Composite particles, cathodes, and all-solid-state batteries

Abstract

To reduce battery resistance.SOLUTION: Composite particles include positive electrode active material particles and a coating film. The coating film covers at least a part of a surface of the positive electrode active material particle. The coating film includes a phosphorus compound. The phosphorus compound includes P and at least one of Na and K.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] Japanese Patent Laid-Open Publication No. 2010-135090 (Patent Document 1) discloses the formation of a polyanion structure-containing compound at the interface between a positive electrode active material and a solid electrolyte. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-135090 Summary of the Invention [Problem to be solved by the invention]

[0004] Sulfide-based all-solid-state batteries (hereinafter abbreviated as "all-solid-state batteries") have been developed. All-solid-state batteries contain a sulfide solid electrolyte. If the sulfide solid electrolyte comes into direct contact with the positive electrode active material particles, the sulfide solid electrolyte may deteriorate. Deterioration of the sulfide solid electrolyte (ion conduction path) may increase battery resistance. Therefore, it has been proposed to form a coating film on the surface of the positive electrode active material particles. The coating film prevents direct contact between the positive electrode active material particles and the sulfide solid electrolyte, thereby reducing the deterioration of the sulfide solid electrolyte.

[0005] Phosphate compounds have been known as raw materials for coating films. The coating process can be carried out, for example, by the following method. That is, a phosphate compound is dissolved in a solvent to prepare a coating liquid. The coating liquid is then attached to the surface of the positive electrode active material particles. The coating liquid attached to the particle surface is then dried to form a coating film. It is believed that the coating film contains a phosphorus compound.

[0006] Conventionally, coating solutions that do not contain impurities have been used because it is believed that impurities may adversely affect the properties of the coating film. For example, impurities such as sodium (Na) and potassium (K) are thought to have the potential to inhibit the movement of lithium (Li) ions.

[0007] An object of the present disclosure is to reduce battery resistance. [Means for solving the problem]

[0008] 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.

[0009] 1. The composite particles include 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 includes a phosphorus compound. The phosphorus compound includes phosphorus and at least one of sodium and potassium.

[0010] In the present disclosure, contrary to conventional thinking, Na and K are intentionally added to the coating film (phosphorus compound). According to the new findings of the present disclosure, the inclusion of Na and K in the coating film can actually reduce battery resistance. Phosphate compounds may be decomposed into smaller molecules in the coating solution, for example, by solvolysis. For example, Na and K may increase the stability of the phosphate compounds in the coating solution, thereby forming a high-quality coating film and reducing battery resistance. However, the details of this mechanism are currently unknown.

[0011] 2. The composite particles described in "1." above may satisfy the relationship of the following formula (1). C Na / C P ≧0.01…(1) In the above formula (1), C Na , C P indicates the element concentration measured by X-ray photoelectron spectroscopy. Naindicates the elemental concentration of sodium. P indicates the elemental concentration of phosphorus.

[0012] The surface composition of the composite particles can be identified by X-ray photoelectron spectroscopy (XPS). The surface composition of the composite particles corresponds to the composition of the coating film. Na / C P " indicates the composition ratio on the particle surface. By satisfying the above formula (1), a reduction in battery resistance is expected.

[0013] 3. The composite particles described in the above "1." or "2." may have a coverage of, for example, 85% or more. The coverage is measured by X-ray photoelectron spectroscopy.

[0014] When the coating film contains Na and K, the coverage rate tends to be higher. The improved stability of the phosphate compound in the coating solution makes it easier to form a continuous coating film, which may be improving the coverage rate. The improved coverage rate may reduce the chance of contact between the sulfide solid electrolyte and the positive electrode active material particles, thereby reducing battery resistance.

[0015] 4. The positive electrode contains the composite particles according to any one of the above items "1." to "3." and a sulfide solid electrolyte.

[0016] 5. The all-solid-state battery includes the positive electrode described in "4." above.

[0017] 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, and the solute contains at least one of sodium and potassium, and phosphorus. The coating liquid satisfies the relationship of the following formula (2). nNa / n P ≧0.02…(2) In the above formula (2), n P indicates the molar concentration of phosphorus in the coating solution. Na indicates the molar concentration of sodium in the coating solution.

[0018] When the coating liquid satisfies the relationship of the above formula (2), the composite particles described in "1." above can be formed.

[0019] 7. In the method for producing composite particles described in "6." above, the mass fraction of sodium in the coating liquid is, for example, 1.46 × 10 4 It may be ppm or more.

