JP7750165B2 - Composite particles, cathodes and solid-state batteries - Google Patents

Description

This disclosure relates to composite particles, positive electrodes, and all-solid-state batteries.

JP 2017-220339 A (Patent Document 1) discloses oxide-coated active material particles in which the surfaces of active material particles are coated with an oxide-based solid electrolyte, and composite active material particles in which the surfaces of the oxide-coated active material particles are further coated with a sulfide-based solid electrolyte.

JP 2017-220339 A

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.

It has been proposed to coat the surface of positive electrode active material particles sequentially with an oxide solid electrolyte and a sulfide solid electrolyte. By interposing the oxide solid electrolyte between the sulfide solid electrolyte and the positive electrode active material particles, it is expected that the opportunity for contact between the sulfide solid electrolyte and the positive electrode active material particles will be reduced. However, there is room for improvement in the rate of resistance increase in high-potential environments.

The purpose of this disclosure is to reduce the rate of resistance increase.

The technical configuration and effects of this disclosure are explained below. However, the mechanism of action in this specification includes speculation. The mechanism of action does not limit the technical scope of this disclosure.

1. The composite particles include positive electrode active material particles and a coating. The coating covers at least a portion of the surface of the positive electrode active material particles. The coating includes a first layer and a second layer. At least a portion of the first layer is interposed between the positive electrode active material particles and the second layer. The first layer includes a glass network-forming element. The second layer includes a sulfide solid electrolyte.

Conventionally, lithium niobate ( _LiNbO3 ) has been used as the oxide solid electrolyte (first layer). The first layer containing _LiNbO3 tends to be hard. On the other hand, the second layer containing a sulfide solid electrolyte tends to be soft. The mismatch in hardness between the first and second layers may reduce adhesion between the first and second layers. According to the new findings of the present disclosure, in a high-potential environment, diffusion resistance tends to increase in areas with low adhesion.

In the composite particles described in "1." above, the first layer contains a glass network-forming element. The first layer containing a glass network-forming element tends to be soft. Therefore, it is expected that the mismatch in hardness between the first and second layers will be reduced. By improving the adhesion between the first and second layers, it is expected that the diffusion resistance will be less likely to increase in a high-potential environment. In other words, a reduction in the rate of resistance increase is expected.

2. In the composite particles described in "1." above, the glass network-forming element may include, for example, at least one element selected from the group consisting of phosphorus (P), boron (B), silicon (Si), nitrogen (N), sulfur (S), germanium (Ge), and hydrogen (H).

3. In the composite particles described in "1." or "2." above, the first layer may contain, for example, at least one selected from the group consisting of a phosphate skeleton and a borate skeleton.

The first layer, which contains a phosphate skeleton and a borate skeleton, is expected to have moderate hardness.

4. In the composite particles described in any one of items "1." to "3." above, the coverage rate of the second layer may be, for example, 20% or more.

A coverage rate of 20% or more is expected to reduce diffusion resistance, for example.

5. In the composite particle according to any one of the above items "1." to "4.", the sulfide solid electrolyte may be composed of, for example, 60% or more of a first conductive phase and the remainder. The remainder includes a second conductive phase and a third conductive phase. The first conductive phase includes a crystalline phase of _PS4 . The second _conductive phase includes an amorphous phase of _PS4 . The third conductive phase includes a crystalline phase of _P2S6 .

The first conductive phase is, so to speak, a high ion conductive phase. The second conductive phase and the third conductive phase are, so to speak, low ion conductive phases. The first conductive phase can have a higher ion conductivity than the second conductive phase and the third conductive phase. By having the composition ratio of the first conductive phase be 60% or more, a reduction in diffusion resistance is expected.

6. In the composite particles described in any one of items "1." to "5." above, the second layer may have a thickness of, for example, 0.1 to 10 μm.

7. In the composite particle described in any one of items "1." to "6." above, at least one of the first layer and the second layer may further contain conductive carbon. The mass fraction of the conductive carbon may be, for example, 1 to 10% of the composite particle.

By further including conductive carbon in at least one of the first and second layers, improved electronic conductivity is expected.

