Positive electrode and battery

Abstract

This positive electrode (10) is provided with a positive electrode current collector (1) and a positive electrode mixture layer (2) disposed on the positive electrode current collector (1), the positive electrode mixture layer (2) containing a positive electrode active material and a solid electrolyte, the solid electrolyte containing a first solid electrolyte material and a second solid electrolyte material, 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 stacked in the thickness direction, and when a layer closer to the positive electrode current collector (1) is defined as a first layer and a layer farther from the positive electrode current collector (1) is defined as a second layer among the plurality of layers, the second solid electrolyte material has a higher ionic conductivity than the first solid electrolyte material. The ratio of the volume of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is greater than the ratio of the volume of the first solid electrolyte material in the first layer to the volume of the solid electrolyte.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a positive electrode and a battery. BACKGROUND

[0002] In recent years, research and development of all-solid batteries using a solid electrolyte are active. In the past, a solid electrolyte was sometimes decomposed by an active material. The decomposition of the solid electrolyte causes a decrease in capacity and the like, and adversely affects the battery characteristics.

[0003] Patent Literature 1 discloses a battery provided with a positive electrode including a first solid electrolyte material, the first solid electrolyte material including lithium, at least one selected from metal elements other than lithium and semi-metal elements, and at least one selected from chlorine and bromine, and not containing sulfur.

[0004] Patent Literature 2 discloses an all-solid battery having, in order, a current collector, a first electrode layer, and a solid electrolyte layer, the first electrode layer having a laminated structure in which a plurality of mixed agent layers are laminated, the volume ratio of an active material in the mixed agent layer with respect to the solid electrolyte decreasing at a specific inclination from the current collector toward the solid electrolyte layer.

[0005] PRIOR ART DOCUMENTS

[0006] Patent Literature 1: Japanese Patent No. 7145439

[0007] Patent Literature 2: Japanese Patent No. 6973310 SUMMARY

[0008] PROBLEMS TO BE SOLVED BY THE INVENTION

[0009] In the related art, there is room for improvement in terms of the balance between output characteristics and high-temperature resistance.

[0010] MEANS FOR SOLVING THE PROBLEMS

[0011] The positive electrode of the present disclosure is provided with a positive electrode current collector and a positive electrode mixed agent layer disposed on the positive electrode current collector,

[0012] The positive electrode mixed agent layer includes a positive electrode active material and a solid electrolyte,

[0013] The solid electrolyte includes a first solid electrolyte material and a second solid electrolyte material,

[0014] The ion conductivity of the first solid electrolyte material is higher than that of the second solid electrolyte material,

[0015] The positive electrode mixed agent layer includes a plurality of layers laminated in the thickness direction,

[0016] When a layer close to the positive electrode current collector among the plurality of layers is set as a first layer and a layer far from the positive electrode current collector is set as a second layer, a proportion of a volume of the first solid electrolyte material with respect to a volume of the solid electrolyte in the second layer is greater than a proportion of a volume of the first solid electrolyte material with respect to a volume of the solid electrolyte in the first layer.

[0017] Another positive electrode of the present disclosure has a positive electrode current collector and a positive electrode mixture layer disposed on the positive electrode current collector,

[0018] The positive electrode mixture layer contains a positive electrode active material and a solid electrolyte,

[0019] The solid electrolyte contains a first solid electrolyte material and a second solid electrolyte material,

[0020] The second solid electrolyte material has a higher oxidation potential than the first solid electrolyte material,

[0021] The positive electrode mixture layer contains a plurality of layers stacked in a thickness direction,

[0022] When a layer close to the positive electrode current collector among the plurality of layers is set as a first layer and a layer far from the positive electrode current collector is set as a second layer, a proportion of a volume of the first solid electrolyte material with respect to a volume of the solid electrolyte in the second layer is greater than a proportion of a volume of the first solid electrolyte material with respect to a volume of the solid electrolyte in the first layer.

[0023] Effects of the Invention

[0024] According to the technology of the present disclosure, a battery having both output characteristics and high-temperature resistance can be provided. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 is a cross-sectional view showing the general structure of one example of a positive electrode of Embodiment 1.

[0026] Figure 2 is a cross-sectional view showing the general structure of another example of a positive electrode of Embodiment 1.

[0027] Figure 3 is a cross-sectional view showing the general structure of a battery 100 of Embodiment 2.

[0028] Figure 4 is a graph showing the initial discharge characteristics of the batteries of Example 1 and Comparative Examples 1 to 3.

[0029] Figure 5 is a graph showing the discharge voltage behavior of the batteries of Example 1 and Comparative Examples 1 to 3 at SOC 50%.

[0030] Figure 6 This is a graph showing the voltage changes caused by high-temperature storage of the batteries in Example 1 and Comparative Examples 1-3. Detailed Implementation

[0031] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. The present disclosure is not limited to the following embodiments.

