Cathode active material, all-solid-state battery, and method for manufacturing cathode active material

Abstract

To reduce a battery resistance.SOLUTION: A cathode active material contains: an active material particle; and a coating film. The coating film coates at least one part of a front surface of the active material particle. The coating film contains: oxygen; and a glass formation element. The glass formation element contains phosphorus and silicon. The cathode active material satisfies the relations of formula (1) of "CLi / CX≤2.50" and formula (2) of "0<CSi / CX". Each of CLi, CX, and CSi indicates an element concentration measured by X-ray photoelectron spectroscopy. The CLi indicates an element concentration of lithium. The CX indicates a total element concentration of the glass formation element. The CSi indicates the element concentration of silicon.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a positive electrode active material, an all-solid-state battery, and a method for manufacturing a positive electrode active material. [Background technology]

[0002] Japanese Patent Application Laid-Open No. 2012-099323 (Patent Document 1) discloses a coating layer having a polyanion structural portion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-099323 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. In the positive electrode, active material particles have a high potential. If the sulfide solid electrolyte comes into direct contact with the active material particles in the positive electrode, 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 active material particles. The coating film prevents direct contact between the active material particles and the sulfide solid electrolyte, thereby reducing the deterioration of the sulfide solid electrolyte. However, the coating film is also a resistive component. Even if the deterioration of the sulfide solid electrolyte can be reduced, the high resistance of the coating film may prevent the desired battery resistance from being achieved.

[0005] An object of the present disclosure is to reduce battery resistance. [Means for solving the problem]

[0006] 1. The positive electrode active material includes active material particles and a coating film. The coating film covers at least a portion of the surface of the active material particles. The coating film includes oxygen and a glass-forming element. The glass-forming element includes phosphorus and silicon. The positive electrode active material satisfies the relationships of the following formulas (1) and (2). C Li / C X ≦2.50 …(1) 0 <C Si / C X …(2) In the above formulas (1) and (2), C Li , C X and C Si indicates the element concentration measured by X-ray photoelectron spectroscopy. Li indicates the elemental concentration of lithium. X indicates the total concentration of glass-forming elements. Si indicates the elemental concentration of silicon.

[0007] Patent Document 1 proposes a coating layer containing a polyanion structure. The coating layer in Patent Document 1 corresponds to the coating film in the present disclosure. The polyanion structure contains Li3PO4-Li4SiO4. In the examples of Patent Document 1, the molar ratio in the coating film is "Li / P / Si=7 / 1 / 1." The Li contained in the coating film is thought to be a carrier for ion conduction. According to conventional knowledge, the higher the Li composition ratio, the more the battery resistance is expected to decrease.

[0008] However, according to the new findings of the present disclosure, the battery resistance can be significantly reduced by reducing the Li composition ratio to a specific value or less. The left side of the above formula (1) represents the Li composition ratio. C LiThe element concentrations such as these are measured by X-ray photoelectron spectroscopy (XPS). XPS acquires information on the outermost surface of the object to be measured (positive electrode active material). In other words, the Li composition ratio measured by XPS is considered to represent the Li composition ratio in the coating film. As shown in the above formula (1), a Li composition ratio of 2.5 or less is expected to reduce battery resistance. The Li composition ratio in Patent Document 1 is considered to be about 3.5.

[0009] Phosphorus (P) is a glass-forming element. That is, P can form an oxide glass (glass network) together with oxygen (O). Silicon (Si) is also a glass-forming element. The coexistence of two or more glass-forming elements can form a complex glass network. The glass network is formed by two or more anions (PO4 3- , SiO4 4- The coexistence of two or more anions is expected to produce a mixed anion effect, which is expected to promote ion conduction and thus reduce battery resistance.

[0010] 2. The positive electrode active material described in the above item "1" may include, for example, the following configuration. The glass-forming elements further include boron. The positive electrode active material further satisfies the relationship of the following formula (3). C Si / C X <0.10 …(3)

[0011] Boron (B) is also a glass-forming element. The combination of P and B is expected to promote the mixed anion effect. Si may be present in trace amounts compared to P and B. For example, P and B may form the framework of the glass network, with Si being partially introduced. The introduction of a trace amount of Si into the glass network is expected to promote ionic conduction.

[0012] 3. The all-solid-state battery includes a positive electrode and a negative electrode. The positive electrode includes the positive electrode active material described in "1" or "2" above and a sulfide solid electrolyte.

