Battery

Abstract

A battery 2000 of the present disclosure comprises: a positive electrode 203; a negative electrode 201 including graphite and zinc: and a solid-electrolyte layer 202 positioned between the positive electrode 203 and the negative electrode 201. In the negative electrode 201, the ratio of the mass of the zinc to the sum of the mass of the graphite and the mass of the zinc is 10-60 mass%. Said ratio may be 20-40 mass%.

Description

[Technical Field]

[0001] The present disclosure relates to batteries. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, for example, are used as power sources for devices such as portable electronic devices, electric vehicles, and power storage devices. Non-aqueous electrolyte secondary batteries are charged and discharged by, for example, transferring lithium ions between a positive electrode and a negative electrode. Improvements in energy density and input / output density are being sought for non-aqueous electrolyte secondary batteries.

[0003] In recent years, all-solid-state secondary batteries have attracted attention as non-aqueous electrolyte secondary batteries. All-solid-state secondary batteries have, for example, a positive electrode, a negative electrode, and a solid electrolyte layer located between the positive electrode and the negative electrode. All-solid-state secondary batteries use a solid electrolyte as a medium for conducting lithium ions. Compared to conventional batteries that use an electrolytic solution as a medium for conducting lithium ions, all-solid-state secondary batteries are characterized in that all components are made of solid materials. All-solid-state secondary batteries are disclosed, for example, in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2018-106984 [Patent Document 2] Japanese Patent Application Publication No. 2018-137056 [Non-patent literature]

[0005] [Non-Patent Document 1] Jiqiang Wang et al, "Investigations of binary lithium-zinc, lithium-cadmium and lithium-lead alloys as negative electrodes in organic solvent-based electrolyte", Solid State Ionics 1986, Vol. 20, p. 185-189. Summary of the Invention [Problem to be solved by the invention]

[0006] In the prior art, it is desirable to improve the cycle characteristics of batteries. [Means for solving the problem]

[0007] The battery of the present disclosure comprises: A positive electrode and a negative electrode comprising graphite and zinc; a solid electrolyte layer located between the positive electrode and the negative electrode; Equipped with In the negative electrode, the ratio of the mass of zinc to the total mass of graphite and zinc is 10% by mass or more and 60% by mass or less. [Effects of the Invention]

[0008] According to the present disclosure, the cycle characteristics of a battery can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a battery according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery according to the second embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing a schematic configuration of a three-electrode battery. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Findings that formed the basis of this disclosure) Graphite has traditionally been used as the negative electrode active material in non-aqueous electrolyte secondary batteries. In recent years, silicon has been proposed as a negative electrode active material to improve the energy density of non-aqueous electrolyte secondary batteries. Silicon is one of the materials that can form an alloy with lithium. Silicon has a larger capacity per mass than graphite. However, silicon expands and contracts significantly during charging and discharging. Therefore, batteries using silicon as the negative electrode active material have a problem in that their cycle characteristics tend to deteriorate due to poor contact between active materials or between the active material and the current collector.

[0011] In all-solid-state batteries, all interfaces between the active material and the electrolyte are solid-solid interfaces. Therefore, compared to conventional batteries that use an electrolyte solution as a medium for conducting lithium ions, in all-solid-state batteries, deterioration of the bonding state at the solid-solid interface due to expansion and contraction of the active material has a significant impact on battery performance. In particular, when materials such as silicon, which expand and contract significantly during charge and discharge, are used as the negative electrode active material in all-solid-state batteries, issues related to reduced cycle characteristics are likely to arise.

[0012] As a result of extensive research, the present inventors have newly discovered that the cycle characteristics of solid-state batteries can be improved by using a mixture of graphite and zinc with an appropriately adjusted mass ratio as the negative electrode active material. When zinc is used as the negative electrode active material, it can form an alloy with lithium and is one of the materials that is expected to improve the energy density of non-aqueous electrolyte secondary batteries. Furthermore, the volume expansion rate when zinc is alloyed with lithium to form LiZn is 1 / 100 that of silicon when it is alloyed with Li. 22 The volume expansion coefficient of zinc is smaller than that of Si5. For example, the volume expansion coefficient of zinc is approximately 200%, and that of silicon is approximately 400%. However, for the following reasons (1) to (3), the use of zinc as a negative electrode active material for all-solid-state secondary batteries has not been fully investigated. (1) The true specific gravity of zinc is 7.1 g / cm 3, which is larger than that of graphite and silicon. For example, the true specific gravity of graphite and silicon is about 2.3 g / cm 3 (2) The theoretical capacity density per unit mass of zinc is 410 mAh / g, which is higher than that of graphite but lower than that of silicon. For example, the theoretical capacity density per unit mass of graphite is 372 mAh / g. The theoretical capacity density per unit mass of silicon is 4198 mAh / g. (3) When a battery using zinc as the negative electrode active material is discharged from a fully charged state, the composition of the negative electrode active material changes from LiZn to Li by releasing Li. 0.4 As disclosed in Non-Patent Document 1, the composition of the negative electrode active material is changed to Li 0.4 When it changes to Zn, the discharge reaction rate slows down, and as a result, the initial charge / discharge efficiency of this battery tends to be low.

[0013] In the field of all-solid-state batteries, proposals have been made to control the particle size of the active material and to charge and discharge the battery while applying pressure to the battery element in order to improve battery performance by suppressing deterioration of the bonding state at the solid-solid interface due to expansion and contraction of the active material. For example, Patent Document 1 discloses applying a confining pressure of 10 MPa or 45 MPa to the battery element for an all-solid-state battery using silicon particles with a specific average particle size as the negative electrode active material. Patent Document 2 discloses applying a confining pressure of 21 MPa to the battery element for an all-solid-state battery using silicon as the negative electrode active material using a confining member. Furthermore, Patent Document 2 discloses that the depth of charge of a battery can be estimated with high accuracy based on changes in the confining pressure caused by expansion and contraction of the active material when the battery is repeatedly charged and discharged. Reducing the confining pressure applied to the battery element is desirable from the perspective of miniaturizing the members used to confine the battery element and improving the overall energy density of the battery.

[0014] (Summary of one aspect of the present disclosure) The battery according to the first aspect of the present disclosure comprises: A positive electrode and a negative electrode comprising graphite and zinc; a solid electrolyte layer located between the positive electrode and the negative electrode; Equipped with In the negative electrode, the ratio of the mass of zinc to the total mass of graphite and zinc is 10% by mass or more and 60% by mass or less.

[0015] According to the first aspect, zinc in the negative electrode tends to expand during battery charging. When zinc expands, pressure is applied to the stack including the positive electrode, negative electrode, and solid electrolyte layer inside the battery in a direction that compresses the stack. At this time, voids in the negative electrode tend to decrease, and the bonding state of the solid-solid interface in the negative electrode tends to improve. For example, the bonding state of the interface between graphite and zinc in the negative electrode tends to improve. When graphite and zinc are mixed in an appropriate ratio, the improved bonding state of the interface can improve the cycle characteristics of the battery.

[0016] In the second aspect of the present disclosure, for example, in the battery according to the first aspect, the ratio may be 20 mass % or more and 40 mass % or less. With this configuration, the input / output characteristics of the battery can be improved.

[0017] In a third aspect of the present disclosure, for example, the battery according to the first or second aspect may further include a laminate including the positive electrode, the negative electrode, and the solid electrolyte layer, and a restraining member that restrains the laminate. With this configuration, the input / output characteristics and cycle characteristics of the battery can be improved.

[0018] In a fourth aspect of the present disclosure, for example, in the battery according to the third aspect, the restraining pressure applied to the stack by the restraining member may be 10 MPa or more and 200 MPa or less. With this configuration, the input / output characteristics and cycle characteristics of the battery can be improved.

[0019] In a fifth aspect of the present disclosure, for example, in the battery according to the fourth aspect, the confining pressure may be 10 MPa or more and 50 MPa or less. With this configuration, the input / output characteristics and cycle characteristics of the battery can be improved.

