Additive composition, composition for electrode, electrode, and lithium ion secondary battery

Abstract

Provided is an additive composition for an electrode of a lithium ion secondary battery, the additive composition containing lithium phosphate and a zirconium compound, and the zirconium element content with respect to the total amount of the lithium phosphate and the zirconium compound being 100-10,000 mass ppm.

Description

Additive composition, electrode composition, electrode, and lithium ion secondary battery

[0001] The present disclosure relates to an additive composition, an electrode composition, an electrode, and a lithium ion secondary battery.

[0002] Lithium-ion secondary batteries may contain various additives to improve battery performance. For example, lithium phosphate is known as an additive for suppressing heat generation during overcharge of lithium-ion secondary batteries. When a lithium-ion secondary battery with lithium phosphate added to the positive electrode is overcharged, hydrogen fluoride generated by decomposition of the electrolyte on the surface of the positive electrode reacts with the lithium phosphate to produce phosphate ions. These phosphate ions migrate to the negative electrode, forming a phosphate film on the surface of the negative electrode. As a result, the reaction at the negative electrode of the lithium-ion secondary battery is stabilized, suppressing heat generation during overcharge (see Patent Document 1).

[0003] Patent Document 1: JP 2021-125377 A

[0004] Lithium ion secondary batteries containing lithium phosphate as an additive have room for improvement in battery performance during high-temperature storage. An object of one embodiment of the present disclosure is to provide an additive composition that enables the production of a lithium ion secondary battery with excellent battery performance during high-temperature storage, as well as an electrode composition, an electrode, and a lithium ion secondary battery that use the additive composition.

[0005] Means for solving the above problems include the following aspects. <1> An additive composition for an electrode of a lithium ion secondary battery, comprising lithium phosphate and a zirconium compound, wherein the content of zirconium element in the total amount of the lithium phosphate and the zirconium compound is 100 ppm by mass to 10,000 ppm by mass. <2> The additive composition according to <1>, wherein the lithium phosphate is in the form of particles having a volume average particle diameter of 50 nm to 5,000 nm. <3> The additive composition according to <1> or <2>, wherein the lithium phosphate is in the form of particles having a volume average particle diameter of 50 nm or more and less than 500 nm. <4> The zirconium compound is ZrO ２The additive composition according to any one of <1> to <3>, comprising: <5> The additive composition according to any one of <1> to <4>, further comprising a dispersant. <6> The additive composition according to <5>, wherein the dispersant comprises a titanate-based coupling agent. <7> A composition for an electrode, comprising the additive composition according to any one of <1> to <6>, and an electrode active material. <8> The composition for an electrode according to <7>, wherein the content of lithium phosphate in the solid content of the composition for an electrode is 0.01% by mass to 3.00% by mass. <9> The composition for an electrode according to <7> or <8>, wherein the content of lithium phosphate in the solid content of the composition for an electrode is 0.05% by mass to 1.50% by mass. <10> The composition for an electrode according to any one of <7> to <9>, wherein the amount of lithium phosphate in the composition for an electrode is 0.01 parts by mass to 3.00 parts by mass per 100 parts by mass of the electrode active material. <11> The electrode composition according to any one of <7> to <10>, wherein the amount of lithium phosphate per 100 parts by mass of the electrode active material in the electrode composition is 0.01 parts by mass to 1.50 parts by mass. <12> An electrode for a lithium ion secondary battery, comprising lithium phosphate, a zirconium compound, and an electrode active material, wherein the zirconium content in the total amount of the lithium phosphate and the zirconium compound is 100 ppm by mass to 10,000 ppm by mass. <13> The electrode according to <12>, wherein the lithium phosphate is in the form of particles having a volume average particle diameter of 50 nm to 5,000 nm. <14> The electrode according to <12> or <13>, wherein the zirconium compound is present outside the particles of the electrode active material. <15> A lithium ion secondary battery comprising the electrode according to any one of <12> to <14>.

[0006] According to one embodiment of the present disclosure, there are provided an additive composition that enables a lithium ion secondary battery having excellent battery performance during high-temperature storage to be obtained, as well as an electrode composition, an electrode, and a lithium ion secondary battery that use this additive composition.

[0007] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. In this specification, when a composition contains multiple substances corresponding to each component, the amount of each component in the composition means the total amount of the multiple substances present in the composition, unless otherwise specified. In the numerical ranges described in stages in this specification, the upper or lower limit value described in a certain numerical range may be replaced by the upper or lower limit value of another numerical range described in stages, or may be replaced by a value shown in the examples. In this specification, the term "process" includes not only an independent process, but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0008] [Additive Composition] The additive composition of the present disclosure is an additive composition for an electrode of a lithium ion secondary battery, and includes lithium phosphate and a zirconium compound, wherein the content of elemental zirconium in the total amount of the lithium phosphate and the zirconium compound is 100 ppm by mass to 10,000 ppm by mass. Hereinafter, the content of elemental zirconium in the total amount of the lithium phosphate and the zirconium compound is also referred to as the "zirconium content."

[0009] As will be shown in the examples described later, a lithium ion secondary battery obtained using an additive composition having a zirconium content of 100 ppm by mass to 10,000 ppm by mass exhibits superior battery performance during high-temperature storage compared to a lithium ion secondary battery obtained using an additive composition having a zirconium content outside the range of 100 ppm by mass to 10,000 ppm by mass.

