Composite particle, positive electrode and all-solid-state battery

Abstract

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

Description

[Technical Field]

[0001] The present disclosure relates to composite particles, positive electrodes, all-solid-state batteries, and methods for producing composite particles. [Background technology]

[0002] Patent Document 1 (JP 2016-39062 A) discloses a cathode composite material and a sulfide all-solid-state battery having a cathode active material made of lithium nickel manganese oxide with a layered structure and a glass electrolyte that coats the surface of the cathode active material. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-39062 Summary of the Invention [Problem 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 sulfide-based all-solid-state batteries, the coating film is expected to reduce resistance by preventing direct contact between the sulfide solid electrolyte and the positive electrode active material particles. However, there is still room for improvement in reducing resistance.

[0005] Therefore, an objective of the present disclosure is to reduce resistance. [Means for solving the problem]

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

[0007] [1] The composite particles include positive electrode active material particles and a coating film. The positive electrode active material particles include a lithium-containing composite oxide having a layered rock salt structure. The coating film covers at least a portion of the surface of the positive electrode active material particles. The coating film includes a phosphorus compound. The composite particles satisfy the relationship of the following formula (1). C Li / C P ≦2.5 (1) In the above formula (1), C Li indicates the elemental concentration of lithium (Li) determined from the peak area of ​​the Li1s spectrum measured by X-ray photoelectron spectroscopy. P indicates the elemental concentration of phosphorus (P) determined from the peak area of ​​the P2p spectrum measured by X-ray photoelectron spectroscopy. The composite particles generate carbon dioxide (CO2) of 0.1 mass% or more when heated from room temperature to 600°C at a rate of 10°C / min, as determined by temperature programmed desorption-mass spectrometry (TPD-MS).

[0008] CO2 originates from lithium carbonate (Li2CO3). Li2CO3 is an impurity formed when lithium hydroxide (LiOH), a reaction product of Li present on the surface of the positive electrode active material particles and adsorbed water, further reacts with CO2 in the atmosphere. Such impurities adhere to the surface of the positive electrode active material particles and cannot be easily removed.

[0009] On the other hand, when forming a coating film, the adhesion between the positive electrode active material particles and the coating film is important. If the adhesion is weak, for example, when the positive electrode active material particles and the solid electrolyte are kneaded in a solvent, the shear force of the kneading may cause the coating film to peel off, resulting in a decrease in battery performance.

[0010] According to the new findings of the present disclosure, it is expected that the smaller the composition ratio of Li in the coating film, the stronger the bond between the coating film and the impurities (Li2CO3 and LiOH) present on the surface of the positive electrode active material particles, i.e., the stronger the adhesion between the positive electrode active material particles and the coating film, and the lower the resistance.

[0011] [2] The lithium-containing composite oxide having a layered rock salt structure is represented by the following formula (2): Li a Ni x Co y Me 1-x-y O2(2) In the above formula (2), Me includes at least one selected from the group consisting of Mn and Al, a may satisfy the relationship 0.90≦a≦1.20. x may satisfy the relationship 0.30≦x≦0.90. y may satisfy the relationship 0.10≦y≦0.40.

[0012] [3] x may satisfy the relationship 0.50≦x≦0.90.

[0013] In the above formula (2), materials in which x is 0.5 or more are also called high-nickel materials, which can have high capacity and high output.

[0014] [4] The positive electrode includes the composite particles according to any one of the above [1] to [3] and a sulfide solid electrolyte.

[0015] [5] An all-solid-state battery includes the positive electrode described in [4] above.

[0016] [6] A method for producing composite particles includes the following steps (a) and (b): (a) A mixture is prepared by mixing a coating liquid with positive electrode active material particles. (b) Drying the mixture produces composite particles. The coating liquid contains a solute and a solvent.

[0017] The coating liquid adhered to the surface of the positive electrode active material particles is dried to form a coating film. The coating liquid described in [6] above can form the coating film described in [1] above.

[0018] [7] The solute may contain a phosphate compound. The coating liquid may, for example, satisfy the relationship of the following formula (3). 0≦n Li / n P <1.1 (3) In the above formula (3), n Li represents the molar concentration of lithium in the coating solution. P indicates the molar concentration of phosphorus in the coating solution.

[0019] [8] (b) above may include forming composite particles, for example, by spray drying. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a conceptual diagram showing a composite particle in this embodiment. [Figure 2] FIG. 2 is a conceptual diagram showing the all-solid-state battery according to this embodiment. [Figure 3] FIG. 3 is a schematic flowchart of the method for producing composite particles in this embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0021] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure.

