Patent Application
20220069418
This Nonprovisional application claims priority under 35 U.S.C. § 119 on Patent Application No. 2020-148408 filed in Japan on Sep. 03, 2020, Patent Application No. 2021-089536 filed in Japan on May 27, 2021, and Patent Application No. 2021-142194 filed in Japan on Sep. 01, 2021, the entire contents of which are hereby incorporated by reference.
The present invention relates to a porous layer for a nonaqueous electrolyte secondary battery (hereinafter, referred to as a “nonaqueous electrolyte secondary battery porous layer”).
Nonaqueous electrolyte secondary batteries, particularly lithium-ion secondary batteries, have high energy densities, and are thus in wide use as batteries for personal computers, mobile telephones, portable information terminals, and the like. Recently, such nonaqueous electrolyte secondary batteries have been developed as batteries for vehicles.
The end-of-charge voltages of conventional nonaqueous electrolyte secondary batteries are approximately 4.1 V to 4.2 V (4.2 V to 4.3 V (vs Li/Li+) as voltages relative to the electric potentials of lithium reference electrodes). In contrast, the end-of-charge voltages of recent nonaqueous electrolyte secondary batteries are increased to not less than 4.3 V, which is higher than those of the conventional nonaqueous electrolyte secondary batteries, so that the utilization rates of positive electrodes are increased and thereby the capacities of batteries are increased. For this purpose, it is important that resins contained in nonaqueous electrolyte secondary battery porous layers do not change in quality even when the resins are placed under high-voltage conditions.
Patent Literature 1 is one of documents which disclose resins having such a property. Patent Literature 1 discloses a wholly aromatic polyamide in which aromatic rings located at the respective terminals of its molecular chain each does not have an amino group and in which one or more aromatic rings each have an electron-withdrawing substituent. According to Patent Literature 1, the wholly aromatic polyamide hardly changes in color even when the wholly aromatic polyamide receives a high voltage.
[Patent Literature 1]
Japanese Patent Application Publication Tokukai No. 2003-40999
One of functional groups each having an electron-withdrawing property is a sulfonyl group. Therefore, it can be expected that employing a resin containing a sulfonyl group allows obtainment of a nonaqueous electrolyte secondary battery porous layer which does not change in quality even under a high-voltage condition. However, as a result of conducting studies, the inventors of the present invention found that a nonaqueous electrolyte secondary battery porous layer which contains (i) a resin containing a sulfonyl group and (ii) a filler is poor in adhesiveness to a polyolefin porous film and peels off in powder form (powder falling occurs).
The object of an aspect of the present invention is to provide a nonaqueous electrolyte secondary battery porous layer which has both high-voltage resistance and adhesiveness.
The inventors of the present invention found that the above object can be attained by a nonaqueous electrolyte secondary battery porous layer which contains a block copolymer that has a block containing a large number of sulfonyl groups (block A) and a block containing a small number of sulfonyl groups (block B). Specifically, the present invention encompasses the following features.
<1>
A nonaqueous electrolyte secondary battery porous layer containing:
a block copolymer; and
a filler,
the block copolymer having:
—(NH—Ar1—NHCO—Ar2—CO)— Formula (1); and
—(NH—Ar3—NHCO—Ar4—CO)— Formula (2),
wherein:
The nonaqueous electrolyte secondary battery porous layer as described in <1>, wherein:
not less than 50% of the units which are contained in the block A and which are each represented by Formula (1) are each 4,4′-diphenylsulfonyl terephthalamide; and
not less than 50% of the units which are contained in the block
B and which are each represented by Formula (2) are each paraphenylene terephthalamide.
<3>
The nonaqueous electrolyte secondary battery porous layer as described in <1> or <2>, wherein the block copolymer has a triblock structure of block B-block A-block B.
<4>
The nonaqueous electrolyte secondary battery porous layer as described in any one of <1> through <3>, wherein
in a molecule corresponding to a mode in a molecular weight distribution of the block copolymer,
the block A contains 10 to 1000 units each represented by Formula (1), and
the block B contains 10 to 500 units each represented by Formula (2).
<5>
The nonaqueous electrolyte secondary battery porous layer as described in any one of <1> through <4>, further containing:
a polymer which contains no units each represented by Formula (1) and which contains 5 to 200 units each represented by Formula (2).
<6>
The nonaqueous electrolyte secondary battery porous layer as described in any one of <1> through <5>, wherein when a weight of the nonaqueous electrolyte secondary battery porous layer is regarded as 100% by weight, the nonaqueous electrolyte secondary battery porous layer comprises the filler in a proportion of 20% by weight to 90% by weight.
<7>
The nonaqueous electrolyte secondary battery porous layer as described in any one of <1> through <6>, wherein the filler contains aluminum oxide.
<8>
A nonaqueous electrolyte secondary battery laminated separator containing:
a polyolefin porous film; and
a nonaqueous electrolyte secondary battery porous layer as described in any one of <1> through <7>,
the nonaqueous electrolyte secondary battery porous layer being formed on one surface or both surfaces of the polyolefin porous film.
<9>
A nonaqueous electrolyte secondary battery containing:
a nonaqueous electrolyte secondary battery porous layer as described in any one of <1> through <7> or a nonaqueous electrolyte secondary battery laminated separator as described in <8>.
According to an aspect of the present invention, a nonaqueous electrolyte secondary battery porous layer which has both high-voltage resistance and adhesiveness is provided.
The following description will discuss embodiments of the present invention. Note, however, that the present invention is not limited to the embodiments. The present invention is not limited to arrangements described below, but may be altered in various ways by a skilled person within the scope of the claims. The present invention also encompasses, in its technical scope, any embodiment derived by combining technical means disclosed in differing embodiments. Note that a numerical range “A to B” herein means “not less (lower) than A and not more (higher) than B” unless otherwise stated.
[1. Nonaqueous Electrolyte Secondary Battery Porous Layer]
A nonaqueous electrolyte secondary battery porous layer in accordance with an embodiment of the present invention contains a block copolymer and a filler. Each of these components will be described below.
In this specification, the nonaqueous electrolyte secondary battery porous layer may be abbreviated to “porous layer”. Further, in this specification, a laminated separator for a nonaqueous electrolyte secondary battery (hereinafter referred to as a “nonaqueous electrolyte secondary battery laminated separator”) may be abbreviated to “laminated separator”.
[Block Copolymer]
The block copolymer has a block A and a block B. The block
A contains, as a main component, units each represented by the following Formula (1). The block B contains, as a main component, units each represented by the following Formula (2).
—(NH—Ar1—NHCO—Ar2—CO)— Formula (1)
—(NH—Ar3—NHCO—Ar4—CO)— Formula (2)
The units each represented by Formula (1) account for preferably not less than 80%, more preferably not less than 90%, and still more preferably not less than 95% of all units contained in the block A. In an embodiment, the block A is represented by the units each represented by Formula (1), in its entirety, except for the terminals. The units each represented by Formula (2) account for preferably not less than 80%, more preferably not less than 90%, and still more preferably not less than 95% of all units contained in the block B. In an embodiment, the block B is represented by the units each represented by Formula (2), in its entirety, except for the terminals.
When the block copolymer has the units each represented by Formula (1) and the units each represented by Formula (2) in the above respective ranges, the block copolymer comes to have the properties of an aromatic polyamide. An aromatic polyamide is excellent in heat resistance and the like, and is suitable as a material of a nonaqueous electrolyte secondary battery porous layer.
In Formulae (1) and (2), Ar1, Ar2, Ar3, and Ar4 may each vary from unit to unit. Ar1, Ar2, Ar3, and Ar4 are each independently a divalent group having one or more aromatic rings.
In this specification, an “aromatic ring” indicates a cyclic compound which satisfies the Hückel's rule. Examples of the aromatic ring include benzene, naphthalene, anthracene, azulene, pyrrole, pyridine, furan, and thiophene. In an embodiment, an aromatic ring is composed solely of carbon atoms and hydrogen atoms. In an embodiment, the aromatic ring is a benzene ring or a condensed ring derived from two or more benzene rings (such as naphthalene and anthracene).
At least some of all Ar1 have a structure in which two aromatic rings are connected by a sulfonyl bond. Ar3 may have a structure in which two aromatic rings are connected by a sulfonyl bond. The lower limit of the proportion of Ar1 and Ar3 each having the structure in which two aromatic rings are connected by a sulfonyl bond to all Ar1 and Ar3 is not less than 30%, preferably not less than 35%, and more preferably not less than 40%. The upper limit of the proportion is not more than 70%, preferably not more than 65%, and more preferably not more than 60%.
The proportion of Ar1 having the structure in which two aromatic rings are connected by a sulfonyl bond to all Ar1 is not less than 50%, preferably not less than 80%, and more preferably not less than 90%. In an embodiment, all Ar1 each have the structure in which two aromatic rings are connected by a sulfonyl bond.
