Composite positive electrode active material, positive electrode mixture, all-solid-state lithium-ion battery, and mobile body

Abstract

To provide a composite positive electrode active material capable of realizing high energy density, a positive electrode mixture containing the same, an all-solid-state lithium ion battery, and a mobile body.SOLUTION: A composite positive electrode active material in which the surface of a positive electrode active material is coated with a solid electrolyte, a positive electrode mixture containing the same, an all-solid-state lithium ion battery, and a mobile body.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a composite positive electrode active material that can be used in lithium ion batteries, particularly all-solid-state secondary batteries, a positive electrode mixture containing the same, an all-solid-state lithium ion battery, and a mobile body. [Background technology]

[0002] In recent years, various industrial demands have led to active development of safe batteries. For example, lithium ion batteries are being used not only in the fields of information-related devices and communication devices, but also in the field of automobiles. In the field of automobiles, safety is particularly important because batteries are related to human life.

[0003] Most of the lithium-ion batteries currently on the market use electrolytes that contain flammable organic solvents, which can lead to overheating and fires if a short circuit occurs. In response to this, research is underway into all-solid-state batteries that use solid electrolytes instead of electrolytes.

[0004] Since the all-solid-state battery does not use flammable organic solvents, the possibility of fire or explosion can be significantly reduced even if a short circuit occurs, and therefore such an all-solid-state battery can be significantly safer than a lithium-ion battery that uses an electrolyte.

[0005] In addition, compared to lithium-ion batteries that use electrolytes, all-solid-state batteries allow for various improvements such as simplified safety devices and cooling mechanisms and the adoption of bipolar structures, which are expected to lead to improved energy density.

[0006] However, there is a demand for even higher energy density, and various studies on this issue are being conducted.

[0007] As an example, Patent Document 1 proposes filling voids that are inevitably formed during the manufacturing process of a solid secondary battery with a solid having lithium ion conductivity. More specifically, the positive electrode has positive electrode voids with a porosity in the range of 3% or more and less than 15%, and the positive electrode voids are filled with a first organic electrolyte having lithium ion conductivity.

[0008] Patent Document 2 discloses that, regarding a positive electrode mixture used in an all-solid-state battery, the energy density per volume can be improved by setting the ratio of the average particle size of a first positive electrode active material and a second positive electrode active material contained in the positive electrode mixture within a specific range. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] JP 2020-129446 A [Patent Document 2] JP 2019-106286 A Summary of the Invention [Problem to be solved by the invention]

[0010] The problem to be solved by the present invention is to provide a composite positive electrode active material, which can realize a high energy density, a positive electrode mixture containing the same, an all-solid-state lithium ion battery, and a mobile body. [Means for solving the problem]

[0011] The battery capacity of all-solid-state lithium-ion secondary batteries is rate-limited by the positive electrode active material. Therefore, in order to achieve a higher energy density, it is necessary to either improve the capacity of the positive electrode active material or increase the ratio of the positive electrode active material in the battery. On the other hand, the microstructure in the positive electrode mixture is important for bringing out the characteristics of all-solid-state batteries, and a design that takes into account the contact area between the positive electrode active material particles and the solid electrolyte and the ion / electron conduction path is required.

[0012] The present inventors have prepared a composite active material in which a positive electrode active material and a solid electrolyte are composited by a mechanochemical method, and have found that the use of this composite active material can improve the active material ratio in the positive electrode mixture in a battery, thereby enabling a high energy density, and have completed the present invention.

[0013] In order to solve the above problems, the following aspects of the invention are provided. [1] A composite positive electrode active material in which the surface of the positive electrode active material is coated with a solid electrolyte. [2] The composite positive electrode active material according to [1], wherein 90% or more of an area of ​​the surface of the positive electrode active material is covered with the solid electrolyte. [3] The composite positive electrode active material according to [1] or [2], wherein a mass ratio of the positive electrode active material to the solid electrolyte is 99:1 to 80:20. [4] The composite positive electrode active material according to any one of [1] to [3], wherein a mass ratio of the positive electrode active material to the solid electrolyte is 95:5 to 90:10. [5] The composite positive electrode active material according to any one of [1] to [4], wherein the solid electrolyte is an LPS-X-based solid electrolyte. [6] The LPS-X solid electrolyte is Li 6 P.S. 5 The composite positive electrode active material according to [5], wherein the positive electrode active material is Cl. [7] The positive electrode active material is lithium cobalt oxide LiCoO 2 , Lithium nickel oxide LiNiO 2 , Lithium manganese oxide LiMn 2 O 4 , Lithium iron phosphate LiFePO 4 , or lithium cobalt oxide partially substituted with nickel and manganese, Li(Ni-Co-Mn)O 2 The composite positive electrode active material according to any one of [1] to [6], [8] The positive electrode active material is LiNi0.6 Co 0.2 Mn 0.2 O 2 The composite positive electrode active material according to any one of [1] to [7], comprising (NCM622). [9] The positive electrode active material is LiNi 0.8 Co 0.1 Mn 0.1 O 2 The composite positive electrode active material according to any one of [1] to [8], comprising (NCM811).

[10] The composite positive electrode active material according to any one of [1] to [9], wherein a layer containing a lithium ion conductive oxide is present between the positive electrode active material and the solid electrolyte.

[11] The lithium ion conductive oxide is LiNbO 3 The composite positive electrode active material according to

[10] ,

[12] A positive electrode mixture comprising the composite positive electrode active material according to any one of [1] to

[11] , a LGPS-based solid electrolyte, and a conductive assistant.

[13] The positive electrode mixture according to

[12] , wherein a mass ratio of the LGPS-based solid electrolyte is 30 mass % or less.

