Method for producing composite particles, a positive electrode, and an all-solid-state battery

Abstract

To provide a method for manufacturing composite particles, a positive electrode, and an all-solid-state battery, and composite particles, a positive electrode, and an all-solid-state battery that can reduce resistance.SOLUTION: In a method for manufacturing a composite particle including a positive electrode active material particle, and a coating film, the coating film covers at least a portion of the surface of the positive electrode active material particles, and the coating film contains a phosphorus compound, and the glass transition temperature of the coating film is 300°C.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Patent Document 1 (Japanese Patent Application Laid-Open No. 2010-135090) discloses a positive electrode active material including a reaction suppression portion formed by a vapor phase method and composed of a polyanion structure-containing compound containing lithium, and an all-solid-state battery including the positive electrode active material.

Prior Art Document

Patent Document

[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 that the direct contact between the sulfide solid electrolyte and the positive electrode active material particles is inhibited by the coating film, thereby reducing the resistance. However, there is still room for improvement in reducing the resistance.

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

Means for Solving the Problems

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

[0007] [1] The present disclosure relates to a method for manufacturing composite particles. The composite particles include a positive electrode active material particle and a coating film. 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. The glass transition temperature (Tg) of the coating film is 300°C or lower.

[0008] Although the technique of coating a positive electrode active material particle containing lithium (Li) with a compound containing phosphorus (P) is well-known, the prior art has not been able to reduce the resistance to a sufficient level for practical use. In an all-solid-state battery, the formation of an interface between the positive electrode active material and a sulfide solid electrolyte (hereinafter, also simply referred to as "solid electrolyte") is important, and by being joined at the atomic level, a diffusion path for Li ions is formed, and an improvement in ionic conductivity is expected.

[0009] The coating film on the surface of the positive electrode active material particle is required to function as a buffer layer for suppressing the reaction between the positive electrode active material and the solid electrolyte, but also plays an important role in the adhesion between the positive electrode active material and the solid electrolyte.

[0010] The inventors have found that composite particles including a coating film containing P and having a Tg of 300°C or lower have flexibility not possessed by conventional positive electrode active material particles. By such composite particles, a reduction in resistance is expected.

[0011] [2] The method for manufacturing composite particles may include the following (a) and (b).

[0012] (a) A mixture is prepared by mixing a coating liquid and positive electrode active material particles.

[0013] (b) Composite particles are manufactured by drying the mixture by a spray drying method.

[0014] The coating liquid contains a solute and a solvent.

[0015] A coating film can be formed by drying a coating solution adhering to the surface of the positive electrode active material particles by a spray drying method. The coating film described in the above [2] can be formed by the coating solution described in the above [1].

[0016] 〔3〕The coating solution may satisfy, for example, the relationship of the following formula (1).

[0017] 0≦n Li / n P <1.1 (1) In the above formula (1), n Li represents the molar concentration of lithium in the coating solution. n P represents the molar concentration of phosphorus in the coating solution.

[0018] 〔4〕The method for manufacturing the positive electrode may include the following (c) to (e).

[0019] (c) Prepare a positive electrode slurry containing the composite particles manufactured by the method for manufacturing the composite particles described in any one of [1] to [3] and a sulfide solid electrolyte.

[0020] (d) Form a positive electrode active material layer by applying the positive electrode slurry to the surface of the positive electrode current collector.

[0021] (e) Manufacture the positive electrode by rolling the positive electrode active material layer and the positive electrode current collector at 170°C or higher.

[0022] By applying a positive electrode slurry containing the above composite particles and a solid electrolyte to the surface of the positive electrode current collector, a positive electrode active material layer is formed. By rolling the positive electrode current collector on which the positive electrode active material layer is formed at 170°C or higher, the positive electrode active material layer is densified, the adhesion between the coating film and the solid electrolyte is improved, and a reduction in resistance is expected.

[0023] 〔5〕In the above (e), a positive electrode active material layer having a filling rate of 90% or more may be obtained.

[0024] The manufacturing method of the all-solid-state battery includes a positive electrode manufactured by the manufacturing method of the positive electrode described in the above [4] or [5].

