Nonaqueous electrolyte secondary battery

Abstract

To provide a nonaqueous electrolyte secondary battery excellent in battery characteristics after charge / discharge cycles.SOLUTION: The nonaqueous electrolyte secondary battery includes: a negative electrode which includes a current collector and a negative electrode mixture layer formed on the current collector and containing a negative electrode active material, the negative electrode active material containing at least one selected from the group consisting of elemental silicon particles, silicon oxide particles, and silicon carbide particles; and a nonaqueous electrolyte which contains at least one triester compound selected from the group consisting of a phosphate triester compound represented by formula (I), a phosphite triester compound represented by formula (II), and a borate triester compound represented by formula (III).SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a non-aqueous electrolyte secondary battery.

Background Art

[0002] Power storage devices such as lithium-ion secondary batteries, which are small, lightweight, and have high output, have been further improved in performance in recent years. Along with the improvement in performance, they are being increasingly used not only in small electrical products but also in large product fields such as automobiles. Lithium-ion secondary batteries are required to meet specific requirements for various characteristics such as output characteristics, charge-discharge characteristics, and gas generation. For example, the capacity retention rate and output characteristics after charge-discharge cycle tests are also very important evaluation items.

[0003] Patent Document 1 describes that in a lithium-ion secondary battery having a negative electrode active material layer containing a carbon-based active material and a silicon-based active material, by adopting an electrolyte containing tris(trifluoromethyl)phosphoric acid and lithium difluoro(oxalato-O,O')borate, etc., the cycle life can be improved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, in order to further improve the energy density, studies have been made on using silicon compounds such as silicon oxide and silicon itself as the negative electrode active material. However, when silicon compounds etc. are doped with lithium ions, their volume expands greatly, resulting in a problem that the charge-discharge capacity after charge-discharge cycles decreases significantly. An object of one aspect of the present disclosure is to provide a non-aqueous electrolyte secondary battery containing a silicon compound or the like as a negative electrode active material, which has excellent battery characteristics after charge and discharge cycles.

Means for Solving the Problems

[0006] As a result of intensive studies to solve the above problems, the present inventors have found that by blending at least one triester compound selected from the group consisting of a specific phosphoric acid triester compound, a specific phosphorous acid triester compound, and a specific boric acid triester compound into a non-aqueous electrolyte, it is possible to improve the capacity retention rate and the resistance increase rate after charge and discharge cycles of a non-aqueous electrolyte secondary battery containing a silicon compound or the like as a negative electrode active material, and thus completed the present disclosure. That is, one aspect of the present disclosure includes the following. <1> A non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the negative electrode includes a current collector and a negative electrode composite material layer formed on the current collector and containing a negative electrode active material, the negative electrode active material includes at least one selected from the group consisting of silicon single crystal particles, silicon oxide particles, and silicon carbide particles, and the non-aqueous electrolyte contains at least one triester compound selected from the group consisting of a phosphoric acid triester compound represented by the following formula (I), a phosphorous acid triester compound represented by the following formula (II), and a boric acid triester compound represented by the following formula (III).

[0007]

Chemical formula

[0008] <2>The non-aqueous electrolyte secondary battery according to <1>, wherein the non-aqueous electrolyte further contains a cyclic carbonate compound represented by the following formula (IV).

[0009]

Chemical formula

[0010] <3>The non-aqueous electrolyte secondary battery according to <1>, wherein the non-aqueous electrolyte further contains at least one fluorophosphate selected from the group consisting of monofluorophosphate and difluorophosphate. <4>The non-aqueous electrolyte secondary battery according to <1>, wherein the negative electrode active material contains carbon single particles and at least one selected from the group consisting of silicon single particles, silicon oxide particles, and silicon carbide particles. <5>The non-aqueous electrolyte secondary battery according to <4>, wherein the total content of the silicon single particles, the silicon oxide particles, and the silicon carbide particles is 30% by mass or less when the total amount of the negative electrode active material is 100% by mass.

Advantages of the Invention

[0011] According to one aspect of the present disclosure, it is possible to improve the capacity retention rate and the resistance increase rate after charge and discharge cycles of a non-aqueous electrolyte secondary battery containing a silicon compound or the like as a negative electrode active material.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

[0013] In describing the present disclosure, specific examples will be given for explanation. However, the present disclosure is not limited to the following content as long as it does not depart from the gist of the present disclosure, and can be implemented with appropriate modifications.