[0013] 4. The method for producing a positive electrode active material includes the following steps (a) to (c): (a) Prepare the coating solution. (b) A mixture is prepared by mixing the coating liquid with active material particles. (c) The mixture is dried to produce a positive electrode active material. The coating liquid contains a glass-forming material, which includes a condensed phosphate compound and silicon, and the condensed phosphate compound contains 83% or more by mass of diphosphorus pentoxide.

[0014] The mass fraction of diphosphorus pentoxide (P2O5) in a condensed phosphate compound (hereinafter referred to as "P2O5 concentration") is an indicator of the degree of polymerization. It is believed that the higher the P2O5 concentration, the higher the degree of polymerization of the condensed phosphate compound. A P2O5 concentration of 83% or higher is expected to reduce battery resistance. This is thought to be because the continuity of the glass network in the coating film can be improved.

[0015] 5. The method for producing a positive electrode active material according to the above item "4" may include, for example, the following configuration: (a) above includes the following (a1) and (a2): (a1) A condensed phosphate compound is synthesized by a dehydration condensation reaction of a phosphate compound. (a2) Silicon is added to the reaction system of the dehydration condensation reaction.

[0016] By adding Si to the dehydration condensation reaction system, Si can be introduced into the phosphate network (condensed phosphate compound). By incorporating Si into the phosphate network in advance, it is expected that the ionic conductivity will be improved.

[0017] 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. The present embodiment and the example are illustrative in all respects. The present embodiment and the example are non-restrictive. The technical scope of the present disclosure encompasses all modifications within the meaning and scope equivalent to the claims. For example, it is originally intended that any configuration may be extracted from the present embodiment and the example and that they may be arbitrarily combined. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a conceptual diagram of the positive electrode active material in this embodiment. [Figure 2] FIG. 2 is a schematic flowchart of the method for producing a positive electrode active material in this embodiment. [Figure 3] FIG. 3 is a conceptual diagram of the all-solid-state battery according to this embodiment. [Figure 4] FIG. 4 is a table showing the experimental results. [Figure 5] FIG. 5 is a graph showing the relationship between the Si composition ratio and the battery resistance. [Figure 6] FIG. 6 is a graph showing the relationship between P2O5 concentration and battery resistance. DETAILED DESCRIPTION OF THE INVENTION

[0019] <Terminology> "Element concentration (C Li , C X , C Si) indicates a value measured by the following procedure. For example, an XPS device manufactured by ULVAC-PHI (product name "PHI X-tool") or an equivalent device is prepared. The positive electrode active material (powder) is placed in the 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 manufactured by ULVAC-PHI (product name "MulTiPak") or an equivalent device 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 ) The peak area of ​​the B1s spectrum is converted into the element concentration of B (C B The peak area of ​​the Si2p spectrum is converted into the elemental concentration of Si (C Si ) is converted to C X is the total element concentration of the glass-forming elements. For example, if three glass-forming elements, P, B, and Si, are detected, the formula "C X =C P +C B +C Si "By C X is obtained.

[0020] A "glass-forming element" can form an oxide glass having a network structure by bonding with O. The glass-forming element may include, for example, P, Si, B, nitrogen (N), sulfur (S), germanium (Ge), and hydrogen (H). A "glass-forming material" refers to a material containing a glass-forming element. The glass-forming material may be a simple substance, a compound, or a mixture.

[0021] "P2O5 concentration" refers to a value measured using the following procedure: 0.1 mL of sample (condensed phosphate compound) and 0.9 mL of distilled water are placed in a plastic cuvette. The absorbance at a wavelength of 360 nm is measured. The P2O5 concentration of the sample is determined from the relationship between absorbance and P2O5 concentration (calibration curve).

[0022] Unless otherwise specified, numerical ranges such as "m to n%" include the upper and lower limits. That is, "m to n%" indicates a numerical range of "m% or more and n% or less." Furthermore, "m% or more and n% or less" includes "more than m% but less than n%."

[0023] Unless otherwise specified, the order of execution of multiple steps, actions, operations, etc. included in various methods is not limited to the order described. For example, multiple steps may proceed simultaneously. For example, multiple steps may occur one after the other.