The proportion of Ar3 having the structure in which two aromatic rings are connected by a sulfonyl bond to all Ar3 is not more than 50%, preferably not more than 20%, and more preferably not more than 10%. In an embodiment, all Ar3 do not have the structure in which two aromatic rings are connected by a sulfonyl bond.
Thus, it can be said that the block A is a block which contains a relatively large number of sulfonyl groups, whereas the block B is a block which contains a relatively small number of sulfonyl groups. By employing the block copolymer which has such two types of blocks, the resulting porous layer has both high-voltage resistance and adhesiveness.
Examples of the structure in which two aromatic rings are connected by a sulfonyl bond include 4,4′-diphenylsulfonyl, 3,4′-diphenylsulfonyl, and 3,3′-diphenylsulfonyl.
Examples of a structure which is different from the structure in which two aromatic rings are connected by a sulfonyl bond include the following.
In an embodiment, the structure in which two aromatic rings are connected by a sulfonyl bond is 4,4′-diphenylsulfonyl. In an embodiment, the structure which is different from the structure in which two aromatic rings are connected by a sulfonyl bond is para-phenyl.
In an embodiment, at least some of the units which are contained in the block A and which are each represented by Formula (1) are 4,4′-diphenylsulfonyl terephthalamide. The lower limit of the proportion of 4,4′-diphenylsulfonyl terephthalamide to the units which are contained in the block A and which are each represented by Formula (1) is preferably not less than 50%, more preferably not less than 80%, and still more preferably not less than 90%. Monomers from which 4,4′-diphenylsulfonyl terephthalamide is formed are readily available, and also 4,4′-diphenylsulfonyl terephthalamide is easy to handle.
In an embodiment, at least some of the units which are contained in the block B and which are each represented by Formula (2) are paraphenylene terephthalamide. The lower limit of the proportion of paraphenylene terephthalamide to the units which are contained in the block B and which are each represented by Formula (2) is preferably not less than 50%, more preferably not less than 80%, and still more preferably not less than 90%. Monomers from which paraphenylene terephthalamide is formed are readily available, and also paraphenylene terephthalamide is easy to handle.
The block copolymer may have a structure which is composed of units other than the units each represented by Formula (1) or (2). Examples of such a structure include a polyimide backbone.
(Structure of Block Copolymer)
The number of blocks which the block copolymer has is not limited to any particular number. In an embodiment, the block copolymer has a diblock structure of block A-block B. In an embodiment, the block copolymer has a triblock structure of block A-block B-block A or block B-block A-block B. In an embodiment, the block copolymer has a tetrablock structure of block A-block B-block A-block B. Among the above structures, the triblock structure of block B-block A-block B is preferable.
In one molecule of the block copolymer, the number of the units which are contained in the block A and which are each represented by Formula (1) is preferably 10 to 1000, and more preferably 20 to 300. When the number of the units each represented by Formula (1) falls within the above range, a sufficiently large number of sulfonyl groups are contained in a molecule, and accordingly the porous layer has high high-voltage resistance. In one molecule of the block copolymer, the number of the units which are contained in the block B and which are each represented by Formula (2) is preferably 10 to 500, and more preferably 15 to 200. When the number of the units each represented by Formula (2) falls within the above range, the porous layer has high adhesiveness.
Note, here, that the number of the units each represented by Formula (1) and the number of the units each represented by Formula (2), which numbers are indicated as preferable numbers, are each the number in a molecule corresponding to the mode in the molecular weight distribution of the block copolymer. The molecular weight distribution of the block copolymer can be experimentally obtained by, for example, gel permeation chromatography.
The molecular weight of the block copolymer is preferably 0.5 dL/g to 5 dL/g, and more preferably 0.8 dL/g to 2.5 dL/g, when expressed as an intrinsic viscosity. When the molecular weight falls within the above range, a favorable coating property can be achieved, and also the porous layer can have favorable strength.
The proportion of the block copolymer to the porous layer is preferably 10% by weight to 80% by weight, and more preferably 30% by weight to 60% by weight, when the weight of the porous layer is regarded as 100% by weight. When the proportion falls within the above range, it is possible to sufficiently impart, to the porous layer, high-voltage resistance derived from the electron-withdrawing property of the sulfonyl groups contained in the block copolymer.
(Method of Producing Block Copolymer)
The block copolymer can be synthesized according to a conventional method. For example, by employing the following procedure, it is possible to synthesize the block copolymer which has a diblock structure of block A-block B (the block copolymer which has another block structure can be also synthesized by applying the following procedure).
1. A diamine represented by NH2—Ar1—NH2 and a dicarboxylic halide represented by XOOC—Ar2—COOX (X is a halogen atom such as F, Cl, Br, and I), which serve as monomers, are polymerized according to a publicly known polymerization method for forming an aromatic polyamide. In this manner, the block A, which contains the units each represented by Formula (1), is synthesized.
2. After synthesis of the block A is completed, a diamine represented by NH2−Ar3—NH2 and a dicarboxylic halide represented by XOOC—Ar4—COOX (X is a halogen atom such as F, Cl, Br, and I), which serve as monomers, are polymerized according to a publicly known polymerization method for forming an aromatic polyamide. In this manner, the block B, which contains the units each represented by Formula (2), is synthesized in the state of being connected to the block A.
(Polymer Which Does Not Contain Unit Represented by Formula (1) but Contains Units Each Represented by Formula (2))
When the block copolymer is synthesized by the above-described procedure, a by-product which is constituted by only a lastly synthesized block can be also produced. For example, when the block copolymer which has the triblock structure of block B-block A-block B is synthesized, a polymer which is constituted by only the block B (i.e., a polymer which does not contain a unit represented by Formula (1) but contains units each represented by Formula (2)) is produced as a by-product.
Therefore, the nonaqueous electrolyte secondary battery porous layer in accordance with an embodiment of the present invention may contain a polymer which does not contain a unit represented by Formula (1) but contains units each represented by Formula (2). The nonaqueous electrolyte secondary battery porous layer in accordance with an embodiment of the present invention may contain (i) a polymer which does not contain a unit represented by Formula (1) but contains units each represented by Formula (2) and (ii) the block copolymer which has the triblock structure of block B-block A-block B.
The polymer which does not contain a unit represented by Formula (1) but contains the units each represented by Formula (2) contains 5 to 200, and preferably 10 to 150 units each represented by Formula (2). The amount of such a polymer contained in the porous layer is preferably not more than 50 parts by weight, and more preferably not more than 20 parts by weight, with respect to 100 parts by weight of the block copolymer.
It is possible to determine, from the molecular weight distribution of the resin components of the porous layer, whether or not the porous layer contains the polymer which does not contain a unit represented by Formula (1) but contains the units each represented by Formula (2). Specifically, when a peak corresponding to the polymer which does not contain a unit represented by Formula (1) but contains the units each represented by Formula (2) is present in a molecular weight distribution curve, it can be said that the porous layer contains the polymer. In this case, the molecular weight distribution curve of the resin components of the porous layer has two or more peaks. The molecular weight distribution curve is experimentally obtained by gel permeation chromatography.
The number of the unis which are each represented by Formula (2) and which are contained in the polymer that does not contain a unit represented by Formula (1) but contains the units each represented by Formula (2) can be calculated from the molecular weight distribution curve. The abundance ratio of the polymer which does not contain a unit represented by Formula (1) but contains the units each represented by Formula (2) to the block copolymer can be also calculated from the molecular weight distribution curve.
[Filler]
As to the filler, there are the following types of fillers: organic fillers and inorganic fillers.
Examples of the organic fillers include: homopolymers and copolymers which are each obtained from one or more monomers such as styrene, vinyl ketone, acrylonitrile, methyl methacrylate, ethyl methacrylate, glycidyl methacrylate, glycidyl acrylate, and/or methyl acrylate; fluorine-based resins such as polytetrafluoroethylene, a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-ethylene copolymer, and polyvinylidene fluoride; melamine resins; urea resins; polyolefins; and polymethacrylates. Each of these organic fillers may be used alone or two or more of these organic fillers may be alternatively used in combination. Among these organic fillers, a polytetrafluoroethylene powder is preferable in terms of chemical stability.
Examples of the inorganic fillers include materials each made of an inorganic matter such as metal oxide, metal nitride, metal carbide, metal hydroxide, carbonate, or sulfate. Specific examples of the inorganic fillers include: powders of aluminum oxide (such as alumina), boehmite, silica, titania, magnesia, barium titanate, aluminum hydroxide, calcium carbonate, and the like; and minerals such as mica, zeolite, kaolin, and talc. Each of these inorganic fillers may be used alone or two or more of these inorganic fillers may be alternatively used in combination. Among these inorganic fillers, aluminum oxide is preferable in terms of chemical stability.
