Composite cathode active material

Abstract

To provide a composite positive electrode active material which can reduce the resistance increase rate of a battery.SOLUTION: The composite positive electrode active material includes: a lithium metal oxide as a positive electrode active material; and a coating layer for covering a part of the surface of the positive electrode active material. The coating layer includes a Li element, a B element, and an O element. The mole ratio Li / B of the Li element to the B element of the coating layer is in the range of 0.1 to 0.8. The intensity ratio Iα / Iβ of the intensity Iα of the peak of 720 cm-1 to the intensity Iβ of the peak of 780 cm-1 in a Raman spectrum measurement is in the range of 1.0 to 1.5. The coverage of the coating layer covering the positive electrode active material is larger than 57%.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to composite positive electrode active materials. [Background technology]

[0002] With the recent rapid spread of information-related devices and communication devices such as personal computers, video cameras, and mobile phones, the development of batteries to be used as power sources for these devices has become increasingly important. In addition, the automotive industry is also working to develop high-output, high-capacity batteries for electric vehicles and hybrid vehicles.

[0003] Patent Document 1 discloses that a lithium metal composite oxide having a coating layer containing Li, B, and O is used as a positive electrode active material for a sulfide solid battery.

[0004] Patent Document 2 discloses a positive electrode active material for a non-aqueous secondary battery, which is a lithium nickel cobalt manganese composite oxide containing boron on the surface. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2020 / 022305 [Patent Document 2] Japanese Patent Application Publication No. 2018-045802 Summary of the Invention [Problem to be solved by the invention]

[0006] There is a need to further reduce the rate of increase in resistance (rate of resistance change) of batteries.

[0007] The present disclosure has been made in view of the above circumstances, and has as its main object to provide a composite positive electrode active material that can reduce the rate of increase in battery resistance. [Means for solving the problem]

[0008] The composite positive electrode active material of the present disclosure is a composite positive electrode active material including a lithium metal oxide as a positive electrode active material and a coating layer covering at least a portion of the surface of the positive electrode active material, the coating layer contains Li, B, and O; the molar ratio Li / B of Li element to B element in the coating layer is 0.1 to 0.8; In Raman spectroscopy, 780cm -1 Intensity of the peak Iβ at 720 cm -1 The intensity ratio Iα / Iβ of the peak intensity Iα is 1.0 to 1.5, The coverage of the coating layer covering the positive electrode active material is greater than 57%.

[0009] In the composite positive electrode active material of the present disclosure, the positive electrode active material is positive electrode active material particles, The composite positive electrode active material may be composite positive electrode active material particles.

[0010] In the composite positive electrode active material of the present disclosure, the composite positive electrode active material may be for a sulfide all-solid-state battery.

[0011] A method for producing a composite positive electrode active material according to the present disclosure is a method for producing the composite positive electrode active material, comprising: supplying the slurry containing the positive electrode active material and the coating liquid to a spray dryer, forming the slurry into droplets, and air-drying the droplets of the slurry to obtain a precursor of a composite positive electrode active material; and calcining the precursor, The coating liquid contains a lithium source, a boron source, and an oxygen source.

[0012] In the method for producing a composite positive electrode active material of the present disclosure, the precursor may be fired at 300°C to 400°C in the firing step. [Effects of the Invention]

[0013] The present disclosure can provide a composite positive electrode active material that can reduce the rate of increase in resistance of a battery. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 shows Raman spectra of the composite positive electrode active materials obtained by firing at firing temperatures of 200°C, 300°C, 400°C, and 500°C. [Figure 2] FIG. 2 is a graph showing the relationship between the firing temperature of the precursor of the composite positive electrode active material and Iα / Iβ of the resulting composite positive electrode active material. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, embodiments of the present disclosure will be described. It should be noted that matters other than those specifically mentioned in this specification that are necessary for implementing the present disclosure (for example, the general configuration and manufacturing process of a composite positive electrode active material that does not characterize the present disclosure) can be understood as design matters for those skilled in the art based on conventional technology in the relevant field. The present disclosure can be implemented based on the contents disclosed in this specification and common general technical knowledge in the relevant field. In this specification, the use of "to" to indicate a range of values ​​means that the values ​​before and after it are included as the lower and upper limits. Any combination of upper and lower limits in the numerical range can be adopted.

[0016] 1. Composite positive electrode active material The composite positive electrode active material of the present disclosure is a composite positive electrode active material including a lithium metal oxide as a positive electrode active material and a coating layer covering at least a portion of the surface of the positive electrode active material, the coating layer contains Li, B, and O; the molar ratio Li / B of Li element to B element in the coating layer is 0.1 to 0.8; In Raman spectroscopy, 780cm -1 Intensity of the peak Iβ at 720 cm -1 The intensity ratio Iα / Iβ of the peak intensity Iα is 1.0 to 1.5, The coverage of the coating layer covering the positive electrode active material is greater than 57%.

[0017] The composite positive electrode active material of the present disclosure has a Raman spectrum of 780 cm -1 Intensity of the peak Iβ at 720 cm -1 The intensity ratio Iα / Iβ of the peak intensities Iα is 1.0 to 1.5. 780cm -1 The peak at 760 to 785 cm may be, for example, a peak corresponding to a six-membered boric acid ring having a BO unit. -1 The peaks in the range of 780 cm -1 This may be considered as the peak of 720cm -1 The peak at 715 to 735 cm may be, for example, a peak corresponding to chain metaboric acid (BO3). -1 The peaks in the range of 720 cm -1 This may be considered as the peak of

[0018] The shape of the composite positive electrode active material is not particularly limited, and may be a plate shape, a particle shape, etc. The composite positive electrode active material may be composite positive electrode active material particles. The average particle size D50 of the composite positive electrode active material particles may be 1 to 20 μm, or may be 5 to 10 μm.

[0019] In this disclosure, unless otherwise specified, the average particle size of particles is the volume-based median diameter (D50) value measured by laser diffraction / scattering particle size distribution measurement. Furthermore, in this disclosure, the median diameter (D50) is the diameter (volume average diameter) at which the cumulative volume of particles is half (50%) of the total volume when particles are arranged in order from smallest to largest particle size.

