Composite particles, a positive electrode, an all-solid-state battery, and a method for producing the composite particles

Abstract

To reduce resistance.SOLUTION: Composite particles include positive electrode active material particles, and a coating film, the positive electrode active material particles include a lithium-containing composite oxide with a layered rock salt structure, the coating film covers at least a portion of the surface of the positive electrode active material particles, the coating film includes a phosphorus compound, and the following formula (1) of CLi / CP≤2.5 is satisfied. In the formula (1), CLi represents the elemental concentration of lithium determined from the peak area of the Li1s spectrum measured by X-ray photoelectron spectroscopy, CP represents the elemental concentration of phosphorus determined from the peak area of the P2p spectrum measured by X-ray photoelectron spectroscopy, and the amount of carbon dioxide generated when heating from room temperature to 600°C at a rate of 10°C / min by heating gas mass spectrometry is 0.1 mass% or more.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to composite particles, a positive electrode, an all-solid-state battery, and a method for manufacturing the composite particles.

Background Art

[0002] Patent Document 1 (Japanese Patent Application Laid-Open No. 2016-39062) discloses a positive electrode composite material and a sulfide all-solid-state battery having a positive electrode active material made of lithium nickel manganate having a layered structure and a glass electrolyte covering the surface of the positive electrode active material.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] It has been proposed to form a coating film on the surface of positive electrode active material particles. For example, in a sulfide-based all-solid-state battery, it is expected to reduce resistance by the coating film inhibiting direct contact between the sulfide solid electrolyte and the positive electrode active material particles. However, there is room for improvement in reducing resistance.

[0005] Therefore, an object of the present disclosure is to reduce resistance.

Means for Solving the Problems

[0006] Hereinafter, the technical configuration and effects of the present disclosure will be described. However, the mechanism of action in this specification includes assumptions. The mechanism of action does not limit the technical scope of the present disclosure.

[0007] [1] The composite particles include cathode active material particles and a coating film. The cathode active material particles include a lithium-containing composite oxide having a layered rock salt structure. The coating film covers at least a part of the surface of the cathode active material particles. The coating film contains a phosphorus compound.

[0008] The composite particles satisfy the relationship of the following formula (1). C Li / C P ≦2.5 (1) In the above formula (1), C Li represents the elemental concentration of lithium (Li) obtained from the peak area of the Li1s spectrum measured by X-ray photoelectron spectroscopy. C P represents the elemental concentration of phosphorus (P) obtained from the peak area of the P2p spectrum measured by X-ray photoelectron spectroscopy.

[0009] When the composite particles are heated from room temperature to 600 °C at a rate of 10 °C / min by temperature programmed desorption-mass spectrometry (TPD-MS), the amount of carbon dioxide (CO2) generated is 0.1 mass% or more.

[0010] CO2 is derived from lithium carbonate (Li2CO3). Li2CO3 is an impurity formed by further reaction of lithium hydroxide (LiOH), which is a reaction product of Li present on the surface of the cathode active material particles and adsorbed moisture, with CO2 in the atmosphere. Such impurities adhere closely to the surface of the cathode active material particles and cannot be easily removed.

[0011] On the other hand, in forming the coating film, the adhesion between the cathode active material particles and the coating film is important. When the adhesion is weak, for example, when the cathode active material particles and the solid electrolyte are kneaded in a solvent, the coating film is peeled off by the shearing force during kneading, leading to a decrease in battery performance.

[0012] According to the new findings of the present disclosure, the smaller the composition ratio of Li in the coating film, the stronger the bond between the impurities (Li2CO3 and LiOH) present on the surface of the positive electrode active material particles and the coating film, that is, the adhesion between the positive electrode active material particles and the coating film is increased, and a reduction in resistance is expected.

[0013] [2] The lithium-containing composite oxide having a layered rock salt structure is represented by the following formula (2): Li a Ni x Co y Me 1-x-y O2(2) In the above formula (2), Me contains at least one selected from the group consisting of Mn and Al, a may satisfy the relationship of 0.90 ≦ a ≦ 1.20.

[0014] x may satisfy the relationship of 0.30 ≦ x ≦ 0.90. y may satisfy the relationship of 0.10 ≦ y ≦ 0.40.

[0015] [3] x may satisfy the relationship of 0.50 ≦ x ≦ 0.90. In the above formula (2), a material in which x is 0.5 or more is also referred to as a high nickel material. The high nickel material can have high capacity and high output.

[0016] [4] The positive electrode includes the composite particles according to any one of [1] to [3] above and a sulfide solid electrolyte.

[0017] [5] The all-solid-state battery includes the positive electrode according to [4] above. [6] The method for producing the composite particles includes the following (a) and (b).

[0018] (a) A mixture is prepared by mixing a coating solution and positive electrode active material particles. (b) The composite particles are produced by drying the mixture.

[0019] The coating liquid contains a solute and a solvent. When the coating liquid adhering to the surface of the positive electrode active material particles dries, a coating film can be formed. The coating film described in the above [6] can be formed by the coating liquid described in the above [1].

[0020] 〔7〕The solute may contain a phosphate compound. The coating liquid may, for example, satisfy the following relationship of formula (3).