[0020] In a sixth aspect of the present disclosure, for example, in the battery according to the fourth or fifth aspect, the confining pressure may be 30 MPa or more and 50 MPa or less. With this configuration, the output characteristics of the battery can be further improved.

[0021] In a seventh aspect of the present disclosure, for example, in the battery according to any one of the first to sixth aspects, the negative electrode may contain graphite particles and zinc particles. With this configuration, the negative electrode can be easily produced.

[0022] In an eighth aspect of the present disclosure, for example, in the battery according to any one of the first to seventh aspects, the negative electrode may have a negative electrode mixture layer containing graphite and zinc, and a negative electrode current collector in contact with the negative electrode mixture layer, and in the negative electrode mixture layer, the ratio of the mass of zinc to the total mass of graphite and zinc may be 10% by mass or more and 60% by mass or less. With this configuration, the cycle characteristics of the battery can be improved.

[0023] In a ninth aspect of the present disclosure, for example, in the battery according to any one of the first to eighth aspects, the negative electrode may further contain a solid electrolyte having lithium ion conductivity. This configuration improves ion conductivity in the negative electrode, further improving the input / output characteristics of the battery.

[0024] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0025] (Embodiment 1) FIG. 1 is a cross-sectional view showing a schematic configuration of a battery 2000 according to the first embodiment.

[0026] The battery 2000 in the first embodiment includes an anode 201 , a solid electrolyte layer 202 , and a cathode 203 .

[0027] The negative electrode 201 includes a negative electrode material 1000. The negative electrode material 1000 includes graphite and zinc. In the negative electrode 201, the ratio P of the mass of zinc to the total mass of the graphite and zinc is 10% by mass or more and 60% by mass or less. The ratio P may be 20% by mass or more and 40% by mass or less.

[0028] The solid electrolyte layer 202 is located between the positive electrode 203 and the negative electrode 201 .

[0029] According to the above configuration, the cycle characteristics of the battery 2000 can be improved.

[0030] The negative electrode 201, the solid electrolyte layer 202, and the positive electrode 203 are stacked, for example, in this order. In other words, the battery 2000 includes, for example, a laminate 210 including the negative electrode 201, the solid electrolyte layer 202, and the positive electrode 203. The laminate 210 functions, for example, as a battery element.

[0031] In the negative electrode material 1000, graphite and zinc function as active materials. Each of the graphite and zinc may have a particulate shape. In other words, the negative electrode material 1000 may include graphite particles 101 and zinc particles 102. In the present disclosure, the shape of a "particle" may be acicular, spherical, ellipsoidal, or the like. In the negative electrode material 1000, a plurality of the graphite particles 101 and a plurality of the zinc particles 102 may be in contact with each other, thereby forming an electron conduction path.

[0032] The negative electrode material 1000 may further include a solid electrolyte 103. The solid electrolyte 103, for example, fills spaces between the plurality of graphite particles 101 and the plurality of zinc particles 102. The solid electrolyte 103 may also have a particle shape. Many particles of the solid electrolyte 103 may be compressed and bonded to each other, thereby forming ion conduction paths.

[0033] In the first embodiment, the median diameter of the graphite particles 101 may be 0.1 μm or more and 100 μm or less, and the median diameter of the zinc particles 102 may be 0.1 μm or more and 100 μm or less.

[0034] When the median diameter of the graphite particles 101 and the median diameter of the zinc particles 102 are 0.1 μm or more, the graphite particles 101, the zinc particles 102, and the solid electrolyte 103 tend to form a well-dispersed state in the negative electrode material 1000. As a result, the charging characteristics of the battery are improved.

[0035] When the median diameter of the graphite particles 101 and the median diameter of the zinc particles 102 are 100 μm or less, the diffusion rate of lithium within the graphite particles 101 and the zinc particles 102 is sufficiently ensured, thereby enabling the battery to operate at high power output.

[0036] The median diameter of the graphite particles 101 and the median diameter of the zinc particles 102 may be larger than the median diameter of the solid electrolyte 103. This allows the graphite particles 101, zinc particles 102, and solid electrolyte 103 to form a good dispersed state.

[0037] The graphite constituting the graphite particles 101 may be natural graphite or artificial graphite.

[0038] An oxide film may be formed on the surface of the zinc particles 102. The oxygen content in the zinc particles 102 is not particularly limited, and is, for example, 2 mass % or less.

[0039] For example, a solid electrolyte having lithium ion conductivity can be used as the solid electrolyte 103. In this case, a high-capacity lithium ion battery can be provided by using the negative electrode material 1000.

[0040] At least one selected from an inorganic solid electrolyte and an organic solid electrolyte can be used as the solid electrolyte 103. The solid electrolyte 103 may include at least one selected from the group consisting of a sulfide solid electrolyte, an oxide solid electrolyte, a halide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte. Specific examples of the sulfide solid electrolyte, the oxide solid electrolyte, the halide solid electrolyte, the polymer solid electrolyte, and the complex hydride solid electrolyte will be described later for the solid electrolyte layer 202. At least one selected from the group consisting of all the solid electrolytes described later can be used as the solid electrolyte 103.

[0041] In order to achieve a good dispersion state, it is desirable that the solid electrolyte 103 be made of a soft material. In this respect, at least one selected from the group consisting of sulfide solid electrolytes and halide solid electrolytes is suitable as the solid electrolyte 103.

[0042] The shape of solid electrolyte 103 in embodiment 1 is not particularly limited and may be, for example, needle-like, spherical, oval-spherical, scale-like, etc. For example, solid electrolyte 103 may be granular.

[0043] For example, when the solid electrolyte 103 in the first embodiment is particulate (e.g., spherical), the median diameter may be 0.01 μm or more and 100 μm or less. When the median diameter is 0.01 μm or more, the contact interfaces between the particles of the solid electrolyte 103 do not increase too much, and an increase in the ionic resistance inside the negative electrode material 1000 can be suppressed. This enables the battery to operate at high power output.

[0044] When the median diameter of the solid electrolyte 103 is 100 μm or less, the graphite particles 101, zinc particles 102, and solid electrolyte 103 tend to be well dispersed in the negative electrode material 1000. This facilitates achieving a high capacity battery.

[0045] In the first embodiment, the median diameter of the solid electrolyte 103 may be smaller than the median diameters of the graphite particles 101 and the zinc particles 102. This allows the graphite particles 101, the zinc particles 102, and the solid electrolyte 103 to be better dispersed in the negative electrode material 1000.

[0046] The negative electrode material 1000 may further contain other active materials in addition to the graphite particles 101 and the zinc particles 102. The shape of the other active materials is not particularly limited and may be, for example, acicular, spherical, or ellipsoidal. For example, the shape of the other active materials may be particulate.

[0047] The median diameter of the other active material may be 0.1 μm or more and 100 μm or less.

[0048] When the median diameter of the other active material is 0.1 μm or more, the other active material and the solid electrolyte 103 tend to form a well-dispersed state in the negative electrode material 1000. As a result, the charging characteristics of the battery are improved.

[0049] When the median diameter of the other active material is 100 μm or less, the diffusion rate of lithium within the active material is sufficiently ensured, enabling the battery to operate at high power.

[0050] The median diameter of the other active material may be larger than the median diameter of the solid electrolyte 103. This allows the active material and the solid electrolyte 103 to form a good dispersed state.

[0051] Other active materials include materials that have the property of absorbing and releasing metal ions (e.g., lithium ions). Examples of other active materials that can be used include metal materials, carbon materials other than graphite, oxides, nitrides, tin compounds, and silicon compounds. The metal material may be a single metal. Alternatively, the metal material may be an alloy. Examples of metal materials include lithium metal and lithium alloys. Examples of carbon materials include coke, partially graphitized carbon, carbon fiber, spherical carbon, and amorphous carbon. From the viewpoint of capacity density, silicon (Si), tin (Sn), silicon compounds, and tin compounds can be preferably used.

[0052] The other active material may include a single active material, or may include a plurality of active materials having different compositions.

[0053] According to the above configuration, the charging capacity of the battery can be improved.