[0024] <Cathode active material> The positive electrode active material may consist of one particle. The positive electrode active material may contain two or more particles. That is, the positive electrode active material may be a powder (an aggregate of particles). The positive electrode active material may have a D50 of, for example, 1 to 30 μm, 10 to 20 μm, or 1 to 10 μm. "D50" refers to the particle size at which the cumulative distribution is 50% in the volume-based particle size distribution (cumulative distribution). The particle size distribution can be measured by a laser diffraction method.

[0025] FIG. 1 is a conceptual diagram of a positive electrode active material according to this embodiment. The positive electrode active material 5 includes composite particles. The composite particles have a core-shell structure. That is, the positive electrode active material 5 includes active material particles 1 and a coating film 2. The positive electrode active material 5 can be referred to as, for example, a "coated active material."

[0026] <Coating film> The coating film 2 is a shell of the positive electrode active material 5. The coating film 2 covers at least a portion of the surface of the active material particle 1. The coverage may be, for example, 94% or more. The coverage may be, for example, 95% or more, 96% or more, or 97% or more. The coverage may be, for example, 100% or less, 97% or less, 96% or less, or 95% or less.

[0027] The "coverage" is measured by XPS. The element concentrations of various elements on the surface of the positive electrode active material are measured by XPS. The coverage is calculated by the following formula (4). θ=CX / (C X +C Y ) …(4) In the above formula (4), θ represents the coverage. The coverage is expressed as a percentage (%). C X represents the total element concentration of glass-forming elements. For example, when the coating film 2 contains P, B, and Si, the formula "C X =C P +C B +C Si " by C X is obtained. C Y indicates the total element concentration of the constituent elements (excluding Li and O) of the active material particle 1. For example, if the active material particle 1 is "LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 When the compound has the composition "C Y =C Co +C Ni +C Mn " by C Y For example, if the active material particles are "LiNi 0.8 Co 0.15 Al 0.05 When the compound has the composition "C Y =C Co +C Ni +C Al " by C Y is obtained.

[0028] The thickness of the coating film 2 may be, for example, 5 to 100 nm, 5 to 50 nm, 10 to 30 nm, or 20 to 30 nm. The thickness of the coating film 2 can be measured, for example, by observing the cross section of the composite particle. The cross section observation can be performed, for example, using a scanning electron microscope (SEM).

[0029] The coating film 2 contains O and a glass-forming element (X). The glass-forming element includes P and Si. In addition to P and Si, the glass-forming element may further include, for example, at least one element selected from the group consisting of B, N, S, Ge, and H. The glass-forming element may include, for example, P, Si, and B. The coating film 2 may include, for example, a phosphate skeleton, a silicic acid skeleton, a boric acid skeleton, or the like. For example, when the TOF-SIMS (Time-of-Flight Secondary Ion Mass Spectrometry) spectrum of the positive electrode active material 5 shows PO2 - , PO3 - , SiO3 - , SiO4 - , Si2O5 - , BO2 - , BO3 - It may also include fragment peaks derived from the like.

[0030] The coating film 2 may contain Li. In this embodiment, the relationship of the following formula (1) is satisfied. C Li / C X ≦2.50 …(1) By satisfying the relationship of the above formula (1), a reduction in battery resistance is expected. Two or more Li sources are conceivable in the coating film 2. For example, the coating film 2 may contain Li derived from a Li compound contained in the coating liquid. For example, the coating film 2 may contain Li that has diffused from the active material particles 1 during the formation of the coating film 2.

[0031] Li composition ratio (C Li / C X ) may be, for example, 2.46 or less, 2.45 or less, 2.42 or less, 2.37 or less, or 1.40 or less. The Li composition ratio may be, for example, 0.1 or more, 0.5 or more, 1.0 or more, 1.40 or more, or 2.00 or more.

[0032] As long as the relationship of the following formula (2) is satisfied, the Si composition ratio is arbitrary. 0 <CSi / C X …(2)

[0033] For example, the relationship of the following formula (3) may be satisfied. C Si / C X <0.10 …(3)

[0034] Si composition ratio (C Si / C X ) may be, for example, 0.01 or more, 0.02 or more, 0.03 or more, 0.04 or more, 0.05 or more, or 0.06 or more. The Si composition ratio may be, for example, 0.09 or less, 0.08 or less, 0.07 or less, or 0.06 or less.

