Positive electrode for non-aqueous electrolyte secondary battery and non-aqueous electrolyte secondary battery

Abstract

By more effectively preventing exposure of the positive electrode current collector when a foreign object such as a nail penetrates the positive electrode current collector, the effect of preventing short circuits in non-aqueous electrolyte secondary batteries is improved more than ever before. [Solution] A positive electrode (1) for a non-aqueous electrolyte secondary battery includes a positive electrode current collector (11), a positive electrode composite layer (12), and an intermediate layer (13) provided between the positive electrode current collector and the positive electrode composite layer, wherein the intermediate layer contains first particles and second particles, the first particles are insulating and contain boron nitride, and the second particles contain at least one of a metal hydroxide and a metal oxide and a flame-retardant component, the ratio of the major axis to the minor axis of the first particles (major axis / minor axis) being 3.0 or more and 30 or less, the 50% cumulative value of the volume-based particle size distribution of the first particles being 0.01 μm or more and 8 μm or less, and the 50% cumulative value of the volume-based particle size distribution of the second particles being 0.01 μm or more and 8 μm or less.

Description

[Technical Field]

[0001] The present invention relates to a positive electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery including the same. [Background technology]

[0002] Non-aqueous electrolyte secondary batteries, including lithium-ion secondary batteries, are widely used as power sources for smartphones, laptops, and other devices, and have recently been used as large batteries for automobiles and other applications. On the other hand, while lithium ion secondary batteries have the advantage of high energy density, they require sufficient safety measures because they use a non-aqueous electrolyte. In recent years, as batteries have become larger, ensuring safety has become even more important.

[0003] For example, when a lithium-ion secondary battery is installed in a vehicle, such as when the battery is being driven, there is a risk that a sharp foreign object such as a nail may fly into the battery and pierce it while the battery is in use. If a sharp foreign object such as a nail pierces the battery, there is a risk of a short circuit between the positive electrode and the negative electrode. In particular, if the positive electrode current collector and the positive electrode composite layer are deformed, the positive electrode composite layer may peel off from the positive electrode current collector, and the exposed positive electrode current collector may come into contact with the negative electrode, causing a short circuit with relatively low resistance and generating a very large amount of Joule heat.

[0004] Therefore, as a countermeasure against the penetration of a foreign object into a lithium-ion secondary battery, it is conceivable to provide an intermediate layer that can prevent exposure of the positive electrode current collector even if the positive electrode composite layer peels off from the positive electrode current collector due to deformation. As described in Patent Document 1, such an intermediate layer is provided between the positive electrode current collector and the positive electrode active material layer, and includes particles made of a metal oxide and low Young's modulus particles made of a solid electrolyte material or a resin material. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-87647 Summary of the Invention [Problem to be solved by the invention]

[0006] However, according to the investigations of the present inventors, it has been found that there is still room for further improvement in the short circuit suppression effect of the conventional intermediate layer as described above.

[0007] The present invention aims to improve the short-circuit suppression effect of nonaqueous electrolyte secondary batteries more than ever before by more effectively suppressing exposure of the positive electrode current collector when a foreign object such as a nail penetrates the positive electrode current collector, by devising the composition of the intermediate layer and the shape of the particles that form the intermediate layer. [Means for solving the problem]

[0008] That is, the present invention is as follows. [1] A positive electrode for a non-aqueous electrolyte secondary battery, comprising: a positive electrode current collector; a positive electrode mixture layer; and an intermediate layer provided between the positive electrode current collector and the positive electrode mixture layer, the intermediate layer contains first particles and second particles, the first particles are insulating particles containing boron nitride, the second particles contain at least one of a metal hydroxide and a metal oxide and a flame retardant component, the ratio of the major axis to the minor axis of the first particles (major axis / minor axis) is 3.0 or more and 30 or less, the first particles have a volume-based particle size distribution with an integrated value of 50% of 0.01 μm or more and 8 μm or less; The positive electrode for a non-aqueous electrolyte secondary battery, wherein the second particles have a 50% cumulative value of a particle size distribution on a volume basis of 0.01 μm or more and 8 μm or less. [2] The positive electrode for a non-aqueous electrolyte secondary battery according to [1], wherein the first particles are made of boron nitride. [3] The amount of P2 desorbed from the second particles by a temperature-programmed desorption mass spectrometer (TDS-MS) from 80°C to 1400°C (MS1) is 200 × 10-6 mol / g or more 2500×10 -6 mol / or less, The amount of H2O desorbed from the second particles at temperatures between 80 °C and 200 °C (MS2) was 50 × 10 -6 mol / g or more 1000×10 -6 mol / or less, The positive electrode for a non-aqueous electrolyte secondary battery according to [1] or [2], wherein the ratio (MS1 / MS2) of the amount of desorbed P2 to the amount of desorbed H2O satisfies the following formula (1): 0.5≦(MS1 / MS2)≦10 (1) [4] The positive electrode for a non-aqueous electrolyte secondary battery according to any one of [1] to [3], wherein the second particles are at least one of the metal hydroxide and the metal oxide, the surface or the interior of which is modified with a flame retardant. [5] The positive electrode for a non-aqueous electrolyte secondary battery according to any one of [1] to [4], wherein the metal hydroxide contains at least one selected from the group consisting of kaolinite, pseudoboehmite, boehmite, and aluminum hydroxide. [6] The positive electrode for a non-aqueous electrolyte secondary battery according to any one of [1] to [5], wherein the metal oxide is activated alumina. [7] The positive electrode for a non-aqueous electrolyte secondary battery according to [4], wherein the flame retardant contains at least one selected from the group consisting of phosphoric acid, a phosphoric acid ester, a phosphonic acid, a phosphonic acid ester, a phosphinic acid, and a phosphinic acid ester. [8] The positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims [1] to [7], wherein the thickness of the intermediate layer is 0.1 µm or more and 10 µm or less. [9] The positive electrode for a non-aqueous electrolyte secondary battery according to any one of [1] to [8], wherein the intermediate layer further contains a conductive agent.

[10] The positive electrode for a non-aqueous electrolyte secondary battery according to [9], wherein the conductive agent is at least one of carbon nanofibers and carbon black.

[11] A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution, A non-aqueous electrolyte secondary battery, wherein the positive electrode is the positive electrode for a non-aqueous electrolyte secondary battery according to any one of [1] to

[10] . [Effects of the Invention]

[0009] According to the present invention, by incorporating first particles containing boron nitride and setting the aspect ratio (major axis / minor axis) of these first particles to be 3.0 or more and 30 or less, the intermediate layer containing the first particles can deform to conform as closely as possible to the surface shape of the positive electrode current collector when a foreign object such as a nail penetrates the positive electrode current collector, thereby making it possible to suppress exposure of the positive electrode current collector more than ever before. Boron nitride can capture active oxygen, thereby suppressing the decomposition reaction of the electrolyte and suppressing the temperature rise of the battery. Since the intermediate layer further contains second particles containing at least one of a metal hydroxide and a metal oxide and a flame-retardant component, the endothermic reaction of the metal hydroxide or metal oxide and the effect of inhibiting the electrolyte decomposition reaction by radical scavenging by the flame-retardant component can further suppress the temperature rise of the battery, thereby dramatically improving safety. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic diagram showing the overall structure of a nonaqueous electrolyte secondary battery according to one embodiment of the present invention; [Figure 2] FIG. 1 is a graph showing the results of confirming whether or not heat is generated at 150° C. or less in the presence of an electrolyte solution in Examples and Comparative Examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0011] A specific configuration of a nonaqueous electrolyte secondary battery according to one embodiment of the present invention will be described below. <1. Basic structure of non-aqueous electrolyte secondary battery> 1, the nonaqueous electrolyte secondary battery 100 according to this embodiment is a lithium ion secondary battery including a positive electrode 1, a negative electrode 2, a separator 3, a nonaqueous electrolyte solution 4, and a container 5 that accommodates these components. FIG. 1 is a schematic cross-sectional view showing the cross section of the nonaqueous electrolyte secondary battery 100. The shape of the lithium ion secondary battery is not particularly limited, but may be, for example, any of a cylindrical shape, a prismatic shape, a laminate shape, a button shape, or the like.

[0012] (1-1. Positive electrode) The positive electrode 1 includes a positive electrode current collector 11 and a positive electrode mixture layer 12 formed on the positive electrode current collector 11 . The positive electrode current collector 11 may be any conductive material, for example, a plate or foil, and is preferably made of aluminum, stainless steel, nickel-plated steel, or the like. The positive electrode mixture layer 12 contains a positive electrode active material, and may further contain a conductive agent and a positive electrode binder.

