Positive electrode and battery

Abstract

A positive electrode 10 according to the present disclosure includes a positive electrode current collector 1 and a positive electrode mixture layer 2 that is disposed on the positive electrode current collector 1. The positive electrode mixture layer 2 contains a positive electrode active material and a solid electrolyte. The solid electrolyte contains a first solid electrolyte material and a second solid electrolyte material, and the first solid electrolyte material has a higher ionic conductivity than the second solid electrolyte material. The positive electrode mixture layer 2 includes a plurality of layers that are stacked upon each other in the thickness direction, and if a layer that is close to the positive electrode current collector 1 among the plurality of layers is taken as a first layer and a layer that is farther from the positive electrode current collector 1 among the plurality of layers is taken as a second layer, the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer is greater than the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer.

Description

cathode, and battery

[0001] The present disclosure relates to positive electrodes and batteries.

[0002] In recent years, research and development of all-solid-state batteries using solid electrolytes has been actively pursued. In conventional batteries, the solid electrolyte can be decomposed by the active material. This decomposition of the solid electrolyte can have adverse effects on battery performance, such as a decrease in capacity.

[0003] Patent Document 1 discloses a battery having a positive electrode including a first solid electrolyte material that contains lithium, at least one selected from the group consisting of metal elements and metalloid elements other than lithium, and at least one selected from the group consisting of chlorine and bromine, and does not contain sulfur.

[0004] Patent Document 2 discloses an all-solid-state battery having, in this order, a current collector, a first electrode layer having a laminated structure in which a plurality of composite layers are stacked, and a solid electrolyte layer, in which the volume ratio of the active material to the solid electrolyte in the composite layer decreases at a specific gradient from the current collector toward the solid electrolyte layer.

[0005] Patent No. 7145439 Patent No. 6973310

[0006] The conventional technology has room for improvement in terms of both output characteristics and high temperature resistance.

[0007] The positive electrode of the present disclosure comprises: a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer includes a positive electrode active material and a solid electrolyte, wherein the solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material, wherein the first solid electrolyte material has higher ionic conductivity than the second solid electrolyte material, and the positive electrode mixture layer includes a plurality of layers stacked in a thickness direction, wherein a layer of the plurality of layers closer to the positive electrode current collector is defined as a first layer and a layer of the plurality of layers farther from the positive electrode current collector is defined as a second layer, and a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the second layer is larger than a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the first layer.

[0008] a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer includes a positive electrode active material and a solid electrolyte, the solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material, the second solid electrolyte material having a higher oxidation potential than the first solid electrolyte material, the positive electrode mixture layer includes a plurality of layers stacked in a thickness direction, and when a layer of the plurality of layers closer to the positive electrode current collector is defined as a first layer and a layer farther from the positive electrode current collector is defined as a second layer, a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the second layer is larger than a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the first layer.

[0009] According to the technology of the present disclosure, it is possible to provide a battery that combines output characteristics and high-temperature resistance.

[0010] FIG. 1 is a cross-sectional view showing a schematic configuration of an example of a positive electrode according to Embodiment 1. FIG. 2 is a cross-sectional view showing a schematic configuration of another example of a positive electrode according to Embodiment 1. FIG. 3 is a cross-sectional view showing a schematic configuration of a battery 100 according to Embodiment 2. FIG. 4 is a graph showing the initial discharge characteristics of the batteries of Example 1 and Comparative Examples 1 to 3. FIG. 5 is a graph showing the discharge voltage behavior of the batteries of Example 1 and Comparative Examples 1 to 3 at an SOC of 50%. FIG. 6 is a graph showing the change in voltage due to high-temperature storage of the batteries of Example 1 and Comparative Examples 1 to 3.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0012] (Embodiment 1) A positive electrode according to embodiment 1 includes a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector. The positive electrode mixture layer includes a positive electrode active material and a solid electrolyte. The solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material, and the first solid electrolyte material has higher ionic conductivity than the second solid electrolyte material. The positive electrode mixture layer includes multiple layers stacked in the thickness direction, and when a layer closer to the positive electrode current collector is designated as a first layer and a layer farther from the positive electrode current collector is designated as a second layer, the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer is greater than the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer.

[0013] In the present disclosure, the thickness direction refers to the stacking direction of the positive electrode mixture layer and the positive electrode current collector.

[0014] For example, the first layer and the second layer are adjacent to each other. That is, of two adjacent layers in the positive electrode mixture layer, the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the layer farther from the positive electrode current collector may be greater than the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the layer closer to the positive electrode current collector.