[0020] 8. In the method for producing composite particles according to the above item "6." or "7.", the solute may contain at least one selected from the group consisting of metaphosphoric acid and polyphosphoric acid.

[0021] Metaphosphoric acid and polyphosphoric acid are phosphate compounds. Metaphosphoric acid and polyphosphoric acid may have longer molecular chains than other phosphate compounds. When the solute contains at least one of metaphosphoric acid and polyphosphoric acid, it is expected that, for example, a coating film having continuity will be easily formed. This is expected to result in, for example, an improvement in coverage.

[0022] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure. [Brief explanation of the drawings]

[0023] [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

[0024] <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 incidental impurities or unrelated to the disclosed technology. The term "consisting essentially of..." is semi-closed. Semi-closed terms allow for the addition of elements that do not substantially affect the basic and novel characteristics of the disclosed technology.

[0025] "At least one of A and B" includes "A or B" as well as "A and B." "At least one of A and B" can also be written as "A and / or B."

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

[0027] 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).

[0028] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0029] 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.

[0030] All numerical values ​​are modified by the term "about." The term "about" may mean, for example, ±5%, ±3%, ±1%, etc. All numerical values ​​may be approximate values ​​that may vary depending on the application of the disclosed technology. All numerical values ​​may be expressed with significant figures. Measured values ​​may be average values ​​of multiple measurements. The number of measurements may be three or more, five or more, or ten or more. In general, the more measurements are made, the more reliable the average value is expected to be. Measured values ​​may be rounded to the nearest significant figure. Measured values ​​may include errors, such as those associated with the detection limits of the measuring device.

[0031] Geometric terms (e.g., "parallel," "perpendicular," and the like) should not be interpreted in a strict sense. For example, "parallel" may deviate slightly from the strict meaning of "parallel." Geometric terms may include, for example, tolerances, errors, and the like in design, work, and manufacturing. The dimensional relationships in each drawing may not match the actual dimensional relationships. To facilitate understanding of the disclosed technology, the dimensional relationships (length, width, thickness, and the like) in each drawing may be changed. Furthermore, some configurations may be omitted.

[0032] 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.

[0033] "D50" refers to the particle size at which the cumulative frequency from the smaller particle size side reaches 50% in a volume-based particle size distribution. D50 can be measured by a laser diffraction method.

[0034] <XPS Measurement> (composition ratio on particle surface) The composition ratio on the particle surface, C Na / C P "," "C K / C P " can 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 of ​​the P2p spectrum is used to determine the elemental concentration of P (C P ) The peak area of ​​the Na1s spectrum is converted into the elemental concentration of Na (C Na ) is converted to K2p 3 / 2 The peak area of ​​the spectrum is the element concentration of K (C K ) is converted to C Na C P By dividing by this, the composition ratio "C Na / C P " is obtained. C K C P By dividing by this, the composition ratio "C K / CP " is required.

[0035] (coverage rate) The coverage is also measured by XPS. By analyzing the above measurement data, C1s, O1s, P2p, Na1s, K2p 3 / 2 , M2p (or M2p 3 / 2 The ratio of each element (element concentration) can be calculated from the peak area of ​​each element. The coverage rate can be calculated using the following formula (3). θ=(P+Na+K) / (P+Na+K+M)×100…(3) In the above formula (3), θ represents the coverage (%), and P, Na, K, and M represent the proportions of each element.

[0036] "M2p (or M2p 3 / 2 )" and M in the above formula (3) are constituent elements of the positive electrode active material particles and represent an element other than Li and O. That is, the positive electrode active material particles may be represented by the following formula (4). LiMO2…(4) M may consist of one element or multiple elements. M may be, for example, at least one element selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). When M contains multiple elements, the total composition ratio of each element may be 1.

[0037] For example, the positive electrode 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′): θ=(P+Na+K) / (P+Na+K+Ni+Co+Mn)×100…(3') Ni in the above formula (3') is Ni2p 3 / 2 The element ratio of nickel is calculated from the peak area of ​​Co2p 3 / 2 The element ratio of cobalt determined from the peak area of ​​Mn is Mn2p 3 / 2 The element ratio of manganese determined from the peak area is shown.

[0038] <Film thickness measurement> The film thickness (thickness of the coating film) can be measured by the following procedure: A sample is prepared by embedding composite particles in a resin material. The sample is 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 20 fields of view for each of 10 composite particles. The arithmetic average of the film thicknesses at a total of 200 locations is considered to be the film thickness.

