JP2023153516A - Composite particles, positive electrodes, all-solid-state batteries, and methods for producing composite particles - Google Patents

Abstract

To improve the electronic conductivity of a coating film in composite particles (coated cathode active material) provided with a phosphorus-based coating film.SOLUTION: Composite particles include positive electrode active material particles and a coating film that covers at least a portion of the surface of the positive electrode active material particles. The coating film includes a phosphorus compound and a carbon material. The phosphorus compound includes at least one of a first element (glass network forming element) and a second element (transition element), and phosphorus. In the coating film, the relationship of the formula (1): CLi/(CP+CE1+CE2)≤2.5 is satisfied. CLi, CP, CE1, CE2 indicate the elemental concentration of each element measured by XPS.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to composite particles, positive electrodes, all-solid-state batteries, and methods for manufacturing composite particles.

JP-A No. 2010-135090 (Patent Document 1) discloses that by coating a positive electrode active material for an all-solid-state battery with a polyanion structure-containing compound (for example, Li ₃ PO ₄ ), the positive electrode active material and sulfide solid electrolyte can be combined. A technique has been disclosed for suppressing an increase in interfacial resistance over time (an increase in battery resistance over time) due to contact with the battery.

Japanese Patent Application Publication No. 2010-135090

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

Conventionally, LiNbO ₃ and Li ₃ PO ₄ are known as materials for coating films. LiNbO ₃ may have low resistance compared to Li ₃ PO ₄ . Therefore, LiNbO ₃ is becoming more popular. However, according to the new findings of the present inventors, phosphorus compounds such as Li ₃ PO ₄ are superior to LiNbO ₃ in terms of durability under high voltage. The present inventors also discovered that a phosphorus-based coating film containing a specific phosphorus compound has low resistance. However, the phosphorus-based coating film had room for improvement in electrical conductivity.

An object of the present disclosure is to improve the electronic conductivity of a coating film in composite particles (coated positive electrode active material) provided with a phosphorus-based coating film.

[1] comprising positive electrode active material particles and a coating film that covers at least a portion of the surface of the positive electrode active material particles,
The coating film includes a phosphorus compound and a carbon material,
The phosphorus compound includes at least one of a first element that is a glass network forming element and a second element that is a transition element, and phosphorus,
In the coating film, composite particles satisfy the relationship of the following formula (1).

C _Li /(C _P +C _E1 +C _E2 )≦2.5…(1)

(In the above formula (1),
C _Li , C _P , C _E1 , C _E2 indicate element concentrations measured by X-ray photoelectron spectroscopy,
C _Li indicates the elemental concentration of lithium,
C _P indicates the elemental concentration of phosphorus,
C _E1 indicates the element concentration of the first element,
C _E2 represents the element concentration of the second element. )

According to the composite particles of [1] above, the electron conductivity of the coating film can be improved in the composite particles (coated positive electrode active material) provided with the phosphorus-based coating film.
The reason for this is thought to be that the electronic conductivity of the phosphorus-based coating layer is improved by forming conductive paths using the carbon material.
As a result, in positive electrodes and all-solid-state batteries using the composite particles, the output power is suppressed while suppressing the increase in interfacial resistance over time (increase in battery resistance over time) due to contact between the positive electrode active material and the sulfide solid electrolyte. can be improved.

[2] The composite particle according to [1], wherein the first element is at least one selected from the group consisting of boron, silicon, nitrogen, sulfur, germanium, and hydrogen.

[3] The composite particle according to [1] or [2], wherein the second element is at least one selected from the group consisting of a second transition element and a third transition element.

[4] The composite particle according to any one of [1] to [3], wherein the carbon material includes at least one selected from the group consisting of rubber-based carbon, carbon black, and carbon nanofibers.

[5] The composite particle according to any one of [1] to [4], wherein the carbon material includes a material produced by heat treatment of an alkoxide compound.

[6] A positive electrode comprising the composite particles according to any one of [1] to [5] and a sulfide solid electrolyte.

[7] An all-solid-state battery comprising the positive electrode according to [6].

[8] (a) preparing a mixture by mixing a coating liquid, a carbon material, and positive electrode active material particles; and (b) manufacturing composite particles by drying the mixture;
including;
The coating liquid includes a solute and a solvent,
The solute includes at least one of a first element that is a glass network forming element and a second element that is a transition element, and phosphorus.
Method for producing composite particles.

By drying the coating liquid and carbon material adhering to the surface of the positive electrode active material particles, a coating film containing the carbon material can be generated on the surface of the positive electrode active material particles. That is, the coating film described in [1] above can be produced.

[9] (a) preparing a mixture by mixing a coating liquid and positive electrode active material particles;
(b) producing composite particles by drying the mixture; and
(c) heat-treating the composite particles;
including;
The coating liquid includes a solute and a solvent,
The solute includes at least one of a first element that is a glass network forming element and a second element that is a transition element, phosphorus, and an alkoxide-based compound.
Method for producing composite particles.

When the coating liquid adhering to the surface of the positive electrode active material particles is dried and the alkoxide compound is carbonized by heat treatment, a coating film containing a carbon material can be generated on the surface of the positive electrode active material particles. That is, the coating film described in [1] above can be produced.

FIG. 2 is a conceptual diagram showing an example of composite particles in this embodiment. It is a conceptual diagram which shows another example of the composite particle in this embodiment. FIG. 2 is a conceptual diagram showing an example of conventional composite particles. FIG. 1 is a conceptual diagram showing an all-solid-state battery in this embodiment. 1 is a schematic flowchart of a method for manufacturing composite particles in this embodiment.

