Lithium secondary battery

Abstract

This lithium secondary battery contains lithium phosphate and a cyclic sulfate compound (I) represented by formula (I). R11 represents an alkylene group, an alkenylene group, a group represented by formula (i-1), a group represented by formula (i-2), or a group represented by formula (i-3); R12 represents an oxygen atom, an alkylene group, an alkenylene group, or an oxymethylene group; R13 represents an alkyl group, an alkenyl group, or an oxymethylene group; R14 represents a halogen atom, an alkyl group, a halogenated alkyl group, an alkoxy group, or a group represented by formula (i-4); and R15 represents an oxygen atom, an alkylene group, an alkenylene group having 2-6 carbon atoms, or an oxymethylene group.

Description

Lithium-ion battery 【0001】 This disclosure relates to lithium secondary batteries. 【0002】 Lithium-ion batteries may contain various additives to improve battery performance. For example, lithium phosphate is known as an additive to suppress heat generation during overcharging of lithium-ion batteries. When overcharging occurs in a lithium-ion battery with lithium phosphate added to the positive electrode, hydrogen fluoride generated by the decomposition of the electrolyte on the surface of the positive electrode reacts with lithium phosphate to produce phosphate ions. These phosphate ions move 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 battery is stabilized, and heat generation during overcharging is suppressed (see, for example, Patent Document 1). 【0003】 Patent Document 1: Japanese Unexamined Patent Publication No. 2021-125377 【0004】 In lithium secondary batteries containing lithium phosphate as an additive, there is a need to further reduce the DC resistance and volume change during high-temperature storage. Here, the volume change during high-temperature storage is caused by gas generation. The object of one embodiment of this disclosure is to provide a lithium secondary battery in which the DC resistance and volume change during high-temperature storage are reduced. 【0005】 Means for solving the above problems include the following embodiments: <1> A lithium secondary battery containing lithium phosphate and a cyclic sulfate ester compound (I) represented by the following formula (I). 【0006】 【0007】 In formula (I), R １１ R represents an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (i-1), a group represented by formula (i-2), or a group represented by formula (i-3), where R １２ R represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group, and * represents the bond position. In formula (i-2), R １３represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an oxymethylene group, * represents the bonding position, and in formula (i-3), R １４ represents a halogen atom, an alkyl group having 1 to 6 carbon atoms, a halogenated alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or a group represented by formula (i-4), * represents the bonding position, and in formula (i-4), R １５ represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group, and * represents the bonding position. 【0008】 <2> In the above formula (I), R １１ is a group represented by formula (i-1) or a group represented by formula (i-2), R １２ is an oxymethylene group, R １３ is a propyl group, the lithium secondary battery according to <1>. <3> The lithium phosphate is in the form of particles having a volume average particle diameter of 50 nm to 5000 nm, the lithium secondary battery according to <1> or <2>. <4> Further, it contains a disulfonic acid ester compound (II) represented by the following formula (II), the lithium secondary battery according to any one of <1> to <3>. 【0009】 【0010】 In formula (II), R ２１ represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a halogenated alkylene group having 1 to 3 carbon atoms. R ２２ and R ２３ each independently represent an alkyl group having 1 to 6 carbon atoms, or a phenyl group, or together represent an alkylene group having 1 to 10 carbon atoms, or a 1,2-phenylene group, and the said 1,2-phenylene group may be substituted by a halogen atom, an alkyl group having 1 to 12 carbon atoms, or a cyano group. 【0011】 <5> In the above formula (II), R ２１ is a methylene group, R ２２ and R ２３The lithium secondary battery according to <4>, wherein each is independently an alkyl group having 1 to 3 carbon atoms, or an alkylene group having 1 to 3 carbon atoms or a 1,2-phenylene group formed integrally, and the 1,2-phenylene group may be substituted with a halogen atom, an alkyl group having 1 to 3 carbon atoms, and a cyano group. <6> The lithium secondary battery according to any one of <1> to <5>, comprising electrodes and a non-aqueous electrolyte, wherein the lithium phosphate is contained in the electrodes and the cyclic sulfate ester compound (I) is contained in the non-aqueous electrolyte. <7> The lithium secondary battery according to any one of <1> to <6>, wherein the electrodes further contain a dispersant. <8> The lithium secondary battery according to <7>, wherein the dispersant contains a titanate coupling agent. <9> The lithium secondary battery according to <6>, wherein the electrodes include a positive electrode and a negative electrode, and the positive electrode includes a positive electrode layer containing a positive electrode active material and the lithium phosphate. <10> The lithium secondary battery according to <9>, wherein the lithium phosphate content is 0.01% by mass to 10.0% by mass with respect to the total amount of solids in the positive electrode layer. 【0012】 According to one embodiment of the present disclosure, a lithium secondary battery is provided in which the DC resistance after high-temperature storage and the volume change during high-temperature storage are reduced. 【0013】 In this specification, numerical ranges expressed using "~" mean a range that includes the numbers before and after "~" as the lower and upper limits. In this specification, the amount of each component in a composition means the total amount of multiple substances present in the composition, unless otherwise specified, if there are multiple substances corresponding to each component in the composition. In numerical ranges described stepwise in this specification, the upper or lower limit stated in one numerical range may be replaced with the upper or lower limit of another numerical range described stepwise, or with the values ​​shown in the examples. In this specification, the term "process" includes not only independent processes, but also processes that cannot be clearly distinguished from other processes, as long as their intended purpose is achieved. 【0014】[Lithium secondary battery] The lithium secondary battery of this disclosure contains lithium phosphate and a cyclic sulfate ester compound (I) represented by formula (I) described below. 【0015】 The lithium secondary battery of this disclosure is a lithium secondary battery in which the DC resistance after high-temperature storage and the volume change during high-temperature storage are reduced. This effect is obtained by a combination of lithium phosphate and a cyclic sulfate ester compound (I). Lithium phosphate mainly contributes to the reduction of DC resistance after high-temperature storage, and cyclic sulfate ester compound (I) mainly contributes to the reduction of volume change during high-temperature storage. 【0016】 The lithium secondary battery of this disclosure has suppressed initial (i.e., pre-storage) DC resistance and also exhibits excellent capacity retention during high-temperature storage. 【0017】 <Lithium Phosphate> The lithium secondary battery of this disclosure contains at least one type of lithium phosphate. The type of lithium phosphate contained in the lithium secondary battery of this disclosure is not particularly limited, Li ３ PO ４ (Trilithium phosphate), LiH ２ PO ４ (Lithium dihydrogen phosphate), Li ２ HPO ４ Lithium phosphate can be selected from (lithium monohydrogen phosphate), etc. Among these, Li ３ PO ４ This is preferable. The lithium phosphate contained in the lithium secondary battery of this disclosure may be one type or a combination of two or more types. 