[0032] (Implementation Method 1)

[0033] The positive electrode of Embodiment 1 includes a positive current collector and a positive electrode additive layer disposed on the positive current collector. The positive electrode additive 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, wherein the ionic conductivity of the first solid electrolyte material is higher than that of the second solid electrolyte material. The positive electrode additive layer includes multiple layers stacked along the thickness direction. When the layer closest to the positive current collector is designated as the first layer and the layer furthest from the positive current collector is designated as the second layer, the volume ratio of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is greater than the volume ratio of the first solid electrolyte material in the first layer to the volume of the solid electrolyte.

[0034] In this disclosure, the thickness direction refers to the stacking direction of the positive electrode additive layer and the positive electrode current collector.

[0035] For example, the first layer and the second layer are adjacent to each other. That is, among the above-mentioned multiple layers of the positive electrode mixture layer, in two adjacent layers, the volume ratio of the first solid electrolyte material in the layer farther from the positive electrode current collector to the volume ratio of the solid electrolyte can be greater than the volume ratio of the first solid electrolyte material in the layer closer to the positive electrode current collector to the volume ratio of the solid electrolyte.

[0036] Figure 1 This is a cross-sectional view showing a general structure of an example of the positive electrode in Embodiment 1. The positive electrode 10 includes a positive current collector 1 and a positive electrode additive layer 2. The positive electrode additive layer 2 contains a positive electrode active material (not shown) and a solid electrolyte (not shown). The solid electrolyte contains a first solid electrolyte material and a second solid electrolyte material, wherein the ionic conductivity of the first solid electrolyte material is higher than that of the second solid electrolyte material. The positive electrode additive layer 2 is composed of layers 2a and 2b stacked in the thickness direction. Figure 1 In the positive electrode 10 shown, among these two adjacent layers, layer 2a, which is closer to the positive current collector 1, corresponds to the first layer, and layer 2b, which is farther away from the positive current collector 1, corresponds to the second layer. The volume ratio of the first solid electrolyte material to the solid electrolyte in the second layer is greater than the volume ratio of the first solid electrolyte material to the solid electrolyte in the first layer.

[0037] Based on the above structure, the ionic conductivity of the positive electrode flux layer 2 increases from the side of the positive electrode current collector 1 to the side opposite to the positive electrode current collector 1. This suppresses the uneven concentration of lithium ions in the thickness direction within the positive electrode flux layer 2 during battery operation, resulting in a good lithium ion distribution. Therefore, the positive electrode of Embodiment 1 improves the battery's output characteristics. Furthermore, the positive electrode of Embodiment 1 also improves the battery's high-temperature resistance. Generally, solid electrolyte materials tend to have lower oxidation resistance as ionic conductivity increases. In the positive electrode of Embodiment 1, which includes a first solid electrolyte material and a second solid electrolyte material satisfying the above relationship, sufficient oxidation resistance is provided, thereby mitigating battery degradation caused by high-temperature storage.

[0038] In the positive electrode of Embodiment 1, the oxidation potential of the second solid electrolyte material can be higher than that of the first solid electrolyte material.

[0039] This disclosure provides a positive electrode 10 from another aspect, which includes a positive current collector 1 and a positive electrode flux layer 2 disposed on the positive current collector 1.

[0040] Positive electrode mixture layer 2 contains positive electrode active material and solid electrolyte.

[0041] The solid electrolyte comprises a first solid electrolyte material and a second solid electrolyte material.

[0042] The oxidation potential of the second solid electrolyte material is higher than that of the first solid electrolyte material.

[0043] The positive electrode compound layer 2 comprises multiple layers stacked along the thickness direction.

[0044] When the layer 2a closest to the positive electrode current collector 1 is designated as the first layer and the layer 2b furthest from the positive electrode current collector 1 is designated as the second layer, the ratio of the volume of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is greater than the ratio of the volume of the first solid electrolyte material in the first layer to the volume of the solid electrolyte.

[0045] Based on the above configuration, the uneven concentration of lithium ions in the thickness direction within the positive electrode binder layer 2 during battery operation can be suppressed, resulting in a good lithium ion distribution. Therefore, the positive electrode of Embodiment 1 can achieve a battery with improved output characteristics.

[0046] The positive electrode disclosed herein can be used, for example, in all-solid-state batteries. That is, the positive electrode can be a positive electrode for all-solid-state batteries.

[0047] The ratio of the volume of the first solid electrolyte material in the first layer to the volume of the solid electrolyte is calculated as (volume of the first solid electrolyte material in the first layer) / (volume of the solid electrolyte in the first layer) × 100 [%]. Similarly, the ratio of the volume of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is calculated as (volume of the first solid electrolyte material in the second layer) / (volume of the solid electrolyte in the second layer) × 100 [%].

[0048] The ratio of the volume of the first solid electrolyte material in the first layer to the volume of the solid electrolyte, and the ratio of the volume of the first solid electrolyte material in the second layer to the volume of the solid electrolyte, can be determined by cutting a cross-section of the positive electrode mixture layer 2 along the thickness direction and performing elemental imaging analysis such as scanning electron microscopy (SEM) and energy dispersive X-ray diffraction (EDS) from the ratio of the detected elements in the solid electrolyte in the first and second layers.

[0049] The solid electrolyte may consist solely of a first solid electrolyte material and a second solid electrolyte material. In this 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.