Hereinafter, embodiments of the present disclosure (hereinafter may be abbreviated as "this embodiment") and examples of the present disclosure (hereinafter may be abbreviated as "present example") will be described. However, this embodiment and this example do not limit the technical scope of the present disclosure.

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

When a compound is expressed by a stoichiometric formula (for example, "LiCoO ₂ ", etc.), the stoichiometric formula is only a representative example of the compound. A compound may have a non-stoichiometric composition. For example, when lithium cobalt oxide is expressed as "LiCoO ₂ ", unless otherwise specified, lithium cobalt oxide is not limited to the composition ratio "Li/Co/O=1/1/2", but can be any composition ratio. It may contain Li, Co and O in a compositional ratio. Furthermore, doping, substitution, etc. with trace elements may be acceptable.

<Composite particles>
Referring to FIG. 1, composite particles 5 include positive electrode active material particles 1 and coating film 2. The composite particles 5 may be referred to as a "coated positive electrode active material," for example.

The composite particles 5 may form, for example, aggregates. That is, one composite particle 5 may include two or more positive electrode active material particles 1. The composite particles 5 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.

In this specification, "D50" indicates a particle size at which the cumulative frequency from the smaller particle size side reaches 50% in the volume-based particle size distribution. D50 can be measured by laser diffraction.

《Coating film》
The coating film 2 covers at least a portion of the surface of the positive electrode active material particles 1. The coating film 2 is a shell of the composite particles 5.
Coating film 2 includes a phosphorus compound and carbon material 31.

(phosphorus compound)
The phosphorus compound includes at least one of the first element (E1) and the second element (E2), and P. Note that in this specification, the first element may be abbreviated as "E1", and the second element may be abbreviated as "E2".

The first element (E1) is an element that has glass-forming ability (glass network-forming element), that is, an element that can form an oxide glass having a network structure by combining with O. Addition of E1 is expected to produce a mixed anion effect.

E1 is, for example, at least one member selected from the group consisting of boron (B), silicon (Si), nitrogen (N), sulfur (S), germanium (Ge), and hydrogen (H). E1 is, for example, at least one selected from the group consisting of B and Si. E1 may form oxide glass alone. E1 may form a composite oxide glass together with P.

The second element (E2) is a transition element. “Transition elements” are elements from Groups 3 to 11 of the periodic table.

E2 has a larger ionic radius than P. E2 can inhibit crystallization of phosphorus compounds. E2 is, for example, at least one selected from the group consisting of a first transition element (3d transition element), a second transition element (4d transition element), a third transition element (5d, 4f transition element), and a fourth transition element. It is one type. E2 is, for example, at least one selected from the group consisting of second transition elements and third transition elements. Third transition elements include lanthanides. That is, E2 may include, for example, lanthanoids.

E2 is, for example, lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), Dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), lutetium (Lu), scandium (Sc), copper (Cu), Y, zirconium (Zr), molybdenum (Mo ), technetium (Tc), ruthenium (Ru), rhodium (Rh), palladium (Pd), silver (Ag), hafnium (Hf), tantalum (Ta), tungsten (W), rhenium (Re), osmium (Os) ), iridium (Ir), platinum (Pt), and gold (Au).
E2 is, for example, at least one selected from the group consisting of La, Ce, Zr, and Y. E2 is, for example, at least one selected from the group consisting of La, Ce, and Y.

The ratio of P contained in the phosphorus compound (or composite particles) is, for example, 1 to 10% by mass based on the total amount of composite particles 5.

The phosphorus compound may further contain, for example, Li, O, carbon (C), and the like.

The phosphorus compound may include, for example, a phosphoric acid skeleton. That is, the phosphorus compound may be a phosphoric acid compound. When the phosphorus compound contains a phosphate skeleton, fragments such as PO ₂ ^- and PO ₃ ^- can be detected when the composite particles 5 are analyzed by, for example, TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry).

In the coating film (or phosphorus compound), the Li composition ratio "C _Li /(C _P +C _E1 +C _E2 )" is 2.5 or less [see formula (1) above]. When the composition ratio of Li is 2.5 or less and at least one of E1 and E2 is present, battery resistance can be significantly reduced.

The composition ratio of Li may be, for example, 2.38 or less, 2.26 or less, 2.18 or less, or 2.03 or less. It may be 1.89 or less, 1.73 or less, 1.42 or less, or 1.1 or less. The composition ratio of Li may be, for example, 0.1 or more, 0.5 or more, or 1.05 or more. The composition ratio of Li may be, for example, 1.05 to 2.38.
Note that the composition ratio of Li may be zero. That is, Li may not be present on the surface of the coating film (composite particle), and the coating film (or phosphorus compound) may not contain Li at all.

