Cathode layer

Abstract

To provide a cathode layer capable of reducing resistance of a battery.SOLUTION: There is provided a cathode layer including at least a cathode active material and a solid electrolyte. The cathode active material is cathode active material particles, an average particle diameter of the cathode active material particles is 2.5 μm or more and 4.5 μm or less, and a normalized interface length value A (μm-1) obtained by dividing a length (μm) of an interface between the cathode active material and the solid electrolyte confirmed from a SEM image of a cross section of the cathode layer by an area (μm2) of the cathode active material in the SEM image is 1.15 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode layer. [Background technology]

[0002] Various technologies have been proposed for batteries such as those disclosed in Patent Document 1. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2021 / 176759 Summary of the Invention [Problem to be solved by the invention]

[0004] Even if the area ratio of the solid electrolyte at a predetermined distance from the surface of the positive electrode active material particle is high in a cross-sectional image of the positive electrode layer, if the length of the contact interface between the positive electrode active material particle and the solid electrolyte particle in the positive electrode layer is short, the resistance of the battery is high.

[0005] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a positive electrode layer that can reduce the resistance of a battery. [Means for solving the problem]

[0006] That is, the present disclosure includes the following aspects. <1> A positive electrode layer including at least a positive electrode active material and a solid electrolyte, the positive electrode active material is positive electrode active material particles, the positive electrode active material particles have an average particle size of 2.5 μm or more and 4.5 μm or less, The length (μm) of the interface between the positive electrode active material and the solid electrolyte confirmed from the SEM image of the cross section of the positive electrode layer was defined as the area (μm 2 ) divided by the normalized interface length A (μm -1) is 1.15 or more.

[0007] <2> The average particle size of the positive electrode active material particles is 3.0 μm or more and 4.0 μm or less. <1> The positive electrode layer according to claim 1.

[0008] <3> The solid electrolyte is a sulfide solid electrolyte. <1> or <2> The positive electrode layer according to claim 1.

[0009] <4> The positive electrode active material is a lithium ion conductive compound-coated positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with a lithium ion conductive compound. <1> ~ <3> 10. The positive electrode layer according to any one of the above items.

[0010] <5> The aforementioned <1> ~ <4> 10. A solid-state battery having the positive electrode layer according to any one of claims 1 to 9. [Effects of the Invention]

[0011] The positive electrode layer of the present disclosure can reduce the resistance of the battery. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a graph showing the relationship between the normalized interface length value A and the normalized battery resistance. [Figure 2] FIG. 2 is a graph showing the relationship between the average particle size of the positive electrode active material particles, the electronic conductivity of the positive electrode layer, and the ionic conductivity of the positive electrode layer. [Figure 3] FIG. 3 is a graph showing the relationship between the average particle size of the positive electrode active material particles and the packing rate of the positive electrode layer. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of the positive electrode layer that do not characterize the present disclosure) can be understood as design matters for those skilled in the art based on prior art in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. In this disclosure, a fully charged battery means that the battery's State of Charge (SOC) is 100%. SOC indicates the ratio of the charge capacity to the fully charged capacity of the battery, and the fully charged capacity is SOC 100%. The SOC may be estimated from, for example, the open circuit voltage (OCV) of the battery. In the present disclosure, unless otherwise specified, the average particle size of particles is the median diameter (D50) value, which is the particle size at 50% of the cumulative value in the volume-based particle size distribution measured by laser diffraction / scattering particle size distribution measurement.

[0014] In the present disclosure, a positive electrode layer including at least a positive electrode active material and a solid electrolyte, the positive electrode active material is positive electrode active material particles, the positive electrode active material particles have an average particle size of 2.5 μm or more and 4.5 μm or less, The length (μm) of the interface between the positive electrode active material and the solid electrolyte confirmed from the SEM image of the cross section of the positive electrode layer was defined as the area (μm 2 ) divided by the normalized interface length A (μm -1 ) is 1.15 or more.