[0025] 〔7〕The composite particles include positive electrode active material particles and a coating film. The coating film covers at least a part of the surface of the positive electrode active material particles. The coating film contains a phosphorus compound. The glass transition temperature (Tg) of the coating film is 300 °C or lower.

[0026] 〔8〕The composite particles may satisfy the following relationship of formula (2).

[0027] C Li / C P ≦2.5 (2) In the above formula (2), C Li represents the elemental concentration of lithium (Li) obtained from the peak area of the Li1s spectrum measured by X-ray Photoelectron Spectroscopy (XPS). C P represents the elemental concentration of phosphorus (P) obtained from the peak area of the P2p spectrum measured by X-ray Photoelectron Spectroscopy.

[0028] 〔9〕The positive electrode includes a positive electrode active material layer and a positive electrode current collector. The positive electrode includes the composite particles described in the above [7] or [8] and a sulfide solid electrolyte.

[0029] 〔10〕The filling rate of the positive electrode active material layer may be 90% or more.

[0030] 〔11〕The all-solid-state battery includes the positive electrode described in the above [9] or

[10] .

Brief Description of Drawings

[0031]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0032] Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "the present embodiment"), and examples of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the present example do not limit the technical scope of the present disclosure.

[0033] <Definition of Terms, etc.> Descriptions of "comprising", "including", "having", and variations thereof (e.g., "consisting of", etc.) are in an open-ended format. The open-ended format may further include additional elements in addition to the essential elements, or may not include them. The description of "consisting of" is in a closed format. However, even in the closed format, additional elements that are usually incidental impurities or are unrelated to the disclosed technology are not excluded. The description of "substantially consisting of" is in a semi-closed format. In the semi-closed format, the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology is allowed.

[0034] Expressions such as "may" and "can" are used in an allowable sense, "having the possibility of doing", rather than in an obligatory sense, "must do".

[0035] 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)".

[0036] 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 proceed in sequence.

[0037] For example, a numerical range such as "m to n%" includes upper and lower limit values 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 or lower limit value. For example, a new numerical range may be set by arbitrarily combining a value within the numerical range with a value described in another part of this specification, in a table, in a figure, etc.

[0038] 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.

[0039] "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 an equivalent product) manufactured by Shimadzu Corporation may be used.

[0040] 《DSC Measurement》 The coating film Tg can be measured by the following procedure. A Differential Scanning Calorimetry (DSC) instrument is prepared. For example, a DSC instrument "Product name DSC7000X" (or equivalent) manufactured by Hitachi High-Technologies Corporation may be used. Sample powder is prepared by drying the coating solution. 3 mg of the sample powder is placed in a pressure-resistant stainless-steel container inside a glove box filled with argon (Ar) gas (dew point: -70°C), and the lid is caulked and sealed. The pressure-resistant stainless-steel container is taken out of the glove box and heated from room temperature to 500°C at a heating rate of 1°C / min under a nitrogen (N) gas flow by a DSC apparatus. In the obtained profile (vertical axis: heat quantity, horizontal axis: temperature), Tg is read from the region where the baseline shifts.

[0041] 《Measurement of filling ratio》 The filling ratio can be measured by the following procedure. In a positive electrode cut to a predetermined area, the area, thickness, and mass of the positive electrode active material layer are measured, and the apparent density of the positive electrode active material layer is determined (apparent density of the positive electrode active material layer = mass / (area × thickness)). Next, the true density of the positive electrode active material layer is determined from the true density and content of the constituent components of the positive electrode active material layer (true density of the positive electrode active material layer = mass / Σ (content of each constituent component / true density of each constituent component)). The filling ratio (%) is obtained by dividing the apparent density by the true density.

[0042] 《XPS measurement》 (Composition ratio on the particle surface) C in the above formula (2) 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.

[0043] (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, and M2p3.

[0044] The coating rate is obtained by the following formula (3).

[0045] θ = P / (P + M) × 100 (3) In the above formula (4), θ represents the coating rate (%). P and M represent the ratios of the respective elements.

