Battery

Abstract

A battery 10 according to the present disclosure comprises: a positive electrode 21 that has a first surface 21p and a second surface 21q; a negative electrode 23; a solid electrolyte layer 25 that is disposed between the positive electrode 21 and the negative electrode 23 so as to be in contact with the first surface 21p of the positive electrode 21; and a collector layer 27 that is disposed on the positive electrode 21 so as to be in contact with the second surface 21q, and that contains a conductive additive and an inorganic solid material that does not have the ability to occlude and release metal ions.

Description

battery

[0001] This disclosure relates to batteries.

[0002] Recently, batteries using solid electrolytes have been attracting attention.

[0003] Patent Document 1 describes a flat-type all-solid-state battery including a laminate in which a positive electrode, a solid electrolyte layer, and a negative electrode are stacked. The laminate is housed in a coin-shaped battery container. A flexible conductive porous member made of a molded graphite body is placed between the laminate and the battery container.

[0004] International Publication No. 2020 / 066323

[0005] This disclosure provides a technique for reducing electrical resistance between the positive electrode and the battery container.

[0006] This disclosure provides a battery comprising: a positive electrode having a first surface and a second surface; a negative electrode; a solid electrolyte layer disposed between the positive electrode and the negative electrode so as to be in contact with the first surface of the positive electrode; and a current collector layer disposed on the positive electrode so as to be in contact with the second surface, comprising an inorganic solid material that does not have the ability to intercept and release metal ions and a conductive additive.

[0007] According to this disclosure, the electrical resistance between the positive electrode and the battery container can be reduced.

[0008] Figure 1 is a cross-sectional view showing a schematic configuration of a battery according to one embodiment of the present disclosure. Figure 2 is a cross-sectional view showing a schematic configuration of a modified battery.

[0009] (Knowledge forming the basis of this disclosure) Batteries using solid electrolytes have superior heat resistance compared to conventional batteries using non-aqueous electrolytes, and are therefore intended for use not only at room temperature but also at high temperatures. The solid electrolyte contained in the positive electrode may decompose when used in environments hotter than room temperature. One way to suppress the decomposition of the solid electrolyte is to reduce the content of the conductive additive in the positive electrode as much as possible. By reducing the content of the conductive additive in the positive electrode as much as possible, the surface area of ​​the contact interface between the solid electrolyte and the conductive additive in the positive electrode decreases. This suppresses the decomposition of the solid electrolyte in the positive electrode and further improves the heat resistance of batteries using solid electrolytes.

[0010] However, reducing the content of the conductive additive in the positive electrode lowers the electron conductivity in the in-plane direction of the positive electrode, increasing the electrical resistance between the positive electrode and the battery container. To reduce electrical resistance, it is conceivable to place a conductive porous member between the positive electrode and the battery container, as described in Patent Document 1. However, according to the inventors' studies, the effect of the conductive porous member in reducing electrical resistance is limited, and there is room for improvement in the prior art.

[0011] The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0012] (Embodiment) Figure 1 is a cross-sectional view showing a schematic configuration of a battery according to one embodiment of the present disclosure. The battery 10 comprises a laminate 12 and a battery container 14. The laminate 12 is housed in the battery container 14. The laminate 12 is the main body of the battery 10 and includes a positive electrode 21, a negative electrode 23, a solid electrolyte layer 25, and a current collector layer 27. Inside the battery container 14, the current collector layer 27, the positive electrode 21, the solid electrolyte layer 25, and the negative electrode 23 are arranged in this order. The positive electrode 21 has a first surface 21p and a second surface 21q. The solid electrolyte layer 25 is arranged between the positive electrode 21 and the negative electrode 23 so as to be in contact with the first surface 21p of the positive electrode 21. The current collector layer 27 is arranged on the positive electrode 21 so as to be in contact with the second surface 21q of the positive electrode 21. The current collector layer 27 is a layer comprising an inorganic solid material and a conductive additive. Inorganic solid materials are materials that do not have the ability to intercept and release metal ions. The metal ions are charge carriers in the battery 10, and are typically lithium ions or sodium ions.

[0013] In this specification, "inorganic solid material that does not have the ability to absorb and release metal ions" means that the amount of metal ions absorbed into a unit mass of inorganic solid material, and the amount of metal ions released from a unit mass of inorganic solid material, are 1 / 2 or less, preferably 1 / 10 or less, of the amount of metal ions absorbed and released from a unit mass of positive electrode active material contained in the positive electrode 21, on a molar basis.