[0015] The length (μm) of the interface between the positive electrode active material and the solid electrolyte as confirmed from a SEM (scanning electron microscope) image of a cross section of the positive electrode layer of the present disclosure is expressed as the area (μm 2 ) divided by the normalized interface length A (μm -1 ) is 1.15 μm -1 It is sufficient if it is 1.39 μm or more. -1It may be 1.76 μm or more. -1 It may be the following: The normalized interface length value A may be controlled by at least one method selected from the group consisting of changing the average particle size of the positive electrode active material particles, changing the average particle size of the solid electrolyte particles, changing the volume fraction of the solid electrolyte in the positive electrode layer, changing the coverage of the solid electrolyte that covers the positive electrode active material or the lithium ion conductive compound-coated positive electrode active material, and changing the coating method of the solid electrolyte. In the present disclosure, the normalized interface length value A is 1.15 μm -1 In the present disclosure, by using a combination of positive electrode active material particles having a predetermined average particle size and a predetermined solid electrolyte, it is possible to obtain a positive electrode layer in which the contact area (interface length) between the positive electrode active material particles and the solid electrolyte is of a predetermined size.

[0016] The positive electrode layer contains at least a positive electrode active material and a solid electrolyte, and may contain a binder, a conductive material, and the like, as necessary.

[0017] The positive electrode layer of the present disclosure may have a solid electrolyte on at least a portion of the surface of the positive electrode active material, may have a solid electrolyte on the entire surface of the positive electrode active material, may have a solid electrolyte on at least a portion of the surface of the lithium ion conductive compound-coated positive electrode active material, or may have a solid electrolyte on the entire surface of the lithium ion conductive compound-coated positive electrode active material. The coverage of the solid electrolyte covering the positive electrode active material or the lithium ion conductive compound-coated positive electrode active material is not particularly limited as long as it satisfies the normalized interface length value A defined in the present disclosure. The coverage of the solid electrolyte is, for example, 70% or more, may be 90% or more, or may be 100%. The method for covering the solid electrolyte is not particularly limited, and a conventionally known method can be appropriately adopted.

[0018] The positive electrode active material may be, for example, an oxide active material. 0.8 Co 0.15 Al0.05 O2, LiCoO2, LiMnO2, LiNiO2, LiVO2, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiMn2O4, Li(Ni 0.5 Mn 1.5 )O4, LiFePO4, LiMnPO4, LiNiPO4, LiCuPO4, etc. The positive electrode active material is positive electrode active material particles. The average particle size of the positive electrode active material particles may be 2.5 μm or more and 4.5 μm or less, and may be 3.0 μm or more and 4.0 μm or less.

[0019] The positive electrode active material may be a lithium ion conductive compound coated positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with a lithium ion conductive compound. The lithium ion conductive compound may cover at least a part of the surface of the positive electrode active material, or may cover the entire surface of the positive electrode active material.

[0020] Examples of lithium ion conductive compounds include B2O3, Li2B4O7, LiBPO4, Li3PO4, LiPO3, and LiNbO3. The thickness of the coating of the lithium ion conductive compound is, for example, 0.1 nm or more, and may be 1 nm or more. On the other hand, the thickness of the lithium ion conductive compound is, for example, 100 nm or less, and may be 20 nm or less. The coverage of the lithium ion conductive compound coating the positive electrode active material is not particularly limited as long as it satisfies the normalized interface length value A defined in the present disclosure. The coverage of the lithium ion conductive compound coating the positive electrode active material is, for example, 70% or more, or may be 90% or more, or even 100%. The method for coating the lithium ion conductive compound is not particularly limited, and a conventionally known method can be appropriately adopted.

[0021] Examples of the solid electrolyte include sulfide solid electrolytes and oxide solid electrolytes. Examples of sulfide solid electrolytes include solid electrolytes containing Li, M (where M is at least one of P, As, Sb, Si, Ge, Sn, B, Al, Ga, and In), and S. The sulfide solid electrolyte may further contain at least one of O and a halogen element. Examples of sulfide solid electrolytes include Li2S-P2S5, Li2S-SiS2, LiX-Li2S-SiS2, LiX-Li2S-P2S5, LiX-Li2O-Li2S-P2S5, LiX-Li2S-P2O5, LiX-Li3PO4-P2S5, and Li3PS4. The term "Li2S-P2S5" above refers to a material obtained using a raw material composition containing Li2S and P2S5, and the same applies to other terms. Furthermore, the "X" in the LiX represents a halogen element. Examples of halogen elements include F, Cl, Br, and I. The raw material composition containing LiX may contain one or more types of LiX. When two or more types of LiX are contained, the mixing ratio of the two or more types is not particularly limited. The molar ratio of each element in the sulfide solid electrolyte can be controlled by adjusting the content of each element in the raw materials. The molar ratio and composition of each element in the sulfide solid electrolyte can be measured, for example, by ICP atomic emission spectrometry.

