Method for producing positive electrode active material

Abstract

To reduce a rate of increase in resistance.SOLUTION: A method for manufacturing a cathode active material includes the following (a) and (b): (a) a slurry is prepared by dispersing active material particles in a coating liquid, and (b) the slurry is dried by a spray drying method, thereby manufacturing the cathode active material. The active material particles include an O2 type layered oxide. The coating liquid includes a solute and a solvent. The solute includes at least one selected from a group consisting of Nb, P, and B. The slurry has solid content concentration of more than 42% and 51% or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a positive electrode active material, a positive electrode active material, and an all-solid-state battery. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2022-097885 (Patent Document 1) discloses a positive electrode active material having an O2 type structure. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-097885 Summary of the Invention [Problem to be solved by the invention]

[0004] An all-solid-state battery includes a positive electrode active material and a sulfide solid electrolyte. The sulfide solid electrolyte can form an ion conduction path within the electrode. Direct contact of the sulfide solid electrolyte with the positive electrode active material can accelerate degradation of the sulfide solid electrolyte. This is thought to be due to the high potential of the positive electrode active material. Accelerated degradation of the sulfide solid electrolyte can increase the rate of resistance increase after endurance (e.g., after high-temperature storage).

[0005] Applying a coating film to a positive electrode active material (active material particles) has been investigated. By interposing a coating film between the sulfide solid electrolyte and the positive electrode active material, deterioration of the sulfide solid electrolyte can be reduced. The coating film can be formed, for example, by a spray-drying method.

[0006] Traditionally, layered oxides with an O3-type structure (hereinafter also referred to as "O3-type layered oxides") have been widely used as positive electrode active materials. Recently, layered oxides with an O2-type structure (hereinafter also referred to as "O2-type layered oxides") have also been investigated. O2-type layered oxides are expected to have high capacity.

[0007] When O2-type layered oxides are applied to all-solid-state batteries, it has been found that the coating film thickness should be 4 nm or more to sufficiently reduce the degradation of the sulfide solid electrolyte. Generally, the thicker the coating film, the higher the coverage rate. However, on the surface of O2-type layered oxides, it tends to be difficult to increase the coverage rate even if the coating film is made thicker. Insufficient coverage may result in an increased rate of resistance increase.

[0008] The present disclosure aims to reduce the rate of increase in resistance. [Means for solving the problem]

[0009] The technical configuration and effects of the present disclosure will be described below. However, the mechanism of action in this specification includes speculation. The mechanism of action does not limit the technical scope of the present disclosure.

[0010] 1. A method for producing a positive electrode active material includes the following steps (a) and (b): (a) A slurry is prepared by dispersing active material particles in a coating liquid. (b) The slurry is dried by a spray drying method to produce a positive electrode active material. The active material particles include an O2-type layered oxide. The coating liquid includes a solute and a solvent. The solute includes at least one element selected from the group consisting of Nb, P, and B. The slurry has a solids concentration of more than 42% and not more than 51%.

[0011] In the spray drying method, a slurry is sprayed to form droplets of the slurry. The droplets contain a coating liquid and active material particles. The coating liquid is a precursor of a coating film. When the droplets are dried, a coating film can be deposited on the surface of the active material particles. Typically, in the spray drying method, the solids concentration of the slurry is adjusted to be high. This is because a high solids concentration is advantageous for drying. Conventionally, the solids concentration of the slurry can be, for example, 60% or more.

[0012] In the method for producing a positive electrode active material described in "1" above, the solid content of the slurry is particularly reduced. That is, the solid content is 51% or less. Although the details of the mechanism are unknown, when the solid content of the slurry is 51% or less, a thick coating film with a high coverage tends to be deposited on the surface of the O2-type layered oxide (active material particles). However, when the solid content is 42% or less, both the thickness and coverage of the coating film tend to decrease.

[0013] 2. In the method for producing a positive electrode active material described in the above item "1," the coating liquid may further contain a surfactant. The surfactant may include, for example, at least one selected from the group consisting of polyether-modified silicone and polyethylene glycol alkyl ether.

[0014] By including a surfactant in the coating liquid, an improvement in coverage is expected.

[0015] 3. The positive electrode active material includes active material particles and a coating film. The active material particles include an O2-type layered oxide. The coating film covers at least a portion of the surface of the active material particles. The coating film includes at least one element selected from the group consisting of Nb, P, and B. The coating film has a thickness of 4 nm or more. The coating film covers 80% or more of the surface of the active material particles. The coverage is measured by X-ray photoelectron spectroscopy.

[0016] For example, according to the method for producing a positive electrode active material described in "1" or "2" above, a coating film having a thickness of 4 nm or more and a coverage of 80% or more can be realized on the surface of the O2-type layered oxide.

[0017] 4. The positive electrode active material described in the above item "3" may have, for example, a D10 of 3 μm or less in the volume-based particle size distribution.

[0018] During spray drying, granulation (particle aggregation) of the active material particles can occur. Granulation can inhibit an increase in the coverage rate. If the D10 after spray drying is 3 μm or less, granulation may have been slight.

[0019] 5. The positive electrode active material according to the above item "3" or "4" may have a D90 of 15 μm or less in the volume-based particle size distribution.

[0020] When the D90 after spray drying was 15 μm or less, there was a possibility that granulation was slight.

[0021] 6. An all-solid-state battery includes the positive electrode active material according to any one of the above items "3" to "5" and a sulfide solid electrolyte.

[0022] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure. The present embodiment and the example are illustrative in all respects. The present embodiment and the example are non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is originally intended that any configuration may be extracted from the present embodiment and the example and that they may be arbitrarily combined. [Brief explanation of the drawings]

[0023] [Figure 1] FIG. 1 is a schematic flowchart of a method for producing a positive electrode active material in this embodiment. [Figure 2] FIG. 2 is a conceptual diagram showing the positive electrode active material in this embodiment. [Figure 3] FIG. 3 is a conceptual diagram showing the all-solid-state battery according to this embodiment. [Figure 4] FIG. 4 is a table showing the details of the experiment. [Figure 5] FIG. 5 is a graph showing the relationship between the coverage and the resistance increase rate. [Figure 6]FIG. 6 is a graph showing the relationship between D10 and the rate of increase in resistance. [Figure 7] FIG. 7 is a graph showing the relationship between D90 and the rate of increase in resistance. DETAILED DESCRIPTION OF THE INVENTION

[0024] <<Terms and definitions, etc.>> Some of the terms used in this specification are explained below. Terms not explained here may be defined and explained each time they are used in this specification.

[0025] The terms "comprise," "include," "have," and variations thereof (e.g., "consisting of") are open-ended. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even closed-ended terms do not exclude additional elements that are normally incidental impurities or unrelated to the disclosed technology. The term "consisting essentially of..." is semi-closed. Semi-closed terms allow for the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology.

[0026] Expressions such as "may" and "may" are used in the permissive sense, meaning "to have the possibility," rather than in the obligatory sense, meaning "to have to."

[0027] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0028] "At least one of A and B" includes "A or B" as well as "A and B." "At least one of A and B" can also be written as "A and / or B."

[0029] Elements expressed in the singular include the plural unless otherwise specified. For example, "particle" includes not only "one particle" but also "multiple particles (particle group)" and "aggregates of particles (powder, powder)."

