Coating liquid, method for producing composite particles, composite particles, and all-solid battery

Abstract

The present application relates to a coating liquid, a method for producing composite particles, composite particles, and an all-solid battery. The coating liquid contains a solute and a solvent. The solute contains a phosphoric acid compound. "I0 / (I0+I1+I2)" is 0.7 or less. In 31 In a P-NMR spectrum, "I0" represents the area of a signal from a Q 0 unit of PO4, "I1" represents the area of a signal from a Q 1 unit of PO4, and "I2" represents the area of a signal from a Q 2 unit of PO4.

Description

Background of the Invention Technical Field

[0002] This disclosure relates to coating liquid, methods for manufacturing composite particles, composite particles, and all-solid-state batteries. Background Technology

[0004] International Publication No. 2017 / 094416 discloses impregnation of positive electrode active material in a coating forming solution containing lithium metaphosphate. Summary of the Invention

[0005] This invention proposes a method for forming a phosphorus (P)-containing coating on the surface of positive electrode active material particles. Conventionally, for example, an aqueous solution of lithium metaphosphate has been used as the coating solution.

[0006] A coating can be applied to the surface of the positive electrode active material particles. For example, in sulfide-based all-solid-state batteries, a higher coating rate is expected to reduce the degradation of the sulfide solid electrolyte. This is believed to be due to reduced direct contact between the positive electrode active material particles and the sulfide solid electrolyte. However, when using conventional coating solutions to increase the coating rate, there is a tendency for the coating to become thicker. By increasing the coating thickness, the battery resistance may increase.

[0007] The purpose of this disclosure is to provide composite particles containing a thin coating with high coverage.

[0008] The technical structure and effects of this disclosure are described below. However, the mechanism of action in this specification includes conjecture. The mechanism of action does not limit the technical scope of this disclosure.

[0009] 1. The coating solution contains a solute and a solvent. The solute contains a phosphoric acid compound.

[0010] The coating liquid satisfies the following relationship (1).

[0011] {I0 / (I0+I1+I2)}≤0.7(1)

[0012] In equation (1) above, I0 represents... 31 Q from PO4 in the P-NMR spectrum 0 The area of ​​the signal in the cell. I1 represents the signal area in the cell. 31 Q from PO4 in the P-NMR spectrum 1 The area of ​​the signal in the cell. I2 represents the signal area in the cell. 31 Q from PO4 in the P-NMR spectrum 2 The area of ​​the signal in the unit.

[0013] In the coating solution, the phosphoric acid compound can take various forms. That is, the coating solution can contain various PO4 units. For example, the coating solution can contain Q... 0 Unit, Q 1 Unit and Q2 Units. The solute composition can be determined based on their ratio of presence. Q 0 Unit, Q 1 Unit and Q 2 The unit is represented by the following equations (1-0) to (1-2).

[0014] [Chemistry 1]

[0015]

[0016] Q 0 The unit has the structure of the above equation (1-0). Q 0 The unit does not have bonding bonds. It is assumed that Q... 0 The unit comes from free PO4 unit (phosphoric acid).

[0017] Q 1 The unit has the structure of the above equation (1-1). Q 1 The unit has one bond. It is assumed that Q... 1 Units such as dimers derived from PO4 (P2O7) are examples.

[0018] Q 2 The unit has the structure of the above equation (1-2). Q 2 The unit has two bonding bonds. It is assumed that Q... 2 Units, for example, come from chain structures (chain condensed phosphoric acid).

[0019] It should be noted that equations (1-0) to (1-2) above are merely representative examples of each unit. Each unit can also include various variations. For example, the "-OH" in each equation can be dissociated, and "-O" can be used instead. - The form "" can be used. For example, H can be replaced with other elements. For example, it can take the form "-OLi", "-ONa", etc.

[0020] Hereinafter, the left side of the above equation (1) will be denoted as "Q". 0 "Unit ratio". It is believed that Q... 0 The smaller the unit ratio, the greater the proportion of long-chain phosphoric acid compounds.

[0021] Regarding conventional coating solutions, there is a Q 0 There is a tendency for the unit ratio to be large. That is, the Q of conventional coating liquids... 0 The unit ratio exceeds 0.7.

[0022] Based on the new insights presented in this disclosure, if Q 0 When the unit ratio decreases to below 0.7, the coverage rate increases, and the coating film can be formed thinner. It is believed that the presence of long-chain phosphoric acid compounds facilitates the formation of continuous coating films. As a result, the coverage rate is considered to be increased, and the coating film can be formed thinner.