[0022] The sulfide solid electrolyte may be a sulfide glass, a crystallized sulfide glass (glass ceramics), or a crystalline material obtained by a solid-phase reaction treatment of a raw material composition. The crystalline state of the sulfide solid electrolyte can be confirmed, for example, by subjecting the sulfide solid electrolyte to powder X-ray diffraction measurement using CuKα radiation.

[0023] Sulfide glass can be obtained by subjecting a raw material composition (e.g., a mixture of Li2S and P2S5) to amorphous processing, such as mechanical milling.

[0024] Glass ceramics can be obtained, for example, by heat treating sulfide glass. The heat treatment temperature may be any temperature higher than the crystallization temperature (Tc) of the sulfide glass observed by thermal analysis, and is usually 195° C. or higher. On the other hand, there is no particular upper limit to the heat treatment temperature. The crystallization temperature (Tc) of sulfide glass can be measured by differential thermal analysis (DTA). The heat treatment time is not particularly limited as long as it is a time that allows the desired crystallinity of the glass ceramic to be obtained, but is, for example, in the range of 1 minute to 24 hours, and particularly in the range of 1 minute to 10 hours. The heat treatment method is not particularly limited, but may be, for example, a method using a firing furnace.

[0025] Examples of oxide solid electrolytes include substances having a garnet-type crystal structure containing Li, La, A (A is at least one of Zr, Nb, Ta, and Al), and O. Examples of oxide solid electrolytes include Li2O-B2O3-P2O5, Li2O-SiO2, Li2O-B2O3, Li 1.3 Al 0.3 Ti 0.7 (PO4)3, Li5La3Ta2O 12 , Li7La3Zr2O 12 , Li6BaLa2Ta2O 12 , Li 3.6 Si 0.6 P 0.4 O4, Li4SiO4, Li3PO4, and Li 3+x PO 4-x N x (1≦x≦3) etc. may also be used.

[0026] The solid electrolyte may be in the form of particles from the viewpoint of ease of handling. Furthermore, the average particle size (D50) of the solid electrolyte particles is not particularly limited, but the lower limit may be 0.5 μm or more, or 0.7 μm or more, and the upper limit may be 3.5 μm or less, or 1.0 μm or less.

[0027] Examples of binders include acrylonitrile butadiene rubber (ABR), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and styrene-butadiene rubber (SBR).

[0028] Examples of conductive materials include carbon materials, metal particles, conductive polymers, etc. Examples of carbon materials include particulate carbon materials such as acetylene black (AB) and ketjen black (KB), and fibrous carbon materials such as carbon fibers, carbon nanotubes (CNT), and carbon nanofibers (CNF).

[0029] The content of the positive electrode active material in the positive electrode layer is not particularly limited, and may be 50.00 to 99.00 mass %, or may be 72.20 mass % or more, or may be 82.04 mass % or less. The content of the solid electrolyte in the positive electrode layer is not particularly limited, and may be 1.00 to 30.00 mass %, or may be 15.65 mass % or more, or may be 24.3 mass % or less. The porosity of the positive electrode layer may be 2 to 10%, that is, the packing rate of the positive electrode layer may be 90 to 98%. The proportion of the positive electrode active material particles in the filled portion of the positive electrode layer may be 52 to 74%.

[0030] A battery of the present disclosure comprises a positive electrode layer of the present disclosure, typically comprising a positive electrode including a positive electrode layer of the present disclosure, an electrolyte layer, and a negative electrode.

[0031] The positive electrode of the present disclosure includes a positive electrode current collector and a positive electrode layer of the present disclosure formed by drying a positive electrode slurry applied to at least one surface of the positive electrode current collector. The positive electrode slurry may contain the positive electrode active material, the solid electrolyte, the conductive material, the binder, a thickener, a solvent, and the like. The method for applying the positive electrode slurry is not particularly limited, and any conventionally known method can be used.