[0030] Geometric terms (such as "parallel," "perpendicular," and the like) should not be interpreted in a strict sense. For example, "parallel" may deviate slightly from the strict meaning of "parallel." Geometric terms may include, for example, tolerances, errors, and the like in design, work, and manufacturing. The dimensional relationships in each drawing may not match the actual dimensional relationships. To aid the reader's understanding, the dimensional relationships (length, width, thickness, and the like) in each drawing may be changed. Furthermore, some components may be omitted.

[0031] Numerical ranges such as "m to n%" include the upper and lower limits unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." "Equal to or more" and "equal to or less" are represented by an inequality sign "≦." "More than" and "less than" are represented by an inequality sign "<" without an equality sign. A numerical value arbitrarily selected from within the numerical range may be used as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described elsewhere in this specification, in a table, a figure, or the like.

[0032] All numerical values ​​are modified by the term "about." The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximate values ​​that may vary depending on the application of the disclosed technology. All numerical values ​​may be expressed with significant figures. Unless otherwise specified, measured values ​​may be average values ​​of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, the more reliable the average value is expected to be. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors, such as those associated with the detection limits of the measuring device.

[0033] The stoichiometric composition formula shows a representative example of a compound. The compound may have a non-stoichiometric composition. For example, "Al2O3" is not limited to a compound having a substance ratio (molar ratio) of "Al / O=2 / 3". Unless otherwise specified, the molar ratio of Al and O is arbitrary. Furthermore, for example, the compound may be doped with a trace element. A portion of Al and O may be substituted with another element.

[0034] The term "derivative" refers to a compound in which a part of a parent compound has been modified by at least one method selected from the group consisting of introduction of a substituent, substitution of an atom, oxidation, reduction, and other chemical reactions. The modification may be at one or more locations. The "substituent" may include at least one selected from the group consisting of, for example, alkyl groups, alkenyl groups, alkynyl groups, cycloalkyl groups, unsaturated cycloalkyl groups, aromatic groups, heterocyclic groups, halogen atoms (such as F, Cl, Br, and I), OH groups, SH groups, CN groups, SCN groups, OCN groups, nitro groups, alkoxy groups, unsaturated alkoxy groups, amino groups, alkylamino groups, dialkylamino groups, aryloxy groups, acyl groups, alkoxycarbonyl groups, acyloxy groups, aryloxycarbonyl groups, acylamino groups, alkoxycarbonylamino groups, aryloxycarbonylamino groups, sulfonylamino groups, sulfamoyl groups, carbamoyl groups, alkylthio groups, arylthio groups, sulfonyl groups, sulfinyl groups, ureido groups, phosphoric acid amide groups, sulfo groups, carboxy groups, hydroxamic acid groups, sulfino groups, hydrazino groups, imino groups, and silyl groups. These substituents may be further substituted. When there are two or more substituents, the substituents may be the same or different. Multiple substituents may be bonded to each other to form a ring. Derivatives of polymer compounds (resin materials) may also be called "modified products."

[0035] The "copolymer" includes at least one selected from the group consisting of unspecified type, statistical type, random type, alternating type, periodic type, block type, and graft type.

[0036] The "solids concentration" of the slurry to be spray-dried indicates the total mass fraction of the components other than the solvent.

[0037] "D10" indicates the particle size at which the cumulative total reaches 10% in the volume-based particle size distribution (cumulative distribution). Similarly, "D50" indicates the particle size at which the cumulative total reaches 50%. "D90" indicates the particle size at which the cumulative total reaches 90%. Particle size distribution can be measured by laser diffraction. For example, particle size distribution can be measured using a Microtrac-Bell "Product Name: Aerotrac II" (or an equivalent product).

[0038] "O2-type layered oxide" refers to a layered oxide having an O2-type structure. An "O2-type structure" is a type of layered crystal structure. In an O2-type structure, two types of oxide layers (MeO2 layers) with different oxygen positions exist in the unit cell. The MeO2 layer contains a metal (Me) and oxygen (O). In the O2-type structure, Li occupies an octahedral site. The "O" in the O2-type comes from octahedral. Whether an object has an O2-type structure can be determined by X-ray diffraction (XRD) spectroscopy. If one of the peaks assigned to the O2-type structure shows the highest diffraction intensity in the XRD spectrum of the object, the object is considered to have an O2-type structure. CuKα radiation can be used in the XRD measurement.

[0039] The "coverage" is measured by X-ray photoelectron spectroscopy (XPS). For example, an XPS device manufactured by ULVAC-PHI, Inc., "Product Name: PHI X-tool" (or equivalent) may be used. The positive electrode active material (powder) is placed in the XPS device. Narrow scan analysis is performed with a pass energy of 224 eV. The measurement data is processed using analysis software. For example, analysis software manufactured by ULVAC-PHI, Inc., "Product Name: MultiPak" (or equivalent) may be used. By analyzing the XPS spectrum, the ratio of each element (element concentration) can be determined from the peak areas of Li1s, C1s, O1s, B1s, P2p, Me2p3, etc. The coverage is calculated using the following formula (1-1). θ=X / (X+Me)×100 …(1-1) In the above formula (1-1), θ represents the coverage (%). X represents the ratio of elements contained in the coating film (excluding Li and O). X includes at least one element selected from the group consisting of Nb, P, and B. Me represents the ratio of elements contained in the active material particles (excluding Li and O). Me may include, for example, at least one element selected from the group consisting of Ni, Co, Mn, and Al. For example, when the coating film contains B and P and the active material particles contain Ni, Co and Mn, the right side of the above formula (1-1) can be modified to "(P+B) / (P+B+Ni+Co+Mn)".

[0040] The "thickness of the coating film" is calculated by the following formula (1-2). t=W / A …(1-2) t: coating thickness W: Deposition volume of coating film A: BET specific surface area of ​​the positive electrode active material

[0041] The dimension of the BET specific surface area is [length] 2 ×[mass] -1The BET specific surface area is measured by the gas adsorption method (BET single point method). The deposition volume of the coating film is a value per unit mass of the positive electrode active material. The dimension of the deposition volume of the coating film is [length] 3 ×[mass] -1 For example, the mass concentration of the substance derived from the coating film is measured by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy). From the density of the substance, the volume of the substance per unit mass of the positive electrode active material (i.e., the deposition volume) can be calculated.

[0042] <<Method of manufacturing positive electrode active material>> FIG. 1 is a schematic flowchart of a method for producing a positive electrode active material according to this embodiment. Hereinafter, the "method for producing a positive electrode active material according to this embodiment" may be abbreviated as "this production method." This production method includes "(a) preparation of a slurry" and "(b) spray drying." This production method may further include, for example, "(c) heat treatment."

[0043] (a) Preparation of slurry The manufacturing method includes preparing a slurry by dispersing active material particles in a coating liquid. The slurry can be prepared using any dispersing device. However, the solids concentration of the slurry is greater than 42% and less than or equal to 51%. By having the solids concentration of the slurry greater than 42% and less than or equal to 51%, a desired coating film can be formed. The solids concentration of the slurry may be, for example, 43% or more, 45% or more, 47% or more, or 49% or more. The solids concentration of the slurry may be, for example, 49% or less, 47% or less, 45% or less, or 43% or less.

[0044] (active material particles) The active material particles may have a D50 of, for example, 3 to 10 μm. The active material particles contain an O2-type layered oxide. The O2-type layered oxide can be generated, for example, by ion exchange. That is, a P2-type layered oxide containing Na ions is prepared. The Na ions in the P2-type layered oxide are exchanged with Li ions. By exchanging Na ions with Li ions, the P2-type structure can transition to a more stable O2-type structure. The O2-type layered oxide contains Li, metal (Me), and oxygen (O). The O2-type layered oxide may have a composition represented by, for example, the following formula (1-3). Li a Mn x Ni y Co z Me (1-x-y-z) O2…(1-3) In the above formula (1-3), for example, the relationships of 0≦x≦1, 0≦y≦1, 0≦z≦1, and 0<x + y + z≦1 may be satisfied. For example, the relationship of 0.5≦a≦1 may be satisfied. Me may be at least one selected from the group consisting of, for example, Al, Fe, Mg, Ca, Ti, Cr, Cu, Zn, Nb, and Mo.