[0015] FIG. 1 is a cross-sectional view showing a schematic configuration of an example of a positive electrode according to the first embodiment. The positive electrode 10 includes a positive electrode current collector 1 and a positive electrode mixture layer 2. The positive electrode mixture layer 2 includes a positive electrode active material (not shown) and a solid electrolyte (not shown). The solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material, and the first solid electrolyte material has higher ionic conductivity than the second solid electrolyte material. The positive electrode mixture layer 2 includes a layer 2a and a layer 2b stacked in the thickness direction. In the positive electrode 10 shown in FIG. 1 , of these two adjacent layers, the layer 2a closer to the positive electrode current collector 1 corresponds to the first layer, and the layer 2b farther from the positive electrode current collector 1 corresponds to the second layer. The ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer is greater than the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer.

[0016] According to the above configuration, the ionic conductivity of the positive electrode mixture layer 2 increases from the positive electrode current collector 1 side toward the opposite side from the positive electrode current collector 1. This suppresses unevenness in the lithium ion concentration in the thickness direction within the positive electrode mixture layer 2 during battery operation, resulting in a favorable lithium ion distribution. Therefore, the positive electrode according to embodiment 1 can improve the output characteristics of the battery. Furthermore, the positive electrode according to embodiment 1 can also improve the high-temperature resistance of the battery. Generally, solid electrolyte materials tend to have lower oxidation resistance as their ionic conductivity increases. However, the positive electrode according to embodiment 1 includes the first solid electrolyte material and the second solid electrolyte material that satisfy the above relationship, and has sufficient oxidation resistance, thereby reducing deterioration of the battery due to high-temperature storage.

[0017] In the positive electrode according to the first embodiment, the second solid electrolyte material may have a higher oxidation potential than the first solid electrolyte material.

[0018] From another aspect, the present disclosure provides a cathode (10), comprising: a cathode current collector (1); and a cathode mixture layer (2) disposed on the cathode current collector (1); the cathode mixture layer (2) includes a cathode active material and a solid electrolyte; the solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material; the second solid electrolyte material has a higher oxidation potential than the first solid electrolyte material; the cathode mixture layer (2) includes a plurality of layers stacked in a thickness direction; and when a layer (2a) closer to the cathode current collector (1) is defined as a first layer and a layer (2b) farther from the cathode current collector (1) is defined as a second layer in the plurality of layers, a ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer is larger than a ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer.

[0019] According to the above configuration, unevenness in the lithium ion concentration in the thickness direction within the positive electrode mixture layer 2 during battery operation can be suppressed, resulting in a good lithium ion distribution. Therefore, the positive electrode according to embodiment 1 can realize a battery with improved output characteristics.

[0020] The positive electrode of the present disclosure is used in, for example, an all-solid-state battery. That is, the positive electrode may be a positive electrode for an all-solid-state battery.

[0021] The ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer is a value calculated by (volume of the first solid electrolyte material present in the first layer) / (volume of the solid electrolyte present in the first layer) × 100[%]. Similarly, the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer is a value calculated by (volume of the first solid electrolyte material present in the second layer) / (volume of the solid electrolyte present in the second layer) × 100[%].

[0022] The ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer and the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer can be determined from the ratios of detected elements in the solid electrolyte in the first layer and the second layer by cutting out a cross section along the thickness direction of the positive electrode mixture layer 2 and performing element mapping analysis such as scanning electron microscope analysis (SEM) and energy dispersive X-ray (EDS).

[0023] The solid electrolyte may consist of only the first solid electrolyte material and the second solid electrolyte material, in which case the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte is the ratio of the volume of the first solid electrolyte material to the sum of the volumes of the first solid electrolyte material and the second solid electrolyte material.

[0024] The ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer may be 0% or more and 50% or less, or 0% or more and 30% or less, and the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer may be 50% or more and 100% or less, or 70% or more and 100% or less.

[0025] The ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer may be 0% or more and 50% or less, and the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer may be 50% or more and 100% or less.

[0026] The positive electrode mixture layer 2 may be composed of only two layers in the thickness direction, that is, the positive electrode mixture layer 2 may be composed of only the first layer and the second layer.

[0027] The positive electrode mixture layer 2 may be composed of only two layers in the thickness direction, and the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer may be 0% or more and 50% or less, and the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer may be 50% or more and 100% or less.

[0028] The volume ratio of the second solid electrolyte material to the volume of the solid electrolyte in the first layer may be 50% or more and 100% or less, or 70% or more and 100% or less. The volume ratio of the second solid electrolyte material to the volume of the solid electrolyte in the second layer may be 0% or more and 50% or less, or 0% or more and 30% or less.