[0039] 《ICP measurement》 The molar ratio in the coating solution "n Na / n P "," "n K / n P " is 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 P, Na, and K (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 (Inductively Coupled Plasma Atomic Emission Spectroscopy) 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 solution of coating solution) is measured using the ICP-AES device. The mass concentrations of P, Na, and K in the coating solution are determined from the emission intensity of the sample solution and the calibration curve. The mass concentrations of P, Na, and K are then converted to molar concentrations. The molar concentration of Na (n Na ) is the molar concentration of P (n P ) to obtain the molar ratio "n Na / n P " is calculated. The molar concentration of K (n K ) is the molar concentration of P (n P ) to obtain the molar ratio "nK / n P " is required.

[0040] <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, for example, an aggregate. 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.

[0041] <Coating film> 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. The phosphorus compound contains P and at least one of Na and K.

[0042] For example, the phosphorus compound may contain P and at least one selected from the group consisting of Na, K, rubidium (Rb), cesium (Cs), Fr (francium), beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra).

[0043] The phosphorus compound may further contain, for example, lithium (Li), oxygen (O), carbon (C), etc. P may have a mass fraction of, for example, 1 to 10% with respect to the composite particle 5. The composite particle may, for example, satisfy the relationship of the following formula (5). C Li / C P ≦2.5…(5) In the above formula (5), C Li indicates the element concentration of Li. P indicates the element concentration of P. Li , C P is measured by XPS. The peak area of ​​the Li1s spectrum isLi It is converted to "C Li / C P " indicates the composition ratio of Li to P on the particle surface. When the relationship of the above formula (5) is satisfied, for example, a reduction in battery resistance is expected.

[0044] The phosphorus compound may contain, for example, a phosphate skeleton. That is, the phosphorus compound may be a phosphate compound. When the phosphorus compound contains a phosphate skeleton, for example, when the composite particle 5 is analyzed by TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry), it is found that PO2 - , PO3 - Fragments such as:

[0045] The composition ratio on the particle surface, C Na / C P " may be, for example, 0.01 or more. Na / C P By making the composition ratio "C" equal to or greater than 0.01, it is expected that the battery resistance will be reduced. Na / C P " may be, for example, 0.11 or more, or 0.49 or more. Na / C P " may be, for example, 0.49 or less, or 0.11 or less.

[0046] The composition ratio on the particle surface (C Na +C K ) / C P " may be, for example, 0.01 or more. Na +C K ) / C P " may be, for example, 0.11 or more, or 0.49 or more. Na +C K ) / C P " may be, for example, 0.49 or less, or 0.11 or less.

[0047] The coverage may be, for example, 85% or more. A coverage of 85% or more is expected to reduce battery resistance. The coverage may be, for example, 88% or more, or 89% or more. The coverage may be, for example, 100% or less, 95% or less, or 89% or less.

[0048] 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.

[0049] 《Cathode active material particles》 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 (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. The primary particle may have a maximum Feret diameter of, for example, 0.1 to 3 μm.

[0050] The positive electrode active material particles 1 may contain any component. The positive electrode active material particles 1 may contain, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. For example, "(NiCoMn)" in "Li(NiCoMn)O2" indicates that the sum of the composition ratios in parentheses is 1. As long as the sum is 1, the amount of each component is arbitrary. Li(NiCoMn)O2 may be, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.8 Co 0.1 Mn 0.1 Li(NiCoAl)O2 may contain, for example, LiNi 0.80 Co 0.15 Al 0.05It may contain O2 etc.

[0051] <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 includes a power-generating element 50. 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 a metal foil laminate film. The exterior body may house the 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.

[0052] 《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, an Al foil. The positive electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0053] 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.

[0054] 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 sulfur (S). The sulfide solid electrolyte may contain, for example, Li, P, and S. The sulfide solid electrolyte may further contain, for example, oxygen (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 type or an argyrodite type. 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.

[0055] For example, "LiI-LiBr-Li3PS4" refers to a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li3PS4 in any molar ratio. For example, the sulfide solid electrolyte may be produced by a mechanochemical method. "Li2S-P2S5" includes Li3PS4. Li3PS4 can be produced, for example, by mixing Li2S and P2S5 in a molar ratio of Li2S / P2S5 = 75 / 25.

[0056] 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.

[0057] 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).