[0014] In the present disclosure, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. In a numerical range described stepwise in the present disclosure, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of another numerically described stepwise range. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. In the present disclosure, "mass" and "weight" are synonymous, and "mass%" and "weight%" are synonymous. In the present disclosure, a combination of two or more preferred embodiments is a more preferred embodiment. In the notation of a group (atomic group) in the present disclosure, a notation that does not describe substitution and non-substitution includes both those that do not contain a substituent and those that contain a substituent. In the present disclosure, the term "step" includes not only an independent step but also a step that cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0015] [Non-aqueous electrolyte secondary battery] A non-aqueous electrolyte secondary battery, which is one aspect of the present disclosure (hereinafter may be abbreviated as "non-aqueous electrolyte secondary battery"), is a non-aqueous electrolyte secondary battery including a "positive electrode", a "negative electrode", a "non-aqueous electrolyte", and a "separator". The "negative electrode" includes a "current collector" and a "negative electrode composite material layer containing a negative electrode active material formed on the current collector". The "negative electrode active material" includes at least one selected from the group consisting of "silicon single particles", "silicon oxide particles", and "silicon carbide particles". And the "non-aqueous electrolyte" contains at least one triester compound selected from the group consisting of "phosphoric acid triester compounds represented by the following formula (I)", "phosphorous acid triester compounds represented by the following formula (II)", and "boric acid triester compounds represented by the following formula (III)".

[0016] [Chemical formula] (In formulas (I) to (III), R 1 each independently represents a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-) as a substituent.)

[0017] As a result of repeated studies to obtain a non-aqueous electrolyte secondary battery having excellent battery characteristics after charge-discharge cycles in a non-aqueous electrolyte secondary battery containing a silicon compound or the like as a negative electrode active material, the present inventors found that by blending at least one triester compound selected from the group consisting of a phosphoric acid triester compound represented by formula (I), a phosphorous acid triester compound represented by formula (II), and a boric acid triester compound represented by formula (III) into the non-aqueous electrolyte, it is possible to improve the capacity retention rate and the resistance increase rate after charge-discharge cycles.

[0018] [Non-aqueous electrolyte] The non-aqueous electrolyte contains at least one triester compound selected from the group consisting of a phosphoric acid triester compound represented by the formula (I), a phosphorous acid triester compound represented by the formula (II), and a boric acid triester compound represented by the formula (III). Hereinafter, the "phosphoric acid triester compound represented by the formula (I)", the "phosphorous acid triester compound represented by the formula (II)", the "boric acid triester compound represented by the formula (III)", etc. will be described in detail.

[0019] (Phosphoric acid triester compound represented by the formula (I), phosphorous acid triester compound represented by the formula (II), boric acid triester compound represented by the formula (III))

[0020] [Chemical formula]

[0021] R 1Each independently represents a "hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-)", and the "hydrocarbon group" is not limited to an aliphatic hydrocarbon group having a linear structure, but may be a hydrocarbon group having at least one structure selected from the group consisting of a branched structure, a cyclic structure, and a carbon-carbon unsaturated bond structure (a carbon-carbon double bond structure and a carbon-carbon triple bond structure). Also, since the number of these structures is not limited, (acyclic) aliphatic hydrocarbon groups, monocyclic aliphatic hydrocarbon groups, polycyclic aliphatic hydrocarbon groups, monocyclic aromatic hydrocarbon groups, and polycyclic aromatic hydrocarbon groups are all included in the "hydrocarbon group". Also, of course, alkyl groups, alkenyl groups, alkynyl groups, aryl groups, etc. are all included in the "hydrocarbon group". Also, "which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-)" means that the hydrogen atoms of the hydrocarbon group may be substituted with a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and the carbon atoms of the hydrocarbon group may be substituted with an oxa group (-O-).

[0022] R 1 The number of carbon atoms of the hydrocarbon group of is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0023] R 1 Examples of include a methyl group (-CH3), an ethyl group (-CH2CH3), a vinyl group (-CH=CH2), an n-propyl group (-CH2CH2CH3), an i-propyl group (-CH(CH3)2), an n-butyl group (-CH2CH2CH2CH3), an isobutyl group (-CH2CH(CH3)2), an s-butyl group (-CH(CH3)CH2CH3), a t-butyl group (-C(CH3)2), a hexyl group (-CH2CH2CH2CH2CH2CH3), a cyclohexyl group (-C6H 11 )), a phenyl group (-C6H5), etc., and a methyl group (-CH3) is particularly preferred.

