Composite particles, cathodes, and solid-state batteries

Abstract

To reduce battery resistance.SOLUTION: Composite particles includes positive electrode active substance particles and a coating film covering at least part of a surface of the positive electrode active substance particles. The coating film includes a first layer covering at least part of a surface of the positive electrode active substance particles and a second layer covering at least part of a surface of the first layer. The first layer includes an alkaline oxide containing Li and M. M is at least one of niobium and carbon. The second layer contains a phosphorus compound.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Japanese Patent Application Laid-Open No. 2010-135090 (Patent Document 1) describes a polyanion structure-containing compound (e.g., PO4 3- A positive electrode active material for an all-solid-state battery is disclosed, which is provided with a reaction suppressing portion (coating film) made of a compound having an orthophosphate skeleton. [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, which can reduce the deterioration of the sulfide solid electrolyte. This is expected to reduce battery resistance.

[0005] However, when the coating film is made of a phosphorus compound, a neutralization reaction between the highly acidic phosphorus compound (such as a phosphate compound) and the alkaline positive electrode active material may occur during the coating film formation process or during battery operation, resulting in the formation of a high-resistance layer and an increase in battery resistance (such as initial resistance).

[0006] An object of the present disclosure is to reduce battery resistance. [Means for solving the problem]

[0007] 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.

[0008] (1) A battery comprising: positive electrode active material particles; and a coating film covering at least a portion of the surface of the positive electrode active material particles; the coating film includes a first layer that covers at least a portion of the surface of the positive electrode active material particles, and a second layer that covers at least a portion of the surface of the first layer, the first layer contains an alkaline oxide containing Li and M, where M is at least one of niobium (Nb) and carbon (C); the second layer contains a phosphorus compound; composite particles.

[0009] In the composite particle (1), the first layer containing the alkaline oxide is interposed between the second layer containing the phosphorus compound and the positive electrode active material particles, thereby suppressing the reaction between the phosphorus compound in the second layer and the positive electrode active material particles, thereby reducing the battery resistance. Furthermore, although the first layer is characterized by low resistance, when the first layer is in contact with the surrounding solid electrolyte in the positive electrode, the alkaline oxide (a compound containing Li and at least one of Nb and C) decomposes during high-potential charging and discharging, which may increase the battery resistance (increase the rate of increase in battery resistance). In contrast, in the composite particle (1) above, the second layer is interposed between the first layer and the solid electrolyte, which suppresses the decomposition of the alkaline oxide in the first layer. This reduces the battery resistance. From the above, it is expected that the battery resistance will be reduced in a battery using the composite particles of (1) above.

[0010] (2) The composite particles according to (1), wherein the alkaline oxide is lithium niobate (LiNbO3) or lithium carbonate (Li2CO3).

[0011] (3) The composite particle according to (1) or (2), wherein the phosphorus compound is a phosphate compound.

[0012] (4) A positive electrode comprising the composite particles according to any one of (1) to (3) and a sulfide solid electrolyte.

[0013] (5) An all-solid-state battery comprising the positive electrode according to (4), a negative electrode, and a separator.

[0014] 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]

[0015] [Figure 1] FIG. 1 is a conceptual diagram showing a composite particle in this embodiment. [Figure 2] FIG. 2 is a schematic flowchart of the method for producing composite particles in this embodiment. [Figure 3] FIG. 3 shows the results of STEM-EELS measurements. [Figure 4] FIG. 4 is a diagram showing the results of XPS measurement example 1. [Figure 5] FIG. 5 is a diagram showing the results of XPS measurement example 2. DETAILED DESCRIPTION OF THE INVENTION

[0016] <Terms and definitions> The terms "comprising," "including," and "having" 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, closed-ended terms do not exclude additional elements that are normally incidental impurities or unrelated to the disclosed technology.

[0017] 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."

[0018] 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).

[0019] 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.

[0020] 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.

[0021] 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.

[0022] "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.

[0023] <Composite particles> FIG. 1 is a conceptual diagram showing a composite particle in this embodiment. The composite particle 100 may be referred to as, for example, a "coated cathode active material." The composite particle 100 includes cathode active material particles 110 and a coating film 120. The composite particle 100 may form, for example, an aggregate. That is, one composite particle 100 may include two or more cathode active material particles 110. The composite particle 100 may have a D50 of, for example, 1 to 50 μm, 1 to 20 μm, or 5 to 15 μm.

[0024] <Coating film> The coating film 120 is a shell of the composite particle 100. The coating film 120 covers at least a portion of the surface of the positive electrode active material particle 110. The coating film 120 includes a first layer 121 and a second layer 122. The first layer 121 covers at least a portion of the surface of the positive electrode active material particle 110. The second layer 122 covers at least a portion of the surface of the first layer 121.

[0025] From the viewpoint of enhancing the effects of the present disclosure, it is preferable that the first layer 121 covers substantially the entire surface of the positive electrode active material particles, and it is preferable that the second layer 122 covers substantially the entire surface of the first layer 121. However, within the scope of the effects of the present disclosure, a portion of the surface of the positive electrode active material particle may not be coated with the first layer 121, and a portion of the surface of the first layer 121 may not be coated with the second layer 122. For example, the first layer 121 and the second layer 122 may overlap entirely or partially. That is, within the scope of the effects of the present disclosure, the coating film 120 may partially include a single-layer structure. For example, the coverage of the first layer 121 may be higher than the coverage of the second layer 122. In other words, a portion of the first layer 121 may be exposed on the surface of the coating film 120 as long as the effects of the present disclosure are achieved. For example, the coverage of the first layer 121 may be lower than the coverage of the second layer 122. In other words, a portion of the second layer 122 may be in contact with the surface of the positive electrode active material particle 110 as long as the effects of the present disclosure are achieved.

[0026] For example, the coating film 120 may include a first layer 121 and a second layer 122, each of which is made up of a single layer. For example, the coating film 120 may include a plurality of first layers 121 and a plurality of second layers 122. For example, the first layers 121 and the second layers 122 may be alternately stacked. The total number of first layers 121 and second layers 122 may be, for example, 2 to 10 layers, or 2 to 4 layers.