[14] The positive electrode mixture according to

[12] or

[13] , wherein the mass ratio of the LGPS-based solid electrolyte is less than 10 mass %.

[15] The positive electrode mixture according to any one of

[12] to

[14] , wherein the conductive assistant contains vapor grown carbon fiber (VGCF).

[16]

[12] . An all-solid-state lithium-ion battery comprising: a positive electrode containing the positive electrode mixture according to any one of

[12] to

[15] ; a negative electrode; and a solid electrolyte layer containing a sulfide-based compound sandwiched between the positive electrode and the negative electrode.

[17]

[16] A moving object, which is an airplane, comprising the all-solid-state lithium-ion battery according to the present invention and powered by the all-solid-state lithium-ion battery. Effect of the Invention

[0014] The present invention provides a composite positive electrode active material capable of realizing high energy density, a positive electrode mixture containing the same, an all-solid-state lithium ion battery, and a mobile body.

[0015] Typically, the composite positive electrode active material according to the present invention can improve the mass ratio (mixing ratio) in the positive electrode mixture without decreasing the discharge capacity compared to a non-composite positive electrode active material. In other words, the composite positive electrode active material has an advantageous effect in increasing the energy density of an all-solid-state battery.

[0016] Furthermore, the composite positive electrode active material according to the present invention makes it possible to obtain an all-solid-state battery having cycle characteristics comparable to those of a non-composite positive electrode active material. [Brief description of the drawings]

[0017] [Figure 1] 1 is a scanning electron microscope photograph showing an example of a composite positive electrode active material in which the surface of the positive electrode active material is covered with a solid electrolyte. [Diagram 2] 1 is an example of a chart of elemental peaks observed by low energy ion scattering spectroscopy to determine coverage. [Diagram 3] FIG. 2 is a conceptual diagram for explaining a mechanochemical method for producing a composite positive electrode active material. [Figure 4] FIG. 1 is a conceptual diagram showing a configuration example of an all-solid-state battery for evaluating battery characteristics. [Diagram 5] FIG. 1 is a graph showing an example of an initial discharge capacity versus a mass ratio of a solid electrolyte in a positive electrode mixture. [Figure 6] FIG. 13 is a diagram showing an example of cycle characteristics. [Figure 7] FIG. 1 is a diagram illustrating an example of a system configuration of an aircraft. [Figure 8] FIG. 1 is a diagram showing an example of the initial discharge capacity of an all-solid-state battery using a composite positive electrode active material (NCM811). [Figure 9]FIG. 1 is a diagram showing an example of the initial discharge capacity of an all-solid-state battery when the mass ratio of the positive electrode active material (NCM622) to the solid electrolyte (LPSCl) in the composite positive electrode active material is changed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] [Composite positive electrode active material] In one embodiment of the composite positive electrode active material of the present invention, the surface of the positive electrode active material is coated with a solid electrolyte.

[0019] The composite means to combine the positive electrode active material and the solid electrolyte integrally, and in this embodiment, the solid electrolyte is deposited on the surface of the positive electrode active material, and the surface of the positive electrode active material is covered with the solid electrolyte. In addition, the composite positive electrode active material may be a physical integration of the positive electrode active material and the solid electrolyte, and may not involve chemical changes such as changes in the crystal structure.

[0020] [Coverage] FIG. 1 is a scanning electron microscope photograph showing an example of a composite positive electrode active material. The photograph on the left is for reference and shows a positive electrode active material whose surface is not covered with a solid electrolyte. In the composite positive electrode active material in the photograph in the center, 95.2% by area of ​​the surface of the positive electrode active material is covered with a solid electrolyte. In the composite positive electrode active material in the photograph on the right, 92.0% by area of ​​the surface of the positive electrode active material is covered with a solid electrolyte.

[0021] The coverage rate is calculated from the ratio of the presence intensity of a characteristic element observed when the surface of the positive electrode active material is not covered with a solid electrolyte, measured by low-energy ion scattering spectroscopy or the like, to the presence intensity of the aforementioned element when the surface of the positive electrode active material is covered with a solid electrolyte. That is, the coverage rate (area %)=100-(presence intensity of element after covering / presence intensity of element before covering)×100.

[0022] Figure 2 is an example of a chart in which the intensity of Nb present on the surface of the positive electrode active material was measured by low-energy ion scattering spectroscopy before and after coating. Line 1 is the peak before coating, which corresponds to the 0 area % coverage in Figure 1. Line 2 and Line 3 are the peaks after coating, which correspond to the 95.2 area % and 92.0 area % coverage in Figure 1, respectively.

[0023] The coverage is not particularly limited. In general, it is considered that the higher the coverage, the lower the interface resistance of the positive electrode active material. From this viewpoint, the coverage may be 90.0 area% or more, more preferably the coverage may be 95.0 area% or more, and even more preferably the coverage may be 97.0 area% or more. On the other hand, the upper limit of the coverage may be 100 area%, but may be appropriately adjusted in consideration of the desired interface resistance, manufacturing cost, etc., and typically the coverage may be 99.0 area% or less, or the coverage may be 98.0 area% or less.

[0024] (compound) The means for compounding is not particularly limited as long as it is possible to obtain a state in which the surface of the positive electrode active material is covered with the solid electrolyte. The positive electrode active material and the solid electrolyte may be compounded by a mechanochemical method to prepare a compound active material in which the positive electrode active material is covered with the solid electrolyte.

[0025] The raw material composition, the positive electrode active material and the solid electrolyte, are treated by a mechanochemical method. The mechanochemical method (also called mechanochemical treatment) refers to a synthesis method that utilizes a mechanochemical reaction. The mechanochemical reaction refers to a chemical reaction such as an amorphous reaction, a crystallization reaction, a solid-solution reaction, or a phase transition reaction that utilizes high energy that is generated locally due to mechanical energy such as friction and compression during the crushing process of a solid material.