[0022] <Definitions of terms, etc.> The terms "comprise," "include," "have," and variations thereof (e.g., "consisting of") are open-ended. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even closed-ended terms do not exclude additional elements that are normally associated impurities or unrelated to the disclosed technology. The term "consisting essentially of..." is semi-closed. Semi-closed terms allow for the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology.

[0023] Expressions such as "may" and "may" are used in the permissive sense, meaning "to have the possibility," rather than in the obligatory sense, meaning "to have to."

[0024] Elements expressed in the singular include the plural unless otherwise specified. For example, a "particle" can mean not only a single particle but also an aggregate of particles (powder, powder, particle group).

[0025] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may proceed one after the other.

[0026] For example, unless otherwise specified, a numerical range such as "m to n%" includes both the upper and lower limits. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% and less than n%." Furthermore, a numerical value arbitrarily selected from within the numerical range may be set as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a numerical value within the numerical range with a numerical value described elsewhere in this specification, in a table, a figure, or the like.

[0027] When a compound is expressed by a stoichiometric formula (e.g., "LiCoO2"), the stoichiometric formula is merely a representative example of the compound. The compound may have a non-stoichiometric composition. For example, when lithium cobalt oxide is expressed as "LiCoO2," unless otherwise specified, the lithium cobalt oxide 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 or substitution with trace elements may be permitted.

[0028] "D50" refers to the particle size at which the cumulative frequency of the smaller particle sizes reaches 50% in a volume-based particle size distribution. D50 can be measured by a laser diffraction method. For example, a laser diffraction particle size distribution analyzer "SALD-7500" (or an equivalent) manufactured by Shimadzu Corporation may be used.

[0029] <TPD-MS measurement> The amount of CO2 generated can be measured by the following procedure. A TPD-MS instrument is prepared. For example, a TPD-MS instrument manufactured by MicrotrackBell, Inc., "Product Name BELCAT II" (or an equivalent) may be used. A sample powder consisting of 5 mg of composite particles is prepared. The sample powder is placed in a container and heated from room temperature to 600°C at a rate of 10°C / min under a helium (He) gas flow of 50 ml / min. The amount of CO2 generated (m / z = 44) is quantified using a mass spectrometer and integrated to determine the amount of CO2.

[0030] <XPS Measurement> (composition ratio of particle surface) C in the above formula (1) Li , C Pcan be measured by the following procedure. An XPS instrument is prepared. For example, an XPS instrument manufactured by ULVAC-PHI, Inc., product name PHI X-tool (or equivalent) may be used. A sample powder consisting of composite particles is placed in the XPS instrument. Narrow scan analysis is performed with a pass energy of 224 eV. The measurement data is processed by analysis software. For example, an analysis software manufactured by ULVAC-PHI, Inc., product name MulTiPak (or equivalent) may be used. The peak area (integral value) of the Li1s spectrum is used to determine the elemental concentration of Li (C Li ) The peak area of ​​the P2p spectrum is converted into the elemental concentration of P (C P ) is converted to C Li C P By dividing by , the composition ratio of the particle surface (C Li / C P ) is obtained.

[0031] (coverage rate) The coverage is also measured by XPS. By analyzing the above measurement data, the ratio of each element can be determined from the peak areas of C1s, O1s, P2p, Ni2p3, Co2p3, and Me2p3. The coverage rate is calculated by the following formula (4). θ=P / (P+Ni+Co+Me)×100 (4) In the above formula (4), θ represents the coverage (%). P, nickel (Ni), Co (cobalt), and Me represent the ratio of each element. "Me2p3" and Me in the above formula (4) may be composed of manganese (Mn) or aluminum (Al), or may be composed of Mn and Al. When Me contains Mn and Al, the sum of the composition ratios of each element may be 1.

[0032] For example, the positive electrode active material particles are "LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2”, the above formula (4) can be transformed into the following formula (4′): θ=P / (P+Ni+Co+Mn)×100 (4') Mn in the above formula (4') represents the element ratio of Mn determined from the peak area of ​​Mn2p3.