[0027] The coating film 120 may further include additional layers, so long as it includes the first layer 121 and the second layer 122. The coating film 120 may further include, for example, a third layer and a fourth layer (not shown). The third layer and the fourth layer may have a different composition from the first layer 121 and the second layer 122.

[0028] <1st layer> The first layer 121 contains an alkaline oxide containing Li and M. M is at least one of niobium (Nb) and carbon (C). The alkaline oxide is an oxide or a precursor thereof that has a pH of greater than 7 when dissolved in water.

[0029] The alkaline oxide may be represented by, for example, the following formula (3) or (4): Li y Nb z O x …(3) Li y C z O x …(4) In the above formulas (3) and (4), y, z, and x are any numbers. y, z, and x can be identified, for example, by XPS or the like. y may, for example, satisfy the relationship 0≦y<2.5. When y is less than 2.5, a reduction in initial resistance is expected. y may, for example, be 1.5 or less, 1 or less, or 0.5 or less.

[0030] Examples of alkaline oxides represented by formula (3) include LiNbO3, Li3NbO4, Li8Nb2O9, LiNb3O8, and LiNbO2. An example of the alkaline oxide represented by formula (4) is Li2CO3. The alkaline oxide contains Li2CO3 as a main phase and may also contain a portion of LiHCO3, which may be produced from Li2CO3 in the atmosphere.

[0031] <Second layer> The second layer 122 includes a phosphorus compound. The phosphorus compound is a compound containing at least P.

[0032] Examples of phosphorus compounds include phosphate compounds. The first layer 121 may contain, for example, a phosphate skeleton. The presence of the phosphate skeleton can be confirmed by TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry). When the second layer 122 contains a phosphate skeleton, TOF-SIMS of the composite particle 100 reveals that PO2 - , PO3 - Fragments such as:

[0033] The second layer 122 may further contain Li. The phosphorus compound may be represented by, for example, the following formula (5). Li y PO x …(5) In the above formula (5), y and x are any numbers. y and x can be identified, for example, by XPS or the like. y may, for example, satisfy the relationship 0≦y<2.5. When y is less than 2.5, a reduction in initial resistance is expected. y may, for example, be 1.5 or less, 1 or less, 0.5 or less, or zero.

[0034] The phosphorus compound represented by formula (5) is, for example, Li 0.5 PO3 and PO x , Li4P2O7, and Li3PO4.

[0035] <Film Thickness> The coating film 120 (entire film) may have a thickness of, for example, 5 to 100 nm, 5 to 50 nm, 10 to 30 nm, or 20 to 30 nm.

[0036] The thickness (t1) of the first layer 121 and the thickness (t2) of the second layer 122 may, for example, satisfy the relationship "t1 / t2=1 / 9 to 9 / 1", or may satisfy the relationship "t1 / t2=3 / 7 to 7 / 3", or may satisfy the relationship "t1 / t2=4 / 6 to 6 / 4".

[0037] 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.

[0038] <Coverage rate> The coverage of the surface of the positive electrode active material particle 110 with the coating film 120 may be, for example, 95% or more. A coverage of 95% or more is expected to reduce the initial resistance. The coverage may be, for example, 95 to 100%, or 96 to 100%.

[0039] The coverage can be measured, for example, by XPS (X-ray Photoelectron Spectroscopy). For example, an XPS device manufactured by ULVAC-PHI, Inc., product name: PHI X-tool (or an equivalent product) may be used. A sample powder consisting of composite particles is placed in the XPS. Narrow scan analysis is performed. The measurement data is processed by analysis software. For example, analysis software manufactured by ULVAC-PHI, Inc., product name: MulTiPak (or an equivalent product) may be used. Multiple elements are detected by analyzing the measurement data. The ratio of each detected element is calculated from the area of ​​each peak. The coverage can be calculated using the following formula: θ={I1 / (I0+I1)}×100 θ: Coverage rate [%] I0: Ratio of elements derived from core particles (positive electrode active material particles) I1: Ratio of elements derived from the coating layer (coating film)

[0040] 《Cathode active material particles》 The positive electrode active material particle 110 is the core of the composite particle 100. The positive electrode active material particle 110 may be a secondary particle (an aggregate of primary particles). The positive electrode active material particle 110 (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.

[0041] The positive electrode active material particles 110 (positive electrode active material) may contain, for example, a transition metal oxide, a polyanion compound, or the like. The composition within one particle (positive electrode active material) may be uniform or non-uniform. For example, the composition may be graded from the surface toward the center of the particle. The composition may change continuously or discontinuously (in steps).

[0042] <Transition metal oxides: space group R-3m> The transition metal oxide may have any crystal structure. The transition metal oxide may include, for example, a crystal structure belonging to the space group R-3m. For example, a compound represented by the general formula "LiMO2" may have a crystal structure belonging to the space group R-3m. The transition metal oxide may be represented by, for example, the following formula (C-1):

[0043] Li 1-a Ni x M 1-x O2…(C-1) In the formula, the relationships of -0.5≦a≦0.5 and 0≦x≦1 are satisfied. M may include, for example, at least one selected from the group consisting of Co, Mn, and Al.

[0044] In the above formula (C-1), x may satisfy, for example, the relationship of 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x ≤ 1. a may satisfy, for example, the relationship of -0.4 ≤ a ≤ 0.4, -0.3 ≤ a ≤ 0.3, -0.2 ≤ a ≤ 0.2, or -0.1 ≤ a ≤ 0.1.

[0045] The transition metal oxide may include, for example, at least one selected from the group consisting of LiCoO2, LiMnO2, LiNi 0.9 Co 0.1 O2, LiNi 0.9 Mn 0.1 O2, and LiNiO2.

[0046] 〈NCM〉 The transition metal oxide may be represented, for example, by the following formula (C-2). The compound represented by the following formula (C-2) may also be referred to as "NCM".