[0013] The positive electrode active material is, for example, a lithium-containing transition metal oxide or solid solution oxide, and is not particularly limited as long as it is a material that can electrochemically absorb and release lithium ions. The shape of the positive electrode active material is not particularly limited, but it is preferably in the form of particles. Examples of the lithium-containing transition metal oxide include Li 1.0 Ni 0.88 Co 0.1 Al 0.01 Mg 0.01 O2, but also LiCoO2 and other Li-Co based composite oxides, LiNi x Co y Mn z Examples of solid solution oxides include Li·Ni·Co·Mn-based composite oxides such as LiO2, Li·Ni-based composite oxides such as LiNiO2, and Li·Mn-based composite oxides such as LiMn2O4. a Mn x Coy Ni z O2 (1.150≦a≦1.430, 0.45≦x≦0.6, 0.10≦y≦0.15, 0.20≦z≦0.28), LiMn 1.5 Ni 0.5 O4, etc. The content (content ratio) of the positive electrode active material is not particularly limited as long as it is a content that is applicable to the positive electrode composite layer 12 of the nonaqueous electrolyte secondary battery 100. These compounds may be used alone or in combination.

[0014] The conductive agent is not particularly limited as long as it is capable of increasing the conductivity of the positive electrode 1. Specific examples of the conductive agent include those containing one or more selected from carbon black, natural graphite, artificial graphite, fibrous carbon, and sheet carbon. Examples of the carbon black include furnace black, channel black, thermal black, ketjen black, and acetylene black. Examples of the fibrous carbon include carbon nanotubes and carbon nanofibers, and examples of the sheet-like carbon include graphene. The content of the conductive agent in positive electrode composite layer 12 is not particularly limited, but from the viewpoint of achieving both electrical conductivity and battery capacity, it is preferably 0.1 mass % or more and 5 mass % or less, and more preferably 0.5 mass % or more and 3 mass % or less, relative to the entire positive electrode composite layer 12.

[0015] Examples of the positive electrode binder include fluorine-containing resins such as polyvinylidene fluoride, ethylene-containing resins such as styrene-butadiene rubber, ethylene-propylene-diene terpolymer, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene, polyvinyl alcohol, carboxymethyl cellulose or carboxymethyl cellulose derivatives (such as salts of carboxymethyl cellulose), and nitrocellulose. The positive electrode binder is not particularly limited as long as it can bind the positive electrode active material and the conductive agent onto the positive electrode current collector 11.

[0016] (1-2. Negative electrode) The negative electrode 2 includes a negative electrode current collector 21 and a negative electrode mixture layer 22 formed on the negative electrode current collector 21 . The negative electrode current collector 21 may be any conductive material, and is preferably, for example, in the form of a plate or foil, and is made of copper, stainless steel, nickel-plated steel, or the like.

[0017] The negative electrode mixture layer 22 contains a negative electrode active material, and may further contain a conductive agent and a negative electrode binder. The negative electrode active material is not particularly limited as long as it can electrochemically absorb and release lithium ions. Examples of the negative electrode active material include graphite active materials (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), Si-based active materials or Sn-based active materials (for example, a mixture of fine particles of silicon (Si) or tin (Sn) or an oxide thereof with a graphite active material, fine particles of silicon or tin, and an alloy based on silicon or tin), metallic lithium, and Li4Ti5O 12 Examples of the negative electrode active material include titanium oxide compounds such as those listed above, and lithium nitrides. One of the above-listed materials may be used alone, or two or more may be used in combination. Silicon oxide is represented by SiOx (0≦x≦2).

[0018] The conductive agent is not particularly limited as long as it is capable of increasing the conductivity of the negative electrode 2, and for example, the same agents as those described in the section on the positive electrode 1 can be used. The content of the conductive agent in the negative electrode composite layer 22 is not particularly limited, but from the viewpoint of achieving both electrical conductivity and battery capacity, it is preferably 0.1 mass % or more and 5 mass % or less, and more preferably 0.5 mass % or more and 3 mass % or less, relative to the entire negative electrode composite layer 22.

[0019] The negative electrode binder is not particularly limited as long as it can bind the negative electrode active material and the conductive agent onto the negative electrode current collector 21. The negative electrode binder may be, for example, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), styrene-butadiene copolymer (SBR), or metal salt of carboxymethyl cellulose (CMC). One type of binder may be used alone, or two or more types may be used in combination.

[0020] (1-3. Separator) There are no particular limitations on the separator 3, and any material may be used as long as it is suitable for use as a separator for a lithium ion secondary battery. As the separator 3, it is preferable to use a porous film, a nonwoven fabric, or the like, which exhibits excellent high-rate discharge performance, either alone or in combination. Examples of resins constituting the separator 3 include polyolefin resins typified by polyethylene, polypropylene, etc., polyester resins typified by polyethylene terephthalate, polybutylene terephthalate, etc., polyvinylidene difluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene difluoride-tetrafluoroethylene copolymer, vinylidene difluoride-trifluoroethylene copolymer, vinylidene difluoride- ... copolymer), vinylidene fluoride-hexafluoroacetone copolymer, vinylidene fluoride-ethylene copolymer, vinylidene difluoride-propylene copolymer, vinylidene fluoride-trifluoropropylene copolymerExamples of the porosity of the separator 3 include vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, vinylidene fluoride-ethylene-tetrafluoroethylene copolymer, etc. The porosity of the separator 3 is not particularly limited, and any porosity of the separators of conventional lithium ion secondary batteries can be applied.

[0021] The separator 3 may further include a surface layer that covers the surface of the porous membrane or nonwoven fabric. The surface layer may contain an adhesive for bonding to the electrodes to fix the battery element. Examples of the adhesive include vinylidene fluoride-hexafluoropropylene copolymer, acid-modified vinylidene fluoride polymer, and styrene-(meth)acrylic acid ester copolymer.

[0022] (1-4.Non-aqueous electrolyte) The nonaqueous electrolyte 4 can be the same as any nonaqueous electrolyte conventionally used in lithium ion secondary batteries, without any particular limitation. The nonaqueous electrolyte 4 has a composition in which an electrolyte salt is contained in a nonaqueous solvent, which is a solvent for the electrolyte. Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate, ethylene carbonate, butylene carbonate, chloroethylene carbonate, fluoroethylene carbonate, and vinylene carbonate; cyclic esters such as γ-butyrolactone and γ-valerolactone; chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate; methylformate, methylacetate, methylbutyrate, ethylpropionate, and propylpropionate. propionate, tetrahydrofuran or its derivatives, 1,3-dioxane, 1,4-dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane (1,4-dibutoxyethane, or methyldiglyme, ethers such as ethylene glycol monopropyl ether and propylene glycol monopropyl ether, nitriles such as acetonitrile and benzonitrile, dioxolane or its derivatives, ethylene sulfide, sulfolane, sultone or its derivatives, etc., can be used alone or in combination of two or more. When two or more of the nonaqueous solvents are used in combination, the mixing ratio of the nonaqueous solvents can be the same as that used in conventional lithium ion secondary batteries.

[0023] Examples of the electrolyte salt include LiClO4, LiBF4, LiAsF6, LiPF6, and LIPF6-x (C n F 2n+1 )x[However, 1 <x<6、n=1or2]、LiSCN、LiBr、LiI、Li2SO4、Li2B 10 Cl 10, inorganic ion salts containing one of lithium (Li), sodium (Na) or potassium (K) such as NaClO4, NaI, NaSCN, NaBr, KClO4, KSCN, LiCF3SO3, LiN(CF3SO2)2, LiN(C2F5SO2)2, LiN(CF3SO2)(C4F9SO2), LiC(CF3SO2)3, LiC(C2F5SO2)3, (CH3)4NBF4, (CH3)4NBr, (C2H5)4NClO4, (C2H5)4NI, (C3H7)4NBr, (n-C4H9)4NClO4, (n-C4H9)4NI, (C2H5)4N-maleate, (C2H5)4N-benzoate, (C2H5)4N-phtalate, lithium stearyl sulfonic acid Examples of suitable ionic salts include organic ionic salts such as lithium, octyl sulfonic acid lithium, and dodecyl benzenesulfonic acid lithium. These ionic compounds can be used alone or in combination of two or more. The concentration of the electrolyte salt may be the same as that of nonaqueous electrolytes used in conventional lithium-ion secondary batteries and is not particularly limited. In this embodiment, it is preferable to use a nonaqueous electrolyte 4 containing the aforementioned lithium compound (electrolyte salt) at a concentration of approximately 0.8 mol / L to 1.5 mol / L.

[0024] Various additives may be added to the non-aqueous electrolyte solution 4. Examples of such additives include negative electrode additives, positive electrode additives, ester-based additives, carbonate-based additives, sulfate-based additives, phosphate-based additives, borate-based additives, acid anhydride-based additives, and electrolyte-based additives. Any one of these additives may be added to the non-aqueous electrolyte solution, or multiple types of additives may be added to the non-aqueous electrolyte solution.