[0033] <Film thickness measurement> The film thickness (thickness of the coating film) can be measured by the following procedure: A sample is prepared by embedding composite particles in a resin material. The sample is cross-sectioned using an ion milling device. For example, an ion milling device manufactured by Hitachi High-Technologies Corporation, product name Arblade (registered trademark) 5000 (or an equivalent product) may be used. The cross-section of the sample is observed using an SEM (Scanning Electron Microscope). For example, an SEM device manufactured by Hitachi High-Technologies Corporation, product name SU8030 (or an equivalent product) may be used. The film thickness is measured in five fields of view for each of 10 composite particles. The arithmetic average of the film thicknesses at a total of 50 locations is considered to be the film thickness.

[0034] 《ICP measurement》 (Composition ratio of positive electrode active material particles) The a, x, and y in the above formula (2) can be measured by the following procedure. A standard solution is prepared by diluting 0.01 g of positive electrode active material particles with pure water. An inductively coupled plasma atomic emission spectroscopy (ICP-AES) instrument is prepared. For example, an ICP-AES instrument manufactured by Shimadzu Corporation, model number ICPE-9000 (or an equivalent model), may be used. The emission intensity of the standard solution is measured using the ICP-AES instrument. A calibration curve is created from the emission intensity of the standard solution. The mole fractions of Li, Ni, Co, and Me contained in the positive electrode active material particles are determined from the emission intensity of the sample solution and the calibration curve.

[0035] (P adhesion amount) The mass fraction of P contained in the composite particles (also referred to as "P deposition amount" or "P content") can be measured using 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 with pure water to 100 mL. Aqueous solutions of P (1000 ppm, 10000 ppm) are prepared. A standard solution is prepared by diluting 0.01 g of the solution with pure water. An ICP-AES instrument is prepared. For example, an ICP-AES instrument manufactured by Shimadzu Corporation, model number ICPE-9800 (or equivalent), may be used. The emission intensity of the standard solution is measured using the ICP-AES instrument. A calibration curve is created from the emission intensity of the standard solution. The mass fraction of P contained in the composite particles is determined from the emission intensity of the sample liquid and the calibration curve.

[0036] (mass concentration of Li, P, and Na in the coating solution) The mass concentrations of Li, P, and Na in the coating solution are measured using the following procedure. 100 ml of sample solution is prepared by diluting 0.01 g of coating solution with pure water. Aqueous solutions of Li, P, and Na (1000 ppm, 10000 ppm) are prepared. Standard solutions are prepared by diluting 0.01 g of the aqueous solutions with pure water. An ICP-AES device is prepared. The emission intensity of the standard solution is measured using the ICP-AES device. 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 using the ICP-AES device. The mass concentrations of Li, P, and Na in the coating solution are determined from the emission intensity of the sample solution and the calibration curve. The mass concentrations of Li and P are then converted to molar concentrations. The molar concentration of Li (n Li ) is the molar concentration of P (n P ) to obtain the molar ratio (n Li / n P ) is obtained.

[0037] <Composite particles> FIG. 1 is a conceptual diagram showing a composite particle in this embodiment. The composite particle 5 may be referred to as, for example, a "coated cathode active material." The composite particle 5 includes a cathode active material particle 1 and a coating film 2. The composite particle 5 may form an aggregate, for example. That is, one composite particle 5 may include two or more cathode active material particles 1. The composite particle 5 may have a D50 of, for example, 1 to 50 μm, 1 to 20 μm, or 5 to 15 μm.

[0038] The coating film 2 is a shell of the composite particle 5. The coating film 2 covers at least a part of the surface of the positive electrode active material particle 1. The coating film 2 contains a phosphorus compound. By including the phosphorus compound in the coating film 2, a reduction in resistance is expected.

[0039] The phosphorus compound may contain, for example, Li, oxygen (O), carbon (C), etc. P may be contained in the composite particle 5 at a mass fraction of, for example, 0.2 to 10%.

[0040] In the composite particle 5, the composition ratio of the particle surface (C Li / C P The composition ratio (C) is 2.5 or less (see formula (1) above). Li / C P When the composition ratio (C) is 2.5 or less, the resistance can be significantly reduced. Li / C P ) may be, for example, 2.12 or less, 1.96 or less, 1.89 or less, or 1.73 or less. Li / C P ) may be zero. Li / C P ) may be, for example, 0.1 or more, 0.5 or more, or 1.0 or more. Li / C P ) may be, for example, 1.73 to 2.5.

[0041] The coverage may be, for example, 80% or more, 85% or more, or 90% or more.

[0042] The coating film 2 may have a thickness of, for example, 5 to 100 nm, 5 to 50 nm, 10 to 30 nm, or 20 to 30 nm.