[0047] Li 1-a Ni x Co y Mn z O2…(C-2) In the formula, the relationships of -0.5 ≤ a ≤ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0048] In the above formula (C-2), x may satisfy, for example, the relationship of 0 < x ≤ 0.1, 0.1 ≤ x ≤ 0.2, 0.2 ≤ x ≤ 0.3, 0.3 ≤ x ≤ 0.4, 0.4 ≤ x ≤ 0.5, 0.5 ≤ x ≤ 0.6, 0.6 ≤ x ≤ 0.7, 0.7 ≤ x ≤ 0.8, 0.8 ≤ x ≤ 0.9, or 0.9 ≤ x < 1.

[0049] In the above formula (C-2), y may satisfy, for example, the relationship of 0 < y ≤ 0.1, 0.1 ≤ y ≤ 0.2, 0.2 ≤ y ≤ 0.3, 0.3 ≤ y ≤ 0.4, 0.4 ≤ y ≤ 0.5, 0.5 ≤ y ≤ 0.6, 0.6 ≤ y ≤ 0.7, 0.7 ≤ y ≤ 0.8, 0.8 ≤ y ≤ 0.9, or 0.9 ≤ y < 1.

[0050] In the above formula (C-2), z may satisfy a relationship such as 0 < z ≤ 0.1, 0.1 ≤ z ≤ 0.2, 0.2 ≤ z ≤ 0.3, 0.3 ≤ z ≤ 0.4, 0.4 ≤ z ≤ 0.5, 0.5 ≤ z ≤ 0.6, 0.6 ≤ z ≤ 0.7, 0.7 ≤ z ≤ 0.8, 0.8 ≤ z ≤ 0.9, or 0.9 ≤ z < 1.

[0051] NCM is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.4 Co 0.3 Mn 0.3 O2, LiNi 0.3 Co 0.4 Mn 0.3 O2, LiNi 0.3 Co 0.3 Mn 0.4 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.4 Mn 0.1 O2, LiNi 0.5 Co 0.1 Mn 0.4 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.7 Co 0.1 Mn 0.2 O2, LiNi 0.7 Co 0.2 Mn 0.1 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, and at least one selected from the group consisting of LiNi 0.9 Co 0.05 Mn 0.05 O2 may be included.

[0052] 〈NCA〉 The transition metal oxide may be represented, for example, by the following formula (C-3). The compound represented by the following formula (C-3) may also be referred to as "NCA".

[0053] Li 1-a Ni x Co y Al z O2…(C-3) In the formula, the relationships of -0.5 ≦ a ≦ 0.5, 0 < x < 1, 0 < y < 1, 0 < z < 1, and x + y + z = 1 are satisfied.

[0054] In the above formula (C-3), x may satisfy, for example, the relationship of 0 < x ≦ 0.1, 0.1 ≦ x ≦ 0.2, 0.2 ≦ x ≦ 0.3, 0.3 ≦ x ≦ 0.4, 0.4 ≦ x ≦ 0.5, 0.5 ≦ x ≦ 0.6, 0.6 ≦ x ≦ 0.7, 0.7 ≦ x ≦ 0.8, 0.8 ≦ x ≦ 0.9, or 0.9 ≦ x < 1.

[0055] In the above formula (C-3), y may satisfy, for example, the relationship of 0 < y ≦ 0.1, 0.1 ≦ y ≦ 0.2, 0.2 ≦ y ≦ 0.3, 0.3 ≦ y ≦ 0.4, 0.4 ≦ y ≦ 0.5, 0.5 ≦ y ≦ 0.6, 0.6 ≦ y ≦ 0.7, 0.7 ≦ y ≦ 0.8, 0.8 ≦ y ≦ 0.9, or 0.9 ≦ y < 1.

[0056] In the above formula (C-3), z may satisfy, for example, the relationship of 0 < z ≦ 0.1, 0.1 ≦ z ≦ 0.2, 0.2 ≦ z ≦ 0.3, 0.3 ≦ z ≦ 0.4, 0.4 ≦ z ≦ 0.5, 0.5 ≦ z ≦ 0.6, 0.6 ≦ z ≦ 0.7, 0.7 ≦ z ≦ 0.8, 0.8 ≦ z ≦ 0.9, or 0.9 ≦ z < 1.

[0057] NCA is, for example, LiNi 0.7 Co 0.1 Al 0.2 O2, LiNi 0.7 Co 0.2 Al 0.1 O2, LiNi 0.8 Co 0.1 Al 0.1 O2, LiNi0.8 Co 0.17 Al 0.03 O2, LiNi 0.8 Co 0.15 Al 0.05 O2 and LiNi 0.9 Co 0.05 Al 0.05 O2.

[0058] <Multi-component system> The positive electrode active material may contain, for example, two or more types of NCM. The positive electrode active material may contain, for example, NCM (0.6≦x) and NCM (x<0.6). "NCM (0.6≦x)" refers to a compound in which x (Ni ratio) in the above formula (C-2) is 0.6 or more. NCM (0.6≦x) may also be referred to as, for example, a "high nickel material." NCM (0.6≦x) is, for example, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc. "NCM (x<0.6)" refers to a compound in which x (Ni ratio) is less than 0.6 in the above formula (C-2). NCM (x<0.6) is, for example, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, etc. The mixing ratio (mass ratio) of NCM(0.6≦x) and NCM(x<0.6) may be, for example, "NCM(0.6≦x) / NCM(x<0.6)=9 / 1 to 1 / 9," "NCM(0.6≦x) / NCM(x<0.6)=9 / 1 to 4 / 6," or "NCM(0.6≦x) / NCM(x<0.6)=9 / 1 to 3 / 7."

[0059] The positive electrode active material may contain, for example, NCA and NCM. The mixing ratio (mass ratio) of NCA and NCM may be, for example, "NCA / NCM = 9 / 1 to 1 / 9," "NCA / NCM = 9 / 1 to 4 / 6," or "NCA / NCM = 9 / 1 to 3 / 7." The Ni ratios of NCA and NCM may be the same or different. The Ni ratio of NCA may be higher than the Ni ratio of NCM. The Ni ratio of NCA may be lower than the Ni ratio of NCM.