【0018】From the viewpoint of dispersibility within the electrode, lithium phosphate is preferably in particulate form. When lithium phosphate is in particulate form, 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, 150 nm or more, or 200 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, 500 nm or less, or 400 nm or less. In this disclosure, the volume-average particle diameter of a particle is the particle diameter (D50) at which the volume accumulation reaches 50% in the volume-based particle size distribution curve measured by laser diffraction-scattering. 【0019】 An example of lithium phosphate included in the lithium secondary battery of this disclosure is particulate lithium phosphate with a volume-average particle diameter of 50 nm to 5000 nm. 【0020】 In the lithium secondary battery of this disclosure, there are no particular limitations on the location in which lithium phosphate is contained. Lithium phosphate is preferably contained in the electrodes (more specifically, the positive electrode or the negative electrode) of the lithium secondary battery of this disclosure, more preferably contained as an additive in the electrode containing the active material (e.g., in the electrode layer containing the active material), and even more preferably contained as an additive in the positive electrode containing the positive electrode active material (e.g., in the positive electrode layer containing the positive electrode active material). To rephrase the above more preferred embodiments, in the lithium secondary battery of this disclosure, the electrodes include a positive electrode and a negative electrode, the positive electrode is more preferably contained in the positive electrode active material and lithium phosphate, and the positive electrode is more preferably contained in the positive electrode layer containing the positive electrode active material and lithium phosphate. 【0021】 When lithium phosphate is included as an additive in an electrode containing an active material, the lithium phosphate content is preferably 0.01% to 10.0% by mass, more preferably 0.05% to 5.0% by mass, and even more preferably 0.1% to 2.0% by mass, relative to the total amount of the active material. 【0022】When lithium phosphate is included as an additive in the positive electrode containing the positive electrode active material (i.e., when the positive electrode includes a positive electrode layer containing the positive electrode active material and lithium phosphate), the lithium phosphate content is preferably 0.01% to 10.0% by mass, more preferably 0.05% to 5.0% by mass, and even more preferably 0.1% to 2.0% by mass, based on the total solid content in the positive electrode layer. 【0023】 (Lithium Phosphate Composition) For the manufacture of the lithium secondary battery of this disclosure, a lithium phosphate composition containing the aforementioned lithium phosphate (e.g., a lithium phosphate dispersion) can be used. For example, when manufacturing an electrode (e.g., an electrode layer) containing an active material and lithium phosphate as an additive, a mixture of a composition containing the active material and a lithium phosphate composition containing lithium phosphate can be used as the electrode composition to manufacture the electrode. 【0024】 -Dispersion medium- The lithium phosphate composition may contain a dispersion medium. Specific examples of dispersion media include amides such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; ureas such as N,N-dimethylethylene urea, N,N-dimethylpropylene urea, and tetramethyl urea; 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; grimes such as diglyme, triglime, and tetraglime; hydrocarbons such as toluene, xylene, and cyclohexane; sulfoxides such as dimethyl sulfoxide; sulfones such as sulfolane; organic solvents such as methanol, ethanol, isopropanol, and n-butanol; mineral oil, and water. The dispersion medium may be used alone or in combination of two or more types. 【0025】When the lithium phosphate composition contains a dispersion medium, the content of the dispersion medium is not particularly limited and can be set considering the desired viscosity of the lithium phosphate composition, the concentration of lithium phosphate, etc. 【0026】 - Dispersant - The lithium phosphate composition may contain a dispersant. Any material that enhances the dispersibility of lithium phosphate, such as a coupling agent or surfactant, can be used as the dispersant without particular limitations. From the viewpoint of maintaining a good dispersed state of lithium phosphate, the dispersant is preferably a coupling agent. In this disclosure, a coupling agent means a compound having a site that reacts with organic materials and a site that bonds with inorganic materials within its molecule. 【0027】 As coupling agents, any coupling agent such as titanate-based coupling agents, aluminate-based coupling agents, or silane-based coupling agents can be used without particular limitation. Specific examples of titanate-based coupling agents include isopropyltriisostearoyl titanate, isopropyltri(dioctyl pyrophosphate) titanate, tetraoctylbis(ditridecylphosphite) titanate, isopropyltri-n-dodecylbenzenesulfonyl titanate, bis(dioctyl pyrophosphate) oxyacetate titanate, and tetraisopropylbis(dioctylphosphite) titanate. Specific examples of aluminate-based coupling agents include alkylacetate aluminum diisopropylate. Specific examples of silane coupling agents 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, with titanate-based coupling agents being more preferred. The dispersant contained in the lithium phosphate composition may be a single type or a combination of two or more types. 【0028】Commercially available coupling agents 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., product name: PrenAct), 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., product name: Orgatics). 【0029】 -Other Components- Lithium phosphate compositions may contain components other than those described above (other components). For example, lithium phosphate compositions may contain thickeners. Specific examples of thickeners include carboxymethylcellulose (CMC), polyvinylpyrrolidone (PVP), and polyvinylidene fluoride (PVDF). 【0030】 -Method for preparing lithium phosphate composition- The method for preparing the lithium phosphate composition is not particularly limited, and a suitable method can be selected depending on the desired form of the lithium phosphate composition. For example, the lithium phosphate composition may be prepared by mixing the raw materials of the lithium phosphate composition using a known device such as a dispenser or mixer. If necessary, processing may be performed to adjust the particle size of the lithium phosphate contained in the lithium phosphate composition. The particle size of lithium phosphate can be adjusted using a known device such as a bead mill, ball mill, or jet mill. The particle size of lithium phosphate may be adjusted for lithium phosphate alone or for a mixture of lithium phosphate and other raw materials. 【0031】 <Cyclic Sulfate Ester Compound (I)> The lithium secondary battery of this disclosure contains at least one cyclic sulfate ester compound (I) represented by the following formula (I) (hereinafter also simply referred to as "compound (I)"). 【0032】 【0033】 In formula (I), R １１R represents an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (i-1), a group represented by formula (i-2), or a group represented by formula (i-3), where R １２ R represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group, and * represents the bond position. In formula (i-2), R １３ R represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an oxymethylene group, and * represents the bond position. In formula (i-3), R １４ represents a halogen atom, a C1-C6 alkyl group, a C1-C6 halogenated alkyl group, a C1-C6 alkoxy group, or a group represented by formula (i-4), where * represents the bond position, and in formula (i-4), R １５ * represents an oxygen atom, an alkylene group with 1 to 6 carbon atoms, an alkenylene group with 2 to 6 carbon atoms, or an oxymethylene group, and * represents the bond position. 