(XPS measurement of Li composition ratio)
The Li composition ratio "C _Li /( _CP + C _E1 + C _E2 )" on the surface of the composite particle can be measured by XPS according to the following procedure. The XPS device is prepared. For example, an XPS device "Product name: PHI X-tool" manufactured by ULVAC-PHI (or an equivalent product) may be used. A sample powder made of composite particles is set in an XPS device. Narrow scan analysis is performed with a pass energy of 224 eV. The measurement data is processed by analysis software. For example, analysis software "product name: MulTiPak" (product name: MulTiPak) manufactured by ULVAC-PHI, Inc. (or an equivalent product) may be used. The peak area (integral value) of the Li1s spectrum is converted to the elemental concentration of Li (C _Li ). The peak area of the P2p spectrum is converted to the elemental concentration of P ( _CP ). For E1 and E2, appropriate spectra are selected depending on their types. For example, in the case of B, the peak area of the B1s spectrum is converted to the elemental concentration of B (C _E1 ). For example, in the case of La, the peak area of the La3d5 spectrum is converted to the elemental concentration (C _E2 ) of La. By dividing C _Li by the sum of C _P , C _E1 and C _{E2 ,} the composition ratio of Li on the particle surface is determined.

For example, when the coating film contains multiple types of E1, C _E1 indicates the total element concentration of the multiple types of E1. The same applies to E2 and C _E2 .

The composition ratio "C _Li /(C _P +C _E1 +C _E2 )" determined by XPS reflects the Li composition ratio in the coating film (phosphorus compound), but is not equivalent to the Li composition ratio in the coating film. This is because XPS can also reflect the composition of the base (positive electrode active material particles). For example, if Li in the base is detected by XPS, the Li composition ratio determined by XPS may become larger than the Li composition ratio in the actual coating film.

The chemical composition of the phosphorus compound may be represented by the following formula (2), for example.
Li _w E ¹ _x E ² _y PO _z …(2)
In the above formula (2), E ¹ represents E1. E ² indicates E2. w, x, y, and z are arbitrary numbers. w, x, y, and z can be identified by, for example, analyzing a portion of the coating film 2 in the cross section of the composite particle 5 using STEM-EDX (Scanning Transmission Electron Microscope - Energy Dispersive X-ray Spectroscopy) or the like. The cross-sectional sample is prepared according to the same procedure as (film thickness measurement) described below.

Specific examples of the phosphorus compound include at least one selected from the group consisting of Li ₃ PO ₄ (LPO), BPO ₄ (BPO), and POx (P ₄ O _6, P ₂ O _5, etc.). .

In the composite particles 5, the coverage rate of the surface of the positive electrode active material particles 1 with the coating film 2 may be, for example, 70% or more. When the coverage is 70% or more, a reduction in battery resistance is expected. The coverage may be, for example, 85% or more, 88% or more, 89% or more, 90% or more, or 94% or more. It may be 95% or more, or it may be 97% or more. The coverage may be, for example, 100% or 99% or less. The coverage may be, for example, 85 to 97% or 90 to 97%.

(XPS measurement of coverage)
Coverage is also measured by XPS. By analyzing the measurement data obtained in the same manner as above (XPS measurement of Li composition ratio) except that the pass energy was 120 eV, each peak area (intensity value) of C1s, O1s, P1s, M2p3, etc. ), the ratio of each element (element concentration) can be found. The coverage rate is determined by the following formula (3).
θ=(P+E1+E2)/(P+E1+E2+M)×100...(3)
In the above formula (3), θ represents the coverage (%). P, E1, E2, and M indicate the ratio of each element.

"M2p3" and M in the above formula (3) are constituent elements of the positive electrode active material particles, and represent elements other than Li and O. That is, the positive electrode active material particles may be represented by the following formula (4).
_LiMO2 ...(4)
M may consist of one type of element or may consist of multiple elements. M may be, for example, at least one selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). When M includes a plurality of elements, the total composition ratio of each element may be 1.

For example, when the positive electrode active material particles are "LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ", the above formula (3) can be transformed into the following formula (3').
θ=(P+E1+E2)/(P+E1+E2+Ni+Co+Mn)×100...(3')
Ni in the above formula (3') represents the elemental ratio of nickel determined from the peak area of Ni2p3. Co indicates the elemental ratio of cobalt determined from the peak area of Co2p3. Mn indicates the elemental ratio of manganese determined from the peak area of Mn2p3.

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

(film thickness measurement)
Film thickness (thickness of coating film) can be measured by the following procedure. A sample is prepared by embedding composite particles in a resin material. The ion milling device performs cross-section processing on the sample. For example, an ion milling device "Product name: Arblade (registered trademark) 5000" manufactured by Hitachi High Technologies (or an equivalent product) may be used. A cross section of the sample is observed using a SEM (Scanning Electron Microscope). For example, a SEM device "product name SU8030" (or equivalent product) manufactured by Hitachi High-Technologies, Inc. may be used. The film thickness is measured in 20 fields of view for each of the 10 composite particles. The arithmetic mean of the film thicknesses at 200 locations in total is considered to be the film thickness.

In addition, in the positive electrode and the battery, by using composite particles containing the above-mentioned phosphorus compound and having a phosphorus-based coating film having low resistance, it is expected that both durability under high voltage and high output can be achieved.

(carbon material)
The carbon material is not particularly limited as long as it contains a carbon element. The shape of the carbon material is not particularly limited, and may be, for example, a particle, an aggregate, a fiber, or the like. The carbon material 31 may include, for example, at least one selected from the group consisting of rubber-based carbon, carbon black, and carbon nanofibers.

The carbon material is preferably a material that does not easily cause decomposition of the solid electrolyte when it comes into contact with the solid electrolyte.