[0050] The volume ratio of the first solid electrolyte material in the first layer to the volume of the solid electrolyte can be greater than 0% and less than 50%, or greater than 0% and less than 30%. The volume ratio of the first solid electrolyte material in the second layer to the volume of the solid electrolyte can be greater than 50% and less than 100%, or greater than 70% and less than 100%.

[0051] The volume ratio of the first solid electrolyte material in the first layer to the volume of the solid electrolyte can be greater than 0% and less than 50%, and the volume ratio of the first solid electrolyte material in the second layer to the volume of the solid electrolyte can be greater than 50% and less than 100%.

[0052] The positive electrode compound layer 2 can consist of only two layers in the thickness direction. That is, the positive electrode compound layer 2 can consist of only the first layer and the second layer mentioned above.

[0053] The positive electrode mixture layer 2 can consist of only two layers in the thickness direction, and the volume ratio of the first solid electrolyte material in the first layer to the volume of the solid electrolyte is more than 0% and less than 50%, and the volume ratio of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is more than 50% and less than 100%.

[0054] The volume ratio of the second solid electrolyte material in the first layer to the volume of the solid electrolyte can be more than 50% and less than 100%, or more than 70% and less than 100%. The volume ratio of the second solid electrolyte material in the second layer to the volume of the solid electrolyte can be more than 0% and less than 50%, or more than 0% and less than 30%.

[0055] Examples of solid electrolytes include halide solid electrolytes, sulfide solid electrolytes, oxide solid electrolytes, and organic polymer solid electrolytes. In this disclosure, "halide solid electrolyte" refers to a solid electrolyte containing halogens but not sulfur. "Sulfide solid electrolyte" refers to a solid electrolyte containing sulfur. "Oxide solid electrolyte" refers to a solid electrolyte containing oxygen. Halide solid electrolytes may contain not only halogens but also oxygen. Oxide solid electrolytes may contain anions other than oxygen (except for sulfide anions and halide anions).

[0056] Halogenated solid electrolytes are, for example, compounds containing Li, M, and X. Here, M is at least one selected from metallic and half-metallic elements other than Li. X is at least one selected from F, Cl, Br, and I.

[0057] "Half-metal elements" are B, Si, Ge, As, Sb, and Te. "Metallic elements" are all elements contained in Groups 1 to 12 of the periodic table (except hydrogen) and all elements contained in Groups 13 to 16 of the periodic table (except B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se).

[0058] M can contain Ti. M can contain both Ti and Al. Based on the above, the oxidation resistance of halide solid electrolytes can be improved.

[0059] M can contain Y. M can be Y. Based on the above, the ionic conductivity of halide solid electrolytes can be improved. Therefore, the battery output can be improved.

[0060] Halogenated solid electrolytes, for example, can be made from Li a Me b Y c The compound represented by X6 satisfies the formula a + mb + 3c = 6 and c > 0. The value of m represents the valence of Me. b can be 0.

[0061] Me can be at least one selected from Mg, Ca, Sr, Ba, Zn, Sc, Al, Ga, Bi, Zr, Hf, Ti, Sn, Ta, and Nb.

[0062] X may contain at least one selected from Cl and Br.

[0063] Examples of sulfide solid electrolytes include the Li2S-P2S5 system, Li2S-SiS2 system, Li2S-B2S3 system, Li2S-GeS2 system, Li2S-SiS2-LiI system, Li2S-SiS2-Li3PO4 system, Li2S-Ge2S2 system, Li2S-GeS2-P2S5 system, or Li2S-GeS2-ZnS system.

[0064] As oxide solid electrolytes, examples include NASICON-type solid electrolyte materials represented by LiTi2(PO4)3 and its elemental substitutes, perovskite-type solid electrolyte materials based on (LaLi)TiO3, and Li... 14 ZnGe4O 16 LISICON-type solid electrolyte materials, represented by Li4SiO4, LiGeO4 and their elemental substitutes, and Li7La3Zr2O 12 Garnet-type solid electrolyte materials, represented by its elemental substitutes, Li3PO4 and its N-substitutes, glasses based on Li-BO compounds such as LiBO2 and Li3BO3 with added Li2SO4, Li2CO3, etc., and glass ceramics, etc.

[0065] As organic polymer solid electrolytes, compounds of polymers and lithium salts can be used, for example. The polymers can have an ethylene oxide structure. Polymers with an ethylene oxide structure can contain a larger amount of lithium salt, thus further improving ionic conductivity. LiPF6, LiBF4, LiSbF6, LiAsF6, LiSO3CF3, LiN(SO2F)2, LiN(SO2CF3)2, LiN(SO2C2F5)2, LiN(SO2CF3)(SO2C4F9), LiC(SO2CF3)3, etc., can be used as lithium salts. One lithium salt can be used alone, or two or more can be used in combination.

[0066] The first solid electrolyte material and the second solid electrolyte material can be halide solid electrolytes.

[0067] The first solid electrolyte material can be the aforementioned material composed of Li. a Me b Y c The compound represented by X6. The first solid electrolyte material can be a compound composed of Li, Y, and X. The first solid electrolyte material can be a compound composed of Li, Y, Br, and Cl, such as Li3YBr3Cl3.