[0014] Because an inorganic solid material is included in the current collector layer 27, the contact between the current collector layer 27 and the positive electrode 21 is improved. Here, if a compound with relatively high hardness is used as the inorganic solid material, the current collector layer 27 bites into the positive electrode 21, thereby improving the contact between the current collector layer 27 and the positive electrode 21. If a compound with relatively low hardness is used as the inorganic solid material, the positive electrode 21 bites into the current collector layer 27, thereby improving the contact between the current collector layer 27 and the positive electrode 21. Furthermore, if a solid electrolyte is used as the inorganic solid material, heating and / or pressurizing after laminating each layer causes the current collector layer 27 and the positive electrode 21 to become one, improving the contact between the current collector layer 27 and the positive electrode 21. Therefore, the structure of the battery 10 of this embodiment, which has a current collector layer 27 with improved contact with the positive electrode 21, is advantageous in reducing electrical resistance compared to conventional batteries in which a carbon sheet or the like is placed on the positive electrode.

[0015] In this embodiment, the battery 10 is a coin cell. The battery container 14 is a coin-shaped container. The battery container 14 includes an outer casing 14a, a sealing casing 14b, and a gasket 16.

[0016] In coin cell batteries, the constraining pressure exerted by the battery container on the laminate is not necessarily high. Therefore, the laminate does not make surface contact with the inner surface of the battery container; instead, it often contacts the inner surface of the battery container at a line or point. Furthermore, the inner surface of the coin cell battery container is not perfectly flat but may be slightly curved. In this case, the laminate and the battery container tend to contact at a line or point. The reasons why the laminate and the battery container contact at a line or point are explained in detail below.

[0017] The sealing can 14b is fitted into the opening of the outer can 14a via a gasket 16. The end 14c of the outer can 14a is crimped inward toward the center of the battery container 14. The gasket 16 contacts the sealing can 14b, sealing the opening of the outer can 14a and creating an airtight seal inside the battery 10. When the end 14c of the outer can 14a is crimped inward, force is applied to the outer can 14a and the sealing can 14b, causing them to bend. When the outer can 14a and the sealing can 14b bend, the proportion of the surface of the pellet-shaped laminate 12 that is in surface contact with the battery container 14 decreases. Consequently, the electronic conductivity between the laminate 12 and the battery container 14 decreases.

[0018] Regarding the positive electrode, as explained earlier, it is desirable to use a small amount of conductive additive in order to suppress the decomposition (oxidative decomposition) of the solid electrolyte. However, reducing the amount of conductive additive in the positive electrode increases the electrical resistance between the positive electrode and the battery container. Since this problem tends to become apparent in coin cells, the technology disclosed herein is particularly suitable for coin cells.

[0019] Regarding the negative electrode, even if a solid electrolyte is included in the negative electrode, the solid electrolyte is not easily decomposed. Therefore, there is no need to reduce the content of the conductive additive in the negative electrode as much as possible, and the negative electrode contains a sufficient amount of conductive additive. When a sufficient amount of conductive additive is included, the electrical resistance between the negative electrode and the battery container is low, even if the negative electrode is in contact with the inner surface of the battery container in a line or at a point.

[0020] (Positive electrode) In this embodiment, the positive electrode 21 is a positive electrode composite layer containing a positive electrode active material, a solid electrolyte, and a conductive additive. The outer casing 14a and the current collector layer 27 play the role of a positive electrode current collector.

[0021] The positive electrode active material may be a material that has the ability to intercept and release lithium ions. Examples of positive electrode active materials include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate. One or more combinations of these positive electrode active materials may be used.

[0022] Conductive additives are used to reduce the resistance of the positive electrode 21. Examples of conductive additives include carbon materials. Examples of carbon materials include carbon black, graphite, fibrous carbon materials, graphene, fullerene, and graphite oxide. Examples of carbon black include acetylene black and Ketjenblack. Examples of fibrous carbon materials include carbon nanotubes, carbon nanofibers, and vapor-processed carbon fibers. One or more combinations of these conductive additives may be used.

[0023] The content C1 of the conductive additive in the positive electrode 21 is, for example, 0.1% by mass or more and 5% by mass or less, and preferably 0.5% by mass or more and 3% by mass or less. With such a configuration, the decomposition of the solid electrolyte due to contact between the conductive additive and the solid electrolyte can be suppressed.

[0024] The ratio of the mass of the conductive additive contained in the positive electrode 21 to the total mass of the conductive additive and the solid electrolyte contained in the positive electrode 21 is preferably 0.2% to 10%, and more preferably 0.8% to 8%, in percentage terms. With such a configuration, the decomposition of the solid electrolyte due to contact between the conductive additive and the solid electrolyte can be suppressed.

[0025] Solid electrolytes are materials that have lithium ion conductivity. Examples of solid electrolytes include halide solid electrolytes, sulfide solid electrolytes, polymer solid electrolytes, and complex hydride solid electrolytes.