[0043] The positive electrode active material particle 1 is the core of the composite particle 5. The positive electrode active material particle 1 may be a secondary particle (an aggregate of primary particles). The positive electrode active material particle 1 (secondary particle) may have a D50 of, for example, 1 to 50 μm, 1 to 20 μm, or 5 to 15 μm.

[0044] The positive electrode active material particles 1 may contain any component. The positive electrode active material particles 1 contain a lithium-containing composite oxide with a layered rock salt structure. The crystal structure of the positive electrode active material particles 1 can be identified by, for example, X-ray diffraction (XRD). The lithium-containing composite oxide is represented, for example, by the following formula (2). Li a Ni x Co y Me 1-x-y O2(2) In the above formula (2), Me includes at least one selected from the group consisting of Mn and Al, a may satisfy the relationship of 0.90≦a≦1.20, x may satisfy the relationship of 0.30≦x≦0.90, and y may satisfy the relationship of 0.10≦x≦0.40. a preferably satisfies the relationship of 0.95≦a≦1.10. x preferably satisfies the relationship of 0.50≦x≦0.90. When the value of x is within this range, the specific capacity tends to increase. The lithium-containing composite oxide may be, for example, Li 1.10 Ni 1 / 3 Co 1 / 3 Mn 1 / 3 O2, Li 1.10 Ni 0.60 Co 0.20 Mn 0.20 O2, Li 1.10 Ni0.82 Co 0.15 Al 0.03 It may be O2 or the like.

[0045] The composite particles 5 generate 0.1 mass% or more of CO2 when heated from room temperature to 600°C at a rate of 10°C / min using TPD-MS. The CO2 measured by TPD-MS originates from Li2CO3 present on the surface. When the amount of CO2 generated is 0.1 mass% or more under the above conditions, it is believed that adhesion between the coating film and impurities (Li2CO3 and LiOH) present on the surface of the positive electrode active material particles 1 is enhanced, resulting in reduced resistance. Furthermore, if the amount of CO2 generated under the above conditions is large, Li may be eluted from the surface of the positive electrode active material particles 1 and inactivated, potentially reducing battery capacity. Furthermore, the impurities may accumulate on the surface of the positive electrode active material particles 1, preventing uniform formation of the coating film and potentially increasing resistance. From these perspectives, the amount of CO2 generated under the above conditions is preferably 1.0 mass% or less, and more preferably 0.8 mass% or less.

[0046] The amount of CO2 generated can be adjusted by the time for which the lithium-containing composite oxide is left standing in the air after production. The time for which the lithium-containing composite oxide is left standing in the air may be, for example, 5 minutes or more, 30 minutes or more, 60 minutes or more, or 120 minutes or more. However, if the lithium-containing composite oxide is left standing for a long period of time, the amount of CO2 generated may increase too much, so the time may be, for example, 300 minutes or less, 180 minutes or less, or 150 minutes or less.

[0047] <All-solid-state battery> FIG. 2 is a conceptual diagram showing an all-solid-state battery according to this 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. The exterior body may house a power generating element 50. The power generating 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 the positive electrode 10, the separator layer 30, and the negative electrode 20.

[0048] 《Positive electrode》 The positive electrode 10 is layered. The positive electrode 10 may include, for example, a positive electrode active material layer and a positive electrode current collector. For example, the positive electrode active material layer may be formed by applying a positive electrode mixture to the surface of the positive electrode current collector. The positive electrode current collector may include, for example, aluminum (Al) foil. The positive electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0049] The positive electrode active material layer may have a thickness of, for example, 10 to 200 μm. The positive electrode active material layer is in close contact with the separator layer 30. The positive electrode active material layer includes a positive electrode mixture. The positive electrode mixture includes composite particles and a sulfide solid electrolyte. That is, the positive electrode 10 includes composite particles and a sulfide solid electrolyte. Details of the composite particles are as described above.

[0050] The sulfide solid electrolyte can form an ion conduction path in the positive electrode active material layer. The 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 per 100 parts by volume of the composite particles (positive electrode active material). The sulfide solid electrolyte contains, for example, Li, P, and sulfur (S). The sulfide solid electrolyte may further contain, for example, O, silicon (Si), etc. The sulfide solid electrolyte may further contain, for example, 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, glass ceramics or argyrodite. The sulfide solid electrolyte may include, for example, at least one selected from the group consisting of LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, and Li3PS4.