[0058] 《Negative electrode》 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 composite material to the surface of the negative electrode current collector. The negative electrode current collector may include, for example, Cu foil, Ni foil, etc. The negative electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0059] 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, SiO x (0 <x<2)、およびLi4Ti5O 12 It may contain at least one selected from the group consisting of:

[0060] <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.

[0061] <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."

[0062] (a) Preparation of the mixture This manufacturing method includes preparing a mixture by mixing a coating liquid with positive electrode active material particles. 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.

[0063] The coating liquid contains a solute and a solvent. The solute contains raw materials for the coating film. The coating liquid may further contain, for example, suspended matter (insoluble components), precipitates, etc.

[0064] The amount of solute may be, for example, 0.1 to 20 parts by mass, 1 to 15 parts by mass, or 5 to 10 parts by mass per 100 parts by mass of solvent. The solvent may contain any component as long as the solute dissolves in it. The solvent may contain, for example, water, alcohol, etc. The solvent may contain, for example, ion-exchanged water, etc.

[0065] The solute includes at least one of Na and K, and P. The solute may include, for example, phosphates of Na and K. The solute may include, for example, sodium orthophosphate, potassium orthophosphate, disodium hydrogen phosphate, dipotassium hydrogen phosphate, etc.

[0066] The solute may include, for example, a phosphoric acid compound, such as phosphoric anhydride (P2O5), orthophosphoric acid, pyrophosphoric acid, or metaphosphoric acid (HPO3) n ] and polyphosphoric acid. The solute may contain, 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 continuity of the coating film is expected to, for example, improve the coverage rate.

[0067] If the solute contains Na, the molar ratio of Na to P is n Na / n P The molar ratio "n Na / n P The molar ratio "n" may be, for example, 0.12 or more, 0.50 or more, or 0.75 or more. Na / n P " may be, for example, 1 or less, or 0.75 or less.

[0068] If the solute contains K, the molar ratio of K to P is n K / n P " is, for example, 2.22 x 10 -5 That's all. The molar ratio "n K / n P " is, for example, 3.80 x 10 -5 It may be more than 9.51 x 10 -5 The molar ratio "n K / nP " is, for example, 8.00 x 10 -3 It may be less than or equal to 9.51 x 10 -5 It may be the following:

[0069] The concentration (mass fraction) of Na in the coating liquid is, for example, 1.46 × 10 4 ppm (1.46%) or more. This is expected to reduce the battery resistance. The Na concentration is, for example, 8.18×10 4 ppm or more, 2.71 x 10 5 ppm or more, 3.58 × 10 5 The concentration of Na may be, for example, 4.30 × 10 ppm or more. 5 ppm (43%) or less, or 3.58 × 10 5 It may be less than ppm.

[0070] The concentration (mass fraction) of K in the coating solution may be, for example, 28 ppm or more. This is expected to reduce battery resistance. The concentration of K may be, for example, 48 ppm or more, or 120 ppm or more. The concentration of K may be, for example, 10,000 ppm or less, or 120 ppm or less.

[0071] The solute may further include, for example, a lithium compound, such as lithium hydroxide, lithium carbonate, or lithium nitrate.

[0072] The mole ratio of Li to P is "n Li / n P " may be, for example, less than 1.1. Li / n P When the molar ratio "n" is less than 1.1, for example, a reduction in battery resistance is expected. Li / n P " may be, for example, 1.07 or less, 0.45 or less, or even zero. Li / n P" may be, for example, 0 to 0.45, or 0.45 to 1.07.

[0073] (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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] (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]

[0078] <Experiment 1> In Experiment 1, the effect of Na was investigated. Composite particles, positive electrodes, and all-solid-state batteries according to Nos. 1 to 4 were manufactured as follows. Hereinafter, for example, "composite particles according to No. 1" may be abbreviated as "No. 1."

[0079] No. 1 Metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was prepared as a phosphate compound. The reagent contained sodium phosphate as an excipient. A phosphate solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid in 166 parts by mass of ion-exchanged water.

[0080] An electrodialysis device (product name "Acilyzer EX3B", manufactured by Astom Co., Ltd.) was prepared. The phosphoric acid solution was desalted using the electrodialysis device. The operating conditions of the device were as follows:

[0081] Electrodialysis cell: Two-compartment electrodialysis cell (bipolar membrane + cation exchange membrane) Alkaline solution, electrode solution: sodium hydroxide aqueous solution (0.5 mol / L) Rated capacity: 4.4A Processing time (operating time): 90 minutes

[0082] After desalting, the molar ratio "n Li / n P The coating solution was prepared by dissolving lithium hydroxide monohydrate in a phosphoric acid solution so that the molar ratio "n" was 0.45. Na / n P " and the Na concentration was measured. The measurement results are shown in Table 1 below. In Table 1 below, for example, "E+02" means "×10 2 " indicates.