[0020] The positive electrode active material may be a lithium metal oxide. Lithium metal oxides include, for example, LiCoO2 and LiNi x M 1-xExamples include lithium transition metal composite oxides represented by LiMnO2 (where x satisfies 0.3≦x<1 and M is at least one element selected from the group consisting of Co, Mn, and Al), LiMnO2, heteroelement-substituted Li-Mn spinel, lithium titanate, lithium metal phosphate, Li2SiO3, and Li4SiO4. As a lithium transition metal composite oxide, lithium nickel cobalt aluminate (LiNi 1-x-y Co x Al y O2, x=0.05~0.2, y=0.05~0.2, NCA), Lithium Nickel Cobalt Manganese Oxide (LiNi x Co y Mn 1-x-y O2, x=0.3-0.8, y=0.1-0.6, NCM), etc. NCM is LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 Examples include O2, NCM-523, NCM-622, and NCM-811. The hetero-element substituted Li-Mn spinel is, for example, LiMn 1.5 Ni 0.5 O4, LiMn 1.5 Al 0.5 O4, LiMn 1.5 Mg 0.5 O4, LiMn 1.5 Co 0.5 O4, LiMn 1.5 Fe 0.5 O4 and LiMn 1.5 Zn 0.5 It is O4 magnitude. Lithium titanate is, for example, Li4Ti5O 12 etc. Examples of lithium metal phosphates include LiFePO4, LiMnPO4, LiCoPO4, and LiNiPO4.

[0021] The shape of the positive electrode active material is not particularly limited, and may be a plate shape, a particle shape, or the like. The positive electrode active material may be positive electrode active material particles. The positive electrode active material particles may be primary particles or secondary particles.

[0022] The coating layer covers at least a portion of the surface of the positive electrode active material. The coating layer contains Li, B, and O elements, and may be lithium borate. Examples of the composition of lithium borate include Li3BO3, Li4B2O5, LiBO2, Li2B4O7, LiB3O5, etc. In the present disclosure, the composition of the coating layer may be any of these, and is not uniquely determined, and a mixture of multiple compositions may be used. The crystalline structure of lithium borate may be any of the crystalline phases having the above composition, and may also be glass or amorphous. The molar ratio Li / B of Li element to B element in the coating layer is 0.1 to 0.8. The coverage of the coating layer that covers the positive electrode active material may be greater than 57%, and may be 80% or greater. The coverage of the coating layer can be calculated by observing a scanning electron microscope (SEM) image of the cross section of the particle, by calculating the element ratio on the surface using X-ray photoelectric spectroscopy (XPS), or by time-of-flight secondary ion mass spectrometry (TOF-SIMS). The thickness of the coating layer is not particularly limited, and may be, for example, 0.1 nm or more, 0.5 nm or more, or 5 nm or more, and may be 500 nm or less, 300 nm or less, 100 nm or less, 50 nm or less, or 40 nm or less.

[0023] 2. Manufacturing method of composite positive electrode active material A method for producing a composite positive electrode active material according to the present disclosure is a method for producing the composite positive electrode active material, comprising: supplying the slurry containing the positive electrode active material and the coating liquid to a spray dryer, forming the slurry into droplets, and air-drying the droplets of the slurry to obtain a precursor of a composite positive electrode active material; and calcining the precursor, The coating liquid contains a lithium source, a boron source, and an oxygen source.

[0024] According to the manufacturing method of the composite positive electrode active material of the present disclosure, the coverage of the coating layer covering the positive electrode active material can be made to be more than 57% with high precision, and a composite positive electrode active material can be obtained in which the coverage of the coating layer covering the positive electrode active material is more than 57%.

[0025] [Step of obtaining precursor] The step of obtaining a precursor is a step of supplying a slurry containing the positive electrode active material and the coating liquid to a spray dryer, forming droplets from the slurry, and air-drying the droplets to obtain a precursor of a composite positive electrode active material.

[0026] The coating liquid forms a coating layer that exhibits a predetermined function on the surface of the positive electrode active material after air drying and baking, which will be described later. The coating layer may have the function of suppressing an increase in interfacial resistance between the positive electrode active material and other materials, for example. The type of coating liquid can be selected according to the type of positive electrode active material to be coated and the desired function. The coating solution contains a lithium source, a boron source, and an oxygen source. The lithium source is not particularly limited as long as it is a raw material containing lithium. The lithium source may contain lithium ions. For example, a coating solution containing lithium ions as the lithium source may be obtained by dissolving a lithium compound such as LiOH, LiNO3, or Li2SO4 in a solvent. Alternatively, the coating solution may contain a lithium alkoxide as the lithium source. For example, LiOH·H2O can be used as the lithium source. The boron source is not particularly limited as long as it is a raw material containing boron. For example, a compound containing boron and oxygen can be used as the boron source. From the viewpoints of ease of handling and excellent quality stability, boron oxide, boron oxoacid, a mixture thereof, or orthoboric acid may be used. The oxygen source is not particularly limited as long as it is a raw material containing oxygen. For example, among the lithium sources and boron sources mentioned above, those containing oxygen can be used as the oxygen source.

[0027] The "slurry" is a suspension or suspension containing a positive electrode active material and a coating liquid, and may be any suspension that has fluidity to the extent that it can be formed into droplets. The solid content concentration at which droplet formation is possible may vary depending on the type of positive electrode active material, the type of coating liquid, the droplet formation conditions, etc. The solid content concentration in the slurry is not particularly limited and may be, for example, 1 vol% or more, 5 vol% or more, 10 vol% or more, 20 vol% or more, 25 vol% or more, 30 vol% or more, 35 vol% or more, 40 vol% or more, 45 vol% or more, 50 vol% or more, or 70 vol% or less, 65 vol% or less, 60 vol% or less, 55 vol% or less, 50 vol% or less, 45 vol% or less, 40 vol% or less, or 35 vol% or less. From the viewpoint of more easily obtaining slurry droplets, the solid content concentration of the slurry may be 40 vol% or less.

