Patent Application
20220246988
The present invention relates to a secondary battery.
In recent years, according to a spread of portable electronic devices, electric vehicles, and the like, in secondary batteries typified by lithium ion secondary batteries, further improvement in performance is required. For example, Patent Literature 1 discloses a lithium ion secondary battery capable of attaining good cycle characteristics, in which the lithium ion secondary battery includes a negative electrode containing a silicon material that is a high-capacity negative electrode active material.
Patent Literature 1: WO 2018/221346
However, in the case of using the negative electrode active material containing silicon as a constituent element, as also described in Patent Literature 1, since expansion and contraction of the negative electrode active material attributable to charging and discharging of the secondary battery are large, the micronization (collapse) of the negative electrode active material is likely to occur. Furthermore, also in the case of using the negative electrode active material containing tin or aluminum as a constituent element, the same phenomenon is likely to occur. As a result, the negative electrode active material is dropped out from the negative electrode, and the discharge capacity or the like of the secondary battery may be decreased.
One aspect of the present invention aims at suppressing a decrease in discharge capacity in a secondary battery using a negative electrode active material containing silicon, tin, or aluminum as a constituent element.
An aspect of the present invention is a secondary battery including: a positive electrode current collector; a negative electrode current collector; an electrolyte layer disposed between the positive electrode current collector and the negative electrode current collector; a positive electrode electrolytic solution filling part partitioned by the positive electrode current collector and the electrolyte layer; and a negative electrode electrolytic solution filling part partitioned by the negative electrode current collector and the electrolyte layer, wherein the negative electrode electrolytic solution filling part includes: a conductive member having a mesh structure and disposed so as to bring the negative electrode current collector and the electrolyte layer into conduction; a negative electrode active material retained in the conductive member; an electrolyte salt; and a non-aqueous solvent dissolving the electrolyte salt, and the negative electrode active material contains at least one selected from the group consisting of silicon, tin, and aluminum, as a constituent element.
In this secondary battery, while the conductive member secures conduction between the negative electrode current collector and the electrolyte layer, in the negative electrode electrolytic solution filling part, the negative electrode active material coexists with the negative electrode electrolytic solution in a state of being retained in the conductive member, and thereby this secondary battery functions as a secondary battery. Then, in this secondary battery, since the negative electrode active material is retained in the conductive member, even in a case where the negative electrode active material containing silicon, tin, or aluminum as a constituent element is micronized by charging and discharging of the secondary battery, the negative electrode active material is easily captured by the mesh structure of the conductive member, and subsequently, this negative electrode active material may function as a negative electrode active material. Therefore, in this secondary battery, as compared to a conventional secondary battery in which the negative electrode active material is retained on the negative electrode current collector, a decrease in discharge capacity caused by the micronization of the negative electrode active material can be suppressed.
In addition, since this secondary battery is provided with the positive electrode electrolytic solution filling part and the negative electrode electrolytic solution filling part separately, electrolytic solutions having compositions suitable for respective electrodes can be separately used as the positive electrode electrolytic solution and the negative electrode electrolytic solution. Therefore, as compared to a conventional secondary battery using a common electrolytic solution in the positive electrode and the negative electrode, the performance of the secondary battery can be improved.
The conductive member may be formed of a carbon material.
The non-aqueous solvent may contain 10% by mass or more of fluoroethylene carbonate on a basis of a total amount of the non-aqueous solvent and may be composed only of fluoroethylene carbonate.
The non-aqueous solvent may contain 10% by mass or more of vinylene carbonate on a basis of a total amount of the non-aqueous solvent and may be composed only of vinylene carbonate.
The non-aqueous solvent may contain 10% by mass or more of at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile)ether, 2-(methylamino)ethanol, and diaminohexane, on a basis of a total amount of the non-aqueous solvent, and may be composed only of the at least one.
The negative electrode active material may contain 10% by mass or more of silicon on a basis of a total amount of the negative electrode active material, as a constituent element. The negative electrode active material may contain 10% by mass or more of tin on a basis of a total amount of the negative electrode active material, as a constituent element.
The negative electrode active material may contain 10% by mass or more of aluminum on a basis of a total amount of the negative electrode active material, as a constituent element.
The positive electrode electrolytic solution filling part may include: a conductive member having a mesh structure and disposed so as to bring the positive electrode current collector and the electrolyte layer into conduction; a positive electrode active material retained in the conductive member; an electrolyte salt; and a non-aqueous solvent dissolving the electrolyte salt.
The non-aqueous solvent contained in the positive electrode electrolytic solution filling part may be a non-aqueous solvent that is different from the non-aqueous solvent contained in the negative electrode electrolytic solution filling part.