[0026] Examples of 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 Examples include Li3PS4, Li7PS6, materials in which sulfur atoms in Li3PS4 are replaced with halogen atoms, and materials in which sulfur atoms in Li7PS6 are replaced with halogen atoms. Among these, sulfide solid electrolytes having an argyrodite crystal structure are recommended because they have excellent ionic conductivity and heat resistance.

[0027] Examples of polymer solid electrolytes include compounds of polymer compounds having an ethylene oxide structure and lithium salts. For example, at least one lithium salt selected from the group consisting of LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3 can be used.

[0028] Examples of complex hydride solid electrolytes include LiBH4-LiI and LiBH4-P2S5.

[0029] The halide solid electrolyte may be a material represented by the following formula (1).

[0030] Li α M β X γ ...Formula (1)

[0031] In equation (1), α, β, and γ are each independently greater than 0, M is at least one selected from the group consisting of metallic elements other than Li and metalloid elements, and X is at least one selected from the group consisting of F, Cl, Br, and I.

[0032] "Semimetal elements" include B, Si, Ge, As, Sb, and Te.

[0033] "Metal elements" include all elements contained in Groups 1 to 12 of the periodic table excluding hydrogen, and all elements contained in Groups 13 to 16 of the periodic table excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. That is, metal elements are a group of elements that can become cations when forming inorganic compounds with halogen elements.

[0034] One or more combinations selected from the above solid electrolytes can be used as the solid electrolyte of the positive electrode 21.

[0035] (Negative electrode) In this embodiment, the negative electrode 23 is a negative electrode composite layer containing a negative electrode active material, a solid electrolyte, and a conductive assistant. The sealed can 14b serves as the negative electrode current collector.

[0036] The negative electrode active material can be a material having the ability to occlude and release lithium ions. Examples of the negative electrode active material include carbon materials, materials capable of forming alloys with lithium, lithium titanate, lithium vanadate, etc. Examples of carbon materials include graphite. Examples of materials capable of forming alloys with lithium include silicon, silicon-containing oxides, tin, zinc alloys, bismuth, germanium, NiBi alloys, etc. Examples of lithium titanate include Li4Ti5O 12 etc. One or more combinations selected from these negative electrode active materials can be used.

[0037] As the solid electrolyte contained in the negative electrode 23, at least one selected from the examples of the solid electrolyte contained in the positive electrode 21 can be used. As the conductive assistant contained in the negative electrode 23, at least one selected from the examples of the conductive assistant contained in the positive electrode 21 can be used.

[0038] (Solid electrolyte layer) The solid electrolyte layer 25 is a layer containing a solid electrolyte and may be composed of a solid electrolyte. As the solid electrolyte contained in the solid electrolyte layer 25, at least one selected from the examples of the solid electrolyte contained in the positive electrode 21 can be used.

[0039] (Current collector layer) As the conductive assistant contained in the current collector layer 27, at least one kind selected from the examples of the conductive assistant contained in the positive electrode 21 can be used. The fibrous carbon material is particularly recommended because it can impart a high electrical conductivity to the current collector layer 27 even in a small amount.

[0040] Since the current collector layer 27 does not function as a positive electrode, it is possible to make the content rate of the conductive assistant contained in the current collector layer 27 different from the content rate of the conductive assistant contained in the positive electrode 21. It is desirable that the content rate C2 of the conductive assistant in the current collector layer 27 is larger than the content rate C1 of the conductive assistant in the positive electrode 21 on a mass basis. According to such a configuration, the electrical conductivity of the current collector layer 27 is increased, and the electrical resistance between the positive electrode 21 and the battery container 14 can be further reduced. In one example, the content rate C2 of the conductive assistant in the current collector layer 27 is 10% by mass or more and 30% by mass or less.

[0041] The content rate C2 of the conductive assistant in the current collector layer 27 is larger than the ratio C11 of the mass of the conductive assistant contained in the positive electrode 21 to the total mass of the conductive assistant contained in the positive electrode 21 and the solid electrolyte contained in the positive electrode 21 on a mass basis. According to such a configuration, the electrical conductivity of the current collector layer 27 is increased, and the electrical resistance between the positive electrode 21 and the battery container 14 can be further reduced. The ratio C11 of the mass of the conductive assistant contained in the positive electrode 21 to the total mass of the conductive assistant contained in the positive electrode 21 and the solid electrolyte contained in the positive electrode 21 is, for example, 0.2% or more and 10% or less.

[0042] In the current collector layer 27, the inorganic solid material plays a role of improving the contact property between the positive electrode 21 and the current collector layer 27. The inorganic solid material is a material that does not have the ability to occlude and release metal ions. Not having the ability to occlude and release metal ions means that the inorganic solid material is not an active material of the battery 10.

[0043] The electrical conductivity of the inorganic solid material may be 10 -6 S / m or less at room temperature. That is, the role of the inorganic solid material is different from the role of the conductive assistant. The inorganic solid material may be an insulating material.