[0028] The phrase "forming the slurry into droplets" means that the slurry containing the positive electrode active material and the coating liquid is formed into particles containing the positive electrode active material and the coating liquid. The "slurry droplets" are particles of a slurry containing a positive electrode active material and a coating liquid. The size of the slurry droplets is not particularly limited. In the method of the present disclosure, "air flow drying" refers to drying slurry droplets while suspending them in a high-temperature air flow (heated gas). "Air flow drying" may include not only drying but also an additional operation using a dynamic air flow. By continuously applying hot air (heated gas) to the slurry droplets during air flow drying, a force is continuously applied to the slurry droplets.

[0029] As the spray dryer, a conventionally known one can be used. The temperature of the heated gas supplied to the spray dryer may be any temperature that allows the solvent to volatilize from the slurry droplets, and may be, for example, 100°C or higher, 110°C or higher, 120°C or higher, 130°C or higher, 140°C or higher, 150°C or higher, 160°C or higher, 170°C or higher, 180°C or higher, 190°C or higher, 200°C or higher, 210°C or higher, or 220°C or higher. The supply volume of the heated gas in the spray dryer can be appropriately set in consideration of the size of the device used, the supply volume of the slurry droplets, etc. For example, the supply volume of the heated gas is 0.10 m 3 / min or more, 0.15m 3 / min or more, 0.20m 3 / min or more, 0.25m 3 / min or more, 0.30m 3 / min or more, 0.35m 3 / min or more, 0.40m 3 / min or more, 0.45m 3 / min or more, or 0.50m 3 / min or more, and may be 5.00m 3 / min or less, 4.00m 3 / min or less, 3.00m 3 / min or less, 2.00m 3 / min or less, or 1.00m 3 / min or less. The supply velocity (flow rate) of the heated gas can also be set appropriately taking into consideration the size of the apparatus used, the supply amount of slurry droplets, etc. For example, the flow rate of the heated gas may be 1 m / sec or more or 5 m / sec or more, or 50 m / sec or less or 10 m / sec or less, in at least a part of the system. The treatment time with heated gas (drying time) can also be set appropriately taking into consideration the size of the device used, the amount of slurry droplets supplied, etc. For example, the treatment time may be 5 seconds or less, or 1 second or less. The heating gas may be substantially inert to the positive electrode active material and the coating liquid. For example, an oxygen-containing gas such as air, an inert gas such as nitrogen or argon, or dry air with a low dew point may be used. In this case, the dew point may be −10° C. or lower, −50° C. or lower, or −70° C. or lower.

[0030] [Firing process] The calcination step is a step of calcining the precursor. The firing device may be, for example, a muffle furnace or a hot plate, but is not limited to these. In the calcination step, the precursor may be calcined at 200°C to 450°C, or may be calcined at 300°C to 400°C. The calcination time may be, for example, 1 hour or more, 2 hours or more, 3 hours or more, 4 hours or more, 5 hours or more, or 6 hours or more, and may be 20 hours or less, 15 hours or less, or 10 hours or less. The calcination atmosphere may be, for example, an air atmosphere, a vacuum atmosphere, a dry air atmosphere, a nitrogen gas atmosphere, or an argon gas atmosphere.

[0031] [battery] The composite positive electrode active material of the present disclosure can be used as a positive electrode material for various batteries, and among batteries, it may be for a sulfide all-solid-state battery. The battery of the present disclosure may include a positive electrode, an electrolyte layer, and a negative electrode. The battery may be a primary battery or a secondary battery, but particularly a secondary battery. Secondary batteries can be repeatedly charged and discharged. Secondary batteries are useful, for example, as automotive batteries. The battery may be an aqueous battery, a non-aqueous battery, an all-solid-state battery, or the like. The battery may also be a lithium battery, a lithium ion battery, or the like. Furthermore, the all-solid-state battery may be an all-solid-state lithium secondary battery, an all-solid-state lithium ion secondary battery, etc. The all-solid-state battery may be a sulfide all-solid-state battery that uses a sulfide-based solid electrolyte as a solid electrolyte. Examples of the shape of the battery include coin type, laminate type, cylindrical type, and square type. The use of the battery is not particularly limited, but examples include power sources for vehicles such as hybrid electric vehicles (HEVs), plug-in hybrid electric vehicles (PHEVs), electric vehicles (BEVs), gasoline-powered vehicles, and diesel-powered vehicles. In particular, the battery may be used as a driving power source for hybrid electric vehicles, plug-in hybrid electric vehicles, or electric vehicles. The battery of the present disclosure may also be used as a power source for mobile objects other than vehicles (e.g., trains, ships, and aircraft), or as a power source for electrical appliances such as information processing devices.

[0032] [Positive electrode] The positive electrode has a positive electrode layer and, if necessary, a positive electrode current collector.

[0033] [Positive electrode layer] The positive electrode layer contains the composite positive electrode active material of the present disclosure, and may contain optional components such as a conductive material, a solid electrolyte, and a binder.

[0034] Known conductive materials can be used, such as carbon materials and metal particles. Examples of the carbon material include at least one material selected from the group consisting of acetylene black, furnace black, VGCF, carbon nanotubes, and carbon nanofibers. From the viewpoint of electron conductivity, at least one material selected from the group consisting of VGCF, carbon nanotubes, and carbon nanofibers may be used. Examples of metal particles include particles of Ni, Cu, Fe, and SUS. The content of the conductive material in the positive electrode layer is not particularly limited.

[0035] Examples of the solid electrolyte include the same ones as those exemplified for the solid electrolyte layer. The content of the solid electrolyte in the positive electrode layer is not particularly limited, but may be, for example, in the range of 1% to 80% by mass when the total mass of the positive electrode layer is taken as 100% by mass.

[0036] Examples of the binding agent (binder) include polyacrylonitrile, polyacrylic acid, polyacrylic acid methyl ester, polyacrylic acid ethyl ester, polyacrylic acid hexyl ester, polymethacrylic acid, polymethacrylic acid methyl ester, polymethacrylic acid ethyl ester, polymethacrylic acid hexyl ester, acrylonitrile butadiene rubber (ABR), butadiene rubber (BR), polyvinylidene fluoride (PVdF), and styrene butadiene rubber (SBR). The content of the binder in the positive electrode layer is not particularly limited.

[0037] The thickness of the positive electrode layer is not particularly limited, but may be, for example, 10 to 100 μm.