[0010] In the additive composition of the present disclosure, the zirconium content may be 200 ppm by mass or more, 500 ppm by mass or more, 800 ppm by mass or more, or 1000 ppm by mass or more. In the additive composition of the present disclosure, the zirconium content may be 5000 ppm by mass or less, 4000 ppm by mass or less, 3000 ppm by mass or less, or 2000 ppm by mass or less. In the additive composition of the present disclosure, the zirconium content is preferably 200 ppm by mass to 5000 ppm by mass, more preferably 500 ppm by mass to 4000 ppm by mass, even more preferably 800 ppm by mass to 3000 ppm by mass, and particularly preferably 1000 ppm by mass to 2000 ppm by mass. The method for measuring the zirconium content of the additive composition is not particularly limited. For example, it may be measured by ICP-AES, which is an optical emission spectroscopy using a high-frequency inductively coupled plasma (ICP) as a light source.

[0011] The electrode of the lithium ion secondary battery to which the additive composition of the present disclosure is applied may be a positive electrode or a negative electrode. From the viewpoint of favorably exhibiting the performance of lithium phosphate as an additive, the electrode of the lithium ion secondary battery to which the additive composition of the present disclosure is applied is preferably a positive electrode.

[0012] The additive composition of the present disclosure may be in a solid state such as a powder, particles, or tablet, or in a fluid state such as a dispersion, paste, or slurry. The additive composition may be in a different form during storage than during electrode production (for example, a solid during storage and a fluid during electrode production).

[0013] (Lithium Phosphate) The type of lithium phosphate contained in the additive composition is not particularly limited, and Li ３ P.O. ４ (trilithium phosphate), LiH ２ P.O. ４ (lithium dihydrogen phosphate), Li ２ HPO ４ (lithium monohydrogen phosphate) and other lithium phosphates. ３ P.O. ４The lithium phosphate contained in the additive composition may be one type alone or a combination of two or more types.

[0014] From the viewpoint of dispersibility in the electrode, lithium phosphate is preferably particulate. When lithium phosphate is particulate, its volume average particle diameter is not particularly limited. For example, the volume average particle diameter of lithium phosphate may be 50 nm or more, 100 nm or more, or 150 nm or more. For example, the volume average particle diameter of lithium phosphate may be 5000 nm or less, 3000 nm or less, 2000 nm or less, 1000 nm or less, less than 500 nm, or 400 nm or less. The volume average particle diameter of lithium phosphate is preferably 50 nm to 5000 nm, more preferably 50 nm to less than 500 nm, even more preferably 50 nm to 400 nm, and particularly preferably 100 nm to 400 nm. In the present disclosure, the volume average particle diameter of particles is the particle diameter (D50) at which the cumulative volume reaches 50% in a volume-based particle size distribution curve measured by a laser diffraction / scattering method. When lithium phosphate is particulate, its shape is not particularly limited. For example, the lithium phosphate particles may be spherical or non-spherical.

[0015] (Zirconium Compound) In the present disclosure, the zirconium compound refers to zirconium alone or a compound composed of zirconium and other elements. Specific examples of compounds composed of zirconium and other elements include zirconium compounds such as zirconia (zirconium oxide), zircon (zirconium silicate mineral), zirconium tungstate, zirconium chloride, zirconium carbonate, zirconium acetate, zirconium nitrate, and organic zirconium compounds. Among these, zirconia is preferred. The zirconium compound contained in the additive composition may be a single type or a combination of two or more types.

[0016] From the viewpoint of dispersibility in the electrode, the zirconium compound is preferably in a particulate form. When the zirconium compound is in a particulate form, the volume average particle diameter thereof is not particularly limited. For example, the volume average particle diameter of the zirconium compound may be 50 nm or more, 100 nm or more, or 150 nm or more. For example, the volume average particle diameter of the zirconium compound may be 5000 nm or less, 3000 nm or less, 2000 nm or less, or 1000 nm or less. The volume average particle diameter of the zirconium compound is preferably 50 nm to 5000 nm. When the zirconium compound is in a particulate form, the shape thereof is not particularly limited. For example, the particle shape of the zirconium compound may be spherical or non-spherical.

[0017] (Dispersion medium) The additive composition may contain a dispersion medium. When the additive composition contains a dispersion medium, for example, lithium phosphate can be well dispersed in a mixture obtained by mixing the additive composition with an electrode material. Specific examples of the dispersion medium include amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; ureas such as N,N-dimethylethyleneurea, N,N-dimethylpropyleneurea, and tetramethylurea; lactones such as γ-butyrolactone and γ-caprolactone; carbonates such as propylene carbonate; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and cyclohexanone; esters such as methyl acetate, ethyl acetate, n-butyl acetate, butyl cellosolve acetate, butyl carbitol acetate, ethyl cellosolve acetate, and ethyl carbitol acetate; glymes such as diglyme, triglyme, and tetraglyme; hydrocarbons such as toluene, xylene, and cyclohexane; sulfoxides such as dimethyl sulfoxide; sulfones such as sulfolane; organic solvents such as alcohols such as methanol, isopropanol, and n-butanol; mineral oil, and water. The dispersion medium may be used alone or in combination of two or more.

[0018] When the additive composition contains a dispersion medium, the content of the dispersion medium is not particularly limited and can be set in consideration of the desired viscosity of the additive composition, the concentration of lithium phosphate, and the like.

