Composite particle, positive electrode, all-solid-state battery, and method for producing composite particle

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

[Technical Field]

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

[0002] Japanese Patent Laid-Open Publication No. 2010-135090 (Patent Document 1) discloses a technology for suppressing an increase in interfacial resistance over time (an increase in battery resistance over time) due to contact between a positive electrode active material and a sulfide solid electrolyte by coating the positive electrode active material for an all-solid-state battery with a compound containing a polyanion structure (e.g., Li3PO4). [Prior art documents] [Patent documents]

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

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

[0005] LiNbO3 and Li3PO4 have been known as coating film materials. LiNbO3 can have lower resistance than Li3PO4. For this reason, LiNbO3 is becoming increasingly popular. However, according to new findings by the present inventors, phosphorus compounds such as Li3PO4 are superior to LiNbO3 in terms of durability under high voltage. The present inventors have also discovered that phosphorus-based coating films containing specific phosphorus compounds have low resistance. However, the electrical conductivity of these phosphorus-based coating films leaves room for improvement.

[0006] 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. [Means for solving the problem]

[0007] [1] A battery 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 contains a phosphorus compound and a carbon material, the phosphorus compound contains phosphorus and at least one of a first element which is a glass network forming element and a second element which is a transition element; The composite particles in the coating film 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 denotes the element concentration measured by X-ray photoelectron spectroscopy, C Li denotes the elemental concentration of lithium, C P indicates the elemental concentration of phosphorus, C E1 represents the element concentration of the first element, CE2 indicates the element concentration of the second element.)

[0008] According to the composite particles of the above [1], the electron conductivity of the coating film can be improved in the composite particles (coated positive electrode active material) provided with a phosphorus-based coating film. The reason for this is believed to be that the formation of a conductive path by the carbon material improves the electronic conductivity of the phosphorus-based coating layer. As a result, in a positive electrode and an all-solid-state battery using the composite particles, it is possible to improve output while suppressing an increase over time in interfacial resistance due to contact between the positive electrode active material and the sulfide solid electrolyte (an increase over time in battery resistance).

[0009] [2] The composite particle according to [1], wherein the first element is at least one element selected from the group consisting of boron, silicon, nitrogen, sulfur, germanium, and hydrogen.

[0010] [3] The composite particle according to [1] or [2], wherein the second element is at least one element selected from the group consisting of second transition elements and third transition elements.

[0011] [4] The composite particles according to any one of [1] to [3], wherein the carbon material comprises at least one selected from the group consisting of rubber-based carbon, carbon black, and carbon nanofiber.

[0012] [5] The composite particles according to any one of [1] to [4], wherein the carbon material includes a material produced by heat treatment of an alkoxide compound.

[0013] [6] A positive electrode comprising the composite particles according to any one of [1] to [5] and a sulfide solid electrolyte.

[0014] [7] An all-solid-state battery comprising the positive electrode according to [6].

[0015] [8] (a) preparing a mixture by mixing a coating liquid, a carbon material, and positive electrode active material particles; and (b) drying the mixture to produce composite particles; Including, the coating liquid contains a solute and a solvent, The solute contains phosphorus and at least one of a first element that is a glass network forming element and a second element that is a transition element. Method for producing composite particles.

[0016] The coating liquid and the carbon material attached to the surface of the positive electrode active material particles are dried, whereby a coating film containing the carbon material can be formed on the surface of the positive electrode active material particles, i.e., the coating film described in [1] above can be formed.

[0017] [9] (a) preparing a mixture by mixing a coating liquid and positive electrode active material particles; (b) drying the mixture to produce composite particles; and (c) subjecting the composite particles to a heat treatment; Including, the coating liquid contains a solute and a solvent, The solute contains at least one of a first element which is a glass network forming element and a second element which is a transition element, phosphorus, and an alkoxide-based compound. Method for producing composite particles.

[0018] The coating solution adhered to the surface of the positive electrode active material particles is dried, and the alkoxide compound is carbonized by heat treatment, whereby a coating film containing a carbon material can be formed on the surface of the positive electrode active material particles, i.e., the coating film described in the above [1] can be formed. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 2 is a conceptual diagram illustrating an example of a composite particle according to the present embodiment. [Figure 2] FIG. 2 is a conceptual diagram showing another example of a composite particle according to the present embodiment. [Figure 3] FIG. 1 is a conceptual diagram showing an example of a conventional composite particle. [Figure 4] FIG. 1 is a conceptual diagram showing an all-solid-state battery according to an embodiment of the present invention. [Figure 5] 1 is a schematic flowchart of a method for producing composite particles in the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, an embodiment of the present disclosure (hereinafter may be abbreviated as "the present embodiment") and an example of the present disclosure (hereinafter may be abbreviated as "the present example") will be described. However, the present embodiment and the example do not limit the technical scope of the present disclosure.