8. The positive electrode contains the composite particles described in any one of items "1." to "7." above.

9. The all-solid-state battery includes the positive electrode described in "8." above.

Below, an embodiment of the present disclosure (hereinafter abbreviated as "this embodiment") and an example of the present disclosure (hereinafter abbreviated as "this example") are described. However, this embodiment and this example do not limit the technical scope of the present disclosure.

FIG. 1 is a conceptual diagram showing a composite particle according to this embodiment. FIG. 2 is a conceptual diagram showing the all-solid-state battery according to this embodiment.

<Terms and definitions>
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.

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

Expressions such as "may" and "may" are used in the permissive sense "to have the possibility" rather than the obligatory sense "to have to."

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

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% but less than n%." Furthermore, a numerical value arbitrarily selected from within the numerical range may be used 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, figure, etc.

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 the average 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 taken, the more reliable the average value is expected to be. Measured values may be rounded off based on the number of significant figures. Measured values may include errors, such as those associated with the detection limits of the measuring device.

Geometric terms (e.g., "parallel," "perpendicular," "orthogonal," etc.) 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, etc. in design, work, manufacturing, etc. The dimensional relationships in each figure may not match the actual dimensional relationships. To facilitate understanding of the disclosed technology, the dimensional relationships (length, width, thickness, etc.) in each figure may be changed. Furthermore, some components may be omitted.

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 also be permitted.

"D50" refers to the particle size at which the cumulative frequency from the smallest particle size reaches 50% in the volume-based particle size distribution. D50 can be measured by laser diffraction.

"Glass network forming element" refers to an element that has glass-forming ability. "Glass forming ability" indicates that the target element can form an oxide glass with a network structure by bonding with oxygen (O).

Coverage
The "coverage" indicates the proportion of the surface of the composite particle that is covered with the second layer. The coverage is calculated by the following formula (α):
Θ={A ₂ /(A ₀ +A ₂ )}×100...(α)
Θ indicates the coverage (%).
A ₀ represents the area ratio of the positive electrode active material particles.
_A2 indicates the area ratio of the sulfide solid electrolyte.

A ₀ and A ₂ are measured by the following procedure.
(1) A microscopic Raman spectrometer is prepared.
(2) The sample (powder of composite particles) is placed in the micro-Raman spectrometer. A measurement area of 80 μm×80 μm is set. Raman mapping measurement is performed in the measurement area.
(3) Multivariate curve resolution (MCR) is performed on the measurement results. Component spectra are characterized by MCR. Appropriate peaks are selected depending on the compositions of the sulfide solid electrolyte and the positive electrode active material particles. For example, a PS ₄ ^-peak appearing near 420 cm ⁻¹ can be considered to be a component derived from the sulfide solid electrolyte. For example, a peak appearing between 700 and 600 cm ⁻¹ can be considered to be a peak derived from the positive electrode active material particles.
(4) Image analysis is performed on each component to create a distribution image. From the distribution image, the area ratio (ratio of pixel numbers) of each component is determined. That is, _A0 and _A2 are determined.

The conditions for Raman mapping measurement may be as follows. The apparatus is an example. The apparatus may be substituted with an equivalent product.
Raman microscope spectrometer: "DXR3xi Imaging Raman Microscope" manufactured by Thermo Fisher Scientific. Laser energy: 1.5 mW.
Exposure time: 120Hz
Number of scans: 10
Scan area: 80 to 100 μm

<Composition ratio of high ion conductive phase>
The composition ratio of the first conductive phase (high ion conductive phase) in the sulfide solid electrolyte is calculated by the following formula (β).
R ₁ = {I ₁ /(I ₁ +I ₂ +I ₃ )}×100...(β)
R ₁ (%) represents the constituent ratio of the first conductive phase.
I ₁ , I ₂ , and I ₃ are measured by 31 P Magic Angle Spinning Nuclear Magnetic Resonance ( ³¹ P MAS NMR) using ^the magic angle sample spinning method.
_I1 represents the sum of the areas (integrated values) of the peaks at chemical shifts of 78 ppm, 83.7 ppm, and 92 ppm in the ^31P MAS NMR spectrum. The peak at 78 ppm is thought to correspond to _PS42b . The peak at 92 ppm is thought to correspond to _PS44d .
I ₂ represents the sum of the area of the peak at a chemical shift of 85 ppm and the area of the peak at a chemical shift of 88 ppm in the ³¹ P MAS NMR spectrum.
_I3 indicates the area of the peak at a chemical shift of 106 ppm in the ³¹ P MAS NMR spectrum.