[0019] (Dispersant) The additive composition may contain a dispersant. When the additive composition contains a dispersant, lithium phosphate can be well dispersed in the additive composition or in a mixture obtained by mixing the additive composition with an electrode material. As the dispersant, any material that has the function of increasing the dispersibility of lithium phosphate, such as a coupling agent or a surfactant, can be used without particular limitation. From the viewpoint of maintaining a well-dispersed state of lithium phosphate, the dispersant is preferably a coupling agent. In the present disclosure, a coupling agent refers to a compound having, within its molecule, a moiety that reacts with an organic material and a moiety that bonds with an inorganic material.

[0020] Coupling agents that can be used without particular limitation include titanate-based coupling agents, aluminate-based coupling agents, and silane coupling agents. Specific examples of titanate-based coupling agents include isopropyl triisostearoyl titanate, isopropyl tri(dioctyl pyrophosphate) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, isopropyl tri-n-dodecylbenzenesulfonyl titanate, bis(dioctyl pyrophosphate)oxyacetate titanate, and tetraisopropyl bis(dioctyl phosphite) titanate. Specific examples of aluminate-based coupling agents include alkyl acetoacetate aluminum diisopropylate. Specific examples of the silane coupling agent include organosilicon compounds such as amino-based silane coupling agents, ureido-based silane coupling agents, vinyl-based silane coupling agents, methacrylic-based silane coupling agents, epoxy-based silane coupling agents, mercapto-based silane coupling agents, and isocyanate-based silane coupling agents. Among the coupling agents, titanate-based coupling agents and aluminate-based coupling agents are preferred, and titanate-based coupling agents are more preferred. The dispersant contained in the additive composition may be one type or a combination of two or more types.

[0021] As the coupling agent, commercially available products may be used. Examples of commercially available coupling agents include titanate-based coupling agents such as TTS, 46B, 55, 41B, 38S, 138S, 238S, 44, 9SA, and ET (manufactured by Ajinomoto Fine-Techno Co., Ltd., trade name: PLENACT), and titanate-based coupling agents such as TA-8, TA-21, TA-23, TA-30, TC-100, TC-401, TC-710, TC-810, TC-1040, TC-245, TC-750, TC-300, TC-310, and TC-400 (manufactured by Matsumoto Fine Chemical Co., Ltd., trade name: ORGATIX).

[0022] (Method for Preparing Additive Composition) The method for preparing the additive composition is not particularly limited, and a suitable method can be selected depending on the desired form of the additive composition. For example, the additive composition may be prepared by mixing the raw materials of the additive composition using a known device such as a disperser or a mixer. If necessary, a treatment for adjusting the particle size of the lithium phosphate contained in the additive composition may be carried out. The particle size of the lithium phosphate can be adjusted using a known device such as a bead mill, a ball mill, or a jet mill. The particle size of the lithium phosphate may be adjusted either for lithium phosphate alone or for a mixture of lithium phosphate with other raw materials.

[0023] (Other Components) The additive composition may contain components (other components) other than the above-mentioned components. For example, the additive composition may contain a thickener. Specific examples of the thickener include carboxymethyl cellulose (CMC), polyvinylpyrrolidone (PVP), and polyvinylidene fluoride (PVDF).

[0024] <Composition for Electrode> The composition for electrode of the present disclosure is a composition for electrode containing the additive composition of the present disclosure described above and an electrode active material.

[0025] The electrode composition of the present disclosure is used to manufacture an electrode for a lithium ion secondary battery. The electrode manufactured using the electrode composition of the present disclosure may be either a positive electrode or a negative electrode. In some embodiments, the electrode composition is used to manufacture a positive electrode.

[0026] The electrode composition of the present disclosure may be in a solid state such as a powder, particles, or tablet, or in a fluid state such as a dispersion, paste, or slurry. The electrode composition may be in a different form during storage than during electrode production (for example, a solid during storage and a fluid during electrode production). When the electrode composition is a fluid, the viscosity may be adjusted using a solvent such as an organic solvent or water.

[0027] The content of lithium phosphate in the solid content of the electrode composition can be selected, for example, from the range of 0.01% by mass to 3.00% by mass. From the viewpoint of fully obtaining the effect of adding lithium phosphate, the content of lithium phosphate in the solid content of the electrode composition is preferably 0.05% by mass or more, more preferably 0.10% by mass or more, even more preferably 0.15% by mass or more, and particularly preferably 0.20% by mass or more. From the viewpoint of ensuring sufficient battery capacity, the content of lithium phosphate in the solid content of the electrode composition is preferably 2.50% by mass or less, more preferably 2.00% by mass or less, even more preferably 1.50% by mass or less, and particularly preferably 1.00% by mass or less. The content of lithium phosphate in the solid content of the electrode composition is preferably 0.01% by mass to 3.00% by mass, more preferably 0.05% by mass to 2.00% by mass, and even more preferably 0.05% by mass to 1.50% by mass.

[0028] The amount of lithium phosphate per 100 parts by mass of the electrode active material in the electrode composition can be selected, for example, from the range of 0.01 parts by mass to 3.00 parts by mass. From the viewpoint of fully obtaining the effect of adding lithium phosphate, the amount of lithium phosphate per 100 parts by mass of the electrode active material is preferably 0.05 parts by mass or more, more preferably 0.10 parts by mass or more, even more preferably 0.15 parts by mass or more, and particularly preferably 0.20 parts by mass or more. From the viewpoint of ensuring sufficient battery capacity, the amount of lithium phosphate per 100 parts by mass of the electrode active material is preferably 2.50 parts by mass or less, more preferably 2.00 parts by mass or less, even more preferably 1.50 parts by mass or less, and particularly preferably 1.00 parts by mass or less. The amount of lithium phosphate per 100 parts by mass of the electrode active material in the electrode composition is preferably 0.01 parts by mass to 3.00 parts by mass, more preferably 0.05% by mass to 2.00% by mass, and even more preferably 0.05% by mass to 1.50% by mass.