[0038] The positive electrode layer can be formed by a conventionally known method. For example, a paste for forming a positive electrode layer is prepared by adding the composite positive electrode active material and, if necessary, other components to a solvent and stirring the mixture, and the paste for forming a positive electrode layer is applied to one surface of a support and dried to obtain a positive electrode layer. Examples of the solvent include butyl acetate, butyl butyrate, mesitylene, tetralin, heptane, and N-methyl-2-pyrrolidone (NMP). The method for applying the paste for forming a positive electrode layer onto one surface of the support is not particularly limited, and examples thereof include a doctor blade method, a metal mask printing method, an electrostatic application method, a dip coating method, a spray coating method, a roll coating method, a gravure coating method, and a screen printing method. The support can be appropriately selected from those having self-supporting properties and is not particularly limited, and examples thereof include metal foils such as Cu and Al foils.

[0039] Alternatively, the positive electrode layer may be formed by pressure molding a powder of a positive electrode mixture containing a composite positive electrode active material and, if necessary, other components. When the powder of the positive electrode mixture is pressure molded, a surface pressure of 1 MPa to 2000 MPa and a linear pressure of 1 ton / cm to 100 ton / cm are typically applied. The method of applying pressure is not particularly limited, but examples thereof include a method of applying pressure using a plate press, a roll press, or the like.

[0040] [Positive electrode current collector] The positive electrode current collector may be a known metal that can be used as a battery current collector. Examples of such metals include metal materials containing one or more elements selected from the group consisting of Cu, Ni, Al, V, Au, Pt, Mg, Fe, Ti, Co, Cr, Zn, Ge, and In. Examples of the positive electrode current collector include SUS, aluminum, nickel, iron, titanium, and carbon. The shape of the positive electrode current collector is not particularly limited, and can be various shapes such as foil, mesh, etc. The thickness of the positive electrode current collector varies depending on the shape, but may be, for example, in the range of 1 μm to 50 μm, or in the range of 5 μm to 20 μm.

[0041] [Negative electrode] The negative electrode has a negative electrode layer and, if necessary, a negative electrode current collector.

[0042] [Negative electrode layer] The negative electrode layer contains at least a negative electrode active material, and optionally contains a solid electrolyte, a conductive material, a binder, and the like. The negative electrode active materials include graphite, mesocarbon microbeads (MCMB), highly oriented pyrolytic graphite (HOPG), hard carbon, soft carbon, lithium, lithium alloys, Si, Si alloys, and Li4Ti5O 12 etc. Examples of lithium alloys include Li-Au, Li-Mg, Li-Sn, Li-Si, Li-Al, Li-B, Li-C, Li-Ca, Li-Ga, Li-Ge, Li-As, Li-Se, Li-Ru, Li-Rh, Li-Pd, Li-Ag, Li-Cd, Li-In, Li-Sb, Li-Ir, Li-Pt, Li-Hg, Li-Pb, Li-Bi, Li-Zn, Li-Tl, Li-Te, and Li-At. Examples of Si alloys include alloys with metals such as Li, and may also be alloys with at least one metal selected from the group consisting of Sn, Ge, and Al. The shape of the negative electrode active material is not particularly limited, and examples thereof include particulate and plate-like shapes. When the negative electrode active material is particulate, the negative electrode active material may be primary particles or secondary particles. The conductive material and binder used in the negative electrode layer may be the same as those exemplified for the positive electrode layer, and the solid electrolyte used in the negative electrode layer may be the same as those exemplified for the solid electrolyte layer. The thickness of the negative electrode layer is not particularly limited, but may be, for example, 10 to 100 μm. The content of the negative electrode active material in the negative electrode layer is not particularly limited, but may be, for example, 20% by mass to 90% by mass. The negative electrode layer may be formed by applying a paste for forming the negative electrode layer containing the negative electrode active material onto a support and drying the paste. The support may be the same as those exemplified for the positive electrode layer.

[0043] [Negative electrode current collector] The material of the negative electrode current collector may be a material that does not alloy with Li, such as SUS, copper, or nickel. The negative electrode current collector may be in the form of, for example, a foil or a plate. The shape of the negative electrode current collector in plan view is not particularly limited, but may be, for example, a circle, an ellipse, a rectangle, or any polygonal shape. The thickness of the negative electrode current collector varies depending on the shape, but may be, for example, in the range of 1 μm to 50 μm, or in the range of 5 μm to 20 μm.

[0044] [Electrolyte layer] The electrolyte layer includes at least an electrolyte. The electrolyte may be an aqueous electrolyte solution, a non-aqueous electrolyte solution, a gel electrolyte, a solid electrolyte, etc. These may be used alone or in combination of two or more.

[0045] The solvent of the aqueous electrolyte solution contains water as a main component. That is, based on the total amount (100 mol%) of the solvent (liquid component) constituting the electrolyte solution, water may account for 50 mol% or more, particularly 70 mol% or more, and even 90 mol% or more. Meanwhile, there is no particular upper limit to the proportion of water in the solvent.

[0046] The solvent contains water as a main component, but may contain a solvent other than water. Examples of the solvent other than water include one or more selected from ethers, carbonates, nitriles, alcohols, ketones, amines, amides, sulfur compounds, and hydrocarbons. The solvent other than water may be 50 mol% or less, particularly 30 mol% or less, and even 10 mol% or less, based on the total amount (100 mol%) of the solvents (liquid components) constituting the electrolytic solution.

[0047] The aqueous electrolyte used in the present disclosure contains an electrolyte. A conventionally known electrolyte can be used for the aqueous electrolyte. Examples of the electrolyte include lithium salts, nitrates, acetates, and sulfates of imide acid compounds. Specific electrolytes include lithium bis(fluorosulfonyl)imide (LiFSI; CAS No. 171611-11-3), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI; CAS No. 90076-65-6), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI; CAS No. 132843-44-8), lithium bis(nonafluorobutanesulfonyl)imide (CAS No. 119229-99-1), lithium nonafluoro-N-[(trifluoromethane)sulfonyl]butanesulfonylamide (CAS No. 176719-70-3), lithium N,N-hexafluoro-1,3-disulfonylimide (CAS No. 189217-62-7), CHClO₃, LiPF₆, LiBF₄, LiSO₄, and LiNO₃.