Based on the same ³¹ P MAS NMR spectrum, the constituent ratio (R ₂ ) of the second conductive phase (low ionic conductive phase) in the sulfide solid electrolyte is calculated by the following formula (γ).
R ₂ = {I ₂ /(I ₁ +I ₂ +I ₃ )}×100...(γ)
Furthermore, the composition ratio (R ₃ ) of the third conductive phase (low ion conductive phase) in the sulfide solid electrolyte is determined by the following formula (δ).
R ₃ = {I ₂ /(I ₁ +I ₂ +I ₃ )}×100...(δ)

The conditions for measuring the ³¹ P MAS NMR spectrum may be as follows. However, the apparatus is an example. The apparatus may be substituted with an equivalent apparatus.
NMR apparatus: "AVANCE III 600", manufactured by Bruker Corporation Observation frequency: 242.94 MHz
Observation width: 250kHz
Measurement method: Single pulse method Flip angle: 90° pulse Repetition waiting time: 5 times or more of _T1 Probe: 4.0 mm
MAS rotation speed: 15 kHz
Chemical shift standard: 85% aqueous phosphoric acid solution (0 ppm)

Thickness measurement
The thicknesses of the first and second layers can be measured by the following procedure: A sample is prepared by embedding composite particles in a resin material. A cross-section of the sample is processed using an ion milling device. For example, an ion milling device manufactured by Hitachi High-Technologies Corporation, product name Arblade (registered trademark) 5000 (or equivalent) may be used. The cross-section of the sample is observed using a scanning electron microscope (SEM). For example, an SEM device manufactured by Hitachi High-Technologies Corporation, product name SU8030 (or equivalent) may be used. The thickness of each layer is measured in 20 fields of view for each of 10 composite particles. The arithmetic average of the thicknesses at 200 locations in total is considered to be the thickness of each layer.

<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 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, for example, a D50 of 1 to 50 μm, a D50 of 1 to 20 μm, or a D50 of 5 to 15 μm.

《Coating》
The coating 120 is a shell of the composite particle 100. The coating 120 covers at least a portion of the surface of the positive electrode active material particle 110. The coating 120 includes a first layer 121 and a second layer 122.

(1st layer)
The first layer 121 is, so to speak, a lower layer. At least a portion of the first layer 121 is interposed between the positive electrode active material particles 110 and the second layer 122. The first layer 121 may directly cover the surface of the positive electrode active material particles 110. A portion of the first layer 121 may not be covered by the second layer 122. A portion of the first layer 121 may be exposed on the surface of the coating 120.

The first layer 121 can be formed by any method. For example, the first layer 121 may be formed by a spray drying method. That is, a coating liquid containing the raw materials of the first layer 121 is formed. The positive electrode active material particles are dispersed in the coating liquid to form a suspension. The suspension is then processed with a spray dryer, whereby the coating liquid dries on the surfaces of the positive electrode active material particles 110, and the first layer 121 can be formed.

The first layer 121 may have a thickness of, for example, 5 to 100 nm, 5 to 50 nm, 10 to 30 nm, or 20 to 30 nm.

The first layer 121 contains a glass network-forming element. By including the glass network-forming element in the first layer 121, the rate of increase in resistance in a high-potential environment can be reduced. "High potential" refers to, for example, a range of 4.2 to 5.0 V vs. Li/Li ⁺ . "V vs. Li/Li ⁺ " refers to a potential relative to the potential (zero) at which Li undergoes an oxidation-reduction reaction. The glass network-forming element may include, for example, at least one element selected from the group consisting of P, B, Si, N, S, Ge, and H. The first layer 121 may include, for example, at least one element selected from the group consisting of P and B.