[0054] In the first embodiment, the graphite particles 101, the zinc particles 102, and the particles of the solid electrolyte 103 may be in contact with each other as shown in FIG.

[0055] The negative electrode material 1000 of the first embodiment may include a plurality of graphite particles 101, a plurality of zinc particles 102, and a plurality of particles of a solid electrolyte 103.

[0056] In the negative electrode material 1000, the content of the solid electrolyte 103 and the total content of the graphite and zinc may be the same or different from each other.

[0057] When the total amount of the negative electrode material 1000 is taken as 100 wt%, the total value of the graphite content and the zinc content can be, for example, 40 wt% or more and 80 wt% or less. By appropriately adjusting the total value of the graphite content and the zinc content, the graphite particles 101, the zinc particles 102, and the solid electrolyte 103 tend to form a good dispersion state.

[0058] The negative electrode material 1000 may contain only graphite particles 101, zinc particles 102, and solid electrolyte 103. In other words, the negative electrode material 1000 may essentially consist of graphite particles 101, zinc particles 102, and solid electrolyte 103. Such a configuration can improve the energy density of the battery. "Containing only graphite particles 101, zinc particles 102, and solid electrolyte 103" means that, except for unavoidable impurities, no other materials are intentionally contained in the negative electrode material 1000.

[0059] Generally, the term "median diameter" refers to the particle size where the cumulative volume in the volume-based particle size distribution is equal to 50%. The volume-based particle size distribution is measured, for example, by a laser diffraction measurement device.

[0060] The weight ratio "w:100-w" of the active material to the solid electrolyte 103 contained in the negative electrode 201 may satisfy 40≦w≦80. When 40≦w is satisfied, the energy density of the battery 2000 is sufficiently ensured. Furthermore, when w≦80 is satisfied, the battery 2000 can operate at high output.

[0061] The negative electrode 201 may have a negative electrode mixture layer containing the negative electrode material 1000 and a negative electrode current collector in contact with the negative electrode mixture layer. In the negative electrode mixture layer, the ratio of the mass of zinc to the total mass of graphite and zinc may be 10% by mass or more and 60% by mass or less, or 20% by mass or more and 40% by mass or less. The negative electrode current collector may be, for example, copper foil.

[0062] The bulk density of the negative electrode mixture layer is not particularly limited, and is, for example, 2.0 g / cm 3 More than 2.8g / cm 3 The bulk density is as follows. In this specification, bulk density may be referred to as packing density. The packing rate of the negative electrode mixture layer is not particularly limited, and is, for example, 62% or more and 71% or less. The packing rate of the negative electrode mixture layer is the ratio of the bulk density of the negative electrode mixture layer to the true density of the negative electrode mixture layer. The true density of the negative electrode mixture layer means the density of the negative electrode mixture layer when no voids exist in the negative electrode mixture layer.

[0063] The thickness of the negative electrode 201 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 201 is 10 μm or more, the energy density of the battery 2000 is sufficiently ensured. When the thickness of the negative electrode 201 is 500 μm or less, the battery 2000 can operate at high power.

[0064] The solid electrolyte layer 202 is a layer containing a solid electrolyte.

[0065] For example, an inorganic solid electrolyte having lithium ion conductivity is used as the solid electrolyte contained in the solid electrolyte layer 202. Examples of the inorganic solid electrolyte that can be used include a sulfide solid electrolyte, an oxide solid electrolyte, and a halide solid electrolyte.

[0066] The solid electrolyte contained in the solid electrolyte layer 202 may be a halide solid electrolyte.

[0067] The halide solid electrolyte is represented, for example, by the following composition formula (1): In composition formula (1), α, β, and γ each independently have a value greater than 0. M includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li. X includes at least one element selected from the group consisting of F, Cl, Br, and I.

[0068] Li α M β X γ ...Equation (1)

[0069] Metalloid elements include B, Si, Ge, As, Sb, and Te. Metal elements include all elements in groups 1 to 12 of the periodic table except for hydrogen, and all elements in groups 13 to 16 except for B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, metal elements are a group of elements that can become cations when forming inorganic compounds with halides.

[0070] Examples of halide solid electrolytes that can be used include Li3YX6, Li2MgX4, Li2FeX4, Li(Al,Ga,In)X4, and Li3(Al,Ga,In)X6.

[0071] The above configuration can improve the output density of the battery 2000. In addition, the thermal stability of the battery 2000 can be improved, and the generation of harmful gases such as hydrogen sulfide can be suppressed.

[0072] In this disclosure, when an element in a formula is expressed as "(Al, Ga, In)", this notation indicates at least one element selected from the group of elements in parentheses. That is, "(Al, Ga, In)" is synonymous with "at least one element selected from the group consisting of Al, Ga, and In". The same applies to other elements. Halide solid electrolytes exhibit excellent ionic conductivity.

[0073] In composition formula (1), M may contain Y (=yttrium). That is, the halide solid electrolyte contained in solid electrolyte layer 202 may contain Y as a metal element.

[0074] The halide solid electrolyte containing Y may be a compound represented by the following composition formula (2).

[0075] Li a M b Y c X6...Formula (2)

[0076] Composition formula (2) satisfies a+mb+3c=6 and c>0. In composition formula (2), M includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li and Y. m is the valence of M. X includes at least one element selected from the group consisting of F, Cl, Br, and I. M includes at least one element selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb. Specific examples of Y-containing halide solid electrolytes include Li3YF6, Li3YCl6, Li3YBr6, Li3YI6, Li3YBrCl5, Li3YBr3Cl3, Li3YBr5Cl, Li3YBr5I, Li3YBr3I3, Li3YBrI5, Li3YClI5, Li3YCl3I3, Li3YCl5I, Li3YBr2Cl2I2, Li3YBrCl4I, Li 2.7 Y 1.1 Cl6, Li 2.5 Y 0.5 Zr 0.5 Cl6, Li 2.5 Y 0.3 Zr 0.7 Cl6 and the like can be used.

[0077] According to the above configuration, the output density of the battery 2000 can be further improved.

[0078] The solid electrolyte contained in the solid electrolyte layer 202 may include a sulfide solid electrolyte.

[0079] According to the above configuration, since the sulfide solid electrolyte having excellent reduction stability is included, a low potential negative electrode material such as graphite or metallic lithium can be used, and the energy density of the battery 2000 can be improved.

[0080] Sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, Li2S-B2S3, Li2S-GeS2, and Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 These can be used in addition to LiX, Li2O, MOq , Li p MO q The element X in "LiX" is at least one element selected from the group consisting of F, Cl, Br, and I. q " and "Li p MO q "The element M is at least one element selected from the group consisting of P, Si, Ge, B, Al, Ga, In, Fe, and Zn. q " and "Li p MO q " p and q in this expression are independent natural numbers.

[0081] Examples of sulfide-based solid electrolytes that can be used include lithium-containing sulfides such as Li2S-P2S5-based, Li2S-SiS2-based, Li2S-B2S3-based, Li2S-GeS2-based, Li2S-SiS2-LiI-based, Li2S-SiS2-Li3PO4-based, Li2S-Ge2S2-based, Li2S-GeS2-P2S5-based, and Li2S-GeS2-ZnS-based.

[0082] The solid electrolyte contained in the solid electrolyte layer 202 may include at least one selected from the group consisting of an oxide solid electrolyte, a polymer solid electrolyte, and a complex hydride solid electrolyte.

[0083] Examples of oxide solid electrolytes include NASICON-type solid electrolytes, such as LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite-type solid electrolytes, and Li 14 ZnGeO 16 , Li4SiO4, LiGeO4 and their element-substituted LISICON-type solid electrolytes, Li7La3Zr2O 12 Garnet-type solid electrolytes, such as those substituted with LiN and its element, LiN and its H-substituted compounds, LiPO4 and its N-substituted compounds, and glass or glass ceramics containing a base material containing Li-BO compounds such as LiBO2 and LiBO3 to which a material such as LiSO4 or LiCO3 has been added can be used.