[0025] 2. Characteristic Configuration of the Non-Aqueous Electrolyte Secondary Battery According to the Present Embodiment The characteristic configuration of the nonaqueous electrolyte secondary battery 100 according to this embodiment will be described below. The positive electrode 1 of the non-aqueous electrolyte secondary battery 100 according to this embodiment includes an intermediate layer 13 between a positive electrode current collector 11 and a positive electrode mixture layer 12 .

[0026] The intermediate layer 13 contains, for example, first particles, second particles, a conductive agent, and an intermediate layer binder.

[0027] The first particles are insulating particles containing boron nitride. The first particles may be composed mainly of boron nitride, or may consist of boron nitride. The "main component" refers to the component that is contained in the particle in the greatest amount, and refers to the component that is contained in the particle at a ratio of, for example, 50% by mass or more, 70% by mass or more, 90% by mass or more, etc., relative to the entire particle. In this embodiment, one example of the first particles is one made of boron nitride.

[0028] The first particles have an aspect ratio, ie, a ratio of their major axis to their minor axis (major axis / minor axis), of 3.0 or more and 30 or less, and more preferably 3.0 or more and 15 or less. The major axis refers to the largest diameter of the particle, and the minor axis refers to the smallest diameter of the particle. For example, if the particle is flaky (thin), the major axis may refer to the longest diameter of the flake, and the minor axis may refer to the thickness of the flake. Examples of methods for measuring the major axis and the minor axis include a method of calculating D50, which is the cumulative value of 50% of the particle size distribution based on the particle size volume in a particle size distribution obtained by a laser diffraction / scattering method, and a method of calculating the major axis and / or the minor axis from a scanning electron microscope image. These measurement methods may be used alone, or a more accurate method may be used by combining both. For example, if the particles are scaly (thin) and have a sufficiently small thickness that it is difficult to accurately measure the thickness using a method for calculating D50, it is possible to measure the major axis as D50 and calculate the minor axis from a scanning electron microscope image. In this embodiment, a scale-like (thin flake-like) particle is used as an example of the first particle, but the shape of the first particle may be any shape as long as it satisfies the aspect ratio condition described above, and may be any of oblate spheroid, scale-like, columnar, and needle-like.

[0029] The particle diameter D50, which is the integrated value of 50% of the volume-based particle size distribution in the particle size distribution of the first particles obtained by a volume-based laser diffraction / scattering method, is 0.01 μm or more and 8 μm or less, more preferably 0.05 μm or more and 7 μm or less, and even more preferably 0.1 μm or more and 6 μm or less.

[0030] The content of the first particles in the intermediate layer 13 is preferably 40% by mass or more and 90% by mass or less, more preferably 50% by mass or more and 80% by mass or less, and even more preferably 60% by mass or more and 70% by mass or less, when the entire intermediate layer 13 is taken as 100% by mass.

[0031] The second particles contain at least one of a metal hydroxide and a metal oxide, and a flame retardant component.

[0032] The second particles may be, for example, composite particles obtained by mixing and heating one or more of metal hydroxide particles and metal oxide particles with a flame retardant component to form a composite. The composite particles used in this embodiment will be specifically described below.

[0033] The composite particles described above are formed by heating and combining one or more of metal hydroxide and metal oxide particles capable of absorbing heat through an endothermic reaction with a flame-retardant component having radical scavenging ability. These composite particles are formed by combining the one or more of the metal hydroxide and metal oxide particles with the flame-retardant component in a state where they are mixed as uniformly as possible. More specifically, the composite particles are an aggregate of one or more of the metal hydroxide and metal oxide particles containing the flame-retardant component on their surfaces and in their interiors. Here, "composite" refers to a state in which multiple particles are chemically bonded to one another via functional groups (e.g., hydroxyl groups and phosphate groups) possessed by one or more of the metal hydroxide and metal oxide particles containing the flame-retardant component on their surfaces and in their interiors, forming a single mass. Here, chemical bonding includes not only covalent bonds but also various types of bonds such as ionic bonds, coordinate bonds, and metallic bonds. The bonding state between particles can be confirmed, for example, by X-ray photoelectron spectroscopy.

[0034] In addition, the BET specific surface area of ​​the composite particles calculated from the adsorption isotherm measured by adsorbing nitrogen onto the composite particles is 8 m 2 / g or more 80m 2 / g or less, and 2 / g or more 75m 2 / g or less is more preferable, and 15m 2 / g or more 75m 2 It is particularly preferable that the saturation coefficient is 1 / g or less.

[0035] The metal hydroxides and metal oxides are not particularly limited as long as they are endothermic substances capable of causing an endothermic reaction. Specific examples of the metal hydroxides and metal oxides include aluminum hydroxide, pseudoboehmite, boehmite, activated alumina, and kaolinite. These may be used alone or in combination of two or more.

[0036] The content of the metal hydroxide particles and metal oxide particles in the composite particles is preferably in the range of 1% by mass to 60% by mass, more preferably in the range of 5% by mass to 50% by mass, and even more preferably in the range of 10% by mass to 40% by mass, based on the total composite particle (100% by mass). When multiple types of metal hydroxide particles and metal oxide particles are used in combination, this content refers to the total content of these.

[0037] The flame retardant component may be any component as long as it has a radical scavenging ability to capture radicals such as oxygen radicals generated in the positive electrode mixture layer. For example, it is preferable that the flame retardant component is derived from one or more flame retardants selected from the group consisting of phosphoric acid, phosphate ester, phosphonic acid, phosphonate ester, phosphinic acid, and phosphinate ester, which are capable of forming a functional group containing phosphorus (P) element by being combined with one or more of the metal hydroxide and metal oxide particles. Examples of the phosphate ester include phenyl phosphate, diphenyl phosphate, and triphenyl phosphate. Examples of the phosphonate ester include phenylphosphonic acid and methylphosphonic acid. Examples of phosphinic acid esters include methylphosphinic acid.

[0038] The content of P (phosphorus), the total content of P (phosphorus) and B (boron), or the total content of P (phosphorus) and Br (bromine) in the composite particles measured by inductively coupled plasma atomic emission spectroscopy (ICP-AES) is preferably in the range of 18% to 30% by mass relative to the total composite particle (100% by mass).The content or total content of these elements is more preferably 18% to 25% by mass.

[0039] The content of P (phosphorus) element in the composite particles is preferably 5% by mass or more and 30% by mass or less, and more preferably 8% by mass or more and 30% by mass or less. The content of B (boron) element in the composite particles may be 0, or may be 1% by mass or more and 25% by mass or less, or may be 5% by mass or more and 15% by mass or less. The content of Br (bromine) element in the composite particles may be 0, or may be 1% by mass or more and 25% by mass or less, or may be 5% by mass or more and 10% by mass or less.

[0040] The content of Al (aluminum) element in the composite particles measured by ICP-AES may be 0, but is preferably 1% by mass to 30% by mass or less, more preferably 3% by mass to 20% by mass or less, and particularly preferably 5% by mass to 15% by mass or less.

[0041] The composite particles preferably have various outgassing amounts due to various modifying groups within the following ranges. The amount of P2 gas desorbed from the composite particles when the composite particles were heated from 80°C to 1400°C was measured by a temperature programmed desorption mass spectrometer (TDS-MS), and the amount of desorbed P2 (referred to as MS1) was 5 x 10 -6 mol / g or more 5000×10 -6 mol / g or less, and in this embodiment, it is particularly 500×10 -6 mol / g or more 2000×10 -6 mol / g or less, and preferably 600×10 -6 mol / g or more 1900×10 -6 mol / g or less is more preferable, and 700×10 -6 mol / g or more 1800×10 -6 It is more preferably mol / g or less.

[0042] In addition, the amount of H2O gas desorbed from the composite particles when the composite particles were heated from 80°C to 200°C was measured by TDS-MS, and the amount of desorbed H2O (referred to as MS2) was 50 × 10 -6 mol / g or more 6000×10 -6 mol / g or less, and in the composite particles of this embodiment, it is 50×10 -6mol / g or more 1000×10 -6 mol / g or less, and preferably 100×10 -6 mol / g or more 950×10 -6 mol / g or less is more preferable, and 200×10 -6 mol / g or more 900×10 -6 It is more preferably mol / g or less.

[0043] Furthermore, the ratio of these gas desorption amounts (M1 / M2) is preferably 0.1 or more and 10 or less, and in the composite particles of this embodiment, it is particularly preferably 0.5 or more and 10 or less, more preferably 0.7 or more and 5.0 or less, and particularly preferably 0.8 or more and 3.0 or less. When the ratio of gas desorption amounts (M1 / M2) satisfies the above-mentioned preferred range, it is possible to achieve a better balance between the temperature rise suppression effect and battery performance, which are achieved by increasing the content of the flame retardant component in the composite particles.