[0023] 2. The coating liquid can further satisfy, for example, the relationship of the following formula (2).

[0024] 0.17≤{I2 / (I0+I1+I2)}(2)

[0025] By further satisfying the relationship in equation (2) above, an increase in coverage rate can be expected.

[0026] 3. The coating liquid can further satisfy, for example, the relationship of the following formula (3).

[0027] I0 <I2(3)

[0028] By further satisfying the relationship in equation (3) above, an increase in coverage rate can be expected.

[0029] 4. The coating liquid can further satisfy, for example, the relationship of the following formula (4).

[0030] 0≤C Li / C P <1.1(4)

[0031] In equation (4) above, C Li This indicates the molar concentration of lithium in the coating solution. (C) P This indicates the molar concentration of phosphorus in the coating solution.

[0032] C Li / C P This indicates the molar ratio (mass ratio) of lithium (Li) to phosphorus (P). A molar ratio less than 1.1 can be expected to result in a reduction in precipitates.

[0033] 5. Solvents may include, for example, water.

[0034] 6. The solute may include, for example, at least one selected from metaphosphoric acid and polyphosphoric acid.

[0035] Through the dissolution of metaphosphoric acid and polyphosphoric acid in solvents, Q exists. 0 The tendency for the unit ratio to decrease.

[0036] 7. The solute may further contain sodium, for example.

[0037] Phosphoric acid compounds with long molecular chains can potentially be reduced in molecular weight by solvent decomposition. According to the novel insights of this disclosure, the stability of phosphoric acid compounds with long molecular chains can potentially be improved by dissolving sodium (Na) in the coating solution.

[0038] 8. The methods for manufacturing composite particles include the following (a) and (b).

[0039] (a) A mixture is prepared by mixing the coating liquid with the positive electrode active material particles.

[0040] (b) To produce composite particles by drying the mixture.

[0041] The composite particles comprise positive electrode active material particles and a coating film. The coating film covers at least a portion of the surface of the positive electrode active material particles. The coating film contains phosphorus.

[0042] Composite particles can also be referred to as "coated positive electrode active materials". The coating solution adhering to the surface of the positive electrode active material particles is dried, thereby forming a coating film. By using the coating solutions described in "1 to 7" above, the formation of a thin coating film and an increase in coverage can be expected.

[0043] 9. The above (b) may include, for example, the formation of composite particles using a spray drying method.

[0044] 10. The composite particles comprise positive electrode active material particles and a coating film. The coating film covers at least a portion of the surface of the positive electrode active material particles. The coating film contains phosphorus. The coating film has a thickness of less than 28.5 nm. The coverage rate, determined by X-ray photoelectron spectroscopy, is greater than 83%.

[0045] The coating coverage can be determined using X-ray photoelectron spectroscopy (XPS). A coating coverage of 83% or higher, for example in sulfide-based all-solid-state batteries, suggests a reduction in the degradation of the sulfide solid electrolyte. A reduction in battery resistance can be expected by keeping the coating thickness below 28.5 nm. Hereinafter, "coating thickness" will sometimes be simply referred to as "film thickness".

[0046] 11. An all-solid-state battery comprises a positive electrode layer, a separator layer, and a negative electrode layer. The separator layer is disposed between the positive and negative electrode layers. The positive electrode layer comprises composite particles and a sulfide solid electrolyte.

[0047] The embodiments of this disclosure (hereinafter referred to as "this embodiment") and the examples of this disclosure (hereinafter referred to as "this example") will be described below. However, this embodiment and this example do not limit the technical scope of this disclosure. Attached Figure Description

[0048] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will now be described with reference to the accompanying drawings, wherein like symbols denote like elements, and wherein:

[0049] Figure 1 for 31 An example of P-NMR spectroscopy;

[0050] Figure 2 This is a schematic flowchart of the method for manufacturing composite particles in this embodiment;

[0051] Figure 3 is a conceptual diagram showing the composite particles in the present embodiment.

[0052] Figure 4 is a conceptual diagram showing the all-solid-state battery in the present embodiment.

[0053] Figure 5 is a graph showing Q 0 the relationship between cell ratio and coverage. DETAILED DESCRIPTION

[0054] <Definition of Terms, Etc.>

[0055] Recitations of "comprising", "including", "having" and variations thereof (e.g., "consisting of", etc.) are open-ended. In addition to essential elements, the open-ended form may further include additional elements, or may not include additional elements. Recitations of "consisting of" are closed-ended. However, even closed-ended forms do not exclude normally accompanying impurities or additional elements unrelated to the technology of the present disclosure. Recitations of "consisting essentially of" are semi-closed-ended. In the semi-closed-ended form, elements that do not substantially affect the basic and novel characteristics of the technology of the present disclosure are allowed.