[0035] When the coating film 2 contains B, the quantitative relationship between P and B is arbitrary. For example, P / C B =99 / 1~1 / 99", "C P / C B =9 / 1~1 / 9" or "C P / C B = 7 / 3 to 3 / 7" relationship may be satisfied. For example, "1 ≤ C P / C B " or "2≦C P / C B " may be satisfied.

[0036] <Active material particles> The active material particle 1 is the core of the positive electrode active material 5. The active material particle 1 may have a D50 of, for example, 1 to 30 μm, 10 to 20 μm, or 1 to 10 μm. The active material particle 1 can reversibly store Li ions. The active material particle 1 may have any crystal structure. The active material particle 1 may include, for example, a layered rock salt structure.

[0037] The active material particles 1 may have any composition. For example, the active material particles 1 may have a composition represented by the following formula (5). Li 1-a Ni x M 1-x O2…(5) In the above formula (5), the relationship of -0.5 ≦ a ≦ 0.5 and 0 < x < 1 is satisfied. M is at least one selected from the group consisting of Co, Mn, and Al. For example, the relationship of 0.5 ≦ x < 1 or 0.6 ≦ x ≦ 0.9 may be satisfied.

[0038] A dopant may be added to the active material particles 1. The dopant may be diffused throughout the particles or may be locally distributed. For example, the dopant may be unevenly distributed on the particle surface. The dopant may be a substitutional solid solution atom or an interstitial solid solution atom. The addition amount of the dopant (molar fraction relative to the whole of the active material particles 1) may be, for example, any of 0.01 to 5%, 0.1 to 3%, or 0.1 to 1%. The dopant may contain, for example, at least one selected from the group consisting of B, C, N, halogen, Si, Na, Mg, Al, Mn, Co, Cr, Sc, Ti, V, Cu, Zn, Ga, Ge, Se, Sr, Y, Zr, Nb, Mo, In, Pb, Bi, Sb, Sn, W, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and actinoids.

[0039] <Method for manufacturing a positive electrode active material> FIG. 2 is a schematic flowchart of the method for manufacturing a positive electrode active material in the present embodiment. Hereinafter, the "method for manufacturing a positive electrode active material in the present embodiment" may be abbreviated as "the present manufacturing method". The present manufacturing method includes "(a) preparation of a coating solution", "(b) preparation of a mixture", and "(c) drying". The present manufacturing method may further include, for example, "(d) heat treatment" or the like.

[0040] <(a) Preparation of a coating solution> The present manufacturing method includes preparing a coating solution. The coating solution includes a solute and a solvent. For example, a coating solution may be formed by dissolving various materials in a solvent. The solvent may contain any component as long as the solute can be dissolved. The solvent may contain, for example, water, alcohol, or the like. The solvent may contain, for example, ion-exchanged water, methanol, ethanol, or the like.

[0041] The amount of solute to be added may be, for example, 0.1 to 20 parts by mass per 100 parts by mass of solvent. The solute includes a glass-forming material. That is, the coating liquid includes a glass-forming material. The glass-forming material includes a condensed phosphate compound and Si. The glass-forming material may further include a boric acid compound, etc. The solute may further include, for example, a Li compound, etc. For example, the coating liquid may be prepared by dissolving a condensed phosphate compound, a Si compound, a Li compound, a boric acid compound, etc. in a solvent.

[0042] The condensed phosphate compound is a P source. The condensed phosphate compound may include, for example, at least one selected from the group consisting of pyrophosphoric acid, polyphosphoric acid, metaphosphoric acid, and phosphoric anhydride. The condensed phosphate compound may be a hydrate, a salt, or the like. The condensed phosphate compound has a P2O5 concentration of 83% or more. The P2O5 concentration may be, for example, 84% or more, 85% or more, 86% or more, 87% or more, 88% or more, or 89% or more. The P2O5 concentration may be, for example, 100% or less, 95% or less, 89% or less, or 84% or less.

[0043] <(a1) Dehydration Condensation> The present production method may include synthesizing a condensed phosphoric acid compound by a dehydration condensation reaction of a phosphoric acid compound. The phosphoric acid compound (starting material) may include, for example, orthophosphoric acid. The phosphoric acid compound may be a hydrate, a salt, or the like. The P2O5 concentration of the condensed phosphoric acid compound can be adjusted by the dehydration condensation conditions. For example, the dehydration condensation reaction may proceed by heating the phosphoric acid compound. The heating temperature may be, for example, 400 to 500°C. The heating time may be, for example, 2 to 6 hours, 2 to 4 hours, or 4 to 6 hours.