[0029] Examples of solid electrolytes include halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, and organic polymer solid electrolytes. In this disclosure, a "halide solid electrolyte" refers to a solid electrolyte that contains a halogen element but does not contain sulfur. A "sulfide solid electrolyte" refers to a solid electrolyte that contains sulfur. An "oxide solid electrolyte" refers to a solid electrolyte that contains oxygen. A halide solid electrolyte may contain not only a halogen element but also oxygen. An oxide solid electrolyte may contain an anion other than oxygen (excluding sulfur anions and halogen anions).

[0030] The halide solid electrolyte is, for example, a compound containing Li, M, and X. Here, M is at least one selected from the group consisting of metal elements and semimetal elements other than Li, and X is at least one selected from the group consisting of F, Cl, Br, and I.

[0031] "Metalloid elements" are B, Si, Ge, As, Sb, and Te. "Metal elements" are all elements in Groups 1 to 12 of the periodic table (excluding hydrogen) and all elements in Groups 13 to 16 of the periodic table (excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se).

[0032] M may contain Ti. M may contain Ti and Al. As a result, the oxidation resistance of the halide solid electrolyte can be improved.

[0033] M may contain Y. M may be Y. As a result, the ionic conductivity of the halide solid electrolyte can be improved, thereby improving the output of the battery.

[0034] The halide solid electrolyte is, for example, Li a Me b Y c X6, where the formula: a + mb + 3c = 6, and c > 0 is satisfied. The value of m represents the valence of Me. b may be 0.

[0035] Me may be at least one selected from the group consisting of Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0036] X may include at least one selected from the group consisting of Cl and Br.

[0037] Examples of sulfide solid electrolytes are LiS-P2S5-based, LiS-SiS2-based, LiS-B2S3-based, LiS-GeS2-based, LiS-SiS2-LiI-based, LiS-SiS2-Li3PO4-based, LiS-Ge2S2-based, LiS-GeS2-P2S5-based, or LiS-GeS2-ZnS-based.

[0038] Examples of oxide solid electrolytes include NASICON-type solid electrolyte materials, such as LiTi2(PO4)3 and its elemental substitution products, (LaLi)TiO3-based perovskite-type solid electrolyte materials, and Li 14 ZnGeO 16 , LiSiCON-type solid electrolyte materials such as LiSiO, LiGeO and their elemental substitution products, LiLaZrO 12Garnet-type solid electrolyte materials, such as LiPO and its element substitution products, LiPO and its N-substituted products, glasses based on Li-B-O compounds such as LiBO and LiBO, and glass ceramics to which LiSO, LiCO, etc. are added, can be used.

[0039] As the organic 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. A polymer compound having an ethylene oxide structure can contain a large amount of lithium salt. This can further increase ionic conductivity. Examples of the lithium salt include LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), and LiC(SO2CF3)3. One lithium salt may be used alone, or two or more may be used in combination.

[0040] The first solid electrolyte material and the second solid electrolyte material may be halide solid electrolytes.

[0041] The first solid electrolyte material is the above-mentioned Li a Me b Y c The first solid electrolyte material may be a compound represented by X. The first solid electrolyte material may be a compound consisting of Li, Y, and X. The first solid electrolyte material may be a compound consisting of Li, Y, Br, and Cl, and may be LiYBrCl.

[0042] The second solid electrolyte material may be a compound consisting of Li, Ti, Al, and F, or a compound consisting of Li, Y, and Cl. The second solid electrolyte material may be Li3YCl6.

[0043] The ionic conductivity of the first solid electrolyte material at 25°C may be 0.01 mS / cm or more and 20 mS / cm or less, 0.1 mS / cm or more and 15 mS / cm or less, or 1 mS / cm or more and 10 mS / cm or less.

[0044] The ionic conductivity of the second solid electrolyte material at 25°C may be 0.001 mS / cm or more and 10 mS / cm or less, 0.005 mS / cm or more and 5 mS / cm or less, or 0.01 mS / cm or more and 1 mS / cm or less.

[0045] The difference in ionic conductivity between the first solid electrolyte material and the second solid electrolyte at 25° C. may be 0.1 mS / cm or more, 0.5 mS / cm or more, 1 mS / cm or more, or 1.5 mS / cm or more. The upper limit of the difference may be, for example, 10 mS / cm or less.

[0046] Li / Li of the first solid electrolyte material + The oxidation potential with respect to .theta. may be 2.5V or more and 4.5V or less, or 3.0V or more and 4.0V or less.

[0047] Li / Li of the second solid electrolyte material + The oxidation potential with respect to .theta. may be 3.5V or more and 5.5V or less, or 3.9V or more and 5.0V or less.

[0048] Li / Li of the first solid electrolyte material and the second solid electrolyte + The difference in oxidation potential with respect to the cation may be 0.1 V or more and 3.0 V or less, or 0.5 V or more and 1.5 V or less.