[0026] Apparatuses for carrying out the treatment by the mechanochemical method include grinding and dispersing machines such as ball mills, bead mills, vibration mills, turbo mills, mechanofusion, and disk mills. As an example, the mechanochemical method using a ball mill will be explained. The balls and mill containers used in the ball mill are made of tungsten carbide (WC) or zirconium oxide (ZrO 2 ) can be suitably used.

[0027] When the treatment is performed using a ball mill, the mill rotation speed during the treatment can typically be, for example, from 100 rpm to 10,000 rpm, and the treatment time can typically be from 0.1 hours to 100 hours.

[0028] FIG. 3 is a conceptual diagram for explaining the mechanochemical method. A raw material composition, a positive electrode active material and a solid electrolyte, are placed in a casing as a powder layer. The rotor rotates so as to slide against the casing. This applies mechanical energy such as impact, compression, and shear to the raw material composition (positive electrode active material and solid electrolyte) contained in the powder layer sandwiched between the casing and the tip of the rotor. As a result, the positive electrode active material and the solid electrolyte are composited to obtain a composite positive electrode active material, in which the surface of the positive electrode active material is coated with the solid electrolyte.

[0029] [Mass ratio of positive electrode active material to solid electrolyte] In the composite positive electrode active material, the mass ratio of the positive electrode active material and the solid electrolyte can be appropriately adjusted according to the desired properties. From the viewpoint of obtaining a high energy density, it is preferable to increase the ratio of the positive electrode active material. On the other hand, if the ratio of the positive electrode active material is too high, the ion / electron conduction path in the positive electrode mixture may be insufficient. From this viewpoint, the mass ratio of the positive electrode active material and the solid electrolyte may be 99:1 to 80:20, 97:3 to 85:15, or 95:5 to 90:10. The range of the mass ratio may be appropriately selected from any range within the range of the mass ratio according to the desired properties.

[0030] [Solid electrolyte] In the composite positive electrode active material, the solid electrolyte covers the surface of the positive electrode active material and can be appropriately selected according to the desired properties. The solid electrolyte may be an LPS-X solid electrolyte. The LPS-X solid electrolyte is preferable because it can act as a conductive path for ions / electrons in the positive electrode mixture. The LPS-X solid electrolyte is a solid electrolyte material that contains at least one element or group such as F, Cl, I, Se, Br, N, or OH as X additionally or substitutedly in at least a part of a sulfide-based solid electrolyte (LPS-based solid electrolyte) consisting of a basic skeleton of Li, P, and S elements. The LPS-X solid electrolyte can further increase ion conductivity and chemical stability by adding or substituting X while maintaining the good ion conductivity and the like of the base LPS-based solid electrolyte. A typical LPS-X solid electrolyte is a sulfide-based solid electrolyte that contains at least one element or group such as F, Cl, I, Se, Br, N, or OH as X additionally or substitutedly in at least a part of a sulfide-based solid electrolyte (LPS-based solid electrolyte) consisting of a basic skeleton of Li, P, and S elements. 6 P.S. 5 It may also be Cl.

[0031] [Cathode active material] In the composite positive electrode active material, the positive electrode active material can be appropriately selected from known positive electrode active materials that are usually used for lithium ion secondary batteries and all-solid-state batteries depending on the desired battery capacity, voltage, and characteristics. As the positive electrode active material, a material that can absorb and release lithium ions is usually used. A typical positive electrode active material is lithium cobalt oxide LiCoO 2 , Lithium nickel oxide LiNiO 2 , Lithium manganese oxide LiMn 2 O 4 , Lithium iron phosphate LiFePO 4 , or lithium cobalt oxide partially substituted with nickel and manganese, Li(Ni-Co-Mn)O 2 may include:

[0032] Li(Ni-Co-Mn)O 2is based on lithium cobalt oxide, with some of it replaced with nickel and manganese, and is known as a positive electrode active material called a ternary or NCM system. It is preferable because it can improve safety while reducing the amount of cobalt used, which is relatively expensive. The composition formula of this positive electrode active material is Li(NixCoyMnz)O 2 In this composition formula, 0.33 <x<1、0<y<0.33、0<z<0.33、ただしx+y+z=1であってもよい。または、0.6≦x≦0.8、0.1≦y≦0.2、0.1≦z≦0.2、ただしx+y+z=1であってもよい。 Typically, the positive electrode active material is LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622). Alternatively, the positive electrode active material may include LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811).

[0033] [Layer containing lithium ion conductive oxide (intermediate layer or buffer layer)] In the composite positive electrode active material, a layer containing a lithium ion conductive oxide may be present between the positive electrode active material and the solid electrolyte. This layer is sometimes called an intermediate layer or a buffer layer because it exists between the positive electrode active material and the solid electrolyte. At the contact interface between the positive electrode active material and the solid electrolyte, the ion conductivity may decrease, which may deteriorate the output characteristics of the battery. The presence of a layer (intermediate layer) made of a lithium ion conductive oxide between the positive electrode active material and the solid electrolyte can effectively reduce the interface resistance.

[0034] The layer (intermediate layer) made of lithium ion conductive oxide may be formed using a tumbling fluidized coating device. In summary, the tumbling fluidized coating device is used to feed a positive electrode active material and tumbling fluidize it while spraying the lithium ion conductive oxide, which is the raw material for the intermediate layer, and drying (heat treatment) to form a layer (intermediate layer) made of lithium ion conductive oxide on the surface of the positive electrode active material. Thereafter, the positive electrode active material is composited with a solid electrolyte, so that a layer (intermediate layer) made of lithium ion conductive oxide can be present between the positive electrode active material and the solid electrolyte.