The first layer 121 may include an oxide glass having a network structure. The oxide glass may include a phosphate skeleton, a borate skeleton, or the like. That is, the first layer 121 may include, for example, at least one skeleton selected from the group consisting of a phosphate skeleton and a borate skeleton. For example, when fragments such as PO ₂ ⁻ and PO ₃ ⁻ are detected in TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) of the composite particle 100, the first layer 121 is considered to include a phosphate skeleton. For example, when fragments such as BO ₂ ⁻ and BO ₃ ⁻ are detected in TOF-SIMS of the composite particle 100, the first layer 121 is considered to include a borate skeleton.

The first layer 121 may further contain, for example, lithium (Li) etc. The chemical composition of the first layer 121 may be represented by, for example, the following formula (ε).
Li _x B _y PO _z …(ε)
In the above formula (ε), x, y, and z are any numbers. For example, x, y, and z can be identified by analyzing a cross section of the composite particle 100 (first layer 121) using STEM-EDX (Scanning Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy) or the like. A cross-sectional sample can be prepared according to the procedure described above in the "Thickness Measurement" section.

In the above formula (ε), x and y may satisfy the relationship of the following formula (ζ), for example.
x/(y+1)≦2.5…(ζ)
When x and y satisfy the relationship of the above formula (ζ), a reduction in the rate of increase in resistance is expected. This is thought to be because the smaller "x/(y+1)" (i.e., the smaller the Li composition ratio), the softer the first layer 121 tends to be. "x/(y+1)" may be, for example, 1 or less, or 0.5 or less. x and y may be zero.

(Second layer)
The second layer 122 is, so to speak, an upper layer. The second layer 122 is exposed on the surface of the composite particle 100. A portion of the second layer 122 may be in contact with the positive electrode active material particle 110. The second layer 122 includes a sulfide solid electrolyte. The sulfide solid electrolyte may be, for example, granular. That is, the second layer 122 may be a particle layer (an aggregate of particles). In a cross-sectional image (e.g., an SEM image) of the second layer 122, the sulfide solid electrolyte may have a maximum Feret diameter of, for example, 0.1 to 0.5 μm. In a powder state (before composite processing), the sulfide solid electrolyte may have a D50 of, for example, 0.01 to 5 μm, a D50 of 0.01 to 1 μm, a D50 of 0.1 to 0.5 μm, or a D50 of 0.1 to 0.3 μm.

The second layer 122 can be formed by any method. For example, the second layer 122 may be formed by a dry particle composite process. For example, the second layer 122 can be formed by mixing sulfide solid electrolyte powder with the positive electrode active material particles 110 (after the first layer 121 has been formed) using a circulating mechanofusion device. During mixing, a cushioning material such as conductive carbon may be used.

The second layer 122 may have a thickness of, for example, 0.1 to 10 μm, 0.5 to 5 μm, or 1 to 3 μm.

The second layer 122 may have, for example, a coverage of 20% or more, a coverage of 40% or more, a coverage of 60% or more, a coverage of 80% or more, or a coverage of 100%. The higher the coverage, the lower the resistance increase rate is expected to be, for example.

The sulfide solid electrolyte contains S. The sulfide solid electrolyte may further contain Li and P. The sulfide solid electrolyte may be, for example, a glass ceramic type or an argyrodite type. The main phase of the sulfide solid electrolyte may have high ionic conductivity. For example, the sulfide solid electrolyte may consist of 60% or more of a first conductive phase and the remainder. The remainder includes a second conductive phase and a third conductive phase. The remainder may further contain, for example, inevitable impurities. An example of the composition ratio is shown in Table 1 below.

The constituent ratios in Table 1 above are determined from the ^31P MAS NMR spectrum and the above formulas (β) to (δ). Measurement Example 1 is an example of the measurement results for glass ceramics. Measurement Example 2 is an example of the measurement results for ceramics. In addition to the _PS4 crystalline phase, the glass ceramics may contain a _PS4 amorphous phase and _{a P2S6} crystalline phase. The ceramics are substantially composed of a _PS4 crystalline phase.

The first conductive phase includes a _PS4 crystalline phase. The first conductive phase may consist of a _PS4 crystalline phase. The first conductive phase may have high ionic conductivity. A higher composition ratio of the first conductive phase is expected to reduce diffusion resistance. Furthermore, as the sulfide solid electrolyte approaches ceramics, the second layer 122 becomes harder, and it is expected that the hardness mismatch between the first layer 121 and the second layer 122 will be reduced. The composition ratio of the first conductive phase may be, for example, 61.6% or more, 70% or more, 80% or more, 90% or more, or 100%.