A content of fluoroethylene carbonate in the positive electrode electrolytic solution filling part may be 0.1% by mass or less on a basis of a total amount of the non-aqueous solvent contained in the positive electrode electrolytic solution filling part. The positive electrode electrolytic solution filling part may not contain fluoroethylene carbonate.
A content of vinylene carbonate in the positive electrode electrolytic solution filling part may be 0.1% by mass or less on a basis of a total amount of the non-aqueous solvent contained in the positive electrode electrolytic solution filling part. The positive electrode electrolytic solution filling part may not contain vinylene carbonate.
According to an aspect of the present invention, in a secondary battery using a negative electrode active material containing silicon, tin, or aluminum as a constituent element, a decrease in discharge capacity can be suppressed.
Hereinafter, embodiments of the present invention will be described with reference to the drawings as appropriate. However, the present invention is not limited to the embodiments described below.
The battery outer casing body 3 may be, for example, a container formed of a laminate film. The laminate film may be, for example, a laminate film in which a polymer film such as a polyethylene terephthalate (PET) film, a metallic foil such as aluminum, copper, or stainless steel, and a sealant layer such as polypropylene are laminated in this order.
The battery outer casing body 3 is sealed so that the positive electrode electrolytic solution and the negative electrode electrolytic solution are not caused to leak out from the positive electrode electrolytic solution filling part 9 and the negative electrode electrolytic solution filling part 10, respectively. In an embodiment, as illustrated in
The positive electrode current collector 6 is formed, for example, of aluminum, titanium, stainless steel, nickel, baked carbon, an electrically conductive polymer, electrically conductive glass, or the like. The thickness of the positive electrode current collector 6 may be 1 μm or more and may be 50 μm or less, for example.
The negative electrode current collector 7 is formed, for example, of copper, stainless steel, nickel, aluminum, titanium, baked carbon, an electrically conductive polymer, electrically conductive glass, an aluminum-cadmium alloy, or the like. The thickness of the negative electrode current collector 7 may be 1 μm or more and may be 50 μm or less, for example.
The electrolyte layer 8 is a layer that allows cations derived from the electrolyte salt (for example, lithium cations) contained in the positive electrode electrolytic solution filling part 9 and the negative electrode electrolytic solution filling part 10 to pass through the layer and does not allow active materials (the positive electrode active material and the negative electrode active material) and components other than the cations (for example, the above-described non-aqueous solvent) contained in the positive electrode electrolytic solution filling part 9 and the negative electrode electrolytic solution filling part 10 to pass through the layer. The electrolyte layer 8 may be, for example, an electrolyte layer 8 that is non-porous (the electrolyte layer 8 having no pores). The thickness of the electrolyte layer 8 is preferably 1 μm or more from the viewpoint of obtaining superior strength, and is preferably 500 μm or less from the viewpoint that the resistance of ion conduction in the electrolyte layer 8 is reduced, and as a result, the resistance of the secondary battery 1 can be reduced.
Such an electrolyte layer 8 may be a solid electrolyte material showing lithium ion conductivity, may be formed of, for example, an oxide-based solid electrolyte, and may be formed of a polymer. In an embodiment, the electrolyte layer 8 may be, for example, a perfluorosulfonic acid-based ion-exchange membrane. The perfluorosulfonic acid-based ion-exchange membrane is, for example, composed of a polymer having a structural unit represented by Formula (1) below.
[In the formula, x, y, m, and n represent an integer of 1 to 20, an integer of 1 to 1000, an integer of 0 or 1, and an integer of 1 to 10, respectively, and X represents a hydrogen atom, an alkali metal atom, or an alkali earth metal atom.]
Such a polymer can be synthesized, for example, by a known method and can also be purchased as Nafion (registered trademark, manufactured by DowDuPont, Inc.), Dow Film (manufactured by DowDuPont, Inc.), Aciplex (registered trademark, manufactured by Asahi Kasei Corp.), or Flemion (registered trademark, manufactured by AGC Inc.).
In another embodiment, the polymer constituting the electrolyte layer 8 may be, for example, polyvinyl alcohol, polyacrylamide, polyvinylpyrrolidone, polyethylene oxide, polyacrylic acid, polymethacrylic acid, sulfonated polyimide, sulfonated poly(etheretherketone), sulfonated poly(ether sulfone), or sulfonated poly(p-phenylene). These polymers are preferably ion-exchanged for use.