[0051] The positive electrode active material layer may further contain, for example, a conductive material. The conductive material can form an electron conduction path within the positive electrode active material layer. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the composite particles (positive electrode active material). 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 nanotubes (CNT), and graphene flakes.

[0052] The positive electrode active material layer may further contain, for example, a binder. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the composite particles (positive electrode active material). 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).

[0053] 《Negative electrode》 The negative electrode 20 is a counter electrode of the positive electrode 10. The negative electrode 20 is layered. The negative electrode 20 may include, for example, a negative electrode active material layer and a negative electrode current collector. For example, the negative electrode active material layer may be formed by applying a negative electrode mixture to the surface of the negative electrode current collector. The negative electrode current collector may include, for example, copper (Cu) foil, Ni foil, etc. The negative electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0054] The negative electrode active material layer may have a thickness of, for example, 10 to 200 μm. The negative electrode active material layer is in close contact with the separator layer 30. The negative electrode active material layer includes a negative electrode composite. The negative electrode composite includes negative electrode active material particles and a sulfide solid electrolyte. The negative electrode composite may further include a conductive material and a binder. The sulfide solid electrolytes in the negative electrode composite and the positive electrode composite may be the same or different. The negative electrode active material particles may include any component. The negative electrode active material particles may include, for example, graphite, Si, silicon oxide [SiO x (0 <x<2)〕、およびLi4Ti5O12 It may contain at least one selected from the group consisting of:

[0055] <<Separator layer>> The separator layer 30 is interposed between the positive electrode 10 and the negative electrode 20. The separator layer 30 separates the positive electrode 10 from the negative electrode 20. The separator layer 30 includes a sulfide solid electrolyte. The separator layer 30 may further include a binder. The sulfide solid electrolytes in the separator layer 30 and the positive electrode composite may be the same or different. The sulfide solid electrolytes in the separator layer 30 and the negative electrode composite may be the same or different.

[0056] <Method of manufacturing composite particles> 3 is a schematic flowchart of a method for producing composite particles according to this embodiment. Hereinafter, "a method for producing composite particles according to this embodiment" may be abbreviated as "the present production method." The present production method includes "(a) preparation of a mixture" and "(b) production of composite particles." The present production method may further include, for example, "(c) heat treatment."

[0057] (a) Preparation of the mixture This manufacturing method includes preparing a mixture by mixing a coating liquid with positive electrode active material particles. The details of the positive electrode active material particles are as described above. The mixture may be, for example, a suspension or a wet powder. For example, a suspension may be formed by dispersing positive electrode active material particles (powder) in a coating liquid. For example, a wet powder may be formed by spraying the coating liquid into the powder. In this manufacturing method, any mixing device, granulating device, etc. may be used.

[0058] The coating liquid contains a solute and a solvent. The solute contains a film material (raw material for the coating film). The coating liquid may further contain, for example, suspended matter (insoluble components), precipitates, etc.

[0059] The solute may include, for example, a phosphate compound. This allows the solute to contain P. The phosphate compound may be, for example, phosphoric anhydride (PO), orthophosphoric acid, pyrophosphoric acid, or metaphosphoric acid (HPO) n ] and polyphosphoric acid. The phosphate compound may be, for example, at least one selected from the group consisting of metaphosphoric acid and polyphosphoric acid. Metaphosphoric acid and polyphosphoric acid may have longer molecular chains than other phosphate compounds. It is believed that the long molecular chains of the phosphate compound make it easier to produce a coating film with continuity. The coating film with continuity is expected to, for example, improve the coverage rate.

[0060] The solute may further contain sodium (Na). Dissolving Na in the coating liquid may improve the stability of the phosphate compound. The concentration (mass concentration) of Na in the coating liquid 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%.

[0061] The solute may further contain a lithium compound. For example, the solute may contain lithium hydroxide, lithium carbonate, lithium nitrate, etc. The molar ratio of Li to P (n Li / n P ) may be, for example, less than 1.1 (see formula (3) above). Li / n P ) is less than 1.1, the composition ratio (C Li / C P ) is expected to decrease. Li / n P ) may be, for example, 0.75 or less, 0.30 or less, or even zero. Li / n P ) may be, for example, 0 to 0.30, or 0.30 to 0.75.

[0062] (b) Production of Composite Particles The present production method includes drying the mixture to produce composite particles. The coating solution attached to the surfaces of the positive electrode active material particles is dried to produce a coating film. Any drying method can be used in this production method.