[0021] In this specification, elements expressed in the singular include the plural unless otherwise specified. For example, a "particle" can mean not only "one particle" but also "an aggregate of particles (powder, powder, particle group)."

[0022] When a compound is expressed by a stoichiometric formula (e.g., "LiCoO2"), the stoichiometric formula is merely a representative example of the compound. The compound may have a non-stoichiometric composition. For example, when lithium cobalt oxide is expressed as "LiCoO2," unless otherwise specified, the lithium cobalt oxide is not limited to a composition ratio of "Li / Co / O=1 / 1 / 2" and may contain Li, Co, and O in any composition ratio. Furthermore, doping or substitution with trace elements may be permitted.

[0023] <Composite particles> 1, composite particle 5 includes positive electrode active material particle 1 and coating film 2. Composite particle 5 can be called, for example, a "coated positive electrode active material" or the like.

[0024] The composite particles 5 may form, for example, an aggregate. That is, one composite particle 5 may contain 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.

[0025] In this specification, "D50" refers to the particle size at which the cumulative frequency from the smaller particle size side reaches 50% in a volume-based particle size distribution. D50 can be measured by a laser diffraction method.

[0026] <Coating film> The coating film 2 covers at least a part of the surface of the positive electrode active material particle 1. The coating film 2 is a shell of the composite particle 5. The coating film 2 contains a phosphorus compound and a carbon material 31 .

[0027] (phosphorus compounds) The phosphorus compound contains at least one of a first element (E1) and a second element (E2), and P. In this specification, the first element may be abbreviated as "E1", and the second element may be abbreviated as "E2".

[0028] The first element (E1) is an element with glass-forming ability (glass network forming element), that is, an element that can form an oxide glass with a network structure by bonding with O. The addition of E1 is expected to produce a mixed anion effect.

[0029] E1 is, for example, at least one 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 an oxide glass by itself. E1 may also form a complex oxide glass together with P.

[0030] The second element (E2) is a transition element. A "transition element" is an element in Groups 3 to 11 of the periodic table.

[0031] E2 has a larger ionic radius than P. E2 can inhibit the crystallization of the phosphorus compound. E2 is, for example, at least one element selected from the group consisting of first transition elements (3d transition elements), second transition elements (4d transition elements), third transition elements (5d, 4f transition elements), and fourth transition elements. E2 is, for example, at least one element selected from the group consisting of second transition elements and third transition elements. The third transition elements include lanthanoids. That is, E2 may, for example, include a lanthanoid.

[0032] 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.

[0033] The ratio of P contained in the phosphorus compound (or composite particle) is, for example, 1 to 10 mass % with respect to the total amount of the composite particle 5.

[0034] The phosphorus compound may further contain, for example, Li, O, carbon (C), and the like.

[0035] The phosphorus compound may contain, for example, a phosphate skeleton. That is, the phosphorus compound may be a phosphate compound. When the phosphorus compound contains a phosphate skeleton, for example, when the composite particle 5 is analyzed by TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry), it is found that PO2 - or PO3 - Fragments such as:

[0036] In the coating film (or phosphorus compound), the composition ratio of Li is "C Li / (C P +C E1 +C E2 ) is 2.5 or less (see formula (1) above). When the Li composition ratio is 2.5 or less and at least one of E1 and E2 is present, the battery resistance can be significantly reduced.

[0037] The Li composition ratio may be, for example, 2.38 or less, 2.26 or less, 2.18 or less, 2.03 or less, 1.89 or less, 1.73 or less, 1.42 or less, or 1.1 or less. The Li composition ratio may be, for example, 0.1 or more, 0.5 or more, or 1.05 or more. The Li composition ratio may be, for example, 1.05 to 2.38. 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 the phosphorus compound) may not contain any Li at all.

[0038] (XPS measurement of Li composition ratio) The composition ratio of Li on the surface of the composite particle, C Li / (C P +C E1 +C E2) can be measured by XPS in the following procedure. An XPS instrument is prepared. For example, an XPS instrument manufactured by ULVAC-PHI, Inc., product name PHI X-tool (or equivalent) may be used. A sample powder consisting of composite particles is placed in the XPS instrument. Narrow scan analysis is performed with a pass energy of 224 eV. The measurement data is processed by analysis software. For example, an analysis software manufactured by ULVAC-PHI, Inc., product name MulTiPak (or equivalent) may be used. The peak area (integral value) of the Li1s spectrum is used to determine the elemental concentration of Li (C Li ) The peak area of the P2p spectrum is converted into the elemental concentration of P (C P For E1 and E2, the appropriate spectrum is selected depending on the type. For example, in the case of B, the peak area of the B1s spectrum is converted to the element concentration of B (C E1 For example, in the case of La, the peak area of the La3d5 spectrum is converted into the element concentration of La (C E2 ) is converted to C P , C E1 and C E2 In total 、 C Li The Li composition ratio on the particle surface is determined by subtracting

[0039] For example, if the coating film contains multiple types of E1, E1 indicates the total element concentration of multiple species of E1, E2 and C E2 The same is true for .