[0035] The lithium ion conductive oxide can be appropriately selected depending on the desired properties. The lithium ion conductive oxide is LiNbO 3 The raw material for the intermediate layer may be an alkoxide solution of each metal element. LiNbO 3 In this case, the lithium source is ethoxylithium (structural formula: Li(OC 2 H 5 The niobium source was an ethanol solution containing pentaethoxyniobium (structural formula: Nb(OC 2 H5) 5 ) may also be used.

[0036] [Positive electrode mixture] According to one embodiment of the present invention, a positive electrode mixture is provided that includes the composite positive electrode active material, a LGPS-based solid electrolyte, and a conductive assistant. The positive electrode layer formed from the positive electrode mixture can be used in an all-solid-state secondary battery. The composite positive electrode active material is a material that absorbs and releases ions such as lithium ions involved in a battery reaction. The LGPS-based solid electrolyte is a material that conducts ions that are released or rapidly increased by the composite positive electrode active material. The conductive assistant is a material that conducts electrons involved in a battery reaction, and is effective in reducing each internal resistance and improving the life characteristics of a battery. The positive electrode mixture may contain optional components such as a conductive agent, a binder, a thickener, and a filler, as necessary.

[0037] [Conductive assistant] The conductive assistant can be appropriately selected depending on the desired properties such as conductivity. Typically, the conductive assistant may be VGCF (Vapor Grown Carbon Fiber). VGCF is a type of carbon nanotube that can be synthesized by a CVD method or the like. Therefore, it has a cylindrical, elongated fiber shape. In the positive electrode mixture, the mass ratio of the conductive assistant can be appropriately adjusted depending on the desired properties, is not particularly limited, and may be in the range of 1 mass % to 30 mass %.

[0038] [LGPS solid electrolyte] Li 10 GeP 2 S 12 It has a composition of (LGPS) and a characteristic crystal structure (LGPS type crystal structure), and has an extremely high ionic conductivity (12.3 mScm -1 @27°C). LGPS-based solid electrolytes are solid electrolyte materials that contain, in addition to LGPS, a portion of the LGPS composition is added or substituted with other elements (e.g., Si, Sn, Cl, O, etc.), and exhibit high ionic conductivity while generally maintaining the characteristic LGPS-type crystal structure. Typically, LGPS-based solid electrolytes may have compositions such as LiSiPSCl and LiSiPSO. More specific examples include Li 9.54 S 1.74 P 1.44 S 11.7 Cl 0.3 (25mScm -1 @27℃), Li 9.42 S 1.02 P 2.1 S 9.96 O 2.04 (0.32mScm -1 @27°C) or the like.

[0039] In order to realize a high energy density of a battery, it is effective to increase the ratio of the positive electrode active material in the battery. In other words, the energy density of the battery can be increased by lowering the ratio of the LGPS-based solid electrolyte in the positive electrode mixture. From this viewpoint, the mass ratio of the LGPS-based solid electrolyte in the positive electrode mixture may be 30 mass% or less. In general, when the mass ratio of the solid electrolyte in the positive electrode mixture is low, typically 10 mass% or less, sufficient ion conductivity may not be obtained, and the battery capacity may decrease. In the positive electrode mixture containing the composite positive electrode active material according to one embodiment of the present invention, good ion conductivity is maintained and the battery capacity can also be maintained. That is, in one embodiment of the present invention, the ratio of the LGPS-based solid electrolyte in the positive electrode mixture may be less than 10 mass%. This is very useful for realizing a high energy density of the battery. The lower limit of the ratio of the LGPS-based solid electrolyte in the positive electrode mixture can be appropriately adjusted depending on the desired ion conductivity or battery capacity, and may be, for example, 1 mass % or more, 3 mass % or more, or 5 mass % or more.

[0040] In addition, a positive electrode mixture containing a composite positive electrode active material according to one embodiment of the present invention can provide an all-solid-state battery having cycle characteristics comparable to those of a positive electrode mixture containing a non-composite positive electrode active material. Typically, as a cycle characteristic, a discharge capacity retention rate of 90% or more can be exhibited in this embodiment. The discharge capacity retention rate here is determined by performing 30 charge / discharge cycles, and determining the ratio (%) of the 30th discharge capacity to the first discharge capacity (100%).

[0041] [All-solid-state lithium-ion battery] In one embodiment of the present invention, an all-solid-state lithium-ion battery is provided. The all-solid-state lithium-ion battery includes a positive electrode, a negative electrode, and a solid electrolyte layer containing a sulfide-based compound sandwiched between the positive electrode and the negative electrode. The positive electrode, the negative electrode, and the solid electrolyte layer may be stacked to form a laminate. The laminate may be housed in an exterior body.

[0042] The laminate may have an external terminal connected to the positive electrode current collector and an external terminal connected to the negative electrode current collector. In addition, the all-solid-state lithium battery may have a separator between the positive electrode and the negative electrode.

[0043] The all-solid-state lithium ion battery may have a bipolar structure in which a positive electrode active material and a negative electrode active material are disposed on both sides of a current collector. A specific example of the bipolar structure is the structure described in JP-A-2004-95400.

[0044] The all-solid-state lithium ion battery may further include an insulator that insulates the laminate from the exterior body, and a sealant that seals an opening of the exterior body.

[0045] The exterior body may be a container molded from a highly corrosion-resistant metal material such as aluminum, stainless steel, nickel-plated steel, etc. Alternatively, the exterior body may be a container formed into a bag shape from a laminate film having at least one surface treated to be corrosion-resistant.