[0060] <Transition metal oxides: space group C2 / m> The transition metal oxide may have, for example, a crystal structure belonging to the space group C2 / m. The transition metal oxide may be represented by, for example, the following formula (C-4).

[0061] Li2MO3…(C-4) In the formula, M may include, for example, at least one selected from the group consisting of Ni, Co, Mn, and Fe.

[0062] The positive electrode active material may include, for example, a mixture of LiMO2 (space group R-3m) and Li2MO3 (space group C2 / m), or a solid solution of LiMO2 and Li2MO3 (Li2MO3-LiMO2).

[0063] <Transition metal oxides: space group Fd-3m> The transition metal oxide may have, for example, a crystal structure belonging to the space group Fd-3m. The transition metal oxide may be represented by, for example, the following formula (C-5). LiMn 2-x M x O4…(C-5) In the formula, the relationship 0≦x≦2 is satisfied. M may include, for example, at least one selected from the group consisting of Ni, Fe, and Zn.

[0064] LiM2O4 (space group Fd-3m) is, for example, LiMn2O4 and LiMn 1.5 Ni 0.5 The positive electrode active material may contain at least one selected from the group consisting of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m). The positive electrode active material may contain, for example, a mixture of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m). The mixing ratio (mass ratio) of LiMO2 (space group R-3m) and LiM2O4 (space group Fd-3m) may be, for example, "LiMO2 / LiM2O4 = 9 / 1 to 9 / 1," "LiMO2 / LiM2O4 = 9 / 1 to 5 / 5," or "LiMO2 / LiM2O4 = 9 / 1 to 7 / 3."

[0065] <Polyanion Compounds> The polyanion compound may contain, for example, a phosphate (such as LiFePO4), a silicate, a borate, etc. The polyanion compound may be represented, for example, by the following formulas (C-6) to (C-9).

[0066] LiMPO4…(C-6) Li 2-x MPO4F...(C-7) Li2MSiO4…(C-8) LiMBO3…(C-9) In the above formulas (C-6) to (C-9), M may include, for example, at least one selected from the group consisting of Fe, Mn, and Co. In the above formula (C-7), for example, the relationship 0≦x≦2 may be satisfied.

[0067] The positive electrode active material may contain, for example, a mixture of LiMO2 (space group R-3m) and a polyanionic compound. The mixing ratio (mass ratio) of LiMO2 (space group R-3m) and the polyanionic compound may be, for example, "LiMO2 / polyanionic compound = 9 / 1 to 9 / 1," "LiMO2 / polyanionic compound = 9 / 1 to 5 / 5," or "LiMO2 / polyanionic compound = 9 / 1 to 7 / 3."

[0068] Dopant A dopant may be added to the positive electrode active material. The dopant may be diffused throughout the particle or distributed locally. For example, the dopant may be unevenly distributed on the particle surface. The dopant may be a substitutional solid solution atom or an interstitial solid solution atom. The amount of dopant added (molar fraction relative to the entire positive electrode active material) may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%. One type of dopant may be added, or two or more types of dopants may be added. Two or more types of dopants may form a complex.

[0069] The dopant may include at least one selected from the group consisting of, for example, B, C, N, halogen, Si, Na, Mg, Al, Mn, Co, Cr, Sc, Ti, V, Cu, Zn, Ga, Ge, Se, Sr, Y, Zr, Nb, Mo, In, Pb, Bi, Sb, Sn, W, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and actinides.

[0070] For example, the set "Zr, Mg, W, Sm", the set "Ti, Mn, Nb, Si, Mo", or the set "Er, Mg" may be added to the NCA.

[0071] For example, Ti may be added to the NCM. For example, a combination of "Zr, W", a combination of "Si, W", or a combination of "Zr, W, Al, Ti, Co" may be added to the NCM.

[0072] <All-solid-state battery> The all-solid-state battery includes a power generating element, which includes a positive electrode containing the composite particles, a separator, and a negative electrode.

[0073] The all-solid-state battery may include an exterior body. The exterior body may house a power generating element and an electrolyte. The exterior body may have any form. For example, the exterior body may be a metal case or a pouch made of a metal foil laminated film. The case may have any shape. For example, the case may be cylindrical, rectangular, flat, coin-shaped, or the like. The exterior body may contain, for example, Al. The exterior body may house, for example, one power generating element, or may house, multiple power generating elements. The multiple power generating elements may form, for example, a series circuit or a parallel circuit. Within the exterior body, the multiple power generating elements may be stacked in the thickness direction of the all-solid-state battery (cell).

[0074] [Power generation element] The power generating element includes a positive electrode and a negative electrode. The power generating element may further include a separator. The separator is disposed between the positive electrode and the negative electrode. The power generating element may have any shape. The power generating element may be, for example, a laminated type. For example, the power generating element may be formed by alternately stacking positive electrodes and negative electrodes with a separator sandwiched between them. The power generating element may be, for example, a wound type. For example, a laminate may be formed by stacking a strip-shaped positive electrode, a strip-shaped separator, and a strip-shaped negative electrode. The laminate may be spirally wound to form the power generating element. A wound type power generating element may be formed into a flat shape after winding.

[0075] The power generating element may have, for example, an anode-free structure. An "anode-free structure" refers to a structure in which no solid negative electrode active material is present before the first charge. Of course, the power generating element does not have to have an anode-free structure.

[0076] 《Positive electrode》 The positive electrode is layered. The positive electrode 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.

[0077] 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. The positive electrode active material layer includes a positive electrode mixture. The positive electrode mixture may include the above-mentioned composite particles (coated positive electrode active material) and a sulfide solid electrolyte.

[0078] 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.

[0079] 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.

[0080] 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 include, for example, at least one selected from the group consisting of graphite, acetylene black (AB), Ketjen Black (registered trademark), vapor grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes (GF).

[0081] 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), tetrafluoroethylene (PTFE), CMC, PAA, polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyoxyethylene alkyl ether, and derivatives thereof.

[0082] 《Negative electrode》 The negative electrode is layered. The negative electrode 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.

[0083] 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. 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.