[0044] Increasing the phosphorus content of the composite particles improves the effect of suppressing temperature rise inside the battery. On the other hand, increasing the amount of flame retardant such as phosphoric acid or phosphonic acid to increase the phosphorus content increases the hydrophilicity of the composite particles, making it difficult to uniformly mix the composite particles into the slurry used to form the intermediate layer. After extensive research into this issue, the inventors discovered that by using not only phosphoric acid or phosphonic acid with a high phosphorus content but also a flame retardant containing a hydrophobic group such as a phosphate ester or phosphonate ester, it is possible to increase the phosphorus content even more than before while preventing excessive hydrophilicity. The hydrophobic group content of the composite particles can be evaluated by the amount of desorption of the following various gases derived from each hydrophobic group in the composite particles. It is preferable that the amount of desorption of each gas falls within the following range.

[0045] The amount of CH4 gas desorbed from the composite particles when the composite particles were heated from 80°C to 1400°C was measured by TDS-MS. The amount of desorbed CH4 (referred to as MS3) exceeded 0 and was 3000 x 10-6 It is preferable that the concentration is 0 or less, and in this embodiment, it may be 0, but is preferably 3×10 -6 mol / g or more 400×10 -6 mol / g or less, and preferably 40×10 -6 mol / g or more 350×10 -6 mol / g or less is more preferable, and 50×10 -6 mol / g or more 300×10 -6 It is particularly preferable that the content is mol / g or less. Similarly, the amount of desorbed CH3OH (MS4) was measured to be greater than 0 and 6000 x 10 -6 It is preferable that the content of the saturation current is 500 mol / g or less. In this embodiment, it may be 0. -6 mol / g or more 2500×10 -6 mol / g or less, and preferably 600×10 -6 mol / g or more 2450×10 -6 mol / g or less is more preferable, and 700×10 -6 mol / g or more 2400×10 -6 It is particularly preferable that the content is mol / g or less.

[0046] When the composite particles are modified with a functional group containing a hydrophobic group, particularly a phenyl group, the composite particles are more easily dispersed in a non-aqueous solvent such as N-methyl-2-pyrrolidone (NMP) when a slurry is prepared using the solvent. Therefore, the amount of C6H6 desorbed from the composite particles at temperatures between 80°C and 1400°C by TDS-MS (referred to as MS5) exceeds 0 and is 5000 x 10 -6 It is preferable that the content of the hydroxyl group is 0 mol / g or less, and in this embodiment, it may be 0, but it is preferable that the content of the hydroxyl group is 100 mol / g or less. -6 mol / g or more 2500×10 -6 mol / g or less, and preferably 300×10 -6 mol / g or more 2400×10 -6 mol / g or less is more preferable, and 600×10 -6 mol / g or more 2300×10 -6 It is particularly preferable that the content is mol / g or less.

[0047] The shape of the second particles is not particularly limited, but is preferably spherical. The particle diameter D50 (integrated value 50% of the volume-based particle size distribution) of the second particles, determined by a volume-based laser diffraction / scattering method, is 0.01 μm to 8 μm, more preferably 0.05 μm to 5 μm, and even more preferably 0.1 μm to 3 μm. The particle size of the composite particles can be controlled by the preparation conditions of the composite particles. For example, increasing the temperature or the stirring peripheral speed during preparation of the composite particles tends to reduce the particle size of the composite particles. For example, it is possible to make the particle size of the composite particles smaller than the particle size of the metal hydroxide or metal oxide that is the starting material.

[0048] The content of the second particles in the intermediate layer 13 is preferably 1% by mass or more and 40% by mass or less, more preferably 5% by mass or more and 30% by mass or less, and even more preferably 10% by mass or more and 20% by mass or less, when the entire intermediate layer 13 is taken as 100% by mass.

[0049] The conductive agent contains, for example, one or more selected from carbon black, natural graphite, artificial graphite, fibrous carbon, and sheet carbon. Examples of the carbon black include furnace black, channel black, thermal black, ketjen black, and acetylene black. Of these, the fibrous carbon is more preferably used, and carbon nanofibers are even more preferably used, from the viewpoint that a conductive path can be formed even with a small content.

[0050] The content of the conductive agent in the intermediate layer 13 is preferably 0.01% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 5% by mass or less, and even more preferably 1% by mass or more and 3% by mass or less, when the entire intermediate layer 13 is taken as 100% by mass.

[0051] The binder for the intermediate layer is not particularly limited as long as it can bind the components constituting the intermediate layer 13 to each other and can bind the intermediate layer 13 onto the positive electrode current collector 11. Examples of binders for the intermediate layer include fluorine-containing resins such as polyvinylidene fluoride, ethylene-containing resins such as styrene-butadiene rubber, ethylene-propylene-diene terpolymer, acrylonitrile-butadiene rubber, fluororubber, polyvinyl acetate, polymethylmethacrylate, polyethylene, polyvinyl alcohol, carboxymethyl cellulose or carboxymethyl cellulose derivatives (such as salts of carboxymethyl cellulose), and nitrocellulose.

[0052] The content of the intermediate layer binder in the intermediate layer 13 is preferably 0.1% by mass or more and 30% by mass or less, more preferably 5% by mass or more and 25% by mass or less, and even more preferably 10% by mass or more and 20% by mass or less, when the entire intermediate layer 13 is taken as 100% by mass.

[0053] The thickness of the intermediate layer 13 is preferably 0.1 μm or more and 10 μm or less, more preferably 0.5 μm or more and 8 μm or less, and even more preferably 1 μm or more and 5 μm or less.

[0054] By making the thickness of the intermediate layer 13 0.1 μm or more, it is possible to achieve sufficient short-circuit prevention and heat generation suppression effects. Furthermore, by making the thickness of the intermediate layer 13 10 μm or less, it is possible to suppress an increase in electrical resistance and a decrease in the energy density of the battery due to the provision of the intermediate layer 13. The thickness of the intermediate layer 13 can be measured, for example, by the following procedure. First, a cross-sectional sample is prepared by cutting the positive electrode 1 along its thickness direction using a cross-sectional sample preparation device such as a cross polisher. The prepared cross-sectional sample is observed with a scanning electron microscope (SEM), and the thickness of the intermediate layer 13 is calculated from the SEM image. Specifically, the thickness of the intermediate layer 13 is measured at at least three locations on the cross-sectional sample, including near the center and both ends, and the average value is taken as the thickness of the intermediate layer 13.

[0055] The contents of the first particles and the second particles in the intermediate layer 13 can be measured by the following method. First, a cross-sectional sample including the intermediate layer 13 is prepared using a cross-sectional sample preparation device such as a cross-section polisher. SEM-EDS observation is performed at least three locations on the prepared cross-sectional sample, including near the center and both ends, to quantify the mass of major elements such as boron contained in the cross-sectional sample. The molecular structures of the first and second particles constituting the intermediate layer 13 can also be identified from the results of the SEM-EDS observation. Based on the identified molecular structure and the mass of the major element such as boron, the masses of the first and second particles contained in the cross-sectional sample are calculated. Based on the calculated masses of the first and second particles and the mass of the cross-sectional sample, the content of the first and second particles in the intermediate layer 13 can be calculated. The apparatus and conditions used for the measurement are as follows. Measurement equipment: Field emission scanning electron microscope JSM-7800F (FE-SEM, manufactured by JEOL) Energy dispersive analyzer JED100mm (EDS, manufactured by JEOL) Accelerating voltage: 4 kV

[0056] 3. Method for manufacturing a non-aqueous electrolyte secondary battery according to this embodiment Next, a method for manufacturing the nonaqueous electrolyte secondary battery 100 according to this embodiment will be described. (3-1. Method for producing positive electrode) The positive electrode 1 is fabricated, for example, as follows. First, an intermediate layer slurry is formed by dispersing a mixture of first particles, second particles, a conductive agent, and a binder for the intermediate layer in a desired ratio in an appropriate solvent. Next, this intermediate layer slurry is applied to one or both surfaces of a positive electrode current collector 11 and dried to form an intermediate layer 13. Next, a mixture of a positive electrode active material, a conductive agent, and a binder for the positive electrode in a desired ratio is dispersed in a solvent for the positive electrode slurry to form a positive electrode slurry. Next, this positive electrode slurry is applied to the surface of the intermediate layer 13 formed as described above and dried to form a positive electrode composite layer 12. Next, the positive electrode composite layer 12 is pressed to a desired density using a press. In this manner, the positive electrode 1 is fabricated. Note that the application method for each layer is not particularly limited. Possible coating methods include, for example, a knife coater method, a gravure coater method, a reverse roll coater, a slit die coater, etc. Each of the following coating steps is also carried out in the same manner.