[0044] Examples of inorganic solid materials include solid electrolytes, metal oxides, metal carbides, and metal nitrides. Examples of metal oxides include aluminum oxide, magnesium oxide, and zirconium oxide. Examples of metal carbides include tungsten carbide and titanium carbide. Examples of metal nitrides include aluminum nitride and titanium nitride. Among these, solid electrolytes are suitable as inorganic solid materials. Solid electrolytes can be materials that conduct lithium ions. If the current collector layer 27 also contains a solid electrolyte in the positive electrode 21, the affinity between the current collector layer 27 and the positive electrode 21 can be improved by heating and / or pressurizing, which is a process that integrates the current collector layer 27 and the positive electrode 21.

[0045] Furthermore, it is desirable that the thermal expansion coefficient of the solid electrolyte contained in the current collector layer 27 is equivalent to that of the solid electrolyte contained in the positive electrode 21. The ratio of the thermal expansion coefficient of the solid electrolyte contained in the current collector layer 27 to the thermal expansion coefficient of the solid electrolyte contained in the positive electrode 21 is, for example, 0.8 to 1.2, and preferably 0.9 to 1.1. With such a configuration, even if the ambient temperature of the battery 10 fluctuates greatly, the current collector layer 27 is less likely to peel off from the positive electrode 21.

[0046] In this specification, "thermal expansion coefficient" means the linear expansion coefficient (unit: 1 / °C) measured when the temperature is raised from room temperature (25°C) to 100°C.

[0047] The thermal expansion coefficient of a material can be measured by X-ray diffraction. Microscopic thermal expansion characteristics can be detected by measuring the temperature change in the lattice spacing of a crystal lattice as a change in the X-ray diffraction angle. The relationship between the X-ray diffraction angle and the lattice plane spacing is given by Bragg's law, as shown in equation (1) below. In equation (1), d represents the lattice plane spacing, and θ represents the X-ray diffraction angle relative to the lattice plane. The relationship between the rate of change of the plane spacing (Δd / d) and the change in the diffraction angle Δθ is given by equation (2) below. d0 and θ0 represent the lattice plane spacing and the X-ray diffraction angle before thermal expansion, respectively.

[0048] 2dsinθ=nλ (1) Δd / d0=-cotθ0・Δθ (2)

[0049] The thermal expansion coefficient of the current collector layer 27 can be calculated from the thermal expansion coefficients of the materials contained in the current collector layer 27 and the volume ratios of each material contained in the current collector layer 27. Similarly, the thermal expansion coefficient of the positive electrode 21 can be calculated from the thermal expansion coefficients of the materials contained in the positive electrode 21 and the volume ratios of each material contained in the positive electrode 21.

[0050] In this specification, the lithium ion conductivity of the material at 25°C is 10 -6 When the value is S / cm or higher, the material is considered to have lithium ion conductivity.

[0051] As the solid electrolyte, a sulfide solid electrolyte is suitable. Since sulfide solid electrolytes are relatively soft materials, they can easily deform and bite into the positive electrode 21. This strengthens the bond between the current collector layer 27 and the positive electrode 21. Among these, a sulfide solid electrolyte having an argyrodite-type crystal structure is suitable for the current collector layer 27 from the viewpoint of heat resistance.

[0052] Preferably, the inorganic solid material contained in the current collector layer 27 contains a solid electrolyte with the same composition as the solid electrolyte contained in the positive electrode 21. With such a configuration, the affinity between the current collector layer 27 and the positive electrode 21 is increased, and the bond between the current collector layer 27 and the positive electrode 21 can be strengthened. Preferably, both the positive electrode 21 and the current collector layer 27 contain a sulfide solid electrolyte. It is even more preferable that the sulfide solid electrolyte has an argyrodite-type crystal structure.

[0053] It is desirable that the current collector layer 27 does not contain organic materials, except for components that are inevitably mixed in. If the current collector layer 27 does not contain organic materials, the problem of thermal decomposition of organic materials does not exist, and the battery 10 can be suitably used in high-temperature environments.

[0054] For the same reason, it is desirable that the positive electrode 21, the solid electrolyte layer 25, and the negative electrode 23 also do not contain organic materials.

[0055] In this embodiment, the size of the current collector layer 27 in plan view is equal to the size of the positive electrode 21. For example, when the laminate 12 is disc-shaped, the diameter of the current collector layer 27 is equal to the diameter of the positive electrode 21. However, it is not essential that the current collector layer 27 covers the entire surface of the second surface 21q of the positive electrode 21. When the battery 10 is viewed in plan view, it is desirable that the current collector layer 27 has an area of ​​30% or more of the area of ​​the second surface 21q of the positive electrode 21, and more preferably 50% or more. It is most desirable that the current collector layer 27 covers the entire surface of the second surface 21q of the positive electrode 21. With such a configuration, it is easy to obtain the effect of reducing the electrical resistance between the positive electrode 21 and the battery container 14.