[0084] The negative electrode active material particles may contain any component, such as natural graphite, artificial graphite, soft carbon, hard carbon, silicon (Si), SiO, Li silicate, Si-based alloy, tin (Sn), SnO, Sn-based alloy, and Li4Ti5O. 12 It may contain at least one selected from the group consisting of:

[0085] <Carbon-based active material> "Graphite" is a general term for natural graphite and artificial graphite. Graphite may be a mixture of natural graphite and artificial graphite. The mixing ratio (mass ratio) may be, for example, "natural graphite / artificial graphite = 1 / 9 to 9 / 1", "natural graphite / artificial graphite = 2 / 8 to 8 / 2", or "natural graphite / artificial graphite = 3 / 7 to 7 / 3".

[0086] Graphite may contain a dopant. The dopant may contain, for example, at least one selected from the group consisting of B, N, P, Li, and Ca. The addition amount may be, in mole fraction, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%.

[0087] The surface of the graphite may be coated with, for example, amorphous carbon. The surface of the graphite may be coated with, for example, a different material. The different material may contain, for example, at least one selected from the group consisting of P, W, Al, and O. The different material may contain, for example, at least one selected from the group consisting of Al(OH)3, AlOOH, Al2O3, WO3, Li2CO3, LiHCO 3、 and at least one selected from the group consisting of Li3PO4.

[0088] 〈Alloy-based active material〉 SiO may be represented by, for example, the following formula (A-1).

[0089] SiO x …(A-1) In the formula, the relationship of 0 < x < 2 is satisfied.

[0090] In the above formula (A-1), x may satisfy the relationship of, for example, 0.5 ≤ x ≤ 1.5, or 0.8 ≤ x ≤ 1.2.

[0091] The Li silicate may include at least one selected from the group consisting of Li4SiO4, Li2SiO3, Li2Si2O5, and Li8SiO6. The second negative electrode active material may include a mixture of Si and Li silicate. The mixing ratio (mass ratio) may be, for example, "Si / Li silicate = 1 / 9 to 9 / 1," "Si / Li silicate = 2 / 8 to 8 / 2," "Si / Li silicate = 3 / 7 to 7 / 3," or "Si / Li silicate = 4 / 6 to 6 / 4."

[0092] The alloy-based active material (e.g., Si, SiO) may contain an additive. The additive may be, for example, a substitutional solute atom or an interstitial solute atom. The additive may be a deposit attached to the surface of the alloy-based active material. The deposit may be, for example, an element, an oxide, a carbide, a nitride, a halide, or the like. The amount added may be, for example, 0.01 to 5%, 0.1 to 3%, or 0.1 to 1% in terms of mole fraction. The additive may contain, for example, at least one selected from the group consisting of Li, Na, K, Rb, Be, Mg, Ca, Sr, Fe, Ba, B, Al, Ga, In, C, Ge, Sn, Pb, N, P, As, Y, Sb, and S. That is, SiO may be doped with Mg or Na. For example, Mg silicate, Na silicate, etc. may be formed. For example, boron oxide (for example, B2O3, etc.), yttrium oxide (for example, Y2O3, etc.), etc. may be added to SiO.

[0093] <Si-C composite material> The second negative electrode active material may include, for example, a composite material of a carbon-based active material (such as graphite) and an alloy-based active material (such as Si). A composite material containing Si and carbon may also be called a "Si-C composite material." For example, Si fine particles may be dispersed in carbon particles. For example, Si fine particles may be dispersed in graphite particles. For example, Li silicate particles may be coated with a carbon material (such as amorphous carbon). A Si-C composite material and graphite may be mixed and used.

[0094] <Multi-component system> The second negative electrode active material may contain two or more components. The second negative electrode active material may contain a carbon-based active material (such as graphite) and an alloy-based active material (such as Si or SiO). The mixing ratio (mass ratio) of the carbon-based active material to the alloy-based active material may be, for example, "carbon-based active material / alloy-based active material=1 / 9 to 9 / 1," "carbon-based active material / alloy-based active material=2 / 8 to 8 / 2," "carbon-based active material / alloy-based active material=3 / 7 to 7 / 3," or "carbon-based active material / alloy-based active material=4 / 6 to 6 / 4."

[0095] <Binder> The second negative electrode active material may be fixed to the negative electrode current collector 21, the porous body 22, etc., by, for example, a binder. The binder may contain any component. For example, the binder may contain at least one selected from the group consisting of polyacrylic acid (PAA), carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), acrylate butadiene rubber (ABR), polyacrylonitrile (PAN), and derivatives thereof.

[0096] <separator> The separator (layer) is interposed between the positive electrode and the negative electrode. The separator separates the positive electrode from the negative electrode. The separator includes a sulfide solid electrolyte. The separator may further include a binder. The sulfide solid electrolyte may be the same or different between the separator and the positive electrode composite. The sulfide solid electrolyte may be the same or different between the separator and the negative electrode composite.

[0097] This embodiment may be incorporated into, for example, the first to third cell configurations. This embodiment may be combined with, for example, the first to third cell configurations. This embodiment may replace, for example, a part of the first to third cell configurations. For example, the negative electrode in the first cell configuration may be replaced with the negative electrode in this embodiment (negative electrode current collector 21, porous body 22). For example, the negative electrode in the first cell configuration may be used in combination with the negative electrode in this embodiment. Battery performance may be improved by combining the first to third cell configurations with this embodiment, etc.

[0098] <Method of manufacturing composite particles> An example of a method for producing the composite particles will now be described. The method for producing composite particles of the present embodiment includes the steps of: (a) preparing positive electrode active material particles; and (b) forming a coating film (forming a coating film on the surface of the positive electrode active material particles to produce composite particles); Including, The above (b) is (b1) forming the first layer by drying the first coating liquid; and (b2) forming the second layer by drying the second coating liquid; Includes.

[0099] FIG. 2 is a schematic flowchart of a method for producing composite particles according to this embodiment. Hereinafter, the "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 positive electrode active material particles" and "(b) formation of a coating film." The present production method may further include, for example, "(c) heat treatment."