[0049] The positive electrode active material may be a material capable of absorbing and releasing lithium ions. Examples of the positive electrode active material 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. In particular, using a lithium-containing transition metal oxide or a lithium-containing transition metal phosphate as the positive electrode active material can reduce the manufacturing cost of the battery and increase the average discharge voltage. 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 vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0050] The positive electrode active material may contain lithium nickel oxide having a layered rock salt crystal structure. The proportion of Ni among metal elements other than Li contained in the lithium nickel oxide may be 50 atomic % or more. The lithium nickel oxide may also contain other transition metals. The lithium nickel oxide is useful for achieving a high operating voltage.

[0051] The lithium nickel oxide may be represented by the following composition formula (I): Element M1 is at least one selected from the group consisting of V, Co, and Mn. Element M2 is at least one selected from the group consisting of Mg, Al, Ca, Ti, Cu, Zn, and Nb. Composition formula (I) satisfies 0.9≦α≦1.10, −0.05≦β≦0.05, 0.5≦x1<1, 0≦x2≦0.5, and 0<1−x1−x2≦0.5.

[0052] Li α Ni x1 M1 x2 M2 (1-x1-x2) O 2+β ...(I)

[0053] The positive electrode mixture layer 2 may contain other materials such as a conductive additive and a binder.

[0054] The conductive additive is used to reduce the resistance of the positive electrode 10. Examples of the conductive additive include a carbon material and a conductive polymer compound. Examples of the carbon material include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of the conductive polymer compound include polyaniline, polypyrrole, and polythiophene.

[0055] The binder is used to improve the binding properties of the materials that make up the positive electrode 10. Examples of the binder that can be used include polymeric materials such as polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene-butadiene copolymer rubber, polypropylene, polyethylene, and polyimide.

[0056] The positive electrode current collector 1 can be a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or an alloy thereof. Aluminum and its alloys are suitable materials for the positive electrode current collector 1 because they are inexpensive and easy to form into thin films. The sheet or film may be porous or non-porous. Metal foil, metal mesh, or the like may be used as the sheet or film. A carbon material such as carbon may be applied to the surface of the positive electrode current collector 1 as a conductive auxiliary material.

[0057] The ratio "v1:100-v1" of the volume of the positive electrode active material contained in the positive electrode 10 to the total volume of the solid electrolyte may satisfy 30≦v1≦95. Here, v1 indicates the volume ratio of the positive electrode active material when the total volume of the positive electrode active material and the solid electrolyte contained in the positive electrode is taken as 100. When 30≦v1 is satisfied, it is easy to ensure a sufficient energy density of the battery. When v1≦95 is satisfied, it becomes easier for the battery to operate at high power.

[0058] The thickness of the positive electrode 10 may be 10 μm or more and 500 μm or less. When the thickness of the positive electrode 10 is 10 μm or more, the energy density of the battery 100 is sufficiently ensured. When the thickness of the positive electrode 10 is 500 μm or less, the battery can operate at high power.

[0059] In FIG. 1 , the positive electrode mixture layer 2 is composed of a layer 2a and a layer 2b, but the configuration of the positive electrode of the present disclosure is not limited to this. The positive electrode mixture layer may include three or more layers. When the number of layers included in the positive electrode mixture layer is k, for example, the nth layer and the (n+1)th layer from the positive electrode current collector side may correspond to the first layer and the second layer, respectively. Here, k is a natural number of 2 or more, and n is a natural number satisfying 1≦n≦k−1.

[0060] The multiple layers in the positive electrode mixture layer may be stacked such that the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in each layer increases in order from the layer closest to the positive electrode current collector to the layer farthest from the positive electrode current collector.

[0061] 2 is a cross-sectional view showing a schematic configuration of another example of the positive electrode according to Embodiment 1. The positive electrode 11 includes a positive electrode current collector 1 and a positive electrode mixture layer 21, and the positive electrode mixture layer 21 includes a layer 21a, a layer 21b, and a layer 21c in the thickness direction. That is, the positive electrode 11 is an example in which the number k of layers included in the positive electrode mixture layer is 3.

[0062] In the positive electrode 11, the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in each layer of the positive electrode mixture layer 21 may be increased in the order of layer 21a < layer 21b < layer 21c.

[0063] The positive electrode in Embodiment 1 can be manufactured, for example, by the following method. A positive electrode mixture for forming a first layer is prepared by mixing a second solid electrolyte material with a positive electrode active material, and a positive electrode mixture for forming a second layer is prepared by mixing the first solid electrolyte material with a positive electrode active material. The positive electrode mixture for forming the first layer and the positive electrode mixture for forming the second layer are stacked in this order on a positive electrode current collector 1, and then pressed, to obtain a positive electrode including the positive electrode current collector 1 and the positive electrode mixture layer 2.