[0021] 0≦n Li / n P <1.1 (3) In the above formula (3), n Li represents the molar concentration of lithium in the coating liquid. n P represents the molar concentration of phosphorus in the coating liquid.

[0022] 〔8〕The above (b) may, for example, include forming composite particles by a spray drying method.

Brief Description of the Drawings

[0023]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0024] Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "this embodiment"), and examples of the present disclosure (hereinafter may be abbreviated as "this example") will be described. However, this embodiment and this example do not limit the technical scope of the present disclosure.

[0025] <Definitions of Terms, etc.> The descriptions of "comprising", "including", "having", and their variants (e.g., "consisting of", etc.) are in an open-ended form. The open-ended form may further include additional elements or may not include them in addition to the essential elements. The description of "consisting of" is in a closed form. However, even in the closed form, additional elements that are normally accompanying impurities or are irrelevant to the disclosed technology are not excluded. The description of "substantially consisting of" is in a semi-closed form. In the semi-closed form, the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology is allowed.

[0026] Expressions such as "may" and "can" are used in an allowable sense, meaning "having the possibility of doing", rather than in an obligatory sense, meaning "must do".

[0027] Elements expressed in the singular form include the plural form as well, unless otherwise specified. For example, "particle" can mean not only "one particle" but also "an aggregate of particles (powder, powder, particle group)".

[0028] The plurality of steps, operations, and operations included in various methods are not limited to the execution order described, unless otherwise specified. For example, a plurality of steps may proceed simultaneously. For example, a plurality of steps may follow one another.

[0029] For example, a numerical range such as "m to n%" includes the upper limit value and the lower limit value, unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less". Also, "m% or more and n% or less" includes "more than m% and less than n%". Furthermore, a numerically arbitrarily selected value within the numerical range may be used as a new upper limit value or lower limit value. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described in another part of this specification, in a table, in a figure, etc.

[0030] When a compound is represented by a stoichiometric composition formula (e.g., "LiCoO₂", etc.), the stoichiometric composition formula is only a representative example of the compound. The compound may have a non-stoichiometric composition. For example, when lithium cobaltate is represented as "LiCoO₂", unless otherwise specified, lithium cobaltate is not limited to a composition ratio of "Li / Co / O = 1 / 1 / 2", and may contain Li, Co, and O in any composition ratio. Furthermore, doping, substitution, etc. with trace elements may also be allowed.

[0031] "D50" indicates the particle diameter at which the cumulative frequency from the smaller particle diameter side reaches 50% in the volume-based particle size distribution. D50 can be measured by the laser diffraction method. For example, a laser diffraction particle size distribution measuring device "product name SALD-7500" (or equivalent) manufactured by Shimadzu Corporation may be used.

[0032] 《TPD-MS Measurement》 The amount of CO₂ generated can be measured by the following procedure. A TPD-MS device is prepared. For example, a TPD-MS device "product name BELCAT II" (or equivalent) manufactured by MicrotracBEL Corporation may be used. A sample powder composed of 5 mg of composite particles is prepared. The sample powder is placed in a container, and the temperature is raised from room temperature to 600 °C at a heating rate of 10 °C / min under a helium (He) gas flow of 50 ml / min. The amount of CO₂ generated (m / z = 44) is quantified with a mass spectrometer and obtained by integration.

[0033] 《XPS Measurement》 (Composition ratio of particle surface) C in the above formula (1) Li 、C Pcan be measured by the following procedure. An XPS apparatus is prepared. For example, an XPS apparatus "product name PHI X-tool" manufactured by ULVAC-PHI, Inc. (or an equivalent product) may be used. A sample powder composed of composite particles is set in the XPS apparatus. Narrow scan analysis is performed with a pass energy of 224 eV. The measurement data is processed by analysis software. For example, analysis software "product name MulTiPak" manufactured by ULVAC-PHI, Inc. (or an equivalent product) may be used. The peak area (integrated value) of the Li1s spectrum is converted into the elemental concentration (C Li ) of Li. The peak area of the P2p spectrum is converted into the elemental concentration (C P ) of P. C Li is divided by C P to obtain the composition ratio (C Li / C P ) on the particle surface.

[0034] (Coating rate) The coating rate is also measured by XPS. By analyzing the above measurement data, the ratio of each element is obtained from the peak areas of C1s, O1s, P2p, Ni2p3, Co2p3, and Me2p3.

[0035] The coating rate is obtained by the following formula (4). θ = P / (P + Ni + Co + Me) × 100 (4) In the above formula (4), θ represents the coating rate (%). P, nickel (Ni), Co (cobalt), and Me represent the ratios of the respective elements. "Me2p3" and Me in the above formula (4) may consist of manganese (Mn) or aluminum (Al), or may consist of Mn and Al. When Me contains Mn and Al, the sum of the composition ratios of the respective elements may be 1.

[0036] For example, when the positive electrode active material particles are "LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2", the above formula (4) can be transformed into the following formula (4').

[0037] θ = P / (P + Ni + Co + Mn) × 100 (4’) In the above formula (4’), Mn represents the elemental ratio of Mn obtained from the peak area of Mn2p3.