【0034】 In formula (I), R １１ Preferably, this is an alkylene group having 1 to 3 carbon atoms, an alkenylene group having 2 to 3 carbon atoms, a group represented by formula (i-1), a group represented by formula (i-2), or a group represented by formula (i-3), more preferably a group represented by formula (i-1) or a group represented by formula (i-2). 【0035】 In formula (i-1), R １２ Preferably, this is an oxygen atom, an alkylene group having 1 to 3 carbon atoms, an alkenylene group having 2 to 3 carbon atoms, or an oxymethylene group, more preferably an oxymethylene group. 【0036】 In formula (i-2), R １３ The group is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably a propyl group. 【0037】 In formula (i-3), R １４ Preferably, is a halogen atom, a C1-C3 alkyl group, a C1-C3 halogenated alkyl group, a C1-C3 alkoxy group, or a group represented by formula (i-4). １４The halogen atom represented is preferably a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. １４ The halogen atom in the alkyl halide represented by is preferably a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom. 【0038】 In formula (i-4), R １５ Preferably, this is an oxygen atom, an alkylene group having 1 to 3 carbon atoms, an alkenylene group having 2 to 3 carbon atoms, or an oxymethylene group, more preferably an oxymethylene group. 【0039】 An example of a preferred embodiment of formula (I) is R １１ is a group represented by formula (i-1) or formula (i-2), and R １２ R is an oxymethylene group. １３ This is a form in which the group is a propyl group. 【0040】 The compound (I) of the particularly preferred embodiment described above is compound A-1 and compound A-2 below. Of these, compound A-1 is particularly preferred. 【0041】 【0042】 For specific examples of compound (I), refer to the description in International Publication No. 2012 / 053644. 【0043】 In the lithium secondary battery of this disclosure, there are no particular limitations on the location in which compound (I) is contained. Preferably, compound (I) is contained in the non-aqueous electrolyte of the lithium secondary battery of this disclosure. 【0044】 When compound (I) is contained in the non-aqueous electrolyte of the lithium secondary battery of this disclosure, the content of compound (I) relative to the total amount of the non-aqueous electrolyte is preferably 0.01% to 5.0% by mass, more preferably 0.05% to 3.0% by mass, even more preferably 0.1% to 2.0% by mass, even more preferably 0.1% to 1.5% by mass, and particularly preferably 0.5% to 1.5% by mass, relative to the total amount of the non-aqueous electrolyte. 【0045】<Disulfonic Acid Ester Compound (II)> The lithium secondary battery of this disclosure may contain at least one disulfonic acid ester compound (II) represented by the following formula (II) (hereinafter also simply referred to as "compound (II)"). This makes it possible to further reduce the initial DC resistance. 【0046】 【0047】 In formula (II), R ２１ R represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms, or a halogenated alkylene group having 1 to 3 carbon atoms. ２２ and R ２３ Each of these independently represents an alkyl group having 1 to 6 carbon atoms or a phenyl group, or together represents an alkylene group having 1 to 10 carbon atoms or a 1,2-phenylene group, wherein the 1,2-phenylene group may be substituted with a halogen atom, an alkyl group having 1 to 12 carbon atoms, or a cyano group. 【0048】 Preferred embodiments and specific examples of compound (II) can be appropriately referenced to the description in Japanese Patent Application Publication No. 2015-162289. 【0049】 R ２１ Preferably, it is an aliphatic hydrocarbon group having 1 to 10 carbon atoms, more preferably an alkylene group having 1 to 3 carbon atoms, even more preferably a methylene group, a dimethylene group, a trimethylene group, or a dimethylmethylene group, even more preferably a methylene group or a dimethylene group, and even more preferably a methylene group. 【0050】 R ２２ and R ２３ Preferably, each is independently a C1-C3 alkyl group, or a C1-C3 alkylene group or a 1,2-phenylene group (this 1,2-phenylene group may be substituted with a halogen atom, a C1-C3 alkyl group, and a cyano group). 【0051】 An example of a preferred embodiment of formula (II) is R ２１ However, it is a methylene group, R ２２ and R ２３However, each is independently a C1-C3 alkyl group, or a C1-C3 alkylene group or a 1,2-phenylene group (this 1,2-phenylene group may be substituted with a halogen atom, a C1-C3 alkyl group, and a cyano group). 【0052】 In the lithium secondary battery of this disclosure, there are no particular limitations on the location in which compound (II) is contained. Preferably, compound (II) is contained in the non-aqueous electrolyte of the lithium secondary battery of this disclosure. 【0053】 When compound (II) is included in the non-aqueous electrolyte of the lithium secondary battery of this disclosure, the content of compound (II) relative to the total amount of the non-aqueous electrolyte is preferably 0.01% to 5.0% by mass, more preferably 0.05% to 3.0% by mass, even more preferably 0.1% to 1.5% by mass, even more preferably 0.3% to 1.5% by mass, and particularly preferably 0.3% to 1.0% by mass, relative to the total amount of the non-aqueous electrolyte. 【0054】 When both compound (I) and compound (II) are contained in the non-aqueous electrolyte of the lithium secondary battery of this disclosure, the mass ratio of compound (II) / compound (I) in the non-aqueous electrolyte is preferably 0.01 to 3.0, more preferably 0.1 to 2.0, even more preferably 0.2 to 1.0, even more preferably 0.2 to 0.9, and even more preferably 0.3 to 0.7. 【0055】 <Electrodes> The lithium secondary battery of this disclosure may include electrodes (preferably a positive electrode and a negative electrode). The electrodes may include a current collector and an electrode layer disposed in contact with at least one surface of the current collector. 【0056】 (Current Collector) In this disclosure, "current collector" refers to a sheet-like member in a lithium secondary battery that collects electrons generated from the active material and supplies electrons to the active material. Examples of materials for the current collector include copper, aluminum, nickel, stainless steel (SUS), nickel-plated steel, etc. In this disclosure, the current collector at the positive electrode may be referred to as the positive electrode current collector, and the current collector at the negative electrode may be referred to as the negative electrode current collector. 【0057】 (Electrode Layer) The electrode layer is a layer that is in contact with at least one surface of the current collector. In this disclosure, the electrode layer at the positive electrode may be referred to as the positive electrode layer, and the electrode layer at the negative electrode may be referred to as the negative electrode layer. 【0058】 - Active Material - The electrode layer may contain an active material. The active material contained in the positive electrode layer as an electrode layer is called the positive electrode active material, and the active material contained in the negative electrode layer as an electrode layer is called the negative electrode active material. 