[0063] For example, the composite particles may be formed by a spray-drying method. That is, droplets are formed by spraying a suspension from a nozzle. The droplets contain the positive electrode active material particles and the coating liquid. For example, the composite particles can be formed by drying the droplets with hot air. The use of the spray-drying method is expected to improve, for example, the coverage rate.

[0064] The solid content of the suspension for spray drying may be, for example, 1 to 50% or 10 to 30% by volume. 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.

[0065] For example, the composite particles may be produced by a tumbling fluidized bed coating apparatus. In the tumbling fluidized bed coating apparatus, "(a) preparation of a mixture" and "(b) production of composite particles" can be carried out simultaneously.

[0066] (c) Heat Treatment The present production method may include subjecting the composite particles to a heat treatment. The heat treatment may fix the coating film. The heat treatment may also be referred to as "baking." Any heat treatment device may be used in the present production method. 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 performed in air or in an inert atmosphere. [Example]

[0067] The present embodiment will be described below using examples, but the present embodiment is not limited to these.

[0068] <Production of Positive Electrode Active Material Particles> Positive electrode active material particles A to D, which are lithium-containing composite oxides having a layered rock salt structure, were produced as follows.

[0069] 《Cathode active material particles A》 Nickel(II) sulfate hexahydrate (NiSO4·6H2O), cobalt(II) sulfate heptahydrate (CoSO4·7H2O), and manganese(II) sulfate pentahydrate (MnSO4·5H2O) were dissolved in pure water to obtain a raw solution. The molar ratio of Ni, Co, and Mn in the raw solution was 1:1:1, and the total molar concentration of Ni, Co, and Mn in the raw solution was 1.8 mol / L.

[0070] 1 L of 10 g / L aqueous ammonia solution was prepared in a reaction vessel. 1 L of the raw material aqueous solution was added dropwise to the reaction vessel at a rate of 5.2 mL / min, while adjusting the pH to 11.20±0.2 using aqueous sodium hydroxide solution to form a precipitate, thereby obtaining a precursor. 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 was 10 g / L.

[0071] The precursor was mixed with Li2CO3 so that the molar ratio of Li to Ni, Co, and Mn was 1.10, and the mixture was fired in an oxygen atmosphere at 800°C for 5 hours. The mixture was then left to stand in the air for 2 hours to obtain positive electrode active material particles A. The composition of positive electrode active material particles A was measured using the procedure described above. The results are shown in Table 1 below.

[0072] 《Cathode active material particles B~D》 Positive electrode active material particles B were obtained in the same manner as positive electrode active material particles A, except that the molar ratio of Ni, Co, and Mn in the raw material aqueous solution was 3:1:1. Positive electrode active material particles C were obtained in the same manner as positive electrode active material particles A, except that aluminum sulfate (Al2(SO4)3) was used instead of manganese (II) sulfate pentahydrate, and the molar ratio of Ni, Co, and Al was 82:15:3. Positive electrode active material particles D were obtained in the same manner as positive electrode active material particles A, except that they were not left to stand in the air. The compositions of positive electrode active material particles B to D were measured using the procedure described above. The results are shown in Table 1 below.

[0073] <Manufacturing of all-solid-state batteries> Composite particles, positive electrodes, and all-solid-state batteries according to Nos. 1 to 7 were produced as follows. Hereinafter, for example, "composite particles according to No. 1" may be abbreviated as "No. 1."

[0074] No. 1 (coating liquid) A coating solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 166 parts by mass of ion-exchanged water. Li / n P Lithium hydroxide monohydrate (LiOH·H2O) was dissolved in the coating solution so that the σ was 0.30.

[0075] (positive electrode) Positive electrode active material particles A were prepared. 50 parts by mass of the positive electrode active material particle powder was dispersed in 53.7 parts by mass of the coating liquid to prepare a suspension. A spray dryer manufactured by BUCHI (product name: Mini Spray Dryer B-290) was prepared. The suspension was supplied to the spray dryer to produce a powder of composite particles. The supply air temperature of the spray dryer was 200°C, and the supply air volume was 0.45 m 3 The composite particles were heat-treated in air at a temperature of 200°C for 5 hours. Li / C PThe composition ratio (C ) of the particle surface and the amount of CO2 generated (mass%) were measured. The results are shown in Table 1 below. Li / C P ) and CO2 generation (mass%) were measured.