[0038] "Film Thickness Measurement" The film thickness (thickness of the coating film) can be measured by the following procedure. A sample is prepared by embedding composite particles in a resin material. The sample is subjected to cross-section machining using an ion milling apparatus. For example, an ion milling apparatus "Product Name Arblade (registered trademark) 5000" (or an equivalent product) manufactured by Hitachi High-Tech Corporation may be used. The cross-section of the sample is observed by SEM (Scanning Electron Microscope). For example, an SEM apparatus "Product Name SU8030" (or an equivalent product) manufactured by Hitachi High-Tech Corporation may be used. For 10 composite particles, the film thickness is measured in 5 fields of view each. The arithmetic mean of the film thicknesses at a total of 50 locations is regarded as the film thickness.

[0039] "ICP Measurement" (Composition Ratio of Cathode Active Material Particles) a, x, and y in the above formula (2) can be measured by the following procedure. A standard solution is prepared by diluting 0.01 g of cathode active material particles with pure water. An inductively coupled plasma atomic emission spectroscopy (ICP-AES) apparatus is prepared. For example, an ICP-AES apparatus "Product Name ICPE-9000" (or an equivalent product) manufactured by Shimadzu Corporation may be used. The emission intensity of the standard solution is measured using the ICP-AES apparatus. A calibration curve is created from the emission intensity of the standard solution. From the emission intensity of the sample solution and the calibration curve, the mole fractions of Li, Ni, Co, and Me contained in the cathode active material particles are determined.

[0040] (P Adhesion Amount) The mass fraction of P contained in the composite particles (also referred to as "P adhesion amount" or "P content") can be measured by the following procedure. A mixed acid is prepared by mixing hydrochloric acid, nitric acid, and sulfuric acid. The mixing ratio is "hydrochloric acid / nitric acid / sulfuric acid = 2 / 3 / 1 (molar ratio)". A solution is prepared by dissolving the composite particles in the mixed acid. A sample solution is prepared by diluting 0.01 g of the solution to 100 mL with pure water. Aqueous solutions of P (1000 ppm, 10000 ppm) are prepared. Standard solutions are prepared by diluting 0.01 g of the aqueous solutions with pure water. An ICP-AES apparatus is prepared. For example, an ICP-AES apparatus "product name ICPE-9800" manufactured by Shimadzu Corporation (or an equivalent product) may be used. The emission intensity of the standard solution is measured by the ICP-AES apparatus. A calibration curve is created from the emission intensity of the standard solution. The mass fraction of P contained in the composite particles is determined from the emission intensity of the sample solution and the calibration curve.

[0041] (Mass concentrations of Li, P, and Na in the coating solution) The mass concentrations of Li, P, and Na in the coating solution are measured by the following procedure. A 100 ml sample solution is prepared by diluting 0.01 g of the coating solution with pure water. Aqueous solutions of Li, P, and Na (1000 ppm, 10000 ppm) are prepared. Standard solutions are prepared by diluting 0.01 g of the aqueous solutions with pure water. An ICP-AES apparatus is prepared. The emission intensity of the standard solution is measured by the ICP-AES apparatus. A calibration curve is created from the emission intensity of the standard solution. The emission intensity of the sample solution (diluted coating solution) is measured by the ICP-AES apparatus. The mass concentrations of Li, P, and Na in the coating solution are determined from the emission intensity of the sample solution and the calibration curve. Further, the mass concentrations of Li and P are converted to molar concentrations. The molar ratio (n Li ) is obtained by dividing the molar concentration of Li (n P ) by the molar concentration of P (n Li / n P ).

[0042] <Composite particles> Figure 1 is a conceptual diagram showing the composite particles in this embodiment. The composite particle 5 can be referred to as, for example, "coated cathode active material" or the like. The composite particle 5 includes a cathode active material particle 1 and a coating film 2. The composite particle 5 may, for example, form an aggregate. That is, one composite particle 5 may contain two or more cathode active material particles 1. The composite particle 5 may have a D50 of, for example, 1 to 50 μm, or may have a D50 of 1 to 20 μm, or may have a D50 of 5 to 15 μm.

[0043] The coating film 2 is the shell of the composite particle 5. The coating film 2 covers at least a part of the surface of the cathode active material particle 1. The coating film 2 contains a phosphorus compound. By the coating film 2 containing a phosphorus compound, a reduction in resistance is expected.

[0044] The phosphorus compound may contain, for example, Li, oxygen (O), carbon (C), etc. P may be contained in the composite particle 5 at a mass fraction of, for example, 0.2 to 10%.

[0045] In the composite particle 5, the composition ratio (C Li / C P ) is 2.5 or less (see the above formula (1)). By the composition ratio (C Li / C P ) being 2.5 or less, the resistance can be significantly reduced. The composition ratio (C Li / C P ) may be, for example, 2.12 or less, or may be 1.96 or less, or may be 1.89 or less, or may be 1.73 or less. The composition ratio (C Li / C P ) may be zero. The composition ratio (C Li / C P ) may be, for example, 0.1 or more, or may be 0.5 or more, or may be 1.0 or more. The composition ratio (C Li / C P ) may be, for example, 1.73 to 2.5.