[0083] As the positive electrode active material particles, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3)O2 was prepared. A suspension was prepared by dispersing 50 parts by mass of a powder of positive electrode active material particles in 53.7 parts by mass of a coating liquid. 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. Na / C P The coverage was measured. The measurement results are shown in Table 1 below.

[0084] The following materials were prepared: Sulfide solid electrolyte: 10LiI-15LiBr-75Li3PS4 Conductive material: VGCF Binder: SBR Dispersion medium: heptane Positive electrode current collector: Al foil

[0085] A positive electrode slurry was prepared by mixing the 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 3 parts by mass for 100 parts by mass of composite particles. The positive electrode slurry was thoroughly stirred using an ultrasonic homogenizer. A coating film was formed by applying the positive electrode slurry to the surface of a positive electrode current collector. The coating film was dried at 100°C for 30 minutes using a hot plate. A positive electrode blank was thus produced. 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.

[0086] A negative electrode and a separator layer were prepared. The negative electrode active material particles were graphite. The same type of sulfide solid electrolyte was used between the positive electrode, the separator layer, and the negative electrode. A laminate was formed by stacking the positive electrode, the separator layer, and the negative electrode in a cylindrical jig. A power generating element was formed by pressing the laminate. A terminal was connected to the power generating element to form an all-solid-state battery.

[0087] No.2 The coating solution, composite particles, positive electrode, and all-solid-state battery were manufactured in the same manner as in No. 1, except that the treatment time for the desalination treatment was changed to 60 minutes.

[0088] No.3 The coating solution, composite particles, positive electrode, and all-solid-state battery were manufactured in the same manner as in No. 1, except that the treatment time for the desalination treatment was changed to 30 minutes.

[0089] No.4 The coating solution, composite particles, positive electrode, and all-solid-state battery were manufactured in the same manner as in No. 1, except that the desalination treatment was not performed.

[0090] "evaluation" The battery resistance was measured. The measurement results are shown in Table 1 below. The battery resistances in Table 1 below are relative values. In Experiment 1, the resistance of battery No. 1 is defined as 100.

[0091] [Table 1]

[0092] "result" As shown in Table 1 above, the battery resistance is reduced in Nos. 2 to 4 compared to No. 1. In No. 1, the composition ratio "C Na / C P The coating film No. 1 is considered to contain no Na. In Nos. 2 to 4, the composition ratio "C Na / C P" is greater than zero. The coating films of Nos. 2 to 4 are thought to contain Na. Nos. 2 to 4 also tend to have a higher coverage rate than No. 1.

[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, l5 Composite particle, 10 Positive electrode, 20 Negative electrode, 30 Separator layer, 50 Power generating element, 100 All-solid-state battery.

Claims

1. positive electrode active material particles; A coating film; Including, 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 phosphorus compound contains phosphorus and at least one of sodium and potassium, The following formula: (C Na +C K ) / C P ≦0.49 Fulfilling the relationship, In the above formula, C Na , C K , and C P represent element concentrations measured by X-ray photoelectron spectroscopy; C Na denotes the elemental concentration of sodium, C K denotes the elemental concentration of potassium, C P denotes the elemental concentration of phosphorus; composite particles.

2. The following formula: 0.01≦(C Na +C K ) / C P ≦0.49 Further satisfying the relationship, The composite particle according to claim 1 .

3. The following formula: C Na / C P ≦0.49 Further satisfying the relationship, The composite particle according to claim 1 or claim 2.

4. The coating film has a thickness of 10 nm or more. The composite particle according to any one of claims 1 to 3.

5. A coverage of 85% or more; The coverage is measured by X-ray photoelectron spectroscopy. The composite particle according to any one of claims 1 to 4.

6. Composite particles for an all-solid-state battery containing a sulfide solid electrolyte, The composite particle according to any one of claims 1 to 5.

7. Comprising the composite particle according to any one of claims 1 to 5 and a sulfide solid electrolyte, Positive electrode.

8. The positive electrode according to claim 7, All-solid-state battery.

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