[0048] The concentration of the electrolyte in the aqueous electrolyte solution can be appropriately set according to the desired battery characteristics, as long as it does not exceed the saturated concentration of the electrolyte in the solvent, because if a solid electrolyte remains in the aqueous electrolyte solution, the solid may inhibit the battery reaction. For example, when LiTFSI is used as the electrolyte, the aqueous electrolyte solution may contain 1 mol or more, particularly 5 mol or more, or even 7.5 mol or more of LiTFSI per kg of water. The upper limit is not particularly limited, and may be, for example, 25 mol or less.

[0049] The non-aqueous electrolyte solution generally contains a lithium salt and a non-aqueous solvent. Examples of lithium salts include inorganic lithium salts such as LiPF6, LiBF4, LiClO4, and LiAsF6; and organic lithium salts such as LiCF3SO3, LiN(SO2CF3)2(Li-TFSI), LiN(SO2C2F5)2, and LiC(SO2CF3)3. Examples of non-aqueous solvents include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone, sulfolane, acetonitrile (AcN), dimethoxymethane, 1,2-dimethoxyethane (DME), 1,3-dimethoxypropane, diethyl ether, tetraethylene glycol dimethyl ether (TEGDME), tetrahydrofuran, 2-methyltetrahydrofuran, dimethyl sulfoxide (DMSO), and mixtures thereof. From the viewpoint of ensuring a high dielectric constant and a low viscosity, the solvent may be a mixture of a cyclic carbonate compound having a high dielectric constant and a high viscosity, such as EC, PC, or BC, and a chain carbonate compound having a low dielectric constant and a low viscosity, such as DMC, DEC, or EMC, or a mixture of EC and DEC. The concentration of the lithium salt in the non-aqueous electrolyte may be, for example, 0.3 to 5M.

[0050] A gel electrolyte is generally a gel formed by adding a polymer to a non-aqueous electrolyte solution. Specifically, the gel electrolyte can be obtained by adding a polymer such as polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride (PVdF), polyurethane, polyacrylate, or cellulose to the nonaqueous electrolyte solution described above and gelling the mixture.

[0051] The electrolyte layer may be impregnated with an electrolyte such as the aqueous electrolyte solution described above, and a separator may be used to prevent contact between the positive electrode layer and the negative electrode layer. The separator material is not particularly limited as long as it is a porous film, and examples thereof include resins such as polyethylene (PE), polypropylene (PP), polyester, cellulose, and polyamide, among which polyethylene and polypropylene are preferred. The separator may have a single-layer structure or a multi-layer structure. Examples of multi-layer separators include a two-layer structure of PE / PP, or a three-layer structure of PP / PE / PP or PE / PP / PE. The separator may be a nonwoven fabric such as a resin nonwoven fabric or a glass fiber nonwoven fabric.

[0052] [Solid electrolyte layer] The electrolyte layer may be a solid electrolyte layer made of a solid. The solid electrolyte layer includes at least a solid electrolyte. The solid electrolyte contained in the solid electrolyte layer may be any known solid electrolyte that can be used in all-solid-state batteries, and examples of such solid electrolytes include inorganic solid electrolytes such as sulfide-based solid electrolytes, oxide-based solid electrolytes, hydride-based solid electrolytes, halide-based solid electrolytes, and nitride-based solid electrolytes. The sulfide-based solid electrolyte may contain sulfur (S) as the main anion element. The oxide-based solid electrolyte may contain oxygen (O) as the main anion element. The hydride-based solid electrolyte may contain hydrogen (H) as the main anion element. The halide-based solid electrolyte may contain halogen (X) as the main anion element. The nitride-based solid electrolyte may contain nitrogen (N) as the main anion element.

[0053] The sulfide-based solid electrolyte may be sulfide glass, crystallized sulfide glass (glass ceramics), or a crystalline material obtained by a solid-phase reaction treatment of a raw material composition. The crystalline state of the sulfide-based solid electrolyte can be confirmed, for example, by subjecting the sulfide-based solid electrolyte to powder X-ray diffraction measurement using CuKα radiation.

[0054] Sulfide glass can be obtained by subjecting a raw material composition (e.g., a mixture of Li2S and P2S5) to amorphous processing, such as mechanical milling.

[0055] Glass ceramics can be obtained, for example, by heat treating sulfide glass. The heat treatment temperature may be any temperature higher than the crystallization temperature (Tc) of the sulfide glass observed by thermal analysis, and is usually 195° C. or higher. On the other hand, there is no particular upper limit to the heat treatment temperature. The crystallization temperature (Tc) of sulfide glass can be measured by differential thermal analysis (DTA). The heat treatment time is not particularly limited as long as it is a time that allows the desired crystallinity of the glass ceramic to be obtained, but is, for example, in the range of 1 minute to 24 hours, and particularly in the range of 1 minute to 10 hours. The heat treatment method is not particularly limited, but for example, a method using a firing furnace can be mentioned.

[0056] Examples of oxide-based solid electrolytes include solid electrolytes containing Li, Y (Y is at least one of Nb, B, Al, Si, P, Ti, Zr, Mo, W, and S), and O. Specific examples of oxide-based solid electrolytes include Li7La3Zr2O 12 , Li 7-x La3(Zr 2-x Nb x )O 12 (0≦x≦2), Li5La3Nb2O 12 perovskite-type solid electrolytes such as (Li,La)TiO3, (Li,La)NbO3, (Li,Sr)(Ta,Zr)O3; Nasicon-type solid electrolytes such as Li(Al,Ti)(PO4)3 and Li(Al,Ga)(PO4)3; Li-PO-based solid electrolytes such as Li3PO4 and LIPON (a compound in which some of the O in Li3PO4 is substituted with N); and Li-BO-based solid electrolytes such as Li3BO3 and a compound in which some of the O in Li3BO3 is substituted with C. In the present disclosure, the notation "(A, B, C)" in a chemical formula means "at least one selected from the group consisting of A, B, and C."

[0057] The hydride-based solid electrolyte contains, for example, Li and a complex anion containing hydrogen. The complex anion may be, for example, (BH4) - , (NH2) - , (AlH4) - , and (AlH6) 3- etc.