As such a carbon material, for example, a material whose decomposition current when mixed with a solid electrolyte and subjected to CV measurement is 0.05 mA or less is preferable. This decomposition current can be confirmed by the following method.
50 mg of powder containing a solid electrolyte and a carbon material at a mass ratio of 9:1 is put into a mold of a press machine, and pressed at 2.0 tons for 120 seconds to obtain a layered material. The layered material and SUS foil are laminated and pressed at 2.0 tons for 120 seconds. Li foil and SUS foil are laminated in this order on the side opposite to the SUS foil of the layered material, and pressed at 1 ton for 30 seconds. Additionally, McCall was restrained with 6Nm. In this way, a laminate of "SUS foil/carbon material and solid electrolyte/Li/SUS foil" was produced, and CV measurement was performed on the laminate (sweep speed: 0.1 mV/s, voltage range: 2.5V-5V (Li/Li ⁺ )), the above decomposition current can be measured.

Note that the carbon material contained in the coating film may be, for example, a randomly shaped carbon material 32 (see FIG. 2) generated by heat treatment (firing) of an alkoxide compound contained in the coating liquid described below. .

In at least a part of the plurality of carbon materials 31 and 32 (a plurality of carbon particles, etc.) included in the coating film 2, (i) each carbon material (carbon particles, etc.) independently penetrates the coating film, or, (ii) It is preferable that aggregates of a plurality of carbon materials (carbon particles, etc.) that are in contact with each other penetrate the coating film. In this case, it is considered that the electronic conductivity of the phosphorus-based coating film is improved more reliably by forming the conductive path using the carbon material. Note that from the viewpoint of improving electronic conductivity, the above (i) is more preferable.

As shown in FIG. 2, when randomly shaped carbon materials 32 exist in the coating film 2, carbon materials of a size that can penetrate the coating film 2 alone like the carbon material 32a (see (i) above) ) is considered to be more likely to exist.

The carbon content in the coating film is, for example, 1 to 20%.
The carbon content in the coating film can be measured by analyzing a portion of the coating film 2 in the cross section of the composite particle 5 using XPS. Note that the cross-sectional sample is prepared according to the same procedure as described above (film thickness measurement).

《Cathode active material particles》
The positive electrode active material particles 1 are the cores of the composite particles 5. The positive electrode active material particles 1 may be secondary particles (an aggregate of primary particles). The positive electrode active material particles 1 (secondary particles) may have a D50 of 1 to 50 μm, a D50 of 1 to 20 μm, or a D50 of 5 to 15 μm, for example. You can leave it there. The primary particles may have a maximum Feret diameter of 0.1 to 3 μm, for example.

The positive electrode active material particles 1 may contain arbitrary components. The positive electrode active material particles 1 are, 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 May contain. For example, "(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)O ₂ is, for example, Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ , Li(Ni _0.5 Co _0.2 Mn _0.3 )O ₂ , Li(Ni _0.8 Co _0.1 Mn _0.1 )O ₂ etc. may be included.

<All-solid battery>
FIG. 4 is a conceptual diagram showing the all-solid-state battery in this embodiment. All-solid-state battery 100 may include, for example, an exterior body (not shown). The exterior body may be, for example, a pouch made of a metal foil laminate film. The exterior body may house the power generation element 50. Power generation element 50 includes a positive electrode 10, a separator layer 30, and a negative electrode 20. That is, the all-solid-state battery 100 includes a positive electrode 10, a separator layer 30, and a negative electrode 20.

《Positive electrode》
The positive electrode 10 is layered. The positive electrode 10 may include, for example, a positive electrode active material layer and a positive electrode current collector. For example, the positive electrode active material layer may be formed by applying a positive electrode composite material to the surface of the positive electrode current collector. The positive electrode current collector may include, for example, 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 separator layer 30. The positive electrode active material layer includes a positive electrode composite material. The positive electrode composite material includes composite particles (coated positive electrode active material) and a sulfide solid electrolyte. That is, the positive electrode 10 includes composite particles and a sulfide solid electrolyte. Details of the composite particles are as described above.

The sulfide solid electrolyte can form an ionic conduction path within the positive electrode active material layer. The blending amount of the sulfide solid electrolyte may be, for example, 1 to 200 parts by volume, or 50 to 150 parts by volume, based on 100 parts by volume of composite particles (positive electrode active material). It may be 50 to 100 parts by volume. The sulfide solid electrolyte contains S. The sulfide solid electrolyte may contain Li, P, and S, for example. The sulfide solid electrolyte may further contain O, Si, etc., for example. The sulfide solid electrolyte may further contain, for example, halogen. The sulfide solid electrolyte may further contain, for example, iodine (I), bromine (Br), and the like. The sulfide solid electrolyte may be of a glass ceramic type or an argyrodite type, for example. Examples of the sulfide solid electrolyte include LiI-LiBr-Li ₃ PS ₄ , Li ₂ S-SiS ₂ , LiI-Li ₂ S-SiS ₂ , LiI-Li ₂ SP ₂ S ₅ , LiI-Li ₂ O- From the group consisting of Li ₂ S-P ₂ S ₅ , LiI-Li ₂ SP ₂ O ₅ , LiI-Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ and Li ₃ PS ₄ It may contain at least one selected type.

For example, “LiI-LiBr-Li ₃ PS ₄ ” indicates a sulfide solid electrolyte produced by mixing LiI, LiBr, and Li ₃ PS ₄ in an arbitrary molar ratio. For example, a sulfide solid electrolyte may be produced by a mechanochemical method. “Li ₂ SP ₂ S ₅ ” includes Li ₃ PS ₄ . Li ₃ PS ₄ can be produced, for example, by mixing Li ₂ S and P ₂ S ₅ at “Li ₂ S/P ₂ S ₅ =75/25 (molar ratio)”.