[0046] Note that "M2p3" and M in the above formula (3) are constituent elements of the positive electrode active material particles and represent elements other than Li and oxygen (O). That is, the positive electrode active material particles may be represented by the following formula (4).

[0047] LiMO2(4) M may consist of one element or a plurality of elements. M may be, for example, at least one selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). When M contains a plurality of elements, the sum of the composition ratios of the respective elements may be 1.

[0048] For example, when the cathode active material particles are "LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2", the above formula (3) can be transformed into the following formula (3').

[0049] θ = P / (P + Ni + Co + Mn) × 100 (3') Ni in the above formula (3') represents the elemental ratio of nickel obtained from the peak area of Ni2p3. Co represents the elemental ratio of cobalt obtained from the peak area of Co2p3. Mn represents the elemental ratio of manganese obtained from the peak area of Mn2p3.

[0050] 《Film Thickness Measurement》 The film thickness (thickness of the coating film) can be measured by the following procedure. A sample is prepared by embedding the 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 IM4000PLUS" (or an equivalent product) manufactured by Hitachi High-Technologies Corporation may be used. The cross-section of the sample is observed by SEM. For example, an SEM apparatus "product name Regulus8100" (or an equivalent product) manufactured by Hitachi High-Technologies Corporation may be used. For 10 composite particles, the film thickness is measured in 5 fields of view respectively. The arithmetic mean of the film thicknesses at a total of 50 locations is regarded as the film thickness.

[0051] 《ICP Measurement》 (Composition Ratio of Cathode Active Material Particles) The composition ratio of the positive electrode active material particles can be measured by the following procedure. A standard solution is prepared by diluting 0.01 g of the positive electrode 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 by 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 molar fractions of Li and M contained in the positive electrode active material particles are determined.

[0052] (P deposition amount) The mass fraction of P contained in the composite particles (also referred to as "P deposition 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. A standard solution is prepared by diluting 0.01 g of the aqueous solution 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. From the emission intensity of the sample solution and the calibration curve, the mass fraction of P contained in the composite particles is determined.

[0053] (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. 0.01 g of the coating solution is diluted with pure water to prepare 100 ml of a sample solution. Aqueous solutions of Li, P, and Na (1000 ppm, 10000 ppm) are prepared. 0.01 g of the aqueous solution is diluted with pure water to prepare a standard solution. 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. From the emission intensity of the sample solution and the calibration curve, the mass concentrations of Li, P, and Na in the coating solution are determined. Further, the mass concentrations of Li and P are converted to molar concentrations. The molar concentration of Li (n Li ) is divided by the molar concentration of P (n P ) to obtain the molar ratio (n Li / n P ).

[0054] <Method for Producing Composite Particles> The composite particles produced by the method for producing composite particles in the present embodiment include cathode active material particles and a coating film. The coating film covers at least a part of the surface of the cathode active material particles. The coating film contains a phosphorus compound. The Tg of the coating film is 300°C or lower.

[0055] FIG. 1 is an example of a schematic flowchart of the method for producing composite particles in the present embodiment. The method for producing composite particles includes "(a) preparation of a mixture" and "(b) production of composite particles". The method for producing composite particles may further include, for example, "(b') heat treatment", etc. Note that the method for producing composite particles is an example and is not limited thereto.

[0056] 《(a) Preparation of a Mixture》 The method for manufacturing composite particles includes preparing a mixture by mixing a coating solution and cathode active material particles. 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 method for manufacturing composite particles, any mixing device, granulating device, etc. may be used.

[0057] The coating solution contains a solute and a solvent. The solute contains a film-forming material (raw material for the coating film). The coating solution may further contain, for example, a suspension (insoluble component), precipitate, etc.

[0058] The solute may contain, for example, a phosphate compound. Thereby, the solute can 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 can have a longer molecular chain compared to 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 coverage rate is expected.

[0059] 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%.