[0044] <(a2)Si addition> This manufacturing method may include adding Si to the reaction system of the dehydration condensation reaction. When the dehydration condensation reaction of the phosphoric acid compound proceeds, Si can be introduced into the condensed phosphoric acid compound by adding Si. In advance, by incorporating Si into the phosphate network, an improvement in ionic conductivity is expected.

[0045] The addition method is arbitrary. For example, a crucible containing Si may be prepared. For example, a porcelain crucible may contain Si. The phosphoric acid compound is filled into the crucible. By heating the crucible, a dehydration condensation reaction of the phosphoric acid compound may occur. At the same time, Si can be added to the reaction system by eluting Si from the crucible. The Si addition amount can be adjusted by, for example, the Si content of the crucible, the heating temperature, the heating time, etc.

[0046] For example, a Si compound (such as SiO2, etc.) may be added to the phosphoric acid compound during heating. The Si compound may be, for example, in powder form. For example, a mixture of the phosphoric acid compound and the Si compound may be heated.

[0047] The Si addition amount can be represented by the Si concentration in the condensed phosphoric acid compound. The Si concentration (mass fraction) may be, for example, any of 600 ppm or more, 708 ppm or more, 1251 ppm or more, 1488 ppm or more, or 2353 ppm or more. The Si concentration may be, for example, any of 2353 ppm or less, 1488 ppm or less, 1251 ppm or less, or 708 ppm or less. The Si concentration can be measured by inductively coupled plasma atomic emission spectroscopy (ICP - AES).

[0048] The Li compound is a Li source. The solute may contain a Li compound as long as the Li composition ratio in the positive electrode active material 5 can be 2.5 or less. The Li compound may contain, for example, lithium hydroxide, lithium nitrate, lithium carbonate, etc. The timing of adding the Li compound is arbitrary. For example, like Si, the Li compound may be added to the reaction system of the dehydration condensation reaction of the phosphate compound.

[0049] The amount of Li added can be expressed by the Li concentration in the condensed phosphate compound. The Li concentration (mass fraction) may be, for example, 1.4% or more, 1.48% or more, 1.6% or more, 1.65% or more, or 1.7% or more. The Li concentration may be, for example, 1.7% or less, 1.65% or less, 1.6% or less, 1.48% or less, or 1.4% or less.

[0050] <Boric acid compounds> The boric acid compound is a B source. The boric acid compound may include, for example, orthoboric acid, metaboric acid, tetraboric acid, etc. The boric acid compound may be a hydrate, a salt, etc. The timing of adding the boric acid compound is arbitrary. For example, after the condensed phosphoric acid compound is dissolved in the solvent, the boric acid compound may be further dissolved.

[0051] (b) Preparation of the mixture This manufacturing method includes preparing a mixture by mixing a coating liquid with active material particles 1. The mixture may be, for example, either a suspension or a wet powder. For example, a suspension may be formed by dispersing active material particles 1 (powder) in a coating liquid. For example, a wet powder may be formed by spraying the coating liquid into powder. In this manufacturing method, any mixing device, granulating device, etc. may be used.

[0052] <(c) Drying> This manufacturing method includes drying the mixture to produce a positive electrode active material 5. The coating film 2 is formed by drying the coating liquid attached to the surfaces of the active material particles 1. Any drying method can be used in this manufacturing method. For example, the mixture can be dried using a spray dryer. That is, droplets are formed by spraying the suspension from a nozzle. The droplets contain the active material particles 1 and the coating liquid. For example, the droplets can be dried using hot air to form the positive electrode active material 5. The use of the spray drying method is expected to improve, for example, the coverage rate.

[0053] For example, the positive electrode active material 5 may be produced by a tumbling fluidized bed coating apparatus. In the tumbling fluidized bed coating apparatus, "(b) preparation of the mixture" and "(c) drying" can proceed substantially simultaneously.

[0054] <(d) Heat treatment> The present manufacturing method may include subjecting the positive electrode active material 5 to a heat treatment. The coating film 2 can be fixed by the heat treatment. The heat treatment may also be referred to as "baking." Any heat treatment device may be used in the present manufacturing method. The treatment temperature may be, for example, 150 to 300°C. The treatment time may be, for example, 1 to 10 hours. The heat treatment atmosphere may be, for example, either an air atmosphere or an inert atmosphere.