[0032] Examples of thickeners include polysaccharides such as carboxymethyl cellulose (CMC) and methyl cellulose.

[0033] Examples of the solvent include an aqueous solvent and an organic solvent. The aqueous solvent refers to water or a mixed solvent containing water and a polar organic solvent. For example, an appropriate solvent can be selected depending on the types of the positive electrode active material, binder, etc. As the aqueous solvent, water is preferably used because of its ease of handling. Examples of polar organic solvents that can be used in the mixed solvent include alcohols such as methanol, ethanol, and isopropyl alcohol, ketones such as acetone, and ethers such as tetrahydrofuran. Examples of the organic solvent include 1,2,3,4-tetrahydronaphthalene, n-heptane, butyl butyrate, diisobutyl ketone, and N-methyl-2-pyrrolidone (NMP).

[0034] Examples of materials for the positive electrode current collector include metals such as aluminum, copper, SUS, and nickel. The thickness of the positive electrode current collector is, for example, 0.1 μm or more and 100 μm or less. The positive electrode current collector may be in the form of a sheet or the like.

[0035] The electrolyte layer may use an electrolytic solution or a solid electrolyte as the electrolyte. The electrolyte may be any known electrolyte used in lithium ion secondary batteries. The electrolyte layer may be a solid electrolyte layer. The solid electrolyte layer includes at least a solid electrolyte. As the solid electrolyte contained in the solid electrolyte layer, any known solid electrolyte that can be used in solid-state batteries can be used as appropriate, including the above-mentioned oxide solid electrolytes, sulfide solid electrolytes, etc. In order to prevent the positive electrode layer and the negative electrode layer from peeling off from the solid electrolyte layer, a relatively soft sulfide solid electrolyte may be used as the solid electrolyte.

[0036] The solid electrolyte may be used alone or in combination of two or more. When two or more solid electrolytes are used, the two or more solid electrolytes may be mixed, or two or more solid electrolyte layers may be formed to form a multilayer structure. The proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited, but is, for example, 50% by mass or more, may be in the range of 60% by mass or more and 100% by mass or less, may be in the range of 70% by mass or more and 100% by mass or less, or may be 100% by mass.

[0037] The solid electrolyte layer may contain a binder from the viewpoint of exhibiting plasticity, etc. Examples of such binders include the materials exemplified as the binders used in the positive electrode layer described above. However, in order to facilitate achieving high output, the binder content in the solid electrolyte layer may be 5 mass % or less from the viewpoint of preventing excessive aggregation of the solid electrolyte and enabling the formation of a solid electrolyte layer having a uniformly dispersed solid electrolyte.

[0038] The thickness of the solid electrolyte layer is not particularly limited, but is usually 0.1 μm or more and 1 mm or less.

[0039] The negative electrode includes a negative electrode layer and a negative electrode current collector. The negative electrode layer contains a negative electrode active material, and optionally contains a conductive material, a binder, and the like. Examples of the negative electrode active material include carbon active material, oxide active material, and metal active material. Examples of the carbon active material include mesocarbon microbeads (MCMB), highly oriented graphite (HOPG), hard carbon, and soft carbon. Examples of the oxide active material include Nb2O5, Li4Ti5O 12 and SiO. Examples of the metal active material include In, Al, Si, and Sn. Examples of the conductive material and binder include the materials exemplified as the conductive material and binder used in the positive electrode layer described above.

[0040] The material of the negative electrode current collector may be a material that does not alloy with Li, such as SUS, copper, or nickel. The negative electrode current collector may be in the form of, for example, a foil or a plate. The shape of the negative electrode current collector in plan view is not particularly limited, but may be, for example, a circle, an ellipse, a rectangle, or any polygonal shape. The thickness of the negative electrode current collector varies depending on the shape, but may be, for example, in the range of 1 μm to 50 μm, or in the range of 5 μm to 20 μm.