[0084] Examples of oxide-based solid electrolytes include lithium-containing metal oxides such as Li2O-SiO2 and Li2O-SiO2-P2O5; x P y O 1-z N z Lithium-containing metal nitrides such as lithium phosphate (Li3PO4), lithium-containing transition metal oxides such as lithium titanium oxide, and the like can be used.

[0085] Examples of oxide-based solid electrolytes include Li7La3Zr2O 12 (LLZ), Li 1.3 Al 0.3 Ti 1.7 (PO4)3(LATP), (La,Li)TiO3(LLTO), etc. are used.

[0086] As the polymer solid electrolyte, for example, a compound of a polymer compound and a lithium salt can be used. The polymer compound may have an ethylene oxide structure. By having an ethylene oxide structure, the polymer compound can contain a large amount of lithium salt, thereby further increasing ionic conductivity. As the lithium salt, LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, etc. can be used. As the lithium salt, one type of lithium salt selected from these may be used alone, or a mixture of two or more types of lithium salts selected from these may be used.

[0087] Examples of the complex hydride solid electrolyte that can be used include LiBH4-LiI and LiBH4-P2S5.

[0088] The solid electrolyte layer 202 may contain only one solid electrolyte selected from the above-mentioned group of solid electrolytes, or may contain two or more solid electrolytes selected from the above-mentioned group of solid electrolytes. The multiple solid electrolytes have different compositions. For example, the solid electrolyte layer 202 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0089] The thickness of the solid electrolyte layer 202 may be 1 μm or more and 300 μm or less. When the thickness of the solid electrolyte layer 202 is 1 μm or more, the negative electrode 201 and the positive electrode 203 are less likely to short-circuit. When the thickness of the solid electrolyte layer 202 is 300 μm or less, the battery 2000 can operate at high power.

[0090] The positive electrode 203 contributes to the operation of the battery 2000 as a counter electrode to the negative electrode 201 .

[0091] The positive electrode 203 may include a material having the property of absorbing and releasing metal ions (e.g., lithium ions), such as a positive electrode active material. Examples of the positive electrode active material that can be used include metal composite oxides, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, when a lithium-containing transition metal oxide is used as the positive electrode active material, the manufacturing cost can be reduced and the average discharge voltage can be increased.

[0092] The metal composite oxide selected as the positive electrode active material contained in the positive electrode 203 may contain Li and at least one element selected from the group consisting of Mn, Co, Ni, and Al. Examples of such materials include Li(NiCoAl)O2, Li(NiCoMn)O2, and LiCoO2. For example, the positive electrode active material may be Li(NiCoMn)O2.

[0093] The positive electrode 203 may contain a solid electrolyte. The above configuration increases the lithium ion conductivity inside the positive electrode 203, enabling the battery 2000 to operate at high power. The solid electrolyte in the positive electrode 203 may be any of the materials exemplified as the solid electrolyte contained in the solid electrolyte layer 202.

[0094] The median diameter of the active material particles contained in the positive electrode 203 may be 0.1 μm or more and 100 μm or less. When the median diameter of the active material particles is 0.1 μm or more, the active material particles and the solid electrolyte can be well dispersed. This improves the charge capacity of the battery 2000. When the median diameter of the active material particles is 100 μm or less, the diffusion rate of lithium within the active material particles is sufficiently ensured. This enables the battery 2000 to operate at high power.

[0095] The median diameter of the active material particles may be larger than the median diameter of the solid electrolyte particles, thereby achieving a good dispersion state of the active material and the solid electrolyte.

[0096] The volume ratio "v:100-v" of the active material to the solid electrolyte contained in the positive electrode 203 may satisfy 30≦v≦95. When 30≦v is satisfied, the energy density of the battery 2000 is sufficiently ensured. Furthermore, when v≦95 is satisfied, the battery 2000 can operate at high output.

[0097] The thickness of the positive electrode 203 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 203 is 10 μm or more, the energy density of the battery 2000 is sufficiently ensured. When the thickness of the positive electrode 203 is 500 μm or less, the battery 2000 can operate at high output.

[0098] The negative electrode 201 and the positive electrode 203 may contain one or more solid electrolytes to enhance ionic conductivity. The solid electrolyte may be any of the materials exemplified as the solid electrolyte contained in the solid electrolyte layer 202.

[0099] At least one of the negative electrode 201, the solid electrolyte layer 202, and the positive electrode 203 may contain a binder to improve adhesion between particles. The binder is used to improve the binding properties of the materials constituting the electrodes. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamideimide, polyacrylonitrile, polyacrylic acid, polymethyl acrylate, polyethyl acrylate, polyhexyl acrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethyl cellulose, and ethyl cellulose. The binder may be a copolymer of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, chlorotrifluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene. A mixture of two or more materials selected from these may also be used as the binder. The binder may be a styrene-ethylene-butylene-styrene block copolymer (SEBS) or a maleic anhydride-modified hydrogenated SEBS.

[0100] At least one of the negative electrode 201 and the positive electrode 203 may contain a conductive additive to enhance electronic conductivity. Examples of conductive additives that can be used include graphites such as natural graphite or artificial graphite, carbon blacks such as acetylene black and ketjen black, conductive fibers such as carbon fiber or metal fiber, metal powders such as carbon fluoride and aluminum, conductive whiskers such as zinc oxide or potassium titanate, conductive metal oxides such as titanium oxide, and conductive polymer compounds such as polyaniline, polypyrrole, and polythiophene. Using a carbon conductive additive can reduce costs.

[0101] The battery 2000 in the first embodiment can be configured as a battery of various shapes, such as a coin type, a cylindrical type, a square type, a sheet type, a button type, a flat type, or a laminated type.

[0102] (Embodiment 2) The following describes the second embodiment. Explanations that overlap with the first embodiment will be omitted where appropriate.

[0103] FIG. 2 is a cross-sectional view showing a schematic configuration of a battery 2100 according to the second embodiment.

[0104] The battery 2100 in the second embodiment further includes a restraining member 25 in addition to the laminate 210 including the negative electrode 201, the solid electrolyte layer 202, and the positive electrode 203.

[0105] The restraining member 25 restrains the stack 210 and can apply a restraining pressure to the stack 210. The restraining member 25 has, for example, a pair of plate members 26a and 26b, a rod 27, and a fixing member .

[0106] The pair of plate members 26a and 26b are aligned, for example, in the stacking direction of the laminate 210. The laminate 210 is sandwiched between the pair of plate members 26a and 26b. The plate member 26a faces, for example, the negative electrode 201. The plate member 26b faces, for example, the positive electrode 203. The main surfaces of the pair of plate members 26a and 26b each have an area larger than, for example, the main surfaces of the negative electrode 201 and the positive electrode 203. In this specification, the term "main surface" refers to the surface of the referenced member having the largest area. The pair of plate members 26a and 26b allows the restraining member 25 to apply restraining pressure to the laminate 210 in the stacking direction of the laminate 210.

[0107] Each of the pair of plate members 26a and 26b has an opening formed therein, into which, for example, rod 27 can be screwed. The opening of plate member 26a and the opening of plate member 26b are aligned in the stacking direction of stacked body 210, for example.

[0108] The rod 27 extends in the stacking direction of the laminate 210. The rod 27 is screwed into the opening of the plate member 26a and the opening of the plate member 26b. The rod 27 functions as a fastener that fastens the plate member 26a and the plate member 26b together. A male thread may be formed on the side of the rod 27. A specific example of the rod 27 is a bolt.

[0109] Restraint member 25 may have multiple rods 27. The number of rods 27 in restraint member 25 is not particularly limited and may be, for example, 1 to 40. In FIG. 2, restraint member 25 has four rods 27. In detail, plate members 26a and 26b are rectangular in plan view, and the four rods 27 are screwed into openings near the corners of plate members 26a and 26b, respectively. For the sake of explanation, two of the four rods 27, rods 27a and 27b, are shown in FIG. 2.

[0110] The fixing member 28, for example, fixes one of the plate members 26a and 26b to the rod 27. The fixing member 28 has, for example, an internal thread portion that can be threadedly engaged with the rod 27. A specific example of the fixing member 28 is a nut.