[0045] In the above formula (1-3), for example, the relationships of y<x, z<x, y<z, and 0.5≦x≦1 may be satisfied.

[0046] The O2-type layered oxide may consist of an O2-type structure. That is, the O2-type layered oxide may be a single-phase material. The O2-type layered oxide may partially contain an O3-type structure. In the "O3-type structure", there are three types of MeO2 layers with different oxygen positions in the unit cell. Li occupies an octahedral site. For example, the following relationship of formula (1-4) may be satisfied. O3 003 / O2 002 ≦0.3 …(1-4) O3 003 : The intensity of the peak derived from the 003 plane of the O3-type structure in the XRD spectrum O2 002 : The intensity of the peak derived from the 002 plane of the O2-type structure in the XRD spectrum

[0047] In the above formula (1-4), "O3 003 / O2 002 " may be, for example, 0.2 or less, or 0.1 or less.

[0048] The O2-type layered oxide may partially contain a P2-type structure. In the "P2-type structure," two types of MeO2 layers with different oxygen positions exist in the unit cell. Li occupies a triangular prismatic site. The "P" in the P2-type structure comes from prismatic. For example, the relationship of the following formula (1-5) may be satisfied. P2 002 / O2 002 ≦0.3 …(1-5) P2 002 : Intensity of the peak originating from the 002 plane of the P2 type structure in the XRD spectrum O2 002 : Intensity of the peak originating from the 002 plane of the O2 type structure in the XRD spectrum

[0049] In the above formula (1-5), "P2 002 / O2 002 " may be, for example, 0.2 or less, or 0.1 or less.

[0050] O2-type layered oxides are expected to have higher capacity than O3-type layered oxides. On the other hand, O2-type layered oxides tend to have higher resistance than O3-type layered oxides. For example, the present production method may include micronizing the active material particles. For example, the active material particles (O2-type layered oxide) may be pulverized. For example, a precursor of the active material particles (such as a P2-type layered oxide) may be pulverized. Micronizing the active material particles can increase the specific surface area. An increase in the specific surface area is expected to reduce resistance. However, micronizing the active material particles can promote granulation during spray drying. In this embodiment, the use of a specific coating liquid can reduce granulation.

[0051] The active material particles may be solid particles or hollow particles. Hollow particles and solid particles are secondary particles (aggregates of primary particles). In a cross-sectional image of a "hollow particle," the area ratio of the cavity in the center is 30% or more of the cross-sectional area of ​​the entire particle. The ratio of the cavity in a hollow particle may be, for example, 40% or more, 50% or more, or 60% or more. In a cross-sectional image of a "solid particle," the area ratio of the cavity in the center is less than 30% of the cross-sectional area of ​​the entire particle. The ratio of the cavity in a solid particle may be, for example, 20% or less, 10% or less, or 5% or less. A mixture of hollow particles and solid particles may be used as the active material particles. The mixing ratio (mass ratio) of hollow particles to solid particles may be, for example, "hollow particles / solid particles = 1 / 9 to 9 / 1," "hollow particles / solid particles = 2 / 8 to 8 / 2," "hollow particles / solid particles = 3 / 7 to 7 / 3," or "hollow particles / solid particles = 4 / 6 to 6 / 4."

[0052] (coating liquid) The coating liquid contains a solute and a solvent, and may further contain, for example, a suspended solid (insoluble component), a precipitate, or the like.

[0053] The solvent may contain any component as long as the solute can be dissolved in the solvent. The solvent may contain, for example, water, alcohol, etc. The solvent may contain, for example, ion-exchanged water, ethanol, hydrogen peroxide solution, etc.

[0054] The amount of solute may be, for example, 0.1 to 20 parts by mass, 1 to 15 parts by mass, or 5 to 10 parts by mass per 100 parts by mass of the solvent. The solute includes a material for the coating film. The solute includes at least one element selected from the group consisting of Nb, P, and B. The solute may further include, for example, Li.

[0055] The solute may include, for example, phosphoric acid, phosphates, boric acid, borates, niobic acid, niobates, lithium compounds, etc. The solute may include, for example, phosphoric anhydride (P2O5), orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid [(HPO3) n], polyphosphoric acid, orthoboric acid (H3BO3), metaboric acid (HBO2), niobic acid (Nb2O5·3H2O), and at least one selected from the group consisting of lithium hydroxide.

[0056] The coating liquid may further contain a surfactant. By including a surfactant in the coating liquid, an improvement in coverage is expected. The surfactant may be an insoluble component. The surfactant may be a soluble component (solute). The surfactant may, for example, be water-soluble. The dissolved surfactant may improve coverage. The surfactant may be cationic, anionic, amphoteric, or nonionic. The nonionic surfactant may improve coverage. The surfactant may contain, for example, at least one selected from the group consisting of polyether-modified silicone and polyethylene glycol alkyl ether. Examples of polyether-modified silicones include "Product Name: Silsurf C208 (manufactured by SILTECH)" and "Product Name: KF-945 (manufactured by Shin-Etsu Chemical Co., Ltd.)." Examples of polyethylene glycol alkyl ethers include polyethylene glycol monolauryl ether.

[0057] The coating liquid may contain, for example, 0.1 to 1.5% by mass of surfactant. The mass fraction (addition amount) of the surfactant may be, for example, 0.1 to 0.5%, or 0.5 to 1%. The addition amount of the surfactant may be, for example, 0.2 to 0.8%, 0.3 to 0.7%, or 0.4 to 0.6%.

[0058] <(b) Spray drying> This production method includes producing a positive electrode active material by drying the slurry by a spray drying method. Any spray drying device can be used in this production method. For example, droplets can be formed by spraying the slurry from a nozzle. The droplets are dried by hot air. A coating film can be deposited on the surface of the active material particles by drying the slurry. The positive electrode active material (composite particles) can be produced by forming the coating film. The nozzle diameter can be, for example, 0.1 to 10 mm or 0.1 to 1 mm. The hot air temperature can be, for example, 100 to 200°C.

[0059] (c) Heat treatment The present manufacturing method may include subjecting the positive electrode active material to a heat treatment. The heat treatment may fix the coating film. The heat treatment may also be referred to as "baking." Any heat treatment device may be used in the present manufacturing method. The treatment temperature may be, for example, 150 to 300°C. The treatment time may be, for example, 1 to 10 hours. The heat treatment atmosphere may be, for example, air or an inert atmosphere.

[0060] <<Cathode active material>> The positive electrode active material is a powder, and the particle size distribution of the positive electrode active material may have, for example, the following D10, D50, and D90. D10: 1 to 4 μm D50: 3 to 10 μm D90: 5 to 20 μm

[0061] When D50 is 10 μm or less, for example, a reduction in initial resistance is expected. D50 may be, for example, 8 μm or less, or 4.9 μm or less. D50 may be, for example, 3.2 μm or more, or 4.1 μm or more.

[0062] When D10 is 3 μm or less, granulation during spray drying may be slight. D10 may be, for example, 2.9 μm or less, or 2.2 μm or less. D10 may be, for example, 1.8 μm or more.