[0040] XPS composition ratio "C Li / (C P +C E1 +C E2 ) 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 in XPS, the Li composition ratio measured by XPS may be higher than the Li composition ratio in the actual coating film.

[0041] The chemical composition of the phosphorus compound may be represented by, for example, the following formula (2): Li w E 1 x E 2 y PO z …(2) In the above formula (2), E 1 indicates E1. E 2 represents E2. w, x, y, and z are arbitrary numbers. w, x, y, and z can be identified, for example, by analyzing the coating film 2 portion of 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 described below (film thickness measurement).

[0042] Specific examples of phosphorus compounds include Li3PO4 (LPO), BPO4 (BPO), and POx (PO 6、 At least one selected from the group consisting of P2O5, etc.

[0043] In the composite particle 5, the coverage of the coating film 2 on the surface of the positive electrode active material particle 1 may be, for example, 70% or more. A coverage of 70% or more is expected to reduce battery resistance. The coverage may be, for example, 85% or more, 88% or more, 89% or more, 90% or more, 94% or more, 95% or more, or 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%.

[0044] (XPS measurement of coverage) The coverage is also measured by XPS. The measurement data obtained is the same as above (XPS measurement of Li composition ratio), except that the pass energy is set to 120 eV. By analyzing the measurement data, the ratio of each element (element concentration) is calculated from the peak area (intensity value) of C1s, O1s, P1s, M2p3, etc. The coverage is calculated using the following formula (3). θ=(P+E1+E2) / (P+E1+E2+M)×100…(3) In the above formula (3), θ represents the coverage (%), and P, E1, E2, and M represent the ratio of each element.

[0045] "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 element or multiple elements. M may be, for example, at least one element selected from the group consisting of nickel (Ni), cobalt (Co), manganese (Mn), and aluminum (Al). When M contains multiple elements, the total composition ratio of each element may be 1.

[0046] For example, the positive electrode active material particles are "LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2”, the above formula (3) can be transformed into the following formula (3′): θ=(P+E1+E2) / (P+E1+E2+Ni+Co+Mn)×100 …(3') In the above formula (3'), Ni represents the element ratio of nickel determined from the peak area of Ni2p3, Co represents the element ratio of cobalt determined from the peak area of Co2p3, and Mn represents the element ratio of manganese determined from the peak area of Mn2p3.

[0047] The coating film 2 may have a thickness of, for example, 5 to 100 nm, 5 to 50 nm, 10 to 30 nm, or 20 to 30 nm.

[0048] (film thickness measurement) The film thickness (thickness of the coating film) can be measured by the following procedure: A sample is prepared by embedding composite particles in a resin material. The sample is cross-sectioned using an ion milling device. For example, an ion milling device manufactured by Hitachi High-Technologies Corporation, product name Arblade (registered trademark) 5000 (or an equivalent product) may be used. The cross-section of the sample is observed using an SEM (Scanning Electron Microscope). For example, an SEM device manufactured by Hitachi High-Technologies Corporation, product name SU8030 (or an equivalent product) may be used. The film thickness is measured in 20 fields of view for each of 10 composite particles. The arithmetic average of the film thicknesses at a total of 200 locations is considered to be the film thickness.

[0049] In addition, by using composite particles containing the above-mentioned phosphorus compound and having a phosphorus-based coating film with low resistance in a positive electrode and a battery, it is expected that durability under high voltage and high output can both be achieved.

[0050] (carbon materials) The carbon material is not particularly limited as long as it contains carbon elements. The shape of the carbon material is not particularly limited and may be, for example, particles, aggregates, fibers, etc. The carbon material 31 may contain, for example, at least one selected from the group consisting of rubber-based carbon, carbon black, and carbon nanofibers.

[0051] The carbon material is preferably a material that is unlikely to cause decomposition of the solid electrolyte when it comes into contact with the solid electrolyte.