【0059】 The positive electrode active material is not particularly limited as long as it is a material capable of intercalating and releasing lithium ions, and can be appropriately adjusted according to the application of the lithium secondary battery. Preferred examples of positive electrode active materials 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. Specifically, LiMO is an example of a composite oxide having a layered crystal structure. ２ Examples include compounds represented by (where M is at least one transition metal selected from the group consisting of Ni, Co, and Mn), and compounds to which heterogeneous elements are added. Representative examples of composite oxides having a layered crystal structure include LCO (lithium cobaltate), NCM (lithium nickel-cobalt-manganate), and NCA (lithium nickelate or lithium nickel-cobalt-aluminate). Specifically, LiMn is an example of a composite oxide having a spinel-type crystal structure. ２ O ４ Examples include LiMPO ４ Examples include (where M is Fe, Co, Ni, or Mn). The positive electrode active material may be a single type or a combination of two or more types. 【0060】The negative electrode active material is not particularly limited as long as it is a material capable of intercalating and releasing lithium ions, and can be appropriately adjusted according to the application of the lithium secondary battery. Specific examples of negative electrode active materials include carbon materials, silicon, metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides, and transition metal nitrides. Among these, carbon materials and silicon are preferred. 【0061】 Examples of carbon materials include graphite materials, amorphous carbon materials, carbon black, and activated carbon. Examples of graphite materials include natural graphite and artificial graphite. Examples of artificial graphite include graphitized MCMB and graphitized MCF. The graphite material may be coated with a metal or amorphous carbon. Examples of metals used to 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), and mesophase pitch carbon fiber (MCF). The negative electrode active material may be a single material or a combination of two or more materials. 【0062】 The morphology of the active material contained in the electrode layer is not particularly limited. For example, the morphology of the active material may be fibrous, spherical, flake-like, etc. The volume-average particle size of the active material is not particularly limited. For example, the volume-average particle size of the active material may be selected from the range of 5 μm to 50 μm. The active material contained in the electrode layer may be a combination of active materials with different volume-average particle sizes. 【0063】 The content of the active material relative to the total solid content of the electrode layer 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. The content of the active material relative to the total solid content of the electrode layer may be, for example, 99.9% by mass or less, or 99% by mass or less. 【0064】- Binder - The electrode layer may contain a binder. The type of binder is not particularly limited and can be selected from materials used as binders in the manufacture of lithium secondary battery electrodes. Examples of binders include fluororesins, cellulose, polyvinyl acetate, polymethyl methacrylate, polyolefins, and rubber particles. Examples of fluororesins include polytetrafluoroethylene, polyvinylidene fluoride, tetrafluoroethylene-hexafluoropropylene copolymer, and vinylidene fluoride-hexafluoropropylene copolymer. Examples of cellulose include cellulose, nitrocellulose, and carboxymethylcellulose. Examples of rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles. The binder contained in the electrode layer may be one type or a combination of two or more types. 【0065】 -Conductive Additive- The electrode layer may contain a conductive additive. The type of conductive additive is not particularly limited and can be selected from materials used as conductive additives in the manufacture of electrodes for lithium secondary batteries. Examples of conductive additives include conductive carbon materials. Examples of conductive carbon materials include graphite, carbon black, conductive carbon fibers, and fullerenes. Examples of conductive carbon fibers include carbon nanotubes, carbon nanofibers, and carbon fibers. Examples of graphite include artificial graphite and natural graphite. Examples of natural graphite include flake graphite, lumpy graphite, and earthy graphite. The conductive additive contained in the electrode composition may be one type or a combination of two or more types. 【0066】 -Lithium Phosphate- As mentioned above, the electrode layer may contain the aforementioned lithium phosphate as an additive. In this case, the preferred range for the lithium phosphate content is as described above. 【0067】-Other Components- The electrode layer may contain components other than those described above (other components). Examples of other components include thickeners, surfactants, dispersants, wetting agents, and defoaming agents. For example, the electrode (preferably the electrode layer) may contain a dispersant (preferably a dispersant containing a titanate-based coupling agent) as described in the section on lithium phosphate compositions. 【0068】 Other components may include elemental zirconium or zirconium compounds. Specific examples of zirconium compounds include zirconia (zirconium oxide), zircon (zirconium silicate mineral), zirconium tungstate, zirconium chloride, zirconium carbonate, zirconium acetate, zirconium nitrate, and organozirconium compounds. Among these, zirconia is preferred. The elemental zirconium or zirconium compound that may be contained in the electrode layer may be a single type or a combination of two or more types. The elemental zirconium or zirconium compound may be in particulate form. In this case, the particle shape may be spherical or non-spherical. The volume-average particle diameter range of the particulate elemental zirconium or zirconium compound is, for example, 50 nm to 5000 nm. 【0069】 - Electrode Composition - The electrode layer can be manufactured using an electrode composition containing the components described above. The electrode composition may be in a solid state such as powder, particles, or tablets, or in a fluid state such as a dispersion, paste, or slurry. The electrode composition may have different forms during storage and during electrode manufacturing (for example, it may be solid during storage and fluid during electrode manufacturing). If the electrode composition is fluid, its viscosity may be adjusted using a solvent such as an organic solvent or water. 【0070】 Furthermore, as mentioned above, a mixture of a composition containing an active material and a lithium phosphate composition containing lithium phosphate may be used as the electrode composition. 【0071】 <Non-aqueous electrolyte> The lithium secondary battery of this disclosure may include a non-aqueous electrolyte. The non-aqueous electrolyte may include an electrolyte and a non-aqueous solvent. 【0072】 (Electrolyte) The type of electrolyte is not particularly limited. Preferably, the electrolyte contains at least one of a lithium salt containing fluorine (hereinafter sometimes referred to as "fluorine-containing lithium salt") and a lithium salt that does not contain fluorine. 【0073】 Examples of fluorinated lithium salts include inorganic acid anionic salts and organic acid anionic salts. An example of an inorganic acid anionic salt is lithium hexafluoride phosphate (LiPF). ６ ), lithium tetrafluoroborate (LiBF ４ ), lithium hexafluoride arsenate (LiAsF ６ ), lithium tantalate hexafluoride (LiTaF ６ Examples include: ) and others. Examples of organic acid anionic salts include lithium trifluoromethanesulfonate (LiCF ３ SO ３ ), lithium bis(trifluoromethanesulfonyl)imide (Li(CF ３ SO ２ ) ２ N), lithium bis(pentafluoroethanesulfonyl)imide (Li(C) ２ F ５ SO ２ ) ２ Examples include N). Among them, lithium hexafluoride phosphate (LiPF) is an example of a fluorinated lithium salt. ６ ) is even more preferable. 【0074】 Lithium salts that do not contain fluorine include lithium perchlorate (LiClO2). ４ ), lithium aluminum tetrachloride (LiAlCl ４ ), lithium decachlorodecaborate (Li ２ B １０ Cl １０ ) are some examples. 