[0056] Expressions such as "may", "can" are not used in the mandatory meaning "meaning must be done", but are used in the permissive meaning "meaning having the possibility to do".

[0057] Unless otherwise specified, elements expressed in the singular form also include the plural form. For example, "particle" may refer not only to "one particle" but also to "an aggregate of particles (powder, particles, particle group)".

[0058] For the multiple steps, acts and operations included in various methods, unless otherwise specified, the execution order is not limited to the recited order. For example, multiple steps may be performed simultaneously. For example, multiple steps may also be performed before and after each other.

[0059] For example, a numerical range such as "m to n%" includes the upper limit and the lower limit unless otherwise specified. That is, "m to n%" represents a numerical range of "m% or more and n% or less". In addition, "m% or more and n% or less" includes "more than m% and less than n%". Furthermore, a value arbitrarily selected from within the numerical range may be used as a new upper limit or lower limit. For example, a new numerical range may be set by arbitrarily combining a value within the numerical range with values described in other parts of the present specification, tables, drawings, etc.

[0060] All numerical values ​​are modified by the term "approximately". "Approximately" can refer to, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​can be approximate values ​​that vary depending on how the technology of this disclosure is used. All numerical values ​​can be expressed in significant figures. The measured value can be the average of multiple measurements. The number of measurements can be 3 or more, 5 or more, or 10 or more. Generally, the more measurements, the higher the reliability of the average value can be expected. The measured value can be rounded according to the number of significant figures. The measured value may include, for example, errors associated with the detection limits of the measuring device.

[0061] Geometric terms (such as "parallel," "perpendicular," and "orthogonal") should not be interpreted in their strict sense. For example, "parallel" can deviate slightly from the strict meaning of "parallel." Geometric terms may include tolerances and errors in design, operation, and manufacturing. Dimensional relationships in various drawings may sometimes differ from actual dimensional relationships. To aid understanding of the technology disclosed herein, dimensional relationships (length, width, thickness, etc.) in various drawings may be altered. Furthermore, some structural elements may be omitted.

[0062] When a compound is represented by a stoichiometric formula (e.g., "LiCoO2"), that formula is merely a representative example of the compound. Compounds can have non-stoichiometric compositions. For example, when lithium cobalt oxide is represented as "LiCoO2," unless otherwise specified, it is not limited to a composition ratio of "Li / Co / O = 1 / 1 / 2," and can contain Li, Co, and O in any ratio. Furthermore, doping, substitution, etc., based on trace elements are permissible.

[0063] "D50" indicates the particle size at which the cumulative frequency from the smallest side of the particle size distribution reaches 50%. D50 can be determined using laser diffraction.

[0064] 《 31 P-NMR Measurement

[0065] “ 31 "P-NMR" indicates phosphorus 31 nuclear magnetic resonance (P-NMR). 31 P Nuclear Magnetic Resonance). Coating solution 31 P-NMR spectroscopy can be determined using the following steps. Prepare an FT-NMR apparatus. For example, an FT-NMR apparatus manufactured by Nippon Egis Corporation, "Product Name JNM-ECA600I Type I" (or an equivalent), can be used. Fill a microtube with a diameter of 5 mm with the coating solution (sample). Place the microtube in the FT-NMR apparatus. The measurement conditions are as follows.

[0066] Measurement temperature: room temperature (20±5℃)

[0067] Pulse width: 30°, 4.0μs

[0068] Repeatability conditions: ACQTM = 0.56197s, PD = 30s

[0069] Pulse mode: 31Pbcm

[0070] Chemical shift standard: orthophosphoric acid (0 ppm)

[0071] Observation frequency: 242.95MHz

[0072] Observation width: 120 ppm (center observation: 10 ppm)

[0073] Sample rotation speed: 15Hz

[0074] Figure 1 for 31 An example of P-NMR spectroscopy.

[0075] Q from PO4 0 The signal of the unit appears in the chemical shift near 0 ppm. The area (integral value) of this signal is regarded as "I0" of the above equation (1).

[0076] Q from PO4 1 The signal of the unit appears in the chemical shift around -10 to -13 ppm. The area of ​​this signal is considered as "I1" in the above equation (1).

[0077] Q from PO4 2 The signal of the unit appears in the chemical shift around -20 to -25 ppm. The area of ​​this signal is considered as "I2" in the above equation (1).