[0056] The average thickness of the current collector layer 27 is, for example, in the range of 10 μm to 200 μm. By appropriately adjusting the average thickness of the current collector layer 27, it is possible to reduce the electrical resistance between the positive electrode 21 and the battery container 14 while suppressing a decrease in the capacity of the battery 10. The thickness of the current collector layer 27 can be measured by observing the cross-section of the laminate 12. The average value of the measurements at any multiple points (for example, five points) can be considered as the "average thickness".

[0057] Considering that the battery 10 will be used in a high-temperature environment, it is desirable that the difference in thermal expansion coefficients between the current collector layer 27 and the positive electrode 21 be small. The ratio of the thermal expansion coefficient of the positive electrode 21 to the thermal expansion coefficient of the current collector layer 27 is, for example, in the range of 0.5 to 2, preferably in the range of 0.75 to 1.5, and more preferably in the range of 0.9 to 1.1. With such a configuration, even if the ambient temperature of the battery 10 fluctuates greatly, the current collector layer 27 is less likely to peel off from the positive electrode 21.

[0058] In this embodiment, the current collector layer 27 and the positive electrode 21 are integrated. More specifically, the current collector layer 27, the positive electrode 21, the solid electrolyte layer 25, and the negative electrode 23 are integrated. In this specification, if multiple parts cannot be separated nondestructively, they are considered to be integrated. By integrating the current collector layer 27 and the positive electrode 21, the electrical resistance between the current collector layer 27 and the positive electrode 21 can be further reduced.

[0059] For example, the conductive porous member (specifically a flexible graphite sheet) described in Patent Document 1 is merely placed between the battery container and the positive electrode, and the conductive porous member can be separated from the positive electrode.

[0060] One method for integrating the current collector layer 27 and the positive electrode 21 is hot pressing. For example, a layer of material for forming the positive electrode 21 (positive electrode composite material) and a layer of material for forming the current collector layer 27 are stacked in a predetermined container. Then, these layers are heated and pressurized. This results in a current collector layer 27 and a positive electrode 21 that are integrated with each other.

[0061] The heating temperature in a hot press is, for example, between 100°C and 200°C. The applied pressure is, for example, between 50 MPa and 300 MPa.

[0062] Since the material used to form the current collector layer 27 includes an inorganic solid material, hot pressing allows the particles of the inorganic solid material to penetrate the positive electrode 21. This strengthens the bond between the current collector layer 27 and the positive electrode 21. In particular, if the inorganic solid material of the current collector layer 27 is the same material as the solid electrolyte contained in the positive electrode 21, the bond between the current collector layer 27 and the positive electrode 21 is further strengthened.

[0063] The current collector layer 27, positive electrode 21, solid electrolyte layer 25, and negative electrode 23 can be integrated using the same method. Specifically, a layer of material for forming the negative electrode 23 (negative electrode composite), a layer of material for forming the solid electrolyte layer 25, a layer of material for forming the positive electrode 21 (positive electrode composite), and a layer of material for forming the current collector layer 27 are arranged in this order in a predetermined container. These layers are then heated and pressurized. This results in a laminate 12 in which each layer is integrated with the others.

[0064] (Modified Version) Figure 2 is a cross-sectional view showing the schematic configuration of a modified battery. Battery 10a further includes a carbon layer 29 disposed between the laminate 12 and the battery container 14. By arranging a carbon layer 29, which is more flexible than the current collector layer 27, between the current collector layer 27 and the battery container 14, the electrical resistance between the laminate 12 and the battery container 14 can be further reduced. Except for the carbon layer 29, battery 10a has the same configuration as battery 10 shown in Figure 1.

[0065] In detail, the battery 10a comprises a pair of carbon layers 29. On the positive electrode side, the carbon layer 29 is positioned between the battery container 14 and the laminate 12 so as to be in contact with the battery container 14 and the current collector layer 27, respectively. On the negative electrode side, the carbon layer 29 is positioned between the battery container 14 and the laminate 12 so as to be in contact with the battery container 14 and the negative electrode 23, respectively. The carbon layer 29 may be provided only on the positive electrode side. In this case, a reduction in battery capacity due to the carbon layer 29 can be avoided. When the carbon layer 29 is provided on both the positive and negative electrode sides, the electrical resistance between the laminate and the battery container can be further reduced.

[0066] A carbon sheet or the like can be used as the carbon layer 29.