[0058] The halide-based solid electrolyte is, for example, represented by the following composition formula (1). Li α M β X γ ...Equation (1) In composition formula (1), α, β, and γ are each independently a value greater than 0. M includes at least one element selected from the group consisting of metal elements and metalloid elements other than Li. X includes at least one element selected from the group consisting of F, Cl, Br, and I. In the present disclosure, "metalloid elements" refer to B, Si, Ge, As, Sb, and Te. "Metal elements" refer to all elements in Groups 1 to 12 of the periodic table excluding hydrogen, and all elements in Groups 13 to 16 of the periodic table excluding B, Si, Ge, As, Sb, Te, C, N, P, O, S, and Se. In other words, "metalloid elements" or "metal elements" refer to a group of elements that can become cations when forming inorganic compounds with halogen elements. More specific examples of halide-based solid electrolytes include Li3YX6, Li2MgX4, Li2FeX4, LiAlX4, LiGaX4, LiInX4, Li3AlX6, Li3GaX6, and Li3InX6, where X is at least one selected from the group consisting of F, Cl, Br, and I.

[0059] An example of the nitride-based solid electrolyte is Li3N.

[0060] The solid electrolyte may be in the form of particles from the viewpoint of ease of handling. The average particle size of the solid electrolyte particles is not particularly limited, but may be, for example, 10 nm or more, or 100 nm or more, while the average particle size of the solid electrolyte particles is, for example, 25 μm or less, or may be 10 μm or less.

[0061] The solid electrolyte may be used alone or in combination of two or more. When two or more solid electrolytes are used, the two or more solid electrolytes may be mixed, or two or more solid electrolyte layers may be formed to form a multilayer structure. The proportion of the solid electrolyte in the solid electrolyte layer is not particularly limited, but is, for example, 50% by mass or more, may be in the range of 60% by mass or more and 100% by mass or less, may be in the range of 70% by mass or more and 100% by mass or less, or may be 100% by mass.

[0062] The solid electrolyte layer may contain a binder from the viewpoint of exhibiting plasticity, etc. Examples of such binders include the materials exemplified as binders used in the positive electrode layer. However, in order to facilitate achieving high output, the binder may be contained in an amount of 5 mass % or less from the viewpoint of preventing excessive aggregation of the solid electrolyte and enabling the formation of a solid electrolyte layer having a uniformly dispersed solid electrolyte.

[0063] The thickness of the solid electrolyte layer is not particularly limited, but is usually 0.1 μm or more and 1 mm or less. Examples of methods for forming the solid electrolyte layer include a method of applying a paste for forming a solid electrolyte layer containing a solid electrolyte to a support and drying it, and a method of press-molding a powder of a solid electrolyte material containing a solid electrolyte. Examples of the support include the same ones as those exemplified for the positive electrode layer. When press-molding the powder of the solid electrolyte material, a pressure of about 1 MPa to 2000 MPa is typically applied. The pressure application method is not particularly limited, but may be any of the pressure application methods exemplified in the formation of the positive electrode layer.

[0064] The battery may optionally include an exterior body that houses a laminate having a positive electrode current collector, a positive electrode layer, an electrolyte layer, a negative electrode layer, and a negative electrode current collector arranged in this order, a restraining member, and the like. The material of the exterior body is not particularly limited as long as it is stable to the electrolyte, and examples thereof include polypropylene, polyethylene, and resins such as acrylic resin. The restraining member may be any known member usable as a battery restraining member as long as it can apply a restraining pressure to the stack in the stacking direction. For example, a restraining member may include plate-shaped portions that sandwich both surfaces of the stack, rod-shaped portions that connect the two plate-shaped portions, and an adjustment portion that is connected to the rod-shaped portions and adjusts the restraining pressure using a screw structure or the like. The adjustment portion can apply a desired restraining pressure to the stack. The constraining pressure is not particularly limited, but may be, for example, 0.1 MPa or more, 1 MPa or more, or 5 MPa or more. This is because increasing the constraining pressure has the advantage of making it easier to improve the contact between the layers. On the other hand, the constraining pressure may be, for example, 100 MPa or less, 50 MPa or less, or 20 MPa or less. This is because if the constraining pressure is too high, the constraining member will be required to have high rigidity, which may result in the constraining member becoming larger. The battery may have only one of the above laminates, or may be formed by stacking a plurality of laminates.

[0065] When the battery of the present disclosure is an all-solid-state battery, a method for manufacturing the all-solid-state battery may include, for example, first forming a solid electrolyte layer by applying a solid electrolyte layer-forming paste to a support and drying it. Then, forming a positive electrode layer by applying a positive electrode layer-forming paste containing a composite positive electrode active material to one side of the solid electrolyte layer and drying it. Thereafter, the support is peeled off from the solid electrolyte layer, and forming a negative electrode layer by applying a negative electrode layer-forming paste to the other side of the solid electrolyte layer and drying it. If necessary, a positive electrode current collector may be attached to the side of the positive electrode layer opposite the solid electrolyte layer, and a negative electrode current collector may be attached to the side of the negative electrode layer opposite the solid electrolyte layer, thereby completing an all-solid-state battery. [Example]

[0066] Example 1 [Preparation of coating liquid] The coating solution was prepared by dissolving 0.53 g of LiOH·H2O and 7.79 g of H3BO3 in 191.68 mL of water. [Preparation of Slurry Containing Positive Electrode Active Material and Coating Liquid] LiNi as the positive electrode active material 1 / 3 Mn 1 / 3 Co 1 / 3 220 g of O was placed in a mixer container, added to the coating liquid so that the solid content concentration was 60%, and stirred with a magnetic stirrer. [Preparation of precursor for composite positive electrode active material] The slurry prepared above was fed to a spray dryer (B-290 manufactured by Buchi) at a rate of 0.5 g / sec using a liquid pump, and the slurry was turned into droplets and dried under airflow to obtain a precursor of the composite positive electrode active material. The operating conditions of the spray dryer were: inlet air temperature: 200°C, inlet air flow rate: 0.45 m 3 / min. [Firing of composite positive electrode active material precursor] The precursor was heat-treated in an air atmosphere at 400°C for 5 hours using a muffle furnace (KDF S90) to obtain a composite positive electrode active material. The average particle size of the composite positive electrode active material was 5µm.