[0064] The method for manufacturing the positive electrode is not limited to the above. For example, the positive electrode may be obtained by forming a positive electrode mixture layer 2 including a first layer and a second layer by stacking and pressing a positive electrode mixture for forming a first layer and a positive electrode mixture for forming a second layer, and then disposing a positive electrode current collector 1 on the first layer.

[0065] The cathode mixture for forming the first layer may be a mixture of a first solid electrolyte material, a second solid electrolyte material, and a cathode active material, with the second solid electrolyte material being present in a larger volumetric proportion than the first solid electrolyte material. The cathode mixture for forming the second layer may be a mixture of a first solid electrolyte material, a second solid electrolyte material, and a cathode active material, with the first solid electrolyte material being present in a larger volumetric proportion than the second solid electrolyte material. Even when the cathode mixture layer 2 includes three or more layers, a battery can be fabricated by sequentially stacking cathode mixtures having different volumetric proportions of the first solid electrolyte material and the second solid electrolyte material.

[0066] Second Embodiment FIG. 3 is a cross-sectional view showing a schematic configuration of a battery 100 according to a second embodiment.

[0067] The battery 100 includes a positive electrode 10, an electrolyte layer 20, and a negative electrode 30. The electrolyte layer 20 is provided between the positive electrode 10 and the negative electrode 30.

[0068] The positive electrode 10 is the positive electrode according to the first embodiment.

[0069] By including the positive electrode according to the first embodiment, the output characteristics of the battery are improved.

[0070] The electrolyte layer 20 is a layer containing an electrolyte. The electrolyte is, for example, a solid electrolyte. The electrolyte layer 20 may be a solid electrolyte layer.

[0071] The solid electrolyte contained in the electrolyte layer 20 may be any of the solid electrolytes listed in the first embodiment.

[0072] The electrolyte layer 20 may contain a solid electrolyte having the same composition as the first solid electrolyte material or the second solid electrolyte material contained in the positive electrode mixture layer 2 in Embodiment 1. The electrolyte layer 20 may contain a material having the same composition as the first solid electrolyte material as the solid electrolyte. The electrolyte layer 20 may contain a solid electrolyte having a different composition from the first solid electrolyte material and the second solid electrolyte material contained in the positive electrode mixture layer in Embodiment 1.

[0073] The electrolyte layer 20 may include two or more of the materials listed as solid electrolytes. The two or more solid electrolytes have different compositions. For example, the electrolyte layer 20 may include a halide solid electrolyte and a sulfide solid electrolyte.

[0074] The thickness of the electrolyte layer 20 may be 1 μm or more and 300 μm or less. When the thickness of the electrolyte layer 20 is 1 μm or more, the possibility of a short circuit between the positive electrode 10 and the negative electrode 30 is reduced. Furthermore, when the thickness of the electrolyte layer 20 is 300 μm or less, the battery 100 can be easily operated at high power. In other words, when the thickness of the electrolyte layer 20 is appropriately adjusted, sufficient safety of the battery 100 can be ensured and the battery 100 can be operated at high power.

[0075] The negative electrode 30 includes a material that has the property of absorbing and releasing metal ions (e.g., lithium ions) and includes, for example, a negative electrode active material (e.g., negative electrode active material particles).

[0076] The negative electrode active material may be a metal material, a carbon material, an oxide, a nitride, a tin compound, or a silicon compound. The metal material may be a single metal. The metal material may be an alloy. Examples of the metal material include lithium metal or a lithium alloy. Examples of the carbon material include natural graphite, coke, partially graphitized carbon, carbon fiber, spherical carbon, artificial graphite, and amorphous carbon. Examples of the oxide include Li4Ti5O 12 , LiTi2O4, TiO2, etc. From the viewpoint of capacity density, silicon, tin, silicon compounds, or tin compounds can be suitably used.

[0077] The negative electrode 30 may include a negative electrode current collector and a negative electrode mixture layer carried on the surface of the negative electrode current collector. The negative electrode mixture layer may contain a negative electrode active material.

[0078] The negative electrode mixture layer may further contain a solid electrolyte. Such a configuration improves the lithium ion conductivity inside the negative electrode 30, enabling high-power operation of the battery 100. The solid electrolytes listed in embodiment 1 can be used as the solid electrolyte that can be contained in the negative electrode mixture layer.

[0079] The negative electrode current collector is, for example, a foil made of a metal material such as stainless steel, nickel, a nickel alloy, copper, or a copper alloy.