[0060] 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 [refer to the above formula (1)]. When the molar ratio (n Li / n P ) is less than 1.1, it is expected that the composition ratio (C Li / C P ) on the particle surface will decrease. The molar ratio (n Li / n P ) may be, for example, 1.00 or less, 0.75 or less, 0.45 or less, or zero. The molar ratio (n Li / n P ) may be, for example, from 0 to 0.75 or from 0 to 1.00.

[0061] The positive electrode active material particles may be secondary particles (aggregates of primary particles). The positive electrode active material particles (secondary particles) may have a D50 of, for example, 1 to 50 μm, 1 to 20 μm, or 5 to 15 μm.

[0062] The positive electrode active material particles 1 may contain any component. The positive electrode active material particles 1 contain, for example, a lithium-containing composite oxide having a layered rock salt structure. The lithium-containing composite oxide is represented, for example, by the following formula (5).

[0063] Li a MO2(5) In the above formula (5), M contains at least one selected from the group consisting of Ni, Co, Mn, and Al, and a may satisfy the relationship of 0.90 ≤ a ≤ 1.20. 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 0.50 Co 0.20 Mn 0.30 O2, Li 1.10 Ni 0.60Co 0.20 Mn 0.20 O2, Li 1.10 Ni 0.80 Co 0.10 Mn 0.10 It may also be O2 or the like.

[0064] 《(b) Production of Composite Particles》 The method for producing composite particles includes producing composite particles by drying a mixture. When the coating liquid adhering to the surface of the positive electrode active material particles dries, a coating film is formed.

[0065] In the method for producing composite particles, composite particles may be formed by the spray drying method. That is, when a suspension is sprayed from a nozzle, droplets are formed. The droplets contain positive electrode active material particles and a coating liquid. For example, when the droplets are dried by hot air, composite particles can be formed. By using the spray drying method, for example, an improvement in the coating rate is expected.

[0066] The solid content ratio 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.

[0067] The coating film covers at least a part of the surface of the positive electrode active material particles. The coating film contains a phosphorus compound. By including a phosphorus compound in the coating film, a reduction in resistance is expected. The coating film may further contain Li.

[0068] The Tg of the coating film is 300°C or lower. When the Tg of the coating film is 300°C or lower, the flexibility of the coating film increases, and a reduction in resistance is expected. The Tg of the coating film is preferably 250°C or lower, and more preferably 200°C or lower.

[0069] Note that the Tg of the coating film is n in the coating liquidLi / n P can be adjusted by. In the coating liquid, the lower the n Li / n P , the lower the Tg of the coating film tends to be.

[0070] Note that the composite particles may be produced, for example, by a fluidized bed coating apparatus. In the fluidized bed coating apparatus, "(a) Preparation of the mixture" and "(b) Production of the composite particles" can be carried out simultaneously.

[0071] 《(b’) Heat treatment》 The method for producing the composite particles may include subjecting the composite particles to a heat treatment. The coating film can be fixed by the heat treatment. The heat treatment may also be referred to as "firing". In the method for producing the composite particles, 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, the heat treatment may be carried out in air or in an inert atmosphere.

[0072] <Method for manufacturing a positive electrode> FIG. 2 is an example of a schematic flowchart of the method for manufacturing a positive electrode in the present embodiment. The method for manufacturing a positive electrode includes "(c) Preparation of the slurry", "(d) Coating", and "(e) Rolling". Note that the method for manufacturing a positive electrode is an example and is not limited thereto.

[0073] 《(c) Preparation of the slurry》 The method for manufacturing a positive electrode includes preparing a positive electrode slurry containing composite particles and a solid electrolyte. The positive electrode slurry is prepared, for example, by dispersing the composite particles and the solid electrolyte in a dispersion medium. In the method for manufacturing a positive electrode, any mixing device, stirring device, and dispersing device can be used.

[0074] The positive electrode slurry may be prepared to further contain a conductive material, a binder, etc. in addition to the composite particles and the solid electrolyte. The dispersion medium is selected according to the type of the binder, etc. The dispersion medium may contain, for example, heptane, N-methyl-pyrrolidone (NMP), etc. For example, the viscosity of the positive electrode slurry may be adjusted by the amount of the dispersion medium used.