[0067] Example 2 A composite positive electrode active material was obtained in the same manner as in Example 1, except that the coating solution was prepared by dissolving 2.12 g of LiOH·H 2 O and 7.79 g of H 3 BO 3 in 190.09 mL of water.

[0068] Example 3 A composite positive electrode active material was obtained in the same manner as in Example 1, except that a coating solution was prepared by dissolving 2.12 g of LiOH·H2O and 7.79 g of H3BO3 in 190.09 mL of water, and the precursor of the composite positive electrode active material was heat-treated at 300 °C for 5 hours in an air atmosphere.

[0069] Example 4 A composite positive electrode active material was obtained in the same manner as in Example 1, except that the coating solution was prepared by dissolving 4.23 g of LiOH·H 2 O and 7.79 g of H 3 BO 3 in 187.98 mL of water.

[0070] (Comparative Example 1) A composite positive electrode active material was obtained in the same manner as in Example 1, except that a coating solution was prepared by dissolving 2.12 g of LiOH·H2O and 7.79 g of H3BO3 in 190.09 mL of water, and the precursor of the composite positive electrode active material was heat-treated at 200 °C for 5 hours in an air atmosphere.

[0071] (Comparative Example 2) A composite positive electrode active material was obtained in the same manner as in Example 1, except that a coating solution was prepared by dissolving 2.12 g of LiOH·H2O and 7.79 g of H3BO3 in 190.09 mL of water, and the precursor of the composite positive electrode active material was heat-treated at 500 °C for 5 hours in an air atmosphere.

[0072] (Comparative Example 3) A composite positive electrode active material was obtained in the same manner as in Example 1, except that the coating solution was prepared by dissolving 5.29 g of LiOH·H 2 O and 7.79 g of H 3 BO 3 in 186.92 mL of water.

[0073] Comparative Example 4 A coating solution was prepared by dissolving 0.53 g of LiOH·HO and 7.79 g of HBO in 191.68 mL of water. 55 mL of the coating solution was added to 10 g of the positive electrode active material, stirred at 25°C for 1 hour, and then dried at 130°C for 2 hours to obtain a precursor for the composite positive electrode active material. The precursor was then heat-treated in an air atmosphere at 300°C for 5 hours in a muffle furnace (KDF S90) to obtain the composite positive electrode active material.

[0074] [Evaluation of the coverage rate of the coating layer] The coverage of the coating layer was calculated from the ratio of elements present on the outermost surface of the composite positive electrode active material using an X-ray photoelectron spectrometer (XPS, Quantam2000 manufactured by ULVAC-PHI) based on the following formula. Coverage (%) = B / (Mn+Co+Ni+B) x 100

[0075] [Evaluation of the average particle size D50 of the composite positive electrode active material] The composite positive electrode active material was measured for average particle size D50 at 50% cumulative value in the volume-based particle size distribution using a laser diffraction particle size distribution analyzer (SALD-7500 manufactured by Shimadzu Corporation).

[0076] [Evaluation of coating layer thickness] For the composite positive electrode active material, the resin-embedded composite positive electrode active material was cross-sectionally processed using an ion milling device (IM4000PLUS, manufactured by Hitachi High-Technologies), and then observed using an FE-SEM (Regulus8100, manufactured by Hitachi High-Technologies). The thickness of the coating layer was measured at any five points, and the average value was calculated as the thickness of the coating layer.

[0077] [Quantitative analysis of the constituent elements in the coating layer (molar ratio of Li / B)] The Li / B molar ratio in the coating layer was calculated from the ratio of elements present on the outermost surface of the composite positive electrode active material using an X-ray photoelectron spectrometer (XPS, Quantam2000 manufactured by ULVAC-PHI).

[0078] [Iα / Iβ] A semi-quantitative analysis of the boric acid bonding units was performed using a Raman spectrometer (Thermo Fisher Scientific, DXR3xi). -1 The intensity of the peak located at Iα, 780 cm -1 The intensity of the peak located at was designated as Iβ, and the intensity ratio Iα / Iβ was calculated from these. FIG. 1 shows Raman spectra of the composite positive electrode active materials obtained by firing at firing temperatures of 200°C, 300°C, 400°C, and 500°C. In Figure 1, peak A is at 720 cm -1 Peak B is located at 780 cm -1 It is a peak located at FIG. 2 is a graph showing the relationship between the firing temperature of the precursor of the composite positive electrode active material and Iα / Iβ of the resulting composite positive electrode active material. As shown in FIG. 2, Iα / Iβ increases with increasing firing temperature.

[0079] [Preparation of positive electrode] Using each of the composite positive electrode active materials of Examples 1 to 4 and Comparative Examples 1 to 4, positive electrodes were produced by the following method. The composite positive electrode active material and the sulfide-based solid electrolyte (Li2S-P2S5-based glass ceramics containing LiI, D50 = 0.8 μm) were weighed out to a volume ratio of 6:4, and these were placed in heptane together with 3 mass% vapor grown carbon fiber (VGCF) as a conductive material and 0.7 mass% butadiene rubber as a binder. Next, these were mixed to prepare a positive electrode mixture. The prepared positive electrode mixture was thoroughly dispersed using an ultrasonic homogenizer (UH-50 manufactured by SMT), and then coated onto aluminum foil as a positive electrode current collector. The mixture was dried at 100 °C for 30 minutes to form a positive electrode layer on the positive electrode current collector. After that, a 1 cm 2 The positive electrode was obtained by punching out a piece of the sheet.

[0080] [Preparation of negative electrode] A sulfide-based solid electrolyte (Li2S-P2S5-based glass ceramic containing LiI, D50 = 0.8 μm), 1 mass% of vapor-grown carbon fiber (VGCF) as a conductive material, 2 mass% of butadiene rubber as a binder, 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 mixture was placed in a kneading container so that the volume ratio of the solid electrolyte to the particles (D50 = 1 μm) was 7:3, and the mixture was stirred at 15,000 rpm for 60 minutes using a Filmix device to prepare a negative electrode mixture. The prepared negative electrode mixture was applied to a copper foil negative electrode current collector and dried at 100°C for 30 minutes to form a negative electrode layer on the negative electrode current collector. After that, a 1 cm 2 The negative electrode was obtained by punching out the material into a size of 100 mm.