The shape of each of particles of the filler can be a substantially spherical shape, a plate shape, a columnar shape, a needle shape, a whisker shape, a fibrous shape, or the like. The particles can have any shape. The particles preferably have a substantially spherical shape, because such particles facilitate formation of uniform pores.
The average particle diameter of the filler contained in the porous layer is preferably 0.01 μm to 1 μm. In this specification, the “average particle diameter of the filler” indicates a volume-based average particle diameter (D50) of the filler. “D50” means a particle diameter having a value at which a cumulative value reaches 50% in a volume-based particle size distribution. D50 can be measured with use of, for example, a laser diffraction particle size analyzer (product names: SALD2200, SALD2300, etc., manufactured by Shimadzu Corporation).
The proportion of the filler to the porous layer is preferably 20% by weight to 90% by weight, and more preferably 40% by weight to 80% by weight, when the weight of the porous layer is regarded as 100% by weight. When the proportion of the filler falls within the above range, the resulting porous layer has sufficient ion permeability.
[Other Components]
The porous layer may contain one or more components other than the block copolymer and the filler. For example, the porous layer may contain a resin other than the block copolymer.
Examples of such a resin include polyolefins; (meth)acrylate-based resins; fluorine-containing resins; polyamide-based resins; polyimide-based resins; polyamide imide-based resins; polyester-based resins; rubbers; resins each having a melting point or a glass transition temperature of not lower than 180° C.; water-soluble polymers; polycarbonates, polyacetals, and polyether ether ketones.
Among the above resins, (meth)acrylate-based resins, fluorine-containing resins, polyamide-based resins, polyimide-based resins, polyamide imide, polyester-based resins, and water-soluble polymers are preferable.
Preferable examples of the polyolefins include polyethylene, polypropylene, polybutene, and an ethylene-propylene copolymer.
Examples of the fluorine-containing resins include polyvinylidene fluoride (PVDF), polytetrafluoroethylene, a vinylidene fluoride-hexafluoropropylene copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-trifluoroethylene copolymer, a vinylidene fluoride-trichloroethylene copolymer, a vinylidene fluoride-vinyl fluoride copolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, and an ethylene-tetrafluoroethylene copolymer. The fluorine-containing resins are particularly exemplified by fluorine-containing rubbers each having a glass transition temperature of not higher than 23° C.
Preferable examples of the polyamide-based resins include aramid resins such as aromatic polyamides and wholly aromatic polyamides.
Specific examples of the aramid resins include poly(paraphenylene terephthalamide), poly(metaphenylene is ophthalamide), poly(parabenzamide), poly(metabenzamide), poly(4,4′-benzanilide terephthalamide), poly(paraphenylene-4,4′-biphenylene dicarboxylic acid amide), poly(metaphenylene-4,4′-biphenylene dicarboxylic acid amide), poly(paraphenylene-2,6-naphthalene dicarboxylic acid amide), poly(metaphenylene-2,6-naphthalene dicarboxylic acid amide), poly(2-chloroparaphenylene terephthalamide), a paraphenylene terephthalamide/2,6-dichloroparaphenylene terephthalamide copolymer, and a metaphenylene terephthalamide/2,6-dichloroparaphenylene terephthalamide copolymer. Among these aramid resins, poly(paraphenylene terephthalamide) is more preferable.
Preferable examples of the polyester-based resins include aromatic polyesters, such as polyarylate, and liquid crystal polyesters.
Examples of the rubbers include a styrene-butadiene copolymer and a hydride thereof, a methacrylic acid ester copolymer, an acrylonitrile-acrylic acid ester copolymer, a styrene-acrylic acid ester copolymer, ethylene propylene rubber, and polyvinyl acetate.
Examples of the resins each having a melting point or a glass transition temperature of not lower than 180° C. include polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyetherimide, polyamide imide, and polyether amide.
Examples of the water-soluble polymers include polyvinyl alcohol, polyethylene glycol, cellulose ether, sodium alginate, polyacrylic acid, polyacrylamide, and polymethacrylic acid.
Note that, as the resin used for the porous layer, each of these resins may be used alone or two or more of these resins may be alternatively used in combination.
[2. Nonaqueous Electrolyte Secondary Battery Laminated Separator]
An aspect of the present invention is a nonaqueous electrolyte secondary battery laminated separator which includes: a polyolefin porous film; and the above-described porous layer that is formed on one surface or both surfaces of the polyolefin porous film.
[Polyolefin Porous Film]
The nonaqueous electrolyte secondary battery laminated separator in accordance with an embodiment of the present invention includes a polyolefin porous film. The polyolefin porous film has therein many pores connected to one another. This allows a gas and a liquid to pass through the polyolefin porous film from one side to the other side. The polyolefin porous film can be a base material of the nonaqueous electrolyte secondary battery laminated separator. The polyolefin porous film can be one that imparts a shutdown function to the nonaqueous electrolyte secondary battery laminated separator by, when a battery generates heat, melting and thereby making the nonaqueous electrolyte secondary battery laminated separator non-porous.
Note, here, that a “polyolefin porous film” is a porous film which contains a polyolefin-based resin as a main component. Note that the phrase “contains a polyolefin-based resin as a main component” means that the porous film contains the polyolefin-based resin in a proportion of not less than 50% by volume, preferably not less than 90% by volume, and more preferably not less than 95% by volume, relative to the total amount of materials of which the porous film is made.
The polyolefin-based resin which the polyolefin porous film contains as a main component is not limited to any particular one. Examples of the polyolefin-based resin include homopolymers and copolymers which are each a thermoplastic resin and which are each obtained by polymerizing one or more monomers such as ethylene, propylene, 1-butene, 4-methyl-1-pentene, and/or 1-hexene. Specific examples of the homopolymers include polyethylene, polypropylene, and polybutene. Specific examples of the copolymers include an ethylene-propylene copolymer. The polyolefin porous film can be a layer which contains one type of polyolefin-based resin or can be alternatively a layer which contains two or more types of polyolefin-based resins. Among these polyolefin-based resins, polyethylene is more preferable because polyethylene makes it possible to prevent (shut down) a flow of an excessively large electric current at a lower temperature, and high molecular weight polyethylene which contains ethylene as a main component is particularly preferable. Note that the polyolefin porous film can contain a component other than polyolefin, provided that the component does not impair the function of the polyolefin porous film.
Examples of the polyethylene include low-density polyethylene, high-density polyethylene, linear polyethylene (ethylene-α-olefin copolymer), and ultra-high molecular weight polyethylene. Among these polyethylenes, ultra-high molecular weight polyethylene is more preferable, and ultra-high molecular weight polyethylene which contains a high molecular weight component having a weight-average molecular weight of 5×105 to 15×106 is still more preferable. In particular, the polyolefin-based resin which contains a high molecular weight component having a weight-average molecular weight of not less than 1,000,000 is more preferable, because such a polyolefin-based resin allows the polyolefin porous film and the nonaqueous electrolyte secondary battery laminated separator to each have increased strength.
The polyolefin porous film has a thickness of preferably 5 μm to 20 μm. more preferably 7 μm to 15 μm, and still more preferably 9 μm to 15 μm. The polyolefin porous film which has a thickness of not less than 5 μm can sufficiently achieve functions (such as a function of imparting the shutdown function) which the polyolefin porous film is required to have. The polyolefin porous film which has a thickness of not more than 20 μm allows the resulting nonaqueous electrolyte secondary battery laminated separator to be thinner.
The pores in the polyolefin porous film each have a diameter of preferably not more than 0.1 μm, and more preferably not more than not more than 0.06 μm. This makes it possible for the nonaqueous electrolyte secondary battery laminated separator to achieve sufficient ion permeability. Furthermore, this makes it possible to more prevent particles, which constitute an electrode, from entering the polyolefin porous film.
The polyolefin porous film typically has a weight per unit area of preferably 4 g/m2 to 20 g/m2, and more preferably 5 g/m2 to 12 g/m2, so as to allow a battery to have a higher weight energy density and a higher volume energy density.
The polyolefin porous film has an air permeability of preferably 30 s/100 mL to 500 s/100 mL, and more preferably 50 s/100 mL to 300 s/100 mL, in terms of Gurley values. This allows the nonaqueous electrolyte secondary battery laminated separator to achieve sufficient ion permeability.
The polyolefin porous film has a porosity of preferably 20% by volume to 80% by volume, and more preferably 30% by volume to 75% by volume. This makes it possible to (i) increase the amount of an electrolyte retained in the polyolefin porous film and (ii) absolutely prevent (shut down) a flow of an excessively large electric current at a lower temperature.
A method of producing the polyolefin porous film is not limited to a particular method, and any publicly known method can be employed. For example, as disclosed in Japanese Patent No. 5476844, a method can be employed which involves adding a filler to a thermoplastic resin, forming a resulting mixture into a film, and then removing the filler.