[0080] The ratio "v2:100-v2" of the volume of the negative electrode active material to the volume of the solid electrolyte contained in the negative electrode 30 may satisfy 30≦v2≦95. Here, v2 indicates the volume ratio of the negative electrode active material when the total volume of the negative electrode active material and solid electrolyte contained in the negative electrode 30 is taken as 100. When 30≦v2 is satisfied, it is easy to ensure a sufficient energy density of the battery 100. When v2≦95 is satisfied, it is easier for the battery 100 to operate at high power.

[0081] The thickness of the negative electrode 30 may be 10 μm or more and 500 μm or less. When the thickness of the negative electrode 30 is 10 μm or more, it is easy to ensure a sufficient energy density of the battery 100. When the thickness of the negative electrode 30 is 500 μm or less, it is easier for the battery 100 to operate at high power.

[0082] At least one selected from the group consisting of the positive electrode 10, the electrolyte layer 20, and the negative electrode 30 may contain a binder to improve adhesion between particles. The binder is used to improve the binding of the materials constituting the electrode. 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, and carboxymethyl 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. Alternatively, a mixture of two or more materials selected from these may be used as the binder.

[0083] At least one of the positive electrode 10 and the negative electrode 30 may contain a conductive additive for the purpose of increasing 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; carbon fluoride; metal powders such as 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. For example, using a carbon conductive additive can reduce the cost of the battery 100.

[0084] The battery 100 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.

[0085] The battery 100 can be manufactured, for example, by the following method. Materials for forming the positive electrode 10, the electrolyte layer 20, and the negative electrode 30 are prepared. A laminate in which the positive electrode 10, the electrolyte layer 20, and the negative electrode 30 are arranged in this order is manufactured by a known method. At this time, the positive electrode 10 is manufactured by the method described above in the first embodiment, for example. In this way, the battery 100 is obtained.

[0086] (Other Embodiments) (Additional Notes) The above description of the embodiments discloses the following techniques.

[0087] (Technology 1) A positive electrode comprising: a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer includes a positive electrode active material and a solid electrolyte, the solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material, the first solid electrolyte material has higher ionic conductivity than the second solid electrolyte material, the positive electrode mixture layer includes a plurality of layers stacked in a thickness direction, wherein, when a layer of the plurality of layers closer to the positive electrode current collector is defined as a first layer and a layer farther from the positive electrode current collector is defined as a second layer, a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the second layer is larger than a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the first layer.

[0088] This configuration makes it possible to realize a battery that combines output characteristics with high-temperature resistance.

[0089] (Technology 2) The positive electrode according to Technology 1, wherein the second solid electrolyte material has a higher oxidation potential than the first solid electrolyte material. With this configuration, a battery that achieves both output characteristics and high-temperature resistance can be realized.

[0090] (Technology 3) A positive electrode comprising: a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer includes a positive electrode active material and a solid electrolyte, the solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material, the second solid electrolyte material having a higher oxidation potential than the first solid electrolyte material, the positive electrode mixture layer includes a plurality of layers stacked in a thickness direction, wherein, when a layer of the plurality of layers closer to the positive electrode current collector is defined as a first layer and a layer farther from the positive electrode current collector is defined as a second layer, a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the second layer is larger than a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the first layer.

[0091] This configuration makes it possible to realize a battery that combines output characteristics with high-temperature resistance.

[0092] (Technology 4) The positive electrode according to any one of Technologies 1 to 3, wherein a ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the first layer is 0% or more and 50% or less, and a ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in the second layer is 50% or more and 100% or less. With this configuration, a battery that achieves both output characteristics and high-temperature resistance can be realized.

[0093] (Technology 5) The positive electrode according to any one of Technologies 1 to 4, wherein the first layer and the second layer are adjacent to each other. With this configuration, a battery that achieves both output characteristics and high-temperature resistance can be realized.

[0094] (Technology 6) The positive electrode according to any one of Technologies 1 to 5, wherein the plurality of layers are stacked such that a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in each layer increases in order from the layer closest to the positive electrode current collector to the layer farthest from the positive electrode current collector. With this configuration, a battery that achieves both output characteristics and high-temperature resistance can be realized.

[0095] (Technology 7) A battery comprising: the positive electrode according to any one of technologies 1 to 6; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode.

[0096] The battery described in Technology 7 can have improved power output characteristics and high temperature resistance.

[0097] The present disclosure will be described in more detail below using examples. The following examples are merely examples of embodiments, and are not intended to limit the scope of the present disclosure.