[0052] Such a carbon material is preferably one that has a decomposition current of 0.05 mA or less when mixed with a solid electrolyte and subjected to CV measurement. This decomposition current can be confirmed by the following method. 50 mg of powder containing a solid electrolyte and carbon material in a mass ratio of 9:1 was placed into the mold of a press and pressed at 2.0 tons for 120 seconds to obtain a layered product. This layered product was then laminated with SUS foil and pressed at 2.0 tons for 120 seconds. Li foil and SUS foil were then laminated in this order on the side of the layered product opposite the SUS foil, and pressed at 1 ton for 30 seconds. The macor was restrained at 6 N·m. In this way, a "SUS foil / carbon material and solid electrolyte / Li / SUS foil" laminate was produced, and CV measurements were performed on this laminate (sweep rate: 0.1 mV / s, voltage range: 2.5 V-5 V (Li / Li + )) can measure the decomposition current.

[0053] The carbon material contained in the coating film may be, for example, randomly shaped carbon material 32 (see FIG. 2) produced by heat treatment (baking) of an alkoxide compound contained in the coating liquid described below.

[0054] It is preferable that at least some of the multiple carbon materials 31, 32 (multiple carbon particles, etc.) contained in the coating film 2 (i) each carbon material (carbon particle, etc.) penetrates the coating film independently, or (ii) an aggregate of multiple carbon materials (carbon particles, etc.) that are in contact with each other penetrates the coating film. In this case, it is believed that the formation of a conductive path by the carbon material more reliably improves the electronic conductivity of the phosphorus-based coating film. Note that from the viewpoint of improving electronic conductivity, the above (i) is more preferable.

[0055] As shown in FIG. 2, when randomly shaped carbon materials 32 are present in the coating film 2, it is thought that carbon materials of a size that can penetrate the coating film 2 alone, such as carbon material 32a (see (i) above), are more likely to exist.

[0056] The carbon content in the coating film is, for example, 1 to 20%. The carbon content in the coating film can be measured by XPS analysis of the coating film 2 portion of the cross section of the composite particle 5. The cross section sample is prepared according to the same procedure as described above (film thickness measurement).

[0057] 《Cathode active material particles》 The positive electrode active material particle 1 is the core of the composite particle 5. The positive electrode active material particle 1 may be a secondary particle (aggregate of primary particles). The positive electrode active material particle 1 (secondary particle) may have a D50 of, for example, 1 to 50 μm, 1 to 20 μm, or 5 to 15 μm. The primary particle may have a maximum Feret diameter of, for example, 0.1 to 3 μm.

[0058] The positive electrode active material particles 1 may contain any component. The positive electrode active material particles 1 may contain, for example, at least one selected from the group consisting of LiCoO2, LiNiO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and LiFePO4. For example, "(NiCoMn)" in "Li(NiCoMn)O2" indicates that the sum of the composition ratios in parentheses is 1. As long as the sum is 1, the amount of each component is arbitrary. Li(NiCoMn)O2 may contain, for example, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3 )O2, Li(Ni 0.5 Co 0.2 Mn 0.3 )O2, Li(Ni 0.8 Co 0.1 Mn 0.1 ) O2, etc.

[0059] <All-solid-state battery> FIG. 4 is a conceptual diagram showing an all-solid-state battery according to this embodiment. The all-solid-state battery 100 may include, for example, an exterior body (not shown). The exterior body may be, for example, a pouch made of a metal foil laminate film. The exterior body may house a power generating element 50. The power generating element 50 includes a positive electrode 10, a separator layer 30, and a negative electrode 20. That is, the all-solid-state battery 100 includes the positive electrode 10, the separator layer 30, and the negative electrode 20.

[0060] 《Positive electrode》 The positive electrode 10 is layered. The positive electrode 10 may include, for example, a positive electrode active material layer and a positive electrode current collector. For example, the positive electrode active material layer may be formed by applying a positive electrode mixture to the surface of the positive electrode current collector. The positive electrode current collector may include, for example, an Al foil. The positive electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0061] The positive electrode active material layer may have a thickness of, for example, 10 to 200 μm. The positive electrode active material layer is in close contact with the separator layer 30. The positive electrode active material layer includes a positive electrode mixture. The positive electrode mixture includes composite particles (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.

[0062] The sulfide solid electrolyte can form an ion conduction path in the positive electrode active material layer. The amount of the sulfide solid electrolyte may be, for example, 1 to 200 parts by volume, 50 to 150 parts by volume, or 50 to 100 parts by volume per 100 parts by volume of the composite particles (positive electrode active material). The sulfide solid electrolyte contains S. 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 include, for example, at least one selected from the group consisting of LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-P2S5, and Li3PS4.

[0063] 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.

[0064] The positive electrode active material layer may further contain, for example, a conductive material. The conductive material can form an electron conduction path within the positive electrode active material layer. The amount of the conductive material may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the composite particles (positive electrode active material). The conductive material may contain any component. The conductive material may contain, for example, at least one selected from the group consisting of carbon black, vapor grown carbon fiber (VGCF), carbon nanotubes (CNT), and graphene flakes.