The second conductive phase includes an amorphous phase of _PS4 . The second conductive phase may consist of an amorphous phase of _PS4 . The second conductive phase may have low ionic conductivity. The proportion of the second conductive phase may be, for example, 31.7% or less, 20% or less, 10% or less, or 0%.

The third conductive phase includes _{a P2S6} crystalline phase. The third conductive phase may consist of _{a P2S6} crystalline phase. The third conductive phase may have low ionic conductivity. The composition ratio of the third conductive phase may be, for example, 6.2% or less, 6% or less, 3% or less, 1% or less, or 0%.

The sulfide solid electrolyte may be composed of, for example, a first conductive phase and unavoidable impurities. The sulfide solid electrolyte may be composed of, for example, a first conductive phase and the remainder being a second conductive phase and unavoidable impurities. The sulfide solid electrolyte may be composed of, for example, a first conductive phase and the remainder being a third conductive phase and unavoidable impurities. The sulfide solid electrolyte may be composed of, for example, a first conductive phase and the remainder being a second conductive phase, a third conductive phase, and unavoidable impurities.

(Conductive carbon)
At least one of the first layer 121 and the second layer 122 may further contain conductive carbon. The mass fraction of the conductive carbon may be, for example, 1 to 10%, 1 to 5%, or 1 to 3% relative to the composite particle 100. The conductive carbon may include, for example, at least one selected from the group consisting of graphite, carbon black, vapor-grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes. For example, the conductive carbon may be added to the first layer 121 by being added to the coating liquid (the raw material of the first layer 121). For example, the conductive carbon may be added to the second layer 122 by being mixed with the sulfide solid electrolyte during the mechanofusion process.

《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.

The positive electrode active material particles 110 may contain any component. The positive electrode active material particles 110 may contain, for example, at least one selected from the group consisting of LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , Li(NiCoMn)O ₂ , Li(NiCoAl)O ₂ , and LiFePO _4. For example, the "(NiCoMn)" in "Li(NiCoMn)O ₂ " indicates that the sum of the composition ratios in parentheses is 1. The amounts of the individual components are arbitrary as long as the sum is 1. Li(NiCoMn) _O2 may contain, for example, LiNi1 _{/ 3Co1} / _{3Mn1/ 3O2 , LiNi0.5Co0.2Mn0.3O2 , LiNi0.8Co0.1Mn0.1O2 , etc. Li} ( _NiCoAl ) _O2 may contain, for example _{, LiNi0.8Co0.15Al0.05O2 , etc.}

<All-solid battery>
2 is a conceptual diagram showing an all-solid-state battery according to this embodiment. The all-solid-state battery 200 includes a power-generating element 250. The all-solid-state battery 200 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 250. The power-generating element 250 includes a positive electrode 210, a solid electrolyte layer 230, and a negative electrode 220. That is, the all-solid-state battery 200 includes the positive electrode 210, the solid electrolyte layer 230, and the negative electrode 220.

《Positive electrode》
The positive electrode 210 is layered. The positive electrode 210 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.

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 solid electrolyte layer 230. The positive electrode active material layer contains composite particles. Details of the composite particles are as described above. The positive electrode active material layer may be made of composite particles. In addition to the composite particles, the positive electrode active material layer may further contain a sulfide solid electrolyte, a conductive material, a binder, and the like.

The sulfide solid electrolyte can form an ion conduction path within the positive electrode active material layer. The sulfide solid electrolyte added to the positive electrode active material layer may be the same type as or different from the sulfide solid electrolyte contained in the composite particles. The amount of 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 may contain, for example, Li, P, and S. The sulfide solid electrolyte may further contain, for example, O, 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 contain at least _{one selected from the group} consisting _{of , for example, LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2 , LiI - Li2S - P2S5 , LiI} - _Li2O - _{Li2S -P2S5 ,} LiI- _{Li2S -P2O5 ,} LiI- _{Li3PO4 - P2S5 ,} Li2S- _P2S5 , and _{Li3PS4 .}

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 .