[0067] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0068] (Technical 1) A battery comprising: a positive electrode having a first surface and a second surface; a negative electrode; a solid electrolyte layer disposed between the positive electrode and the negative electrode so as to be in contact with the first surface of the positive electrode; and a current collector layer disposed on the positive electrode so as to be in contact with the second surface, comprising an inorganic solid material that does not have the ability to intercept and release metal ions and a conductive additive.

[0069] According to this disclosure, the electrical resistance between the positive electrode and the battery container can be reduced.

[0070] (Technical 2) The battery according to Technical 1, wherein the positive electrode contains a conductive additive, and the content of the conductive additive in the current collector layer is greater by mass than the content of the conductive additive in the positive electrode. With such a configuration, the electrical conductivity of the current collector layer is increased, and the electrical resistance between the positive electrode and the battery container can be further reduced.

[0071] (Technical 3) The battery according to Technical 1 or 2, wherein the positive electrode contains a conductive additive and a solid electrolyte, and the content of the conductive additive in the current collector layer is greater by mass than the ratio of the mass of the conductive additive contained in the positive electrode to the total mass of the conductive additive and the solid electrolyte contained in the positive electrode. With such a configuration, the electrical conductivity of the current collector layer is increased, and the electrical resistance between the positive electrode and the battery container can be further reduced.

[0072] (Technical 4) The electrical conductivity of the inorganic solid material is 10 -6 A battery according to any one of the technical specifications 1 to 3, having a voltage of S / m or less. The inorganic solid material may be an insulating material.

[0073] (Technical 5) A battery according to any one of Technical 1 to 4, wherein the inorganic solid material includes a solid electrolyte. If the current collector layer of the positive electrode also contains a solid electrolyte, the affinity between the current collector layer and the positive electrode can be improved.

[0074] (Technical 6) The battery according to Technical 5, wherein the solid electrolyte includes a sulfide solid electrolyte. Since the sulfide solid electrolyte is a relatively soft material, the positive electrode easily penetrates the current collector layer. This strengthens the bond between the current collector layer and the positive electrode.

[0075] (Technical 7) The battery according to Technical 6, wherein the sulfide solid electrolyte has an argyrodite crystal structure. From the viewpoint of heat resistance, the sulfide solid electrolyte having an argyrodite crystal structure is suitable for the current collector layer.

[0076] (Technical 8) A battery according to any one of Technical 1 to 7, wherein the positive electrode contains a solid electrolyte, and the inorganic solid material contains a solid electrolyte having the same composition as the solid electrolyte contained in the positive electrode. With such a configuration, the affinity between the current collector layer and the positive electrode is increased, and the bond between the current collector layer and the positive electrode can be strengthened.

[0077] (Technical 9) The battery according to any one of Technical 1 to 8, wherein, when the battery is viewed from above, the current collector layer has an area of ​​30% or more of the area of ​​the second surface of the positive electrode. With such a configuration, the effect of reducing the electrical resistance between the positive electrode and the battery container is easily obtained.

[0078] (Technical 10) A battery according to any one of Technical 1 to 9, wherein the average thickness of the current collector layer is in the range of 10 μm or more and 200 μm or less. By appropriately adjusting the average thickness of the current collector layer, it is possible to reduce the electrical resistance between the positive electrode and the battery container while suppressing a decrease in the battery capacity.

[0079] (Technical 11) A battery according to any one of Technical 1 to 10, wherein the ratio of the thermal expansion coefficient of the positive electrode to the thermal expansion coefficient of the current collector layer is in the range of 0.5 or more and 2 or less. Considering that the battery will be used in a high-temperature environment, it is desirable that the difference in thermal expansion coefficients between the current collector layer and the positive electrode be small.

[0080] (Technical 12) A battery according to any one of Technical 1 to 11, wherein the inorganic solid material includes a solid electrolyte, the positive electrode includes a solid electrolyte, and the ratio of the thermal expansion coefficient of the solid electrolyte contained in the current collector layer to the thermal expansion coefficient of the solid electrolyte contained in the positive electrode is 0.8 or more and 1.2. With such a configuration, even if the ambient temperature of the battery fluctuates greatly, the current collector layer is less likely to peel off from the positive electrode.

[0081] (Technical 13) A battery according to any one of Technical 1 to 12, wherein the current collector layer and the positive electrode are integrated. By integrating the current collector layer and the positive electrode, the electrical resistance between the current collector layer and the positive electrode can be further reduced.

[0082] (Technical 14) The battery according to any one of Technical 1 to 13, further comprising a battery container housing a laminate including the current collector layer, the positive electrode, the solid electrolyte layer and the negative electrode, wherein the current collector layer is in contact with the inner surface of the battery container.

[0083] (Technical 15) A battery according to any one of Technical 1 to 14, further comprising a battery container housing a laminate including the current collector layer, the positive electrode, the solid electrolyte layer, and the negative electrode, and further comprising a carbon layer disposed between the laminate and the battery container. The carbon layer can further reduce the electrical resistance between the laminate and the battery container.