Specifically, when, for example, the polyolefin porous film is made of the polyolefin-based resin which contains ultra-high molecular weight polyethylene and low molecular weight polyolefin that has a weight-average molecular weight of not more than 10,000, the polyolefin porous film is preferably produced by, from the viewpoint of production costs, a method including the following steps (1) through (4):
(1) kneading 100 parts by weight of ultra-high molecular weight polyethylene, 5 parts by weight to 200 parts by weight of low molecular weight polyolefin which has a weight-average molecular weight of not more than 10,000, and 100 parts by weight to 400 parts by weight of an inorganic filler such as calcium carbonate to obtain a polyolefin-based resin composition;
(2) forming the polyolefin-based resin composition into a sheet;
(3) removing the inorganic filler from the sheet which has been obtained in the step (2); and
(4) stretching the sheet which has been obtained in the step (3).
Alternatively, the polyolefin porous film may be produced by a method disclosed in any of the above-listed Patent Literatures.
The polyolefin porous film can be alternatively a commercially available product which has the above-described characteristics.
[Physical Properties of Nonaqueous Electrolyte Secondary Battery Laminated Separator]
The laminated separator has an air permeability of preferably not more than 500 s/100 mL, and more preferably not more than 300 s/100mL, in terms of Gurley values. The porous layer included in the laminated separator has an air permeability of preferably not more than 400 s/100 mL, and more preferably not more than 200 s/100mL, in terms of Gurley values. When the air permeabilities fall within the above respective ranges, the laminated separator have sufficient ion permeability.
The air permeability of the porous layer is calculated by Y—X, where X represents the air permeability of the polyolefin porous film and Y represents the air permeability of the laminated separator. The air permeability of the porous layer can be adjusted by, for example, adjusting the intrinsic viscosity of one or more of the resins and/or the weight per unit area of the porous layer. Generally, as the intrinsic viscosity of a resin decreases, a Gurley value tends to decrease. As the weight per unit area of a porous layer decreases, a Gurley value tends to decrease.
The porous layer included in the laminated separator has a thickness of preferably not more than 10 μm, more preferably not more than 7 μm, and still more preferably not more than 5 μm.
In addition to the polyolefin porous film and the porous layer, the laminated separator may have another layer as necessary. Examples of such a layer include an adhesive layer and a protective layer.
[Method of Producing Nonaqueous Electrolyte Secondary Battery Laminated Separator]
The porous layer can be formed with use of a coating solution obtained by dissolving or dispersing the block copolymer, the filler, and optionally one or more components in a solvent. Examples of a method of forming the coating solution include a mechanical stirring method, an ultrasonic dispersion method, a high-pressure dispersion method, and a media dispersion method. The solvent can be, for example, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, or the like.
A method of forming the porous layer can be, for example, a method which involves preparing the above-described coating solution, applying the coating solution to the polyolefin porous film, and then drying the coating solution so that the porous layer is formed.
As a method of coating the polyolefin porous film with the coating solution, a publicly known coating method, such as a knife coater method, a blade coater method, a bar coater method, a gravure coater method, or a die coater method, can be employed.
The solvent (dispersion medium) is generally removed by a drying method. Examples of the drying method include natural drying, air-blow drying, heat drying, and drying under reduced pressure. Note, however, that any method can be employed, provided that the solvent (dispersion medium) can be sufficiently removed. Note also that drying can be carried out after the solvent (dispersion medium) contained in the coating solution is replaced with another solvent. A method of replacing the solvent (dispersion medium) with another solvent and then removing the another solvent can be specifically as follows: (i) the solvent (dispersion medium) is replaced with a poor solvent having a low boiling point, such as water, alcohol, or acetone, (ii) a solute is deposited, and (iii) drying is carried out.
[3. Nonaqueous Electrolyte Secondary Battery Member and Nonaqueous Electrolyte Secondary Battery]
A member for a nonaqueous electrolyte secondary battery (hereinafter referred to as a “nonaqueous electrolyte secondary battery member”) in accordance with an embodiment of the present invention includes a positive electrode, the above-described nonaqueous electrolyte secondary battery laminated separator, and a negative electrode which are disposed in this order. A nonaqueous electrolyte secondary battery in accordance with an embodiment of the present invention includes the above-described nonaqueous electrolyte secondary battery laminated separator. The nonaqueous electrolyte secondary battery typically has a structure in which a negative electrode and a positive electrode face each other with the nonaqueous electrolyte secondary battery laminated separator sandwiched therebetween. The nonaqueous electrolyte secondary battery is configured such that a battery element, which includes the structure and an electrolyte with which the structure is impregnated, is enclosed in an exterior member. The nonaqueous electrolyte secondary battery is, for example, a lithium ion secondary battery which achieves an electromotive force through doping with and dedoping of lithium ions.
[Positive Electrode]
The positive electrode can be, for example, a positive electrode sheet having a structure in which an active material layer, containing a positive electrode active material and a binding agent, is formed on a positive electrode current collector. The active material layer may further contain an electrically conductive agent.
Examples of the positive electrode active material include materials each capable of being doped with and dedoped of lithium ions.
Examples of the materials include lithium complex oxides each containing at least one type of transition metal such as V, Ti, Cr, Mn, Fe, Co, Ni, and/or Cu. Examples of the lithium complex oxides include lithium complex oxides each having a layer structure, lithium complex oxides each having a spinel structure, and solid solution lithium-containing transition metal oxides each constituted by a lithium complex oxide having both a layer structure and a spinel structure. Examples of the lithium complex oxides also include lithium cobalt complex oxides and lithium nickel complex oxides. Further, examples of the lithium complex oxides also include lithium complex oxides each obtained by substituting one or more of transition metal atoms, which constitute a large part of any of the above lithium complex oxides, with another or other elements such as Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg, Ca, Ga, Zr, Si, Nb, Mo, Sn, and/or W.
Examples of the lithium complex oxides each obtained by substituting one or more of transition metal atoms, which constitute a large part of any of the above lithium complex oxides, with another or other elements include: lithium cobalt complex oxides each having a layer structure and each represented by Formula (3) below; lithium nickel complex oxides each represented by Formula (4) below; lithium-manganese complex oxides each having a spinel structure and each represented by Formula (5) below; and solid solution lithium-containing transition metal oxides each represented by Formula (6) below.
Li[Lix(Co1−aM1a)1−x]O2 (3)
where: M1 is at least one type of metal selected from the group consisting of Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, and W; and −0.1≤x≤0.30 and 0≤a≤0.5 are satisfied.
Li[Liy(Ni1−bM2b)1−y]O2 (4)
where: M2 is at least one type of metal selected from the group consisting of Na, K, B, F, Al, Ti, V, Cr, Mn, Fe, Co, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, and W; and −0.1≤y≤0.30 and 0≤b≤0.5 are satisfied.
LizMn2−cM3cO4 (5)
where: M3 is at least one type of metal selected from the group consisting of Na, K, B, F, Al, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Mg, Ga, Zr, Si, Nb, Mo, Sn, and W; and 0.9≤z and 0≤c≤1.5 are satisfied.
Li1+wM4dM5eO2 (6)
where: M4 and M5 are each independently at least one type of metal selected from the group consisting of Al, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg, and Ca; and 0<w≤⅓, 0≤d≤⅔, 0≤e≤⅔, and w+d+e=1 are satisfied.
Specific examples of the lithium complex oxides represented by Formulae (3) to (6) include LiCoO2, LiNiO2, LiMO2, LiNi0.8Co0.2O2, LiNi0.5Mn0.5O2, LiNi0.85Co0.10Al0.05O2, LiNi0.8Co0.15Al0.05O2, LiNi0.5Co0.2Mn.3O2, LiNi0.6Co0.2Mn0.2O2, LiNi0.33Co0.33Mn0.33O2, LiMn2O4, LiMn1.5Ni0.5O4, LiMn1.5Fe0.5O4, LiCoMnO4, Li1.21Ni0.20Mn0.59O2, Li1.22Ni0.20Mn0.58O2, Li1.22Ni0.15Co0.10Mn0.53O2, Li1.07Ni0.35Co0.08Mn0.50O2, and Li1.07Ni0.36Co0.08Mn0.49O2.
Lithium complex oxides other than the lithium complex oxides represented by Formulae (3) to (6) can be also preferably used as the positive electrode active material. Examples of such lithium complex oxides include LiNiVO4, LiV3O6, and Li1.2Fe0.4Mn0.4O2.
Examples of a material which can be preferably used as the positive electrode active material, other than the lithium complex oxides, include phosphates each having an olivine structure. Specific examples of such phosphates include phosphates each having an olivine structure and each represented by the following Formula (7).