[0100] (a) Preparation of Positive Electrode Active Material Particles The present manufacturing method includes preparing positive electrode active material particles, the details of which are as described above.

[0101] (b) Formation of a coating film The present manufacturing method includes forming a coating film on the surface of positive electrode active material particles to manufacture composite particles. The present manufacturing method includes "(b1) Formation of a first layer" and "(b2) Formation of a second layer."

[0102] (b1) Formation of the first layer The manufacturing method includes forming a first layer by drying a first coating liquid. A first coating liquid is prepared. The first coating liquid includes a first solute and a first solvent. The first solute includes a raw material for the first layer.

[0103] 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 first solvent may contain any component as long as the first solute can be dissolved in it. The first solvent may contain, for example, water, alcohol, etc. The first solvent may contain, for example, ion-exchanged water, ethanol, etc.

[0104] The second solute may include, for example, a lithium compound and a niobate compound. Examples of lithium compounds include lithium hydroxide, lithium carbonate, and lithium nitrate. An example of the niobic acid compound is niobic acid [Nb2O5·3H2O].

[0105] The first mixture may be formed by mixing the first coating liquid with the positive electrode active material particles. The first mixture may be, for example, a suspension or a wet powder. For example, a suspension may be formed by dispersing the positive electrode active material particles (powder) in the first coating liquid. For example, a wet powder may be formed by spraying the first coating liquid into the powder. In this production method, any mixing device, granulating device, etc. may be used.

[0106] For example, the first layer can be formed by drying the first mixture. That is, the first layer can be generated by drying the first coating liquid attached to the surface of the positive electrode active material particles. In this production method, any drying method can be used.

[0107] For example, the first coating liquid may be dried by a spray-drying method. That is, the suspension is sprayed from a nozzle to form droplets. The droplets contain the positive electrode active material particles and the first coating liquid. For example, the droplets may be dried with hot air to form primary composite particles (intermediate products).

[0108] 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.

[0109] For example, the first mixture may be formed and the first coating liquid may be dried using a tumbling fluidized bed coating apparatus.

[0110] When the first layer is lithium carbonate, instead of the above step (b1), the first layer can be formed on the surface of the positive electrode active material particles by firing the positive electrode active material particles in a carbon dioxide-containing atmosphere. When synthesizing a positive electrode active material, a compound such as LiOH is usually formed on the surface. Li2CO3 can also be formed on the active material surface by reacting LiOH with carbon dioxide.

[0111] (b2) Formation of the second layer The manufacturing method includes forming a second layer by drying a second coating liquid. A second coating liquid is prepared. The second coating liquid includes a second solute and a second solvent. The second solute includes a raw material for the second layer.

[0112] The amount of solute may be, for example, 0.1 to 20 parts by mass, 1 to 10 parts by mass, or 1 to 5 parts by mass per 100 parts by mass of solvent. The second solvent may contain any component as long as the second solute can be dissolved therein. The second solvent may contain, for example, water, alcohol, etc. The second solvent may contain, for example, ion-exchanged water, ethanol, etc.

[0113] The second solute may include, for example, a phosphoric acid compound. The second solute may include, for example, phosphoric anhydride (P2O5), orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid (HPO3) n] and polyphosphoric acid. The second 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 continuous film (second layer). The continuity of the second layer is expected to, for example, improve the coverage rate.

[0114] The second solute may further include, for example, a lithium compound, such as lithium hydroxide, lithium carbonate, or lithium nitrate.

[0115] The second solute may include, for example, a boric acid compound, such as at least one selected from the group consisting of orthoboric acid, metaboric acid, and tetraboric acid.

[0116] The second mixture may be formed by mixing the second coating liquid with the primary composite particles (intermediate product). The second mixture may be dried to form a second layer. That is, the second layer may be produced by drying the second coating liquid attached to the surface of the primary composite particles. The production of the second layer may produce composite particles (secondary composite particles: final product). The composite particles correspond to the composite particles 100 in FIG. 1. The second coating liquid may be dried, for example, by a spray-drying method, in the same manner as the first coating liquid.

[0117] (c) Heat Treatment The present production method may include subjecting the primary composite particles (intermediate product) and the composite particles (final product) to heat treatment. The heat treatment can fix the coating film (each layer). Heat treatment can also be called "firing." Any heat treatment device can 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. The heat treatment may be performed on either the primary composite particles or the composite particles, or on both the primary composite particles and the composite particles. [Example]

[0118] <Composite particles (coated positive electrode active material)> The composite particles (coated positive electrode active materials) of the following Comparative Examples 1 to 5 and Examples 1 to 6 were produced. In Comparative Examples 1 to 5, composite particles (coated positive electrode active materials) provided with a coating film having a single layer structure were produced, that is, positive electrode active material particles were subjected to a single coating treatment. On the other hand, in Examples 1 to 6, composite particles were produced that had a coating film with a two-layer structure consisting of a first layer (inner layer) and a second layer (outer layer). That is, the positive electrode active material particles were subjected to two coating processes. The first layer contained an alkaline oxide containing Li and M (at least one of niobium and carbon). The second layer contained a phosphorus compound.

[0119] Comparative Example 1 A solution was formed 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 The coating solution was prepared by dissolving lithium hydroxide monohydrate in the solution so that the ratio of n to n was 0.45. Li indicates the molar concentration of Li in the coating solution. P indicates the molar concentration of P in the coating solution.

[0120] As the positive electrode active material particles, NCM (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) was prepared. 50 parts by mass of a powder of positive electrode active material particles was dispersed in 40.3 parts by mass of a coating liquid to prepare a suspension. The suspension was supplied to a spray dryer (product name: Mini Spray Dryer B-290, manufactured by BUCHI) 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.

[0121] In this manner, the composite particles of Comparative Example 1 were produced. The coating film of the composite particles of Comparative Example 1 was Li x PO y (x and y are arbitrary numbers. For example, x is 0.5 and y is 3.) The target thickness of the coating film is 15 nm.