[0057] The composite particles used as the second particles in this embodiment can be produced by mixing at least one of metal hydroxide particles and metal oxide particles with a flame retardant, and heating the mixture. More specifically, a dispersion liquid in which one or more of metal hydroxide particles and metal oxide particles and a flame retardant are dispersed in a suitable solvent is heated to a temperature of, for example, 40°C or higher and 100°C or lower, and reacted at that temperature for 1 hour or higher and 48 hours or lower, and then filtered through filter paper to obtain composite particles. The solvent preferably contains water, and is preferably a mixture of water and an alcohol-based organic solvent such as ethanol or 2-propanol. The heating temperature is preferably 60° C. or higher and 80° C. or lower, and the heating time (reaction time) is preferably 5 hours or higher and 30 hours or lower.

[0058] The volume-based particle size distribution of the metal hydroxide particles used as the starting material at 50% (D50) is preferably 10 nm or more and 10 μm or less, more preferably 0.1 μm or more and 8 μm or less, and even more preferably 0.5 μm or more and 5 μm or less. The same applies to the metal oxide particles used as the starting material. In order to obtain composite particles in which the metal hydroxide is modified with a larger amount of the flame retardant component derived from the flame retardant, it is preferable to use metal hydroxide particles as the starting material with as large a BET specific surface area as possible, and it is preferable to use composite particles obtained by mixing a flame retardant component with metal hydroxide particles having a relatively large BET specific surface area and compositing them, so that the BET specific surface area of ​​the composite particles is within the above-mentioned range. The BET specific surface area of ​​the composite particles tends to decrease when the amount of flame retardant added to the metal hydroxide particles is increased or when the reaction time when the metal hydroxide particles and the flame retardant component are combined is extended. Therefore, the BET specific surface area of ​​the composite particles can be adjusted by changing these conditions, so the BET specific surface area of ​​the metal hydroxide particles as the starting material is not particularly limited, but the BET specific surface area of ​​the metal hydroxide particles can be, for example, 100 m 2 / g or more 500m 2 Similarly, the metal oxide particles used as the starting material preferably have a BET specific surface area of ​​100 m / g or less. 2 / g or more 500m 2 / g or less is preferable.

[0059] (3-2. Method for producing negative electrode) First, a mixture of materials constituting the negative electrode composite layer 22 is dispersed in a negative electrode slurry solvent to prepare a negative electrode slurry. Next, the negative electrode slurry is applied to the negative electrode current collector 21 and dried to form the negative electrode composite layer 22. Next, the negative electrode composite layer 22 is pressed using a press to a desired density. In this way, the negative electrode 2 is prepared.

[0060] (3-3. Method for manufacturing non-aqueous electrolyte secondary battery) Next, the separator 3 is sandwiched between the positive electrode 1 and the negative electrode 2 to produce an electrode structure. The electrode structure is then processed into a desired shape (e.g., cylindrical, rectangular, laminated, button-shaped, etc.) and inserted into a container 5 of that shape. Next, a nonaqueous electrolyte solution is injected into the container, thereby impregnating the electrolyte solution 4 into the pores in the separator 3 and the gaps in the positive electrode 1 and the negative electrode 2. A lithium-ion secondary battery can be produced by the above-mentioned steps.

[0061] 4. Effects of this embodiment According to the nonaqueous electrolyte secondary battery 100 configured as described above, the battery contains first particles containing boron nitride, which has a relatively low Young's modulus, and the aspect ratio (major axis / minor axis) of the first particles is set to be 3.0 or more and 30 or less. Therefore, when a foreign object such as a nail penetrates the positive electrode current collector, the intermediate layer 13 containing the first particles can deform to follow the surface shape of the positive electrode current collector as closely as possible, thereby making it possible to suppress exposure of the positive electrode current collector more than ever before. Boron nitride can capture active oxygen, thereby suppressing the decomposition reaction of the electrolyte and suppressing the temperature rise of the battery. Since the intermediate layer 13 further contains second particles containing a metal hydroxide or metal oxide and a flame-retardant component, the endothermic reaction of the metal hydroxide or metal oxide and the effect of inhibiting the electrolyte decomposition reaction by radical scavenging by the flame-retardant component can further suppress the temperature rise of the battery, thereby dramatically improving safety.

[0062] 5. Other embodiments of the present invention The present invention is not limited to the above-described embodiment. For example, the second particles are not limited to the composite particles described above, and the following can also be used. (5-1. Second embodiment of the present invention) The composite particles described in the second embodiment, like the composite particles described in the previous embodiments, are a composite of one or more of metal hydroxide and metal oxide particles with a flame-retardant component, and their properties and composition are as follows.

[0063] When the composite particles were heated from 80°C to 1400°C, the amount of P2 gas desorbed from the composite particles was measured by TDS-MS. The amount of desorbed P2 (referred to as MS1) was 200 × 10 -6 mol / g or more 2500×10 -6 mol / g or less, and the amount of H2O gas desorbed from the composite particles when heated from 80°C to 1400°C, as measured by TDS-MS (referred to as MS2), is 50 x 10 -6 mol / g or more 1000×10 -6 It is preferably mol / g or less. MS1 is 300 x 10 -6 mol / g or more 2000×10 -6 mol / g or less is more preferable, and 400×10 -6 mol / g or more 1800×10 -6 It is particularly preferable that the content is mol / g or less. MS2 is 100 x 10 -6 mol / g or more 950×10 -6 mol / g or less is more preferable, and 300×10 -6 mol / g or more 900×10 -6 It is particularly preferable that the content is mol / g or less.

[0064] Furthermore, the ratio of these gas desorption amounts (M1 / M2) is preferably 0.1 or more and 10.0 or less, more preferably 0.3 or more and 5.0 or less, and particularly preferably 0.5 or more and 3.0 or less. When the ratio of gas desorption amounts (M1 / M2) satisfies this preferred range, both the temperature rise suppression effect due to increased modification with a flame retardant component and battery performance can be exhibited in a better balance.

[0065] In addition, the BET specific surface area of ​​the composite particles calculated from the adsorption isotherm measured by adsorbing nitrogen onto the composite particles is 8 m 2 / g or more 80m 2 / g or less, and 2 / g or more 75m 2 / g or less is more preferable, and 15m 2 / g or more 75m 2 It is particularly preferable that the saturation coefficient is 1 / g or less.

[0066] In order to obtain composite particles in which the metal hydroxide is modified with a larger amount of the flame retardant component, it is preferable to use metal hydroxide particles as the starting material with as large a BET specific surface area as possible, and it is preferable to set the BET specific surface area of ​​the composite particles obtained by mixing the flame retardant component with metal hydroxide particles having a relatively large BET specific surface area and compositing them within the above-mentioned range. The BET specific surface area of ​​the composite particles tends to decrease when the amount of flame retardant added to the metal hydroxide particles is increased or when the reaction time when combining the metal hydroxide and the flame retardant component is extended. Therefore, the BET specific surface area of ​​the composite particles can be adjusted by changing these conditions, so the BET specific surface area of ​​the metal hydroxide particles as the starting material is not particularly limited, but the specific surface area of ​​the metal hydroxide particles can be set within the above-mentioned range, for example. 2 / g or more 500m 2 The same applies to metal oxide particles.

[0067] The composite particles according to this embodiment preferably have the contents of Al (aluminum) and P (phosphorus) measured by an inductively coupled plasma atomic emission spectroscopy (ICP-AES) within the following ranges. The content of Al element in the composite particles is preferably 1% by mass to 50% by mass, more preferably 3% by mass to 40% by mass, and particularly preferably 5% by mass to 30% by mass. The content of P element in the composite particles is preferably 1% by mass to 50% by mass, more preferably 3% by mass to 40% by mass, and particularly preferably 5% by mass to 30% by mass.

[0068] To further improve the heat-absorbing effect of the composite particles, the composite particles are preferably modified with functional groups such as CH groups and CHOH groups. The degree of modification with these functional groups can be evaluated, similarly to the degree of modification with functional groups containing phosphorus (P) (e.g., phosphonic acid), by the amount of each of the following gases released from these functional groups, and it is preferable that the amount of each gas released falls within the following ranges. Note that the amount of each gas released can be adjusted by the type and content of the metal hydroxide, metal oxide, and flame retardant used in producing the composite particles. The amount of CH4 gas desorbed from the composite particles when the composite particles are heated from 80°C to 1400°C, as measured by TDS-MS (referred to as MS3), may be 0, but may be greater than 0 and may be 1000 x 10 -6 mol / g or less, and may be 10 × 10 -6 mol / g or more 700×10 -6 mol / g or less is more preferable, and 30×10 -6 mol / g or more 500×10 -6 It is particularly preferable that the content is mol / g or less. The amount of desorbed CH3OH (MS4) measured in the same manner may be 0, but may exceed 0 and be 4000 x 10 -6 mol / g or less, and preferably 200×10 -6 mol / g or more 3000×10-6 mol / g or less is more preferable, and 500×10 -6 mol / g or more 3000×10 -6 It is more preferable that it is mol / g or less.