[0078] ICP Measurement

[0079] The mass concentrations of Li, P, and Na in the coating solution can be determined using inductively coupled plasma atomic emission spectrometry (ICP-AES). The determination sequence is as follows: Prepare a 100 ml sample solution by diluting 0.01 g of the coating solution with pure water. Prepare aqueous solutions of Li, P, and Na (1000 ppm and 10000 ppm). Prepare a standard solution by diluting 0.01 g of the aqueous solution with pure water. Prepare an ICP-AES apparatus. For example, an ICP-AES apparatus manufactured by Shimadzu Corporation, "Product Name ICPE-9800" (or an equivalent), can be used. Measure the luminescence intensity of the standard solution using the ICP-AES apparatus. Construct a calibration curve from the luminescence intensity of the standard solution. Measure the luminescence intensity of the sample solution (the diluted coating solution) using the ICP-AES apparatus. Calculate the mass concentrations of Li, P, and Na in the coating solution based on the luminescence intensity of the sample solution and the standard curve. Furthermore, the mass concentrations of Li and P are converted into molar concentrations. This is achieved by converting the molar concentration of Li (Cm) into molar concentrations. Li ) divided by the molar concentration of P (C P ), calculate the molar ratio (C) Li / C P ).

[0080] XPS Measurement

[0081] The coverage of composite particles can be determined using XPS. The measurement sequence is as follows: Prepare the XPS apparatus. For example, the XPS apparatus "PHIX-tool" (or equivalent) manufactured by ULVAC-PHI can be used. Place the sample powder composed of composite particles into the XPS apparatus. Perform narrow-scan analysis using a pass energy of 224 eV. Process the measurement data using analytical software. For example, the analytical software "MulTiPak" (or equivalent) manufactured by ULVAC-PHI can be used. Calculate the ratio of each element based on the intensity values ​​of each peak of C1s, O1s, P2p, Mn2p3, Co2P3, and Ni2P3.

[0082] The coverage rate is calculated using the following formula (5).

[0083] θ=P / (P+Ni+Co+Mn)×100(5)

[0084] In equation (5) above, θ represents the coverage rate (%). P, Ni, Co, and Mn represent the ratios of each element.

[0085] To illustrate, as an example, the determination method for positive electrode active material particles of Li(NiCoMn)O2 is shown here. The right side of the above equation (5) is changed according to the composition of the positive electrode active material particles. For example, when the positive electrode active material particles are LiNiO2, the right side of the above equation (5) is changed to "P / (P+Ni)×100".

[0086] Film Thickness Measurement

[0087] Film thickness (coating thickness) can be determined through the following steps: Prepare a sample by embedding composite particles in a resin material. Section the sample using an ion milling apparatus. For example, the Hitachi High-Tech Arblade 5000 ion milling apparatus (or its equivalent) can be used. The cross-section of the sample is observed using a Scanning Electron Microscope (SEM). For example, the Hitachi High-Tech SU8030 SEM apparatus (or its equivalent) can be used. For 10 composite particles, the film thickness is measured in 20 fields of view. The arithmetic mean of the film thicknesses at the total of 200 measurements is taken as the film thickness.

[0088] <Coating Liquid>

[0089] The coating solution is used to form a coating film on the surface of positive electrode active material particles. The coating solution contains a solute and a solvent. The coating solution may further contain, for example, suspended solids (insoluble components), precipitates, etc.

[0090] Solute

[0091] The solute mass relative to 100 parts by mass can be, for example, 0.1 to 20 parts by mass, 1 to 15 parts by mass, or 5 to 10 parts by mass. Various PO4 units can be generated by dissolving the solute in the solvent.

[0092] Q 0 Unit Ratio

[0093] Q 0 The unit ratio is calculated using "I0 / (I0+I1+I2)" [refer to equation (1) above]. The coating liquid has a Q of 0.7 or less. 0 Unit ratio. Therefore, a high coverage and thin coating film can be expected. Q 0 The smaller the unit ratio, the higher the expected coverage rate. Q 0 The unit ratio can be 0.57 or less, 0.39 or less, 0.15 or less, 0.14 or less, or 0.09 or less. Q 0 The unit ratio can be zero or greater than 0.09. Q 0The unit ratio can be, for example, 0.09 to 0.57.

[0094] Q 1 Unit Ratio

[0095] Q 1 The unit ratio is calculated using "I1 / (I0+I1+I2)". The coating liquid can, for example, have a Q value exceeding 0.05. 1 Unit ratio. Q 1 The unit ratio can be 0.10 or higher, or 0.20 or higher, or 0.40 or higher. Q 1 The unit ratio can be 0.70 or less, 0.60 or less, or 0.5 or less. Q 1 The unit ratio can be, for example, 0.40 to 0.47.