[0063] When D90 is 15 μm or less, granulation during spray drying may be slight. D90 may be, for example, 11.9 μm or less, 10.4 μm or less, 9.3 μm or less, or 8.6 μm or less. D90 may be, for example, 5.8 μm or more.

[0064] The span (dimensionless quantity) of the particle size distribution may be, for example, 1.5 to 2.5, 1.6 to 2.0, or 1.6 to 1.9. The span (Sp) is determined by the following formula (1-6). Sp=(D90-D10) / D50 …(1-6)

[0065] The ratio of D90 to D10 (D90 / D10) may be, for example, 5 or less, 4.5 or less, 4.3 or less, 4.2 or less, 4.1 or less, or 4.0 or less. The ratio (D90 / D10) may be, for example, 3 or more, 3.5 or more, 3.8 or more, or 3.9 or more.

[0066] The ratio of D90 to D50 (D90 / D50) may be, for example, 2.2 or less, 2.1 or less, or 2.0 or less. The ratio (D90 / D50) may be, for example, 1.8 or more, or 1.9 or more.

[0067] The ratio of D50 to D10 (D50 / D10) may be, for example, 2.5 or less, or 2.3 or less. The ratio (D50 / D10) may be, for example, 2.0 or more, or 2.1 or more.

[0068] FIG. 2 is a conceptual diagram showing a positive electrode active material in this embodiment. The positive electrode active material 5 may also be referred to as, for example, a "coated active material." The positive electrode active material 5 includes composite particles. The composite particles have a core-shell structure. That is, the positive electrode active material 5 includes active material particles 1 and a coating film 2. The active material particles 1 are the core of the positive electrode active material 5. The active material particles 1 include an O2-type layered oxide. The details of the active material particles 1 are as described above.

[0069] The coating film 2 is a shell of the positive electrode active material 5. The coating film 2 has a thickness of 4 nm or more. The thickness of the coating film 2 may be, for example, 4.2 nm or more, 4.4 nm or more, or 5.2 nm or more. The thickness of the coating film 2 may be, for example, 50 nm or less, 30 nm or less, 20 nm or less, 15 nm or less, 10 nm or less, 8 nm or less, 5.6 nm or less, or 5.3 nm or less.

[0070] The coverage of the coating film 2 is 80% or more. The higher the coverage, the more reduced the resistance increase rate is expected. The coverage may be, for example, 83% or more, 86% or more, 89% or more, 91% or more, 92% or more, or 94% or more. The coverage may be, for example, 100% or less, 99% or less, 98% or less, 97% or less, 96% or less, or 95% or less.

[0071] The coating film 2 contains at least one element selected from the group consisting of Nb, P, and B. The coating film 2 may further contain Li and O. The coating film 2 may contain, for example, oxide glass or the like. The oxide glass may have a network structure. The coating film 2 may contain, for example, at least one element selected from the group consisting of a phosphate skeleton and a borate skeleton. For example, in a TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) spectrum of the positive electrode active material 5, PO2 - , PO3 - When a fragment such as BO2 is detected, it can be considered that the coating film 2 contains a phosphate backbone. - , BO3 - When a fragment such as the above is detected, it can be considered that the coating film 2 contains a boric acid skeleton.

[0072] The coating film 2 may contain, for example, B, P, and O. When the coating film 2 contains B and P, the molar ratios may satisfy, for example, the relationship "B / P = 9 / 1 to 1 / 9," "B / P = 8 / 2 to 2 / 8," "B / P = 7 / 3 to 3 / 7," or "B / P = 6 / 4 to 4 / 6."

[0073] The positive electrode active material 5 may satisfy, for example, the relationship of the following formula (1-7). 0≦C Li / C x <3 …(1-7) C Li : Elemental concentration of Li measured by XPS C x : Element concentration of elements contained in coating film 2 (excluding Li and O) measured by XPS.

[0074] By using XPS, composition information on the outermost surface of the positive electrode active material 5 can be obtained. The element concentrations measured by XPS are considered to represent the element concentrations in the coating film 2. The element concentration ratio "C Li / C x The smaller "C" is, the more the initial resistance is expected to decrease. Li / C x " may be, for example, 2.5 or less, 2.0 or less, 1.5 or less, or 1.0 or less. Li / C x " may be, for example, 0.1 or more, 0.3 or more, or 0.5 or more. For example, when the coating film 2 contains P and B, the formula "C x =C P +C B "By C x is obtained. C P indicates the element concentration of P, and C B indicates the element concentration of B.

[0075] <<All-solid-state battery>> FIG. 3 is a conceptual diagram showing an all-solid-state battery according to this embodiment. The battery 100 can be used for any purpose. For example, the battery 100 may be used as a power source for an electric vehicle, an electric tool, or the like. The battery 100 can have any shape. For example, the battery 100 may have a plate-like shape. The battery 100 includes a power-generating element 50.

[0076] <Exterior body> The battery 100 may include an exterior body (not shown). The exterior body may house the power generating element 50. The exterior body may have any shape. For example, the exterior body may be a metal case or a pouch made of a metal foil laminated film. The exterior body may contain, for example, Al. The exterior body may house, for example, one power generating element 50, or may house multiple power generating elements 50. The multiple power generating elements 50 may form, for example, a series circuit or a parallel circuit. Within the exterior body, the multiple power generating elements 50 may be stacked in the thickness direction of the battery 100.

[0077] A buffer material may be interposed inside the exterior body between the exterior body and the power generating element 50. The buffer material may be elastically deformable. The buffer material may include, for example, a spring, a cushion, or the like. For example, when the battery 100 is mounted on a power tool, vibrations are applied to the power generating element 50. The vibrations may damage the power generating element 50. The buffer material can reduce the vibrations applied to the power generating element 50.

[0078] <Power generation elements> The power generating element 50 may also be referred to as an "electrode group," an "electrode body," or the like. The power generating element 50 includes a positive electrode 10 and a negative electrode 20. The power generating element 50 may further include a separator layer 30. The separator layer 30 is disposed between the positive electrode 10 and the negative electrode 20. The power generating element 50 may have any configuration. The power generating element 50 may have, for example, a monopolar structure or a bipolar structure. In a bipolar structure, a positive electrode active material layer and a negative electrode active material layer may be disposed on the front and back of a single current collector, respectively.

[0079] <Positive electrode> The positive electrode 10 is in a sheet form. The positive electrode 10 may include, for example, a positive electrode current collector 11 and a positive electrode active material layer 12.

[0080] (Positive electrode current collector) The positive electrode current collector 11 is conductive. The positive electrode current collector 11 supports the positive electrode active material layer 12. The positive electrode current collector 11 may be, for example, in the form of a sheet. The positive electrode current collector 11 may have a thickness of, for example, 5 to 50 μm.

[0081] The positive electrode current collector 11 may have a single-layer structure or a multi-layer structure. The positive electrode current collector 11 may include, for example, at least one selected from the group consisting of a metal layer and a conductive resin layer. The metal layer may include, for example, at least one selected from the group consisting of a metal foil and a metal vapor deposition film. The metal layer may include, for example, at least one selected from the group consisting of Al, Mn, Ti, Fe, and Cr. The metal layer may include, for example, Al foil, Al alloy foil, Ti foil, stainless steel (SUS) foil, etc. The conductive resin layer may include, for example, a matrix resin and a conductive filler. The matrix resin may include, for example, polyolefin, etc. The conductive filler may include, for example, at least one selected from the group consisting of carbon particles, carbon fibers, metal particles, and metal fibers.