[0076] The following materials were prepared: Sulfide solid electrolyte: Li2S-P2S5 glass ceramics containing LiI (D50: 0.8 μm) Conductive material: VGCF Binder: SBR Dispersion medium: heptane Positive electrode current collector: Al foil

[0077] Positive electrode slurry was prepared by mixing composite particles, sulfide solid electrolyte, conductive material, binder, and dispersion medium. The mixing ratio of the composite particles to the sulfide solid electrolyte was "composite particles / sulfide solid electrolyte = 6 / 4 (volume ratio)". The amount of conductive material was 3 parts by mass for 100 parts by mass of composite particles. The amount of binder was 0.7 parts by mass for 100 parts by mass of composite particles. The positive electrode slurry was thoroughly stirred using an ultrasonic homogenizer (Model UH-50) manufactured by SMT Corporation. The positive electrode slurry was applied to the surface of the positive electrode current collector to form a coating film. The coating film was dried on a hot plate at 100°C for 30 minutes. This produced a positive electrode blank. A disk-shaped positive electrode was cut out from the positive electrode blank. The area of ​​the positive electrode was 1 cm. 2 It was.

[0078] (Negative electrode) The same materials as those for the positive electrode were prepared: sulfide solid electrolyte, conductive material, binder, and dispersion medium. A Primix Corporation mixer (product name: Filmix, model: 30-L) was prepared as the mixer. The sulfide solid electrolyte, conductive material, binder, and dispersion medium were placed in the mixer's mixing vessel. The materials in the mixing vessel were stirred at a rotation speed of 20,000 rpm for 30 minutes.

[0079] Li4Ti5O as negative electrode active material particles12 (D50: 1.0 μm), and Cu foil was prepared as a negative electrode current collector. Negative electrode active material particles were added to a stirring vessel. 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 amount of conductive material was 1 part by mass per 100 parts by mass of composite particles. The amount of binder was 2 parts by mass per 100 parts by mass of composite particles. After adding the negative electrode active material particles, the materials in the stirring vessel were stirred at 15,000 rpm for 60 minutes to prepare a negative electrode slurry. The negative electrode slurry was applied to the surface of the negative electrode current collector to form a coating film. The coating film was dried on a hot plate at 100°C for 30 minutes. This produced a negative electrode blank. A disk-shaped negative electrode was cut out from the negative electrode blank. The area of ​​the negative electrode is 1 cm 2 It was.

[0080] (separator layer) A Li2S-P2S5-based glass ceramic (D50: 2.5 μm) containing LiI was prepared as a sulfide solid electrolyte. A die with an inner diameter and cross-sectional area of ​​1 cm2 was used for the press processing. 2 64.8 mg of the sulfide solid electrolyte was placed in a mold, smoothed, and then subjected to a pressure of 1 ton / cm 2 The separator layer was obtained by pressing and compacting the mixture under a pressure of 1000 kJ / cm.

[0081] (All-solid-state battery) In the mold, a positive electrode was placed on one side of the separator layer, and a negative electrode was placed on the other side. 2 The negative electrode, separator layer, and positive electrode were pressed together for 1 minute under a pressure of 1 ton / cm. A stainless steel rod was placed between the positive and negative electrodes, and a pressure of 1 ton / cm was applied. 2 A power generating element was formed by binding the battery element with a binder. A pouch made of aluminum laminate film was prepared as the housing. The battery element was sealed in the housing. This formed an all-solid-state battery.

[0082] No.2 Positive electrode active material particles A were prepared. A coating solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 166 parts by mass of ion-exchanged water. Lithium hydroxide monohydrate was not added to the coating solution. From this point on, composite particles, positive electrodes, and all-solid-state batteries were manufactured in the same manner as in No. 1.

[0083] No.3 Positive electrode active material particles A were prepared. A coating solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 166 parts by mass of ion-exchanged water. Furthermore, the molar ratio (n Li / n P Lithium hydroxide monohydrate was dissolved in the coating solution so that the ρ was 0.75. From this point on, composite particles, positive electrodes, and all-solid-state batteries were fabricated in the same manner as in No. 1.

[0084] No.4 Positive electrode active material particles B were prepared. Composite particles, a positive electrode, and an all-solid-state battery were manufactured in the same manner as in No. 1, except that positive electrode active material particles B were used.

[0085] No.5 Positive electrode active material particles C were prepared. Composite particles, a positive electrode, and an all-solid-state battery were manufactured in the same manner as in No. 1, except that positive electrode active material particles C were used.