[0046] Examples of the shape of the all-solid-state lithium ion battery include a coin type, a button type, a paper type (or a sheet type), a cylindrical type, a square type, and a laminate type (pouch type).

[0047] The all-solid-state lithium ion battery may have a configuration in which the laminate is used as a unit cell, and a plurality of unit cells are sealed inside an exterior body.

[0048] Each component will be described in order below.

[0049] (positive electrode) The positive electrode can be composed of a positive electrode active material layer and a positive electrode current collector.

[0050] The positive electrode active material layer may include the positive electrode mixture according to one embodiment of the present invention described above. The positive electrode active material layer may also include a conductive material and a binder.

[0051] (Conductive materials and binders) The conductive material contained in the positive electrode active material layer may be a carbon material, such as graphite powder, carbon black (e.g., acetylene black), or a fibrous carbon material.

[0052] As the binder, a thermoplastic resin can be used. Examples of the thermoplastic resin include polyimide resin, fluororesins such as polyvinylidene fluoride (hereinafter sometimes referred to as PVdF) and polytetrafluoroethylene, polyolefin resins such as polyethylene and polypropylene, and resins described in WO2019 / 098384A1 or US2020 / 0274158A1.

[0053] (Positive electrode current collector) The positive electrode current collector of the positive electrode can be a strip-shaped member made of a metal material such as Al, Ni or stainless steel.

[0054] As a method for supporting the positive electrode active material layer on the positive electrode current collector, a method of pressurizing the positive electrode active material layer on the positive electrode current collector can be used. For pressurizing, cold pressing or hot pressing can be used.

[0055] The positive electrode can be produced by the above-mentioned methods.

[0056] (Negative electrode) The negative electrode can be composed of a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer contains a negative electrode active material. The negative electrode active material layer may also contain a solid electrolyte and a conductive material. The negative electrode active material, the negative electrode current collector, the solid electrolyte, the conductive material, and the binder can be the same as those described above.

[0057] Examples of a method for supporting the negative electrode active material layer on the negative electrode current collector include a pressure molding method similar to that for the positive electrode, a method in which a paste-like negative electrode mixture containing the negative electrode active material is applied onto the negative electrode current collector, dried, and then pressed and pressure-bonded, and a method in which a paste-like negative electrode mixture containing the negative electrode active material is applied onto the negative electrode current collector, dried, and then sintered.

[0058] (Solid electrolyte layer) The solid electrolyte layer is preferably the LGPS-based solid electrolyte contained in the positive electrode mixture of the present embodiment described above, but may be a solid electrolyte different from this.

[0059] In order to blend the interface between the solid electrolyte layer and the positive electrode active material layer, it is preferable to perform hot pressing after laminating the positive electrode active material layer and the solid electrolyte layer.

[0060] As a sulfide-based solid electrolyte, Li 2 SP 2 S 5 based compounds, Li 2 S-SiS 2 based compounds, Li 2 S-GeS 2 based compounds, Li 2 S.B. 2 S 3 based compounds, LiI-Si 2 SP 2 S 5 system compound, LiI-Li 2 SP 2 O 5 system compound, LiI-Li 3 PO 4 -P 2 S 5 Compounds and Li 10 GeP 2 S 12 Compounds based on the above-mentioned compounds can be mentioned.

[0061] In this specification, the term "sulfide-based solid electrolyte" refers to the "Li-based compound" described before "sulfide-based compound". 2 S" "P 2 S 5 It is used as a general term for solid electrolytes that mainly contain raw materials such as Li. 2 SP 2 S 5 Li 2 S and P 2 S 5 Solid electrolytes mainly containing Li and other materials.2 SP 2 S 5 Li contained in the compounds 2 The ratio of S is, for example, Li 2 SP 2 S 5 It is 50 to 90 mass% of the total Li-based compound. 2 SP 2 S 5 P contained in the compound 2 S 5 The ratio of Li 2 SP 2 S 5 The content of the Li-based compound is 10 to 50 mass %. 2 SP 2 S 5 The ratio of other raw materials contained in the system compound is, for example, Li 2 SP 2 S 5 The content of the Li-based compound is 0 to 30 mass%. 2 SP 2 S 5 Li 2 S and P 2 S 5 Also included are solid electrolytes having different mixture ratios of

[0062] Li 2 SP 2 S 5 Li 2 SP 2 S 5 , Li 2 SP 2 S 5 - LiI, Li 2 SP 2 S 5 -LiCl, Li 2 SP 2 S 5 -LiBr, Li 2 SP 2 S 5 -LiI-LiBr, Li 2 SP 2 S 5 -Li 2 O, Li 2 SP 2 S5 -Li 2 O-LiI and Li 2 SP 2 S 5 -Z m S n (m and n are positive numbers. Z is Ge, Zn or Ga.)

[0063] Li 2 S-SiS 2 Li 2 S-SiS 2 , Li 2 S-SiS 2 - LiI, Li 2 S-SiS 2 -LiBr, Li 2 S-SiS 2 -LiCl, Li 2 S-SiS 2 -B 2 S 3 - LiI, Li 2 S-SiS 2 -P 2 S 5 - LiI, Li 2 S-SiS 2 -P 2 S 5 -LiCl, Li 2 S-SiS 2 -Li 3 PO 4 , Li 2 S-SiS 2 -Li 2 SO 4 and Li 2 S-SiS 2 -Li x MO y (x and y are positive numbers. M is P, Si, Ge, B, Al, Ga, or In.)

[0064] Li 2 S-GeS 2 Li 2 S-GeS 2 and Li 2 S-GeS 2 -P 2 S5 Some examples include:

[0065] The sulfide-based solid electrolyte may be a crystalline material or an amorphous material.