[0068] The second solid electrolyte material can be a compound composed of Li, Ti, Al, and F, or a compound composed of Li, Y, and Cl. For example, the second solid electrolyte material can be Li3YCl6.

[0069] The ionic conductivity of the first solid electrolyte material can be above 0.01 mS / cm and below 20 mS / cm, above 0.1 mS / cm and below 15 mS / cm, or above 1 mS / cm and below 10 mS / cm at 25°C.

[0070] The ionic conductivity of the second solid electrolyte material at 25°C can be above 0.001 mS / cm and below 10 mS / cm, above 0.005 mS / cm and below 5 mS / cm, or above 0.01 mS / cm and below 1 mS / cm.

[0071] The difference in ionic conductivity between the first solid electrolyte material and the second solid electrolyte at 25°C can be greater than 0.1 mS / cm, greater than 0.5 mS / cm, greater than 1 mS / cm, or greater than 1.5 mS / cm. The upper limit of this difference can be, for example, less than 10 mS / cm.

[0072] The first solid electrolyte material relative to Li / Li + The oxidation potential can be above 2.5V and below 4.5V, or above 3.0V and below 4.0V.

[0073] The second solid electrolyte material relative to Li / Li + The oxidation potential can be above 3.5V and below 5.5V, or above 3.9V and below 5.0V.

[0074] The first solid electrolyte material and the second solid electrolyte relative to Li / Li + The difference in oxidation potential can be greater than 0.1V and less than 3.0V, or greater than 0.5V and less than 1.5V.

[0075] The positive electrode active material can be a material capable of absorbing and releasing lithium ions. 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 can be used as positive electrode active materials. In particular, using lithium-containing transition metal oxides or lithium-containing transition metal phosphates as positive electrode active materials can reduce battery manufacturing costs 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.

[0076] The positive electrode active material can contain lithium nickel oxide with a layered rock-salt type crystal structure. The proportion of Ni (other than Li) in the lithium nickel oxide can be 50 atomic percent or more. Lithium nickel oxide can also contain other transition metals. Lithium nickel oxide can be used to achieve high operating voltages.

[0077] Lithium nickel oxide can be represented by the following compositional formula (I). Element M1 is at least one selected from V, Co, and Mn. Element M2 is at least one selected from Mg, Al, Ca, Ti, Cu, Zn, and Nb. Compositional 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.

[0078] Li α Ni x1 M1 x2 M2 (1-x1-x2) O 2+β ・・・(I)

[0079] The positive electrode layer 2 may contain conductive additives, adhesives, and other materials.

[0080] Conductive additives are used to reduce the resistance of the positive electrode 10. Examples of conductive additives include carbon materials and conductive polymers. Examples of carbon materials include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerene, and graphite oxide. Examples of conductive polymers include polyaniline, polypyrrole, and polythiophene.

[0081] Adhesives are used to improve the adhesion of the materials constituting the positive electrode 10. As adhesives, 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 can be used.

[0082] As the positive current collector 1, sheets or thin films made of metallic materials such as aluminum, stainless steel, titanium, and their alloys can be used. Aluminum and its alloys are suitable as materials for the positive current collector 1 because they are inexpensive and easy to fabricate into thin films. The sheets or thin films can be porous or non-porous. Metal foils, metal meshes, etc., can be used as sheets or thin films. Carbon materials such as carbon can be coated on the surface of the positive current collector 1 as conductive auxiliary materials.

[0083] Regarding the ratio of the volume of the positive electrode active material to the total volume of the solid electrolyte in the positive electrode 10, "v1:100-v1", it can satisfy 30≤v1≤95. Here, v1 represents the volume ratio of the positive electrode active material when the total volume of the positive electrode active material and the solid electrolyte in the positive electrode is set to 100. Satisfying 30≤v1 makes it easy to ensure sufficient battery energy density. Satisfying v1≤95 makes it easier for the battery to operate at high output.

[0084] The thickness of the positive electrode 10 can be greater than 10 μm and less than 500 μm. When the thickness of the positive electrode 10 is greater than 10 μm, the energy density of the battery 100 can be sufficiently ensured. When the thickness of the positive electrode 10 is less than 500 μm, the battery can operate at high output.

[0085] Figure 1 In this embodiment, the positive electrode mixture layer 2 is composed of layers 2a and 2b, but the structure of the positive electrode in this disclosure is not limited to the above. The positive electrode mixture layer may contain three or more layers. When the number of layers 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 greater than or equal to 2, n is a natural number, and 1 ≤ n ≤ k-1 is satisfied.

[0086] Multiple layers in the positive electrode mixture layer can be stacked in such a way that the volume ratio of the first solid electrolyte material in each layer to the volume of the solid electrolyte increases in order from the layer closest to the positive electrode current collector to the layer furthest from the positive electrode current collector.