[0086] No.6 Positive electrode active material particles D were prepared. Composite particles, a positive electrode, and an all-solid-state battery were manufactured in the same manner as in No. 1, except that positive electrode active material particles D were used.

[0087] No.7 Positive electrode active material particles A were prepared. A coating solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 166 parts by mass of ion-exchanged water. Furthermore, the molar ratio (n Li / n PLithium nitrate (LiNO3) was dissolved in the coating solution so that the ρ was 2.00. From this point on, composite particles, positive electrodes, and all-solid-state batteries were fabricated in the same manner as in No. 1.

[0088] <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 the symbol for time rate. At a time rate of 1C, the battery's full charge capacity is discharged in 1 hour.

[0089] The SOC (state of charge) of the test battery was adjusted to 50% at a time rate of 1 / 3C. After adjusting the SOC, AC impedance measurements were performed. The amplitude was 10 mV. The frequency range was 0.1 to 10 6 Hz. A Cole-Cole plot was created from this. A circular arc was fitted to the Cole-Cole plot. The distance between the two intersections of the fitted circular arc and the real axis was calculated. This distance was considered to be the "interface resistance." The interface resistance of each all-solid-state battery was evaluated relative to the interface resistance of the all-solid-state battery No. 1 as the reference (1.0). The results are shown in Table 1 below.

[0090] [Table 1]

[0091] <Result> The amount of CO2 generated from the composite particles measured under the above conditions is 0.1 mass% or more, and the composition ratio of the particle surface (C Li / C P ) is 2.5 or less, the interface resistance is significantly reduced.

[0092] No. 6, in which the amount of CO2 generated from the composite particles measured under the above conditions was less than 0.1 mass%, showed a significant increase in the interface resistance. Li / C P ) was greater than 2.5, the interface resistance increased significantly.

[0093] The present embodiment and examples are illustrative in all respects. The present embodiment and examples are not limiting. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is also intended from the beginning that any configuration may be extracted from the present embodiment and examples and that they may be combined in any desired manner. [Explanation of symbols]

[0094] 1 Positive electrode active material particle, 2 Coating film, 5 Composite particle, 10 Positive electrode, 20 Negative electrode, 30 Separator layer, 50 Power generating element, 100 All-solid-state battery.

Claims

1. The positive electrode active material includes particles of a positive electrode active material and a coating film, the positive electrode active material particles contain a lithium-containing composite oxide having a layered rock salt structure, the coating film covers at least a portion of the surface of the positive electrode active material particles, the coating film contains a phosphorus compound, The following formula (1): C Li / C P ≦2.5 (1) Fulfilling the relationship, In the above formula (1), C Li represents the elemental concentration of lithium determined from the peak area of ​​the Li1s spectrum measured by X-ray photoelectron spectroscopy, C P represents the elemental concentration of phosphorus determined from the peak area of ​​the P2p spectrum measured by X-ray photoelectron spectroscopy, Composite particles, wherein the amount of carbon dioxide generated when heated from room temperature to 600°C at a rate of 10°C / min is 0.1 mass% or more, as determined by thermal evolved gas mass spectrometry.

2. The lithium-containing composite oxide having a layered rock salt structure has the following formula (2): Li ａ Ni ｘ Co ｙ Me １－ｘ－ｙ O ２ (2) In the above formula (2), Me includes at least one selected from the group consisting of Mn and Al, a satisfies the relationship 0.90≦a≦1.20, x satisfies the relationship 0.30≦x≦0.90, The composite particle according to claim 1 , wherein y satisfies the relationship 0.10≦x≦0.

40.

3. The composite particle according to claim 2 , wherein x satisfies the relationship 0.50≦x≦0.

90.

4. A positive electrode comprising the composite particles according to claim 1 and a sulfide solid electrolyte.

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

6. (a) preparing a mixture by mixing a coating liquid with positive electrode active material particles; and (b) drying the mixture to produce composite particles; Including, The method for producing composite particles, wherein the coating liquid contains a solute and a solvent.

7. the solute comprises a phosphate compound; The coating liquid is a compound represented by the following formula (3): 0≦n Li / n P <1.1 (3) Fulfilling the relationship, In the above formula (3), n Li represents the molar concentration of lithium in the coating solution, n P The method for producing composite particles according to claim 6 , wherein m represents the molar concentration of phosphorus in the coating liquid.

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

Images