[0046] The coverage rate may be, for example, 80% or more, 85% or more, or 90% or more.

[0047] The coating film 2 may have a thickness of, for example, 5 to 100 nm, 5 to 50 nm, 10 to 30 nm, or 20 to 30 nm.

[0048] The positive electrode active material particles 1 are the core of the composite particles 5. The positive electrode active material particles 1 may be secondary particles (aggregates of primary particles). The positive electrode active material particles 1 (secondary particles) may have a D50 of, for example, 1 to 50 μm, 1 to 20 μm, or 5 to 15 μm.

[0049] The positive electrode active material particles 1 may contain any component. The positive electrode active material particles 1 contain a lithium-containing composite oxide having a layered rock salt structure. The crystal structure of the positive electrode active material particles 1 can be identified by, for example, X-ray diffraction (XRD). The lithium-containing composite oxide is represented by, for example, the following formula (2).

[0050] Li a Ni x Co y Me 1-x-y O2(2) In the above formula (2), Me contains at least one selected from the group consisting of Mn and Al, a may satisfy the relationship of 0.90 ≤ a ≤ 1.20, x may satisfy the relationship of 0.30 ≤ x ≤ 0.90, and y may satisfy the relationship of 0.10 ≤ y ≤ 0.40. It is preferable that a satisfies the relationship of 0.95 ≤ a ≤ 1.10. It is preferable that x satisfies the relationship of 0.50 ≤ x ≤ 0.90. When the value of x is within this range, the specific capacity tends to increase. The lithium-containing composite oxide is, for example, Li 1.10 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Li 1.10 Ni 0.60 Co0.20 Mn 0.20 O2, Li 1.10 Ni 0.82 Co 0.15 Al 0.03 It may also be O2 or the like.

[0051] When the composite particle 5 is heated from room temperature to 600 °C at a rate of 10 °C / min by TPD-MS, the amount of CO2 generated is 0.1 mass% or more. The CO2 measured by TPD-MS is derived from Li2CO3 present on the surface. When the amount of CO2 generated under the above conditions is 0.1 mass% or more, it is considered that the adhesion between the impurities (Li2CO3 and LiOH) present on the surface of the positive electrode active material particle 1 and the coating film is enhanced and the resistance is reduced. Also, when the amount of CO2 generated under the above conditions increases, Li elutes from the surface of the positive electrode active material particle 1 and becomes inactivated, so there is a risk that the battery capacity will decrease, and the impurities accumulate on the surface of the positive electrode active material particle 1, inhibiting the uniform formation of the coating film, so there is a risk that the resistance will increase. From these viewpoints, the amount of CO2 generated under the above conditions is preferably 1.0 mass% or less, and more preferably 0.8 mass% or less.

[0052] Incidentally, the amount of CO2 generated can be adjusted by the time of standing the lithium-containing composite oxide in the air after production. The standing time in the air may be, for example, 5 minutes or more, 30 minutes or more, 60 minutes or more, or 120 minutes or more. However, if the lithium-containing composite oxide is left standing for a long time, there is a risk that the amount of CO2 generated will increase too much, so it may be, for example, 300 minutes or less, 180 minutes or less, or 150 minutes or less.

[0053] <All-solid-state battery> Figure 2 is a conceptual diagram showing the all-solid-state battery in the present embodiment. The all-solid-state battery 100 may include, for example, an exterior body (not shown). The exterior body may be, for example, a pouch made of an aluminum laminate film or the like. The exterior body may house the power generation element 50. The power generation element 50 includes a positive electrode 10, a separator layer 30, and a negative electrode 20. That is, the all-solid-state battery 100 includes a positive electrode 10, a separator layer 30, and a negative electrode 20.

[0054] 《Positive Electrode》 The positive electrode 10 is layered. The positive electrode 10 may include, for example, a positive electrode active material layer and a positive electrode current collector. For example, the positive electrode active material layer may be formed by coating a positive electrode composite material on the surface of the positive electrode current collector. The positive electrode current collector may include, for example, aluminum (Al) foil or the like. The positive electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0055] The positive electrode active material layer may have a thickness of, for example, 10 to 200 μm. The positive electrode active material layer is in close contact with the separator layer 30. The positive electrode active material layer includes a positive electrode composite material. The positive electrode composite material includes composite particles and a sulfide solid electrolyte. That is, the positive electrode 10 includes composite particles and a sulfide solid electrolyte. The details of the composite particles are as described above.

[0056] The sulfide solid electrolyte can form an ion conduction path within the positive electrode active material layer. 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 composite particles (positive electrode active material). The sulfide solid electrolyte contains, for example, Li, P, and sulfur (S). The sulfide solid electrolyte may further contain, for example, O, silicon (Si), etc. The sulfide solid electrolyte may further contain, for example, halogen, etc. The sulfide solid electrolyte may further contain, for example, iodine (I), bromine (Br), etc. The sulfide solid electrolyte may be, for example, glass ceramics or argyrodite. The sulfide solid electrolyte may contain at least one selected from the group consisting of LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, and Li3PS4.