[0082] The positive electrode current collector 11 may further include, for example, a PTC (Positive Temperature Coefficient) layer. The PTC layer increases the resistance when the temperature of the battery 100 becomes high. The PTC layer may include, for example, thermally expandable microcapsules, a conductive material, a binder, and the like. Examples of thermally expandable microcapsules that can be used include "Product Name: Matsumoto Microsphere (registered trademark), manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd." and "Product Name: Expancel (registered trademark), manufactured by Nippon Phillite Co., Ltd." The thermally expandable microcapsules may be coated with a metal material (for example, an Al vapor deposition film, etc.). When the temperature of the battery 100 becomes high, the thermally expandable microcapsules expand, which can increase the resistance of the PTC layer.

[0083] The positive electrode current collector 11 may include, for example, a buffer layer. The buffer layer may include a buffer material. The buffer material may include, for example, a foamed resin. For example, when the positive electrode 10 is subjected to roll press processing, the buffer layer is expected to alleviate the load applied to the metal layer (metal foil, etc.), the positive electrode active material layer 12, etc.

[0084] (Cathode active material layer) The positive electrode active material layer 12 is disposed on the surface of the positive electrode current collector 11. The positive electrode active material layer 12 may be disposed on only one surface of the positive electrode current collector 11. The positive electrode active material layer 12 may be disposed on both the front and back surfaces of the positive electrode current collector 11. The positive electrode active material layer 12 may have a thickness of, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The positive electrode active material layer 12 contains a positive electrode active material and a sulfide solid electrolyte. The positive electrode active material layer 12 may further contain, for example, a conductive material and a binder.

[0085] The positive electrode active material layer 12 includes the positive electrode active material of the present embodiment described above. The positive electrode active material layer 12 may include a single positive electrode active material. The positive electrode active material layer 12 may include multiple types of positive electrode active materials. For example, the positive electrode active material layer 12 may include two or more types of positive electrode active materials having different particle size distributions. For example, mixing large particles and small particles may improve the packing density of the positive electrode active material layer 12. The large particles have a larger D50 than the small particles. The mixing ratio (mass ratio) of the large particles to the small particles may be, for example, "large particles / small particles = 1 / 9 to 9 / 1," "large particles / small particles = 5 / 5 to 9 / 1," or "large particles / small particles = 7 / 3 to 9 / 1."

[0086] The positive electrode active material layer 12 may contain two or more positive electrode active materials having different compositions. Hereinafter, for convenience, the positive electrode active material (coated active material containing an O2-type layered oxide) in this embodiment will be referred to as a first positive electrode active material. The positive electrode active material layer 12 may further contain a second positive electrode active material in addition to the first positive electrode active material. The second positive electrode active material may also be a coated active material. The second positive electrode active material may contain, for example, an O3-type layered oxide, a polyanion compound, or the like. The mixing ratio (mass ratio) of the first positive electrode active material to the second positive electrode active material may be, for example, "first positive electrode active material / second positive electrode active material = 9 / 1 to 1 / 9," "first positive electrode active material / second positive electrode active material = 8 / 2 to 2 / 8," or "first positive electrode active material / second positive electrode active material = 7 / 3 to 3 / 7."

[0087] The O3 type layered oxide may be represented by, for example, the following formulas (1-8) to (1-10). Li 1-a Ni x Me 1-x O2…(1-8) In the above formula (1-8), the relationships of -0.5≦a≦0.5 and 0≦x≦1 are satisfied. Me may include, for example, at least one selected from the group consisting of Co, Mn, and Al.

[0088] Li 1-a Ni x Co y Mn z O2…(1-9) In the above formula (1-9), the relationships of -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0089] Li 1-a Ni x Co y Al z O2…(1-10) In the above formula (1-10), the relationships of -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0090] The polyanion compound may be represented, for example, by the following formula (1-11). LiMePO4…(1-11) In the above formula (1-11), Me may contain, for example, at least one selected from the group consisting of Fe, Mn, and Co.

[0091] (Sulfide solid electrolyte) The sulfide solid electrolyte can form an ion conduction path in the positive electrode active material layer 12. The sulfide solid electrolyte may be, for example, a powder. The sulfide solid electrolyte may have a D50 of, for example, 0.1 to 3 μm. The D50 of the sulfide solid electrolyte may be, for example, 1 μm or less, 0.5 μm or less, or 0.1 μm or less. The D50 of the sulfide solid electrolyte may be, for example, 0.05 μm or more, or 0.1 μm or more. The blending amount of the sulfide solid electrolyte may be, for example, 1 to 200 parts by volume, 50 to 150 parts by volume, or 50 to 100 parts by volume with respect to 100 parts by volume of the positive electrode active material.

[0092] The sulfide solid electrolyte may be, for example, glass ceramics or argyrodite. The sulfide solid electrolyte may be, for example, LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-GeS2-P2S5, Li2S-P2S5, Li 10 GeP2S 12, Li4P2S6, Li7P3S 11 , Li3PS4, Li7PS6, and Li6PS5X (X = Cl, Br, I).

[0093] For example, "LiI-LiBr-Li3PS4" refers to a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li3PS4 in any molar ratio. For example, the sulfide solid electrolyte may be produced by a mechanochemical method. "Li2S-P2S5" includes Li3PS4. Li3PS4 can be produced, for example, by mixing Li2S and P2S5 in a molar ratio of Li2S / P2S5 = 75 / 25.

[0094] The sulfide solid electrolyte may have, for example, a raw material composition represented by the following formula (2-1). xLiI-yLiBr-(100-xy)Li3PS4…(2-1) The above formula (2-1) indicates that the raw material composition is "LiI / LiBr / Li3PS4=x / y / (100-xy)" in terms of molar ratio. For example, the relationships 0≦x≦30, 0≦y≦30, and 0≦x+y≦30 may be satisfied.

[0095] The sulfide solid electrolyte may have a composition represented by the following formula (2-2), for example. Li 4-x Ge 1-x P x S4…(2-2) In the above formula (2-2), for example, the relationship 0.55≦x≦0.76 may be satisfied.

[0096] In addition to the sulfide solid electrolyte, the positive electrode active material layer 12 may further contain other solid electrolytes. Hereinafter, for convenience, the sulfide solid electrolyte may also be referred to as the "first solid electrolyte", and the other solid electrolytes may also be referred to as the "second solid electrolyte". The volume ratio of the first solid electrolyte to the second solid electrolyte may be, for example, "first solid electrolyte / second solid electrolyte = 1 / 99 to 99 / 1", "first solid electrolyte / second solid electrolyte = 1 / 9 to 9 / 1", or "first solid electrolyte / second solid electrolyte = 3 / 7 to 7 / 3". The first solid electrolyte and the second solid electrolyte may be subjected to a composite treatment.

[0097] The second solid electrolyte may contain, for example, at least one selected from the group consisting of a halide solid electrolyte, an oxide solid electrolyte, a hydride solid electrolyte, and a nitride solid electrolyte.

[0098] The halide solid electrolyte may be represented, for example, by the following formula (2-3). Li 6-na M a X6…(2-3) In the above formula (2-3), n represents the oxidation number of M. M may contain, for example, an atom having an oxidation number of +3. M may contain, for example, an atom having an oxidation number of +4. M may contain, for example, at least one selected from the group consisting of Y, Al, Ti, Zr, Ca, and Mg. a may satisfy the relationship 0 < a < 2. X may contain, for example, at least one selected from the group consisting of F, Cl, Br, and I.