The positive electrode active material layer may further contain, for example, a conductive material. The conductive material may 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 based on 100 parts by mass of composite particles (positive electrode active material). The conductive material may contain any component. The conductive material may include, for example, at least one selected from the group consisting of carbon black, vapor grown carbon fiber (VGCF), carbon nanotube (CNT), and graphene flake.

The positive electrode active material layer may further contain a binder, for example. The blending amount of the binder may be, for example, 0.1 to 10 parts by mass based on 100 parts by mass of composite particles (positive electrode active material). The binder may include optional ingredients. The binder is selected from the group consisting of, for example, polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), styrene butadiene rubber (SBR), and polytetrafluoroethylene (PTFE). It may contain at least one kind.

《Negative electrode》
The negative electrode 20 is layered. The negative electrode 20 may include, for example, a negative electrode active material layer and a negative electrode current collector. For example, the negative electrode active material layer may be formed by applying a negative electrode composite material to the surface of the negative electrode current collector. The negative electrode current collector may include, for example, Cu foil, Ni foil, 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 separator layer 30. The negative electrode active material layer includes a negative electrode composite material. The negative electrode composite material includes negative electrode active material particles and a sulfide solid electrolyte. The negative electrode composite material may further include a conductive material and a binder. The sulfide solid electrolyte between the negative electrode composite material and the positive electrode composite material may be of the same type or may be of different types. The negative electrode active material particles may contain 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 .

《Separator layer》
Separator layer 30 is interposed between positive electrode 10 and negative electrode 20. Separator layer 30 separates positive electrode 10 from negative electrode 20. Separator layer 30 includes a sulfide solid electrolyte. Separator layer 30 may further contain a binder. The sulfide solid electrolytes between the separator layer 30 and the positive electrode mixture may be of the same type or different types. The sulfide solid electrolytes between the separator layer 30 and the negative electrode composite material may be of the same type or different types.

<Method for manufacturing composite particles>
FIG. 5 is a schematic flowchart of the method for manufacturing composite particles in this embodiment. Hereinafter, the "method for manufacturing composite particles in this embodiment" may be abbreviated as "this manufacturing method." This production method includes "(a) Preparation of mixture" and "(b) Production of composite particles." This manufacturing method may further include, for example, "(c) heat treatment".

《(a) Preparation of mixture》
This manufacturing method includes preparing a mixture by mixing a coating liquid, a carbon material, and positive electrode active material particles (adhering the coating liquid to the surface of the positive electrode active material particles). Note that the above mixing may be performed after mixing the carbon material and the positive electrode active material in advance. Details of the positive electrode active material particles and the carbon material are as described above.

The mixture may be, for example, a suspension or a wet powder, and it is sufficient that the coating liquid is attached to the surface of the positive electrode active material particles in the mixture. For example, a suspension may be formed by dispersing positive electrode active material particles (powder) and carbon material in a coating liquid. For example, a wet powder may be formed by spraying a coating liquid into a powder containing positive electrode active material particles and a carbon material. In this manufacturing method, any mixing device, granulation device, etc. can be used.

The coating liquid contains a solute (including a solute and a dispersoid) and a solvent (a solvent and a dispersion medium or a solvent). The solute contains at least one of the first element (E1) and the second element (E2) and phosphorus (P) as a raw material for the coating film. The coating liquid may further contain, for example, suspended matter (insoluble components), precipitates, and the like.

The total 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, with respect to 100 parts by mass of the solvent. Good too.

The solvent can contain any component as long as the solute is dissolved. The solvent may include, for example, water, alcohol, and the like. The solvent may include, for example, ion-exchanged water.

Details of E1 and E2 are as described above.
The solute may contain, for example, at least one selected from the group consisting of E1 oxoacid and E1 oxide. The solute may contain, for example, at least one selected from the group consisting of boric acid, silicic acid, nitric acid, sulfuric acid, and germanic acid. The solute may include, for example, orthoboric acid, metaboric acid, and the like.
The solute may include, for example, an oxide of E2. The solute may include, for example, at least one selected from the group consisting of lanthanum oxide, cerium oxide, and yttrium oxide.

The solute may include, for example, a phosphoric acid compound. This allows the solute to contain P. The phosphoric acid compound may be, for example, at least one selected from the group consisting of phosphoric anhydride (P ₂ O ₅ ), orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid [(HPO ₃ ) _n ], and polyphosphoric acid. good. The phosphoric acid compound may be, for example, at least one selected from the group consisting of metaphosphoric acid and polyphosphoric acid. Metaphosphoric acid and polyphosphoric acid may have longer molecular chains than other phosphoric acid compounds. It is thought that the long molecular chain of the phosphoric acid compound makes it easier to produce a continuous coating film. The continuity of the coating film is expected to improve coverage, for example.

In the above coating liquid, for example, the following relationship (5) may be satisfied.
0.040<( _nE1 + _nE2 ) _{/nP≦1.51…} (5)
In the above formula (5),
n _P indicates the molar concentration of P in the coating liquid.
n _E1 indicates the molar concentration of the first element in the coating liquid.
n _E2 indicates the molar concentration of the second element in the coating liquid.