[0057] The positive electrode active material layer may further contain, for example, a conductive material. The conductive material can form an electron conduction path within the positive electrode active material layer. The blending amount of the conductive material may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the composite particles (positive electrode active material). The conductive material may contain any component. The conductive material may contain at least one selected from the group consisting of carbon black, vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene flake.

[0058] The positive electrode active material layer may further contain, for example, a binder. The blending amount of the binder may be, for example, 0.1 to 10 parts by mass with respect to 100 parts by mass of the composite particles (positive electrode active material). The binder may contain any component. The binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), styrene butadiene rubber (SBR), and polytetrafluoroethylene (PTFE).

[0059] 《Negative Electrode》 The negative electrode 20 is the counter electrode of the positive electrode 10. The negative electrode 20 is layered. The negative electrode 20 may include, for example, a negative electrode active material layer and a negative electrode current collector. For example, the negative electrode active material layer may be formed by coating a negative electrode composite material on the surface of the negative electrode current collector. The negative electrode current collector may include, for example, a copper (Cu) foil, a Ni foil, etc. The negative electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0060] The negative electrode active material layer may have a thickness of, for example, 10 to 200 μm. The negative electrode active material layer is in close contact with the separator layer 30. The negative electrode active material layer contains a negative electrode composite material. The negative electrode composite material contains negative electrode active material particles and a sulfide solid electrolyte. The negative electrode composite material may further contain a conductive material and a binder. The sulfide solid electrolyte may be of the same kind or different kinds between the negative electrode composite material and the positive electrode composite material. The negative electrode active material particles may contain any component. The negative electrode active material particles may include, for example, graphite, Si, silicon oxide [SiO x (0 < x < 2)], and Li4Ti5O 12 and may include at least one selected from the group consisting of.

[0061] 《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 contains a sulfide solid electrolyte. The separator layer 30 may further contain a binder. The sulfide solid electrolyte may be of the same kind or different kinds between the separator layer 30 and the positive electrode composite material. The sulfide solid electrolyte may be of the same kind or different kinds between the separator layer 30 and the negative electrode composite material.

[0062] <Method for Manufacturing Composite Particles> Figure 3 is a schematic flowchart of the method for manufacturing composite particles in this embodiment. Hereinafter, the "method for manufacturing composite particles in this embodiment" may be abbreviated as the "present manufacturing method". The present manufacturing method includes "(a) preparation of a mixture" and "(b) manufacture of composite particles". The present manufacturing method may further include, for example, "(c) heat treatment" and the like.

[0063] 《(a) Preparation of a mixture》 The present manufacturing method includes preparing a mixture by mixing a coating solution and cathode active material particles. The details of the cathode active material particles are as described above. The mixture may be, for example, a suspension or wet powder. For example, a suspension may be formed by dispersing cathode active material particles (powder) in the coating solution. For example, wet powder may be formed by spraying the coating solution onto the powder. In the present manufacturing method, any mixing device, granulating device, etc. may be used.

[0064] The coating solution includes a solute and a solvent. The solute includes a film-forming material (raw material of the coating film). The coating solution may further include, for example, a suspension (insoluble component), precipitate, etc.

[0065] The solute may include, for example, a phosphate compound. Thereby, the solute may contain P. The phosphate compound may be, for example, at least one selected from the group consisting of phosphoric anhydride (P2O5), orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid [(HPO3) n , and polyphosphoric acid. The phosphate compound may be, for example, at least one selected from the group consisting of metaphosphoric acid and polyphosphoric acid. Metaphosphoric acid and polyphosphoric acid may have a longer molecular chain than other phosphate compounds. It is considered that when the phosphate compound has a long molecular chain, a continuous coating film is likely to be formed. When the coating film has continuity, for example, an improvement in the coating rate is expected.

[0066] The solute may further contain sodium (Na). When Na is dissolved in the coating solution, the stability of the phosphate compound may be improved. The concentration (mass concentration) of Na in the coating solution may be, for example, 0 to 1%. The concentration of Na may be, for example, 0.6% or less, or 0.5% or less. The concentration of Na may be, for example, 0.5 to 0.6%.

[0067] The solute may further contain a lithium compound. The solute may contain, for example, lithium hydroxide, lithium carbonate, lithium nitrate, etc. The molar ratio (n Li / n P ) of Li to P may be, for example, less than 1.1 (see the above formula (3)). When the molar ratio (n Li / n P ) is less than 1.1, a reduction in the composition ratio (C Li / C P ) on the particle surface is expected. The molar ratio (n Li / n P ) may be, for example, 0.75 or less, or 0.30 or less, or zero. The molar ratio (n Li / n P ) may be, for example, 0 to 0.30, or 0.30 to 0.75.

[0068] <<(b) Production of Composite Particles>> This production method includes producing composite particles by drying the mixture. When the coating solution adhering to the surface of the positive electrode active material particles dries, a coating film is formed. In this production method, any drying method can be used.