[0099] The halide solid electrolyte may be represented, for example, by the following formula (2-4). Li 3-a Ti a Al 1-a F6…(2-4) In the above formula (2-4), a may satisfy the relationship of, for example, 0≦a≦0.1, 0.1≦a≦0.2, 0.2≦a≦0.3, 0.3≦a≦0.4, 0.4≦a≦0.5, 0.5≦a≦0.6, 0.6≦a≦0.7, 0.7≦a≦0.8, 0.8≦a≦0.9, or 0.9≦a≦1.

[0100] The halide solid electrolyte may be represented by, for example, the following formula (2-5): Li3YCl a Br b I 6-a-b …(2-5) In the above formula (2-5), the relationship 0≦a+b≦6 is satisfied. a may satisfy the relationship 0≦a≦1, 1≦a≦2, 2≦a≦3, 3≦a≦4, 4≦a≦5, or 5≦a≦6, for example. b may satisfy the relationship 0≦b≦1, 1≦b≦2, 2≦b≦3, 3≦b≦4, 4≦b≦5, or 5≦b≦6, for example.

[0101] The oxide solid electrolyte is, for example, LiNbO3, Li 1.5 Al 0.5 Ge 1.5 (PO4)3, La 2 / 3-x Li 3x TiO3 and Li7La3Zr2O 12 The hydride solid electrolyte may contain, for example, LiBH4, etc. The nitride solid electrolyte may contain, for example, Li3N, Li3BN2, etc.

[0102] (Conductive material) The conductive material can form an electron conduction path within the positive electrode active material layer 12. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass relative to 100 parts by mass of the positive electrode active material. The conductive material may contain any component. The conductive material may include, for example, at least one selected from the group consisting of graphite, acetylene black (AB), Ketjen Black (registered trademark), vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF). The CNT may include at least one selected from the group consisting of single-walled CNT (SWCNT) and multi-walled CNT (MWCNT).

[0103] (binder) The binder can fix the positive electrode active material layer 12 to the positive electrode current collector 11. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), polytetrafluoroethylene (PTFE), carboxymethyl cellulose (CMC), polyacrylic acid (PAA), polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, and derivatives thereof.

[0104] (Other ingredients) The positive electrode active material layer 12 may further contain, for example, an inorganic filler, an organic filler, a surface modifier, a dispersant, a lubricant, a flame retardant, a protective agent, a flux, a coupling agent, an adsorbent, etc. The positive electrode active material layer 12 may also contain, for example, polyoxyethylene allyl phenyl ether phosphate, zeolite, a silane coupling agent, MoS2, WO3, etc.

[0105] <Negative electrode> The negative electrode 20 is in a sheet form. The negative electrode 20 may include, for example, a negative electrode current collector 21 and a negative electrode active material layer 22.

[0106] (Negative electrode current collector) The negative electrode current collector 21 is conductive. The negative electrode current collector 21 supports the negative electrode active material layer 22. The negative electrode current collector 21 may be, for example, in the form of a sheet. The negative electrode current collector 21 may have a thickness of, for example, 5 to 50 μm.

[0107] The negative electrode current collector 21 may include at least one selected from the group consisting of a metal layer and a conductive resin layer. The negative electrode current collector 21 may further include a PTC layer, a buffer layer, and the like. The conductive resin layer, the PTC layer, and the buffer layer may be the same as those of the positive electrode current collector 11. The metal layer may include at least one selected from the group consisting of Cu, Ni, Fe, Zn, Pb, Ag, and Au, for example. The metal layer may include Cu foil, Cu alloy foil, and the like, for example.

[0108] (Negative electrode active material layer) The negative electrode active material layer 22 is disposed on the surface of the negative electrode current collector 21. The negative electrode active material layer 22 may be disposed on only one surface of the negative electrode current collector 21. The negative electrode active material layer 22 may be disposed on both the front and back surfaces of the negative electrode current collector 21. The negative electrode active material layer 22 may have a thickness of, for example, 10 to 1000 μm, 50 to 500 μm, or 100 to 300 μm. The negative electrode active material layer 22 includes a negative electrode active material and a solid electrolyte. The negative electrode active material layer 22 may further include, for example, a conductive material and a binder.

[0109] (Negative electrode active material) The negative electrode active material may be, for example, a powder or a sheet, and may have a D50 of, for example, 1 to 30 μm, 10 to 20 μm, or 1 to 10 μm.

[0110] (carbon-based active material) The negative electrode active material may include, for example, a carbon-based active material. The carbon-based active material may include at least one selected from the group consisting of graphite, soft carbon, and hard carbon. "Graphite" is a general term for natural graphite and artificial graphite. Graphite may be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1", "natural graphite / artificial graphite = 2 / 8 to 8 / 2", or "natural graphite / artificial graphite = 3 / 7 to 7 / 3".

[0111] Graphite may contain a dopant. The dopant may include at least one selected from the group consisting of B, N, P, Li, and Ca. The addition amount may be, in mole fraction, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%.

[0112] The surface of graphite may be coated with, for example, amorphous carbon. The surface of graphite may be coated with, for example, a different material. The different material may include at least one selected from the group consisting of P, W, Al, and O. The different material may include at least one selected from the group consisting of Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO 3、 and at least one selected from the group consisting of Li3PO4.

[0113] (Alloy-based active material) The negative electrode active material may include, for example, an alloy-based active material. The negative electrode active material may include at least one selected from the group consisting of Si, Li silicate, SiO, Si-based alloy, Sn, SnO, and Sn-based alloy.

[0114] SiO may be represented by, for example, the following formula (3-1).

[0115] SiO x …(3-1) In the above formula (3-1), the relationship of 0 < x < 2 is satisfied.

[0116] In the above formula (3-1), x may satisfy the relationship of, for example, 0.5≦x≦1.5 or 0.8≦x≦1.2.

[0117] The Li silicate may include at least one selected from the group consisting of Li4SiO4, Li2SiO3, Li2Si2O5, and Li8SiO6. The negative electrode active material may include a mixture of Si and Li silicate. The mixing ratio (mass ratio) may be, for example, "Si / Li silicate = 1 / 9 to 9 / 1," "Si / Li silicate = 2 / 8 to 8 / 2," "Si / Li silicate = 3 / 7 to 7 / 3," or "Si / Li silicate = 4 / 6 to 6 / 4."

[0118] The alloy-based active material (e.g., Si, SiO) may contain an additive. The additive may be, for example, a substitutional solute atom or an interstitial solute atom. The additive may be a deposit attached to the surface of the alloy-based active material. The deposit may be, for example, an element, an oxide, a carbide, a nitride, a halide, or the like. The amount added may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1% in terms of mole fraction. The additive may contain, for example, at least one selected from the group consisting of Li, Na, K, Rb, Be, Mg, Ca, Sr, Fe, Ba, B, Al, Ga, In, C, Ge, Sn, Pb, N, P, As, Y, Sb, and S. That is, SiO may be doped with Mg or Na. For example, Mg silicate, Na silicate, etc. may be formed. For example, boron oxide (for example, B2O3, etc.), yttrium oxide (for example, Y2O3, etc.), etc. may be added to SiO.

[0119] (Si-C composite material) The negative electrode active material may include, for example, a composite material of a carbon-based active material (such as graphite) and an alloy-based active material (such as Si). A composite material containing Si and carbon may also be referred to as a "Si-C composite material." For example, Si fine particles may be dispersed within carbon particles. For example, Si fine particles may be dispersed within graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon).