[0066] The solid electrolyte layer can be formed by depositing an inorganic solid electrolyte by sputtering on the surface of the positive electrode active material layer of the above-mentioned positive electrode.

[0067] The solid electrolyte layer can be formed by applying a paste mixture containing a solid electrolyte to the surface of the positive electrode active material layer of the positive electrode and drying it. After drying, the mixture may be press molded and further pressed by cold isostatic pressing (CIP) to form the solid electrolyte layer.

[0068] The laminate can be produced by laminating a negative electrode, using a known method, on a solid electrolyte layer provided on a positive electrode as described above in such a manner that the negative electrode active material layer is in contact with the surface of the solid electrolyte layer.

[0069] In the all-solid-state lithium-ion battery having the above-mentioned configuration, since the positive electrode mixture according to one embodiment of the present invention is included, it is possible to provide an all-solid-state lithium-ion battery having a high energy density, in other words, a large capacity.

[0070] [Mobile object] One embodiment of the present invention provides a moving object that includes the above-described all-solid-state lithium-ion battery and is driven by the all-solid-state lithium-ion battery. Examples of mobile objects include automobiles, electric vehicles, hybrid electric vehicles, motorcycles, bicycles, personal mobility, airplanes, ships, robots (mobile robots), construction machinery, and agricultural machinery (tractors).

[0071] The moving body may be an airplane. In this specification, the airplane includes an "airplane that can be used for aviation with people on board" as defined in the Aviation Act, and an unmanned airplane powered by an all-solid-state lithium-ion battery. An unmanned airplane powered by an all-solid-state lithium-ion battery may be, for example, an unmanned airplane that can be remotely controlled, such as a drone or an unmanned helicopter for spraying pesticides.

[0072] In addition, the all-solid-state lithium ion battery according to this embodiment can have a large energy density per unit mass, and is therefore particularly suitable for use in aircraft.

[0073] (Overview of the aircraft) 7 shows a schematic example of a system configuration of the flying object 100. In this embodiment, the flying object 100 includes a storage battery 110, a power control circuit 120, one or more electric motors 130, one or more propellers 140, one or more sensors 150, and a control device 160. In this embodiment, the storage battery 110 has one or more storage cells 112. The storage cells 112 may be the above-mentioned all-solid-state lithium ion batteries.

[0074] In this embodiment, the flying object 100 flies using electrical energy stored in the storage battery 110. Examples of the flying object 100 include an airplane, an airship or a balloon, a helicopter, a drone, and the like.

[0075] In this embodiment, the storage battery 110 can receive electric energy from an external charging device (not shown) via the power control circuit 120 and store the electric energy in one or more storage cells 112. In addition, the storage battery 110 can supply the electric energy stored in the one or more storage cells 112 to the electric motor 130 via the power control circuit 120.

[0076] In this embodiment, the storage cell 112 can store electric energy (sometimes referred to as charging the storage cell 112). Also, the storage cell 112 can release the stored electric energy (sometimes referred to as discharging the storage cell 112). The storage cell 112 may be a secondary battery.

[0077] The power storage cell 112 may be an all-solid-state battery. The power storage cell 112 may be an all-solid-state secondary battery.

[0078] Examples of carrier ions in secondary batteries include lithium, sodium, potassium, magnesium, calcium, etc. Examples of secondary batteries include sodium ion secondary batteries, lithium ion secondary batteries, lithium metal secondary batteries, lithium air secondary batteries, lithium sulfur secondary batteries, magnesium ion secondary batteries, etc.

[0079] For example, a material that can store a large amount of charge per unit volume is often selected as an active material for a secondary battery mounted on a vehicle. On the other hand, in this embodiment, the storage cell 112 is mounted on the aircraft 100. Therefore, it is preferable that the active material used for the storage cell 112 is a material that can store a large amount of charge per unit mass.

[0080] The mass energy density of the storage cell 112 is preferably 350 [Wh / kg-storage cell] or more, more preferably 400 Wh / kg-storage cell] or more, more preferably 500 Wh / kg-storage cell] or more, even more preferably 600 Wh / kg-storage cell] or more, and even more preferably 700 Wh / g-storage cell] or more. This provides a storage cell that is particularly suitable for use as a power source for an aircraft.

[0081] The volumetric energy density of the storage cell 112 is 300 [Wh / m 3 - Storage cell] 1200 [Wh / m 3 - Storage cell] or less, 400 [Wh / m 3 - Storage cell] 1000 [Wh / m 3When the storage cell 112 is mounted on the aircraft 100 as part of the power source of the aircraft 100, the volumetric energy density of the storage cell 112 may be 600 [Wh / m 3 - Storage cell] or less, 800 [Wh / m 3 -storage cell] or less.

[0082] The energy storage cell 112 may have a mass energy density within the above numerical range and a volume energy density within the above numerical range. This allows the energy storage cell, which is relatively difficult to use as a power source for a vehicle, to be used as a power source for an aircraft.

[0083] In this embodiment, the power control circuit 120 controls the input and output of power of the storage battery 110. The power control circuit 120 may control the input and output of power of the storage battery 110 based on an instruction from the control device 160. The power control circuit 120 includes, for example, a plurality of switching elements that operate based on a control signal from the control device 160.

[0084] In this embodiment, the electric motor 130 receives electric energy from the storage battery 110 via the power control circuit 120. The electric motor 130 rotates the propeller 140 using the electric energy received from the storage battery 110. In this way, the electric motor 130 can generate propulsion force for the flying object 100 using the electric energy stored in the storage cell 112.