[0065] The positive electrode active material layer may further contain, for example, a binder. The amount of binder may be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the composite particles (positive electrode active material). The binder may contain any component. The binder may contain, for example, at least one selected from the group consisting of polyvinylidene fluoride (PVdF), vinylidene fluoride-hexafluoropropylene copolymer (PVdF-HFP), styrene-butadiene rubber (SBR), and polytetrafluoroethylene (PTFE).

[0066] 《Negative electrode》 The negative electrode 20 is layered. The negative electrode 20 may include, for example, a negative electrode active material layer and a negative electrode current collector. For example, the negative electrode active material layer may be formed by applying a negative electrode composite material to the surface of the negative electrode current collector. The negative electrode current collector may include, for example, Cu foil, Ni foil, etc. The negative electrode current collector may have a thickness of, for example, 5 to 50 μm.

[0067] The negative electrode active material layer may have a thickness of, for example, 10 to 200 μm. The negative electrode active material layer is in close contact with the separator layer 30. The negative electrode active material layer includes a negative electrode composite. The negative electrode composite includes negative electrode active material particles and a sulfide solid electrolyte. The negative electrode composite may further include a conductive material and a binder. The sulfide solid electrolytes in the negative electrode composite and the positive electrode composite may be the same or different. The negative electrode active material particles may include any component. The negative electrode active material particles may include, for example, graphite, Si, SiO x (0 <x<2)、およびLi4Ti5O 12 It may contain at least one selected from the group consisting of:

[0068] <Separator layer> The separator layer 30 is interposed between the positive electrode 10 and the negative electrode 20. The separator layer 30 separates the positive electrode 10 from the negative electrode 20. The separator layer 30 includes a sulfide solid electrolyte. The separator layer 30 may further include a binder. The sulfide solid electrolytes in the separator layer 30 and the positive electrode composite may be the same or different. The sulfide solid electrolytes in the separator layer 30 and the negative electrode composite may be the same or different.

[0069] <Method of manufacturing composite particles> 5 is a schematic flowchart of a method for producing composite particles according to this embodiment. Hereinafter, "a method for producing composite particles according to this embodiment" may be abbreviated as "the present production method." The present production method includes "(a) preparation of a mixture" and "(b) production of composite particles." The present production method may further include, for example, "(c) heat treatment."

[0070] (a) Preparation of the mixture This manufacturing method includes preparing a mixture by mixing a coating liquid, a carbon material, and positive electrode active material particles (applying the coating liquid to the surfaces of the positive electrode active material particles). Note that the carbon material and the positive electrode active material may be mixed in advance, and then the above mixing may be carried out. Details of the positive electrode active material particles and the carbon material are as described above.

[0071] The mixture may be, for example, a suspension or a wet powder, as long as the coating liquid adheres to the surfaces 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 a 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, granulating device, etc. may be used.

[0072] 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 a first element (E1) and a second element (E2), and phosphorus (P), as raw materials for the coating film. The coating liquid may further contain, for example, a suspended solid (insoluble component), a precipitate, etc.

[0073] The total amount of solutes may be, for example, 0.1 to 20 parts by mass, 1 to 15 parts by mass, or 5 to 10 parts by mass relative to 100 parts by mass of the solvent.

[0074] The solvent may contain any component as long as the solute dissolves in the solvent. The solvent may contain, for example, water, alcohol, etc. The solvent may contain, for example, ion-exchanged water, etc.

[0075] Details of E1 and E2 are as described above. The solute may include, for example, at least one selected from the group consisting of an oxoacid of E1 and an oxide of E1. The solute may include, 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, etc. 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.

[0076] The solute may include, for example, a phosphate compound. This allows the solute to contain P. The phosphate compound may be, for example, phosphoric anhydride (PO), orthophosphoric acid, pyrophosphoric acid, or metaphosphoric acid (HPO) n ] and polyphosphoric acid. The phosphate compound may be, for example, at least one selected from the group consisting of metaphosphoric acid and polyphosphoric acid. Metaphosphoric acid and polyphosphoric acid may have longer molecular chains than other phosphate compounds. It is believed that the long molecular chains of the phosphate compound make it easier to produce a coating film with continuity. The coating film with continuity is expected to, for example, improve the coverage rate.

[0077] In the coating liquid, for example, the relationship of the following formula (5) may be satisfied. 0.040<(n E1 +n E2 ) / n P ≦1.51 …(5) In the above formula (5), n P indicates the molar concentration of P in the coating solution. 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.

[0078] "(n E1 +n E2 ) / n P " indicates the molar ratio (ratio of amounts of substances) 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 not more than 1.51, a reduction in battery resistance is expected.

[0079] The molar ratio may be, for example, 1.03 or less, 0.67 or less, 0.48 or less, 0.098 or less, or 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.