[0087] Figure 2 This is a cross-sectional view showing the general structure of another example of the positive electrode in Embodiment 1. The positive electrode 11 includes a positive current collector 1 and a positive electrode flux layer 21, which includes layers 21a, 21b, and 21c in the thickness direction. That is, the positive electrode 11 is an example where the number of layers k included in the positive electrode flux layer is 3.

[0088] In the positive electrode 11, the volume ratio of the first solid electrolyte material in each layer of the positive electrode mixture layer 21 to the volume of the solid electrolyte can increase in the order of layer 21a < layer 21b < layer 21c.

[0089] The positive electrode in Embodiment 1 can be manufactured, for example, by the following method. A first-layer positive electrode mixture, formed by mixing a second solid electrolyte material and a positive electrode active material, and a second-layer positive electrode mixture, formed by mixing the first solid electrolyte material and the positive electrode active material, are prepared. The first-layer positive electrode mixture and the second-layer positive electrode mixture are sequentially stacked and pressurized on the positive electrode current collector 1, thereby obtaining a positive electrode having the positive electrode current collector 1 and the positive electrode mixture layer 2.

[0090] The manufacturing method of the positive electrode is not limited to the above. For example, a positive electrode can be obtained by stacking and pressing a positive electrode mixture for forming a first layer and a positive electrode mixture for forming a second layer to form a positive electrode mixture layer 2 having a first layer and a second layer, and then placing a positive electrode current collector 1 on the first layer.

[0091] The positive electrode compound used to form the first layer can be formed by mixing a first solid electrolyte material, a second solid electrolyte material, and a positive electrode active material in such a way that the volume ratio of the second solid electrolyte material is greater than that of the first solid electrolyte material. Similarly, the positive electrode compound used to form the second layer can be formed by mixing the first solid electrolyte material, the second solid electrolyte material, and the positive electrode active material in such a way that the volume ratio of the first solid electrolyte material is greater than that of the second solid electrolyte material. When the positive electrode compound layer 2 comprises three or more layers, positive electrode compounds with altered volume ratios of the first and second solid electrolyte materials can be sequentially stacked to fabricate a battery.

[0092] (Implementation Method 2)

[0093] Figure 3 This is a cross-sectional view showing the general structure of the battery 100 in Embodiment 2.

[0094] The battery 100 has a positive electrode 10, an electrolyte layer 20, and a negative electrode 30. The electrolyte layer 20 is disposed between the positive electrode 10 and the negative electrode 30.

[0095] Positive electrode 10 is the positive electrode of implementation method 1.

[0096] By incorporating the positive electrode of Embodiment 1, the output characteristics of the battery are improved.

[0097] Electrolyte layer 20 is a layer containing an electrolyte. This electrolyte is, for example, a solid electrolyte. Electrolyte layer 20 can be a solid electrolyte layer.

[0098] The solid electrolyte contained in the electrolyte layer 20 may be any solid electrolyte listed in Embodiment 1.

[0099] 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 a solid electrolyte. Alternatively, the electrolyte layer 20 may contain a solid electrolyte having a different composition than the first solid electrolyte material and the second solid electrolyte material contained in the positive electrode mixture layer in Embodiment 1.

[0100] The electrolyte layer 20 may contain two or more materials listed as solid electrolytes. The two or more solid electrolytes have different compositions from each other. For example, the electrolyte layer 20 may contain a halide solid electrolyte and a sulfide solid electrolyte.

[0101] The thickness of the electrolyte layer 20 can 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, it becomes easier for the battery 100 to operate at high output. In other words, by appropriately adjusting the thickness of the electrolyte layer 20, sufficient safety of the battery 100 can be ensured, and the battery 100 can operate at high output.

[0102] The negative electrode 30 contains a material that has the property of absorbing and releasing metal ions (e.g., lithium ions). The negative electrode 30 may contain, for example, a negative electrode active material (e.g., negative electrode active material particles).

[0103] The negative electrode active material can be a metal, carbon, oxide, nitride, tin compound, or silicon compound. The metal can be a pure metal or an alloy. Examples of metal materials include lithium metal or lithium alloys. Examples of carbon materials include natural graphite, coke, semi-graphitized carbon, carbon fibers, spherical carbon, artificial graphite, or amorphous carbon. Examples of oxides include Li₄Ti₅O. 12 Examples of suitable materials include LiTi2O4 and TiO2. From a capacity density perspective, silicon, tin, silicon compounds, or tin compounds are preferred.

[0104] The negative electrode 30 may have a negative electrode current collector and a negative electrode flux layer supported on the surface of the negative electrode current collector. The negative electrode flux layer may contain a negative electrode active material.

[0105] The negative electrode mixture layer may also contain a solid electrolyte. With this configuration, the internal lithium-ion conductivity of the negative electrode 30 is improved, and the battery 100 can operate at high output. The solid electrolyte that can be included in the negative electrode mixture layer can be one of the solid electrolytes listed in Embodiment 1.

[0106] The negative current collector is, for example, a foil made of metal materials such as stainless steel, nickel, nickel alloy, copper, and copper alloy.