"(n _E1 +n _E2 )/n _P " indicates the molar ratio (substance ratio) of the sum of the first element (E1) and the second element (E2) to P in the coating liquid. When the molar ratio is more than 0.040 and less than or equal to 1.51, a reduction in battery resistance is expected.

The molar ratio may be, for example, 1.03 or less, 0.67 or less, 0.48 or less, or 0.098 or less. , 0.051 or less. The molar ratio may be, for example, 0.048 or more, or 0.10 or more. The molar ratio may be, for example, 0.048 to 1.03.

(ICP measurement)
The above molar ratio "(n _E1 +n _E2 )/n _P " in the coating liquid is measured by the following procedure. 100 mL of sample liquid is prepared by diluting 0.01 g of coating liquid with pure water. Aqueous solutions (1000 ppm, 10000 ppm) of P, E1, and E2 are prepared. A standard solution is prepared by diluting 0.01 g of an aqueous solution with pure water. An ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) device is prepared. The luminescence intensity of the standard solution is measured using an ICP-AES device. A calibration curve is created from the luminescence intensity of the standard solution. The ICP-AES device measures the luminescence intensity of the sample solution (diluted coating solution). The mass concentrations of P, E1, and E2 in the coating liquid are determined from the luminescence intensity of the sample liquid and the calibration curve. Furthermore, the mass concentrations of P, E1, and E2 are converted into molar concentrations. The molar ratio is determined by dividing the sum of the molar concentration of E1 (n _E1 ) and the molar concentration of E2 (n _E2 ) by the molar concentration of P (n _P ).

The solute may further contain Li, for example, may further contain a lithium compound. The lithium compound may be, for example, lithium hydroxide, lithium carbonate, lithium nitrate, or the like.

The molar ratio of Li to the sum of P, E1, and E2 " _nLi /( _nP + _nE1 + _nE2 )" may be less than 1.1 or may be 1.0 or less, for example. However, it may be 0.45 or less, 0.1 or less, or 0.05 or less. Note that the molar ratio "n _Li /(n _P +n _E1 +n _E2 )" may be zero, for example. That is, the solute does not need to contain Li. n _Li may be below the detection limit in ICP measurement. It is expected that the smaller the molar ratio "n _Li /(n _P +n _E1 +n _E2 )", the lower the Li composition ratio on the particle surface.

《(b) Manufacture of composite particles》
This manufacturing method includes manufacturing composite particles by drying the above mixture. By drying the coating liquid adhering to the surface of the positive electrode active material particles, a coating film is generated and composite particles are manufactured. Any drying method may be used in this manufacturing method.

When the mixture is a suspension containing positive electrode active material particles, carbon material, and coating liquid, composite particles may be formed by, for example, a spray drying method. That is, composite particles can be formed by spraying a suspension containing positive electrode active material particles and a coating liquid from a nozzle, and drying the sprayed droplets with, for example, hot air. By using the spray drying method, for example, it is expected that the coverage will be improved.

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.

For example, composite particles may be produced in a tumbling fluidized bed coating apparatus. In the tumbling fluidized bed coating apparatus, "(a) Preparation of mixture" (adhesion of coating liquid to the surface of positive electrode active material particles) and "(b) Production of composite particles" can be performed simultaneously.

《(c) Heat treatment》
This manufacturing method may include subjecting the composite particles to heat treatment. The coating film can be fixed by heat treatment. Heat treatment may also be referred to as "calcination." In this manufacturing method, any heat treatment equipment can be used. 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 under an inert atmosphere.

<Modification of method for producing composite particles>
In this embodiment, the following manufacturing method can be adopted as a modification of the above method for manufacturing composite particles.

(a) preparing a mixture by mixing a coating liquid and positive electrode active material particles;
(b) producing composite particles by drying the mixture; and
(c) heat-treating the composite particles;
including;
The coating liquid includes a solute and a solvent,
The solute includes at least one of a first element that is a glass network forming element and a second element that is a transition element, phosphorus, and an alkoxide-based compound.
Method for producing composite particles.

When the coating liquid adhering to the surface of the positive electrode active material particles is dried and the alkoxide compound is carbonized by heat treatment (baking), a coating film containing a carbon material can be generated on the surface of the positive electrode active material particles. That is, the above coating film can be produced.

Since the carbon material contained in the coating film formed in this manner has a random shape, it is expected that carbon material of a size that can penetrate the coating film alone is likely to be included.

An alkoxide compound is a compound containing an alkoxide group (-OR). The alkoxide compound is not particularly limited, but includes, for example, an alkoxide compound containing phosphorus, which is a source of phosphorus. As the alkoxide compound containing phosphorus, triethyl phosphate [OP(OC ₂ H ₅ ) ₃ ], trimethyl phosphate [P(OCH ₃ ) ₃ ], etc. can be suitably used. An alkoxide compound that does not contain phosphorus may also be used. Examples of the alkoxide compounds that do not contain phosphorus include boric acid alkoxide [B(OR) ₃ ]. In the boric acid alkoxide, R preferably has 3 or more carbon atoms, such as tributyl borate [B(O(CH ₂ ) CH ₃ ) ₃ ]. Lithium ethoxide or the like may also be used.

<Example 1>
[Preparation of composite particles]
870.4 parts by mass of hydrogen peroxide solution (mass concentration 30%) was charged into the container. Next, 987.4 parts by mass of ion-exchanged water and 44.2 parts by mass of phosphoric acid [P ₂ O ₅ .3H ₂ O] were charged into the container. Next, 87.9 parts by mass of aqueous ammonia (mass concentration 28%) was charged into the container. The contents of the container were thoroughly stirred to form a solution. The solution is believed to contain a peroxo complex of P. Furthermore, a coating liquid was prepared by dissolving 0.1 parts by mass of lithium hydroxide monohydrate (LiOH·H ₂ O) into the solution.