[0080] (ICP measurement) The molar ratio (n E1 +n E2 ) / n P " is measured using the following procedure. 100 mL of sample solution is prepared by diluting 0.01 g of coating solution with pure water. Aqueous solutions of P, E1, and E2 (1000 ppm, 10000 ppm) are prepared. Standard solutions are prepared by diluting 0.01 g of the aqueous solutions with pure water. An ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) device is prepared. The emission intensity of the standard solution is measured using the ICP-AES device. A calibration curve is created from the emission intensity of the standard solution. The emission intensity of the sample solution (diluted solution of coating solution) is measured using the ICP-AES device. The mass concentrations of P, E1, and E2 in the coating solution are determined from the emission intensity of the sample solution and the calibration curve. The mass concentrations of P, E1, and E2 are then converted to molar concentrations. The molar concentration of E1 (n E1 ) and the molar concentration of E2 (n E2 ) is the molar concentration of P (n P ) to obtain the molar ratio.

[0081] The solute may further contain Li, for example, a lithium compound such as lithium hydroxide, lithium carbonate, or lithium nitrate.

[0082] The molar ratio of Li to the sum of P, E1, and E2 is "n Li / (n P +n E1 +n E2)" may be, for example, less than 1.1, 1.0 or less, 0.45 or less, 0.1 or less, or 0.05 or less. Li / (n P +n E1 +n E2 )" may be zero, for example. That is, the solute may not contain Li. n Li may be below the detection limit in ICP measurement. Li / (n P +n E1 +n E2 ) is expected to be smaller, the Li composition ratio on the particle surface is expected to be lower.

[0083] (b) Production of Composite Particles The present production method includes drying the mixture to produce composite particles. The coating solution adhered to the surfaces of the positive electrode active material particles dries to form a coating film, thereby producing the composite particles. Any drying method can be used in the present production method.

[0084] When the mixture is a suspension containing positive electrode active material particles, a carbon material, and a coating liquid, the composite particles may be formed, for example, by a spray-drying method. That is, the suspension containing the positive electrode active material particles and the coating liquid is sprayed from a nozzle, and the sprayed droplets are dried, for example, by hot air, to form the composite particles. The use of the spray-drying method is expected to improve, for example, the coverage rate.

[0085] 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.

[0086] For example, the composite particles may be produced by a tumbling fluidized bed coating apparatus, in which "(a) preparation of a mixture" (adhesion of a coating liquid to the surfaces of positive electrode active material particles) and "(b) production of composite particles" can be carried out simultaneously.

[0087] (c) Heat Treatment The present production method may include subjecting the composite particles to a heat treatment. The heat treatment may fix the coating film. The heat treatment may also be referred to as "baking." Any heat treatment device may be used in the present production method. The heat treatment temperature may be, for example, 150 to 300°C. The heat treatment time may be, for example, 1 to 10 hours. For example, the heat treatment may be performed in air or in an inert atmosphere.

[0088] <Modification of the method for producing composite particles> In this embodiment, the following manufacturing method can be adopted as a modification of the above-described method for manufacturing composite particles.

[0089] (a) preparing a mixture by mixing a coating liquid with positive electrode active material particles; (b) drying the mixture to produce composite particles; and (c) subjecting the composite particles to a heat treatment; Including, the coating liquid contains a solute and a solvent, The solute contains at least one of a first element which is a glass network forming element and a second element which is a transition element, phosphorus, and an alkoxide-based compound. Method for producing composite particles.

[0090] The coating solution attached to the surface of the positive electrode active material particles is dried, and the alkoxide compound is carbonized by heat treatment (baking), so that a coating film containing a carbon material can be formed on the surface of the positive electrode active material particles. That is, the above-mentioned coating film can be formed.

[0091] The carbon material contained in the coating film formed in this manner has a random shape, and is therefore expected to be easily contained in a size that allows the carbon material to penetrate the coating film alone.

[0092] An alkoxide compound is a compound containing an alkoxide group (-OR). The alkoxide compound is not particularly limited, but examples thereof include alkoxide compounds containing phosphorus, which serves as a phosphorus supply source. As alkoxide compounds containing phosphorus, triethyl phosphate [OP(OC2H5)3], trimethyl phosphate [P(OCH3)3], etc. can be suitably used. An alkoxide compound not containing phosphorus may also be used. As an alkoxide compound not containing phosphorus, for example, boric acid alkoxide [B(OR)3] can be used. As boric acid alkoxides, R preferably has 3 or more carbon atoms, for example, tributyl borate [B(O(CH2)CH3)3] can be used. Lithium ethoxide, etc. can also be used. [Example]

[0093] Example 1 [Preparation of Composite Particles] 870.4 parts by mass of hydrogen peroxide solution (30% by mass concentration) were added to the container. Next, 987.4 parts by mass of ion-exchanged water and 44.2 parts by mass of phosphoric acid (P2O5·3H2O) were added to the container. Next, 87.9 parts by mass of ammonia water (28% by mass concentration) were 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 P. Furthermore, 0.1 parts by mass of lithium hydroxide·monohydrate (LiOH·H2O) was dissolved in the solution to prepare a coating solution.