【0075】When the electrolyte contains a fluorinated lithium salt, the content of the fluorinated lithium salt is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass, relative to the total amount of the electrolyte. When the fluorinated lithium salt contains lithium hexafluoride phosphate (LiPF6), the content of lithium hexafluoride phosphate (LiPF6) is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass, relative to the total amount of the electrolyte. 【0076】 When the non-aqueous electrolyte contains an electrolyte, the concentration of the electrolyte in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.2 mol / L or more and 2 mol / L or less, and even more preferably 0.5 mol / L or more and 2 mol / L or less. 【0077】 When the non-aqueous electrolyte contains lithium hexafluoride phosphate (LiPF6), the concentration of lithium hexafluoride phosphate (LiPF6) in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.2 mol / L or more and 2 mol / L or less, and even more preferably 0.5 mol / L or more and 2 mol / L or less. 【0078】 (Non-aqueous solvent) Various known non-aqueous solvents can be appropriately selected. There may be only one non-aqueous solvent, or there may be two or more. 【0079】Examples of non-aqueous solvents include cyclic carbonates, fluorinated cyclic carbonates, linear carbonates, fluorinated linear carbonates, aliphatic carboxylic acid esters, fluorinated aliphatic carboxylic acid esters, γ-lactones, fluorinated γ-lactones, cyclic ethers, fluorinated cyclic ethers, linear ethers, fluorinated linear ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, and dimethyl sulfoxide phosphate. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of fluorinated cyclic carbonates include fluoroethylene carbonate (FEC). Examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC). Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, and ethyl trimethylbutyrate. Examples of γ-lactones include γ-butyrolactone and γ-valerolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane. Examples of chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. Examples of nitriles include acetonitrile, glutalonitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile. Examples of amides include N,N-dimethylformamide.Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone. 【0080】 The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, linear carbonates, and fluorine-containing linear carbonates. In this case, the total proportion of cyclic carbonates, fluorine-containing cyclic carbonates, linear carbonates, and fluorine-containing linear carbonates is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the non-aqueous solvent. 【0081】 The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and linear carbonates. In this case, the total proportion of cyclic carbonates and linear carbonates in the non-aqueous solvent is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the non-aqueous solvent. 【0082】 The lower limit of the non-aqueous solvent content is preferably 60% by mass or more, more preferably 70% by mass or more, relative to the total amount of the non-aqueous electrolyte. The upper limit of the non-aqueous solvent content is preferably 99% by mass, preferably 97% by mass, and even more preferably 90% by mass, relative to the total amount of the non-aqueous electrolyte. 【0083】 (Cyclic Sulfate Ester Compound (I)) As described above, the non-aqueous electrolyte may contain the aforementioned compound (I) (i.e., cyclic sulfate ester compound (I)) as an additive. The preferred range for the content of compound (I) in this case is as described above. 【0084】 (Disulfonic acid ester compound (II)) As described above, the non-aqueous electrolyte may contain the aforementioned compound (II) (i.e., disulfonic acid ester compound (II)) as an additive. The preferred range of the compound (II) content in this case is as described above. 【0085】 <Separator> The lithium secondary battery of this disclosure may include a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. The positive electrode and the negative electrode are as described above as "electrodes". 【0086】 A separator is a component placed between the positive and negative electrodes to separate them. Examples of separators include porous sheet materials. Examples of separator materials include resins. Resins include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, and polyamide. The separator may be a single-layer or multi-layer porous resin sheet. The thickness of the separator is not particularly limited and can be selected from a range of, for example, 5 μm to 30 μm. 【0087】 <Outer casing> The lithium secondary battery of this disclosure may comprise an outer casing, a positive electrode, a negative electrode, a separator, and a non-aqueous electrolyte. The outer casing is a component that houses the positive electrode, negative electrode, separator, and non-aqueous electrolyte. There are no particular limitations on the type of outer casing, and it can be selected according to the application, shape, size, etc., of the lithium secondary battery. Specific examples of outer casings include an outer casing including a laminate film, an outer casing consisting of a battery can and a battery can lid, etc. 【0088】 The embodiments relating to this disclosure will be described in detail below with reference to examples. However, this disclosure is not limited in any way to the descriptions of these examples. In the following examples, "wt%" means "mass%". 【0089】 [Examples 1-5, Reference Examples, Comparative Examples 1-7] <Li ３ PO ４ Preparation of dispersion > In each example and comparative example, each material was charged according to the charging ratio shown in Table 1, and the dispersion treatment was carried out according to the dispersion conditions shown in Table 1, and particulate Li ３ PO ４ (Hereinafter, Li ３ PO ４ Li containing (also called particles) ３ PO ４ A dispersion was prepared. 【0090】The details of the materials and equipment shown in Table 1 are as follows. The physical properties of each product are catalog values. Li ３ PO ４ : Trilithium phosphate, manufactured by Thermo Fisher Scientific, purity 99.99% or higher. NMP: N-Methyl-2-pyrrolidone, manufactured by Mitsubishi Chemical Corporation, purity 99.9% or higher. S38: Dispersant "Prenact S38" (isopropyltri(dioctylpyrophosphate) titanate) manufactured by Ajinomoto Fine-Techno Co., Inc. Ball mill: Planetary ball mill (P5) manufactured by Fritsch 【0091】 Li ３ PO ４ The average particle size D50 of Li ３ PO ４ particles in the dispersion was measured as follows. The results are shown in Table 1. Li ３ PO ４ The dispersion (0.1 g) and NMP (50 ml) were placed in a 100 ml beaker, the sample mass was crushed with a spatula, and gently mixed with a dropper. Then, using a benchtop ultrasonic cleaner (model W-113, manufactured by Honda Electronics Co., Ltd.), the sample (i.e., Li ３ PO ４ particles) in water was dispersed. The dispersion was carried out for 60 seconds with the benchtop ultrasonic cleaner set to an output of 100 W and 28 kHz. Then, the bubbles generated on the surface of the dispersion in the beaker were removed, and the volume-based particle size distribution of Li ３ PO ４ particles was measured by laser diffraction scattering method. Partica LA960-V2 manufactured by Horiba, Ltd. was used for the measurement. The average particle size D50 was determined from the obtained volume-based particle size distribution. The measurement results of the average particle size D50 of Li ３ PO ４ particles are shown in Table 1. 【0092】 【0093】<Preparation of Cathode Composition> 1520 parts by mass of a cathode active material, 30 parts by mass of Conductive Aid 1, and 30 parts by mass of Conductive Aid 2 were mixed for 10 minutes to obtain a mixture. 50 parts by mass of NMP was added to this mixture and mixed for 20 minutes to obtain a first mixed solution.To the first mixed solution, a PVDF solution (350 parts by mass) was added and kneaded for 30 minutes. Then, an additional PVDF solution (260 parts by mass) was added and kneaded for 15 minutes. Then, an additional PVDF solution (220 parts by mass) was added and kneaded for 15 minutes to obtain a second mixed solution. For viscosity adjustment, 80 parts by mass of NMP was added to the second mixed solution and mixed for 30 minutes, and vacuum degassing was performed for 30 minutes to obtain a third mixture. 