[0029] (Electrode active material) The electrode active material contained in the electrode composition may be an electrode active material contained in the positive electrode of a lithium ion secondary battery (hereinafter also referred to as a positive electrode active material), or an electrode active material contained in the negative electrode of a lithium ion secondary battery (hereinafter also referred to as a negative electrode active material).

[0030] The positive electrode active material is not particularly limited as long as it is a material capable of absorbing and releasing lithium ions, and can be appropriately adjusted depending on the application of the lithium ion secondary battery. Preferred examples of the positive electrode active material include lithium transition metal composite oxides (hereinafter also referred to as composite oxides). Examples of composite oxides include composite oxides having a layered crystal structure, composite oxides having a spinel crystal structure, and composite oxides having an olivine crystal structure. Specific examples of composite oxides having a layered crystal structure include LiMO. ２(M is at least one transition metal selected from the group consisting of Ni, Co, and Mn), and compounds obtained by adding a different element to this compound. Representative examples of composite oxides having a layered crystal structure include LCO (lithium cobalt oxide), NCM (lithium nickel cobalt manganese oxide), and NCA (lithium nickel oxide or lithium nickel cobalt aluminum oxide). Specific examples of composite oxides having a spinel crystal structure include LiMn ２ O ４ Specific examples of composite oxides having an olivine-type crystal structure include LiMPO ４ (M is Fe, Co, Ni, or Mn). The positive electrode active material may be one type or a combination of two or more types.

[0031] The negative electrode active material is not particularly limited as long as it is a material capable of absorbing and releasing lithium ions, and can be appropriately adjusted depending on the application of the lithium ion secondary battery, etc. Specific examples of the negative electrode active material include carbon materials, silicon, metallic lithium, lithium-containing alloys, metals or alloys capable of alloying with lithium, oxides, transition metal nitrides, etc. Among these, carbon materials and silicon are preferred.

[0032] Examples of carbon materials include graphite materials, amorphous carbon materials, carbon black, activated carbon, etc. Examples of graphite materials include natural graphite and artificial graphite. Examples of artificial graphite include graphitized MCMB and graphitized MCF, etc. The graphite material may be coated with a metal or amorphous carbon. Examples of metal materials that coat the graphite material include gold, platinum, silver, copper, and tin. The graphite material may be a mixture of amorphous carbon and graphite. Examples of amorphous carbon materials include hard carbon, soft carbon, coke, mesocarbon microbeads (MCMB), mesophase pitch carbon fiber (MCF), etc. The negative electrode active material may be a single material or a combination of two or more materials.

[0033] The form of the electrode active material contained in the electrode composition is not particularly limited. For example, the electrode active material may be fibrous, spherical, flake-like, or the like. The volume average particle diameter of the electrode active material is not particularly limited. For example, the volume average particle diameter of the electrode active material may be selected from the range of 5 μm to 50 μm. The electrode active material contained in the electrode composition may be a combination of active materials with different volume average particle diameters.

[0034] The content of the electrode active material relative to the total solid content of the electrode composition may be, for example, 10% by mass or more, 30% by mass or more, 50% by mass or more, or 70% by mass or more, and may be, for example, 99.9% by mass or less, or 99% by mass or less, relative to the total solid content of the electrode composition.

[0035] (Binder) The electrode composition may contain a binder. The type of binder is not particularly limited, and can be selected from materials used as binders in the production of electrodes for lithium ion secondary batteries. Examples of binders include fluororesins, cellulose, polyvinyl acetate, polymethyl methacrylate, polyolefins, and rubber particles. Examples of fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymers, and vinylidene fluoride-hexafluoropropylene copolymers. Examples of cellulose include cellulose, nitrocellulose, and carboxymethyl cellulose. Examples of rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles. The electrode composition may contain one type of binder or a combination of two or more types.

[0036] (Conductive Aid) The electrode composition may contain a conductive aid. The type of conductive aid is not particularly limited, and can be selected from materials used as conductive aids in the production of electrodes for lithium ion secondary batteries. Examples of conductive aids include conductive carbon materials. Examples of conductive carbon materials include graphite, carbon black, conductive carbon fiber, fullerene, etc. Examples of conductive carbon fibers include carbon nanotubes, carbon nanofibers, carbon fiber, etc. Examples of graphite include artificial graphite and natural graphite. Examples of natural graphite include flake graphite, lump graphite, and amorphous graphite. The conductive aid contained in the electrode composition may be one type or a combination of two or more types.

[0037] (Other Components) The electrode composition may contain components (other components) other than the components described above. Examples of other components include a thickener, a surfactant, a dispersant, a wetting agent, and an antifoaming agent.

[0038] <Electrode> The electrode of the present disclosure is an electrode for a lithium-ion secondary battery, and includes lithium phosphate, a zirconium compound, and an electrode active material, in which the content of zirconium element in the total amount of the lithium phosphate and the zirconium compound is 100 ppm by mass to 10,000 ppm by mass.

[0039] As will be shown in the examples described later, a lithium ion secondary battery equipped with an electrode containing lithium phosphate and a zirconium compound and having a zirconium content of 100 ppm by mass to 10,000 ppm by mass exhibits superior battery performance during high-temperature storage compared to a lithium ion secondary battery equipped with an electrode having a zirconium content outside the range of 100 ppm by mass to 10,000 ppm by mass.