In the positive electrode electrolytic solution filling part 9, a conductive member is disposed so as to bring the positive electrode current collector 6 and the electrolyte layer 8 into conduction. The conductive member has a mesh structure. The conductive member may be provided in a part of the positive electrode electrolytic solution filling part 9 or may be provided to embed the whole positive electrode electrolytic solution filling part 9. The thickness of the positive electrode electrolytic solution filling part 9 may be 5 μm or more and may be 2000 μm or less, for example.
The conductive member may have, for example, a sheet shape. The conductive member is formed of an electrically conductive material. Examples of the electrically conductive material include a carbon material, a metal material, and an electrically conductive polymer material.
Examples of the carbon material include carbon black, graphite, soft carbon, hard carbon, carbon nanotube, carbon nanofiber, graphene, carbon nanohorn, glassy carbon, and expanded graphite.
Examples of the metal material include nickel, aluminum, copper, stainless steel, gold, and silver.
Examples of the electrically conductive polymer material include materials with which polymer compounds such as polyacetylene, poly(p-phenylenevinylene), polypyrrole, polythiophene, polyaniline, and poly(p-phenylenesulfide) are doped. The doping method is not particularly limited, but may be a method of adding a compound of an electron acceptor (acceptor) such as iodine or arsenic pentafluoride, an electron donor (donor) such as an alkali metal, or the like to the polymer compound.
In an embodiment, a member formed in a mesh structure in advance may be used as the conductive member. Examples of such a conductive member include a conductive member formed of a carbon material such as carbon felt, carbon paper, or carbon cloth and a conductive member formed of a metal material such as punching metal (a metal plate in which a mesh structure is formed by punching).
The positive electrode electrolytic solution filling part 9 contains a positive electrode electrolytic solution, and specifically contains, for example, a positive electrode active material, an electrolyte salt, and a non-aqueous solvent.
In the positive electrode electrolytic solution filling part 9, the positive electrode active material preferably exists in a state of being dispersed in the positive electrode electrolytic solution (a non-aqueous solvent). In other words, the positive electrode active material is not retained (fixed) in the positive electrode current collector 6, and the positive electrode electrolytic solution filling part 9 preferably does not contain a binder for retaining (fixing) the positive electrode active material in the positive electrode current collector 6.
The positive electrode active material may be, for example, a lithium oxide. Examples of the lithium oxide include LixCoO2, LixNiO2, LixMnO2, LixCoyNi1−yO2, LixCoyM1−yOz, LixNi1−yMyOz, LixMn2O4, and LixMn2−yMyO4 (in each formula, M represents at least one element selected from the group consisting of Na, Mg, Sc, Y, Mn, Fe, Co, Cu, Zn, Al, Cr, Pb, Sb, V, and B (provided that, M is an element different from other elements in each formula); and x=0 to 1.2, y=0 to 0.9, and z=2.0 to 2.3). The lithium oxide represented by LixNi1−yMyOz may be LixNi1−(y1+y2)Coy1Mny2Oz (provided that, x and z are the same as those described above, y1=0 to 0.9, y2=0 to 0.9, and y1+y2=0 to 0.9) and may be, for example, LiNi1/3Co1/3Mn1/3O2, LiNi0.5Co0.2Mn0.3O2, LiNi0.6Co0.2Mn0.2O2, or LiNi0.8Co0.16Mn0.1O2. The lithium oxide represented by LixNi1−yMyOz may be LixNi1−(y3+y4)Coy3Aly4Oz (provided that, x and z are the same as those described above, y3=0 to 0.9, y4=0 to 0.9, and y3+y4=0 to 0.9), and may be, for example, LiNi0.8Co0.15Al0.05O2.
The positive electrode active material may be, for example, a phosphoric salt of lithium. Examples of the phosphoric salt of lithium include lithium manganese phosphate (LiMnPO4), lithium iron phosphate (LiFePO4), lithium cobalt phosphate (LiCoPO4), and lithium vanadium phosphate (Li3V2(PO4)3).
A content of the positive electrode active material may be 10 parts by mass or more and may be 80 parts by mass or less, with respect to 100 parts by mass of a total mass of the positive electrode active material, the non-aqueous solvent, and the conductive member contained in the positive electrode electrolytic solution filling part 9.
The electrolyte salt may be, for example, a lithium salt. The lithium salt may be, for example, at least one selected from the group consisting of LiPF6, LiBF4, LiClO4, LiB(C6H5)4, LiCH3SO3, CF3SO2OLi, LiN(SO2F)2 (Li[FSI], lithium bisfluorosulfonyl imide), LiN(SO2CF3)2 (Li[TFSI], lithium bistrifluoromethanesulfonyl imide), and LiN(SO2CF2CF3)2.