【0094】 In Comparative Examples 1 to 2 and 7, and Examples 1 to 5, to the third mixture, a Li ３ PO ４ dispersion was added and mixed for 15 minutes, and vacuum degassing was performed for 15 minutes to obtain a slurry-like cathode composition. Here, the Li ３ PO ４ dispersion was added such that the content (mass %) of Li ３ PO ４ in the total solid content in the cathode layer was the content shown in Table 2. 【0095】 In Comparative Examples 3 to 6, to the third mixture, a Li ３ PO ４ dispersion was not added and mixed for 15 minutes, and vacuum degassing was performed for 15 minutes to obtain a slurry-like cathode composition. 【0096】 Details of the raw materials used in the preparation of the cathode composition are as follows. Cathode active material: NCM811, manufactured by Beijing Easpring Material Technology Co., Ltd., composition formula: LiNi ０．８ Co ０．１ Mn ０．１ O ２ Conductive Aid 1: Conductive carbon black, "Super - P" manufactured by TIMCAL Conductive Aid 2: Flaky graphite, "KS - 6" manufactured by TIMREX PVDF solution: A solution obtained by dissolving polyvinylidene fluoride (PVDF) in NMP such that the content is 8 mass% <Preparation of the positive electrode> On one main surface of the positive electrode current collector (aluminum foil, 20 μm thick), the positive electrode composition is applied until the mass of the positive electrode layer (coating film after drying) is 15.8 mg / cm². ２ The material was coated with a die coater and dried to form a positive electrode layer. Then, similarly, the positive electrode composition was applied to the other main surface of the positive electrode current collector, so that the mass of the positive electrode layer was 15.8 mg / cm². ２ The material was applied and dried to form a positive electrode layer. The positive electrode current collector, with positive electrode layers formed on both sides, was dried in a vacuum drying oven at 130°C for 12 hours, and then the density of the positive electrode layer was 2.9 ± 0.05 g / cm³. ３ The material was pressed using a 35-ton press to obtain the positive electrode. Then, it was slit into a shape that included a positive electrode layer with an area of ​​29 mm x 40 mm and a margin for tab welding. 【0098】 <Preparation of the Negative Electrode Composition> Negative electrode active material (1050 parts by mass) and conductive additive (11 parts by mass) were mixed for 10 minutes to obtain a mixture. CMC solution (450 parts by mass) was added to this mixture and mixed for 20 minutes to obtain a first mixture. CMC solution (150 parts by mass) was added to the first mixture and mixed for 30 minutes, then CMC solution (293.5 parts by mass) was added and mixed for another 30 minutes, and water (450 parts by mass), which is the solvent, was added and mixed for 15 minutes to obtain a second mixture. SBR dispersion (45 parts by mass) was added to the second mixture and kneaded for 15 minutes, and vacuum degassing was performed for 10 minutes to obtain a slurry-like negative electrode composition (solid content concentration: 45% by mass). 【0099】 The details of the raw materials used in the preparation of the negative electrode composition are as follows: Negative electrode active material: Natural graphite Conductive additive: Conductive carbon black, "Super-P" manufactured by TIMCAL Corporation CMC solution: A solution prepared by dissolving carboxymethylcellulose (CMC) in water to a content of 1.2% by mass SBR dispersion: Aqueous dispersion of styrene-butadiene rubber (SBR), manufactured by JSR Corporation, solid content concentration: 50% by mass 【0100】 <Fabrication of the negative electrode> On one main surface of the negative electrode current collector (copper foil, 10 μm thick), the negative electrode composition is applied until the mass of the negative electrode layer (coating film after drying) is 11.0 mg / cm². ２The negative electrode layer was formed by coating it with a die coater and drying it. Then, similarly, the negative electrode composition was applied to the other main surface of the negative electrode current collector, so that the mass of the negative electrode layer was 11.0 mg / cm². ２ The material was coated with a die coater and dried to form the negative electrode layer. The positive electrode current collector, with negative electrode layers formed on both sides, was dried in a vacuum drying oven at 120°C for 12 hours, and then the density of the negative electrode layer was 1.45 ± 0.05 g / cm³. ３ The material was pressed using a small press machine to obtain the negative electrode, and then slit into a shape that included a negative electrode layer with an area of ​​31 mm x 42 mm and a margin for tab welding. 【0101】 <Preparation of Non-Aqueous Electrolyte> Ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed in a ratio of 30:35:35 (mass ratio) as non-aqueous solvents to obtain a mixed solvent. LiPF4 was added to the obtained mixed solvent as the electrolyte. ６ The electrolyte was dissolved in the final non-aqueous electrolyte solution so that the electrolyte concentration in the resulting solution was 1 mole / liter, thereby obtaining an electrolyte solution. 【0102】 In Comparative Examples 2 to 7 and Examples 1 to 5, additives of the types and amounts shown in Table 2 were added to the electrolyte solution obtained above to obtain a non-aqueous electrolyte. The amounts shown in Table 2 are the amounts (mass%) relative to the total amount of the non-aqueous electrolyte. In the Reference Example and Comparative Example 1, no additives were added, and the electrolyte solution obtained above was used as the non-aqueous electrolyte. The additives shown in Table 2 are A-1 below, which is a specific example of compound (I) (i.e., cyclic sulfate ester compound (I)), B-1 below, which is a specific example of compound (II) (i.e., disulfonic acid ester compound (II)), and VC, LiDFP, and LiBOB, which are other additives that do not fall under either compound (I) or compound (II). 【0103】 【0104】<Battery Fabrication> An electrode laminate was obtained by stacking and fixing a negative electrode, separator, positive electrode, separator, and negative electrode in this order. Next, an aluminum tab was joined to the blank space of the positive electrode using an ultrasonic bonding machine, and a nickel tab was joined to the blank space of the negative electrode using an ultrasonic bonding machine. The electrode laminate with the aluminum and nickel tabs joined in this way was sandwiched between laminate sheets, and three sides were heat-sealed to create a structure in which the electrode laminate was covered by an outer casing made of laminate sheets. A porous polyethylene membrane (50 mm x 50 mm) with a void ratio of 45% and a thickness of 25 μm was used as the separator. The obtained structure was dried under reduced pressure in a vacuum dryer at 70°C for 12 hours. Next, an electrolyte (0.3 ± 0.03 g) was poured into the structure, and the opening of the structure was heat-sealed while under vacuum to obtain a battery precursor. 【0105】 The obtained battery precursor was kept in air at 25°C for 24 hours. Next, the battery precursor was subjected to constant current charging at 0.1C for 3 hours (0.1C-CC), followed by a rest period of 12 hours at 25°C. Then, constant current constant voltage charging at 0.1C to 4.3V (SOC 100%) (0.1C-CCCV) was performed, followed by a rest period of 30 minutes. After that, constant current discharge at 0.1C to 2.8V (0.1C-CC) was performed to obtain a stacked battery. 