[0120] (Other active materials) The negative electrode active material is, for example, Li metal, Li-based alloy, and Li4Ti5O 12 It may contain at least one selected from the group consisting of:

[0121] (solid electrolyte) The solid electrolyte can form an ion conduction path within the negative electrode active material layer 22. The solid electrolyte may be particulate. The solid electrolyte may have a D50 of, for example, 0.1 to 3 μm. The D50 of the solid electrolyte may be, for example, 1 μm or less, or 0.5 μm or less. The amount of the solid electrolyte may be, for example, 1 to 200 parts by volume, 50 to 150 parts by volume, or 50 to 100 parts by volume per 100 parts by volume of the negative electrode active material. The solid electrolytes in the negative electrode active material layer 22 and the positive electrode active material layer 12 may be the same or different. The negative electrode active material layer 22 may contain, for example, at least one selected from the group consisting of a sulfide solid electrolyte, a halide solid electrolyte, an oxide solid electrolyte, a hydride solid electrolyte, and a nitride solid electrolyte.

[0122] (Conductive material) The conductive material can form an electron conduction path within the negative electrode active material layer 22. The blending amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the negative electrode active material. The conductive material in the negative electrode active material layer 22 and the positive electrode active material layer 12 may be the same or different.

[0123] (binder) The binder can bond the negative electrode active material layer 22 to the negative electrode current collector 21. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the negative electrode active material. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of styrene butadiene rubber (SBR), acrylate butadiene rubber (ABR), sodium alginate, CMC (CMC-H, CMC-Na, CMC-Li, CMC-NH4, etc.), PAA (PAA-H, PAA-Na, PAA-Li, etc.), polyacrylonitrile (PAN), PVdF, PTFE, acrylic resin (acrylic acid ester copolymer), methacrylic resin (methacrylic acid ester copolymer), PVP, PVA, and derivatives thereof. For example, "CMC-Na" refers to the Na salt of CMC. For example, "CMC-H" refers to acid-type CMC. The same applies to "PAA-Na" and the like.

[0124] (Other ingredients) The negative electrode active material layer 22 may further contain, for example, an inorganic filler, an organic filler, a surface modifier, a dispersant, a lubricant, a flame retardant, a protective agent, a flux, a coupling agent, an adsorbent, etc. The negative electrode active material layer 22 may also contain, for example, a layered silicate (smectite, montmorillonite, bentonite, hectorite, etc.), an inorganic filler (solid alumina, hollow silica, boehmite, etc.), a polysiloxane compound, etc.

[0125] <Separator layer> The separator layer 30 is interposed between the positive electrode 10 and the negative electrode 20. The separator layer 30 separates the positive electrode 10 from the negative electrode 20. The separator layer 30 may have a thickness of, for example, 1 to 50 μm.

[0126] The separator layer 30 may also be referred to as a "solid electrolyte layer." The separator layer 30 includes a solid electrolyte. The separator layer 30 may further include, for example, a binder. The solid electrolytes in the separator layer 30 and the electrode active material layer may be the same or different. The separator layer 30 may include, for example, at least one selected from the group consisting of a sulfide solid electrolyte, a halide solid electrolyte, an oxide solid electrolyte, a hydride solid electrolyte, and a nitride solid electrolyte. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the solid electrolyte. The binders in the separator layer 30 and the electrode active material layer may be the same or different.

[0127] The separator layer 30 may have a single-layer structure or a multi-layer structure. The separator layer 30 may have, for example, a 2- to 5-layer structure. For example, the solid electrolytes in the layers may be different from each other. For example, the densities in the layers may be different from each other. For example, the particle sizes (e.g., D50) of the solid electrolytes in the layers may be different from each other.

[0128] For example, the separator layer 30 may include a first layer 31 and a second layer 32. The first layer 31 is in contact with the positive electrode active material layer 12. The second layer 32 is in contact with the negative electrode active material layer 22. The thickness ratio between the first layer 31 and the second layer 32 may be, for example, "first layer / second layer=1 / 9 to 9 / 1" or "first layer / second layer=3 / 7 to 7 / 3".

[0129] The first layer 31 may have a composition different from that of the second layer 32. For example, the first layer 31 may contain a sulfide solid electrolyte and the second layer 32 may contain a halide solid electrolyte. For example, the first layer 31 may contain a halide solid electrolyte and the second layer 32 may contain a sulfide solid electrolyte. The first layer 31 may contain both a sulfide solid electrolyte and a halide solid electrolyte. The second layer 32 may contain both a sulfide solid electrolyte and a halide solid electrolyte. The volume ratio of the halide solid electrolyte to the sulfide solid electrolyte in the first layer 31 (the first volume ratio) may be larger than the volume ratio of the halide solid electrolyte to the sulfide solid electrolyte in the second layer 32 (the second volume ratio). The first volume ratio may be smaller than the second volume ratio.

Example

[0130] <<Manufacture of Cathode Active Material>> <Synthesis of O2-Type Layered Oxide> (Coprecipitation Synthesis, Preparation of Precursor) MnSO4·5H2O, NiSO4·6H2O, and CoSO4·7H2O were weighed so that the molar ratio was "Mn / Ni / Co = 5 / 2 / 3". By dissolving these materials in distilled water, a first aqueous solution was formed. The concentration of the first aqueous solution was 1.2 mol / L.

[0131] By dissolving Na2CO3 in distilled water, a second aqueous solution was formed. The concentration of the second aqueous solution was 1.2 mol / L.

[0132] A reaction vessel with a baffle was prepared. 1000 mL of pure water was poured into the reaction vessel. The first aqueous solution (500 mL) and the second aqueous solution (500 mL) were each dropped into the reaction solution at a rate of about 4 mL / min.

[0133] After the dropwise addition was completed, the material in the reaction vessel was stirred at room temperature at a speed of 150 rpm. After stirring for 1 hour, the product in the reaction vessel was recovered. The product was dispersed in pure water to form a dispersion. In other words, the product was washed with pure water. Solid-liquid separation of the dispersion was carried out using a centrifuge. The separated precipitate was recovered.

[0134] The precipitate was dried at 120°C for 8 hours. After drying, the precipitate was pulverized in a mortar. The pulverized material was then subjected to air classification to obtain coarse particles (precursor).

[0135] (Na calcination) Na2CO3 was added to distilled water. The aqueous solution was stirred with a stirrer until the Na2CO3 was completely dissolved. This formed a third aqueous solution. The concentration of the third aqueous solution was 1150 g / L.

[0136] Na 0.7 Mn 0.5 Ni 0.2 Co 0.3 The precursor was mixed with the third aqueous solution to form a slurry having a composition of O2.

[0137] The slurry was dried using a spray dryer "Product: DL410" (manufactured by Yamato Scientific Co., Ltd.), and the precursor was coated with Na2CO3. The drying conditions were as follows:

[0138] Slurry delivery speed: 30 mL / min Inlet temperature: 200℃ Circulation air volume: 0.8m 3 / min Spraying air pressure: 0.3MPa

[0139] The precursor was placed in an alumina crucible. The precursor was heat-treated in an electric furnace in an air atmosphere to obtain a fired product. The fired product was recovered from the electric furnace at 250°C. The fired product was pulverized in a dry atmosphere. As a result, a P2-type layered oxide containing Na was obtained.

[0140] (Na / Li ion exchange) The Li source material was formed by mixing LiNO3 with LiCl. The mixing ratio was "LiNO3 / LiCl = 1 / 1 (molar ratio)." The Li source material was mixed with the P2-type layered oxide to form a mixture. The amount of Li source material mixed was 10 times the amount required to exchange all of the Na in the P2-type layered oxide for Li.