[0111] The restraining member 25 has, for example, a plurality of fixing members 28. As an example, two fixing members 28 are attached to one rod 27. Plate members 26a and 26b are sandwiched between the two fixing members 28. By adjusting the positions of the two fixing members 28, a load can be applied to each of the plate members 26a and 26b in a direction in which the plate members 26a and 26b approach each other. This allows a restraining pressure to be applied to the stack 210.

[0112] 2 shows four fixing members 28a, 28b, 28c, and 28d out of the eight fixing members 28 of restraint member 25. Fixing members 28a and 28b are each attached to rod 27a. Plate members 26a and 26b are sandwiched between fixing members 28a and 28b. Fixing members 28c and 28d are each attached to rod 27b. Plate members 26a and 26b are sandwiched between fixing members 28c and 28d.

[0113] The restraining member 25 may further include a sensor that measures the restraining pressure applied to the stack 210. The sensor is located, for example, between the stack 210 and one of the plate members 26a and 26b.

[0114] The restraining pressure applied to the laminate 210 by the restraining member 25 is not particularly limited and is, for example, 10 MPa or more and 200 MPa or less. The restraining pressure may be 10 MPa or more and 50 MPa or less, or 30 MPa or more and 50 MPa or less. Applying the restraining pressure to the laminate 210 by the restraining member 25 tends to suppress poor contact caused by expansion and contraction of the active material. Poor contact can occur, for example, between active materials or between an active material and a current collector. Applying the restraining pressure to the laminate 210 tends to improve the cycle characteristics of the battery 2100.

[0115] Battery 2100 may further include a container 21, leads 23a and 23b.

[0116] The container 21 accommodates the laminate 210. The container 21 is located, for example, between the laminate 210 and the restraining member 25. The container 21 can prevent the laminate 210 from coming into direct contact with the restraining member 25. The container 21 is made of, for example, an aluminum laminate film.

[0117] The lead wire 23a is electrically connected to the negative electrode 201. The lead wire 23b is electrically connected to the positive electrode 203. Each of the lead wires 23a and 23b extends to the outside of the container 24. As an example, the lead wire 23a is made of nickel, and the lead wire 23b is made of aluminum. [Example]

[0118] The present disclosure will be described in detail below using examples and comparative examples, but the present disclosure is not limited to the following examples.

[0119] 1. Preparation of Solid Electrolyte Li2S and P2S5 were weighed out to a molar ratio of Li2S:P2S5 = 75:25, and then crushed and mixed in a mortar. Next, mechanical milling was performed using a planetary ball mill at 510 rpm for 10 hours. This resulted in a glassy sulfide solid electrolyte.

[0120] 2. Preparation of the Negative Electrode (1) Preparation of a negative electrode containing a solid electrolyte First, graphite particles with a median diameter of 8 μm and spherical zinc particles with a median diameter of 4.5 μm (Kishida Chemical Co., Ltd., product number 000-87575) were prepared as negative electrode active materials. The median diameters of the graphite particles and zinc particles were measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-2000). An oxide film was formed on the zinc particles. The oxygen content of the zinc particles was 0.7% by mass. The oxygen content of the zinc particles was measured by an inert gas fusion method using a Horiba, Ltd. EMGA-830.

[0121] Next, negative electrode active materials e1 to e5 were prepared, each having a different mass ratio of graphite particles to zinc particles: 100:0, 80:20, 60:40, 40:60, and 0:100, respectively.

[0122] Next, each of the negative electrode active materials e1 to e5 was mixed with the solid electrolyte so that the volume ratio of the negative electrode active material to the solid electrolyte was 70:30. This resulted in mixtures m1 to m5. The volume ratios were calculated from the true specific gravity of the graphite particles, zinc particles, and solid electrolyte. The true specific gravity of the graphite particles was 2.2 g / cm. 3 The true specific gravity of the zinc particles was 7.1 g / cm 3 The true specific gravity of the solid electrolyte was 1.9 g / cm 3 In the mixtures m1 to m5, the mass ratios of the negative electrode active material to the solid electrolyte were 73:27, 76:24, 79:21, 82:18, and 90:10, respectively.

[0123] Next, a binder and a dispersion medium were added to each of mixtures m1 to m5, and the mixtures were kneaded. Maleic anhydride-modified hydrogenated SEBS (M1913, manufactured by Asahi Kasei Corporation) was used as the binder. This resulted in negative electrode mixture slurries s1 to s5. In each of the negative electrode mixture slurries s1 to s5, the ratio of the total mass of the negative electrode active material and the solid electrolyte to the mass of the binder was 99:1.

[0124] Next, each of the negative electrode mixture slurries s1 to s5 was applied onto a negative electrode current collector. A 10 μm-thick copper foil was used as the negative electrode current collector. The resulting coating film was dried at 100°C to obtain negative electrodes a1 to a5. Each of the negative electrodes a1 to a5 had a negative electrode current collector and a negative electrode mixture layer formed from the negative electrode mixture slurry.

[0125] [Evaluation of packing density of negative electrode mixture layer] Next, the packing density of the negative electrode mixture layer was measured when all-solid-state batteries were fabricated using negative electrodes a1 to a5. Specifically, each of negative electrodes a1 to a5 was first pressed at 600 MPa using a flat press. Next, the packing density of the negative electrode mixture layer included in each of the pressed negative electrodes a1 to a5 was measured. The packing density of the negative electrode mixture layer was calculated by dividing the volume of the negative electrode mixture layer from the mass of the negative electrode mixture layer. The results are shown in Table 1. Furthermore, the packing fractions of the negative electrode mixture layer for negative electrodes a1 to a5 were 85%, 71%, 67%, 62%, and 63%, respectively. As can be seen from these results, the packing fraction of the negative electrode mixture layer tended to decrease as the mass ratio of zinc in the negative electrode mixture layer increased. As described above, the packing fraction is the ratio of the bulk density of the negative electrode mixture layer to the true density of the negative electrode mixture layer. The true density of the negative electrode mixture layer was calculated using the mass ratios and true specific gravities of the graphite, zinc, solid electrolyte, and binder constituting the negative electrode mixture layer. The true specific gravity of the binder was 0.9 g / cm. 3 It was.

[0126] [Table 1]

[0127] (2) Preparation of a negative electrode that does not contain a solid electrolyte First, the graphite particles and zinc particles described in (1) were prepared as negative electrode active materials. Next, negative electrode active materials e6 to e9 were prepared, each containing different mass ratios of graphite particles to zinc particles. In negative electrode active materials e6 to e9, the mass ratios of graphite particles to zinc particles were 100:0, 90:10, 70:30, and 50:50, respectively.

[0128] Next, a binder and a dispersion medium were added to each of the negative electrode active materials e6 to e9, and the mixture was kneaded. Polyvinylidene fluoride (PVDF) was used as the binder. N-methylpyrrolidone (NMP) was used as the dispersion medium. This resulted in negative electrode mixture slurries s6 to s9. In the negative electrode mixture slurries s6 to s9, the mass ratio of the negative electrode active material to the binder was 90:10.

[0129] Next, each of the negative electrode mixture slurries s6 to s9 was applied onto a negative electrode current collector. A 10 μm-thick copper foil was used as the negative electrode current collector. The resulting coating was dried at 80°C and rolled using a rolling roller to obtain negative electrodes b1 to b4. Each of the negative electrodes b1 to b4 had a negative electrode current collector and a negative electrode mixture layer formed from the negative electrode mixture slurry.

[0130] In the rolling process using the rolling rollers, the conditions were appropriately adjusted so that the packing ratio of the negative electrode mixture layer for each of the negative electrodes b1 to b4 was almost constant in the range of 85% to 90%. As mentioned above, the packing ratio is the ratio of the bulk density of the negative electrode mixture layer to the true density of the negative electrode mixture layer. The true density of the negative electrode mixture layer was calculated using the mass ratio and true specific gravity of the graphite, zinc, and binder that make up the negative electrode mixture layer. The true specific gravity of the binder was 1.8 g / cm. 3 It was.