[0096] Q 2 Unit Ratio

[0097] Q 2 The unit ratio is calculated using "I² / (I₀+I₁+I₂)". The coating liquid, for example, can have a Q value exceeding 0.01. 2 Unit ratio. Q 2 The larger the unit ratio, the more likely an increase in coverage can be expected. Q 2 The unit ratio can be 0.03 or higher, 0.17 or higher, 0.39 or higher, or 0.45 or higher [refer to formula (2) above]. Q 2 The unit ratio can be, for example, 0.03 to 0.45.

[0098] Q 2 The unit ratio can be greater than Q. 0 Unit ratio [refer to formula (3) above] Q 2 Unit ratio relative to Q 0 The unit ratio (I2 / I0) can be 2 or more, 2.6 or more, or 5 or more. The ratio (I2 / I0) can be 5 or less. The ratio (I2 / I0) can be 1 to 5.

[0099] Q 1 Unit ratio and Q 2 The sum of the unit ratios [(I1+I2) / (I0+I1+I2)] can be, for example, 0.40 or higher, 0.43 or higher, 0.50 or higher, 0.62 or higher, 0.85 or higher, or 0.91 or higher. Q 1 Unit ratio and Q 2 The sum of the unit ratios can be, for example, 1.00, or less than 0.91. Q 1 Unit ratio and Q 2The sum of the unit ratios can be, for example, 0.43 to 0.91. Q 1 Unit ratio and Q 2 The sum of the unit ratios can, for example, be greater than Q. 0 Unit ratio.

[0100] Phosphoric acid compounds

[0101] The solute contains a phosphoric acid compound. As long as the coating solution has a certain Q... 0 The unit ratio is 0.7 or less, and the solute may contain any phosphoric acid compound. For example, the solute may contain at least one selected from orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, and polyphosphoric acid. The solute may also contain at least one selected from metaphosphoric acid and polyphosphoric acid. By dissolving metaphosphoric acid or polyphosphoric acid in a solvent, Q exists. 0 The tendency for the unit ratio to decrease.

[0102] Lithium Compounds

[0103] The solute may also contain lithium compounds. Examples of solutes include lithium hydroxide, lithium carbonate, and lithium nitrate. The molar ratio of Li to P (Cp) is... Li / C P For example, it can be less than 1.1 [refer to equation (4) above]. Through the molar ratio (C Li / C P A molar ratio (C) less than 1.1 indicates a potential reduction in precipitate. Li / C P For example, it can be below 1.07, below 0.45, or even zero. Molar ratio (C) Li / C P For example, it can be 0 to 0.45, or it can be 0.45 to 1.07.

[0104] "sodium"

[0105] The solute may further include sodium (Na). By dissolving Na in the coating solution, the stability of phosphoric acid compounds with long molecular chains may be improved. The concentration (mass concentration) of Na in the coating solution can, for example, be 0–1%. The concentration of Na can, for example, be less than 0.6% or less than 0.5%. The concentration of Na can, for example, be 0.5–0.6%.

[0106] Solvent

[0107] A solvent can contain any components as long as it dissolves the solute. For example, a solvent can contain water, alcohol, etc. Alternatively, it can contain ion-exchanged water, etc.

[0108] <Methods for Manufacturing Composite Particles>

[0109] Figure 2This is a simplified flowchart of the method for manufacturing the composite particles in this embodiment. Hereinafter, "the method for manufacturing the composite particles in this embodiment" may be simply referred to as "this manufacturing method". This manufacturing method includes "(a) preparation of the mixture" and "(b) manufacturing of the composite particles". This manufacturing method may further include, for example, "(c) heat treatment", etc.

[0110] (a) Preparation of the mixture

[0111] This manufacturing method includes preparing a mixture by mixing a coating liquid and positive electrode active material particles. The mixture can be, for example, a suspension or a wet powder. For example, a suspension can be formed by dispersing the positive electrode active material particles (powder) in the coating liquid. For example, a wet powder can be formed by spraying the coating liquid onto the powder. In this manufacturing method, any mixing apparatus, granulation apparatus, etc., can be used.

[0112] The positive electrode active material particles can be secondary particles (an aggregate of primary particles). For example, positive electrode active material particles (secondary particles) can have a D50 of 1–50 μm, 1–20 μm, or 5–15 μm.