[0098] <Preparation of Battery> (Example 1) [Preparation of First Solid Electrolyte Material] In an argon atmosphere, raw material powders LiBr, YBr3, LiCl, and YCl3 were weighed out so that the molar ratio was LiBr:YBr3:LiCl:YCl3 = 3:1:3:1. Then, a planetary ball mill (manufactured by Fritsch, Model P-7) was used to perform milling treatment at 600 rpm for 25 hours, thereby obtaining a powder of Li3YBr3Cl3 as the first solid electrolyte material. The ionic conductivity of the first solid electrolyte material measured at 25°C was 2 mS / cm. The oxidation potential of the first solid electrolyte material was 3.6 V (vs. Li + / Li).

[0099] [Preparation of Second Solid Electrolyte Material] In an argon atmosphere, raw material powders LiBr, YBr3, LiCl, and YCl3 were weighed out so that the molar ratio of LiCl:YCl3 was 3:1. Then, a planetary ball mill (manufactured by Fritsch, Model P-7) was used to mill the mixture for 25 hours at 600 rpm, thereby obtaining a powder of Li3YCl6 as the second solid electrolyte material. The ionic conductivity of the second solid electrolyte material measured at 25°C was 0.2 mS / cm. The oxidation potential of the second solid electrolyte material was 4.3 V (vs. Li + / Li).

[0100] [Preparation of Positive Electrode Mixture] Positive Electrode Active Material LiNi 0.6 Co 0.2 Mn 0.2 O, a first solid electrolyte material, and vapor-grown carbon fiber (VGCF (manufactured by Resonac Corporation)) as a conductive additive were weighed out to a mass ratio of 60:40:1 and mixed in a mortar to prepare a first positive electrode mixture. VGCF is a registered trademark of Resonac Corporation.

[0101] Positive electrode active material LiNi 0.6 Co 0.2 Mn0.2 O2, the second solid electrolyte material, and VGCF were weighed out to have a mass ratio of 60:40:1 and mixed in a mortar to prepare a second positive electrode mixture.

[0102] [Battery Fabrication] Negative electrode active material Li4Ti5O 12 Li3YBr3Cl3 and VGCF were weighed out to have a mass ratio of 60:40:1 and mixed in a mortar to prepare a negative electrode mixture.

[0103] 15 mg of Li3YBr3Cl3, 9 mg of the first positive electrode mixture, and 9 mg of the second positive electrode mixture were stacked in this order in an insulating outer cylinder and then pressure-molded at 360 MPa to form a solid electrolyte layer and a positive electrode mixture layer. Next, 3 mg of VGCF was stacked on the second positive electrode mixture layer, i.e., the positive electrode mixture layer, and then pressure-molded at 360 MPa to form a positive electrode. Next, 18 mg of the negative electrode mixture was stacked on the Li3YBr3Cl3 layer, i.e., the solid electrolyte layer, and then pressure-molded at 360 MPa to form a laminate consisting of a positive electrode, a solid electrolyte, and a negative electrode. Next, stainless steel current collectors were attached to the positive and negative electrodes, and current collecting leads were attached to the current collectors. Finally, an insulating ferrule was used to isolate the interior of the insulating outer cylinder from the ambient atmosphere and seal it. In this way, the battery of Example 1 was fabricated.

[0104] (Comparative Example 1) [Preparation of Positive Electrode Mixture] Positive Electrode Active Material LiNi 0.6 Co 0.2 Mn 0.2 O 2 , the first solid electrolyte material, and VGCF were weighed out to have a mass ratio of 60:40:1 and mixed in a mortar to prepare a positive electrode mixture of Comparative Example 1.

[0105] [Fabrication of Battery] 15 mg of LiYBrCl and 18 mg of the cathode mixture of Comparative Example 1 were stacked in an insulating outer cylinder and pressure-molded at 360 MPa to form a solid electrolyte layer and a cathode mixture layer. Next, 3 mg of VGCF was stacked on the cathode mixture layer and pressure-molded at 360 MPa to form a cathode. The battery of Comparative Example 1 was fabricated in the same manner as in Example 1.

[0106] (Comparative Example 2) [Preparation of Positive Electrode Mixture] Positive Electrode Active Material LiNi 0.6 Co 0.2 Mn 0.2 O, the first solid electrolyte material, the second solid electrolyte material, and VGCF were weighed out to have a mass ratio of 60:20:20:1 and mixed in a mortar, thereby producing a positive electrode mixture of Comparative Example 2.

[0107] [Fabrication of Battery] A battery of Comparative Example 2 was fabricated in the same manner as in Comparative Example 1, except that the positive electrode mixture of Comparative Example 2 was used to fabricate the positive electrode mixture layer.