[0107] Regarding the ratio of the volume of the negative electrode active material to the volume of the solid electrolyte in the negative electrode 30, "v2:100-v2", it can satisfy 30≤v2≤95. Here, v2 represents the volume ratio of the negative electrode active material when the total volume of the negative electrode active material and the solid electrolyte in the negative electrode 30 is set to 100. When 30≤v2 is satisfied, it is easy to ensure sufficient energy density of the battery 100. When v2≤95 is satisfied, it becomes easier for the battery 100 to operate at high output.

[0108] The thickness of the negative electrode 30 can be greater than 10 μm and less than 500 μm. When the thickness of the negative electrode 30 is greater than 10 μm, it is easy to ensure sufficient energy density of the battery 100. When the thickness of the negative electrode 30 is less than 500 μm, it becomes easier for the battery 100 to operate at high output.

[0109] To improve the adhesion between particles, at least one of the positive electrode 10, the electrolyte layer 20, and the negative electrode 30 may contain a binder. The binder is used to improve the adhesion of the materials constituting the electrode. Examples of binders include polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, aramid resin, polyamide, polyimide, polyamide-imide, polyacrylonitrile, polyacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polymethacrylic acid, polymethyl methacrylate, polyethyl methacrylate, polyhexyl methacrylate, polyvinyl acetate, polyvinylpyrrolidone, polyether, polyethersulfone, hexafluoropolypropylene, styrene-butadiene rubber, carboxymethyl cellulose, etc. Alternatively, copolymers of two or more materials selected from tetrafluoroethylene, hexafluoroethylene, hexafluoropropylene, perfluoroalkyl vinyl ether, vinylidene fluoride, trichlorofluoroethylene, ethylene, propylene, pentafluoropropylene, fluoromethyl vinyl ether, acrylic acid, and hexadiene can be used as binders. Furthermore, mixtures of two or more of these materials can be used as binders.

[0110] To improve electronic conductivity, at least one of the positive electrode 10 and the negative electrode 30 may contain a conductive additive. Examples of conductive additives include graphite-based materials such as natural or artificial graphite; carbon black-based materials such as acetylene black and Ketjen black; conductive fibers such as carbon fibers or metal fibers; fluorinated carbon; metal powders such as aluminum; conductive whiskers such as zinc oxide or potassium titanate; conductive metal oxides such as titanium oxide; and conductive polymers such as polyaniline, polypyrrole, and polythiophene. For example, using a carbon-based conductive additive can reduce the cost of the battery 100.

[0111] Battery 100 can be configured into various shapes such as coin-shaped, cylindrical, square, sheet-shaped, button-shaped, flat, and stacked batteries.

[0112] Battery 100 can be manufactured, for example, by the following method: Materials for forming the positive electrode 10, materials for forming the electrolyte layer 20, and materials for forming the negative electrode 30 are prepared separately. A laminate in which the positive electrode 10, electrolyte layer 20, and negative electrode 30 are sequentially arranged is fabricated using a known method. In this case, the positive electrode 10 is fabricated, for example, by the method described in Embodiment 1. Thus, battery 100 is obtained.

[0113] (Other implementation methods)

[0114] (Postscript)

[0115] Based on the above description of the embodiments, the following technical solution is disclosed.

[0116] (Technical Solution 1)

[0117] A positive electrode includes a positive current collector and a positive electrode flux layer disposed on the positive current collector.

[0118] The positive electrode mixture layer contains a positive electrode active material and a solid electrolyte.

[0119] The solid electrolyte comprises a first solid electrolyte material and a second solid electrolyte material.

[0120] The first solid electrolyte material has a higher ionic conductivity than the second solid electrolyte material.

[0121] The positive electrode mixture layer comprises multiple layers stacked along the thickness direction.

[0122] When the layer closest to the positive current collector is designated as the first layer and the layer furthest from the positive current collector is designated as the second layer, the volume ratio of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is greater than the volume ratio of the first solid electrolyte material in the first layer to the volume of the solid electrolyte.

[0123] Based on this configuration, a battery that combines output characteristics and high-temperature resistance can be realized.

[0124] (Technical Solution 2)

[0125] According to the positive electrode described in technical solution 1, the oxidation potential of the second solid electrolyte material is higher than that of the first solid electrolyte material. With this configuration, a battery that combines high-output characteristics and high-temperature resistance can be realized.

[0126] (Technical Solution 3)

[0127] A positive electrode includes a positive current collector and a positive electrode flux layer disposed on the positive current collector.

[0128] The positive electrode mixture layer contains a positive electrode active material and a solid electrolyte.

[0129] The solid electrolyte comprises a first solid electrolyte material and a second solid electrolyte material.

[0130] The oxidation potential of the second solid electrolyte material is higher than that of the first solid electrolyte material.

[0131] The positive electrode mixture layer comprises multiple layers stacked along the thickness direction.

[0132] When the layer closest to the positive current collector is designated as the first layer and the layer furthest from the positive current collector is designated as the second layer, the volume ratio of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is greater than the volume ratio of the first solid electrolyte material in the first layer to the volume of the solid electrolyte.

[0133] Based on this configuration, a battery that combines output characteristics and high-temperature resistance can be realized.