[0084] (Technical 16) The battery according to Technical 14 or 15, wherein the battery container is a coin-shaped container. The technology of the present disclosure is particularly suitable for coin batteries.

[0085] The following procedures for preparing the test cells were all performed under a dry argon atmosphere.

[0086] (Example 1) Under an argon atmosphere with a dew point of -60°C or lower, the raw material powders LiF, TiF4, and AlF3 were weighed in a molar ratio of LiF:TiF4:AlF3 = 2.7:0.3:0.7. These were crushed and mixed in an agate mortar to obtain a mixture. The mixture was then milled using φ5 mm zirconia balls and a planetary ball mill (Fritsch, P-7 type) for 12 hours at 500 rpm. As a result, Li 2.7 Ti 0.3 Al 0.7 A powdered solid electrolyte having the composition of F6 (hereinafter referred to as "LTAF") was obtained.

[0087] As the positive electrode active material, lithium cobalt oxide (LCO) powder (average particle size 5 μm) was prepared. The LTAF obtained above was attached to the surface of the LCO particles to form a coating layer. The coating layer was formed by compression shearing treatment using a particle compounding device (NOB-MINI, manufactured by Hosokawa Micron Corporation). Specifically, LCO and LTAF were mixed in a mass ratio of 100:13, and the mixture was treated under conditions of rotation speed: 6000 rpm and processing time: 50 min. This obtained a coated positive electrode active material. The target thickness of the coating layer was 40 nm.

[0088] A cathode composite was prepared by mixing a coated cathode active material, a sulfide solid electrolyte, and a conductive additive in an agate mortar. The volume ratio of the coated cathode active material to the sulfide solid electrolyte was coated cathode active material:sulfide solid electrolyte = 35:65. Argyrodite-type sulfide solid electrolyte (Li7PS6) was used as the sulfide solid electrolyte. Carbon nanofiber was used as the conductive additive. The ratio of the mass of the conductive additive to the total mass of the coated cathode active material and sulfide solid electrolyte was 3% by mass.

[0089] A current collector layer forming material was prepared by mixing a sulfide solid electrolyte and a conductive additive in a mass ratio of 6:1. The same sulfide solid electrolyte and conductive additive used in the positive electrode composite material were used.

[0090] Under a dry argon atmosphere, Li4Ti5O is used as the negative electrode active material. 12 A negative electrode composite was prepared by mixing a sulfide solid electrolyte and a conductive additive in an agate mortar (average particle size 2.5 μm). The same sulfide solid electrolyte and conductive additive used in the positive electrode composite were used. The volume ratio of negative electrode active material to sulfide solid electrolyte was negative electrode active material:solid electrolyte = 60:40. The ratio of the mass of the conductive additive to the total mass of the negative electrode active material and sulfide solid electrolyte was 1% by mass.

[0091] A disc-shaped molded body was fabricated by laminating a negative electrode composite, a sulfide solid electrolyte, a positive electrode composite, and a current collector layer forming material in this order. The same sulfide solid electrolyte as the positive electrode composite was used. The molded body was hot-pressed. This yielded the laminate of Example 1. The dimensions of the laminate were 9.4 mm in diameter and 1.5 mm in thickness. In the laminate, the thickness of the current collector layer was 100 μm.

[0092] A laminate was placed in an insulating container with an inner diameter of 9.4 mm. Stainless steel current collectors were placed above and below the laminate, and current collector leads were attached to the current collectors. A restraining jig was used to apply a restraining pressure of 10 MPa to the laminate. This obtained the test cell of Example 1.

[0093] (Comparative Example 1) A laminate of Comparative Example 1 was prepared by the same method as in Example 1, except that carbon nanofibers were deposited in layers on the positive electrode composite layer instead of the current collector layer containing a sulfide solid electrolyte and a conductive additive. The laminate of Comparative Example 1 was placed in an insulating container and a confinement pressure of 10 MPa was applied. This obtained a test cell of Comparative Example 1.

[0094] The carbon nanofiber deposition layer in Comparative Example 1 is a model of the conductive porous member described in Patent Document 1.

[0095] (Comparative Example 2) A laminate of Comparative Example 2 was prepared by the same method as in Example 1, except that a current collector layer containing a sulfide solid electrolyte and a conductive additive was not provided. The laminate of Comparative Example 2 was placed in an insulating container and a confinement pressure of 10 MPa was applied. This obtained a test cell of Comparative Example 2.

[0096] [Charge and Discharge Test] Charge and discharge tests were performed on the test cells of Example 1, Comparative Example 1, and Comparative Example 2 using the following method. First, constant current charging was performed at a current value of 0.05C until the voltage reached 2.75V. After a 60-minute pause, constant current discharging was performed at a current value of 0.05C until the voltage reached 0.9V. The C rate representing the current value is a value based on the theoretical capacity of lithium cobalt oxide.