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 conductive material added to the positive electrode active material layer may be the same type as the conductive carbon that can be contained in the composite particles, or it may be a different type. The amount of 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. For example, the conductive material may contain at least one selected from the group consisting of carbon black, VGCF, CNT, and graphene flakes.

The positive electrode active material layer may further contain, for example, a binder. The binder can bind the solid materials together. 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. For example, the binder may contain at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), styrene butadiene rubber (SBR), butadiene rubber (BR), and polytetrafluoroethylene (PTFE).

《Negative electrode》
The negative electrode 220 is layered. The negative electrode 220 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 to the surface of the negative electrode current collector. The negative electrode current collector may include, for example, copper (Cu) foil, nickel (Ni) foil, or the like. The negative electrode current collector may have a thickness of, for example, 5 to 50 μm.

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 solid electrolyte layer 230. 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, at least one selected from the group consisting of graphite, Si, SiO _x (0<x<2), and Li ₄ Ti ₅ O ₁₂ .

《Solid electrolyte layer》
The solid electrolyte layer 230 may also be referred to as a separator layer. The solid electrolyte layer 230 is interposed between the positive electrode 210 and the negative electrode 220. The solid electrolyte layer 230 separates the positive electrode 210 from the negative electrode 220. The solid electrolyte layer 230 includes a sulfide solid electrolyte. The solid electrolyte layer 230 may further include a binder. The sulfide solid electrolytes in the solid electrolyte layer 230 and the positive electrode 210 may be the same or different. The sulfide solid electrolytes in the solid electrolyte layer 230 and the negative electrode 220 may be the same or different.

<Sample preparation>
Composite particles, positive electrodes, and all-solid-state batteries according to Nos. 1 to 3 were manufactured as follows. Hereinafter, for example, "composite particles according to No. 1" may be abbreviated as "No. 1." For convenience, composite particles including a coating with a single-layer structure will be referred to as "first composite particles," and composite particles including a coating with a two-layer structure will be referred to as "second composite particles."

<No. 1>
<<Preparation of the positive electrode>>
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. The solution is believed to contain a peroxo complex of Nb. Furthermore, 0.1 parts by mass of lithium hydroxide monohydrate ( _LiOH.H2O ) was dissolved in the solution to prepare a coating solution.

LiNi _1/3 Co _1/3 Mn _1/3 O ₂ was prepared as the positive electrode active material particles. 50 parts by mass of the positive electrode active material particle powder was dispersed in 53.7 parts by mass of the coating liquid to prepare a suspension. A spray dryer manufactured by Buchi, product name Mini Spray Dryer B-290, was prepared. The suspension was supplied to the spray dryer to produce powder of first composite particles (intermediate product). The inlet air temperature of the spray dryer was 200°C, and the inlet air volume was 0.45 m ³ /min. The first composite particles were heat-treated in air. The heat treatment temperature was 200°C. The heat treatment time was 5 hours. The first composite particles are considered to include positive electrode active material particles and a coating (first layer). The first layer is considered to include LiNbO ₃ .

90 parts by volume of the first composite particles and 10 parts by volume of a sulfide solid electrolyte ( _Li3PS4 , _D50 =0.1 μm) were mixed using a dry particle compositing device (product name "NOB-MINI", manufactured by Hosokawa Micron Corporation) to form second composite particles (final product). The mixing conditions were as follows:

Temperature of the mixture during mixing: 50°C
Gap between blade and wall: 1 mm
Rotation speed: 3000 rpm
Processing time: 1 minute

The second composite particles are believed to include positive electrode active material particles and coatings (first and second layers). The second layer is believed to include a sulfide solid electrolyte.

The following materials were prepared:
Sulfide solid electrolyte: LiI-Li ₂ S-P ₂ S ₅ (glass ceramic type, D50=0.8 μm)
Conductive material: VGCF
Binder: BR
Dispersion medium: heptane Positive electrode current collector: Al foil

A slurry was prepared by mixing the second composite particles, the sulfide solid electrolyte, the conductive material, the binder, and the dispersion medium. The mixing ratio of the second composite particles to the sulfide solid electrolyte was "second composite particles/sulfide solid electrolyte = 7/3 (volume ratio)." The amount of the conductive material was 3 parts by mass relative to 100 parts by mass of the second composite particles. The amount of the binder was 0.7 parts by mass relative to 100 parts by mass of the second composite particles. The slurry was thoroughly stirred using an ultrasonic homogenizer (product name "UH-50", manufactured by SMT Corporation). The 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 ^cm2 .