[0069] For example, composite particles may be formed by the spray drying method. That is, when the suspension is sprayed from the nozzle, droplets are formed. The droplets contain positive electrode active material particles and the coating solution. For example, when the droplets are dried by hot air, composite particles can be formed. By using the spray drying method, an improvement in the coating rate is expected, for example.

[0070] The solid content fraction of the suspension for spray drying may be, for example, 1 to 50% or 10 to 30% in terms of volume fraction. The nozzle diameter may be, for example, 0.1 to 10 mm or 0.1 to 1 mm. The hot air temperature may be, for example, 100 to 200°C.

[0071] For example, composite particles may be produced by a tumbling fluidized bed coating apparatus. In the tumbling fluidized bed coating apparatus, "(a) preparation of the mixture" and "(b) production of the composite particles" can be carried out simultaneously.

[0072] 《(c) Heat treatment》 This production method may include subjecting the composite particles to heat treatment. The coating film can be fixed by heat treatment. Heat treatment may also be referred to as "firing". In this production method, any heat treatment apparatus can be used. The heat treatment temperature may be, for example, 150 to 300°C. The heat treatment time may be, for example, 1 to 10 hours. For example, heat treatment may be carried out in air or under an inert atmosphere.

Examples

[0073] Hereinafter, the present embodiment will be described using examples, but the present embodiment is not limited thereto.

[0074] <Production of cathode active material particles> Cathode active material particles A to D, which are lithium-containing composite oxides having a layered rock salt structure, were produced as follows.

[0075] 《Cathode active material particles A》 Nickel(II) sulfate hexahydrate (NiSO4·6H2O), cobalt(II) sulfate heptahydrate (CoSO4·7H2O) and manganese(II) sulfate pentahydrate (MnSO4·5H2O) were dissolved in pure water to obtain an aqueous raw material solution. The molar ratio of Ni, Co and Mn in the aqueous raw material solution was 1:1:1, and the total molar concentration of Ni, Co and Mn in the aqueous raw material solution was 1.8 mol / L.

[0076] 1 L of an aqueous ammonia solution at 10 g / L was prepared in a reaction vessel. While dropping 1 L of the raw material aqueous solution into the reaction vessel at a rate of 5.2 mL / min, a precipitate was formed by adjusting the pH to within 11.20 ± 0.2 using an aqueous sodium hydroxide solution, and a precursor was obtained. During the period from the start to the end of the precipitation reaction, the aqueous ammonia solution was appropriately added so that the ammonia concentration in the reaction solution became 10 g / L.

[0077] Li2CO3 was mixed with the precursor so that the molar ratio of Li to Ni, Co, and Mn was 1.10, and it was calcined at 800 °C for 5 hours in an oxygen atmosphere. Then, by allowing it to stand in the air atmosphere for 2 hours, cathode active material particles A were obtained. The composition of the cathode active material particles A was measured by the above-described procedure. The results are shown in Table 1 below.

[0078] 《Cathode Active Material Particles B - D》 Cathode active material particles B were obtained in the same manner as cathode active material particles A, except that the molar ratio of Ni, Co, and Mn in the raw material aqueous solution was dissolved to be 3:1:1. Cathode active material particles C were obtained in the same manner as cathode active material particles A, except that aluminum sulfate (Al2(SO4)3) was used instead of manganese(II) sulfate pentahydrate and the molar ratio of Ni, Co, and Al was dissolved to be 82:15:3. Cathode active material particles D were obtained in the same manner as cathode active material particles A, except that it was not allowed to stand in the air atmosphere. The compositions of the cathode active material particles B - D were measured by the above-described procedure. The results are shown in Table 1 below.

[0079] <Manufacture of All - Solid - State Battery> Composite particles, cathodes, and all - solid - state batteries according to Nos. 1 - 7 were manufactured as follows. Hereinafter, for example, "composite particles according to No. 1" may be abbreviated as "No. 1".

[0080] 《No. 1》 (Coating Liquid) A coating liquid was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) in 166 parts by mass of ion - exchanged water. Further, the molar ratio (n Li / n P Lithium hydroxide monohydrate (LiOH·H2O) was dissolved in the coating solution so that () became 0.30.

[0081] (Positive electrode) Positive electrode active material particles A were prepared. A suspension was prepared by dispersing 50 parts by mass of the powder of the positive electrode active material particles in 53.7 parts by mass of the coating solution. A spray dryer "Product name Mini Spray Dryer B - 290" manufactured by BUCHI was prepared. By supplying the suspension to the spray dryer, a powder of composite particles was produced. The air supply temperature of the spray dryer was 200 °C, and the air supply volume was 0.45 m 3 / min. The composite particles were heat - treated in air. The heat - treatment temperature was 200 °C. The heat - treatment time was 5 hours. By the above - mentioned procedure, the composition ratio (C Li / C P ) and the generation amount of CO2 (mass%) on the particle surface were measured. The results are shown in Table 1 below. In addition, in No.2 - 7 described later, the composition ratio (C Li / C P ) and the generation amount of CO2 (mass%) on the particle surface were also measured.