[0097] Next, the test cell was charged with a constant current at a charge rate of 0.05C until the voltage reached 2.75V. Subsequently, constant voltage charging was performed at a constant voltage of 2.75V until the current value reached 0.01C. After a 60-minute pause, constant current discharge was performed at a current value of 0.05C until the voltage reached 0.9V. The measured value was recorded as "0.05C discharge capacity". Constant current and constant voltage charging was performed using the same method, and after a 60-minute pause, constant current discharge was performed with the current value changed to 0.1C, 0.5C, and 1C. The measured discharge capacities were recorded as "0.1C discharge capacity", "0.5C discharge capacity", and "1C discharge capacity", respectively. The results are shown in Table 1. The discharge capacity values ​​shown in Table 1 represent the values ​​when the 0.05C discharge capacity of Example 1 is used as the reference (=100).

[0098]

[0099] As shown in Table 1, the test cell of Example 1 exhibited a higher discharge capacity than the test cells of Comparative Examples 1 and 2 at all discharge rates. This indicates that the internal resistance of the test cell was reduced by the current collector layer.

[0100] Surprisingly, the discharge capacity of the test cell in Comparative Example 1 was lower than that of the test cell in Comparative Example 2. This trend was particularly pronounced at high discharge rates (0.5C and 1C). The laminate of the test cell in Comparative Example 1 had a carbon nanofiber deposition layer on top of the positive electrode composite layer. The laminate of the test cell in Comparative Example 2 had a structure similar to that of Example 1, but with the current collector layer removed. It is thought that the carbon nanofiber deposition layer actually worsened the electrical contact between the stainless steel current collector and the positive electrode composite layer.

[0101] The technology disclosed herein is useful, for example, in solid-state batteries.

Claims

1. A battery comprising: a positive electrode having a first surface and a second surface; a negative electrode; a solid electrolyte layer disposed between the positive electrode and the negative electrode so as to be in contact with the first surface of the positive electrode; and a current collector layer disposed on the positive electrode so as to be in contact with the second surface, comprising an inorganic solid material that does not have the ability to intercept and release metal ions and a conductive additive.

2. The battery according to claim 1, wherein the positive electrode contains a conductive additive, and the content of the conductive additive in the current collector layer is greater by mass than the content of the conductive additive in the positive electrode.

3. The battery according to claim 1, wherein the positive electrode contains a conductive additive and a solid electrolyte, and the content of the conductive additive in the current collector layer is greater by mass than the ratio of the mass of the conductive additive contained in the positive electrode to the total mass of the conductive additive and the solid electrolyte contained in the positive electrode.

4. The electrical conductivity of the inorganic solid material is 10 -6 The battery according to claim 1, wherein the S / m is less than or equal to S / m.

5. The battery according to claim 1, wherein the inorganic solid material includes a solid electrolyte.

6. The battery according to claim 5, wherein the solid electrolyte comprises a sulfide solid electrolyte.

7. The battery according to claim 6, wherein the sulfide solid electrolyte has an argyrodite-type crystal structure.

8. The battery according to claim 1, wherein the positive electrode includes a solid electrolyte, and the inorganic solid material includes a solid electrolyte having the same composition as the solid electrolyte contained in the positive electrode.

9. The battery according to claim 1, wherein, when the battery is viewed from above, the current collector layer has an area of ​​30% or more of the area of ​​the second surface of the positive electrode.

10. The battery according to claim 1, wherein the average thickness of the current collector layer is in the range of 10 μm or more and 200 μm or less.

11. The battery according to claim 1, wherein the ratio of the thermal expansion coefficient of the positive electrode to the thermal expansion coefficient of the current collector layer is in the range of 0.5 or more and 2 or less.

12. The battery according to claim 1, wherein the inorganic solid material includes a solid electrolyte, the positive electrode includes a solid electrolyte, and the ratio of the thermal expansion coefficient of the solid electrolyte contained in the current collector layer to the thermal expansion coefficient of the solid electrolyte contained in the positive electrode is 0.8 or more and 1.

2.

13. The battery according to claim 1, wherein the current collector layer and the positive electrode are integrated.

14. The battery according to claim 1, further comprising a battery container housing a laminate including the current collector layer, the positive electrode, the solid electrolyte layer, and the negative electrode, wherein the current collector layer is in contact with the inner surface of the battery container.

15. The battery according to claim 1, further comprising a battery container housing a laminate including the current collector layer, the positive electrode, the solid electrolyte layer, and the negative electrode, and further comprising a carbon layer disposed between the laminate and the battery container.

16. The battery according to claim 14, wherein the battery container is a coin-shaped container.

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