follows.
As shown in
According to the composition shown in Table 3δ, the conductive material dispersed material (dispersed material 1δ) and NMP in which 8% by mass PVDF was dissolved were put into a plastic container having a volume of 150 cm and the mixture was then stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation) to obtain a conductive material-containing resin composition. Then, an active material was added thereto and the mixture was stirred at 2,000 rpm for 150 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation). In addition, NMP was then added thereto and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation) to obtain a positive electrode mixture slurry. The non-volatile content of the positive electrode mixture slurry was 75% by mass.
Subsequently, the positive electrode mixture slurry was applied to an aluminum foil using an applicator so that the basis weight per unit of the electrode was 20 mg/cm2 and the coating film was then dried in an electric oven at 120° C.±5 C for 25 minutes to produce an electrode film. Then, the electrode film was rolled by a roll press (3t hydraulic roll press, commercially available from Thank Metal Co., Ltd.) so that the density was 3.1 g/cc to obtain a positive electrode 1δ.
Next, the positive electrode 1δ and the standard negative electrode were punched out into 50 mm×45 mm and 45 mm×40 mm, respectively, and a separator (porous polypropylene film) inserted therebetween was inserted into an aluminum laminate bag and dried in an electric oven at 70° C. for 1 hour. Then, 2 mL of an electrolyte solution (a non-aqueous electrolyte solution obtained by preparing a mixed solvent obtained by mixing ethylene carbonate, dimethyl carbonate, and diethyl carbonate at a ratio of 1:1:1 (volume ratio), additionally adding 1 part by mass of VC (vinylene carbonate) with respect to 100 parts by mass as an additive, and then dissolving LiPF6 at a concentration of 1 M) was injected into a glove box filled with argon gas, and the aluminum laminate was then sealed to produce a battery 1δ.
Acetylene black (Denka Black (registered trademark) HS100, commercially available from Denka Co., Ltd.,), CMC, and water were put into a plastic container having a volume of 150 ml and then stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation). In addition, artificial graphite was added as an active material, and the mixture was stirred at 2,000 rpm for 150 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation). Subsequently, SBR was added thereto and the mixture was stirred at 2,000 rpm for 30 seconds using a rotation/revolution mixer (Awatori Rentaro, ARE-310, commercially available from Thinky Corporation) to obtain a standard negative electrode mixture slurry. The non-volatile content of the standard negative electrode mixture slurry was 48% by mass. The non-volatile content ratio of the active material:conductive material:CMC:SBR in the standard negative electrode mixture slurry was 97:0.5:1:1.5.
HS-100: Denka Black HS-100 (acetylene black, an average primary particle size of 48 nm, a specific surface area of 39 m2/g, commercially available from Denka Co., Ltd.)
Artificial graphite: CGB-20 (commercially available from Nippon Graphite Industries, Co., Ltd.), a non-volatile content of 100%
CMC: #1190 (commercially available from Daicel FineChem Co., Ltd.), a non-volatile content of 100%
SBR: TRD2001 (commercially available from JSR), a non-volatile content of 48%
The negative electrode mixture slurry was applied to a copper foil having a thickness of 20 μm as a current collector using an applicator and then dried in an electric oven at 80° C.±5° C. for 25 minutes. The basis weight per unit area of the electrode was adjusted to 10 mg/cm2. In addition, the sample was rolled by a roll press (3t hydraulic roll press, commercially available from Thank Metal Co., Ltd.) to produce a negative electrode having a mixture layer density of 1.6 g/cm3.
Positive electrode mixture slurries were produced according to the same method as in Example 2-1δ except that the type of the conductive material dispersed material and/or the composition of the mixture slurry was changed according to Table 3δ. Positive electrodes 2δ to 9δ, comparative positive electrodes 1δ to 3δ, batteries 2δ to 9δ, and comparative batteries 1δ to 3δ were produced using the obtained positive electrode mixture slurries.
Table 4δ shows the volume resistivity and peeling strength of the positive electrodes 1δ to 9δ and the comparative positive electrodes 1δ to 3δ, and rate properties and cycle properties of the batteries 1δ to 9δ and the comparative batteries 1δ to 3δ.
The positive electrodes 1δ to 9δ had better electrical conductivity and adhesiveness than the comparative positive electrodes 1δ to 3δ. In addition, the batteries obtained using these positive electrodes had better rate properties and cycle properties than the comparative batteries. According to the present invention, it was possible to provide a non-aqueous electrolyte secondary battery having rate properties and cycle properties that were difficult to realize with conventional conductive material dispersed materials.
While the present invention has been described above with reference to the embodiments, the present invention is not limited to the above description. For the configuration and details of the present invention, various changes that can be understood by those skilled in the art can be made within the scope of the invention.
Priority is claimed on Japanese Patent Application No. 2019-66507 filed Mar. 29, 2019, Japanese Patent Application No. 2019-89540 filed May 10, 2019, Japanese Patent Application No. 2019-114283 filed Jun. 20, 2019, Japanese Patent Application No. 2019-138688 filed Jul. 29, 2019, Japanese Patent Application No. 2020-4142, filed Jan. 15, 2020, and Japanese Patent Application No. 2020-10631, filed Jan. 27, 2020, the content of which are incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-066507 | Mar 2019 | JP | national |
| 2019-089540 | May 2019 | JP | national |
| 2019-114283 | Jun 2019 | JP | national |
| 2019-138688 | Jul 2019 | JP | national |
| 2020-004142 | Jan 2020 | JP | national |
| 2020-010631 | Jan 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/013883 | 3/27/2020 | WO | 00 |