[0069] When the composite particles are modified with a functional group containing a phenyl group, the composite particles are easily dispersed in a non-aqueous solvent such as N-methyl-2-pyrrolidone (NMP) when preparing a slurry for the intermediate layer using the solvent. Therefore, the amount of C6H6 desorbed from the composite particles at temperatures between 80°C and 1400°C by TDS-MS (referred to as MS5) may be 0, but it may be greater than 0 and be 4000 x 10 -6 mol / g or less, and preferably 10×10 -6 mol / g or more 3000×10 -6 mol / g or less is more preferable, and 100×10 -6 mol / g or more 3000×10 -6 It is particularly preferable that the content is mol / g or less.

[0070] The total content of the modifying molecules (i.e., flame-retardant components) in the composite particles is preferably in the range of 10% by mass or more and 99% by mass or less, more preferably in the range of 20% by mass or more and 97% by mass or less, and even more preferably in the range of 30% by mass or more and 95% by mass or less, relative to 100% by mass of the entire composite particle.

[0071] (5-2. Third embodiment of the present invention) Furthermore, the composite particles may be those obtained by combining not only one or more of metal hydroxide particles and metal oxide particles with a flame retardant component, but also conductive particles. The composite particles are as follows:

[0072] The metal hydroxide particles and the metal oxide particles are not particularly limited as long as they can cause an endothermic reaction. Specific examples of the metal hydroxide and the metal oxide include aluminum hydroxide, pseudoboehmite, boehmite, activated alumina, and kaolinite. These may be used alone or in combination of two or more.

[0073] The average primary particle size of the metal hydroxide particles is preferably 10 nm or more and 20 μm or less, and more preferably 50 nm or more and 10 μm or less. The same applies to the metal oxide particles.

[0074] The conductive particles are not particularly limited as long as they are conductive. Specific examples of materials constituting the conductive particles include carbon materials and metal nanoparticles. Examples of the metal nanoparticles include gold nanoparticles, silver nanoparticles, and copper nanoparticles. The carbon material may include one or more selected from carbon black, natural graphite, artificial graphite, fibrous carbon, and sheet-like carbon. Examples of the carbon black include furnace black, channel black, thermal black, ketjen black, and acetylene black. Examples of the fibrous carbon include single-walled carbon nanotubes and multi-walled carbon nanotubes, and examples of the sheet-like carbon include graphene.

[0075] The composite particles contain the conductive particles as described above, and thus have a luminance of 1350 cm measured by Raman spectroscopy. -1 The peak area (A D ) and 1580cm -1 The peak area (A G ) ratio (AD / A G ) is 0.5 or more and 3.5 or less, and the value measured by Raman spectroscopy is 2680 cm -1 Peak half width (G'-FWHM) around 60cm -1 More than 150cm -1 It is preferable that the range is as follows:

[0076] The conductive particles preferably have an average primary particle size or fiber length of 1 nm to 10 μm, more preferably 10 nm to 1 μm. When metal nanoparticles are used as the conductive particles, any particle size can be used as long as the average primary particle size is on the order of nm, but it is preferable that the average primary particle size is 1 nm to 500 nm.

[0077] The content of the metal hydroxide particles and the metal oxide particles in the composite particles is preferably in the range of 1% by mass to 60% by mass, more preferably in the range of 5% by mass to 50% by mass, and even more preferably in the range of 10% by mass to 40% by mass, based on the total amount of the composite particles. When multiple types of metal hydroxide particles and metal oxide particles are used in combination, this content refers to the total content.

[0078] The content of the conductive particles in the composite particles is preferably in the range of 0.1% by mass or more and 25% by mass or less, more preferably in the range of 0.5% by mass or more and 20% by mass or less, and even more preferably in the range of 1% by mass or more and 15% by mass or less, based on the total weight of the composite particles.

[0079] The composite particles have a BET specific surface area and a degree of modification with various modifying groups within the following ranges.

[0080] The specific surface area (BET1) calculated based on the adsorption isotherm measured by adsorbing water vapor onto the composite particles is 8m 2 / g or more 600m 2 / g or less, and the specific surface area (BET2) of the composite particles calculated by an adsorption isotherm measured by adsorbing nitrogen onto the composite particles is 8 m 2 / g or more 600m 2 / g or less.

[0081] BET1 is 10m 2 / g or more 300m 2 / g or less, and 2 / g or more 100m 2 It is more preferable that the saturation coefficient is 1 / g or less. BET2 is 9m 2 / g or more 300m 2 / g or less, and 2 / g or more 100m 2 It is more preferable that the saturation coefficient is 1 / g or less. The specific surface area ratio (BET1 / BET2), which is the ratio between BET1 and BET2, is preferably 0.2 or more and 5.0 or less, more preferably 0.5 or more and 4.0 or less, and particularly preferably 1.0 or more and 3.0 or less.

[0082] In addition, the amount of P2 gas desorbed from the composite particles when the composite particles were heated from 80°C to 1400°C was measured by TDS-MS, and the amount of desorbed P2 (referred to as MS1) was 300 × 10 -6 mol / g or more 3000×10 -6 mol / g or less. The amount of P2 released (M1) is an index showing the degree of modification of the composite particles with phosphonic acid. The amount of H2O desorbed from the composite particles when heated from 80°C to 1400°C, as measured by TDS-MS (referred to as MS2), is preferably 30 x 10-6 mol / g or more and 1500 x 10-6 mol / g or less. This amount of H2O desorbed is a reference value for the degree of modification of the composite particles, and the ratio of these gas desorption amounts (M1 / M2) is preferably 0.5 or more and 5.0 or less, more preferably 1.0 or more and 4.0 or less, and particularly preferably 1.5 or more and 3.0 or less.

[0083] In order to further improve the heat absorption effect of the composite particles, it is preferable that the composite particles are modified with functional groups such as CH groups, CHOH groups, etc. The degree of modification with these functional groups can be evaluated, similarly to the degree of modification with phosphonic acid, by the amount of desorption of the following various gases derived from these functional groups, and it is preferable that the amount of desorption of the various gases satisfy the following ranges. The amount of CH4 gas desorbed from the composite particles when the composite particles were heated from 80°C to 1400°C was measured by TDS-MS, and the amount of CH4 desorbed (referred to as MS3) was 30 x 10 -6 mol / g or more 1000×10 -6 mol / g or less, and the amount of desorbed CH3OH (MS4) measured in the same manner is 10 x 10 -6 mol / g or more 1000×10 -6 It is preferably mol / g or less.

[0084] MS3 is 50 x 10 -6 mol / g or more and 300×10 -6 mol / g or less is more preferable, and 60×10 -6 mol / g or more and 250 × 10 -6 It is particularly preferable that the content is mol / g or less. MS4 is 20 x 10 -6 mol / g or more and 2000×10 -6 mol / g or less, and preferably 25×10 -6 mol / g or more and 1900 × 10 -6 It is particularly preferable that the content is mol / g or less.

[0085] When the composite particles are modified with a functional group containing a phenyl group, the composite particles can be easily dispersed in a solvent when preparing a slurry such as a positive electrode mixture slurry. Therefore, the amount of C6H6 desorbed from the composite particles at temperatures between 80°C and 1400°C (referred to as MS5) was 1 x 10 -6 mol / g or more 4000×10 -6 mol / g or less, and preferably 2×10 mol / g or more and 2000×10 -6mol / g or less is more preferable, and 3×10 -6 mol / g or more 1600×10 -6 It is particularly preferable that the content is mol / g or less.

[0086] The total content of the modifying molecules in the composite particle is preferably in the range of 10% by mass or more and 90% by mass or less, more preferably in the range of 20% by mass or more and 80% by mass or less, and even more preferably in the range of 30% by mass or more and 70% by mass or less, relative to 100% by mass of the entire composite particle.

[0087] The heat absorption by the composite particles achieved by the surface area and degree of modification with various modifying groups as described above is preferably such that the heat absorption at 50°C to 250°C in differential scanning calorimetry is 150 J / g or more and 500 J / g or less, more preferably 170 J / g or more and 5400 J / g or less, and particularly preferably 180 J / g or more and 300 J / g or less.

[0088] In the case where the composite particles already contain conductive particles as in this embodiment, a conductive agent other than the composite particles may or may not be added when forming the intermediate layer. Furthermore, the present invention is not limited to these embodiments, and it goes without saying that various modifications are possible without departing from the spirit of the present invention. [Example]

[0089] The present invention will be described in more detail below based on specific examples. However, the following examples are merely examples of the present invention, and the present invention is not limited to the following examples.