[0085] In this embodiment, the sensor 150 measures various physical quantities related to the position and attitude of the flying object 100. Examples of sensors for measuring various physical quantities related to the position and attitude of the flying object 100 include a GPS signal receiver, an acceleration sensor, an angular acceleration sensor, and a gyro sensor. The sensor 150 may measure various physical quantities related to the state of the storage battery 110. Examples of sensors for measuring various physical quantities related to the state of the storage battery 110 include a temperature sensor, a current sensor, and a voltage sensor.

[0086] In this embodiment, the control device 160 controls the flying object 100. The control device 160 may control the input and output of power to the storage battery 110 by controlling the power control circuit 120. For example, the control device 160 controls the output current, output voltage, input current, input voltage, etc. of the storage battery 110. This allows the control device 160 to control the position and attitude of the flying object 100. The control device 160 may control the position and attitude of the flying object 100 by controlling the power control circuit 120 based on the output from the sensor 150.

[0087] The storage battery 110 may be an example of a secondary battery. The power storage cell 112 may be an example of a secondary battery. The electric motor 130 may be an example of a propulsion force generating device. The secondary battery may be an example of a battery. EXAMPLES

[0088] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples.

[0089] [Example 1] (Preparation of composite positive electrode active material) The positive electrode active material is a ternary positive electrode active material, LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) was prepared. The surface of the positive electrode active material was coated with a lithium ion conductive oxide, LiNbO 3 The layer containing Li was formed using a rolling fluidized coating device. 6 P.S. 5 We prepared LiNbO 3 A layer containing the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) and solid electrolyte Li 6 P.S. 5The LiNbO2 composite positive electrode active material was prepared by mechanochemical treatment. 3 A layer containing the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) is referred to as the uncomposite positive electrode active material and is used as a comparative example.

[0090] (Preparation of electrode mixture) Lithium ion-polysulfide (LGPS) solid electrolyte, which is the raw material for the electrode mixture, is used. 10 GeP 2 S 12 The composite positive electrode active material or non-composite positive electrode active material, the LGPS-based solid electrolyte, and the conductive auxiliary were weighed out at the mixture ratio (mass%) shown in Table 1, and mixed by a table mill to prepare a positive electrode mixture.

[0091] [Table 1]

[0092] (Assembly of all-solid-state batteries) The obtained positive electrode mixture was used to assemble an all-solid-state battery. FIG. 4 is a diagram showing a schematic configuration of the all-solid-state battery. The negative electrode current collector was made of copper mesh, and the negative electrode was made of Li-In metal. Li as the solid electrolyte material for the separator 10 GeP 2 S 12 (LGPS) was used. The positive electrode was formed using the above-mentioned positive electrode mixture. The positive electrode current collector was made of aluminum mesh material and foil. These components were stacked to obtain an all-solid-state battery.

[0093] (Characteristics measurement of all-solid-state batteries) A charge / discharge test was performed on the obtained all-solid-state battery under the following conditions. Temperature: 60℃ Current value: 0.1 C Design capacity: 1.6 mAh / cm 2 Voltage: 1.9-3.6 V (vs. Li-In) Charge / discharge Mode:CCCV-CC

[0094] Figure 5 compares the initial discharge capacity of each all-solid-state battery. The vertical axis shows the discharge capacity (mAh / g), and the horizontal axis shows the mass ratio (mass%) of the LGPS-based solid electrolyte in the positive electrode mixture.

[0095] It was confirmed that when the LGPS-based solid electrolyte ratio in the positive electrode mixture was 30 mass% and 20 mass%, the discharge capacity was maintained at approximately the same level in both all-solid-state batteries. However, when the LGPS-based solid electrolyte ratio was reduced to 10 mass%, a significant capacity decrease was confirmed in the all-solid-state battery containing the non-composite positive electrode active material (comparative example), whereas no capacity decrease was confirmed in the all-solid-state battery containing the composite positive electrode active material (inventive example). Furthermore, it was confirmed that the discharge capacity did not decrease even when the solid electrolyte ratio was reduced to 5 mass%.

[0096] These results confirm that the composite positive electrode active material according to the present invention can improve the mass ratio of the positive electrode active material in the positive electrode mixture compared to the non-composite positive electrode active material (comparative example), and that the composite positive electrode active material is advantageous for achieving high energy density of all-solid-state batteries.

[0097] Figure 6 shows the charge / discharge capacity of the all-solid-state battery after 30 charge / discharge cycles. The all-solid-state battery in this example has a LGPS-based solid electrolyte ratio of 10 mass% in the positive electrode mixture, and the composite positive electrode active material contained in the positive electrode mixture is the positive electrode active material LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) and solid electrolyte Li 6 P.S. 5 It is a composite of 90:10 mass % Cl.

[0098] From the results in FIG. 6, the ratio of the 30th discharge capacity to the first discharge capacity (100%) was 94.0%. This corresponds to the charge / discharge capacity retention rate of the all-solid-state battery. Separately, the retention rate was confirmed for an all-solid-state battery under the same conditions except for using an uncomposite positive electrode active material. It was confirmed that the all-solid-state battery using the composite positive electrode active material according to the present invention had a retention rate almost equivalent to that of an all-solid-state battery (comparative example) using an uncomposite positive electrode active material.

[0099] [Example 2] (Preparation of composite positive electrode active material) The positive electrode active material is a ternary positive electrode active material, LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) was prepared. The positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) and solid electrolyte Li 6 P.S. 5 A composite positive electrode active material was prepared in the same manner as in Example 1, except that SiO2 and Cl were mixed in a mass % ratio of 97:3 to 90:10.