[0041] The type of battery is not particularly limited, but examples include lithium ion batteries. The battery may be a primary battery or a secondary battery. The battery may be a liquid battery using an electrolytic solution as an electrolyte, or may be a solid battery. In the present disclosure, a solid-state battery refers to a battery containing a solid electrolyte. The solid-state battery may be a semi-solid-state battery that contains a solid electrolyte and a liquid-based material, or an all-solid-state battery that does not contain a liquid-based material. Examples of uses of the battery include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the battery may be used as a driving power source for hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), or electric vehicles (BEVs). The battery may also be used as a power source for mobile objects other than vehicles (for example, trains, ships, and aircraft), and as a power source for electrical appliances such as information processing devices. [Example]

[0042] (Examples 1 to 3, Comparative Examples 1 to 3) [Positive electrode production] LiNi as the positive electrode active material 0.8 Co 0.15 Al 0.05 The surface of the positive electrode active material particles was coated with a lithium ion conductive compound. Crystalline sulfide solid electrolyte particles were used as the solid electrolyte. 1,2,3,4-tetrahydronaphthalene was used as the solvent. SBR was used as the binder. VGCF was used as the conductive material. The positive electrode active material, solid electrolyte, binder, and conductive material were mixed in a solvent so that the mass composition ratio of the positive electrode active material, solid electrolyte, binder, and conductive material was as follows, to prepare a positive electrode slurry. Mass composition ratio: positive electrode active material: solid electrolyte: binder: conductive material = 82.04:15.65:0.34:1.97 The prepared positive electrode slurry was applied to a positive electrode current collector, and then dried to obtain a positive electrode having a positive electrode layer on the positive electrode current collector.

[0043] [Solid electrolyte layer fabrication] The solvent used was n-heptane and butyl butyrate. The solid electrolyte was a sulfide glass solid electrolyte. The binder was ABR (acrylonitrile butadiene rubber). The solid electrolyte and binder were mixed in the solvent to prepare a solid electrolyte slurry. The prepared solid electrolyte slurry was coated on a release film, and then dried. The release film was peeled off from the dried solid electrolyte-coated foil to obtain a solid electrolyte layer.

[0044] [Negative electrode production] Diisobutyl ketone was used as the solvent. Li4Ti5O was used as the negative electrode active material. 12 A sulfide glass solid electrolyte was used as the solid electrolyte. SBR was used as the binder. Carbon nanotubes were used as the conductive material. The negative electrode active material, solid electrolyte, binder, and conductive material were mixed in a solvent in the following mass composition ratio to prepare a negative electrode slurry. Mass composition ratio: negative electrode active material: solid electrolyte: binder: conductive material = 72.2: 24.3: 1.8: 2.4 The prepared negative electrode slurry was applied to a negative electrode current collector, and then dried to obtain a negative electrode having a negative electrode layer on the negative electrode current collector.

[0045] [Cell production] The fabricated positive electrode, the fabricated solid electrolyte layer, and the fabricated negative electrode were arranged in this order to obtain a laminate. A positive electrode tab was attached to the positive electrode, and a negative electrode tab was attached to the negative electrode. The laminate was then housed in a laminate film, and the laminate film was evacuated to seal the laminate, producing a laminate cell (sometimes referred to as a cell). The cell restraint pressure was 5 MPa relative to the electrode area.

[0046] [Method for calculating the interface length between the positive electrode active material and the solid electrolyte in the positive electrode layer] First, a binary image of the positive electrode active material and solid electrolyte was created from the cross-sectional SEM image of the positive electrode layer. The binary image was created using image analysis software. In this case, "ImageJ" was used. Next, the area of ​​the positive electrode active material in the binarized image and the contact interface length between the positive electrode active material and the solid electrolyte were calculated using image analysis software. This calculation was performed using MATLAB (registered trademark). These values ​​were used to calculate the normalized interface length value A using the following formula. The results are shown in Table 1. Normalized interface length value A [μm -1 ] = (contact interface length between the positive electrode active material and the solid electrolyte in the analysis image [μm]) / (area of ​​the positive electrode active material in the analysis image [μm 2 ]) The cells of Examples 1 to 3 and Comparative Examples 1 to 3 have the same configuration, except that the average particle size of the positive electrode active material particles in the positive electrode layer, the average particle size of the solid electrolyte particles, and the normalized interface length value A between the positive electrode active material and the solid electrolyte are the values ​​shown in Table 1. The normalized interface length value A was controlled by at least one of changing the average particle size of the particles of the positive electrode active material contained in the positive electrode layer and changing the average particle size of the particles of the solid electrolyte. A positive electrode layer with a larger normalized interface length value A has a larger area of ​​the positive electrode active material capable of lithium ion insertion / extraction reaction than a positive electrode layer with a smaller normalized interface length value A, which leads to a reduction in battery resistance.