[0134] (Technical Solution 4)

[0135] According to any one of technical solutions 1 to 3, in the positive electrode, the volume ratio of the first solid electrolyte material in the first layer to the volume of the solid electrolyte is 0% or more and 50% or less, and the volume ratio of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is 50% or more and 100% or less. With this configuration, a battery that combines output characteristics and high-temperature resistance can be realized.

[0136] (Technical Solution 5)

[0137] According to any one of technical solutions 1 to 4, the first layer and the second layer are adjacent to each other in the positive electrode. With this configuration, a battery that combines output characteristics and high-temperature resistance can be realized.

[0138] (Technical Solution 6)

[0139] According to any one of claims 1 to 5, the plurality of layers are stacked in such a manner that the volume ratio of the first solid electrolyte material in each layer to the volume of the solid electrolyte increases sequentially from the layer closest to the positive electrode current collector to the layer furthest from the positive electrode current collector. With this configuration, a battery possessing both high-output characteristics and high-temperature resistance can be realized.

[0140] (Technical Solution 7)

[0141] A battery comprising a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, as described in any one of technical solutions 1 to 6.

[0142] The battery described in technical solution 7 has improved output characteristics and high temperature resistance.

[0143] Example

[0144] The present disclosure will now be described in more detail with reference to embodiments. The embodiments described below are merely illustrative and are not intended to limit the scope of the disclosure.

[0145] <Battery Making>

[0146] (Example 1)

[0147] [Preparation of the first solid electrolyte material]

[0148] In an argon atmosphere, raw material powders LiBr, YBr3, LiCl, and YCl3 were weighed in a molar ratio of LiBr:YBr3:LiCl:YCl3 = 3:1:3:1. Then, they were ground using a planetary ball mill (Fridge, P-7 type) at 600 rpm for 25 hours to obtain Li3YBr3Cl3 powder 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).

[0149] [Preparation of the second solid electrolyte material]

[0150] In an argon atmosphere, raw material powders LiBr, YBr3, LiCl, and YCl3 were weighed in a molar ratio of LiCl:YCl3 = 3:1. Then, the powder was ground using a planetary ball mill (Fridge, P-7 type) at 600 rpm for 25 hours to obtain Li3YCl6 powder 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).

[0151] [Preparation of the Positive Electrolyte]

[0152] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2O2, a first solid electrolyte material, and vapor-phase carbon fiber (VGCF (manufactured by Resonac)) as a conductive additive are weighed in a mortar at a mass ratio of 60:40:1, thereby preparing the first positive electrode mixture. VGCF is a registered trademark of Resonac.

[0153] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, the second solid electrolyte material, and VGCF are weighed in a mass ratio of 60:40:1 and mixed in a mortar to prepare the second positive electrode mixture.

[0154] [Battery manufacturing]

[0155] The negative electrode active material Li4Ti5O 12 Li3YBr3Cl3 and VGCF were weighed in a mortar at a mass ratio of 60:40:1 and mixed to prepare the negative electrode mixture.

[0156] In an insulating outer cylinder, 15 mg of Li3YBr3Cl3, 9 mg of a first positive electrode mixture, and 9 mg of a second positive electrode mixture are sequentially layered and pressurized at 360 MPa to form a solid electrolyte layer and a positive electrode mixture layer. Next, 3 mg of VGCF is layered on top of the second positive electrode mixture layer (i.e., the positive electrode mixture layer) and pressurized at 360 MPa to form the positive electrode. Then, 18 mg of a negative electrode mixture is layered on top of the Li3YBr3Cl3 layer (i.e., the solid electrolyte layer) and pressurized at 360 MPa. This creates a laminate consisting of a positive electrode, a solid electrolyte, and a negative electrode. Next, stainless steel current collectors are installed on the positive and negative electrodes, respectively, and current collector leads are attached to the current collectors. Finally, an insulating ring is used to seal the interior of the insulating outer cylinder from the external air atmosphere. This completes the fabrication of the battery of Example 1.

[0157] (Comparative Example 1)

[0158] [Preparation of the Positive Electrolyte]

[0159] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, the first solid electrolyte material, and VGCF were weighed in a mass ratio of 60:40:1 and mixed in a mortar to prepare the positive electrode mixture of Comparative Example 1.

[0160] [Battery manufacturing]

[0161] In an insulating outer cylinder, 15 mg of Li3YBr3Cl3 and 18 mg of the positive electrode mixture from Comparative Example 1 were sequentially layered, and the mixture was press-molded at 360 MPa to form a solid electrolyte layer and a positive electrode mixture layer. Next, 3 mg of VGCF was layered on the positive electrode mixture layer, and the mixture was press-molded at 360 MPa to form the positive electrode. The battery of Comparative Example 1 was then manufactured in the same manner as in Example 1.

[0162] (Comparative Example 2)

[0163] [Preparation of the Positive Electrolyte]

[0164] LiNi, the positive electrode active material 0.6 Co 0.2 Mn 0.2 O2, the first solid electrolyte material, the second solid electrolyte material, and VGCF were weighed in a mass ratio of 60:20:20:1 and mixed in a mortar to prepare the positive electrode mixture of Comparative Example 2.