[0122] Comparative Example 2 A coating liquid 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. Other than that, the composite particles of Comparative Example 2 were produced in the same manner as in Comparative Example 1. The coating film of the composite particles of Comparative Example 2 was PO x (x is an arbitrary number.) The target thickness of the coating film is 15 nm.

[0123] Comparative Example 3 Composite particles of Comparative Example 3 were produced in the same manner as in Comparative Example 1, except that 50 parts by mass of the powder of positive electrode active material particles was dispersed in 53.7 parts by mass of the coating liquid. The coating film of the composite particles of Comparative Example 3 was Li x PO y(x and y are arbitrary numbers. For example, x is 0.5 and y is 3.) The target thickness of the coating film is 20 nm.

[0124] Comparative Example 4 Composite particles of Comparative Example 4 were produced in the same manner as in Comparative Example 2, except that 50 parts by mass of the powder of positive electrode active material particles was dispersed in 53.7 parts by mass of the coating liquid. The coating film of the composite particles of Comparative Example 4 was PO x (x is an arbitrary number.) The target thickness of the coating film is 20 nm.

[0125] Comparative Example 5 In Comparative Example 5, the positive electrode active material particles were NCA (LiNi 0.8 Co 0.15 Al 0.05 O2) was prepared. Composite particles of Comparative Example 5 were produced in the same manner as in Comparative Example 1. The coating film of the composite particles of Comparative Example 5 obtained in this manner was a phosphate compound (Li 0.5 The target thickness of the coating film is 15 nm.

[0126] Example 1

[0127] (First coating liquid) 870.4 parts by mass of hydrogen peroxide solution (mass concentration: 30%) was added to the container. Next, 1974.8 parts by mass of ion-exchanged water and 44.2 parts by mass of niobic acid (Nb2O5·3H2O) were added to the container. Next, 87.9 parts by mass of ammonia water (mass concentration: 28%) was added to the container. The contents of the container were thoroughly stirred to form a solution. The solution is believed to contain a peroxo complex of niobium. Furthermore, 0.1 parts by mass of lithium hydroxide·monohydrate (LiOH·H2O) was dissolved in the solution to prepare a first coating liquid.

[0128] (Second coating liquid) A solution was formed by dissolving 5.4 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 +n E1 +n E2 The second coating solution was prepared by dissolving lithium hydroxide monohydrate in the solution so that the % saturation coefficient (σ) was 0.45.

[0129] [Formation of coating film] (Formation of the first layer) As the positive electrode active material particles, NCM (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2) was prepared. 50 parts by mass of a powder of positive electrode active material particles was dispersed in 53.7 parts by mass of a first coating liquid to prepare a suspension. The suspension was supplied to a spray dryer (product name: Mini Spray Dryer B-290, manufactured by BUCHI) to produce a powder of primary composite particles (intermediate product). The supply air temperature of the spray dryer was 200°C, and the supply air volume was 0.45 m 3 / min.

[0130] (Formation of the second layer) A suspension was prepared by dispersing 50 parts by mass of the primary composite particle powder in 53.7 parts by mass of the second coating liquid. The suspension was supplied to a spray dryer (product name: Mini Spray Dryer B-290, manufactured by BUCHI) to produce a powder of composite particles (final product). The inlet air temperature of the spray dryer was 200°C, and the inlet air volume was 0.45 m 3 / min.

[0131] (Heat treatment) The composite particles were heat-treated in air at a temperature of 200°C for 5 hours. In this manner, the composite particles of Example 1 were produced.

[0132] The coating film of the composite particle of Example 1 is composed of a first layer (inner layer) containing LiNbO3 and a second layer (inner layer) containing Li x PO y (x and y are arbitrary numbers. For example, x is 0.5 and y is 3.) The target thickness of the first layer is 5 nm, and the target thickness of the second layer is 10 nm.

[0133] Example 2 A second coating liquid was prepared by dissolving 5.4 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 166 parts by mass of ion-exchanged water. The composite particles of Example 2 were produced in the same manner as in Example 1 except for the above points. The coating film of the composite particle of Example 2 is composed of a first layer containing LiNbO3 and a second layer containing PO x (x is an arbitrary number), and a second layer including the first layer. The target thickness of the first layer is 5 nm, and the target thickness of the second layer is 10 nm.

[0134] Example 3 A first coating liquid was prepared by dissolving 0.5 parts by mass of lithium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 100 parts by mass of ion-exchanged water. In forming the first layer, 60 parts by mass of powder of positive electrode active material particles was dispersed in 30.5 parts by mass of a coating liquid to prepare a suspension. The composite particles of Example 3 were produced in the same manner as in Example 1 except for the above points. The coating film of the composite particle of Example 3 is composed of a first layer containing Li2CO3 and a second layer containing Li x PO y (x and y are arbitrary numbers. For example, x is 0.5 and y is 3.) The target thickness of the first layer is 5 nm, and the target thickness of the second layer is 10 nm.

[0135] Example 4 870.4 parts by mass of hydrogen peroxide solution (mass concentration: 30%) was added to the container. Next, 987.4 parts by mass of ion-exchanged water and 44.2 parts by mass of niobic acid (Nb2O5·3H2O) were added to the container. Next, 87.9 parts by mass of ammonia water (mass concentration: 28%) was added to the container. The contents of the container were thoroughly stirred to form a solution. This solution is believed to contain a peroxo complex of niobium. Furthermore, 0.1 parts by mass of lithium hydroxide·monohydrate (LiOH·H2O) was dissolved in the solution to prepare a first coating liquid. The composite particles of Example 4 were produced in the same manner as in Example 2 except for the above points. The coating film of the composite particle of Example 4 is composed of a first layer containing LiNbO3 and a second layer containing PO x (x is an arbitrary number), and a second layer including the first layer. The target thickness of the first layer is 10 nm, and the target thickness of the second layer is 10 nm.

[0136] Example 5 A first coating liquid was prepared by dissolving 1.0 part by mass of lithium carbonate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 100 parts by mass of ion-exchanged water. The composite particles of Example 5 were produced in the same manner as in Example 3 except for the above points. The coating film of the composite particle of Example 5 is composed of a first layer containing Li2CO3 and a second layer containing Li x PO y (x and y are arbitrary numbers. For example, x is 0.5 and y is 3.) The target thickness of the first layer is 10 nm, and the target thickness of the second layer is 10 nm.