[0090] <Preparation of composite particles to be used as second particles> (Examples 1-4, Comparative Examples 2 and 3) Kaolinite (Al2Si2O5(OH)4, D50: 1 μm, BET: 120 m) was used as metal hydroxide particles. 25.0 g of phenyl phosphate as a flame retardant was used, and these were dispersed in 50 cc of a mixed solution of ethanol and purified water (mixing ratio 1:1). After heating this dispersion at 70°C for 24 hours, it was filtered with water and ethanol, washed with water and ethanol, and the solid on the filter paper was vacuum dried to obtain composite particles (A).

[0091] (Examples 5-8) Activated alumina (D50: 1.5 μm, BET: 312 m) was used as metal oxide particles. 2 Composite particles (B) were obtained by the same procedure as in Example 1, except that 1.0 g of methyl phosphinic acid (1.0 g / g) was used as the flame retardant and 5.0 g of methyl phosphinic acid was used as the flame retardant.

[0092] Examples 9-12 Pseudoboehmite (D50: 1.0 μm, BET: 391 m) was used as metal hydroxide particles. 2 Composite particles (C) were prepared in the same manner as in Example 1, except that 1.0 g of cellulose acylate (C1 / g) was used and 5.0 g of diphenyl phosphate was used as the flame retardant.

[0093] Examples 13-16 Aluminum hydroxide (D50: 1.2 μm, BET: 212 m) was used as metal hydroxide particles. 2 Composite particles (D) were prepared in the same manner as in Example 1, except that 1.0 g of hydroxybenzoates (1.0 g / g) and 5.0 g of phenylphosphonic acid were used as the flame retardant.

[0094] <Creating the intermediate layer> (Examples 1-16, Comparative Examples 2 and 3) The first and second particles shown in Table 1 were used, and the mass ratio of these first and second particles, carbon nanofiber as a conductive agent, and polyvinylidene fluoride as a binder for the intermediate layer was set to 64:16:2:18, and then dispersed and mixed in N-methyl-2-pyrrolidone solvent to prepare an intermediate layer slurry. Next, after drying, the mixture coating amount (areal density) was 0.5 mg / cm on one side. 2 The intermediate layer slurry was applied to both sides of an aluminum current collector foil and dried to prepare an intermediate layer.

[0095] (Comparative Examples 4 to 6) Intermediate layers of Comparative Examples 4 to 6 were prepared in the same manner as in Example 1, except that activated alumina was added as metal oxide particles whose surfaces and interiors were not modified with a flame retardant component.

[0096] <Positive electrode production> (Examples 1-16, Comparative Examples 2-8) A positive electrode mixture slurry was prepared by dispersing and mixing LiCoO (D50: 17 μm), acetylene black, and polyvinylidene fluoride in a mass ratio of 97.7:1.0:1.3 in N-methyl-2-pyrrolidone solvent. After drying, the mixture was applied to a surface with a surface density of 20.50 mg / cm2 on one side. 2 The positive electrode mixture slurry was applied to the intermediate layer so that the density of the mixture layer became 4.15 g / cc, and then the mixture was pressed with a roll press machine so that the density of the mixture layer became 4.15 g / cc, thereby producing a positive electrode.

[0097] (Comparative Example 1) A positive electrode was produced in the same manner as in Example 1, except that no intermediate layer was formed and the positive electrode mixture slurry was directly coated on both sides of an aluminum current collector and dried.

[0098] <Negative electrode production> (Examples 1-16, Comparative Examples 1-8) The negative electrode mixture slurry was prepared by dissolving and dispersing artificial graphite, carboxymethylcellulose sodium salt (CMC), and styrene-butadiene-based aqueous dispersion in an aqueous solvent in a mass ratio of 97.5:1.0:1.5 as dry powders (solids) without solvent. The resulting mixture was then dried to a surface density of 15.0 mg / cm. 2 The negative electrode mixture slurry was applied to both sides of copper foil, which was the negative electrode main current collector, and dried, and then pressed with a roll press machine so that the negative electrode mixture layer density was 1.65 g / cc, thereby producing a negative electrode.

[0099] <Secondary battery cell production> (Examples 1-16, Comparative Examples 1-8) An electrode stack was fabricated by stacking multiple positive and negative electrodes with a porous polypropylene separator between them so that the battery design capacity was 300 mAh. The positive and negative electrodes placed inside the electrode stack had composite layers formed on both sides of the current collector, while the positive or negative electrode placed on the outermost layer had a composite layer formed on only one side. Specifically, the electrode plate area was 8.5 cm. 2 The positive electrode (five on both sides) and the electrode surface area are 10.0 cm 2 Negative electrodes (four double-sided and two single-sided) were fabricated. Next, nickel and aluminum lead wires were welded to the negative and positive electrodes of the electrode stack described above, respectively, within an aluminum laminate film, and the stack was then housed with the lead wires extended to the outside. An electrolyte was then poured into the container, which was then vacuum sealed to fabricate a pre-initial charge secondary battery cell. The electrolyte used was a solvent mixture of ethylene carbonate / dimethyl carbonate / fluoroethylene carbonate in a 15 / 80 / 5 (volume ratio) ratio, with 1.3 M LiPF6 and 1 mass % vinylene carbonate dissolved therein.

[0100] <Evaluation of First Particles, Second Particles, or Metal Oxide Particles> The first particles, second particles, and metal oxide particles (activated alumina) used in the examples and comparative examples were evaluated as follows. (Particle size measurement) The particle diameters of the first particles and the second particles or the metal oxide particles were evaluated as the average particle diameter at 50% (D50) of the particle size distribution based on the particle diameter volume in the particle size distribution obtained by a laser diffraction / scattering method. The particle diameters of the first particles and the second particles or the metal oxide particles were measured using the following measuring device and under the following measuring conditions. Measurement equipment: Laser diffraction / scattering particle size distribution analyzer MT3300 (Microtrac Bell Co., Ltd.) Transparency: Transparent Shape: non-spherical Circulation speed: 7 Measurement time: 30 seconds Number of iterations: 3 Refractive index: a. First particle, second particle, or metal oxide particle: 1.65-0.00i b. Ethanol solvent: 1.36-0.00i

[0101] (ratio of major axis to minor axis of the first particle, aspect ratio) In the present examples and comparative examples, the average particle size (D50) determined by the laser diffraction / scattering method as described above was taken as the major axis of the primary particles. After the first particles were attached to carbon tape, the thickness of 100 randomly selected particles was measured using a scanning electron microscope JSM-7800F (manufactured by JEOL Ltd.), and the arithmetic average was taken as the minor axis of the first particles, and the ratio of the major axis to the minor axis (major axis / minor axis, aspect ratio) described above was calculated.

[0102] (mass of gas desorbed from second particle) Thermal desorption mass spectrometry (TDS-MS) was performed using a thermal desorption analyzer, model TDS-1200, manufactured by Denshi Kagaku Co., Ltd., to measure and analyze the amount of desorbed diphosphorus molecules and water molecules as follows. In the TDS, the sample stage on which the negative electrode active material sample was placed was made of quartz, and the sample dish was made of SiC. The heating rate was 60°C / min. The heating was controlled by monitoring the sample surface temperature. The sample weight was set to 1 mg and corrected for the actual measured weight. A quadrupole mass spectrometer was used for detection, and the applied voltage was 1000V. The amount (μmol / g) of each gas desorbed from the second particle (composite particle) as the temperature increased from 80°C to 1400°C was measured using TDS. The mass numbers [M / z] used in analyzing the measured values ​​were 18 for HO and 62 for P2, and all of the gases corresponding to these mass numbers were considered to be the above-mentioned substances. Here, for the amount of HO gas, only the integrated value from 80°C to 200°C was used from the results over the entire temperature range to determine the amount of desorbed HO.

[0103] <Check whether or not heat is generated at 150°C or less when second particles or metal oxide particles coexist with an electrolyte> 2.0 mg of each of the second particles (composite particles) or metal oxide particles (activated alumina) prepared as described above and 0.5 mg of the same electrolyte solution as used in preparing the secondary battery cells were placed in a dedicated airtight container and crimped, and then the endothermic peaks of the second particles or metal oxide particles were measured under the following conditions to confirm the presence or absence of an exothermic peak below 150°C. A clear exothermic peak was observed near 100°C in Comparative Examples 4 to 6, but this exothermic peak was not observed in Examples 1 to 16 and Comparative Examples 2 to 3. The maximum endothermic peak temperature of each particle was determined using a differential scanning calorimeter: DSC (manufactured by Hitachi High-Tech Science Corporation) by heating at a heating rate of 5 K / min in accordance with JIS K7121, and the endothermic decomposition temperature peak was confirmed.