[0082] The following materials were prepared. Sulfide solid electrolyte: Li2S - P2S5 - based glass ceramics containing LiI (D50: 0.8 μm) Conductive material: VGCF Binder: SBR Dispersion medium: Heptane Positive electrode current collector: Al foil A composite particle, a sulfide solid electrolyte, a conductive material, a binder, and a dispersion medium were mixed to prepare a positive electrode slurry. The mixing ratio of the composite particle to the sulfide solid electrolyte was "composite particle / sulfide solid electrolyte = 6 / 4 (volume ratio)". The compounding amount of the conductive material was 3 parts by mass with respect to 100 parts by mass of the composite particle. The compounding amount of the binder was 0.7 parts by mass with respect to 100 parts by mass of the composite particle. The positive electrode slurry was sufficiently stirred by an ultrasonic homogenizer "Model UH-50" manufactured by SMT Co., Ltd. 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 using a hot plate. Thereby, a positive electrode raw sheet was manufactured. A disk-shaped positive electrode was cut out from the positive electrode raw sheet. The area of the positive electrode was 1 cm 2 It was.

[0083] (Negative electrode) As the sulfide solid electrolyte, the conductive material, the binder, and the dispersion medium, the same materials as those of the positive electrode were prepared. As a stirring device, a stirring device (product name "Filmix", model "30-L type") manufactured by Primix Co., Ltd. was prepared. The sulfide solid electrolyte, the conductive material, the binder, and the dispersion medium were put into the stirring container of the stirring device. The materials in the stirring container were stirred at a rotation speed of 20000 rpm for 30 minutes.

[0084] As negative electrode active material particles, Li4Ti5O 12(D50: 1.0 μm), and a Cu foil was prepared as the negative electrode current collector. Negative electrode active material particles were additionally charged into the stirring container. Stirring was performed at 15,000 rpm for 60 minutes. The mixing ratio of the negative electrode active material particles and the sulfide solid electrolyte was "composite particles / sulfide solid electrolyte = 7 / 3 (volume ratio)". The compounding amount of the conductive material was 1 part by mass with respect to 100 parts by mass of the composite particles. The compounding amount of the binder was 2 parts by mass with respect to 100 parts by mass of the composite particles. After charging the negative electrode active material particles, the materials in the stirring container were stirred at a rotation speed of 15,000 rpm for 60 minutes to prepare a negative electrode slurry. A coating film was formed by coating the negative electrode slurry on the surface of the negative electrode current collector. The coating film was dried at 100 °C for 30 minutes using a hot plate. Thus, a negative electrode precursor was manufactured. A disk-shaped negative electrode was cut out from the negative electrode precursor. The area of the negative electrode was 1 cm 2 It was.

[0085] (Separator layer) As the sulfide solid electrolyte, Li2S-P2S5-based glass ceramics containing LiI (D50: 2.5 μm) were prepared. As a mold for press working, a cylindrical ceramic having an inner diameter cross-sectional area of 1 cm 2 was prepared. 64.8 mg of the sulfide solid electrolyte was put into the mold, smoothed, and then pressed at a pressure of 1 ton / cm 2 to obtain a separator layer.

[0086] (All-solid-state battery) In the above mold, a positive electrode was disposed on one side of the separator layer and a negative electrode was disposed on the other side. The negative electrode, the separator layer, and the positive electrode were pressed together at a pressure of 6 ton / cm 2 for 1 minute. Stainless steel rods were inserted into the positive electrode and the negative electrode and constrained at 1 ton / cm 2 to form a power generation element. As a casing, a pouch made of an aluminum laminate film was prepared. The battery element was enclosed in the casing. Thus, an all-solid-state battery was formed.

[0087] 《No.2》 Positive electrode active material particles A were prepared. A coating solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) in 166 parts by mass of ion-exchanged water. Lithium hydroxide monohydrate was not added to the coating solution. Thereafter, composite particles, a positive electrode, and a all-solid-state battery were manufactured in the same manner as in No.1.

[0088] 《No.3》 Positive electrode active material particles A were prepared. A coating solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) in 166 parts by mass of ion-exchanged water. Further, lithium hydroxide monohydrate was dissolved in the coating solution so that the molar ratio (n Li / n P ) became 0.75. Thereafter, composite particles, a positive electrode, and a all-solid-state battery were manufactured in the same manner as in No.1.

[0089] 《No.4》 Positive electrode active material particles B were prepared. Composite particles, a positive electrode, and a all-solid-state battery were manufactured in the same manner as in No.1, except that positive electrode active material particles B were used.

[0090] 《No.5》 Positive electrode active material particles C were prepared. Composite particles, a positive electrode, and a all-solid-state battery were manufactured in the same manner as in No.1, except that positive electrode active material particles C were used.

[0091] 《No.6》 Positive electrode active material particles D were prepared. Composite particles, a positive electrode, and a all-solid-state battery were manufactured in the same manner as in No.1, except that positive electrode active material particles D were used.

[0092] 《No.7》 Positive electrode active material particles A were prepared. A coating solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Corporation) in 166 parts by mass of ion-exchanged water. Further, lithium hydroxide monohydrate was dissolved in the coating solution so that the molar ratio (n Li / n P) was adjusted to 2.00, and lithium nitrate (LiNO3) was dissolved in the coating solution. Thereafter, composite particles, a positive electrode, and a all-solid-state battery were manufactured in the same manner as in No.1.