[0055] <All-solid-state battery> FIG. 3 is a conceptual diagram of an all-solid-state battery according to this embodiment. The battery 100 may have any desired shape. For example, the battery 100 may have a plate-like shape. The battery 100 includes a power generating element 50. The battery 100 may include an exterior body (not shown). The exterior body may house the power generating element 50. The exterior body may be, for example, a pouch made of an Al laminate film. The power generating element 50 includes a positive electrode 10 and a negative electrode 20. The power generating element 50 may further include a separator layer 30. The separator layer 30 is disposed between the positive electrode 10 and the negative electrode 20. The power generating element 50 may have any desired structure. For example, the power generating element 50 may have either a monopolar structure or a bipolar structure.

[0056] The positive electrode 10 may include, for example, a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector may include, for example, an Al foil. The positive electrode active material layer may be disposed on the surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material and a sulfide solid electrolyte.

[0057] The amount of sulfide solid electrolyte may be, for example, 1 to 200 parts by volume relative to 100 parts by volume of the positive electrode active material. The sulfide solid electrolyte may be, for example, glass ceramics or argyrodite. Examples of sulfide solid electrolytes include LiI-LiBr-Li3PS4, Li2S-SiS2, LiI-Li2S-SiS2, LiI-Li2S-P2S5, LiI-Li2O-Li2S-P2S5, LiI-Li2S-P2O5, LiI-Li3PO4-P2S5, Li2S-GeS2-P2S5, Li2S-P2S5, and Li 10 GeP2S 12 , Li4P2S6, Li7P3S 11 , Li3PS4, Li7PS6, and Li6PS5X (X = Cl, Br, I).

[0058] For example, "LiI-LiBr-Li3PS4" indicates 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. The mixing ratio may be specified by adding a number before each raw material. For example, "10LiI-15LiBr-75Li3PS4" indicates that the raw material mixing ratio is "LiI / LiBr / Li3PS4 = 10 / 15 / 75 (molar ratio)."

[0059] The positive electrode active material layer may further contain, for example, a conductive material and a binder. The amounts of the conductive material and the binder may each independently be, for example, 0.1 to 10 parts by mass per 100 parts by mass of the positive electrode active material. The conductive material may include, for example, acetylene black, vapor grown carbon fiber (VGCF), etc. The binder may include, for example, polyvinylidene fluoride (PVDF), styrene butadiene rubber (SBR), etc. [Example]

[0060] <Sample> The experimental results are shown in a table in Figure 4. Positive electrode active materials and all-solid-state batteries according to Nos. 1 to 7 were manufactured as follows.

[0061] No.1 A coating liquid was prepared by dissolving 10.8 parts by mass of a condensed phosphoric acid compound (manufactured by Rasa Kogyo Co., Ltd.) in 166 parts by mass of ion-exchanged water.

[0062] The procedure for producing the condensed phosphoric acid compound was as follows: A mixture was prepared by mixing orthophosphoric acid and lithium hydroxide monohydrate. The mass fraction of lithium hydroxide monohydrate in the mixture was 6%. The mixture was placed in a porcelain crucible. The crucible was stored in an electric furnace for 6 hours. The temperature of the electric furnace was set to 300°C. The condensed phosphoric acid compound was produced by the dehydration condensation reaction of orthophosphoric acid. In the dehydration condensation conditions in Figure 4, "Temperature" refers to the temperature set in the electric furnace (heating temperature), and "Time" refers to the holding time (heating time).

[0063] 50 parts by mass of active material particles (LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 A suspension was prepared by dispersing 53.7 parts by mass of ZnO (O2) in 53.7 parts by mass of the coating liquid. The suspension was supplied to a spray dryer (product name "Mini Spray Dryer B-290", manufactured by BUCHI) to produce the positive electrode active material. The inlet air temperature of the spray dryer was 200°C, and the inlet air volume was 0.45 m 3 The positive electrode active material was heat-treated in air at a temperature of 200°C.