A content of the electrolyte salt may be 0.5 mol/L or more, 0.7 mol/L or more, or 0.8 mol/L or more, and may be 1.5 mol/L or less, 1.3 mol/L or less, or 1.2 mol/L or less, on a basis of a total amount of the non-aqueous solvent.
The non-aqueous solvent is a solvent that can dissolve an electrolyte salt contained in the positive electrode electrolytic solution filling part 9. Examples of the non-aqueous solvent include a non-aqueous solvent that can be suitably used in both the positive electrode electrolytic solution and the negative electrode electrolytic solution, and a non-aqueous solvent that can be suitably used only in the positive electrode electrolytic solution (that is not suitable for the negative electrode electrolytic solution). The non-aqueous solvent is used singly or in combination of two or more types thereof.
The non-aqueous solvent that can be suitably used in both the positive electrode electrolytic solution and the negative electrode electrolytic solution may be, for example, an aprotic solvent that is suitable for both the positive electrode electrolytic solution and the negative electrode electrolytic solution. Examples of such an aprotic solvent include diethyl carbonate, dimethyl ether, diethyl ether, dioxolane, 4-methyl dioxolane, sulfolane, dimethyl sulfoxide, propionitrile, benzonitrile, N,N-dimethylacetamide, and diethylene glycol.
The non-aqueous solvent that can be suitably used only in the positive electrode electrolytic solution (that is not suitable for the negative electrode electrolytic solution) may be a solvent that is excellent in oxidation resistance but is not excellent in reduction resistance (when the solvent is contained in the negative electrode electrolytic solution, decomposition is promoted, and thus the film resistance is increased). Examples of such a solvent include ethylene carbonate, hexafluoroisopropyl-ethylene carbonate, trans-difluoroethylene carbonate, cis-difluoroethylene carbonate, trishexafluoroisopropyl phosphate, tris(2,2,2-trifluoroethyl)phosphate, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, acetonitrile, succinonitrile, glutaronitrile, adiponitrile, chloroethylene carbonate, and nitromethane. Among these, the non-aqueous solvent that can be suitably used only in the positive electrode electrolytic solution (that is not suitable for the negative electrode electrolytic solution) may be at least one selected from the group consisting of tris(2,2,2-trifluoroethyl)phosphate, acetonitrile, succinonitrile, adiponitrile, chloroethylene carbonate, nitromethane, and ethylene carbonate.
A content of the non-aqueous solvent that can be suitably used in both the positive electrode electrolytic solution and the negative electrode electrolytic solution may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, and may be 95% by mass or less, 90% by mass or less, or 80% by mass or less, on a basis of a total amount of the non-aqueous solvent contained in the positive electrode electrolytic solution filling part 9. A content of the non-aqueous solvent that can be suitably used only in the positive electrode electrolytic solution (that is not suitable for the negative electrode electrolytic solution) may be 0.1% by mass or more, 1% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more, and may be 100% by mass or less, 95% by mass or less, or 90% by mass or less, on a basis of a total amount of the non-aqueous solvent contained in the positive electrode electrolytic solution filling part 9.
In an embodiment, the positive electrode electrolytic solution filling part 9 may not contain a non-aqueous solvent described below that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution). In an embodiment, the positive electrode electrolytic solution filling part 9 may not contain fluoroethylene carbonate or may not contain vinylene carbonate, and may not contain at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile)ether, 2-(methylamino)ethanol, and diaminohexane. In another embodiment, a content of the non-aqueous solvent that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution), the fluoroethylene carbonate, the vinylene carbonate, or at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile)ether, 2-(methylamino)ethanol, and diaminohexane may be 0.1% by mass or less on a basis of a total amount of the non-aqueous solvent contained in the positive electrode electrolytic solution filling part 9.
As described above, in the secondary battery 1 according to the present embodiment, since the positive electrode electrolytic solution filling part 9 and the negative electrode electrolytic solution filling part 10 are independently provided, in the positive electrode electrolytic solution filling part 9, the non-aqueous solvent that is suitable only for the positive electrode electrolytic solution can be used and the non-aqueous solvent that is suitable only for the negative electrode electrolytic solution may not be used. As a result, properties of the whole secondary battery 1 can be further improved.
The positive electrode electrolytic solution filling part 9 may further include an electrical conducting material. The electrical conducting material may be, for example, a carbon material such as carbon black such as acetylene black or ketjen black, graphite, graphene, carbon nanotube, or carbon nanofiber. These electrical conducting materials may be dispersed in the positive electrode electrolytic solution to form an electron conduction network. The electrical conducting material has preferably a particle shape and more preferably a bulky particle shape. A content of the electrical conducting material may be 5 parts by mass or more and may be 50 parts by mass or less, with respect to 100 parts by mass of a total mass of the positive electrode active material, the non-aqueous solvent, and the conductive member contained in the positive electrode electrolytic solution filling part 9.