[0094] As the positive electrode active material particles, Li(Ni 1 / 3 Co 1 / 3 Mn 1 / 3)O2 was prepared. 10% by mass of carbon material (graphite powder) was added to the positive electrode active material particles, and the mixture was mixed under vacuum at 3000 rpm for 1 minute using a mixer (Mixertaro, Thinky Corporation). 50 parts by mass of the resulting mixture was dispersed in 53.7 parts by mass of the coating liquid to prepare a suspension. The suspension was spray-dried to prepare a powder of composite particles.

[0095] 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. Note that, in the composite particles of Example 1, the coating film is thought to contain Li3PO4 (LPO).

[0096] [Fabrication of all-solid-state batteries] (Preparation of positive electrode) The following materials were prepared: Sulfide solid electrolyte: Li2S-P2S5 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

[0097] A positive electrode slurry was prepared by mixing the composite particles, sulfide solid electrolyte, conductive material, binder, and dispersion medium. The mixing ratio of the composite particles to the sulfide solid electrolyte was "composite particles / sulfide solid electrolyte = 7 / 3 (volume ratio)". The amount of conductive material was 3 parts by mass for 100 parts by mass of the composite particles. The amount of binder was 0.7 parts by mass for 100 parts by mass of the composite particles. The positive electrode slurry was thoroughly stirred using an ultrasonic homogenizer (UH-50 manufactured by SMT). The positive electrode slurry was applied to the surface of the positive electrode current collector to form a coating film. The coating film was dried on a hot plate at 100°C for 30 minutes. This produced a positive electrode blank. A disk-shaped positive electrode was cut out from the positive electrode blank. The area of the positive electrode was 1 cm. 2 It was.

[0098] (Preparation of negative electrode) A sulfide solid electrolyte (Li2S-P2S5-based glass ceramic containing LiI, D50: 0.8 μm), 1 mass% of a conductive additive (VGCF), 2 mass% of a binder (SBR), and heptane were placed in the kneading vessel of a Filmix device (30-L model manufactured by Primix) and stirred at 20,000 rpm for 30 minutes. Next, the negative electrode active material (Li4Ti5O 12 The negative electrode mixture was prepared by adding the solid electrolyte (particles, D50:1 μm) and the solid electrolyte in a volume ratio of 6:4 to a kneading vessel and stirring at 15,000 rpm for 60 minutes using a Filmix device. The prepared negative electrode mixture was applied to copper foil and dried at 100 °C for 30 minutes. A negative electrode blank was thus produced. A disk-shaped negative electrode was cut out from the negative electrode blank. The area of the negative electrode was 1 cm. 2 It was.

[0099] (Preparation of separator layer) Inner diameter cross-sectional area 1cm 2 64.8 mg of sulfide solid electrolyte (Li2S-P2S5 glass ceramics containing LiI, D50: 2.5 μm) was placed in the cylindrical ceramic, smoothed, and then subjected to 1 ton / cm 2 The separator layer (solid electrolyte layer) was formed by pressing.

[0100] (Battery construction) The fabricated positive electrode was placed on one side of the solid electrolyte layer, and the fabricated negative electrode was placed on the other side of the solid electrolyte layer, and they were pressed at 6 ton / cm2 for 1 minute. Next, terminals (stainless steel rods) were inserted into the positive and negative electrodes, and they were restrained at 1 ton to fabricate an all-solid-state battery (all-solid-state lithium-ion battery).

[0101] <Example 2> In Example 2, the amount of the carbon material was changed so that the content of the carbon material in the coating film was 10 mass %. Otherwise, the composite particles and the battery of Example 2 were produced in the same manner as in Example 1.

[0102] Example 3 In Example 3, instead of directly blending a carbon material into the coating liquid, an alkoxide-based compound (lithium ethoxide, triethyl phosphate) was added to the coating liquid, and the alkoxide-based compound was carbonized in the heat treatment process to generate a carbon material in the coating film. The amount of the alkoxide-based compound added to the coating liquid was adjusted so that the content of the carbon material in the coating film was approximately 5 mass%. Specifically, 1 mmol of lithium ethoxide (manufactured by Kojundo Chemical Co., Ltd.) and 1 mmol of triethyl phosphate (manufactured by Kojundo Chemical Co., Ltd.) were mixed with 30 mL of IPA (isopropyl alcohol) to obtain a sol-gel solution. The obtained sol-gel solution was added to the same coating liquid as in Example 1. Note that no carbon material was added. Furthermore, the composite particles obtained by spray drying were heat-treated at 200°C to 450°C for 5 hours in an N2 and Ar atmosphere. Other than that, the composite particles and battery of Example 3 having a coating film with a thickness of 20 nm were prepared in the same manner as in Example 1.