[0104] <Evaluation of secondary batteries> (Cycle characteristics) The secondary battery cells fabricated in Examples 1 to 16 and Comparative Examples 1 to 8 were charged at a constant current of 0.1 CA (design capacity) to 4.4 V in a thermostatic chamber at 25°C, followed by constant voltage charging at 4.4 V to 0.05 CA. They were then discharged at a constant current of 0.1 CA to 3.0 V. Furthermore, in a thermostatic chamber at 25°C, one cycle of constant current charging at 0.2 CA, constant voltage charging at 0.05 CA, and constant current discharging at 0.2 CA was performed under conditions of a charge cut-off voltage of 4.4 V and a discharge cut-off voltage of 3.0 V, and the initial discharge capacity was measured. A life test was then performed on these secondary batteries, consisting of 100 cycles of constant current charging at 0.5 CA, constant voltage charging at 0.05 CA, and constant current discharging at 0.5 CA at 45°C, under conditions of a charge cut-off voltage of 4.4 V and a discharge cut-off voltage of 3.0 V. After 100 cycles, the discharge capacity was measured at a constant current charge of 0.2 CA, a constant voltage charge of 0.05 CA, and a discharge of 0.2 CA, and the capacity retention rate after 100 cycles was calculated by dividing the measured capacity by the initial discharge capacity.

[0105] (nail penetration test) A nail penetration test was conducted on the center of each of the secondary battery cells (10 cells for each of Examples 1 to 16 and Comparative Examples 1 to 8) by using a nail having a diameter of 3 mm and penetrating it at a speed of 1 mm / s. If the external temperature of the battery reached 50°C or higher 5 seconds after the nail was inserted, this was deemed to be an "abnormality," and the abnormality occurrence rate for the 10 tested batteries was evaluated.

[0106] (heating test) The secondary battery cells (10 cells each) fabricated in Examples 1 to 16 and Comparative Examples 1 to 8 were charged at a constant current of 0.1 CA (design capacity) to 4.45 V in a thermostatic chamber at 25°C, followed by constant voltage charging at 4.45 V to 0.05 CA. Subsequently, they were discharged at a constant current of 0.1 CA to 3.0 V. Furthermore, in a thermostatic chamber at 25°C, one cycle of constant current charging at 0.2 CA, constant voltage charging at 0.05 CA, and constant current discharging at 0.2 CA was performed under the conditions of a charge cut-off voltage of 4.45 V and a discharge cut-off voltage of 3.0 V. The cells were then charged at a constant current / constant voltage to 4.45 V again, forming initial cells. These secondary batteries were left in a thermostatic chamber heated to 165°C for one hour, and a battery voltage drop below 4.2 V was considered an "abnormality." The abnormality occurrence rate for the 10 tested batteries was evaluated.

[0107] (Evaluation results) Table 1 shows the types, properties and locations of the first particles, second particles and metal oxide particles used in place of the second particles used in the examples and comparative examples described above. The evaluation results of Examples 1 to 16 and Comparative Examples 1 to 8 are summarized in Table 2.

[0108] [Table 1]

[0109] [Table 2]

[0110] (Consideration) The results in Table 2 show that in Examples 1 to 16, the incidence of abnormalities in the nail penetration test was sufficiently suppressed. In Examples 1 to 16, insulating first particles containing boron nitride were used, and the ratio of the major axis to the minor axis (major axis / minor axis) of these first particles was set to a range of 3.0 to 30. Additionally, the second particles contained at least one of a metal hydroxide and a metal oxide and a flame-retardant component. This is believed to be because these particles were able to sufficiently suppress temperature rises inside the battery even under conditions where a short circuit is likely to occur. On the other hand, in Comparative Examples 1 to 8 (Comparative Example 1, which did not include an intermediate layer; Comparative Examples 2 and 3, in which the aspect ratio of the first particles contained in the intermediate layer was outside the above range; Comparative Examples 4 to 6, in which metal oxide particles were used directly instead of the second particles; and Comparative Examples 7 and 8, in which no second particles were included), the incidence of abnormalities was clearly higher than in Examples 1 to 16. One of the reasons for the effect of Examples 1 to 16 is thought to be that when a nail penetrates, the intermediate layer containing the first particles with an adjusted aspect ratio and a low Young's modulus deforms to follow the shape of the nail or the current collector, thereby reducing the exposure rate of the positive electrode current collector.In addition, another reason is thought to be that the first particles containing boron nitride, which has an active oxygen scavenging effect, and the second particles containing one or more of a metal hydroxide and a metal oxide and a flame retardant component are present in the vicinity of the positive electrode current collector, so that even if a micro-short circuit occurs, heat generation at the short circuit site can be reduced. On the other hand, when first particles with too high an aspect ratio are contained in the intermediate layer as in Comparative Example 2, it is presumed that the number of first particles present in the intermediate layer decreases, and the first particles break rather than deform when a nail penetrates, making it impossible to sufficiently reduce the exposure rate of the positive electrode current collector. It was confirmed that all of the composite particles used as the second particles in Examples 1 to 16 exhibited high effectiveness. The properties of these composite particles were within the ranges confirmed in Examples 1 to 16, for example, MS1 of 200×10 -6 mol / g or more 2500×10 -6 mol / or less, MS2 is 50 × 10 -6 mol / g or more 1000×10 -6It is presumed that the ratio of the desorbed gas amounts (MS1 / MS2) is not limited to the range of 0.5 to 10, and that the same effect is also obtained in the ranges described in the above-mentioned embodiments. Furthermore, it was confirmed that Examples 1 to 16 not only suppressed the internal short circuit that occurs when a nail is pierced into the battery and sufficiently suppressed the rise in the internal temperature of the battery, but also suppressed the deterioration of battery performance such as cycle characteristics. [Explanation of symbols]

[0111] 100...Nonaqueous electrolyte secondary battery 1...Positive electrode 11...Positive electrode current collector 12 Positive electrode mixture layer 13 Middle Class 2...Negative electrode 21...Negative electrode current collector 22...Negative electrode composite material layer 3. Separator 4...Non-aqueous electrolyte 5...container

Claims

1. A positive electrode for a non-aqueous electrolyte secondary battery, comprising: a positive electrode current collector; a positive electrode mixture layer; and an intermediate layer provided between the positive electrode current collector and the positive electrode mixture layer, the intermediate layer contains first particles and second particles, the first particles are insulating particles containing boron nitride, the second particles contain at least one of a metal hydroxide and a metal oxide and a flame retardant component, the ratio of the major axis to the minor axis of the first particle (major axis / minor axis) is 3.0 or more and 30 or less; the first particles have a volume-based particle size distribution with an integrated value of 50% of the first particles being 0.01 μm or more and 8 μm or less; the second particles have a volume-based particle size distribution with an integrated value of 50% of the second particles being 0.01 μm or more and 8 μm or less; Positive electrode for non-aqueous electrolyte secondary batteries.

2. 2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the first particles are made of boron nitride.

3. The desorption P of the second particles from 80°C to 1400°C by a temperature programmed desorption mass spectrometer (TDS-MS) ２ Amount (MS1) is 200 x 10 －６ mol / g or more 2500×10 －６ mol / or less, Desorption H from the second particles at temperatures from 80°C to 200°C by TDS-MS ２ O amount (MS2) is 50 x 10 －６ mol / g or more 1000×10 －６ mol / or less, The desorbed H ２ The amount of desorbed P relative to the amount of O ２ 2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the ratio of the amounts (MS1 / MS2) satisfies the following formula (1): 0.5≦(MS1 / MS2)≦10...(1)

4. the second particles are the metal hydroxides whose surfaces or interiors are modified with a flame retardant; The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1 .

5. 2. The positive electrode for a non-aqueous electrolyte secondary battery in accordance with claim 1, wherein the metal hydroxide is at least one selected from the group consisting of kaolinite, pseudoboehmite, boehmite, and aluminum hydroxide.

6. 2. The positive electrode for a non-aqueous electrolyte secondary battery in accordance with claim 1, wherein the metal oxide is activated alumina.

7. 5. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 4, wherein the flame retardant contains at least one selected from the group consisting of phosphoric acid, a phosphoric acid ester, a phosphonic acid, a phosphonic acid ester, a phosphinic acid, and a phosphinic acid ester.

8. 2. The positive electrode for a non-aqueous electrolyte secondary battery in accordance with claim 1, wherein the thickness of the intermediate layer is 0.1 μm or more and 10 μm or less.

9. 2. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 1, wherein the intermediate layer further contains a conductive agent.

10. 10. The positive electrode for a non-aqueous electrolyte secondary battery according to claim 9, wherein the conductive agent is at least one of carbon nanofibers and carbon black.

11. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte solution, A non-aqueous electrolyte secondary battery, wherein the positive electrode is the positive electrode for a non-aqueous electrolyte secondary battery according to any one of claims 1 to 10.

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