Li(Ni _1/3 Co _1/3 Mn _1/3 )O ₂ was prepared as positive electrode active material particles. 10% by mass of carbon material (graphite powder) was added to the positive electrode active material particles, and mixed for 1 minute at 3000 rpm using a mixer (Rentaro, Shinky Co., Ltd.) under vacuum. A suspension was prepared by dispersing 50 parts by mass of the obtained mixture into 53.7 parts by mass of the coating liquid. A powder of composite particles was prepared by spray drying the suspension.

The obtained composite particles were heat treated in an air atmosphere. The heat treatment temperature was 200°C. The heat treatment time was 5 hours. As a result, composite particles (coated positive electrode active material) of Example 1 having a coating film with a thickness of 20 nm were obtained. In addition, in the composite particles of Example 1, the coating film is considered to contain Li ₃ PO ₄ (LPO).

[Fabrication of all-solid-state battery]
(Preparation of positive electrode)
The following materials were prepared.
Sulfide solid electrolyte: Li ₂ SP ₂ S _5- based glass ceramics containing LiI (D50: 0.8 μm)
Conductive material: VGCF (vapor grown carbon fiber)
Binder: SBR (butadiene rubber)
Dispersion medium: heptane Positive electrode current collector: Al foil

A positive electrode slurry was prepared by mixing composite particles, a sulfide solid electrolyte, a conductive material, a binder, and a dispersion medium. The mixing ratio of the composite particles and the sulfide solid electrolyte was "composite particles/sulfide solid electrolyte = 7/3 (volume ratio)". The amount of the conductive material blended was 3 parts by mass based on 100 parts by mass of composite particles. The blending amount of the binder was 0.7 parts by mass based on 100 parts by mass of composite particles. The positive electrode slurry was sufficiently stirred using an ultrasonic homogenizer (SMT: UH-50). A coating film was formed by applying the positive electrode slurry to the surface of the positive electrode current collector. The coating was dried on a hot plate at 100° C. for 30 minutes. In this way, a positive electrode original fabric was manufactured. A disk-shaped positive electrode was cut out from the positive electrode material. The area of the positive electrode was 1 cm ² .

(Preparation of negative electrode)
A sulfide solid electrolyte (Li ₂ S-P ₂ S ₅ -based glass ceramics containing LiI, D50: 0.8 μm) and 1% by mass of a conductive additive were placed in a kneading container of a FILMIX device (model 30-L manufactured by PRIMIX). agent (VGCF), 2% by mass binder (SBR), and heptane, and the mixture was stirred at 20,000 rpm for 30 minutes.
Next, the negative electrode active material ( ₁₂ particles of Li ₄ Ti ₅ O, D50: 1 μm) and the solid electrolyte were put into a kneading container so that the volume ratio was 6:4, and the mixture was mixed at 15,000 rpm for 60 minutes using a Filmix device. A negative electrode mixture was prepared by stirring. The prepared negative electrode mixture was applied onto copper foil and dried at 100° C. for 30 minutes. In this way, a negative electrode original fabric was manufactured. A disk-shaped negative electrode was cut out from the negative electrode material. The area of the negative electrode was 1 cm ² .

(Preparation of separator layer)
64.8 mg of sulfide solid electrolyte (Li ₂ S-P ² _{S 5} -based glass ceramics containing LiI, D50: 2.5 μm) was placed in a cylindrical ceramic with an inner diameter cross-sectional area of 1 cm 2, smoothed, and then 1 ton / ^cm2 to form a separator layer (solid electrolyte layer).

(Preparation of battery)
The produced positive electrode was stacked on one side of the solid electrolyte layer, and the produced negative electrode was stacked on the other side of the solid electrolyte layer, and pressing was performed at 6 ton/cm ₂ for 1 minute. Next, an all-solid-state battery (all-solid lithium ion battery) was produced by restraining the positive and negative electrodes with terminals (stainless steel rods) at 1 ton.

<Example 2>
In Example 2, the blending amount of the carbon material was changed so that the content of the carbon material in the coating film was 10% by mass. Composite particles and a battery of Example 2 were produced in the same manner as in Example 1 except for the above.

<Example 3>
In Example 3, the carbon material was not directly blended into the coating liquid, but an alkoxide compound (lithium ethoxide, triethyl phosphate) was added to the coating liquid, and the alkoxide compound was carbonized in the heat treatment process. A carbon material was generated within the coating film. Note that the amount of the alkoxide compound added to the coating liquid was adjusted so that the content of the carbon material in the coating film was approximately 5% by mass.
Specifically, 1 mmol of lithium ethoxide (manufactured by Kojundo Kagaku Co., Ltd.) and 1 mmol of triethyl phosphate (manufactured by Kojundo Kagaku Co., Ltd.) were mixed in 30 mL of IPA (isopropyl alcohol) to obtain a sol-gel solution. The obtained sol-gel solution was added to the same coating solution as in Example 1. Note that no carbon material was added. Further, as heat treatment for the composite particles obtained by spray drying, heat treatment was performed at 200° C. to 450° C. for 5 hours in an N ₂ and Ar atmosphere.
Composite particles and a battery of Example 3 having a coating film with a thickness of 20 nm were produced in the same manner as in Example 1 except for the above.