[0103] <Comparative Example 1> In Comparative Example 1, no carbon material was mixed into the raw materials of the coating film. In other respects, the composite particles and the battery of Comparative Example 1 were produced in the same manner as in Example 1.

[0104] <Evaluation> [Electrical conductivity of composite particles] The composite particles of the above Examples and Comparative Examples were evaluated for electronic conductivity (electrical conductivity: electronic conductivity) using a powder resistivity measurement system (Loresta). Table 1 shows the measurement results of electrical conductivity. (1) Measure the film thickness blank of the McCall cell (or set it to zero). (2) 100 mg of weighed composite particle powder is introduced into the McCall cell. (3) The McCormack cell is tightened with a torque of 2 N to press the composite particles in the McCormack cell to obtain a layered product. The film thickness of the layered product is measured, and the resistance value of the layered product is measured with a HiTester. (4) Change the torque to 6N and 10N and repeat (3). (5) From the resistance values measured in (3) and (4) above, the resistivity is calculated, and the electrical conductivity, which is the reciprocal of the resistivity, is calculated.

[0105] [Battery DC resistance] For each of the batteries (all-solid-state batteries) of the above examples and comparative examples, the DC resistance was evaluated by the following method.

[0106] (Check initial capacity) Each battery was subjected to three cycles of constant current-constant voltage (CC-CV) charging and constant current (CC) discharging at a 1 / 3C rate. The discharge capacity at the third cycle was confirmed as the initial capacity. "C" is the unit of current rate. "1C" indicates the current rate at which the SOC (State of Charge) reaches 100% from 0% in one hour of charging.

[0107] (Measurement of DC resistance) The DC resistance was measured for the batteries whose initial capacities were confirmed. Table 1 shows the measurement results of DC resistance (ratio when the DC resistance of Comparative Example 1 is set to 1.00). The smaller the DC resistance, the higher the output characteristics (discharge rate) of the battery.

[0108] [Table 1]

[0109] The results shown in Table 1 show that 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. Furthermore, it is also shown that the batteries (all-solid-state batteries) produced using each of the composite particles of Examples 1 to 3 have lower DC resistance and higher battery output compared to the battery produced using the composite particles of Comparative Example 1.

[0110] The electrical conductivity of the composite particles was particularly high in Example 3. In Example 3, as shown in Fig. 2, the presence of randomly shaped carbon material 32 in coating film 2 and the presence of carbon material 32a that individually penetrates coating film 2 is thought to have increased the electrical conductivity of the composite particles.

[0111] The present embodiment and examples are illustrative in all respects. The present embodiment and examples are not limiting. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is also intended from the beginning that any configuration may be extracted from the present embodiment and examples and that they may be combined in any desired manner. [Explanation of symbols]

[0112] 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 generating element, 100 All-solid-state battery.

Claims

1. a positive electrode active material particle; and a coating film that covers at least a portion of the surface of the positive electrode active material particle; the coating film contains a phosphorus compound and a carbon material, The phosphorus compound is Li ３ P.O. ４ and The coating film has a thickness of 5 to 50 nm, the content of the carbon material in the coating film is 1 to 20%; The carbon material is a fired product of an alkoxide-based compound.

2. The composite particle according to claim 1 , wherein the alkoxide-based compound includes an alkoxide compound containing phosphorus.

3. 2. The composite particle according to claim 1, wherein the content of the carbon material in the coating film is 5 to 10%.

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

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

6. The positive electrode active material particles are Li(NiCoMn)O ２ The composite particle of claim 1 , comprising:

7. A method for producing the composite particles according to claim 1 or 2, (a) preparing a mixture by mixing a coating liquid with positive electrode active material particles; (b) drying the mixture to produce composite particles; and (c) subjecting the composite particles to a heat treatment; Including, the coating liquid contains a solute and a solvent, The solute contains phosphorus and an alkoxide compound. Method for producing composite particles.

8. A method for producing the composite particles according to claim 1 or 2, (a) preparing a mixture by mixing a carbon material and positive electrode active material particles; (b) preparing a suspension by dispersing the mixture in a coating liquid; (c) spray drying the suspension to produce composite particles; and (d) subjecting the composite particles to a heat treatment; Including, The coating liquid contains a solute and a solvent. Method for producing composite particles.

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