[0100] (Preparation of electrode mixture) Lithium ion-polysulfide (LGPS) solid electrolyte, which is the raw material for electrode mixtures, is used. 10 GeP 2 S 12 The composite positive electrode active material or non-composite positive electrode active material, the LGPS-based solid electrolyte, and the conductive auxiliary were weighed out in the mixture ratio (mass%) shown in Table 2, and mixed by a table mill to prepare a positive electrode mixture.

[0101] [Table 2]

[0102] An all-solid-state battery was assembled in the same manner as in Example 1, and the characteristics of the all-solid-state battery were measured.

[0103] As a comparative example, LiNbO 3 A layer containing the positive electrode active material LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) was prepared, and an all-solid-state battery was assembled using this, and its characteristics were measured. In the all-solid-state battery of this comparative example (without SE coating), the mass ratio of the LGPS-based solid electrolyte in the electrode mixture was about 10 mass% (same as that of the example).

[0104] Figure 8 compares the initial discharge capacity of each all-solid-state battery. The vertical axis is the potential (V vs InLi) and the horizontal axis is the discharge capacity (mAh / g).

[0105] The composite positive electrode active material according to the present invention had an improved discharge capacity compared to the comparative example (without SE coating). In other words, it was confirmed that the composite positive electrode active material according to the present invention is advantageous for increasing the energy density of all-solid-state batteries.

[0106] [Example 3] Cathode active material LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) and solid electrolyte Li 6 P.S. 5 Composite positive electrode active materials were prepared in the same manner as in Example 1, except that SiO2 and Cl were mixed in mass % ratios of 99:1, 97:3, and 95:5.

[0107] The electrode mixture was prepared, the all-solid-state battery was assembled, and the characteristics of the all-solid-state battery were measured in the same manner as in Example 1. In the electrode mixture, the mixture ratio (mass ratio) of the composite positive electrode active material, the LGPS-based solid electrolyte, and the conductive assistant was 85:10:5.

[0108] As a comparative example, LiNbO 3 A layer containing the positive electrode active material LiNi 0.6 Co 0.2Mn 0.2 O 2 (NCM622) was prepared, and an all-solid-state battery was assembled using this, and its characteristics were measured. In the all-solid-state battery of this comparative example (without SE coating), the mass ratio of the LGPS-based solid electrolyte in the electrode mixture was about 10 mass% (same as that of the example).

[0109] Figure 9 compares the initial discharge capacity of each all-solid-state battery. The vertical axis is potential (V vs InLi) and the horizontal axis is discharge capacity (mAh / g).

[0110] The composite positive electrode active material according to the present invention had an improved discharge capacity compared to the comparative example (without SE coating). Specifically, it was confirmed that when the mass ratio of the positive electrode active material to the solid electrolyte was 99:1 or more, that is, when the mass ratio of the solid electrolyte in the composite positive electrode active material was 1 mass% or more, a discharge capacity exceeding 150 mAh / g was exhibited. From these results, it was confirmed that the composite positive electrode active material according to the present invention is advantageous for increasing the energy density of all-solid-state batteries.

Claims

1. A composite positive electrode active material in which the surface of the positive electrode active material is coated with a solid electrolyte.

2. 2. The composite positive electrode active material according to claim 1, wherein 90% or more by area of ​​the surface of the positive electrode active material is covered with the solid electrolyte.

3. 2. The composite positive electrode active material according to claim 1, wherein a mass ratio of the positive electrode active material to the solid electrolyte is 99:1 to 80:

20.

4. 2. The composite positive electrode active material according to claim 1, wherein a mass ratio of the positive electrode active material to the solid electrolyte is 95:5 to 90:

10.

5. 2. The composite positive electrode active material according to claim 1, wherein the solid electrolyte is an LPS-X based solid electrolyte.

6. The LPS-X solid electrolyte is Li ６ P.S. ５ The composite positive electrode active material according to claim 5 , wherein the metal is Cl.

7. The positive electrode active material is lithium cobalt oxide LiCoO ２ , lithium nickel oxide LiNiO ２ , Lithium manganese oxide LiMn ２ O ４ , lithium iron phosphate LiFePO ４ , or lithium cobalt oxide partially substituted with nickel and manganese, Li(Ni-Co-Mn)O ２ The composite positive electrode active material of claim 1 .

8. The positive electrode active material is LiNi ０．６ Co ０．２ Mn ０．２ O ２ 2. The composite positive electrode active material of claim 1 comprising (NCM622).

9. The positive electrode active material is LiNi ０．８ Co ０．１ Mn ０．１ O ２ 2. The composite positive electrode active material of claim 1 comprising (NCM811).

10. 2. The composite positive electrode active material according to claim 1, wherein a layer containing a lithium ion conductive oxide is present between the positive electrode active material and the solid electrolyte.

11. The lithium ion conductive oxide is LiNbO ３ The composite positive electrode active material of claim 10 .

12. A positive electrode mixture comprising the composite positive electrode active material according to any one of claims 1 to 11, a LGPS-based solid electrolyte, and a conductive assistant.

13. The positive electrode mixture according to claim 12, wherein the mass ratio of the LGPS-based solid electrolyte is 30 mass% or less.

14. The positive electrode mixture according to claim 12, wherein the mass ratio of the LGPS-based solid electrolyte is less than 10 mass%.

15. The positive electrode mixture according to claim 12 , wherein the conductive assistant comprises vapor grown carbon fiber (VGCF).

16. 13. An all-solid-state lithium ion battery comprising: a positive electrode containing the positive electrode mixture according to claim 12; a negative electrode; and a solid electrolyte layer containing a sulfide-based compound sandwiched between the positive electrode and the negative electrode.

17. A moving object, the moving object being an airplane, comprising the all-solid-state lithium ion battery according to claim 16 and powered by the all-solid-state lithium ion battery.

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