[0040] In the electrode of the present disclosure, the zirconium content may be 200 ppm by mass or more, 500 ppm by mass or more, 800 ppm by mass or more, or 1000 ppm by mass or more. In the electrode of the present disclosure, the zirconium content may be 5000 ppm by mass or less, 4000 ppm by mass or less, 3000 ppm by mass or less, or 2000 ppm by mass or less. The method for measuring the zirconium content of the electrode is not particularly limited. For example, it may be measured by ICP-AES, which is an optical emission spectroscopy using a high-frequency inductively coupled plasma (ICP) as a light source.

[0041] The electrode of the present disclosure may be a positive electrode or a negative electrode, but from the viewpoint of favorably exhibiting the performance of lithium phosphate as an additive, the electrode of the present disclosure is preferably a positive electrode.

[0042] From the viewpoint of favorably exhibiting performance as an additive to lithium phosphate, it is preferable that the lithium phosphate is present outside the particles of the electrode active material. From the viewpoint of favorably exhibiting performance as an additive to lithium phosphate, it is preferable that the zirconium compound is present outside the particles of the electrode active material. In the present disclosure, the state of "being present outside the particles of the electrode active material" includes both a state of being attached to the surface of the particles of the electrode active material and a state of not being attached to the surface of the particles of the electrode active material.

[0043] The details and preferred embodiments of the lithium phosphate, zirconium compound, and electrode active material contained in the electrode of the present disclosure are the same as those of the lithium phosphate, zirconium compound, and electrode active material contained in the additive composition or electrode composition described above. The electrode of the present disclosure may contain components that may be contained in the additive composition or electrode composition described above.

[0044] The electrode of the present disclosure may include a current collector and an electrode layer disposed on at least one surface of the current collector, the electrode layer including lithium phosphate, a zirconium compound, and an electrode active material. Examples of materials for the current collector include copper, aluminum, nickel, stainless steel (SUS), and nickel-plated steel.

[0045] <Lithium-ion secondary battery> The lithium-ion secondary battery of the present disclosure includes the electrode of the present disclosure. That is, in the lithium-ion secondary battery of the present disclosure, at least one of the positive electrode and the negative electrode contains lithium phosphate and a zirconium compound, and the zirconium content in the total amount of the lithium phosphate and the zirconium compound is 100 ppm by mass to 10,000 ppm by mass.

[0046] The configuration of the lithium ion secondary battery is not particularly limited. The lithium ion secondary battery includes, for example, an outer casing, a positive electrode, a negative electrode, a separator, and an electrolyte. The outer casing is a member that houses the positive electrode, the negative electrode, the separator, and the electrolyte. The separator is a member that is disposed between the positive electrode and the negative electrode and separates the positive electrode and the negative electrode. The lithium ion secondary battery may be one that uses an electrolytic solution in which the electrolyte is dissolved in a non-aqueous solvent, or one that uses a solid electrolyte (an all-solid-state battery). The all-solid-state battery may not include a separator.

[0047] (Exterior Body) The type of exterior body is not particularly limited and can be selected depending on the application, shape, size, etc. of the lithium ion secondary battery. Specific examples of the exterior body include an exterior body including a laminate film and an exterior body consisting of a battery can and a battery can lid.

[0048] (Separator) The separator may be, for example, a porous sheet. The separator may be made of a resin. Examples of the resin include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, and polyamide. The separator may be a porous resin sheet having a single layer or multilayer structure. The thickness of the separator is not particularly limited and can be selected, for example, from the range of 5 μm to 30 μm.

[0049] (Electrolyte) The type of electrolyte is not particularly limited. Specific examples of the electrolyte include lithium hexafluorophosphate (LiPF ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium hexafluoroarsenate (LiAsF ６ ), lithium hexafluorotantalate (LiTaF ６), lithium perchlorate (LiClO ４ ), lithium aluminum tetrachloride (LiAlCl ４ ), lithium decachlorodecaborate (Li ２ B １０ Cl １０ ), lithium trifluoromethanesulfonate (LiCF ３ SO ３ Among these, LiPF ６ The electrolyte contained in the lithium ion secondary battery may be one type or a combination of two or more types.

[0050] Examples of non-aqueous solvents that dissolve the electrolyte include carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, γ-lactones, cyclic ethers, chain ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, etc. The non-aqueous solvents may be used alone or in combination of two or more.

[0051] In one embodiment of the present disclosure, the non-aqueous solvent may contain a carbonate, and may contain a cyclic carbonate and a chain carbonate. Specific examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoropropylene carbonate, etc. Specific examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), dipropyl carbonate (DPC), methyl 2,2,2-trifluoroethyl carbonate, etc. The non-aqueous solvent may contain ethylene carbonate, ethyl methyl carbonate, or dimethyl carbonate, respectively.

[0052] Hereinafter, embodiments of the present disclosure will be described in detail with reference to examples, but the present disclosure is not limited to the descriptions of these examples.

[0053] <Preparation of Additive Compositions> In Examples 1 to 7 and Comparative Example 3, additive compositions were used that contained lithium phosphate, dispersion medium, and dispersant in the amounts shown in Table 1, had a zirconium content derived from zirconia shown in Table 1, and were subjected to treatment for adjusting the particle size of lithium phosphate under the conditions shown in Table 1. In Comparative Examples 1 and 2, micron-sized lithium phosphate particles obtained by pulverizing the lithium phosphate for 60 minutes using a jet mill were used.