Liv(M6fM7gM8hM9i)jPO4 (7)
where: M6 is Mn, Co, or Ni; M7 is Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, or Mo; M8 is a transition metal, optionally excluding the elements in the groups VIA and VIIA, or a representative element; M9 is a transition metal, optionally excluding the elements in the groups VIA and VIIA, or a representative element; and 1.2≥a≥0.9, 1≥b≥0.6, 0.4≥c≥0, 0.2≥d≥0, 0.2≥e≥0, and 1.2≥f≥0.9 are satisfied.
When the positive electrode active material is a lithium-metal complex oxide, each of particles of the lithium-metal complex oxide preferably has a coating layer on a surface thereof. Examples of a material of which the coating layer is made include metal complex oxides, metal salts, boron-containing compounds, nitrogen-containing compounds, silicon-containing compounds, sulfur-containing compounds. Among these materials, metal complex oxides are suitably used.
The metal complex oxides are preferably oxides each having lithium ion conductivity. Examples of such metal complex oxides include metal complex oxides of Li and at least one type of element selected from the group consisting of Nb, Ge, Si, P, Al, W, Ta, Ti, S, Zr, Zn, V, and B. When the positive electrode active material is a material particles of which each have a coating layer, the coating layer suppresses a side reaction which occurs at the interface between the positive electrode active material and the electrolyte at high voltages, and the resulting secondary battery can achieve a longer life. Moreover, the coating layer suppresses formation of a high-resistance layer at the interface between the positive electrode active material and the electrolyte, and the resulting secondary battery can achieve high output.
Examples of the electrically conductive agent include carbonaceous materials such as natural graphite, artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired products of organic polymer compounds.
Examples of the binding agent include: thermoplastic resins such as polyvinylidene fluoride, a vinylidene fluoride copolymer, polytetrafluoroethylene, a vinylidene fluoride-hexafluoropropylene copolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, an ethylene-tetrafluoroethylene copolymer, a vinylidene fluoride-tetrafluoroethylene copolymer, a vinylidene fluoride-trifluoroethylene copolymer, a vinylidene fluoride-trichloroethylene copolymer, a vinylidene fluoride-vinyl fluoride copolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene copolymer, thermoplastic polyimide, polyethylene, and polypropylene; acrylic resins; and styrene-butadiene rubber. Note that the binding agent serves also as a thickener.
Examples of the positive electrode current collector include electric conductors such as Al, Ni, and stainless steel. Among these electric conductors, Al is more preferable because Al is easily processed into a thin film and is inexpensive.
Examples of a method of producing the positive electrode sheet include: a method which involves pressure-molding, on the positive electrode current collector, the positive electrode active material, the electrically conductive agent, and the binding agent which constitute a positive electrode mix; and a method which involves (i) forming, into a paste, the positive electrode active material, the electrically conductive agent, and the binding agent with use of an appropriate organic solvent to obtain the positive electrode mix, (ii) coating the positive electrode current collector with the positive electrode mix, (iii) drying the positive electrode mix, and then (iv) pressuring the resulting sheet-shaped positive electrode mix on the positive electrode current collector so that the sheet-shaped positive electrode mix is firmly fixed to the positive electrode current collector.
[Negative Electrode]
The negative electrode can be, for example, a negative electrode sheet having a structure in which an active material layer, containing a negative electrode active material and a binding agent, is formed on a negative electrode current collector. The active material layer may further contain an electrically conductive agent.
Examples of the negative electrode active material include carbon materials, chalcogen compounds (such as oxides and sulfides), nitrides, metals, and alloys each of which is capable of being doped with and dedoped of lithium ions at electric potentials lower than that of the positive electrode.
Examples of the carbon materials which can be used as the negative electrode active material include graphites such as natural graphite and artificial graphite, cokes, carbon black, pyrolytic carbons, carbon fibers, and fired products of organic polymer compounds.
Examples of the oxides which can be used as the negative electrode active material include: oxides of silicon which are represented by a formula SiOx (where x is a positive real number), such as SiO2 and SiO; oxides of titanium which are represented by a formula TiOx (where x is a positive real number), such as TiO2 and TiO; oxides of vanadium which are represented by a formula VxOy (where x and y are each a positive real number), such as V2O5 and VO2; oxides of iron which are represented by a formula FexOy (where x and y are each a positive real number), such as Fe3O4, Fe2O3, and FeO; oxides of tin which are represented by a formula SnOx (where x is a positive real number) such as SnO2 and SnO; oxides of tungsten which are represented by a general formula WOx (where x is a positive real number) such as WO3 and WO2; and complex metal oxides each of which contains lithium and titanium or vanadium, such as Li4Ti5O12 and LiVO2.
Examples of the sulfides which can be used as the negative electrode active material include: sulfides of titanium which are represented by a formula TixSy (where x and y are each a positive real number), such as Ti2S3, TiS2, and TiS; sulfides of vanadium which are represented by a formula VSx (where x is a positive real number), such as V3S4, VS2, and VS; sulfides of iron which are represented by a formula FexSy (where x and y are each a positive real number), such as Fe3S4, FeS2, and FeS; sulfides of molybdenum which are represented by a formula MoxSy (where x and y are each a positive real number), such as Mo2S3 and MoS2; sulfides of tin which are represented by a formula SnS (where x is a positive real number) such as SnS2 and SnS; sulfides of tungsten which are represented by a formula WS, (where x is a positive real number), such as WS2; sulfides of antimony which are represented by a formula SbxSy (where x and y are each a positive real number), such as Sb2S3; and sulfides of selenium which are represented by a formula SexSy (where x and y are each a positive real number), such as Se5S3, SeS2, and SeS.
Examples of the nitrides which can be used as the negative electrode active material include lithium-containing nitrides such as Li3N and Li3−xAxN (where A is one or both of Ni and Co, and 0<x<3 is satisfied).
Each of these carbon materials, oxides, sulfides, and nitrides may be used alone or two or more of these carbon materials, oxides, sulfides, and nitrides may be used in combination. These carbon materials, oxides, sulfides, and nitrides can be each crystalline or amorphous. One or more of these carbon materials, oxides, sulfides, and nitrides are mainly supported by the negative electrode current collector, and the resulting negative electrode current collector is used as an electrode.
Examples of the metals which can be used as the negative electrode active material include lithium metals, silicon metals, and tin metals.
It is also possible to use a complex material which contains Si or Sn as a first constituent element and also contains second and/or third constituent elements. The second constituent element is, for example, at least one type of element selected from cobalt, iron, magnesium, titanium, vanadium, chromium, manganese, nickel, copper, zinc, gallium, and zirconium. The third constituent element is, for example, at least one type of element selected from boron, carbon, aluminum, and phosphorus.
In particular, since a high battery capacity and excellent battery characteristics are achieved, the above metal material is preferably a simple substance of silicon or tin (which may contain a slight amount of impurities), SiOv (0<v≤2), SnOw (0≤w≤2), an Si—Co—C complex material, an Si—Ni—C complex material, an Sn—Co—C complex material, or an Sn—Ni—C complex material.
Examples of the negative electrode current collector include Cu, Ni, and stainless steel. Among these materials, Cu is more preferable because Cu is not easily alloyed with lithium particularly in a lithium-ion secondary battery and is easily processed into a thin film.
Examples of a method of producing the negative electrode sheet include: a method which involves pressure-molding, on the negative electrode current collector, the negative electrode active material which constitutes a negative electrode mix; and a method which involves (i) forming the negative electrode active material into a paste with use of an appropriate organic solvent to obtain the negative electrode mix, (ii) coating the negative electrode current collector with the negative electrode mix, (iii) drying the negative electrode mix, and then (iv) pressing the resulting sheet-shaped negative electrode mix on the negative electrode current collector so that the sheet-shaped negative electrode mix is firmly fixed to the negative electrode current collector. The paste preferably contains an electrically conductive agent as described above and a binding agent as described above.
[Nonaqueous Electrolyte]
The nonaqueous electrolyte can be, for example, a nonaqueous electrolyte obtained by dissolving a lithium salt in an organic solvent. Examples of the lithium salt include LiClO4, LiPF6, LiAsF6, LiSbF6, LiBF4, LiSO3F, LiCF3SO3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(COCF3), Li(C4F9SO3), LiC(SO2CF3)3, Li2B10Cl10, LiBOB (BOB refers to bis(oxalato)borate), lower aliphatic carboxylic acid lithium salt, and LiAlCl4. Each of these lithium salts may be used alone or two or more of these lithium salts may be used as a mixture. Among these lithium salts, it is preferable to use at least one fluorine-containing lithium salt selected from the group consisting of LiPF6, LiAsF6, LiSbF6, LiBF4, LiSO3F, LiCF3SO3, LiN(SO2CF3)2, and LiC(SO2CF3)3.