[0075] 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, a halogen, etc. The sulfide solid electrolyte may further contain, for example, iodine (I), bromine (Br), etc. The sulfide solid electrolyte may be, for example, a glass ceramic or an argyrodite. The sulfide solid electrolyte may contain at least one selected from the group consisting of, for example, 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. 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).

[0076] The conductive material may contain any component. The conductive material may contain, for example, at least one selected from the group consisting of carbon black, vapor-grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene flake. 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).

[0077] The binder may contain any component. The binder may contain, for example, 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). 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 (cathode active material).

[0078] 《(d) Coating》 The method for manufacturing the cathode includes forming a cathode active material layer by applying a cathode slurry onto the surface of a cathode current collector. The cathode slurry is applied onto the surface of the cathode current collector by, for example, a coating device. In the method for manufacturing the cathode, any coating device can be used. The applied cathode slurry is dried. For example, the coating film is dried by heating or hot air. Thereby, a cathode active material layer can be formed. The cathode active material layer may be formed to have a thickness of, for example, 10 to 200 μm.

[0079] The cathode current collector may contain, for example, aluminum (Al) foil or the like. The cathode current collector may have a thickness of, for example, 5 to 50 μm.

[0080] 《(e) Rolling》 The method for manufacturing the cathode includes manufacturing the cathode by rolling the cathode active material layer and the cathode current collector at 170°C or higher. By rolling the cathode active material layer and the cathode current collector at 170°C or higher, the flexibility of the coating film in the cathode active material layer increases, and the adhesion to the solid electrolyte improves. Thereby, the voids between the composite particles that do not contribute to charge and discharge and the solid electrolyte decrease, and a reduction in resistance is expected. Also, if the rolling temperature is too high, the solid electrolyte may deteriorate. Therefore, for example, it is preferable to roll the cathode active material layer and the cathode current collector at 200°C or lower.

[0081] The positive electrode active material layer and the positive electrode current collector are rolled, for example, by a roll press machine. In the method for manufacturing a positive electrode, any roll press machine can be used. For example, in a roll press machine having two rotating rolls, an integral body of the positive electrode active material layer and the positive electrode current collector may be passed through the roll gap of the roll press machine.

[0082] For example, in a roll press machine having two rotating rolls, when the temperature of at least one of the two rolls is heated to 170°C or higher, the positive electrode active material layer and the positive electrode current collector are rolled. The temperature of the roll may be, for example, 200°C or lower. Note that the temperature of the roll means the temperature of the roll surface.

[0083] The heating means of the roll is not particularly limited, and for example, a heater or the like is used. Examples of the heater include an infrared heater (IR heater), an electric heater, and the like.

[0084] By rolling, a positive electrode active material layer having a filling rate of 90% or more may be obtained. When the positive electrode active material layer has a filling rate of 90% or more, more reduction in resistance is expected. By rolling, for example, a positive electrode active material layer having a filling rate of 93% or more may be obtained, a positive electrode active material layer having a filling rate of 94% or more may be obtained, or a positive electrode active material layer having a filling rate of 95% or more may be obtained. By rolling, for example, a positive electrode active material layer having a filling rate of 100% may be obtained, a positive electrode active material layer having a filling rate of 99% or less may be obtained, or a positive electrode active material layer having a filling rate of 97% or less may be obtained. The filling rate of the positive electrode active material layer by rolling may be, for example, 90 to 95%.

[0085] The positive electrode raw sheet is manufactured by rolling. The raw sheet can be cut into a predetermined planar size according to the specifications of the battery.

[0086] <Method for manufacturing all-solid-state battery> The manufacturing method of the all-solid-state battery includes "(f) Manufacturing of the all-solid-state battery including a positive electrode". For example, a negative electrode and a separator layer are respectively prepared. For example, a laminate is formed by laminating a positive electrode, a separator layer, and a negative electrode in this order. A power generation element can be formed by subjecting the laminate to pressing. Terminals and the like are connected to the power generation element. The all-solid-state battery can be manufactured by enclosing the power generation element in an exterior body.