[0054] The details of the materials and equipment shown in Table 1 are as follows. The physical properties of each product are catalog values. Lithium phosphate: Li ３ P.O. ４ , manufactured by Thermo Fisher Scientific, purity 99.99% or more Dispersion medium: N-methyl-2-pyrrolidone (NMP), manufactured by Mitsubishi Chemical Corporation, purity 99.9% or more Dispersant: isopropyl tri(dioctyl pyrophosphate) titanate, "Plenact S38" manufactured by Ajinomoto Fine-Techno Co., Ltd. Ball mill: planetary ball mill (P5) manufactured by Fritsch Bead mill: Easy Nano RMB type manufactured by Imex Jet mill: "Super Jet Mill, SJ-1500" manufactured by Nisshin Engineering Inc.

[0055] The particle size of the lithium phosphate shown in Table 1 was measured by the method described below. The additive compositions obtained in Examples 1 to 6 and Comparative Example 3 or the lithium phosphate particles obtained in Comparative Examples 1 and 2 (0.1 g) and NMP (50 ml) were placed in a 100 ml beaker, and the sample lumps were crushed with a spatula and gently mixed with a dropper. Next, the sample was dispersed in water using a tabletop ultrasonic cleaner (Honda Electronics Co., Ltd., Model W-113). The dispersion was performed for 60 seconds with the tabletop ultrasonic cleaner set to an output of 100 W and 28 kHz. After that, bubbles formed on the surface of the dispersion in the beaker were removed, and the volume-based particle size distribution of the lithium phosphate was measured by laser diffraction scattering. A Partica LA960-V2 manufactured by Horiba, Ltd. was used for the measurement. The average particle size (D50) was calculated from the obtained volume-based particle size distribution. Although the sample to be measured may contain zirconia particles, the amount is so small that it is considered that it does not affect the measured particle size of the lithium phosphate particles.

[0056] The zirconium content shown in Table 1 was measured by the method described below. Approximately 0.025 g of a sample, calculated as solid content, was collected, subjected to dry ashing (including acid fusion treatment with potassium hydrogen sulfate), and the volume was adjusted to 25 ml. This sample was further diluted and the amount of zirconium (Zr) was quantified by ICP-AES. The ICP-AES measuring device used was a 720-ES manufactured by Agilent Technologies. The content (ppm by mass) of zirconium element (Zr) in the total amount of lithium phosphate and zirconium compound was calculated from the obtained measurement value and the amounts of lithium phosphate and zirconium compound contained in the additive composition. The results are shown in Table 1.

[0057]

[0058] <Preparation of Positive Electrode Composition> A positive electrode active material (1,520 parts by mass), conductive additive 1 (30 parts by mass), and conductive additive 2 (30 parts by mass) were mixed for 10 minutes to obtain a mixture. NMP (50 parts by mass) was added to this mixture and mixed for 20 minutes to obtain a first mixed solution. PVDF solution (350 parts by mass) was added to the first mixed solution and kneaded for 30 minutes. PVDF solution (260 parts by mass) was then added and kneaded for 15 minutes. PVDF solution (220 parts by mass) was then added and kneaded for 15 minutes to obtain a second mixed solution. To adjust the viscosity, NMP (80 parts by mass) was added to the second mixed solution and mixed for 30 minutes, followed by vacuum degassing for 30 minutes to obtain a third mixed solution. The additive composition in the amount (solid content equivalent) shown in Table 2 was added to the third mixture, and the mixture was mixed for 15 minutes, followed by vacuum degassing for 15 minutes to obtain a slurry positive electrode composition (solid content concentration: 64.82 mass %).

[0059] The details of the raw materials used in preparing the positive electrode composition are as follows: Positive electrode active material: NCM811, manufactured by Beijing Dangsheng Co., Ltd., composition formula: LiNi ０．8 Co ０．1 Mn ０．1 O ２ Conductive additive 1: conductive carbon black, "Super-P" manufactured by TIMCAL Conductive additive 2: flake graphite, "KS-6" manufactured by TIMREX PVDF solution: a solution in which polyvinylidene fluoride (PVDF) was dissolved in NMP so that the content was 8% by mass

[0060] <Preparation of Positive Electrode> The mass of the positive electrode layer (coating film after drying) was 15.8 mg / cm ２ The positive electrode composition was applied to one main surface of a positive electrode current collector (aluminum foil, thickness: 20 μm) using a die coater, and then dried so that the mass of the positive electrode layer became 15.8 mg / cm ２ The positive electrode composition was similarly applied to the other main surface of the positive electrode current collector, and then dried. The positive electrode current collector with the positive electrode composition applied to both sides was dried in a vacuum drying oven at 130°C for 12 hours. Then, the density of the positive electrode layer was adjusted to 2.9±0.05 g / cm. ３ The electrode was pressed with a 35-ton press so as to obtain an electrode coating area (29 mm x 40 mm) and a margin for tab welding.

[0061] <Preparation of Negative Electrode Composition> A negative electrode active material (1050 parts by mass) and a conductive additive (11 parts by mass) were mixed for 10 minutes to obtain a mixture. A CMC solution (450 parts by mass) was added to this mixture and mixed for 20 minutes to obtain a first mixed solution. A CMC solution (150 parts by mass) was added to the first mixed solution and mixed for 30 minutes, and a CMC solution (293.5 parts by mass) was further added and mixed for 30 minutes. Water (450 parts by mass) as a solvent was added and mixed for 15 minutes to obtain a second mixed solution. An SBR dispersion (45 parts by mass) was added to the second mixed solution and kneaded for 15 minutes. Vacuum degassing was performed for 10 minutes to obtain a slurry negative electrode composition (solid content concentration: 45% by mass).