【0106】<Battery Performance Evaluation 1: Initial DCIR> For a stacked battery (design capacity 70mAh), constant current constant voltage charging (0.1C-CCCV) was performed at 0.1C to 3.75V in a temperature environment of 25°C, and the initial DCIR was measured. Next, constant current discharge (0.1C-CC-10s) was performed at 0.1C for 10 seconds, followed by constant current charging (0.1C-CC-10s) at 0.1C for 10 seconds. Next, constant current discharge (0.2C-CC-10s) was performed at 0.2C for 10 seconds, followed by constant current charging (0.2C-CC-10s) at 0.2C for 10 seconds. Next, constant current discharge (0.5C-CC-10s) was performed at 0.5C for 10 seconds, followed by constant current charging (0.5C-CC-10s) at 0.5C for 10 seconds. Next, a constant current discharge (1.0C - CC - 10s) was performed at 1.0C for 10 seconds, followed by a constant current charge (1.0C - CC - 10s) at 1.0C for 10 seconds. Then, a constant current discharge (2.0C - CC - 10s) was performed at 2.0C for 10 seconds, followed by a constant current charge (2.0 - CC - 10s) at 2.0C for 10 seconds. The DC resistance (DCIR) was determined based on the voltage drop (= voltage before discharge - voltage 10 seconds after discharge) and current value (i.e., the current value corresponding to the discharge rates of 0.1C to 2.0C) for each discharge rate from 0.1C to 2.0C due to the "CC 10s discharge". 【0107】 As a reference example, the DC resistance (DCIR) of a stacked battery prepared in the same manner as the example, except that lithium phosphate dispersion was not added to the positive electrode and an electrolyte without additives was used, was determined. The DC resistance (DCIR) value was calculated as the first relative value, with the DC resistance (DCIR) of the reference example set to 100, and evaluated according to the following criteria. An evaluation of "A" or "B" indicates that the initial DCIR is good. The results are shown in Table 2. 【0108】 A: The first relative value is 100 or less. B: The first relative value is greater than 100 and 105 or less. C: The first relative value is greater than 105. 【0109】<Battery Performance Evaluation 2: High-Temperature Storage Capacity Retention Rate> For a stacked battery (design capacity 70mAh), constant current constant voltage charging (0.1C-CCCV) was performed at 0.1C to 4.3V in a 25°C environment, followed by a 30-minute pause. Next, constant current discharge (0.1C-CC) was performed at 0.1C to 2.8V, and the discharge capacity before storage was measured. Next, constant current constant voltage charging (0.1C-CCCV) was performed at 0.1C to 4.3V. Then, the charged battery was left standing in a 60°C atmosphere for 28 days to obtain a battery after high-temperature storage. For the battery after high-temperature storage, constant current discharge (0.1C-CCC) was performed at 0.1C to 2.8V, followed by a 30-minute pause. Next, constant current constant voltage charging (0.1C-CCCV) was performed at 0.1C to 4.3V (SOC 100%), followed by a 30-minute pause. Next, a constant current discharge (0.1C-CC) was performed at 0.1C until the voltage reached 2.8V, and the second discharge capacity after storage (hereinafter referred to as "post-storage recovery discharge capacity") 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 / Post-storage recovery discharge capacity 【0110】 As a reference example, the high-temperature storage capacity retention rate of a stacked battery prepared in the same manner as the example, except that lithium phosphate dispersion was not added to the positive electrode and an electrolyte without additives was used, was determined. The high-temperature storage capacity retention rate of the reference example was set to 100, and the value of the high-temperature storage capacity retention rate was calculated as the second relative value and evaluated according to the following criteria. An evaluation of "A" or "B" indicates that the high-temperature storage capacity retention rate is good. The results are shown in Table 2. 【0111】 A: The second relative value is 100 or higher. B: The second relative value is greater than 98 and less than 100. C: The second relative value is 98 or less. 【0112】 <Battery Performance Evaluation 3: DCIR after High-Temperature Storage> A stacked battery (design capacity 70 mAh) was charged to 4.3 V at 0.1 C using constant current constant voltage charging (0.1 C-CCCV) in a 25°C environment. The charged battery was then left to stand for 28 days in a 60°C atmosphere to obtain a battery after high-temperature storage. The DC resistance (DCIR) of the battery after high-temperature storage was determined in the same manner as in "Battery Performance Evaluation 1" described above. 【0113】As a reference example, the DC resistance (DCIR) of a stacked battery prepared in the same manner as the example, except that lithium phosphate dispersion was not added to the positive electrode and an electrolyte without additives was used, was determined. The DC resistance (DCIR) of the reference example was set to 100, and the DC resistance (DCIR) value was calculated as the third relative value and evaluated according to the following criteria. An evaluation of "A" or "B" indicates that the DCIR after high-temperature storage has been reduced. The results are shown in Table 2. 【0114】 A: The third relative value is 95 or less. B: The third relative value is greater than 95 but less than 100. C: The third relative value is 100 or greater. 【0115】 <Battery Performance Evaluation 4: Volume Change During High-Temperature Storage> After initial resistance measurement, the lithium secondary battery was measured using a specific gravity measuring device (SGM-300P, Shimadzu Corporation) based on the Archimedes method, and this was recorded as the volume before storage. The volume of the battery after high-temperature storage (hereinafter referred to as "post-storage volume") was measured in the same manner as the "volume before storage" described above. The volume change during high-temperature storage was calculated using the following formula: Volume change during high-temperature storage = Volume after high-temperature storage / Volume before high-temperature storage 【0116】 As a reference example, the volume change during high-temperature storage was determined for a stacked battery prepared in the same manner as the example, except that lithium phosphate dispersion was not added to the positive electrode and an electrolyte without additives was used. The value was calculated as the fourth relative value, with the volume change during high-temperature storage of the reference example set to 100, and evaluated according to the following criteria. An evaluation of "A" or "B" indicates that the volume change during high-temperature storage has been reduced. The results are shown in Table 2. 【0117】 A: The fourth relative value is 90 or less. B: The fourth relative value is greater than 90 but less than 100. C: The fourth relative value is 100 or greater. 【0118】 【0119】 As shown in Table 2, lithium phosphate (Li ３ PO ４In the lithium secondary batteries of each example, which contained compound (I) (i.e., cyclic sulfate ester compound (I)), the DC resistance (DCIR) after high-temperature storage and the volume change during high-temperature storage were reduced. Furthermore, the lithium secondary batteries of each example also showed reduced initial DC resistance and excellent capacity retention during high-temperature storage. Compared to the lithium secondary batteries of each example, the lithium secondary batteries of Comparative Examples 1, 2, 4, 6, and 7, which did not contain compound (I), showed large volume changes during high-temperature storage. Compared to the lithium secondary batteries of each example, Li ３ PO ４ In comparative examples 3 to 5, the lithium secondary batteries that did not contain the compound exhibited high DC resistance after high-temperature storage. 【0120】 The disclosure of Japanese Patent Application No. 2024-217108, filed on 11 December 2024, is incorporated herein by reference in its entirety. All documents, patent applications, and technical standards described herein are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard were specifically and individually noted to be incorporated by reference.