[0064] A positive electrode slurry was prepared by mixing the positive electrode active material, sulfide solid electrolyte (10LiI-15LiBr-75Li3PS4), conductive material (VGCF), binder (SBR), and dispersion medium (heptane). The mixture ratio of the positive electrode active material and sulfide solid electrolyte was "positive electrode active material / sulfide solid electrolyte = 6 / 4 (volume ratio)." The amounts of the conductive material and binder were each 3 parts by mass per 100 parts by mass of the positive electrode active material. The positive electrode slurry was thoroughly stirred using an ultrasonic homogenizer. A coating film was formed by coating the surface of a positive electrode current collector (Al foil). 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.

[0065] A negative electrode and a separator layer were prepared. The negative electrode active material was graphite. The same type of sulfide solid electrolyte was used between the positive electrode, separator layer, and negative electrode. A stack was formed by stacking the positive electrode, separator layer, and negative electrode in this order inside a cylindrical jig. A power generating element was formed by pressing the stack. A terminal was connected to the power generating element to form an all-solid-state battery.

[0066] No.2~No.6 As shown in FIG. 4, a positive electrode active material and an all-solid-state battery were produced in the same manner as in No. 1, except that the dehydration condensation conditions were changed.

[0067] No.7 A phosphoric acid solution was prepared by dissolving 10.8 parts by mass of a condensed phosphoric acid compound in 166 parts by mass of ion-exchanged water. P / C B A coating solution was prepared by dissolving boric acid (manufactured by Nacalai Tesque, Inc.) in a phosphoric acid solution so that the ratio of the positive electrode active material to the total electrode active material was 1. A positive electrode active material and an all-solid-state battery were manufactured in the same manner as in No. 4, except for the above.

[0068] <Evaluation> The P2O5 concentration, Li concentration, and Si concentration were measured in the condensed phosphate compound. The Li composition ratio, Si composition ratio, and coverage of the positive electrode active material were measured using an XPS device. The resistance (battery resistance) of the all-solid-state battery was measured. The measurement results are shown in Figure 4.

[0069] <Result> FIG. 5 is a graph showing the relationship between the Si composition ratio and the battery resistance. In FIG. 5, the results of No. 1 to No. 6 are plotted. Si / C X ) is greater than 0, the battery resistance tends to decrease significantly.

[0070] Figure 6 is a graph showing the relationship between P2O5 concentration and battery resistance. The results of No. 1 to No. 6 are plotted in Figure 6. When the P2O5 concentration is 83% or higher, there is a tendency for battery resistance to decrease significantly. [Explanation of symbols]

[0071] 1 active material particle, 2 coating film, 5 positive electrode active material, 10 positive electrode, 20 negative electrode, 30 separator layer, 50 power generating element, 100 battery (all-solid-state battery).

Claims

1. The active material particles and the coating film are included. the coating film covers at least a part of the surface of the active material particles, the coating film contains oxygen and a glass-forming element; the glass-forming elements include phosphorus and silicon; the coating film is made of a phosphorus oxide; The phosphorus oxide forms a glass network, the glass network comprises phosphate anions and silicate anions; Formula (1) and Formula (2): C Li / C X ≦2.50 …(1) 0.03≦C Si / C X ≦0.06 …(2) Fulfilling the relationship, In the formula (1) and the formula (2), C Li , C X and C Si indicate the element concentration based on the atomic number measured by X-ray photoelectron spectroscopy, and C Li indicates the elemental concentration of lithium, and C X represents the total element concentration of the glass-forming elements, and C Si indicates the elemental concentration of silicon, Cathode active material.

2. The glass-forming elements further include boron; The positive electrode active material according to claim 1 .

3. a positive electrode and a negative electrode; The positive electrode comprises the positive electrode active material according to claim 1 or 2 and a sulfide solid electrolyte. All-solid-state battery.

4. The method for producing a positive electrode active material according to claim 1, (a) preparing a coating solution; (b) preparing a mixture by mixing the coating liquid with active material particles; and (c) drying the mixture to produce a positive electrode active material; Including, the coating liquid comprises a glass-forming material; the glass-forming material comprises a condensed phosphate compound and silicon; The condensed phosphoric acid compound contains 83% or more by mass of diphosphorus pentoxide. A method for producing a positive electrode active material.

5. The (a) is (a1) synthesizing the condensed phosphoric acid compound by a dehydration condensation reaction of a phosphoric acid compound; and, (a2) adding silicon to the reaction system of the dehydration condensation reaction; Including, The method for producing a positive electrode active material according to claim 4 .

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