[0062] Details of the raw materials used in preparing the negative electrode composition are as follows: Negative electrode active material: natural graphite Conductive additive: conductive carbon black, "Super-P" manufactured by TIMCAL CMC solution: solution in which carboxymethyl cellulose (CMC) is dissolved in water so that the content is 1.2 mass % SBR dispersion: aqueous dispersion of styrene butadiene rubber (SBR), manufactured by JSR Corporation, solid content: 50 mass %

[0063] <Preparation of negative electrode> The mass of the negative electrode layer (coating film after drying) was 11.0 mg / cm ２ The negative electrode composition was applied to one main surface of a negative electrode current collector (copper foil, thickness: 10 μm) using a die coater, and then dried so that the mass of the negative electrode layer became 11.0 mg / cm ２ The negative electrode composition was applied to the other main surface of the negative electrode current collector and dried so that the density of the negative electrode layer became 1.45±0.05 g / cm. The negative electrode current collector with the negative electrode composition applied to both sides was dried in a vacuum drying oven at 120°C for 12 hours. ３ The electrode was then pressed using a small press so that the electrode had a thickness of 31 mm x 42 mm. The electrode was then slit to provide an electrode application area (31 mm x 42 mm) and a margin for tab welding.

[0064] <Battery Fabrication> An electrode stack was obtained by stacking and fixing a negative electrode, separator, positive electrode, separator, and negative electrode in this order. Next, an aluminum tab was bonded to the margin of the positive electrode using an ultrasonic bonding machine, and a nickel tab was bonded to the margin of the negative electrode using an ultrasonic bonding machine. This was sandwiched between laminate sheets, and three sides were heat-sealed to produce a structure in which the electrode stack was covered with an outer casing. A polyethylene porous film (50 mm x 50 mm) with a porosity of 45% and a thickness of 25 μm was used as the separator. Before injecting the electrolyte solution, the structure was dried under reduced pressure at 70°C for 12 hours in a vacuum dryer. The electrolyte solution (0.3±0.03 g) was injected into the structure, and the opening of the structure was heat-sealed while drawing a vacuum, to obtain a battery precursor. The electrolyte solution was a mixed solvent containing ethylene carbonate (EC), methyl ethyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC=3:3:4, and LiPF ６ was dissolved to a concentration of 1.0 mol / L and used.

[0065] The battery precursor was maintained in the atmosphere at 25°C for 24 hours. The battery precursor was then subjected to a constant current charge (0.1C-CC) at 0.1C for 3 hours, followed by a 12-hour pause at 25°C. Next, a constant current / constant voltage charge (0.1C-CCCV) was performed at 0.1C to 4.2V (SOC 100%), followed by a 30-minute pause. Subsequently, a constant current discharge (0.1C-CC) was performed at 0.1C to 2.8V, yielding a stacked battery.

[0066] <Battery Performance Evaluation 1: Initial DCIR> A laminated battery (design capacity 70 mAh) was subjected to a constant current constant voltage charge (0.1C-CCCV) at 0.1C to 4.2V in a temperature environment of 25 ° C., and the initial DCIR was measured. Next, a constant current discharge (0.1C-CC-10s) was performed at 0.1C for 10 seconds, and a constant current charge (0.1C-CC-10s) was performed at 0.1C for 10 seconds. Next, a constant current discharge (0.2C-CC-10s) was performed at 0.2C for 10 seconds, and a constant current charge (0.2C-CC-10s) was performed at 0.2C for 10 seconds. Next, a constant current discharge (0.5C-CC-10s) was performed at 0.5C for 10 seconds, and a constant current charge (0.5C-CC-10s) was performed at 0.5C for 10 seconds. Next, a constant current discharge (1.0C-CC-10s) was performed at 1.0 C for 10 seconds, and a constant current charge (1.0C-CC-10s) was performed at 1.0 C for 10 seconds. Next, a constant current discharge (2.0C-CC-10s) was performed at 2.0 C for 10 seconds, and a constant current charge (2.0C-CC-10s) was performed at 2.0 C for 10 seconds. The DC resistance (DCIR) was calculated based on the voltage drop (= voltage before discharge start - voltage 10 seconds after discharge start) due to "CC10s discharge" at each discharge rate of 0.1C to 2.0C and the current value (i.e., each current value corresponding to a discharge rate of 0.1C to 2.0C).

[0067] As a reference example, the DC resistance (DCIR) of a stacked battery fabricated in the same manner as in the examples, except that no additive composition was added to the positive electrode, was measured. The DC resistance (DCIR) value was calculated as a first relative value when the DC resistance (DCIR) of the reference example was set to 100, and evaluation was performed according to the following criteria. An evaluation of "A" or "B" was considered to indicate good initial DCIR. The results are shown in Table 2.

[0068] A: The first relative value is equal to or less than 102. B: The first relative value is greater than 102 and equal to or less than 105. C: The first relative value is greater than 105.