<<Preparation of negative electrode>>
The following materials were prepared:
Negative electrode active material particles: Li ₄ Ti ₅ O ₁₂ (D50=1 μm)
Sulfide solid electrolyte: LiI-Li ₂ S-P ₂ S ₅ (glass ceramic type, D50=0.8 μm)
Conductive material: VGCF
Binder: BR
Dispersion medium: heptane Negative electrode current collector: Cu foil

A slurry was prepared by mixing the sulfide solid electrolyte, conductive material, binder, and dispersion medium using a stirring device (Filmix (registered trademark) "Model 30-L" manufactured by Primix Corporation). The stirring speed (number of rotations) was 2,000 rpm, and the stirring time was 30 minutes. After stirring for 30 minutes, negative electrode active material particles were added to the slurry, and the slurry was further stirred. The stirring speed was 15,000 rpm, and the stirring time was 60 minutes.

The mixing ratio of the negative electrode active material particles to the sulfide solid electrolyte was "negative electrode active material particles/sulfide solid electrolyte = 6/4 (volume ratio)." The amount of conductive material was 1 part by mass per 100 parts by mass of negative electrode active material particles. The amount of binder was 2 parts by mass per 100 parts by mass of negative electrode active material particles.

The slurry was applied to the surface of the negative electrode current collector to form a coating film. The coating film was dried on a hot plate at 100°C for 30 minutes. This produced a negative electrode blank. A disk-shaped negative electrode was cut out from the negative electrode blank. The area of the negative electrode was 1 ^cm2 .

<<Fabrication of solid electrolyte layer>>
The following materials were prepared:
Sulfide solid electrolyte: LiI-Li ₂ S-P ₂ S ₅ (glass ceramic type, D50=2.5 μm)

A ceramic cylindrical jig was prepared. The area of the hollow cross section (cross section perpendicular to the axial direction) was 1 ^cm2 . Powder of sulfide solid electrolyte was filled into the cylindrical jig. The powder was smoothed and leveled. The sulfide solid electrolyte was pressed inside the cylindrical jig to form a solid electrolyte layer. The pressure of the press was 1 ton/ ^cm2 .

"assembly"
A laminate was formed by stacking a positive electrode, a solid electrolyte layer, and a negative electrode in a cylindrical jig. The solid electrolyte layer was disposed between the positive electrode and the negative electrode. The laminate was pressed to form a power generating element. The pressure used in the press was 6 ton/ ^{cm2. Two stainless steel rods were inserted into the cylindrical jig so as to sandwich the power generating element. The stainless steel rods were restrained so that a load of 1 ton was applied to the power generating element. The stainless steel rods may function as terminals. In this} manner, an all-solid-state battery was manufactured.

<No. 2>
A coating solution was prepared by dissolving 10.8 parts by mass of metaphosphoric acid (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) in 166 parts by mass of ion-exchanged water. Except for the use of this coating solution, first composite particles were formed in the same manner as in No. 1. The first layer of No. 1 is believed to contain a phosphate skeleton (PO _z ). P is a glass network-forming element. After the formation of the first composite particles, second composite particles, a positive electrode, and an all-solid-state battery were sequentially produced in the same manner as in No. 1.

<No. 3>
No. 2. A slurry was prepared by mixing the first composite particles prepared in Example 2, a sulfide solid electrolyte, a conductive material, a binder, and a dispersion medium. The mixing ratio of the first composite particles to the sulfide solid electrolyte was "first composite particles/sulfide solid electrolyte = 7/3 (volume ratio)." The amount of conductive material was 3 parts by mass relative to 100 parts by mass of the first composite particles. The amount of binder was 0.7 parts by mass relative to 100 parts by mass of the first composite particles. The slurry was thoroughly stirred using an ultrasonic homogenizer (product name "UH-50", manufactured by SMT Corporation). The 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 using a hot plate. This produced a positive electrode blank. A disk-shaped positive electrode was cut out from the positive electrode blank. The area of the positive electrode was 1 ^cm2 . After this, all-solid-state batteries were manufactured in the same manner as No. 1.