[0131] [Evaluation of packing density of negative electrode mixture layer] Next, the packing density of the negative electrode mixture layer was measured for negative electrodes b1 to b4. The packing density of the negative electrode mixture layer was calculated by dividing the volume of the negative electrode mixture layer from the mass of the negative electrode mixture layer. The results are shown in Table 2.

[0132] [Table 2]

[0133] 3. Evaluation of charge / discharge characteristics 1 (1) Evaluation of all-solid-state batteries [Battery construction] All-solid-state batteries A1 to A5 each having one of the negative electrodes a1 to a5 as a working electrode and a lithium-indium alloy layer as a counter electrode were fabricated by the following method.

[0134] First, 80 mg of the solid electrolyte was weighed and placed in an insulating cylinder. The cross-sectional area of ​​the inner diameter of the insulating cylinder was 0.7 cm. 2The solid electrolyte in the insulating cylinder was pressure-molded at a pressure of 50 MPa. Next, a negative electrode was punched out to have the same size as the inner diameter of the insulating cylinder. The negative electrode was placed on one surface of the solid electrolyte so that the negative electrode mixture layer of this negative electrode was in contact with the solid electrolyte. Next, the negative electrode and solid electrolyte were pressure-molded at a pressure of 600 MPa to produce a laminate consisting of a negative electrode and a solid electrolyte layer. Next, metallic indium, metallic lithium, and metallic indium were placed in this order on the solid electrolyte layer of the laminate. The thickness of the metallic indium was 200 μm. The area of ​​the main surface of the metallic indium was 0.66 cm 2 The thickness of the metallic lithium was 300 μm. The area of ​​the main surface of the metallic lithium was 0.58 cm 2 This resulted in the production of a three-layer laminate consisting of a negative electrode, a solid electrolyte layer, and an indium-lithium-indium layer.

[0135] Next, both ends of the three-layer stack were clamped with stainless steel pins. A 150 MPa pressure was applied to the stack using bolts. The pins and bolts functioned as restraining members. This resulted in all-solid-state batteries A1 to A5, each having one of the negative electrodes a1 to a5 as the working electrode and a lithium-indium alloy layer as the counter electrode.

[0136] The theoretical capacities of the negative electrodes a1 to a5 included in the batteries A1 to A5 are shown in Table 3. The theoretical capacity of the negative electrode means the capacity per unit area of ​​the negative electrode. The theoretical capacity of the negative electrode can be calculated from the mass of graphite and zinc in the negative electrode mixture layer, the theoretical capacity density per unit mass of graphite, and the theoretical capacity density per unit mass of zinc.

[0137] [Charge / discharge test] Batteries A1 to A5 were charged at a constant current of 0.05C rate (20-hour rate) at room temperature. The batteries were charged until the potential of the working electrode reached -0.615 V relative to the counter electrode. The batteries were then discharged until this potential reached 0.4 V. In this procedure, charging refers to the reduction of the working electrode, and discharging refers to the oxidation of the working electrode.

[0138] Table 3 shows the ratio of the initial charge capacity of the battery to the theoretical capacity of the negative electrode, the initial charge / discharge efficiency, and the discharge capacity density for batteries A1 to A5. In Table 3, the initial charge / discharge efficiency is the ratio of the initial discharge capacity to the initial charge capacity. The discharge capacity density means the initial discharge capacity per volume of the negative electrode mixture layer before the charge / discharge test. The discharge capacity densities in Table 3 are normalized by setting the discharge capacity density of battery A1, which does not contain zinc as a negative electrode active material, at 100.

[0139] Next, the above charge / discharge test was performed for an additional 29 cycles. In other words, the charge / discharge test was performed for a total of 30 cycles. The capacity retention rates of the battery at the 20th cycle and the 30th cycle are shown in Table 3. The capacity retention rate refers to the ratio of the discharge capacity of a battery after a specific number of charge / discharge cycles to the initial discharge capacity.

[0140] After the above charge-discharge tests, batteries A1 to A5 were charged at a constant current of 0.3 C rate (10 / 3 hour rate) at room temperature. The batteries were charged until the potential of the working electrode reached -0.615 V relative to the counter electrode. Table 3 shows the ratio of the charge capacity of the battery at 0.3 C rate to the charge capacity of the battery at 0.05 C rate at the 30th cycle of the charge-discharge test. In this specification, the "ratio of the charge capacity of the battery at 0.3 C rate to the charge capacity of the battery at 0.05 C rate at the 30th cycle of the charge-discharge test" is sometimes referred to as the "0.3 C / 0.05 C charge capacity ratio."

[0141] (2) Evaluation of three-electrode batteries without a solid electrolyte layer [Battery construction] Three-electrode batteries B1 to B4 were fabricated, each having one of the negative electrodes b1 to b4 as the working electrode and no solid electrolyte layer. Metallic lithium was used as the counter and reference electrodes in the three-electrode batteries. An electrolyte solution was used as a medium capable of conducting lithium ions.

[0142] FIG. 3 is a cross-sectional view showing the schematic configuration of a three-electrode battery. As shown in FIG. 3, the three-electrode battery 5000 included a working electrode 511, a counter electrode 512, a reference electrode 513, two separators 514, an electrolyte 515, and a container 516. The working electrode 511, the counter electrode 512, and the reference electrode 513 were immersed in the electrolyte 515. The reference electrode 513, the working electrode 511, and the counter electrode 512 were arranged in this order. One of the two separators 514 was positioned between the working electrode 511 and the counter electrode 512. The other separator 514 was positioned between the working electrode 511 and the reference electrode 513. The container 516 contained the working electrode 511, the counter electrode 512, the reference electrode 513, the two separators 514, and the electrolyte 515.

[0143] The working electrode 511 was fabricated by the following method. First, the negative electrode was cut into a size of 20 mm x 20 mm. A lead wire was attached to this negative electrode, and it was dried in a vacuum at 110°C for 2 hours. The lead wire was made of nickel. In this way, the working electrode 511 was obtained.

[0144] Metallic lithium was used for the counter electrode 512 and the reference electrode 513. The separator 514 was made of polyethylene. The electrolyte 515 contained a mixed solvent of ethylene carbonate and ethyl methyl carbonate and lithium hexafluorophosphate (LiPF6). In the mixed solvent, the volume ratio of ethylene carbonate to ethyl methyl carbonate was 3:7. The concentration of LiPF6 in the electrolyte 515 was 1 mol / L. The container 516 was made of aluminum laminate film.

[0145] Table 3 shows the theoretical capacities of the negative electrodes b1 to b4 provided in the batteries B1 to B4.

[0146] [Charge / discharge test] For cells B1 to B4, at room temperature, 0.25 mA / cm 2The battery was charged at a constant current of 0 V. The battery was charged until the potential of the working electrode reached 0 V, relative to the reference electrode. The battery was then discharged until this potential reached 1 V. This charge-discharge test was then repeated for another 29 cycles. In other words, the charge-discharge test was repeated for a total of 30 cycles.

[0147] For batteries B1 to B4, the ratio of the initial charge capacity of the battery to the theoretical capacity of the negative electrode, the initial charge / discharge efficiency, the discharge capacity density, the capacity retention rate of the battery at the 20th cycle, and the capacity retention rate of the battery at the 30th cycle are shown in Table 3. In Table 3, the discharge capacity density is a value normalized by setting the discharge capacity density of battery B1, which does not contain zinc in the negative electrode active material, at 100.

[0148] [Observation of the negative electrode after charge / discharge test] After the charge-discharge test, the batteries B1 to B4 were disassembled to observe the state of the negative electrode. In the batteries B1 to B4, detachment of the negative electrode mixture layer from the electrode plate was not observed.

[0149] [Table 3]

[0150] As shown in Table 3, the initial charge capacities of batteries A1 to A5 were almost the same as the theoretical capacities of negative electrodes a1 to a5, respectively. For batteries A1 to A5, the initial charge / discharge efficiency of the battery tended to decrease as the mass ratio of zinc contained in the negative electrode active material increased.