[0081] [Preparation of solid electrolyte layer] Inner diameter cross-sectional area 1cm 2 64.8 mg of sulfide-based solid electrolyte (Li2S-P2S5-based glass ceramics containing LiI, D50 = 2.5 μm) was placed in the cylindrical ceramic, smoothed, and then subjected to 1 ton / cm 2 The mixture was pressed with a pressure of 1000 kJ / cm 2 to form a solid electrolyte layer.

[0082] [Battery construction] The prepared positive electrode was placed on one side of the solid electrolyte layer so that the positive electrode layer was in contact with the solid electrolyte layer, and the prepared negative electrode was placed on the other side so that the negative electrode layer was in contact with the solid electrolyte layer. 2 Then, stainless steel rods were inserted into both electrodes and restrained at 1 ton to obtain an all-solid-state lithium-ion secondary battery.

[0083] [Evaluation of initial battery resistance] The capacity of the all-solid-state lithium-ion secondary battery was confirmed by constant current-constant voltage charging and discharging at a 1 / 3C rate between 1.5V and 3.0V. The battery was then adjusted to an SOC of 50% at a 1 / 3C rate. The initial interface resistance was then determined by AC impedance measurement. AC impedance at 25℃, 10mV, 0.1 to 10 6 The interfacial resistance was measured in Hz, and an arc was fitted to the Cole-Cole plot. The distance between the two intersections of the fitted arc and the real axis was taken as the interfacial resistance. The obtained interfacial resistance was taken as the initial resistance. The interface resistance of the all-solid-state lithium-ion secondary battery according to Example 1 was set as the reference (1.0), and the interface resistance of the all-solid-state lithium-ion secondary batteries according to each Example and Comparative Example was evaluated relative to the reference (1.0). The results are shown in Table 1.

[0084] [Resistance change rate] After measuring the initial interface resistance, the battery was charged to 3.0 V by constant current and constant voltage, and then subjected to a 5-day storage test at 60°C. If the voltage dropped below 2.98 V, additional charging was performed as needed to maintain the battery voltage. After the storage test, the interface resistance was measured using the AC impedance, and the ratio to the initial interface resistance was taken as the resistance change rate (resistance increase rate). The results are shown in Table 1.

[0085] [Table 1]

[0086] [Evaluation results] As shown in Comparative Example 1, even if the coverage exceeds 57% and the Li / B ratio is in the range of 0.1 to 0.8, if Iα / Iβ is less than 1.0, the resistance change rate increases. If Iα / Iβ is less than 1.0, the decomposition potential of the coating layer decreases. In a structure in which BO4 units are introduced, the regularity decreases relatively, and the stability of the structure decreases. Furthermore, the presence of BO4 units increases the B 3+ This is thought to be because the distance between cations such as methyl cations becomes shorter, resulting in a decrease in the stability of the structure.

[0087] As shown in Comparative Example 2, even if the coverage exceeds 57% and the Li / B ratio is in the range of 0.1 to 0.8, resistance increases when Iα / Iβ is greater than 1.5. This is because, during heat treatment to increase the ratio, a chemical reaction occurs between the positive electrode active material and the coating layer at a baking temperature of 500°C or higher, forming a high-resistance layer, which increases resistance.

[0088] As shown in Comparative Example 3, even if the coverage exceeds 57% and Iα / Iβ is in the range of 1.0 to 1.5, when the Li / B ratio exceeds 0.8, the rate of resistance change increases. When the Li / B ratio exceeds 0.8, the coating layer contains a large amount of Li, which reduces its decomposition potential. The more Li a compound contains, the more easily the Li in the compound is released when placed in a high-potential environment, and it is thought that the structure of the compound changes (decomposes) as Li is removed. The product of decomposition has poor Li-ion conductivity, so the rate of resistance change increases. By keeping the Li / B ratio of the coating layer at 0.8 or less, decomposition is less likely even at high potentials, such as 4.5 V or higher. If the Li / B ratio is less than 0.1, the Li ion conductivity will decrease due to the lack of Li ions in the coating layer. Also, the excess boron in the coating layer prevents Li from penetrating into the lithium borate structure, resulting in the formation of other electrochemically inactive compounds, which will increase the resistance.

[0089] As shown in Comparative Example 4, even when the Li / B ratio is 0.1 to 0.8 and Iα / Iβ is in the range of 1.0 to 1.5, the initial resistance is high and the rate of resistance change increases when the coverage is 57% or less.

[0090] As shown in Examples 1 to 4, it was demonstrated that when the coverage exceeds 57%, the Li / B ratio is 0.1 to 0.8, and Iα / Iβ is in the range of 1.0 to 1.5, the lithium ion conductivity in the coating layer is increased, the initial resistance is reduced, and an increase in the rate of resistance change can be suppressed.

Claims

1. A composite positive electrode active material comprising a lithium metal oxide as a positive electrode active material and a coating layer covering at least a part of the surface of the positive electrode active material, the coating layer contains Li, B, and O; a molar ratio Li / B of Li element to B element in the coating layer is 0.1 to 0.4; In Raman spectroscopy, 780 cm －１ The intensity of the peak Iβ at 720 cm －１ The intensity ratio Iα / Iβ of the peak intensities Iα is 1.5, the coverage of the coating layer covering the positive electrode active material is 80 to 82%; The thickness of the coating layer is 19 to 21 nm.

2. the positive electrode active material is positive electrode active material particles, The composite positive electrode active material of claim 1 , wherein the composite positive electrode active material is a composite positive electrode active material particle.

3. The composite positive electrode active material according to claim 1 or 2, which is for a sulfide all-solid-state battery.

4. A method for producing the composite positive electrode active material according to any one of claims 1 to 3, supplying the slurry containing the positive electrode active material and the coating liquid to a spray dryer, forming the slurry into droplets, and air-drying the droplets of the slurry to obtain a precursor of a composite positive electrode active material; and calcining the precursor, The method for producing a composite positive electrode active material, wherein the coating liquid contains a lithium source, a boron source, and an oxygen source.

5. The method for producing a composite positive electrode active material according to claim 4 , wherein the precursor is fired at 400° C. in the firing step.

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