[0087] For example, a negative electrode slurry may be prepared by mixing negative electrode active material particles, a sulfide solid electrolyte, a conductive material, a binder, and a dispersion medium. The dispersion medium may contain, for example, heptane, butyl butyrate, or the like. A negative electrode active material layer may be manufactured by applying the slurry to the surface of a negative electrode current collector. 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 negative electrode active material layer may be compressed after drying. The negative electrode active material layer may have a thickness of, for example, 10 to 200 μm. The negative electrode active material particles may contain any component. The negative electrode active material particles may contain, for example, graphite, Si, SiO x (0 < x < 2), and Li4Ti5O 12 and may contain at least one selected from the group consisting of. The sulfide solid electrolyte may be of the same type or different types between the negative electrode composite material and the positive electrode composite material. The conductive material and the binder may be of the same type or different types between the negative electrode composite material and the positive electrode composite material. The negative electrode current collector may contain, for example, a copper (Cu) foil, a Ni foil, or the like. The negative electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0088] For example, a separator layer may be formed by pressing a sulfide solid electrolyte. For example, a slurry may be prepared by mixing a sulfide solid electrolyte, a binder, and a dispersion medium. For example, a separator layer may be formed by applying the slurry to the surface of an electrode (positive electrode or negative electrode). For example, a separator layer may be formed by applying the slurry to the surface of a temporary support (e.g., a metal foil). The separator layer may be transferred from the temporary support to the surface of the electrode. The same type of sulfide solid electrolyte or different types of sulfide solid electrolytes may be used between the positive electrode, the separator layer, and the negative electrode.

[0089] <Composite particles> The composite particles include positive electrode active material particles and a coating film. The coating film covers at least a part of the surface of the positive electrode active material particles. The coating film contains a phosphorus compound. The glass transition temperature (Tg) of the coating film is 300°C or lower.

[0090] FIG. 3 is a conceptual diagram showing the composite particles in the present embodiment. The composite particles 5 are produced by the manufacturing method described above. The composite particles 5 may be referred to as, for example, "coated positive electrode active material" or the like. The composite particles 5 include positive electrode active material particles 1 and a coating film 2. The composite particles 5 may form aggregates, for example. That is, one composite particle 5 may contain two or more positive electrode active material particles 1. The positive electrode active material particles 1 are the core of the composite particles 5. The details of the positive electrode active material particles 1 are as described above.

[0091] The coating film 2 is the shell of the composite particles 5. The coating film may have a thickness of, for example, 5 to 100 nm, 5 to 50 nm, 10 to 30 nm, or 20 to 30 nm. The coating film 2 may further contain, for example, oxygen (O), carbon (C), etc. P may be contained in the composite particles at a mass fraction of, for example, 0.2 to 10%. The details of the coating film 2 are as described above.

[0092] In the composite particles, the composition ratio (C Li / C P ) is 3.5 or less, preferably 2.5 or less (see the above formula (2)). When the composition ratio (C Li / C P ) is 2.5 or less, the resistance can be further reduced. The composition ratio (C Li / C P ) may be, for example, 1.96 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 2.65.

[0093] The coating rate may be, for example, 80% or more, or may be 85% or more, or may be 90% or more. The details of the composite particles 5 are as described above.

[0094] <Positive electrode> The positive electrode 10 is layered. The positive electrode 10 includes a positive electrode active material layer and a positive electrode current collector. The positive electrode active material layer is in close contact with the separator layer 30. The positive electrode active material layer contains a positive electrode composite material. The positive electrode composite material contains composite particles and a sulfide solid electrolyte. The sulfide solid electrolyte can form an ion conduction path in the positive electrode active material layer. The positive electrode active material layer may further contain, for example, a conductive material and a binder. The conductive material can form an electron conduction path in the positive electrode active material layer. The details of the positive electrode 10 are as described above.

[0095] <All-solid-state battery> Figure 4 is a conceptual diagram showing the all-solid-state battery according to 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.