[0151] Assume that the charge-discharge efficiency of graphite in the negative electrode active material is 94%, and that of zinc is 60%. In this case, the calculated charge-discharge efficiencies of batteries A2 to A5 are 87%, 80%, 73%, and 60%, respectively, which are almost identical to the measured values ​​in Table 3. The assumed value of the graphite charge-discharge efficiency corresponds to the initial charge-discharge efficiency of battery A1. The assumed value of the zinc charge-discharge efficiency is calculated based on the change in the composition of lithium-absorbed zinc from LiZn to Li during discharge of a battery containing a negative electrode active material consisting only of zinc. 0.4 This corresponds to the charge-discharge efficiency when the material is converted to Zn.

[0152] From the above results, it can be seen that in batteries A2 to A5, the composition of the lithium-zinc alloy changes to Li 0.4 It is estimated that the reaction rate slowed down after reaching Zn. 0.4 It is estimated that the discharge ended when lithium equivalent to the composition of Zn was absorbed inside the zinc.

[0153] The initial charge-discharge efficiency of Batteries A2 to A5 tended to be lower than that of Battery A1, but the discharge capacity density of Batteries A2 to A5 was improved due to the smaller thickness of the negative electrode mixture layer.

[0154] The 0.3C / 0.05C charge capacity ratios of batteries A2 to A4 were more than three times larger than that of battery A5. In particular, the 0.3C / 0.05C charge capacity ratios of batteries A2 and A3 were superior to that of battery A1.

[0155] When the negative electrode active material expands during battery charging, pressure is applied to the battery element in the direction that compresses the battery element, tending to reduce the voids in the negative electrode mixture layer. In Batteries A2 to A3, the zinc particles expand during battery charging, which is thought to have improved the bonding state of the solid-solid interface within the negative electrode mixture layer. This is presumably why the 0.3C / 0.05C charge capacity ratio improved in Batteries A2 to A3.

[0156] In batteries A1 to A5, the capacity retention rate after 30 charge-discharge cycles was 100% or more. In particular, batteries A2 to A4, in which the mass ratio of zinc to the total mass of graphite and zinc in the negative electrode was 10% by mass or more and 60% by mass or less, exhibited high capacity retention rates. On the other hand, in batteries B1 to B4, the capacity retention rate after 30 charge-discharge cycles decreased from 95% to 63% as the mass ratio of zinc in the negative electrode active material increased. These results demonstrate that batteries containing a mixture of graphite and zinc with an appropriately adjusted mass ratio as the negative electrode active material can achieve better cycle characteristics by using a solid electrolyte as a lithium ion conducting medium than when using a liquid electrolyte.

[0157] For batteries B2 to B4, the capacity decreased from the first to the 20th cycle in the charge-discharge test, but remained the same from the 20th to the 30th cycle. For batteries B2 to B4, the discharge capacities of graphite and zinc in the first charge-discharge test can be estimated using the following equations (1) and (2). Based on the results of calculations using the following equations (1) and (2), the ratio of zinc discharge capacity to total discharge capacity was calculated. For batteries B2 to B4, the ratio of zinc discharge capacity to total discharge capacity was 6%, 17%, and 35%, respectively. This ratio was almost identical to the capacity loss rate after 20 cycles of the charge-discharge test. From these results, it is estimated that for batteries B2 to B4, zinc was no longer able to contribute to charge-discharge from the first to the 20th cycle in the charge-discharge test. In other words, it is estimated that for batteries B2 to B4, only graphite contributed to charge-discharge from the 20th to the 30th cycle in the charge-discharge test. Discharge capacity of graphite = theoretical capacity of graphite × charge / discharge efficiency of graphite Equation (1) Zinc discharge capacity = Zinc theoretical capacity × Zinc utilization rate × Zinc charge / discharge efficiency Equation (2)

[0158] In the above formula (1), the charge-discharge efficiency of graphite corresponds to the initial charge-discharge efficiency of battery B1. In formula (2), the zinc utilization rate is the ratio of the initial charge capacity of the battery to the theoretical capacity of the negative electrode. The charge-discharge efficiency of zinc is 60%. The charge-discharge efficiency of zinc is calculated by the ratio of the composition of zinc that absorbs lithium to LiZn during battery discharge. 0.4 The calculation is based on the assumption that the graphite is converted to Zn. Based on the results of batteries A1 and B1, the graphite utilization rate in equation (1) is assumed to be 100%.

[0159] In batteries containing zinc as the negative electrode active material, poor contact between the active materials or between the active material and the current collector due to the expansion and contraction of the active material may occur. This may lead to concerns about a decrease in the cycle performance of the battery. However, in batteries B2 to B4, if poor contact occurs, it is likely that poor contact occurs not only with the zinc but also with the graphite. Therefore, in batteries B2 to B4, poor contact due to repeated charge-discharge cycles is unlikely to reduce the contribution of zinc to the charge-discharge process alone. Furthermore, no detachment of the negative electrode mixture layer from the electrode plate was observed in the negative electrodes of batteries B2 to B4 after charge-discharge testing.

[0160] The following factors are thought to explain why the capacity retention rate decreased as the mass ratio of zinc in the negative electrode active material increased in Batteries B2 to B4: (1) Poor contact between the active materials or between the active material and the current collector due to the expansion and contraction of the negative electrode active material; and (2) High-resistance regions containing lithium oxide and other substances were formed on the surface or inside of the zinc due to a side reaction between zinc and the electrolyte. It is presumed that these high-resistance regions prevented zinc from contributing to charge and discharge in Batteries B2 to B4.

[0161] In contrast, since batteries A2 to A5 did not use an electrolyte, it is presumed that side reactions between zinc and the electrolyte hardly occurred. Furthermore, in batteries A2 to A5, a large confining pressure was applied to the battery element. Therefore, it is presumed that poor contact between the active materials and between the active material and the current collector due to the expansion and contraction of the negative electrode active material was sufficiently suppressed in batteries A2 to A5. Based on the above, it is presumed that batteries A2 to A5 had better cycle characteristics than batteries B2 to B4.

[0162] 4. Evaluation of charge / discharge characteristics 2 Using the negative electrode a1 and the negative electrode a3, all-solid-state secondary batteries C1 to C4 and D1 to D3 were produced by the following method.

[0163] (1) Preparation of the positive electrode First, particles having a core made of Li(NiCoMn)O2 and a coating layer made of LiNbO3 were prepared as the positive electrode active material. The core of the particles was covered with the coating layer. The median diameter of the particles was 5 μm. The median diameter of the particles was measured using a laser diffraction particle size distribution analyzer (Shimadzu Corporation, SALD-2000).

[0164] Next, the solid electrolyte was added to the positive electrode active material so that the mass ratio of the positive electrode active material to the solid electrolyte was 85:15. Next, a binder and a dispersion medium were further added to the resulting mixture, and they were kneaded. Maleic anhydride-modified hydrogenated SEBS was used as the binder. This resulted in a positive electrode mixture slurry. In the positive electrode mixture slurry, the ratio of the total mass of the positive electrode active material and the solid electrolyte to the mass of the binder was 98:2.

[0165] Next, this positive electrode mixture slurry was applied onto a positive electrode current collector. Aluminum foil with a thickness of 15 μm was used as the positive electrode current collector. The resulting coating film was dried at 100°C to obtain a positive electrode. The positive electrode had a positive electrode current collector and a positive electrode mixture layer formed from the positive electrode mixture slurry. Specifically, two types of positive electrodes c1 and c2 were fabricated using the above procedure. The thicknesses of the positive electrode mixture layers of the positive electrodes c1 and c2 were different from each other.

[0166] (2) Preparation of solid electrolyte layer First, a binder and a dispersion medium were added to the solid electrolyte, and the mixture was kneaded. Maleic anhydride-modified hydrogenated SEBS was used as the binder. This resulted in a solid electrolyte mixture slurry. In the solid electrolyte mixture slurry, the ratio of the mass of the solid electrolyte to the mass of the binder was 100:2.