In the negative electrode electrolytic solution filling part 10, a conductive member is disposed so as to bring the negative electrode current collector 7 and the electrolyte layer 8 into conduction. The conductive member has a mesh structure. The conductive member may be provided in a part of the negative electrode electrolytic solution filling part 10 or may be provided to embed the whole negative electrode electrolytic solution filling part 10. The thickness of the negative electrode electrolytic solution filling part 10 may be 5 μm or more and may be 2000 μm or less, for example. The conductive member in the negative electrode electrolytic solution filling part 10 may be the same as the material described as the conductive member in the positive electrode electrolytic solution filling part 9.
The negative electrode electrolytic solution filling part 10 includes a negative electrode electrolytic solution, and specifically includes, for example, a negative electrode active material, an electrolyte salt, and a non-aqueous solvent.
In the negative electrode electrolytic solution filling part 10, the negative electrode active material preferably exists in a state of being dispersed in the negative electrode electrolytic solution (a non-aqueous solvent). In other words, the negative electrode active material is not retained (fixed) in the negative electrode current collector 7, and the negative electrode electrolytic solution filling part 10 preferably does not contain a binder for retaining (fixing) the negative electrode active material in the negative electrode current collector 7.
The negative electrode active material contains at least one selected from the group consisting of silicon, tin, and aluminum, as a constituent element. A content of silicon may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, and may be 100% by mass or less, 95% by mass or less, or 90% by mass or less, on a basis of a total amount of the negative electrode active material. A content of tin may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, and may be 100% by mass or less, 95% by mass or less, or 90% by mass or less, on the basis of the total amount of the negative electrode active material. A content of aluminum may be 10% by mass or more, 15% by mass or more, or 20% by mass or more, and may be 100% by mass or less, 95% by mass or less, or 90% by mass or less, on the basis of the total amount of the negative electrode active material.
The negative electrode active material containing silicon as a constituent element may contain an elemental silicon, or may contain a compound containing silicon as a constituent element (silicon-containing compound). The negative electrode active material containing tin as a constituent element may contain an elemental tin, and may contain a compound containing tin as a constituent element (tin-containing compound).
The silicon-containing compound or the tin-containing compound may be, for example, an alloy (a silicon alloy or a tin alloy) containing silicon or tin and at least one selected from the group consisting of nickel, copper, iron, cobalt, manganese, zinc, indium, silver, titanium, germanium, bismuth, antimony, and chromium as a constituent element. The silicon-containing compound or the tin-containing compound may be an oxide, a nitride, or a carbide. Examples of such a silicon-containing compound include a silicon oxide such as SiO, SiO2, or LiSiO, a silicon nitride such as Si3N4 or Si2N2O, and a silicon carbide such as SiC. Examples of such a tin-containing compound include a tin oxide such as SnO, SnO2, or LiSnO.
The negative electrode active material containing aluminum as a constituent element may be, for example, an aluminum alloy such as a lithium aluminum alloy.
A content of the negative electrode active material may be 10 parts by mass or more and may be 80 parts by mass or less, with respect to 100 parts by mass of a total mass of the negative electrode active material, the non-aqueous solvent, and the conductive member contained in the negative electrode electrolytic solution filling part 10.
The electrolyte salt may be, for example, a lithium salt. The lithium salt may be the same as the lithium salt described as the electrolyte salt contained in the positive electrode electrolytic solution filling part 9. A content of the electrolyte salt may be 0.5 mol/L or more, 0.7 mol/L or more, or 0.8 mol/L or more, and may be 5 mol/L or less, 3 mol/L or less, or 2 mol/L or less, on a basis of a total amount of the non-aqueous solvent.
The non-aqueous solvent is a solvent that can dissolve an electrolyte salt contained in the negative electrode electrolytic solution filling part 10. Examples of the non-aqueous solvent include the non-aqueous solvent that can be suitably used in both the positive electrode electrolytic solution and the negative electrode electrolytic solution, and the non-aqueous solvent that can be suitably used only in the positive electrode electrolytic solution (that is not suitable for the negative electrode electrolytic solution) which are mentioned above. The non-aqueous solvent is used singly or in combination of two or more types thereof.
The non-aqueous solvent that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution) may be a solvent that is excellent in reduction resistance but is not excellent in oxidation resistance (when the solvent is contained in the positive electrode electrolytic solution (particularly, the positive electrode electrolytic solution using a 4-V class positive electrode such as lithium cobaltate as the positive electrode active material), oxidative decomposition is promoted, and thus the resistance is increased).