[0069] <Battery Performance Evaluation 2: High-Temperature Storage Capacity Retention Rate> A laminated battery (design capacity 70 mAh) was subjected to constant-current, constant-voltage charging (0.1C-CCCV) at 0.1C to 4.2V in a temperature environment of 25°C, followed by a 30-minute pause. Subsequently, a constant-current, constant-voltage discharging (0.1C-CCCV) at 0.1C to 2.8V was performed, and the discharge capacity before storage was measured. Subsequently, a constant-current, constant-voltage charging (0.1C-CCCV) at 0.1C to 4.2V was performed. The charged battery was then left to stand in a 60°C atmosphere for 28 days to obtain a battery after high-temperature storage. Subsequently, a constant-current, constant-voltage discharging (0.1C-CCCV) at 0.1C to 2.8V was performed, followed by a 30-minute pause. Subsequently, a constant-current, constant-voltage charging (0.1C-CCCV) at 0.1C to 4.2V (SOC 100%) was performed, followed by a 30-minute pause. Next, a constant current discharge (0.1C-CC) of 0.1C was performed to 2.8V, and the second discharge capacity after storage (hereinafter referred to as "recovered discharge capacity after storage") was measured. The high-temperature storage capacity retention rate was calculated using the following formula: High-temperature storage capacity retention rate = discharge capacity before storage / recovered discharge capacity after storage

[0070] As a reference example, the high-temperature storage capacity retention of a laminated battery fabricated in the same manner as in the examples, except that no additive composition was added to the positive electrode, was determined. The high-temperature storage capacity retention value was calculated as a second relative value when the high-temperature storage capacity retention value of the reference example was set to 100, and evaluation was performed according to the following criteria. A rating of "A" or "B" was considered to indicate a good high-temperature storage capacity retention value. The results are shown in Table 2.

[0071] A: The second relative value is 100 or more. B: The second relative value is more than 98 and less than 100. C: The second relative value is 98 or less.

[0072] <Battery Performance Evaluation 3: DCIR After High-Temperature Storage> A laminated battery (design capacity 70 mAh) was subjected to constant-current, constant-voltage charging (0.1C-CCCV) at 0.1C up to 4.2V in a temperature environment of 25°C. The charged battery was then left to stand in an atmosphere of 60°C for 28 days to obtain a battery after high-temperature storage. The direct current resistance (DCIR) of the battery after high-temperature storage was determined in the same manner as in "Battery Performance Evaluation 1" described above.

[0073] As a reference example, the DC resistance (DCIR) of a stacked battery fabricated in the same manner as in the examples, except that no additive composition was added to the positive electrode, was measured. The DC resistance (DCIR) value was calculated as a third relative value when the DC resistance (DCIR) of the reference example was set to 100, and evaluation was performed according to the following criteria. A rating of "AA," "A," or "B" was considered to indicate good DCIR after high-temperature storage. The results are shown in Table 2.

[0074] AA: The third relative value is 80 or less. A: The third relative value is more than 80 and 95 or less. B: The third relative value is more than 95 and less than 100. C: The third relative value is 100 or more.

[0075]

[0076] As shown in the results of Tables 1 and 2, lithium ion secondary batteries obtained using additive compositions having a zirconium content of 100 ppm by mass to 10,000 ppm by mass exhibit superior battery performance during high-temperature storage compared to lithium ion secondary batteries obtained using additive compositions having a zirconium content outside the range of 100 ppm by mass to 10,000 ppm by mass.

[0077] The disclosure of Japanese Patent Application No. 2024-034261 is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned herein are incorporated by reference to the same extent as if each individual publication, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. An additive composition for an electrode of a lithium ion secondary battery, comprising lithium phosphate and a zirconium compound, wherein the content of zirconium element in the total amount of the lithium phosphate and the zirconium compound is 100 ppm by mass to 10,000 ppm by mass.

2. The additive composition according to claim 1, wherein the lithium phosphate is in the form of particles having a volume average particle size of 50 nm to 5,000 nm.

3. The additive composition according to claim 1, wherein the lithium phosphate is in the form of particles having a volume average particle size of 50 nm or more but less than 500 nm.

4. The zirconium compound is ZrO ２ 10. The additive composition of claim 1 comprising:

5. The additive composition of claim 1 further comprising a dispersant.

6. The additive composition of claim 5, wherein said dispersant comprises a titanate-based coupling agent.

7. An electrode composition comprising the additive composition according to any one of claims 1 to 6 and an electrode active material.

8. The electrode composition according to claim 7, wherein the content of lithium phosphate in the solid content of the electrode composition is 0.01% by mass to 3.00% by mass.

9. The electrode composition according to claim 7, wherein the content of lithium phosphate in the solid content of the electrode composition is 0.05% by mass to 1.50% by mass.

10. The electrode composition according to claim 7, wherein the amount of lithium phosphate in the electrode composition is 0.01 to 3.00 parts by mass per 100 parts by mass of the electrode active material.

11. The electrode composition according to claim 7, wherein the amount of lithium phosphate in the electrode composition is 0.01 to 1.50 parts by mass per 100 parts by mass of the electrode active material.

12. An electrode for a lithium ion secondary battery, comprising lithium phosphate, a zirconium compound, and an electrode active material, wherein the zirconium content in the total amount of the lithium phosphate and the zirconium compound is 100 ppm by mass to 10,000 ppm by mass.

13. The electrode according to claim 12, wherein the lithium phosphate is in the form of particles having a volume average particle size of 50 nm to 5,000 nm.

14. The electrode of claim 12, wherein the zirconium compound is present external to the particles of the electrode active material.

15. A lithium ion secondary battery comprising the electrode according to any one of claims 12 to 14.