[0096] 《Negative Electrode》 The negative electrode 20 is a counter electrode to the positive electrode 10. The negative electrode 20 is in a layered form. The negative electrode 20 includes a negative electrode active material layer and a negative electrode current collector. The negative electrode active material layer is in close contact with the separator layer 30. The details of the negative electrode 20 are as described above.

[0097] 《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 details of the separator layer 30 are as described above.

Examples

[0098] Hereinafter, the present embodiment will be described using examples, but the present embodiment is not limited thereto.

[0099] <Manufacture of Positive Electrode Active Material Particles> Positive electrode active material particles, which are lithium-containing composite oxides having a layered rock salt structure, were manufactured as follows.

[0100] 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 a raw material aqueous solution. The molar ratio of Ni, Co, and Mn in the raw material aqueous solution was 1:1:1, and the total molar concentration of Ni, Co, and Mn in the raw material aqueous solution was 1.8 mol / L.

[0101] 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 of the reaction solution became 10 g / L.

[0102] Lithium carbonate (Li2CO3) was mixed with the precursor so that the molar ratio of Li to Ni, Co, and Mn was 1.10, and the mixture was calcined at 800 °C for 5 hours in an oxygen atmosphere to obtain positive electrode active material particles. By the above-described procedure, the composition of the positive electrode active material particles was measured. The composition of the positive electrode active material particles was Li 1.10 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2.

[0103] <Manufacture of All-Solid-State Battery> Composite particles, a positive electrode, and an all-solid-state battery according to Nos. 1 to 7 were manufactured as follows. Hereinafter, for example, "composite particles according to No. 1" may be abbreviated as "No. 1".

[0104] 《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, lithium hydroxide monohydrate (LiOH·H2O) was dissolved in the coating liquid so that the molar ratio (n Li / n P ) became 0.75. By the above-described procedure, Tg was measured. The results are shown in Table 1 below. In Nos. 2 to 7 described later, Tg is also measured in the same manner.

[0105] (Positive Electrode) The above-mentioned positive electrode active material particles were prepared. 50 parts by mass of the powder of the positive electrode active material particles were dispersed in 53.7 parts by mass of the coating liquid to prepare a suspension. 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 ) on the particle surface was measured. The results are shown in Table 1 below. In addition, in No. 2 to 7 described later, the composition ratio (C Li / C P ) on the particle surface will be measured in the same manner.

[0106] The following materials were prepared.

[0107] 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 Composite particles and a sulfide solid electrolyte were prepared. The composite particles and the sulfide solid electrolyte were weighed in a glove box filled with Ar gas (dew point: -30°C). By mixing these with a conductive material, a binder, and a dispersion medium, a positive electrode slurry was prepared. The mixing ratio was "composite particles / 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 particles. The compounding amount of the binder was 0.7 parts by mass with respect to 100 parts by mass of the composite particles. 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 a positive electrode current collector. The coating film was dried at 100°C for 30 minutes using a hot plate. After drying, the coating film was pressed at 100 kN by a roll press machine equipped with two rotating rolls (roll temperature: 170°C). 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 Thereafter. The filling rate was measured according to the above procedure. The results are shown in Table 1 below. It should be noted that in Nos. 2 to 7 described later, the filling rate will be measured in the same manner.

[0108] (Negative electrode) As the sulfide solid electrolyte, conductive material, binder, and dispersion medium, the same materials as those for 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, conductive material, binder, and dispersion medium were put into the stirring container of the stirring device. The materials in the stirring container were stirred at a rotational speed of 20,000 rpm for 30 minutes.

[0109] 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 blending amount of the conductive material was 1 part by mass with respect to 100 parts by mass of the composite particles. The blending 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. Thereby, 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.

[0110] (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 and compacted at a pressure of 1 ton / cm 2 to obtain a separator layer.

[0111] (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. A stainless steel rod was inserted into the positive electrode and the negative electrode and constrained at 0.3 ton / cm 2 to form a power generation element. As a housing, a pouch made of an aluminum laminate film was prepared. The battery element was enclosed in the housing. Thereby, an all-solid-state battery was formed.