<Evaluation>
The initial capacity of the all-solid-state battery was confirmed. The charge and discharge conditions were as follows:
Charging: Constant current-constant voltage method, rate = 1/3C
Discharge: Constant current method, rate = 1/3C

"C" is the symbol for the current rate (hourly rate). A rate of 1C will fully discharge the battery's rated capacity in 1 hour.

After confirming the initial capacity, the SOC (State of Charge) of the solid-state battery was adjusted to 40%. The solid-state battery was discharged at a rate of 2C for 5 seconds. The initial resistance was calculated from the voltage drop after 5 seconds.

After measuring the initial resistance, the SOC of the all-solid-state battery was adjusted to 100%. At 100% SOC, the positive electrode potential was 4.5 V vs. Li/Li ⁺ . After adjusting the SOC, the all-solid-state battery was stored in a thermostatic chamber at 60°C for 14 days. After 14 days, the post-endurance resistance was measured under the same conditions as the initial resistance. The resistance increase rate was calculated by dividing the post-endurance resistance by the initial resistance. The resistance increase rate is expressed as a percentage. The resistance increase rate is shown in Table 2 below.

<Results>
Sample No. 2 had a lower resistance increase rate than Sample No. 1. The first layer of Sample No. 2 contains a glass network former (P). The first layer of Sample No. 1 does not contain a glass network former. Sample No. 2 is considered to be superior to Sample No. 1 in terms of adhesion between the first and second layers.

No. 2 had a lower resistance increase rate than No. 3. The coating of No. 2 includes a second layer. The coating of No. 3 does not include a second layer. No. 2 is thought to have an advantage over No. 3 in terms of ionic connection between the sulfide solid electrolyte in the positive electrode and the composite particles.

The present embodiment and examples are illustrative in all respects. They are not limiting. The technical scope of this disclosure encompasses all modifications that are equivalent in meaning and scope to the claims. For example, it is anticipated from the outset that any configuration may be extracted from the present embodiment and examples and that they may be combined in any manner.

100 Composite particle, 110 Positive electrode active material particle, 120 Coating, 121 First layer, 122 Second layer, 200 All-solid-state battery, 210 Positive electrode, 220 Negative electrode, 230 Solid electrolyte layer, 250 Power generating element.

Claims (8)

positive electrode active material particles;
A coating;
Including,
the coating covers at least a portion of the surface of the positive electrode active material particles,
the coating includes a first layer and a second layer;
at least a portion of the first layer is interposed between the positive electrode active material particles and the second layer;
the first layer consists essentially of an oxide glass;
The oxide glass comprises lithium as an optional component, phosphorus as an essential component, and oxygen as the balance,
The oxide glass contains a network structure formed by bonding of phosphorus and oxygen as a main skeleton,
In the first layer, a composition ratio of lithium to phosphorus is equal to or greater than 0 and equal to or less than 0.5,
The second layer includes a sulfide solid electrolyte.
composite particles. the first layer comprises a phosphate backbone;
The composite particle according to claim 1 . The coverage of the second layer is 20% or more.
The composite particle according to claim 1 or claim 2. The sulfide solid electrolyte comprises 60% or more of a first conductive phase and the remainder,
the remainder includes a second conductivity phase and a third conductivity phase;
The first conductive phase comprises a crystalline phase of _PS4 ;
the second conductive phase comprises an amorphous phase of _PS4 ;
The third conductive phase comprises a crystalline phase of _{P2S6 ;}
The composite particle according to claim 1 or claim 2. the second layer has a thickness of 0.1 to 10 μm;
The composite particle according to claim 1 or claim 2. the second layer further comprises conductive carbon;
The mass fraction of the conductive carbon is 1 to 10% relative to the composite particles.
The composite particle according to claim 1 or claim 2. Comprising the composite particles of claim 1 .
Positive electrode. The positive electrode according to claim 7,
All-solid-state battery.