Examples of the non-aqueous solvent that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution) include γ-butyrolactone, ethyl acetate, ethyl pentanoate, dimethyl malonate, diethyl malonate, diethyl methylmalonate, diethyl succinate, diethyl glutarate, diethyl azelate, ethyl heptanoate, heptanoic acid, tetrahydrofuran, 1,2-dimethoxyethane, ethyl propyl ether, tetraethylene glycol dimethyl ether, ethylene glycol bis(3-aminopropyl)ether, diethylene glycol bis(3-aminopropyl)ether, ethylene glycol bis(propionitrile)ether, bis[2-(2-methoxyethoxy)ethyl ether], 12-crown-4, 18-crown-6, taurine, N-methyltaurine, 2-(methylamino)ethanol, diaminohexane, methylenebis(2-chloroaniline), 1-methyl-2-pyrrolidinone, 1,3-dimethyl-2-imidazolidinone, N,N-dimethylformacetamide, N-methyl-piperazine, trimethylamine, triethylamine, N,N-dimethylpropylamine, dimethylformamide, diethylformamide, 1,1,3,3-tetramethylurea, N,N-dimethyl-propyleneurea, cyclohexane, piperidine, cyclopentane, decahydronaphthalene, tetrahydronaphthalene, pyrrolidine, quinoline, and 3-pyrroline. Among these, the non-aqueous solvent that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution) may be at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, y-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile)ether, 2-(methylamino)ethanol, and diaminohexane.
Furthermore, examples of the non-aqueous solvent that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution) also include vinylene carbonate, propane sultone, 1,4-butane sultone, 1,3-propene sultone, ethylmethane sultone, ethylene sulfite, trifluoromethane ethylene carbonate, fluorobenzene, and fluoroethylene carbonate. Among these, the non-aqueous solvent that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution) may be vinylene carbonate or fluoroethylene carbonate.
A content of the non-aqueous solvent that can be suitably used in both the positive electrode electrolytic solution and the negative electrode electrolytic solution may be 1% by mass or more, 3% by mass or more, or 5% by mass or more, and may be 95% by mass or less, 90% by mass or less, or 80% by mass or less, on a basis of a total amount of the non-aqueous solvent contained in the negative electrode electrolytic solution filling part 10. A content of the non-aqueous solvent that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution) may be 0.1% by mass or more, 1% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more, and may be 100% by mass or less, 95% by mass or less, or 90% by mass or less, on a basis of a total amount of the non-aqueous solvent contained in the negative electrode electrolytic solution filling part 10.
In an embodiment, from the viewpoint that the generation of a film, which is called a solid-electrolyte-interface (SEI), on the surface of the negative electrode active material can be further suitably suppressed, the non-aqueous solvent may contain 0.1% by mass or more, 1% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more of vinylene carbonate, on a basis of a total amount of the non-aqueous solvent, and more preferably may be composed only of vinylene carbonate.
In an embodiment, from the viewpoint that the generation and loss of the SEI on the surface of the negative electrode active material can be suitably suppressed, the non-aqueous solvent may contain 0.1% by mass or more, 1% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more of fluoroethylene carbonate, on a basis of a total amount of the non-aqueous solvent, and more preferably may be composed only of fluoroethylene carbonate.
In an embodiment, from the viewpoint that the generation and loss of the SEI on the surface of the negative electrode active material can be suitably suppressed, the non-aqueous solvent may contain 0.1% by mass or more, 1% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more of at least one selected from the group consisting of 12-crown-4, 18-crown-6, 1,2-dimethoxyethane, tetraethylene glycol dimethyl ether, γ-butyrolactone, 1-methyl-2-pyrrolidinone, ethyl heptanoate, tetrahydrofuran, ethylene glycol bis(propionitrile)ether, 2-(methylamino)ethanol, and diaminohexane, on a basis of a total amount of the non-aqueous solvent, and more preferably may be composed only of the at least one.
In an embodiment, the negative electrode electrolytic solution filling part 10 may not contain the aforementioned non-aqueous solvent that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution). In another embodiment, a content of the non-aqueous solvent that can be suitably used only in the negative electrode electrolytic solution (that is not suitable for the positive electrode electrolytic solution) may be 0.1% by mass or less on a basis of a total amount of the non-aqueous solvent contained in the negative electrode electrolytic solution filling part 10.