[0113] A single type of positive electrode active material particle can be used, or two or more types can be used in combination. The positive electrode active material particles may, for example, contain at least one selected from LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. For example, in "Li(NiCoMn)O2", "(NiCoMn)" indicates that the total composition ratio within the parentheses is 1. As long as the total is 1, the individual component amounts are arbitrary. Li(NiCoMn)O2 may, for example, contain Li(Ni... 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Li(Ni) 0.5 Co 0.2 Mn 0.3 O2, Li(Ni) 0.8 Co 0.1 Mn 0.1 O2, etc.

[0114] (b) Manufacturing of Composite Particles

[0115] This manufacturing method involves producing composite particles by drying a mixture. A coating solution adhering to the surface of the positive electrode active material particles is dried, thereby forming a coating film. Any drying method can be used in this manufacturing method.

[0116] For example, spray drying can be used to form composite particles. That is, droplets are formed by spraying a suspension from a nozzle. The droplets contain positive electrode active material particles and a coating liquid. For example, composite particles can be formed by drying the droplets using hot air. By using spray drying, improvements in coating efficiency can be expected, for example.

[0117] The solid content of the suspension used for spray drying can be, for example, 1-50% by volume fraction, or 10-30%. The nozzle diameter can be, for example, 0.1-10 mm, or 0.1-1 mm. The hot air temperature can be, for example, 100-200°C.

[0118] For example, a rotating flow layer coating apparatus can be used to manufacture composite particles. In a rotating flow layer coating apparatus, "(a) preparation of mixture" and "(b) manufacture of composite particles" can be performed simultaneously.

[0119] (c) Heat Treatment

[0120] This manufacturing method may also include heat treatment of the composite particles. Heat treatment can fix (set) the coating. This heat treatment can also be referred to as "firing". In this manufacturing method, any heat treatment apparatus can be used. The heat treatment temperature can be, for example, 150–300°C. The heat treatment time can be, for example, 1–10 hours. For example, heat treatment can be performed in air or in an inert atmosphere.

[0121] <Composite Particles>

[0122] Figure 3 This is a conceptual diagram illustrating the composite particle in this embodiment. The composite particle 5 comprises positive electrode active material particles 1 and a coating film 2. The composite particle 5 can, for example, form an aggregate. 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 particle 5. Details of the positive electrode active material particles 1 are as described above.

[0123] The coating 2 is the shell of the composite particles 5. The coating 2 covers at least a portion of the surface of the positive electrode active material particles 1. The composite particles 5 have a coverage rate of 83% or higher. It is expected that a higher coverage rate will reduce the degradation of the sulfide solid electrolyte in the all-solid-state battery. The coverage rate can be, for example, 85% or higher, 88% or higher, 91% or higher, or 92% or higher. The coverage rate can be, for example, less than 100%, less than 99%, or less than 95%. The coverage rate can be, for example, 83-92%.

[0124] Coating 2 has a thickness of 28.5 nm or less. The thinner the film, the greater the expected reduction in battery resistance. Coating 2 can, for example, have a thickness of 26.9 nm or less, 26.8 nm or less, 26.2 nm or less, or 25.4 nm or less. Coating 2 can, for example, have a thickness of 10 nm or more, 20 nm or more, or 25.4 nm or more. Coating 2 can, for example, have a thickness of 25.4–28.5 nm.

[0125] Coating 2 contains a phosphorus compound. That is, coating 2 contains phosphorus (P). Coating 2 may further contain phosphorus (Li). Coating 2 may also further contain oxygen (O), carbon (C), etc.

[0126] <All-solid-state batteries>

[0127] Figure 4 This is a conceptual diagram of the all-solid-state battery in this embodiment. The all-solid-state battery 100 may include, for example, an outer packaging (not shown). The outer packaging may be, for example, an aluminum laminated bag. The outer packaging can house the power generation element 50. The power generation element 50 includes a positive electrode layer 10, a separator layer 30, and a negative electrode layer 20. That is, the all-solid-state battery 100 includes a positive electrode layer 10, a separator layer 30, and a negative electrode layer 20. The all-solid-state battery 100 may further include, for example, a positive current collector, a positive electrode tab, a negative current collector, and a negative electrode tab (all not shown).