[0137] Example 6 In Example 6, the positive electrode active material particles were NCA (LiNi 0.8 Co 0.15 Al 0.05 O2) was prepared. The composite particles of Example 6 were produced in the same manner as in Example 3 except for the above. The coating film of the composite particle of Example 6 is composed of a first layer (inner layer) containing LiNbO3 and a second layer (inner layer) containing Li x PO y (x and y are arbitrary numbers. For example, x is 0.5 and y is 3.) The target thickness of the first layer is 5 nm, and the target thickness of the second layer is 10 nm.

[0138] <All-solid-state battery> 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

[0139] Positive electrode slurry was prepared by mixing the composite particles of the above examples and comparative examples, a sulfide solid electrolyte, a conductive material, a binder, and a 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 per 100 parts by mass of the composite particles. The amount of binder was 3 parts by mass per 100 parts by mass of the composite particles. The positive electrode slurry was thoroughly stirred using an ultrasonic homogenizer. The positive electrode slurry was applied to the surface of a positive electrode current collector to form a coating film. The coating film was dried at 100°C for 30 minutes on 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.

[0140] A negative electrode and a separator were prepared. The negative electrode active material particles were graphite. The same type of sulfide solid electrolyte was used between the positive electrode, separator, and negative electrode. A stack was formed by stacking the positive electrode, separator, and negative electrode in a cylindrical jig. A power generating element was formed by pressing the stack. A terminal was connected to the power generating element to form an all-solid-state battery.

[0141] <Evaluation> (battery resistance measurement) The battery resistance (initial resistance) of the all-solid-state battery was measured. The measurement results of the battery resistance are shown in Table 1.

[0142] [Table 1]

[0143] The results shown in Table 1 show that the battery resistance is clearly lower in the examples in which the coating film has a layered structure including an alkaline oxide layer (first layer) and a phosphorus compound layer (second layer) than in the comparative examples in which the coating film has a single-layer structure consisting of only a phosphorus compound layer (second layer). In addition, when the coating film is changed from a single-layer structure to a multilayer structure in order to improve the durability of the coating film, the resistance of the coating film usually increases. However, in the composite particles of the examples having a two-layer structure, the overall resistance actually decreased, which was an unexpected result.

[0144] <Structural analysis of coating film of composite particles> (1) STEM-EELS measurements on the positive electrode The composite particles of Example 1 were subjected to the following analysis in order to confirm that the coating film had a two-layer structure. The positive electrode of the battery produced using the composite particles of Example 1 was thinned and cross-sectioned while cooled at -90°C using a focused ion beam (FIB) device (NB5000, manufactured by Hitachi High-Technologies). After cross-sectioning, the sample was transferred to a scanning transmission electron microscope (STEM) (Hitachi High-Tech, HD-2700) using an atmosphere-blocking holder, and elemental analysis was performed using an electron energy loss spectroscopy (EELS) (Ametec, GATAN Enfinium). The EELS analysis conditions were as follows: EELS mapping data was acquired in a 3 nm step, 47 × 21 pixel, 141 × 63 nm area. EELS line data integrated in the x direction was extracted from the mapping data. After background subtraction, the spectra were overlapped in the two ranges. 30~150eV: Nb-M2,3 Mn-M2.3 Co-M2,3 Li-K Ni-M2,3 100~400eV: P-L2,3 S-L2,3 BK Nb-M4,5 S-L1

[0145] The STEM-EELS measurement results are shown in Figure 3. In Figures 3(a) and (b), the numbers after "Point" indicate the measurement points when the range from the solid electrolyte outside the coating film to the positive electrode active material particles inside the coating film was measured in 3 nm steps. From the results shown in Figures 3(a) and (b), it can be confirmed that a coating film having a two-layer structure was formed, as shown in Figure 3(c).

[0146] (2) XPS measurements on composite particles (2-1) Measurement example 1 Example 1 (Coating film: Li2Co3 / PO x ) and Comparative Example 4 (coating film: PO x XPS measurements were performed on composite particles (coated positive electrode active material) of the above. Note that, as Reference Example 1, XPS measurements were also performed on composite particles formed by coating positive electrode active material particles (NCM) with a single-layer coating film of Li2Co3. The measurement results are shown in Figure 4. The results shown in Figures 4(a) and (b) show that for the composite particles of Example 3, the Li2CO3 and PO x The fact that both peaks are confirmed indicates that the coating film has a two-layer structure.

[0147] (2-2) Measurement example 2 Example 2 (Coating film: LiNbO3 / PO x ) and Comparative Example 4 (coating film: PO xXPS measurement was performed on composite particles (coated positive electrode active material) of the above. Note that, as Reference Example 2, XPS measurement was also performed on composite particles formed by coating positive electrode active material particles (NCM) with a single-layer coating film of Nb. The measurement results are shown in FIG. In the results shown in Fig. 5(a) and (b), for the composite particles of Example 2, the LiNbO3 and PO x The fact that both peaks are confirmed indicates that the coating film has a two-layer structure.

[0148] 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]

[0149] 100 composite particles, 110 positive electrode active material particles, 120 coating film, 121 first layer, 122 second layer.

Claims

1. a positive electrode active material particle; and a coating film that covers at least a portion of the surface of the positive electrode active material particle; the coating film includes a first layer that covers at least a portion of the surface of the positive electrode active material particle, and a second layer that covers at least a portion of the surface of the first layer, the first layer includes an alkaline oxide containing Li and M, where M is at least one of niobium and carbon; The second layer has the general formula Li y P.O. x (0<x, 0≦y<2.5), composite particles.

2. The composite particle of claim 1 , wherein the alkaline oxide is lithium niobate or lithium carbonate.

3. A positive electrode comprising the composite particles according to claim 1 or 2 and a sulfide solid electrolyte.

4. An all-solid-state battery comprising the positive electrode according to claim 3 , a negative electrode, and a separator.

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