As described above, in the secondary battery 1 according to the present embodiment, since the positive electrode electrolytic solution filling part 9 and the negative electrode electrolytic solution filling part 10 are independently provided, the negative electrode electrolytic solution filling part 10 may employ the non-aqueous solvent that is suitable only for the positive electrode electrolytic solution and may not employ the non-aqueous solvent that is suitable only for the negative electrode electrolytic solution. As a result, the generation of a film, which is called a SEI, on the surface of the negative electrode active material is suppressed to a minimum. The SEI is a factor that influences the lifetime characteristics of the secondary battery, and the SEI grows during repeating charging and discharging hundreds of times, so that the battery resistance is increased and the initial capacity may not be attained. Therefore, by using the non-aqueous solvent, which can suppress the formation of the SEI, only in the negative electrode electrolytic solution, the reduction resistance of the negative electrode electrolytic solution is improved, and the lifetime of the secondary battery 1 is further improved.
The negative electrode electrolytic solution filling part 10 may further contain an electrical conducting material. The electrical conducting material may be the same as the material described as the electrical conducting material contained in the positive electrode electrolytic solution filling part 9. A content of the electrical conducting material may be 5 parts by mass or more and may be 50 parts by mass or less, with respect to 100 parts by mass of a total mass of the negative electrode active material, the non-aqueous solvent, and the conductive member contained in the negative electrode electrolytic solution filling part 10.
Concerning this secondary battery as described above, while the conductive member secures conduction between the negative electrode current collector 7 and the electrolyte layer 8, in the negative electrode electrolytic solution filling part 10, the negative electrode active material coexists with the negative electrode electrolytic solution in a state of being retained in the conductive member, and thereby this secondary battery functions as a secondary battery. Then, in this secondary battery, since the negative electrode active material is retained in the conductive member, even in a case where the negative electrode active material containing silicon, tin, or aluminum as a constituent element is micronized by charging and discharging of the secondary battery, the negative electrode active material is easily captured by the mesh structure of the conductive member, and subsequently, this negative electrode active material may function as a negative electrode active material.
On the other hand, concerning a conventional secondary battery in which the negative electrode active material is retained on the negative electrode current collector 7, when the negative electrode active material is micronized by charging and discharging of the secondary battery, the negative electrode active material is dropped out from the negative electrode current collector 7, and thus the electrode containing the negative electrode active material cannot function, so that the discharge capacity or the like of the secondary battery may be decreased.
Therefore, in this secondary battery 1, since the negative electrode active material is not fixed to the negative electrode current collector 7 through a binder and is dispersed in the negative electrode electrolytic solution, as compared to the conventional secondary battery in which the negative electrode active material is retained on the negative electrode current collector, a decrease in discharge capacity caused by the micronization of the negative electrode active material can be suppressed.
In addition, since this secondary battery is provided with the positive electrode electrolytic solution filling part 9 and the negative electrode electrolytic solution filling part 10 separately, electrolytic solutions having compositions suitable for respective electrodes can be separately used as the positive electrode electrolytic solution and the negative electrode electrolytic solution. On the other hand, in a conventional secondary battery using the common electrolytic solution in the positive electrode and the negative electrode, for example, in the case of adding a component suitable for the negative electrode to the electrolytic solution, when this component is not suitable for the positive electrode, the addition amount or the like may be restricted so that the performance of the whole secondary battery is not degraded. Therefore, in the secondary battery of the present embodiment in which such a restriction does not occur, as compared to the conventional secondary battery using the common electrolytic solution in the positive electrode and the negative electrode, the performance of the secondary battery can be improved.
Hereinafter, the present invention will be described in detail by means of Examples; however, the present invention is not limited to Examples.
50 parts by mass of lithium cobaltate and 20 parts by mass of acetylene black were dispersed in 30 parts by mass of acetonitrile (dehydration grade, manufactured by FUJIFILM Wako Pure Chemical Corporation) and 3 parts by mass of LiBF4 (manufactured by KISHIDA
CHEMICAL Co., Ltd.) by a ball mill, thereby producing a positive electrode electrolytic solution. Furthermore, 50 parts by mass of Si (manufactured by Aldrich, Inc., nano silicon (100 nm or less)) and 20 parts by mass of acetylene black were dispersed in 30 parts by mass of 1-methyl-2-pyrrolidinone (dehydration grade, manufactured by FUJIFILM Wako Pure Chemical Corporation) and 3 parts by mass of LiBF4 while being pulverized by a bead mill, thereby producing a negative electrode electrolytic solution.