Examples of the organic solvent include carbonates such as propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, 4-trifluoromethyl-1,3-dioxolane-2-on, and 1,2-di(methoxy carbonyloxy)ethane; ethers such as 1,2-dimethoxyethane, 1,3-dimethoxypropane, pentafluoropropyl methylether, 2,2,3,3-tetrafluoropropyl difluoro methylether, tetrahydrofuran, and 2-methyl tetrahydrofuran; esters such as methyl formate, methyl acetate, and γ-butyrolactone; nitriles such as acetonitrile and butyronitrile; amides such as N,N-dimethylformamide and N,N-dimethylacetamide; carbamates such as 3-methyl-2-oxazolidone; sulfur-containing compounds such as sulfolane, dimethyl sulfoxide, and 1,3-propane sultone; and compounds each prepared by introducing a fluoro group into any of these organic solvents (i.e., compounds each prepared by substituting one or more hydrogen atoms of any of these organic solvents with one or more respective fluorine atoms).
The organic solvent is preferably a mixed solvent obtained by mixing two or more of the above organic solvents. Particularly, the organic solvent is preferably a mixed solvent containing a carbonate, still more preferably a mixed solvent containing a cyclic carbonate and an acyclic carbonate or a mixed solvent containing a cyclic carbonate and an ether. The mixed solvent containing a cyclic carbonate and an acyclic carbonate is preferably a mixed solvent containing ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate. The nonaqueous electrolyte which contains such a mixed solvent has advantages of having a wider operating temperature range, being less prone to deterioration even when used at a high voltage, being less prone to deterioration even when used for a long period of time, and less prone to decomposition even when the negative electrode active material is a graphite material such as natural graphite or artificial graphite.
It is preferable to use, as the nonaqueous electrolyte, a nonaqueous electrolyte containing (i) a lithium salt containing fluorine (such as LiPF6) and (ii) an organic solvent containing a fluorine substituent, because such a nonaqueous electrolyte allows the resulting nonaqueous electrolyte secondary battery to have increased safety. It is further preferable to use a mixed solvent containing a dimethyl carbonate and an ether having a fluorine substituent (such as pentafluoropropyl methylether or 2,2,3,3-tetrafluoropropyl difluoro methylether), because such a mixed solvent allows the resulting nonaqueous electrolyte secondary battery to have a high capacity maintenance ratio even when the nonaqueous electrolyte secondary battery is discharged at a high voltage.
[Method of Producing Nonaqueous Electrolyte Secondary Battery Member and Method of Producing Nonaqueous Electrolyte Secondary Battery]
A method of producing the nonaqueous electrolyte secondary battery member can be, for example, a method which involves disposing the positive electrode, the above-described nonaqueous electrolyte secondary battery laminated separator, and the negative electrode in this order.
A method of producing the nonaqueous electrolyte secondary battery can be, for example, the following method. First, the nonaqueous electrolyte secondary battery member is placed in a container which is to be a housing of the nonaqueous electrolyte secondary battery. Next, the container is filled with the nonaqueous electrolyte, and then the container is hermetically sealed while pressure inside the container is reduced. In this manner, it is possible to produce the nonaqueous electrolyte secondary battery.
The present invention is not limited to the embodiments, but can be altered by a skilled person in the art within the scope of the claims. The present invention also encompasses, in its technical scope, any embodiment derived by combining technical means disclosed in differing embodiments.
The following description will discuss embodiments of the present invention in more detail with reference to Examples and Comparative Examples. Note, however, that the present invention is not limited to such Examples and Comparative Examples.
[Methods of Measuring Various Physical Properties]
In Examples and Comparative Examples below, physical properties were measured by methods below.
(1) Intrinsic Viscosity
A solution was prepared by dissolving 0.5 g of a polymer, the intrinsic viscosity of which was to be measured, in 100 mL of 96% to 98% sulfuric acid. Subsequently, a period of time which the solution took to flow at 30° C. and a period of time which 96% to 98% sulfuric acid took to flow were measured with use of a capillary viscometer. The intrinsic viscosity was calculated by the following expression with use of the measured periods of time.
Intrinsic viscosity=ln(T/T0)/C [unit: dL/g]
where:
T represents the period of time which the sulfuric acid solution containing the polymer took to flow;
T0 represents the period of time which the sulfuric acid took to flow; and
C represents the concentration of the polymer in the solution (dL/g).
(2) High-Voltage Resistance
A test battery was prepared which included a nonaqueous electrolyte secondary battery laminated separator prepared in each of
Examples and Comparative Examples. The test battery was subjected to a trickle charge test under a high-voltage condition. After the test, the test battery was disassembled, and the color of a portion of a nonaqueous electrolyte secondary battery porous layer which part had been in contact with a positive electrode active material layer was visually checked. Evaluation was made in accordance with the following criteria.
Pass: the porous layer was colorless. Namely, even when the trickle charge test was conducted under the high-voltage condition, oxidization of resins was prevented.
Fail: the porous layer changed in color to brown. Namely, the resins were oxidized due to the trickle charge test under the high-voltage condition.
A specific procedure of the test was as follows.
1. A positive electrode and a negative electrode were prepared. The positive electrode was an electrode hoop which had been purchased from Hassan Co., Ltd and which had a thickness of 58 μm and a density of 2.5 g/cm3. The composition of a positive electrode active material was such that the amount of LiNi0.5Co0.2Mn0.3O2 was 92 parts by weight, the amount of an electrically conductive material was 5 parts by weight, and the amount of a binding agent was 3 parts by weight. The negative electrode was an electrode hoop which had been purchased from Hassan Co., Ltd and which had a thickness of 48 μm and a density of 1.5 g/cm3. The composition of a negative electrode active material was such that the amount of natural graphite was 98 parts by weight, the amount of a binding agent was 1 part by weight, and the amount of carboxymethyl cellulose was 1 part by weight.
2. A nonaqueous electrolyte secondary battery member was produced.
The positive electrode, the laminated separator, and the negative electrode were disposed in this order in a laminate pouch. In so doing, the laminated separator was disposed such that (i) the porous layer of the laminated separator and a positive electrode active material layer of the positive electrode were in contact with each other and (ii) a polyethylene porous film of the laminated separator and a negative electrode active material layer of the negative electrode were in contact with each other.
3. The nonaqueous electrolyte secondary battery member was stored in a bag which was made up of an aluminum layer and a heat-sealing layer that was formed on the aluminum layer, and 230 μL of a nonaqueous electrolyte was injected into the bag. The nonaqueous electrolyte was one that had been prepared by dissolving LiPF6 at a concentration of 1 mol/L in a mixed solvent obtained by mixing ethylene carbonate, ethyl methyl carbonate, and diethyl carbonate at a ratio of 3:5:2 (volume ratio).
4. The bag was heat-sealed while pressure inside the bag was reduced. A test battery was thus produced.
5. The test battery was charged with a constant electric current with use of a charge-discharge test apparatus manufactured by Toyo System Co., Ltd. The test battery was charged with a constant electric current under the following conditions: a temperature was set to 25° C., an electric current was set to 1 C, and a final voltage was set to 4.5 V (i.e., 4.6 V (vs Li/Li+)).
6. The test battery was trickle-charged with use of a charge-discharge test apparatus manufactured by Toyo System Co., Ltd. The test battery was trickle-charged under the following conditions: a temperature was set to 25° C., a voltage was set to 4.5 V (i.e., 4.6 V (vs Li/Li+)), and a period of time was set to 168 hours.
7. After the trickle charging was finished, the test battery was disassembled, and the laminated separator was taken out. The color of a surface of the porous layer was visually observed.
(3) Adhesiveness
A surface of the porous layer of the laminated separator produced in each of Examples and Comparative Examples was visually checked to evaluate adhesiveness. Evaluation was made in accordance with the following criteria.
Pass: Peeling-off of the porous layer was not seen. Namely, adhesiveness between the polyolefin porous film and the porous layer was high.
Fair: Peeling-off of the porous layer was not seen, but adhesiveness between the polyolefin porous film and the porous layer was low. Fail: Peeling-off in scales of the porous layer was seen. Namely, adhesiveness between the polyolefin porous film and the porous layer was low.
A block copolymer in which a block A accounted for 50% of the entirety of a molecule and a block B accounted for 50% of the entirety of the molecule was synthesized by the following procedure. The block A was constituted by poly(4,4′-diphenylsulfonyl terephthalamide). The block B was constituted by poly(paraphenylene terephthalamide).
1. A 0.5-L separable flask having a stirring blade, a thermometer, a nitrogen incurrent canal, and a powder addition port was sufficiently dried.
2. 420 g of N-methylpyrrolidone was introduced into the flask. Further, 27.27 g of calcium chloride (which had been dried at 200° C. for 2 hours) was added, and a resulting mixture was heated to 100° C.