[0165] [Battery manufacturing]

[0166] Except that the positive electrode agent of Comparative Example 2 was used in the fabrication of the positive electrode agent layer, the battery of Comparative Example 2 was fabricated in the same manner as that of Comparative Example 1.

[0167] (Comparative Example 3)

[0168] The battery of Comparative Example 3 was prepared by sequentially stacking 15 mg of Li3YBr3Cl3, 9 mg of the second positive electrode mixture, and 9 mg of the first positive electrode mixture, i.e., the stacking order of the first positive electrode mixture and the second positive electrode mixture was reversed in Example 1. Otherwise, the battery of Comparative Example 3 was prepared in the same manner as in Example 1.

[0169] <Charge and Discharge Test>

[0170] Charge-discharge tests were conducted on the batteries of Examples 1 and Comparative Examples 1-3 under the following conditions. The batteries were charged at a constant current of 0.0016 A at a 1C rate relative to their theoretical capacity at 25°C until a voltage of 4.3V was reached. Then, they were discharged at a constant current of 0.0016 A at a 1C rate until a voltage of 2.5V was reached. Figure 4 These are graphs showing the initial discharge characteristics of the batteries of Example 1 and Comparative Examples 1-3. Figure 4 In the comparison, the discharge curves of Example 1 and Comparative Example 1 almost overlap.

[0171] The batteries of Example 1 and Comparative Examples 1-3 were charged to 50% State of Charge (SOC). For these batteries, constant current discharge was performed for 30 seconds at a current value of 0.0016A, which is 1C rate. Figure 5The graph shows the discharge voltage behavior of the batteries with a SOC of 50% in Example 1 and Comparative Examples 1-3.

[0172] <High-Temperature Preservation Test>

[0173] High-temperature storage tests were conducted on the batteries of Examples 1 and Comparative Examples 1-3 under the following conditions: The batteries of Examples 1 and Comparative Examples 1-3 were stored at 125°C for 400 hours. The voltage shift across the terminals of the batteries during high-temperature storage was measured. Figure 6 This is a graph showing the voltage changes caused by high-temperature storage of the batteries in Example 1 and Comparative Examples 1-3. Figure 6 In the figure, the curves of Example 1, Comparative Example 2 and Comparative Example 3 overlap.

[0174] (Inspection)

[0175] from Figure 4 It can be confirmed that the battery of Example 1 has discharge characteristics equal to or better than those of the batteries of Comparative Examples 1 to 3. Figure 5 It can be confirmed that the battery of Example 1 has superior instantaneous output power compared to the batteries of Comparative Examples 2 and 3. Regarding instantaneous output, there is no significant difference between the battery of Example 1 and the battery of Comparative Example 1. Figure 6 It can be confirmed that the battery of Example 1, compared with the battery of Comparative Example 1, suppressed the degradation caused by high-temperature storage. Regarding storage degradation, the battery of Example 1 has the same performance as the batteries of Comparative Examples 2 and 3. Therefore, it can be seen that the battery of Example 1 combines both output characteristics and high-temperature resistance.

[0176] Industry availability

[0177] The technology disclosed herein can be used, for example, in all-solid-state secondary batteries.

Claims

1. A positive electrode comprising a positive current collector and a positive electrode flux layer disposed on the positive current collector. The positive electrode mixture layer contains a positive electrode active material and a solid electrolyte. The solid electrolyte comprises a first solid electrolyte material and a second solid electrolyte material. The first solid electrolyte material has a higher ionic conductivity than the second solid electrolyte material. The positive electrode mixture layer comprises multiple layers stacked along the thickness direction. When the layer closest to the positive current collector is designated as the first layer and the layer furthest from the positive current collector is designated as the second layer, the volume ratio of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is greater than the volume ratio of the first solid electrolyte material in the first layer to the volume of the solid electrolyte.

2. The positive electrode according to claim 1, The oxidation potential of the second solid electrolyte material is higher than that of the first solid electrolyte material.

3. A positive electrode, comprising a positive current collector and a positive electrode flux layer disposed on the positive current collector. The positive electrode mixture layer contains a positive electrode active material and a solid electrolyte. The solid electrolyte comprises a first solid electrolyte material and a second solid electrolyte material. The oxidation potential of the second solid electrolyte material is higher than that of the first solid electrolyte material. The positive electrode mixture layer comprises multiple layers stacked along the thickness direction. When the layer closest to the positive current collector is designated as the first layer and the layer furthest from the positive current collector is designated as the second layer, the volume ratio of the first solid electrolyte material in the second layer to the volume of the solid electrolyte is greater than the volume ratio of the first solid electrolyte material in the first layer to the volume of the solid electrolyte.

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

5. The positive electrode according to any one of claims 1 to 3, 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, The plurality of layers are stacked in such a manner that the volume of the first solid electrolyte material in each layer relative to the volume of the solid electrolyte increases in order from the layer closest to the positive current collector to the layer furthest from the positive current collector.

7. A battery comprising a positive electrode, a negative electrode, and an electrolyte layer disposed between the positive electrode and the negative electrode, as described in any one of claims 1 to 3.

Images