<Comparative example 1>
In Comparative Example 1, no carbon material was blended into the raw materials for the coating film. Composite particles and a battery of Comparative Example 1 were produced in the same manner as in Example 1 in other respects.

<Evaluation>
[Electrical conductivity of composite particles]
The electronic conductivity (electrical conductivity: electronic conductivity) of each of the composite particles of the above Examples and Comparative Examples was evaluated using a powder resistivity measurement system (Loresta). Table 1 shows the measurement results of electrical conductivity.
(1) Measure the film thickness blank of the McCorl cell (or perform a zero point set).
(2) Introduce 100 mg of weighed composite particle powder into the Macor cell.
(3) Tighten the Macor Cell with a torque of 2N and press the composite particles within the Macor Cell to obtain a layered material. The film thickness of the layered material is measured, and the resistance value of the layered material is measured using a high tester.
(4) Change the torque to 6N and 10N and repeat (3).
(5) From the resistance values measured in (3) and (4) above, determine the resistivity, and determine the electrical conductivity, which is the reciprocal of the resistivity.

[Battery DC resistance]
The DC resistance of each of the batteries (all-solid-state batteries) of the above Examples and Comparative Examples was evaluated by the following method.

(Checking initial capacity)
For each cell, three cycles of constant current-constant voltage (CC-CV) charging and constant current (CC) discharging were repeated at 1/3C rate. The discharge capacity at the third cycle was confirmed as the initial capacity. Note that "C" is a unit of current rate. "1C" indicates a current rate at which the SOC (state of charge) reaches 100% from 0% after one hour of charging.

(Measurement of DC resistance)
The direct current resistance of the batteries whose initial capacity was confirmed was measured. Table 1 shows the measurement results of DC resistance (ratio when the DC resistance of Comparative Example 1 is set to 1.00). Note that the smaller the DC resistance, the higher the output characteristics (discharge rate) of the battery.

From the results shown in Table 1, the composite particles of Examples 1 to 3 in which the coating film contains a carbon material have extremely high electrical conductivity compared to the composite particles of Comparative Example 1 in which the coating film does not contain a carbon material. I can see that In addition, the batteries (all-solid-state batteries) produced using each of the composite particles of Examples 1 to 3 had lower DC resistance than the battery produced using the composite particles of Comparative Example 1, and the battery output It can be seen that the is large.

In addition, especially in Example 3, the electrical conductivity of the composite particles was high. In Example 3, as shown in FIG. 2, there are randomly shaped carbon materials 32 in the coating film 2, and there is a carbon material that penetrates the coating film 2 alone, such as the carbon material 32a. It is thought that the electrical conductivity of the composite particles increased.

This embodiment and this example are illustrative in all respects. This embodiment and this example are not restrictive. The technical scope of the present disclosure includes all changes within the meaning and scope equivalent to the description of the claims. For example, it is planned from the beginning that arbitrary configurations will be extracted from this embodiment and this example and that they will be combined arbitrarily.

1 positive electrode active material particles, 2 coating film, 31, 32, 32a carbon material, 5 composite particles, 10 positive electrode, 20 negative electrode, 30 separator layer, 50 power generation element, 100 all-solid battery.

Claims (9)

comprising positive electrode active material particles and a coating film that covers at least a portion of the surface of the positive electrode active material particles,
The coating film includes a phosphorus compound and a carbon material,
The phosphorus compound includes at least one of a first element that is a glass network forming element and a second element that is a transition element, and phosphorus,
In the coating film, composite particles satisfy the relationship of the following formula (1).

C _Li /(C _P +C _E1 +C _E2 )≦2.5…(1)

(In the above formula (1),
C _Li , C _P , C _E1 , C _E2 indicate element concentrations measured by X-ray photoelectron spectroscopy,
C _Li indicates the elemental concentration of lithium,
C _P indicates the elemental concentration of phosphorus,
C _E1 indicates the element concentration of the first element,
C _E2 represents the element concentration of the second element. ) The composite particle according to claim 1, wherein the first element is at least one selected from the group consisting of boron, silicon, nitrogen, sulfur, germanium, and hydrogen. The composite particle according to claim 1, wherein the second element is at least one selected from the group consisting of a second transition element and a third transition element. The composite particle according to claim 1, wherein the carbon material includes at least one selected from the group consisting of rubber-based carbon, carbon black, and carbon nanofibers. The composite particle according to claim 1, wherein the carbon material includes a material produced by heat treatment of an alkoxide compound. A positive electrode comprising the composite particles according to claim 1 and a sulfide solid electrolyte. An all-solid-state battery comprising the positive electrode according to claim 6. (a) preparing a mixture by mixing a coating liquid, a carbon material, and positive electrode active material particles; and (b) manufacturing composite particles by drying the mixture.
including;
The coating liquid includes a solute and a solvent,
The solute includes at least one of a first element that is a glass network forming element and a second element that is a transition element, and phosphorus.
Method for producing composite particles. (a) preparing a mixture by mixing a coating liquid and positive electrode active material particles;
(b) producing composite particles by drying the mixture; and
(c) heat-treating the composite particles;
including;
The coating liquid includes a solute and a solvent,
The solute includes at least one of a first element that is a glass network forming element and a second element that is a transition element, phosphorus, and an alkoxide-based compound.
Method for producing composite particles.

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