[0141] The mixture was placed in an alumina crucible. The mixture was subjected to heat treatment in an air atmosphere. The heat treatment temperature was 280°C and the heat treatment time was 1 hour. As a result, Na in the P2-type layered oxide was exchanged for Li. After the heat treatment, the layered compound was dispersed in pure water to form a dispersion. In other words, the layered compound was washed with pure water. The dispersion was subjected to solid-liquid separation by vacuum filtration. The precipitate was dried at 120°C for 8 hours. In this way, the O2-type layered oxide was synthesized.

[0142] <No.1> 870.4 parts by mass of hydrogen peroxide solution (mass concentration: 30%) was added to the container. Next, 987.4 parts by mass of ion-exchanged water and 44.2 parts by mass of niobic acid [Nb2O5·3H2O] were added to the container. Next, 87.9 parts by mass of ammonia water (mass concentration: 28%) was added to the container. The contents of the container were thoroughly stirred to form a coating liquid. The coating liquid is believed to contain a peroxo complex of Nb.

[0143] A slurry was prepared by dispersing active material particles in a coating liquid. The solid content of the slurry was 42%. The active material particles were the O2-type layered oxide obtained above. A spray dryer manufactured by BUCHI, product name: Mini Spray Dryer B-290, was prepared. The slurry was dried using the spray dryer to produce a positive electrode active material. The supply air temperature of the spray dryer was 200°C, and the supply air volume was 0.45 m 3 / min. The positive electrode active material was heat-treated in an air atmosphere. The heat treatment temperature was 200°C. The heat treatment time was 5 hours. The coating film No. 1 is thought to contain Nb.

[0144] <No.2> Figure 4 is a table showing the experimental details. No. 2 differs from No. 1 in the concentration of the coating liquid and the solids concentration of the slurry. Furthermore, in No. 2, a surfactant was added to the coating liquid. Except for these differences, a positive electrode active material was produced in the same manner as No. 1.

[0145] <No.3> An aqueous solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 166 parts by mass of ion-exchanged water. Furthermore, boric acid (manufactured by Nacalai Tesque, Inc.) was dissolved in the aqueous solution so that the molar ratio of P / B was 1 / 1, thereby preparing a coating solution. Active material particles were dispersed in the coating solution to prepare a slurry. The solids concentration of the slurry was 42%. Except for these factors, a positive electrode active material was prepared in the same manner as in No. 1.

[0146] <No.4、5> A positive electrode active material was prepared in the same manner as in No. 3, except that the solid content of the slurry was changed.

[0147] <No.6~8> A positive electrode active material was prepared in the same manner as in No. 4, except that the concentration of the coating solution was changed.

[0148] <No.9> A positive electrode active material was prepared in the same manner as in No. 5, except that the concentration of the coating solution was changed.

[0149] <No.10> A positive electrode active material was prepared in the same manner as in No. 8, except that a surfactant was added to the coating solution.

[0150] <No.11> A positive electrode active material was prepared in the same manner as in No. 10, except that the amount of surfactant added was changed.

[0151] <No.12> A positive electrode active material was prepared in the same manner as in No. 10, except that the type of surfactant was changed.

[0152] <No.13> A positive electrode active material was prepared in the same manner as in No. 11, except that the type of surfactant was changed.

[0153] <<Evaluation>> <Test Battery Manufacturing> A positive electrode slurry was prepared by mixing the positive electrode active material, sulfide solid electrolyte, conductive material, binder, and dispersion medium. The mixing ratio of the positive electrode active material and the sulfide solid electrolyte was "positive electrode active material / sulfide solid electrolyte = 6 / 4 (volume ratio)". The composition of the other components was "positive electrode active material / conductive material / binder = 100 / 3 / 3 (mass ratio)". The positive electrode slurry was thoroughly stirred using an ultrasonic homogenizer. A coating film was formed by coating the positive electrode slurry on the surface of the positive electrode current collector. The coating film was dried at 100°C for 30 minutes on a hot plate. This produced a positive electrode blank. A disk-shaped positive electrode was cut out from the positive electrode blank. The area of ​​the positive electrode was 1 cm. 2 It was.

[0154] A negative electrode and a separator layer were prepared. The negative electrode active material was graphite. The same type of sulfide solid electrolyte was used between the positive electrode, the separator layer, and the negative electrode. A stack was formed by stacking the positive electrode, the separator layer, and the negative electrode in this order inside a cylindrical jig. A power generating element was formed by pressing the stack. A terminal was connected to the power generating element to produce a test battery (all-solid-state battery).

[0155] <Measurement of resistance increase rate> The OCV (Open Circuit Voltage) of the test battery was adjusted to 3.85V in a thermostatic chamber (set temperature: 25°C). After adjusting the OCV, the test battery was discharged for 0.1 seconds at a current of 3C, and the initial resistance was measured. "C" is the symbol indicating the time rate of the current. A current of 1C discharges the rated capacity of the battery in 1 hour.

[0156] The test battery was stored in a thermostatic chamber (set temperature: 60°C) for 4 weeks. During storage, the OCV of the test battery was controlled at 4.80V.

[0157] After 4 weeks of storage, the resistance after endurance testing was measured in a thermostatic chamber (set temperature: 25°C) in the same manner as the initial resistance. The resistance increase rate was calculated by dividing the resistance after endurance testing by the initial resistance.

[0158] <<Results>> In FIG. 4, when the solid content concentration of the slurry is more than 42% and not more than 51%, the resistance increase rate tends to be low.

[0159] When the coating film thickness is 4 nm or more and the coverage is 80% or more, the resistance increase rate tends to be small.

[0160] Figure 5 is a graph showing the relationship between coverage and resistance increase rate. The results of Nos. 3 to 13 are plotted in the graph of Figure 5. When the coating liquid contains a surfactant, the coverage rate tends to be high. When the coverage rate is 80% or higher, the resistance increase rate is good.

[0161] Figure 6 is a graph showing the relationship between D10 and the rate of increase in resistance. The results of Nos. 3 to 13 are plotted in the graph of Figure 6. When the coating liquid contains a surfactant, D10 tends to be small. The smaller D10 tends to be the smaller the rate of increase in resistance.

[0162] Figure 7 is a graph showing the relationship between D90 and the rate of increase in resistance. The results of Nos. 3 to 13 are plotted in the graph of Figure 7. When the coating liquid contains a surfactant, D90 tends to be small. The smaller D90 tends to be the smaller the rate of increase in resistance. [Explanation of symbols]

[0163] 1 active material particles, 2 coating film, 5 positive electrode active material, 10 positive electrode, 11 positive electrode current collector, 12 positive electrode active material layer, 20 negative electrode, 21 negative electrode current collector, 22 negative electrode active material layer, 30 separator layer, 31 first layer, 32 second layer, 50 power generating element, 100 battery (all-solid-state battery).

Claims

1. (a) preparing a slurry by dispersing active material particles in a coating liquid; and (b) drying the slurry by a spray drying method to produce a positive electrode active material; Including, the active material particles contain an O2-type layered oxide, the coating liquid includes a solute and a solvent; the solute contains at least one selected from the group consisting of Nb, P, and B; The slurry has a solids concentration of more than 42% and not more than 51%. A method for producing a positive electrode active material.

2. The coating liquid further contains a surfactant, The surfactant includes at least one selected from the group consisting of polyether-modified silicone and polyethylene glycol alkyl ether. The method for producing the positive electrode active material according to claim 1 .

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