[0093] <Evaluation> The capacity of the evaluation battery was confirmed by constant current-constant voltage charging and constant current discharging. The time rate of charge and discharge was 1 / 3C. "C" is a symbol representing the time rate. At a time rate of 1C, the full charge capacity of the battery is discharged in 1 hour.

[0094] The SOC (state of charge) of the evaluation battery was adjusted to 50% at a time rate of 1 / 3C. After adjusting the SOC, AC impedance measurement was carried out. The amplitude was 10 mV. The frequency range was 0.1~10 6 Hz. As a result, a Cole-Cole plot was created. An arc was fitted to the Cole-Cole plot. The distance between the two intersections of the fitted arc and the real axis was obtained. This distance was regarded as the "interface resistance". Using the interface resistance of the all-solid-state battery according to No.1 as a reference (1.0), the interface resistance of each all-solid-state battery was relativized and evaluated. The results are shown in Table 1 below.

[0095]

Table 1

[0096] <Results> For No.1 to No.5, where the CO2 generation amount of the composite particles measured under the above conditions was 0.1 mass% or more and the composition ratio (C Li / C P ) was 2.5 or less, the interface resistance was significantly reduced.

[0097] For No.6, where the CO2 generation amount of the composite particles measured under the above conditions was less than 0.1 mass%, the interface resistance was significantly increased. For No.7, where the composition ratio (C Li / C P ) was greater than 2.5, the interface resistance was significantly increased.

[0098] This embodiment and these examples are illustrative in all respects. This embodiment and these examples are not restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the description of the claims. For example, any configurations are extracted from this embodiment and these examples, and their arbitrary combinations are also initially contemplated.

Description of Reference Numerals

[0099] 1 Positive electrode active material particles, 2 Coating film, 5 Composite particles, 10 Positive electrode, 20 Negative electrode, 30 Separator layer, 50 Power generation element, 100 All-solid-state battery.

Claims

1. comprising a positive electrode active material particle and a coating film, wherein the positive electrode active material particle contains a lithium-containing composite oxide having a layered rock salt structure, the coating film covers at least a part of the surface of the positive electrode active material particle, the coating film contains a phosphorus compound, satisfies the following formula (1): C Li / C P ≤2.5 (1) and in the above formula (1), C Li represents the elemental concentration of lithium determined from the peak area of the Li 1s spectrum measured by X-ray photoelectron spectroscopy, C P represents the elemental concentration of phosphorus determined from the peak area of the P2p spectrum measured by X-ray photoelectron spectroscopy, when the temperature is raised from room temperature to 600 ° C at a rate of 10 ° C / min by thermogravimetric analysis of evolved gas, the amount of carbon dioxide generated is 0.1 mass% or more, the lithium-containing composite oxide having a layered rock salt structure is represented by the following formula (2): Li ａ Ni ｘ Co ｙ Me １－ｘ－ｙ O ２ (2) and in the above formula (2), Me contains at least one selected from the group consisting of Mn and Al, a satisfies the relationship of 0.90 ≤ a ≤ 1.20, x satisfies the relationship of 0.30 ≤ x ≤ 0.90, y satisfies the relationship of 0.10 ≤ y ≤ 0.40, a composite particle.

2. The composite particle according to claim 1, wherein the amount of carbon dioxide generated when the temperature is raised from room temperature to 600 ° C at a rate of 10 ° C / min by thermogravimetric analysis of evolved gas is 1.0 mass% or less.

3. The composite particle according to claim 1, wherein x satisfies the relationship of 0.50 ≤ x ≤ 0.

90.

4. A positive electrode comprising the composite particle according to any one of claims 1 to 3 and a sulfide solid electrolyte.

5. An all-solid-state battery comprising the positive electrode according to claim 4.

6. (a) preparing a mixture by mixing a coating liquid and positive electrode active material particles, and (b) producing composite particles by drying the mixture, wherein the positive electrode active material particle contains a lithium-containing composite oxide having a layered rock salt structure, the lithium-containing composite oxide having a layered rock salt structure is represented by the following formula (2): Li ａ Ni ｘ Co ｙ Me １－ｘ－ｙ O ２ (2) and in the above formula (2), Me contains at least one selected from the group consisting of Mn and Al, a satisfies the relationship of 0.90 ≤ a ≤ 1.20, x satisfies the relationship of 0.30 ≤ x ≤ 0.90, y satisfies the relationship of 0.10 ≤ y ≤ 0.40, the coating liquid contains a solute and a solvent, the solute contains a phosphoric acid compound, the coating liquid satisfies the following formula (3): 0 ≤ n Li / n P <1.1 (3) and in the above formula (3), n Li indicates the molar concentration of lithium in the coating liquid, n P A method for producing composite particles, where n represents the molar concentration of phosphorus in the coating liquid.

7. The method for producing a composite particle according to claim 6, wherein (b) includes forming the composite particle by a spray drying method.

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