3. After the calcium chloride completely dissolved, 20.34 g of 4,4′-diaminodiphenylsulfone was added at 100° C., and then a resulting mixture was completely dissolved.
4. A resulting solution was cooled to room temperature. While the temperature of the solution was maintained at 25±2° C., 16.54 g in total of terephthalic acid dichloride was added in 3 separate portions. A reaction was then caused to occur for 1 hour. In this manner, the block A was synthesized.
5. 8.87 g of 1,4-phenylenediamine was added to the resulting solution, and completely dissolved over 30 minutes.
6. While the temperature of a resulting solution was maintained at 25±2° C., 16.46 g in total of terephthalic acid dichloride was added in 3 separate portions. A reaction was then caused to occur for 1 hour. In this manner, the block B was caused to extend from both sides of the block A.
7. While the temperature of the solution was maintained at 25±2° C., the solution was matured for 1 hour. Thereafter, the solution was stirred for 30 minutes under reduced pressure, and air bubbles were removed. In this manner, the solution which contained a block copolymer (1) was obtained.
Part of the solution which contained the block copolymer (1) was collected, and a sample of the block copolymer (1) was deposited by water. Measurement was carried out with use of the sample. The intrinsic viscosity of the block copolymer (1) was 1.24 dL/g.
A solution containing a comparative block copolymer (1) was obtained by a procedure similar to that in Synthesis Example 1, except that the amounts of monomers were changed so that a block A accounted for 25% of the entirety of a molecule and a block B accounted for 75% of the entirety of the molecule. The intrinsic viscosity of the comparative block copolymer (1) was 2.10 dL/g.
A solution containing a comparative block copolymer (2) was obtained by a procedure similar to that in Synthesis Example 1, except that the amounts of monomers were changed so that a block A accounted for 90% of the entirety of a molecule and a block B accounted for 10% of the entirety of the molecule. The intrinsic viscosity of the comparative block copolymer (2) was 1.10 dL/g.
A random copolymer in which 50% of diamine units were derived from 4,4′-diaminodiphenylsulfone and 50% of the diamine units were derived from 1,4-phenylenediamine was synthesized by the following procedure.
1. A 0.5-L separable flask having a stirring blade, a thermometer, a nitrogen incurrent canal, and a powder addition port was sufficiently dried.
2. 420 g of N-methylpyrrolidone was introduced into the flask. Further, 27.27 g of calcium chloride (which had been dried at 200° C. for 2 hours) was added, and a resulting mixture was heated to 100° C.
3. After the calcium chloride completely dissolved, the temperature of a resulting solution was returned to room temperature. Subsequently, 20.34 g of 4,4′-diaminodiphenylsulfone and 8.87 g of 1,4-phenylenediamine were added and completely dissolved.
4. While the temperature of a resulting solution was maintained at 25±2° C., 16.46 g in total of terephthalic acid dichloride was added in 5 separate portions.
5. While the temperature of a resulting solution was maintained 25±2° C., the solution was matured for 1 hour to obtain the solution which contained a comparative random copolymer (1).
Part of the solution which contained the comparative random copolymer (1) was collected, and a sample of the comparative random copolymer (1) was deposited by water. Measurement was carried out with use of the sample. The intrinsic viscosity of the comparative random copolymer (1) was 0.75 dL/g.
A solution containing a comparative random copolymer (2) was obtained by a procedure similar to that in Comparative Synthesis Example 3, except that the amounts of monomers were changed so that 25% of diamine units were derived from 4,4′-diaminodiphenylsulfone and 75% of the diamine units were derived from 1,4-phenylenediamine. The intrinsic viscosity of the comparative random copolymer (2) was 1.30 dL/g.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 1, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a coating solution (1). The solid content concentration of the coating solution (1) was 5% by weight.
The coating solution (1) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the coating solution (1) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a porous layer (1) was formed. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the porous layer (1). The laminated separator including the porous layer (1) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Comparative Synthesis Example 1, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a comparative coating solution (1). The solid content concentration of the comparative coating solution (1) was 5% by weight.
The comparative coating solution (1) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the comparative coating solution (1) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a comparative porous layer (1) was formed. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the comparative porous layer (1). The laminated separator including the comparative porous layer (1) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Comparative Synthesis Example 2, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a comparative coating solution (2). The solid content concentration of the comparative coating solution (2) was 5% by weight.
The comparative coating solution (2) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the comparative coating solution (2) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a comparative porous layer (2) was formed. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the comparative porous layer (2). It was not possible to stably measure the thickness of the laminated separator including the comparative porous layer (2), because the porous layer peeled off in scales.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Comparative Synthesis Example 3, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a comparative coating solution (3). The solid content concentration of the comparative coating solution (3) was 5% by weight.
The comparative coating solution (3) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the comparative coating solution (3) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a comparative porous layer (3) was formed. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the comparative porous layer (3). It was not possible to stably measure the thickness of the laminated separator including the comparative porous layer (3), because the porous layer peeled off in scales.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Comparative Synthesis Example 4, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a comparative coating solution (4). The solid content concentration of the comparative coating solution (4) was 5% by weight.
The comparative coating solution (4) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the comparative coating solution (4) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a comparative porous layer (4) was formed. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the comparative porous layer (4). It was not possible to stably measure the thickness of the laminated separator including the comparative porous layer (4), because the porous layer peeled off in scales.
A solution containing a block copolymer (2) was obtained by a procedure similar to that in Synthesis Example 1, except that the amounts of monomers were changed so that a block A accounted for 60% of the entirety of a molecule and a block B accounted for 40% of the entirety of the molecule. The intrinsic viscosity of the block copolymer (2) was 1.20 dL/g.
A solution containing a block copolymer (3) was obtained by a procedure similar to that in Synthesis Example 1, except that the amounts of monomers were changed so that a block A accounted for 40% of the entirety of a molecule and a block B accounted for 60% of the entirety of the molecule. The intrinsic viscosity of the block copolymer (3) was 1.25 dL/g.
A solution containing a block copolymer (4) was obtained by a procedure similar to that in Synthesis Example 1, except that the amounts of monomers were changed so that a block A accounted for 30% of the entirety of a molecule and a block B accounted for 70% of the entirety of the molecule. The intrinsic viscosity of the block copolymer (4) was 1.42 dL/g.
A block copolymer in which a block A accounted for 50% of the entirety of a molecule and a block B accounted for 50% of the entirety of the molecule was synthesized by the following procedure.
1. A 0.5-L separable flask having a stirring blade, a thermometer, a nitrogen incurrent canal, and a powder addition port was sufficiently dried.
2. 420 g of N-methylpyrrolidone was introduced into the flask. Further, 27.27 g of calcium chloride (which had been dried at 200° C. for 2 hours) was added, and a resulting mixture was heated to 100° C.
3. After the calcium chloride completely dissolved, 13.84 g of 4,4′-diaminodiphenylsulfone was added at 100° C., and then a resulting mixture was completely dissolved.
4. A resulting solution was cooled to room temperature. While the temperature of the solution was maintained at 25±2° C., 11.24 g in total of terephthalic acid dichloride was added in 3 separate portions. A reaction was then caused to occur for 1 hour. In this manner, the block A was synthesized.
5. 6.02 g of 1,4-phenylenediamine was added to the resulting solution, and completely dissolved over 30 minutes.
6. While the temperature of a resulting solution was maintained at 25±2° C., 11.22 g in total of terephthalic acid dichloride was added in 3 separate portions. A reaction was then caused to occur for 1 hour. In this manner, the block B was caused to extend from both sides of the block A.
7. While the temperature of the solution was maintained at 25±2° C., the solution was matured for 1 hour. Thereafter, the solution was stirred for 30 minutes under reduced pressure, and air bubbles were removed. In this manner, the solution which contained a block copolymer (5) was obtained. The intrinsic viscosity of the block copolymer (5) was 1.60 dL/g.
A solution containing a comparative block copolymer (3) was obtained by a procedure similar to that in Synthesis Example 1, except that the amounts of monomers were changed so that a block A accounted for 10% of the entirety of a molecule and a block B accounted for 90% of the entirety of the molecule.
A block copolymer in which a block A accounted for 50% of the entirety of a molecule and a block B accounted for 50% of the entirety of the molecule was synthesized by the following procedure.
1. A 0.5-L separable flask having a stirring blade, a thermometer, a nitrogen incurrent canal, and a powder addition port was sufficiently dried.
2. 420 g of N-methylpyrrolidone was introduced into the flask. Further, 27.27 g of calcium chloride (which had been dried at 200° C. for 2 hours) was added, and a resulting mixture was heated to 100° C.
3. After the calcium chloride completely dissolved, 12.01 g of 4,4′-diaminodiphenylsulfone was added at 100° C., and then a resulting mixture was completely dissolved.