[0128] Positive Electrode Layer

[0129] The positive electrode layer 10 comprises composite particles and a sulfide solid electrolyte. Details of the composite particles are as described above. The sulfide solid electrolyte can form an ion conduction pathway within the positive electrode layer 10. The amount of the sulfide solid electrolyte relative to 100 parts by volume of the composite particles (positive electrode active material) can be, for example, 1 to 200 parts by volume. The amount of the sulfide solid electrolyte relative to 100 parts by volume of the composite particles (positive electrode active material) can also be, for example, 50 to 150 parts by volume. The amount of the sulfide solid electrolyte relative to 100 parts by volume of the composite particles (positive electrode active material) can also be, for example, 50 to 100 parts by volume. The sulfide solid electrolyte, for example, contains 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, halogens, etc. The sulfide solid electrolyte may further contain, for example, iodine (I), bromine (Br), etc. The sulfide solid electrolyte can be, for example, a glass ceramic or an argyrodiite. The sulfide solid electrolyte may contain at least one of the following: Li I-LiBr-Li3PS4, Li2S-SiS2, Li I-Li2S-SiS2, Li I-Li2S-P2S5, Li I-Li2O-Li2S-P2S5, Li I-Li2S-P2O5, Li I-Li3PO4-P2S5, Li2S-P2S5, and Li3PS4.

[0130] The positive electrode layer 10 may further comprise a conductive material. The conductive material can form an electron conduction pathway within the positive electrode layer 10. The amount of the conductive material relative to 100 parts by mass of the composite particles (positive electrode active material) can be, for example, 0.1 to 10 parts by mass. The conductive material can contain any composition. For example, the conductive material may contain at least one selected from carbon black, vapor-grown carbon fibers (VGCF), carbon nanotubes (CNTs), and graphene sheets.

[0131] The positive electrode layer 10 may further include, for example, an adhesive. The amount of adhesive relative to 100 parts by mass of the composite particles (positive electrode active material) may be, for example, 0.1 to 10 parts by mass. The adhesive may contain any components. For example, the adhesive may contain at least one selected from polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE).

[0132] Negative Electrode Layer

[0133] The negative electrode layer 20 is the counter electrode of the positive electrode layer 10. The negative electrode layer 20 contains negative electrode active material particles and a sulfide solid electrolyte. The sulfide solid electrolyte may be common to both the negative electrode layer 20 and the positive electrode layer 10, or they may be different. The negative electrode layer 20 may further contain conductive materials and a binder. The negative electrode active material particles can contain any composition. For example, the negative electrode active material particles may contain materials selected from graphite, Si, and silicon dioxide (SiO₂). x (0 < x < 2) and Li4Ti5O 12 At least one of them.

[0134] Separator Layer

[0135] A separator layer 30 is located between the positive electrode layer 10 and the negative electrode layer 20. The separator layer 30 separates the positive electrode layer 10 from the negative electrode layer 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 common to or different from that in the separator layer 30 and the positive electrode layer 10. The sulfide solid electrolyte may be common to or different from that in the separator layer 30 and the negative electrode layer 20.

[0136] <Manufacturing of Composite Particles>

[0137] The following describes the manufacture of composite particles involving No. 1 to No. 8. Hereinafter, for example, "composite particle of No. 1" may be abbreviated as "No. 1".

[0138] No.1

[0139] A coating solution was prepared by dissolving 10.8 parts by mass of orthophosphoric acid (85%, manufactured by Kishida Chemical Co., Ltd.) in 166 parts by mass of ion-exchanged water. Then, 2.1 parts by mass of lithium hydroxide monohydrate (LiOH·H2O) was dissolved in the coating solution.

[0140] Through the aforementioned steps, Q 0 Unit ratio [I0 / (I0+I1+I2)], molar ratio (C Li / C P The concentrations of α and β were determined. The results are shown in Table 1 below.

[0141] As positive electrode active material particles, prepare Li(Ni) 1 / 3 Co 1 / 3 Mn 1 / 3 O2. A suspension is prepared by dispersing the positive electrode active material particles in a coating solution. A BUCHI Mini SprayDryer B-290 is used. The composite particle powder is produced by supplying the suspension to the spray dryer. The air supply temperature of the spray dryer is 200°C, and the air supply volume is 0.45 m³ / h. 3 / minute. The composite particles are heat-treated in air. The heat treatment temperature is 200℃. The heat treatment time is 5 hours.

[0142] The coating rate and film thickness were measured using the steps described above. The results are shown in Table 1 below.

[0143] A positive electrode layer comprising composite particles and a sulfide solid electrolyte is formed. Then, a test battery containing the positive electrode layer is manufactured. The test battery is an all-solid-state battery. The initial resistance of the test battery is measured. The results are shown in Table 1 below. The initial resistance values ​​in Table 1 are relative values. The initial resistance of No. 4 is defined as 1.