An electrolyte layer having a size of 10 cm×10 cm (manufactured by DowDuPont, Inc., trade name Nafion 212) was prepared, and carbon felt (manufactured by AvCarb Material Solutions, AvCarb G100 Soft Graphite Battery Felt) was disposed as a conductive member on both surfaces of the electrolyte layer. Next, an aluminum foil having a thickness of 20 μm (positive electrode current collector) was disposed on the conductive member of the electrolyte layer on one side and a copper foil having a thickness of 20 μm (negative electrode current collector) was disposed on the conductive member on the other side, thereby obtaining a laminate. Subsequently, the above-described positive electrode electrolytic solution was injected between the positive electrode current collector and the electrolyte layer, the above-described negative electrode electrolytic solution was injected between the negative electrode current collector and the electrolyte layer, and then the laminate was hot-pressed at 40° C. The laminate was covered with an aluminum laminate bag (outer casing body) so that parts of the positive electrode current collector and the negative electrode current collector protruded to the outside and the bag was sealed, thereby obtaining a secondary battery.
The obtained secondary battery was charged at 25° C. at a current corresponding to 0.1 C to 4.2 V and then discharged at a current corresponding to 0.1 C to 2.5 V, and an initial (first cycle) discharge capacity X was measured. This cycle of charging and discharging was performed twice, and then a cycle of charging at a current corresponding to 0.5 C. and discharging at a current corresponding to 0.5 C. was performed 100 times. A discharge capacity Y after 100 cycles was measured and a capacity retention rate (=Y/X×100 (%)) was calculated to be 91%.
50 parts by mass of LiNi0.5Mn1.5O2 and 20 parts by mass of acetylene black were dispersed in 30 parts by mass of acetonitrile (dehydration grade) and 3 parts by mass of LiBF4 (manufactured by KISHIDA CHEMICAL Co., Ltd.) by a ball mill, thereby producing a positive electrode electrolytic solution. Furthermore, 50 parts by mass of Si (manufactured by Aldrich, Inc., nano silicon (100 nm or less)) and 20 parts by mass of acetylene black were dispersed in 30 parts by mass of 1,2-dimethoxyethane (manufactured by KISHIDA CHEMICAL Co., Ltd.) and 3 parts by mass of LiBF4 while being pulverized by a bead mill, thereby producing a negative electrode electrolytic solution.
Lithium ion conduction glass (manufactured by OHARA INC., LICGC) was prepared as the electrolyte layer. Carbon felt (manufactured by AvCarb Material Solutions, AvCarb G100 Soft Graphite Battery Felt) was disposed as the conductive member on both surfaces of the electrolyte layer. Next, an aluminum foil having a thickness of 20 μm (positive electrode current collector) was disposed on the conductive member of the electrolyte layer on one side and a copper foil having a thickness of 20 μm (negative electrode current collector) was disposed on the conductive member on the other side, thereby obtaining a laminate. Subsequently, the above-described positive electrode electrolytic solution was injected between the positive electrode current collector and the electrolyte layer, the above-described negative electrode electrolytic solution was injected between the negative electrode current collector and the electrolyte layer, and then the laminate was hot-pressed at 40° C. The laminate was covered with an aluminum laminate bag (outer casing body) so that parts of the positive electrode current collector and the negative electrode current collector protruded to the outside, a glass plate was then interposed between both surfaces, and an external pressure of 0.3 MP was applied thereto so as to seal the bag, thereby obtaining a secondary battery.
The obtained secondary battery was charged at 25° C. at a current corresponding to 0.1 C to 5.0 V and then discharged at a current corresponding to 0.1 C to 3.0 V, and an initial (first cycle) discharge capacity X was measured. This cycle of charging and discharging was performed twice, and then a cycle of charging at a current corresponding to 0.5 C and discharging at a current corresponding to 0.5 C was performed 100 times. A discharge capacity Y after 100 cycles was measured and a discharge capacity retention rate (=Y/X×100 (%)) was calculated to be 91%.
Production of a secondary battery and evaluation of the secondary battery were performed in the same manner as in Example 2-1, except that the solvent of the positive electrode electrolytic solution and the solvent of the negative electrode electrolytic solution were changed to solvents shown in Table 1. Note that, the electrolytic solution solvent was used after being subjected to a dehydration treatment as necessary. Results of the capacity retention rate are shown in Table 1.
From the above description, it was confirmed that the secondary battery according to an aspect of the present invention (the secondary battery using a negative electrode active material containing silicon, tin, or aluminum as a constituent element) can suppress a decrease in discharge capacity.
1: secondary battery, 2: electrode group, 3: battery outer casing body, 4: positive electrode current collector tab, 5: negative electrode current collector tab, 6: positive electrode current collector, 7: negative electrode current collector, 8: electrolyte layer, 9: positive electrode electrolytic solution filling part, 10: negative electrode electrolytic solution filling part.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2019/023562 | Jun 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/022705 | 6/9/2020 | WO | 00 |