4. A resulting solution was cooled to room temperature. While the temperature of the solution was maintained at 25±2° C., 9.76 g in total of terephthalic acid dichloride was added in 3 separate portions. A reaction was then caused to occur for 1 hour. In this manner, the block A was synthesized.
5. 9.67 g of 4,4′-diaminodiphenyl ether was added to the resulting solution, and completely dissolved over 30 minutes.
6. While the temperature of a resulting solution was maintained at 25±2° C., 9.74 g in total of terephthalic acid dichloride was added in 3 separate portions. A reaction was then caused to occur for 1 hour. In this manner, the block B was caused to extend from both sides of the block A.
7. While the temperature of the solution was maintained at 25±2° C., the solution was matured for 1 hour. Thereafter, the solution was stirred for 30 minutes under reduced pressure, and air bubbles were removed. In this manner, the solution which contained a comparative block copolymer (4) was obtained.
A block copolymer in which a block A accounted for 50% of the entirety of a molecule and a block B accounted for 50% of the entirety of the molecule was synthesized by the following procedure.
1. A 0.5-L separable flask having a stirring blade, a thermometer, a nitrogen incurrent canal, and a powder addition port was sufficiently dried.
2. 420 g of N-methylpyrrolidone was introduced into the flask. Further, 27.27 g of calcium chloride (which had been dried at 200° C. for 2 hours) was added, and a resulting mixture was heated to 100° C.
3. After the calcium chloride completely dissolved, 11.94 g of 4,4′-diaminodiphenylsulfone was added at 100° C., and then a resulting mixture was completely dissolved.
4. A resulting solution was cooled to room temperature. While the temperature of the solution was maintained at 25±2° C., 14.09 g in total of 4,4′-oxybis(benzoyl chloride) was added in 3 separate portions. A reaction was then caused to occur for 1 hour. In this manner, the block A was synthesized.
5. 5.19 g of 1,4-phenylenediamine was added to the resulting solution, and completely dissolved over 30 minutes.
6. While the temperature of the solution was maintained at 25±2° C., 14.07 g in total of 4,4′-oxybis(benzoyl chloride) was added in 3 separate portions. A reaction was then caused to occur for 1 hour. In this manner, the block B was caused to extend from both sides of the block A.
7. While the temperature of the solution was maintained at 25±2° C., the solution was matured for 1 hour. Thereafter, the solution was stirred for 30 minutes under reduced pressure, and air bubbles were removed. In this manner, the solution which contained a comparative block copolymer (5) was obtained.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 2, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a coating solution (2). The solid content concentration of the coating solution (2) was 5% by weight.
The coating solution (2) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the coating solution (2) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a porous layer (2) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the porous layer (2). The laminated separator including the porous layer (2) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 3, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a coating solution (3). The solid content concentration of the coating solution (3) was 5% by weight.
The coating solution (3) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the coating solution (3) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a porous layer (3) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the porous layer (3). The laminated separator including the porous layer (3) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 4, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a coating solution (4). The solid content concentration of the coating solution (4) was 5% by weight.
The coating solution (4) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the coating solution (4) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a porous layer (4) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the porous layer (4). The laminated separator including the porous layer (4) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Comparative Synthesis Example 5, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a comparative coating solution (5). The solid content concentration of the comparative coating solution (5) was 5% by weight.
The comparative coating solution (5) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the comparative coating solution (5) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a comparative porous layer (5) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the comparative porous layer (5). The laminated separator including the comparative porous layer (5) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Comparative Synthesis Example 6, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a comparative coating solution (6). The solid content concentration of the comparative coating solution (6) was 5% by weight.
The comparative coating solution (6) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the comparative coating solution (6) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a comparative porous layer (6) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the comparative porous layer (6). It was not possible to stably measure the thickness of the laminated separator including the comparative porous layer (6), because the porous layer peeled off in scales.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Comparative Synthesis Example 7, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a comparative coating solution (7). The solid content concentration of the comparative coating solution (7) was 5% by weight.
The comparative coating solution (7) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the comparative coating solution (7) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a comparative porous layer (7) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the comparative porous layer (7). It was not possible to stably measure the thickness of the laminated separator including the comparative porous layer (7), because the porous layer peeled off in scales.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 5, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a coating solution (5). The solid content concentration of the coating solution (5) was 5% by weight.
The coating solution (5) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the coating solution (5) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a porous layer (5) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the porous layer (5). The laminated separator including the porous layer (5) had a thickness of 13 um.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 5, 120 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a coating solution (6). The solid content concentration of the coating solution (6) was 5% by weight.
The coating solution (6) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the coating solution (6) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a porous layer (6) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the porous layer (6). The laminated separator including the porous layer (6) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 5, 25 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a coating solution (7). The solid content concentration of the coating solution (7) was 5% by weight.
The coating solution (7) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the coating solution (7) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a porous layer (7) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the porous layer (7). The laminated separator including the porous layer (7) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 5, 900 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a coating solution (8). The solid content concentration of the coating solution (8) was 5% by weight.
The coating solution (8) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the coating solution (8) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a porous layer (8) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the porous layer (8). The laminated separator including the porous layer (8) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 5, 1900 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a comparative coating solution (8). The solid content concentration of the comparative coating solution (8) was 5% by weight.
The comparative coating solution (8) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the comparative coating solution (8) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a comparative porous layer (8) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the comparative porous layer (8). It was not possible to stably measure the thickness of the laminated separator including the comparative porous layer (8), because the porous layer peeled off in scales.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 5, 18 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) was added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a comparative coating solution (9). The solid content concentration of the comparative coating solution (9) was 5% by weight.
The comparative coating solution (9) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the comparative coating solution (9) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a comparative porous layer (9) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the comparative porous layer (9). The laminated separator including the comparative porous layer (9) had a thickness of 13 μm.
With respect to 100 parts by weight of the resins which were contained in the solution obtained in Synthesis Example 5, 100 parts by weight of aluminum oxide (average particle diameter: 0.013 μm) and 100 parts by weight of aluminum oxide (average particle diameter: 0.7 μm) were added. A resulting mixture was diluted with NMP, and uniformly dispersed with use of a pressure type disperser to obtain a coating solution (9). The solid content concentration of the coating solution (9) was 6% by weight.
The coating solution (9) was applied to a polyethylene porous film (thickness: 10 μm), and then the polyethylene porous film to which the coating solution (9) was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a porous layer (9) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the porous layer (9). The laminated separator including the porous layer (9) had a thickness of 13 μm.
(Results)
Tables 1 to 4 shows results of evaluating the high-voltage resistance and the adhesiveness of the porous layers produced in Examples and Comparative Examples.
As shown in Tables 1 to 4, the porous layers produced in Examples 1 to 9 had both favorable high-voltage resistance and favorable adhesiveness.
On the other hand, the porous layer produced in Comparative Example 1 had favorable adhesiveness, but had poor high-voltage resistance. This is considered to be because the proportion of the block A contained in the porous layer was excessively low and the porous layer could not contain a sufficient number of sulfonyl groups. The porous layer produced in Comparative Example 2 had poor adhesiveness, and this made it impossible to assemble a battery. This is considered to be because the proportion of the block B contained in the porous layer was excessively low. The porous layers produced in Comparative Examples 3 and 4 had poor adhesiveness, and this made it impossible to assemble batteries. It is suggested, from these facts, that a random copolymer does not allow both high-voltage resistance and adhesiveness to be achieved.
The porous layer produced in Comparative Example 5 had favorable adhesiveness, but had poor high-voltage resistance. This is considered to be because the proportion of the block A was excessively low and could not contain a sufficient number of sulfonyl groups. The porous layers produced in Comparative Examples 6 to 8 had poor adhesiveness, and made it impossible to assemble a battery. The porous layer produced in Comparative Example 9 did not have sufficient pores therein, and could not be subjected to a withstand voltage test.
A solution which contained only poly(4,4′-diphenylsulfonyl terephthalamide was applied to a polyethylene porous film (thickness: 10 μm) as a coating solution, and then the polyethylene porous film to which only poly(4,4′-diphenylsulfonyl terephthalamide was applied was treated in an oven at 50° C. and a humidity of 70% for 2 minutes so that a reference porous layer (1) was formed on the polyethylene porous film. Thereafter, the resulting polyethylene porous film was washed with water and dried to obtain a laminated separator including the reference porous layer (1). A surface of the reference porous layer (1) was visually observed, and peeling-off of the porous layer was not seen. From this fact, it is suggested that a problem which relates to the adhesiveness of a porous layer and which is to be solved by an aspect of the present invention does not occur when only a resin having a sulfonyl group is used, but occurs when a resin having a sulfonyl group and a filler are used.
The present invention is applicable to, for example, a nonaqueous electrolyte secondary battery.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-148408 | Sep 2020 | JP | national |
| 2021-089536 | May 2021 | JP | national |
| 2021-142194 | Sep 2021 | JP | national |