[0144] No. 2

[0145] A coating solution was prepared by dissolving 2.7 parts by mass of lithium metaphosphate (manufactured by Mitsutsu Kagaku Pharmaceutical Co., Ltd.) in 50 parts by mass of ion-exchanged water. Otherwise, composite particles and experimental cells were manufactured in the same manner as in No. 1.

[0146] No. 3

[0147] A suspension was prepared by mixing the coating solution and positive electrode active material particles of No. 1. Composite particles were then manufactured by feeding the suspension into a spray dryer. In No. 3, the coating conditions (mixing ratio of coating solution to positive electrode active material particles) were changed to increase the coverage. Furthermore, test cells were manufactured in the same manner as in No. 1.

[0148] No. 4

[0149] A coating solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm and Koichi Chemical Co., Ltd.) in 166 parts by mass of ion-exchanged water. Then, 2.1 parts by mass of lithium hydroxide monohydrate was dissolved in the coating solution. The composite particles and experimental cells were then manufactured in the same manner as in No. 1.

[0150] No. 5

[0151] Except that lithium hydroxide monohydrate was not added to the coating solution, the composite particles and test cells were manufactured in the same manner as No. 4.

[0152] No. 6

[0153] By changing the amount of lithium hydroxide monohydrate added to the coating solution, the molar ratio (C) is changed. Li / C P In addition, composite particles and experimental batteries were manufactured in the same manner as No.4.

[0154] No.7

[0155] By changing the amount of lithium hydroxide monohydrate added to the coating solution, the molar ratio (C) is changed. Li / C P In addition, composite particles and experimental batteries were manufactured in the same manner as No.4.

[0156] No. 8

[0157] A coating solution was prepared by dissolving 10 parts by mass of polyphosphoric acid (product name: polyphosphoric acid-116T, manufactured by Nippon Chemical Industry Co., Ltd.) in 166 parts by mass of ion-exchanged water. Otherwise, composite particles and experimental cells were manufactured in the same manner as in No. 4.

[0158] [Table 1]

[0159]

[0160] The P and Na concentrations listed in Table 1 above are mass concentrations. Furthermore, the initial resistance values ​​listed in Table 1 above are relative values ​​with the initial resistance value of No. 4 set to 1.

[0161] <Results>

[0162] Figure 5 To show Q 0 A coordinate graph showing the relationship between unit ratio and coverage rate. In Q... 0 High coverage is achieved in regions with a cell ratio below 0.7. Q can be observed. 0 The smaller the unit ratio, the higher the coverage rate. In Q... 0 In regions where the unit ratio is below 0.7, a tendency for low initial resistance can also be observed (see No. 4 to 8 of Table 1 above).

[0163] In Q 0 In regions with a cell ratio exceeding 0.7, a tendency towards low coverage and high initial resistance can be observed (refer to No. 1 and 2 in Table 1 above). This is attributed to the deterioration of the sulfide solid electrolyte due to direct contact between the positive electrode active material particles and the sulfide solid electrolyte.

[0164] Q 0 When the unit ratio exceeds 0.7, the coverage can be increased, for example, by adjusting the coating conditions (see No. 3 in Table 1 above). However, in Q... 0 When the cell ratio exceeds 0.7, the film thickness increases with the higher coverage ratio. Due to the increase in film thickness, a significant increase in initial resistance can be observed.

[0165] This embodiment and example are illustrative in all respects. This embodiment and example are not restrictive. The scope of this disclosure includes the meaning equivalent to the claims and all modifications within that scope. For example, it was originally conceived that arbitrary structures could be extracted from this embodiment and example and combined arbitrarily.

Claims

1. A method for manufacturing composite particles, comprising: (a) A mixture is prepared by mixing the coating solution with positive electrode active material particles; and (b) By drying the mixture, composite particles are produced. in, The coating solution comprises a solute and a solvent, wherein the solute comprises a phosphoric acid compound and lithium hydroxide monohydrate, and the coating solution satisfies the following equation (1): {I0 / (I0+I1+I2)}≤0.7 (1), where I0 represents the relationship in the above equation (1). 31 Q from PO4 in the P-NMR spectrum 0 The area of ​​the signal in the cell, I1 represents the signal area in the cell. 31 Q from PO4 in the P-NMR spectrum 1 The area of ​​the signal in the cell, I2 represents the signal area in the cell. 31 Q from PO4 in the P-NMR spectrum 2 The area of ​​the signal in the cell. The composite particles comprise the positive electrode active material particles and the coating film. The coating covers at least a portion of the surface of the positive electrode active material particles, and the coating contains phosphorus.

2. The method for manufacturing composite particles according to claim 1, wherein, (b) includes forming the composite particles using a spray drying method.

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