[0047] [Charge / discharge evaluation] The laminated cell was subjected to charge / discharge evaluation. The tests performed were as follows: Activation, capacity measurement, and battery resistance measurement were performed at 25°C. Activation: CCCV charge 0.333C-0.01C cutoff voltage upper limit 2.80V → CCCV discharge 0.333C-0.01C cutoff voltage lower limit 1.5V ·Capacitance measurement: The program is the same as activation above. Battery resistance measurement: The voltage change ΔV value when a current of 2.5C rate was applied at SOC 20% was read, and the battery resistance was calculated using Ohm's law V=IR. Durability test: A cycle test was carried out at a voltage range of 1.50 to 2.80 V, at 60°C, and at a rate of 1C. After the durability test, the capacity was measured again, and then the battery resistance after the durability test was measured. The normalized battery resistance is shown in Table 1. The normalized battery resistance is the battery resistance value of Examples 1 to 3 and Comparative Examples 2 and 3 when the battery resistance of Comparative Example 1 is set to 1.

[0048] [Table 1]

[0049] FIG. 1 is a graph showing the relationship between the normalized interface length value A and the normalized battery resistance. As shown in FIG. 1 and Table 1, in the present disclosure, the resistance of the battery can be reduced by setting the normalized interface length value A to 1.15 or more.

[0050] [Electron conductivity measurement of the positive electrode layer] The electronic conductivity of each positive electrode layer was measured by a direct current polarization method for each positive electrode layer in Examples 1 to 3. The results are shown in Table 2.

[0051] [Measurement of ionic conductivity in the positive electrode layer] A five-layer symmetrical cell consisting of a Li metal negative electrode layer / solid electrolyte layer / positive electrode layer / solid electrolyte layer / Li metal negative electrode layer was prepared, and the ionic conductivity of each positive electrode layer of Examples 1 to 3 was measured by DC polarization for the five-layer symmetrical cell. The results are shown in Table 2.

[0052] [Measurement of filling rate of positive electrode layer] The density of each positive electrode layer at a packing rate of 100% was calculated from the volume and density of each raw material contained in each positive electrode layer in Examples 1 to 3. The bulk density of each positive electrode layer was calculated by measuring the volume and mass of each positive electrode layer. The packing rate of each positive electrode layer was calculated from the density and bulk density of each positive electrode layer at a packing rate of 100%. The results are shown in Table 2.

[0053] [Table 2]

[0054] FIG. 2 is a graph showing the relationship between the average particle size of the positive electrode active material particles, the electronic conductivity of the positive electrode layer, and the ionic conductivity of the positive electrode layer. FIG. 3 is a graph showing the relationship between the average particle size of the positive electrode active material particles and the packing rate of the positive electrode layer. As shown in FIGS. 2 and 3 and Table 2, the electrochemical properties (electronic conductivity and ionic conductivity) and mechanical properties (filling rate of the positive electrode layer) of the positive electrode layer do not change significantly depending on the average particle size of the positive electrode active material particles.

Claims

1. A positive electrode layer including at least a positive electrode active material and a solid electrolyte, the positive electrode active material is positive electrode active material particles, the positive electrode active material particles have an average particle size of 2.5 μm or more and 4.5 μm or less; The length (μm) of the interface between the positive electrode active material and the solid electrolyte confirmed from the SEM image of the cross section of the positive electrode layer was defined as the area (μm ２ Normalized interface length value A (μm －１ ) is 1.15 or more.

2. The positive electrode layer according to claim 1 , wherein the positive electrode active material particles have an average particle size of 3.0 μm or more and 4.0 μm or less.

3. The positive electrode layer according to claim 1 , wherein the solid electrolyte is a sulfide solid electrolyte.

4. The positive electrode layer according to claim 1 , wherein the positive electrode active material is a lithium ion conductive compound-coated positive electrode active material in which at least a portion of the surface of the positive electrode active material is coated with a lithium ion conductive compound.

5. A solid-state battery comprising the positive electrode layer according to claim 1.

Images