[0112] 《No.2》 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. Furthermore, lithium hydroxide monohydrate was dissolved in the coating solution so that the molar ratio (n Li / n P ) was 0.45. Thereafter, composite particles, a positive electrode, and a all-solid-state battery were manufactured in the same manner as in No.1.

[0113] 《No.3》 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.

[0114] 《No.4》 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. Furthermore, lithium hydroxide monohydrate was dissolved in the coating solution so that the molar ratio (n Li / n P ) was 1.00. Thereafter, composite particles, a positive electrode, and a all-solid-state battery were manufactured in the same manner as in No.1.

[0115] 《No.5》 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. Furthermore, lithium nitrate (LiNO3) was dissolved in the coating solution so that the molar ratio (n Li / n P ) was 2.00. Thereafter, composite particles, a positive electrode, and a all-solid-state battery were manufactured in the same manner as in No.1.

[0116] 《No.6》 870.4 parts by mass of hydrogen peroxide solution (mass concentration: 30%) was put into a container. Next, 987.4 parts by mass of ion-exchanged water and 44.2 parts by mass of niobic acid [Nb2O5·3H2O] were put into the container. Next, 87.9 parts by mass of aqueous ammonia (mass concentration: 28%) was put into the container. By sufficiently stirring the contents of the container, a solution was formed. The solution is considered to contain a peroxo complex of Nb. Further, 0.1 part by mass of lithium hydroxide monohydrate was dissolved in the solution to prepare a coating solution. Thereafter, in the same manner as in No. 1, composite particles, a positive electrode, and an all-solid-state battery were manufactured.

[0117] <Evaluation> The capacity of the evaluation battery was confirmed by constant current-constant voltage charging and constant current discharging. The charge-discharge time rate 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.

[0118] The SOC (state of charge) of the evaluation battery was adjusted to 50% at a time rate of 1 / 3C. After the adjustment of SOC, AC impedance measurement was carried out. The amplitude was 10 mV. The frequency range was 0.1 to 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 determined. 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 resistances of the respective all-solid-state batteries were relativized and evaluated. The results are shown in Table 1 below.

[0119]

Table 1

[0120] <Results> For No. 1 to 4 in which the Tg of the coating film is 300 °C or lower, the interface resistance is significantly reduced.

[0121] For No. 5 where the Tg of the coating film exceeds 300 °C, the interfacial resistance increased significantly. For No. 6 where the coating film has no Tg, the interfacial resistance increased.

[0122] 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 includes all modifications within the meaning and scope equivalent to the description of the claims. For example, it has also been initially planned that any configurations are extracted from this embodiment and these examples and combined arbitrarily.

Explanation of Reference Numerals

[0123] 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, the coating film covering at least a part of the surface of the positive electrode active material particle, a method for producing composite particles, wherein a glass transition temperature of the coating film is 300°C or lower, (a) preparing a mixture by mixing a coating liquid and the positive electrode active material particle, and (b) producing composite particles by drying the mixture by a spray drying method, comprising, the coating liquid containing a solute and a solvent, the solute containing metaphosphoric acid, a method for producing composite particles.

2. the solute further containing a lithium compound, the coating liquid represented by the following formula (1): 0 ≦ n Li / n P < 1.1 (1) satisfying the relationship of, in the above formula (1), n Li represents a molar concentration of lithium in the coating liquid, n P represents a molar concentration of phosphorus in the coating liquid, the method for producing composite particles according to Claim 1.

3. (c) preparing a positive electrode slurry containing composite particles produced by the method for producing composite particles according to Claim 1 and a sulfide solid electrolyte, (d) forming a positive electrode active material layer by applying the positive electrode slurry onto the surface of a positive electrode current collector, and, (e) producing a positive electrode by rolling the positive electrode active material layer and the positive electrode current collector at 170°C or higher, comprising, a method for producing a positive electrode.

4. The method for manufacturing a positive electrode according to claim 3, wherein in the step (e), the positive electrode active material layer having a filling rate of 90% or more is obtained.

5. (f) Manufacturing an all-solid-state battery including the positive electrode manufactured by the manufacturing method according to claim 3, The method for manufacturing an all-solid-state battery, including the above steps.

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