[0108] Comparative Example 3 A battery of Comparative Example 3 was fabricated in the same manner as in Example 1, except that 15 mg of LiYBrCl, 9 mg of the second positive electrode mixture, and 9 mg of the first positive electrode mixture were stacked in this order, i.e., the stacking order of the first positive electrode mixture and the second positive electrode mixture was reversed from that of Example 1.

[0109] <Charge / Discharge Test> Charge / discharge tests were conducted on the batteries of Example 1 and Comparative Examples 1 to 3 under the following conditions. At 25°C, constant current charging was performed at a current value of 0.0016 A, which corresponds to a 1C rate relative to the theoretical capacity of the battery, until the voltage reached 4.3 V. Next, constant current discharging was performed at a current value of 0.0016 A, which corresponds to a 1C rate, until the voltage reached 2.5 V. Figure 4 is a graph showing the initial discharge characteristics of the batteries of Example 1 and Comparative Examples 1 to 3. In Figure 4, the discharge curves of Example 1 and Comparative Example 1 almost overlap.

[0110] The batteries of Example 1 and Comparative Examples 1 to 3 were charged to a state of charge (SOC) of 50%. These batteries were then subjected to constant current discharge at a current value of 0.0016 A, which corresponds to a 1 C rate, for 30 seconds. Figure 5 is a graph showing the discharge voltage behavior of the batteries of Example 1 and Comparative Examples 1 to 3 at an SOC of 50%.

[0111] <High-Temperature Storage Test> A high-temperature storage test was conducted on the batteries of Example 1 and Comparative Examples 1 to 3 under the following conditions. The batteries of Example 1 and Comparative Examples 1 to 3 were stored at 125°C for 400 hours. The change in the voltage across the batteries during high-temperature storage was measured. Figure 6 is a graph showing the change in voltage due to high-temperature storage of the batteries of Example 1 and Comparative Examples 1 to 3. In Figure 6, the plots for Example 1, Comparative Example 2, and Comparative Example 3 overlap.

[0112] (Discussion) From FIG. 4, it was confirmed that the battery of Example 1 had discharge characteristics equal to or better than those of the batteries of Comparative Examples 1 to 3. From FIG. 5, it was confirmed that the battery of Example 1 had better instantaneous output than the batteries of Comparative Examples 2 and 3. There was no significant difference in instantaneous output between the battery of Example 1 and the battery of Comparative Example 1. From FIG. 6, it was confirmed that the battery of Example 1 was more inhibited from deterioration due to high-temperature storage than the battery of Comparative Example 1. With regard to storage deterioration, the battery of Example 1 had performance equivalent to that of the batteries of Comparative Examples 2 and 3. From the above, the battery of Example 1 achieved both output characteristics and high-temperature resistance.

[0113] The technology of the present disclosure is useful for, for example, all-solid-state secondary batteries.

Claims

1. A positive electrode comprising: a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer includes a positive electrode active material and a solid electrolyte, the solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material, the first solid electrolyte material has higher ionic conductivity than the second solid electrolyte material, the positive electrode mixture layer includes a plurality of layers stacked in a thickness direction, wherein a layer closer to the positive electrode current collector is designated a first layer and a layer farther from the positive electrode current collector is designated a second layer, a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the second layer is greater than a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the first layer.

2. The positive electrode according to claim 1, wherein the second solid electrolyte material has a higher oxidation potential than the first solid electrolyte material.

3. A positive electrode comprising: a positive electrode current collector; and a positive electrode mixture layer disposed on the positive electrode current collector, wherein the positive electrode mixture layer includes a positive electrode active material and a solid electrolyte, the solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material, the second solid electrolyte material has a higher oxidation potential than the first solid electrolyte material, the positive electrode mixture layer includes a plurality of layers stacked in a thickness direction, and when a layer of the plurality of layers closer to the positive electrode current collector is defined as a first layer and a layer farther from the positive electrode current collector is defined as a second layer, a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the second layer is larger than a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the first layer.

4. The positive electrode according to any one of claims 1 to 3, wherein a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the first layer is 0% or more and 50% or less, and a ratio of a volume of the first solid electrolyte material to a volume of the solid electrolyte in the second layer is 50% or more and 100% or less.

5. The positive electrode according to any one of claims 1 to 3, wherein the first layer and the second layer are adjacent to each other.

6. The positive electrode according to any one of claims 1 to 3, wherein the plurality of layers are laminated such that the ratio of the volume of the first solid electrolyte material to the volume of the solid electrolyte in each layer increases in order from the layer closest to the positive electrode current collector to the layer furthest from the positive electrode current collector.

7. A battery comprising: a positive electrode according to any one of claims 1 to 3; a negative electrode; and an electrolyte layer disposed between the positive electrode and the negative electrode.

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