[0167] Next, this solid electrolyte mixture slurry was applied onto the negative electrode a1 or a3, and the resulting coating film was dried at 100°C to obtain a laminate t1 of the negative electrode a1 and the solid electrolyte layer, and a laminate t2 of the negative electrode a3 and the solid electrolyte layer.

[0168] (3) Battery construction First, cathode c1 or cathode c2 was stacked with laminate t1 or laminate t2 so that the cathode mixture layer of the cathode was in contact with the solid electrolyte layer. Next, the stack was pressed at a pressure of 600 MPa to obtain a three-layer laminate including a cathode, anode, and solid electrolyte layer. Specifically, laminate t3 was obtained, including cathode c1, anode a1, and solid electrolyte layer, and laminate t4 was obtained, including cathode c2, anode a3, and solid electrolyte layer. In the stacks, the solid electrolyte layer was located between the cathode and anode.

[0169] Next, a battery C1 having the same structure as the battery 2100 in FIG. 2 was fabricated using the laminate t3. In the battery C1, the container was made of an aluminum laminate film. The lead wire connected to the positive electrode was made of aluminum. The lead wire connected to the negative electrode was made of nickel. The areas of the main surfaces of the positive and negative electrodes were 2.3 cm2. 2 In the battery C1, no restraining pressure was applied to the laminate t3.

[0170] In battery C1, the thickness of the positive electrode mixture layer was about 80 μm. The capacity per unit area of ​​the positive electrode was 4.3 mAh / cm 2 The thickness of the negative electrode mixture layer was approximately 113 μm. The theoretical capacity per unit area of ​​the negative electrode was 1.2 times the capacity per unit area of ​​the positive electrode. The thickness of the solid electrolyte layer was approximately 50 μm.

[0171] Next, a battery C4 was produced from the battery C2 by the same method as the battery C1, except that the laminate t3 was subjected to the confinement pressure shown in Table 4. Furthermore, a battery D3 was produced from the battery D1 by the same method as the battery C1, except that the laminate t4 was used instead of the laminate t3 and the confinement pressure shown in Table 4 was applied to the laminate t4.

[0172] In batteries D1 to D3, the thickness of the positive electrode mixture layer was approximately 94 μm. The capacity per unit area of ​​the positive electrode was 5.2 mAh / cm 2The thickness of the negative electrode mixture layer was approximately 87 μm. The theoretical capacity per unit area of ​​the negative electrode was 1.2 times the capacity per unit area of ​​the positive electrode. The thickness of the solid electrolyte layer was approximately 50 μm.

[0173] The capacities per unit area of ​​the positive and negative electrodes of batteries D1 to D3 are different from those of batteries C1 to C4. However, as shown in Table 3, the initial charge-discharge efficiency of negative electrode a3 is lower than that of negative electrode a1. The discharge capacities of batteries D1 to D3 in the initial charge-discharge test are almost the same as those of batteries C1 to C4.

[0174] (4) Charge / discharge test First, charge / discharge test 1 was conducted on batteries C1 to C4 and batteries D1 to D3. In charge / discharge test 1, the batteries were charged at a constant current of 0.05C at room temperature. The batteries were charged until the battery voltage reached 4.2V. Next, the batteries were discharged until the voltage reached 2.5V.

[0175] Table 4 shows the discharge capacities at a 0.05C rate in the initial charge-discharge test 1 for batteries C1 to C4 and batteries D1 to D3. The discharge capacities at a 0.05C rate in Table 4 are normalized values, with the discharge capacity of battery C1, which contains only graphite as the negative electrode active material and to which no restraining pressure is applied, set at 100.

[0176] Next, the above-mentioned charge / discharge test 1 was performed for an additional four cycles. In other words, charge / discharge test 1 was performed for a total of five cycles. Next, charge / discharge test 2 was performed on the battery. In charge / discharge test 2, the battery was charged at a constant current of 0.3 C rate. The battery was charged until the battery voltage reached 4.2 V. Furthermore, while the battery voltage was maintained at 4.2 V, the battery was charged until the current value reached a value of 0.05 C rate. Next, the battery was discharged at a constant current of 0.3 C rate. The battery was discharged until the battery voltage reached 2.5 V. Charge / discharge test 2 was performed for 195 cycles. In other words, charge / discharge tests 1 and 2 were performed for the battery for a total of 200 cycles.

[0177] Table 4 shows the discharge capacities at a 0.3C rate in the initial charge / discharge test 2 for batteries C1 to C4 and batteries D1 to D3. In Table 4, the discharge capacity refers to the capacity per mass of the positive electrode active material in the battery. The discharge capacities at a 0.3C rate in Table 4 are normalized by setting the discharge capacity at a 0.05C rate of battery C1 as 100. Table 4 also shows the ratio of the discharge capacity at a 0.3C rate in the initial charge / discharge test 2 to the discharge capacity at a 0.05C rate in the initial charge / discharge test 1. In this specification, the "ratio of the discharge capacity at a 0.3C rate in the initial charge / discharge test 2 to the discharge capacity at a 0.05C rate in the initial charge / discharge test 1" may be referred to as the "0.3C / 0.05C discharge capacity ratio."

[0178] Furthermore, Table 4 shows the capacity retention rate, which is the ratio of the discharge capacity at a 0.3C rate in the 195th cycle of Charge / Discharge Test 2 to the discharge capacity at a 0.3C rate in the initial Charge / Discharge Test 2. Note that the discharge capacity of Battery C1 significantly decreased with repeated charge / discharge cycles. Therefore, the charge / discharge tests for Battery C1 were terminated before a total of 200 cycles of Charge / Discharge Tests 1 and 2 were performed. Table 4 also shows the capacity retention rate of Battery C1 after a total of 50 cycles of Charge / Discharge Tests 1 and 2. That is, in Table 4, the capacity retention rate of Battery C1 means the ratio of the discharge capacity at a 0.3C rate in the 45th cycle of Charge / Discharge Test 2 to the discharge capacity at a 0.3C rate in the initial Charge / Discharge Test 2.

[0179] [Table 4]

[0180] As can be seen from Table 4, batteries D1 to D3, which had negative electrodes a3 in which the ratio of the mass of zinc to the total mass of graphite and zinc was 10% by mass or more and 60% by mass or less, exhibited superior capacity retention rates compared to batteries C1 to C4. In particular, the discharge capacities at a 0.3C rate of batteries D2 and D3 exceeded those of batteries C3 and C4, respectively. Note that the confining pressure applied to batteries D2 and D3 was the same as that of batteries C3 and C4, respectively. [Industrial Applicability]

[0181] The battery of the present disclosure can be used, for example, as an all-solid-state secondary battery.

Claims

1. A positive electrode and a negative electrode comprising graphite and zinc; a solid electrolyte layer located between the positive electrode and the negative electrode; a laminate including the positive electrode, the negative electrode, and the solid electrolyte layer; a restraining member that restrains the stack; Equipped with In the negative electrode, a ratio of the mass of zinc to the total value of the mass of graphite and the mass of zinc is 10% by mass or more and 60% by mass or less, The restraining pressure applied to the laminate by the restraining member is 10 MPa or more and 200 MPa or less. battery.

2. The ratio is 20% by mass or more and 40% by mass or less, The battery of claim 1 .

3. The confining pressure is 10 MPa or more and 50 MPa or less, The battery according to claim 1 or 2.

4. The confining pressure is 30 MPa or more and 50 MPa or less, The battery according to any one of claims 1 to 3.

5. The negative electrode includes graphite particles and zinc particles. The battery of any one of claims 1 to 4.

6. the negative electrode has a negative electrode mixture layer containing graphite and zinc, and a negative electrode current collector in contact with the negative electrode mixture layer, In the negative electrode mixture layer, a ratio of the mass of zinc to the total value of the mass of graphite and the mass of zinc is 10 mass% or more and 60 mass% or less. The battery of any one of claims 1 to 5.

7. The negative electrode further contains a solid electrolyte having lithium ion conductivity. The battery of any one of claims 1 to 6.

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