Claims

1. A lithium secondary battery containing lithium phosphate and a cyclic sulfate ester compound (I) represented by the following formula (I). [In formula (I), R １１ R represents an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (i-1), a group represented by formula (i-2), or a group represented by formula (i-3), where R １２ R represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group, and * represents the bond position. In formula (i-2), R １３ R represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or an oxymethylene group, and * represents the bond position. In formula (i-3), R １４ represents a halogen atom, a C1-C6 alkyl group, a C1-C6 halogenated alkyl group, a C1-C6 alkoxy group, or a group represented by formula (i-4), where * represents the bond position, and in formula (i-4), R １５ * represents an oxygen atom, an alkylene group with 1 to 6 carbon atoms, an alkenylene group with 2 to 6 carbon atoms, or an oxymethylene group, and * represents the bond position.

2. In the above formula (I), R １１ is a group represented by formula (i-1) or formula (i-2), and R １２ R is an oxymethylene group. １３ The lithium secondary battery according to claim 1, wherein is a propyl group.

3. The lithium secondary battery according to claim 1, wherein the lithium phosphate is in particulate form with a volume-average particle diameter of 50 nm to 5000 nm.

4. Further, the lithium secondary battery according to claim 1, comprising a disulfonic acid ester compound (II) represented by the following formula (II). [In formula (II), R ２１ represents an aliphatic hydrocarbon group having 1 to 10 carbon atoms or a halogenated alkylene group having 1 to 3 carbon atoms. R ２２ and R ２３ each independently represent an alkyl group having 1 to 6 carbon atoms or a phenyl group, or together represent an alkylene group having 1 to 10 carbon atoms or a 1,2-phenylene group, and the 1,2-phenylene group may be substituted with a halogen atom, an alkyl group having 1 to 12 carbon atoms, or a cyano group. ] 5. In equation (II) above, R ２１ is a methylene group, R ２２ and R ２３ Each of these is independently a C1-C3 alkyl group, or a C1-C3 alkylene group or a 1,2-phenylene group formed collectively, wherein the 1,2-phenylene group may be substituted with a halogen atom, a C1-C3 alkyl group, and a cyano group. Lithium secondary battery according to claim 4.

6. A lithium secondary battery according to claim 1, comprising electrodes and a non-aqueous electrolyte, wherein the lithium phosphate is contained in the electrodes and the cyclic sulfate ester compound (I) is contained in the non-aqueous electrolyte.

7. The lithium secondary battery according to claim 1, wherein the electrode further contains a dispersant.

8. The lithium secondary battery according to claim 7, wherein the dispersant comprises a titanate-based coupling agent.

9. The lithium secondary battery according to claim 6, wherein the electrode comprises a positive electrode and a negative electrode, and the positive electrode comprises a positive electrode layer containing a positive electrode active material and lithium phosphate.

10. The lithium secondary battery according to claim 9, wherein the content of lithium phosphate is 0.01% by mass to 10.0% by mass with respect to the total amount of solids in the positive electrode layer.

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