[0024] Examples of the triphosphate ester compound represented by the formula (I) include compounds represented by the following formula. The non-aqueous electrolyte may contain two or more triphosphate ester compounds represented by the formula (I). In addition, in this specification, Me represents a methyl group, Et represents an ethyl group, t Bu represents a t-butyl group, and Ph represents a phenyl group.

[0025]

Chemical formula

[0026] Examples of the triphosphite ester compound represented by the formula (II) include compounds represented by the following formula. The non-aqueous electrolyte may contain two or more triphosphite ester compounds represented by the formula (II).

[0027]

Chemical formula

[0028] Examples of the boric acid triester compound represented by the formula (III) include compounds represented by the following formula. The non-aqueous electrolyte may contain two or more boric acid triester compounds represented by the formula (III).

[0029]

Chemical formula

[0030] The total content of at least one non-aqueous electrolyte selected from the group consisting of a triphosphate ester compound represented by formula (I), a triphosphite ester compound represented by formula (II), and a triborate ester compound represented by formula (III) is usually 0.01% by mass or more and 5.0% by mass or less, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more as the lower limit value, preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). When the total content of these compounds is within the above range, it becomes easier to control the capacity retention rate and the resistance increase rate after charge and discharge cycles to good values.

[0031] (Other additives) The non-aqueous electrolyte preferably further contains a cyclic carbonate compound represented by the following formula (IV).

[0032] [Chemical formula] (In formula (IV), X represents a fluoro group (-F), a chloro group (-Cl), or a bromo group (-Br), R 2 each independently represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-), and h represents an integer of 0 to 3.)

[0033] X represents a "fluoro group (-F)", a "chloro group (-Cl)", or a "bromo group (-Br)", and the fluoro group (-F) is particularly preferred.

[0034] R 2Each independently represents a "fluoro group (-F)", "chloro group (-Cl)", "bromo group (-Br)", or "hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), chloro group (-Cl), bromo group (-Br), and oxa group (-O-)" as a substituent. However, the "hydrocarbon group" is R 1 is synonymous with the case of

[0035] R 2 When R is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0036] R 2 Examples of R include a fluoro group (-F), chloro group (-Cl), bromo group (-Br), methyl group (-CH3), ethyl group (-CH2CH3), vinyl group (-CH=CH2), n-propyl group (-CH2CH2CH3), i-propyl group (-CH(CH3)2), n-butyl group (-CH2CH2CH2CH3), isobutyl group (-CH2CH(CH3)2), s-butyl group (-CH(CH3)CH2CH3), t-butyl group (-C(CH3)2), hexyl group (-CH2CH2CH2CH2CH2CH3), cyclohexyl group (-C6H 11 )), phenyl group (-C6H5), etc.

[0037] h represents an integer from 0 to 3, and 0 is particularly preferred.

[0038] Examples of the cyclic carbonate compound represented by formula (IV) include compounds represented by the following formula including fluoroethylene carbonate (FEC). The non-aqueous electrolyte may contain two or more cyclic carbonate compounds represented by formula (IV).

[0039]

Chemical formula

[0040] The total content of the cyclic carbonate compound represented by the formula (IV) in the non-aqueous electrolyte is usually 0.01% by mass or more and 5.0% by mass or less, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more as the lower limit value, and preferably 4.0% by mass or less, preferably 3.5% by mass or less, still more preferably 3.0% by mass or less, and particularly preferably 2.5% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). When the total content of the cyclic carbonate compound represented by the formula (IV) is within the above range, it becomes easy to control the capacity retention rate and the resistance increase rate after charge and discharge cycles to good values.

[0041] The cyclic carbonate compound represented by the formula (IV) can also be used as a non-aqueous solvent described later. When used as a non-aqueous solvent, the total content of the cyclic carbonate compound represented by the formula (IV) in the non-aqueous electrolyte is usually 5% by mass or more and 50% by mass or less, preferably 7% by mass or more, more preferably 10% by mass or more, still more preferably 15% by mass or more as the lower limit value, and preferably 40% by mass or less, more preferably 30% by mass or less, still more preferably 20% by mass or less, and particularly preferably 15% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass).

[0042] The non-aqueous electrolyte preferably further contains at least one fluorophosphate selected from the group consisting of monofluorophosphate and difluorophosphate.

[0043] Examples of the monofluorophosphate include lithium monofluorophosphate, sodium monofluorophosphate, ammonium monofluorophosphate, etc. Examples of the difluorophosphate include lithium difluorophosphate, sodium difluorophosphate, ammonium difluorophosphate, etc. Among them, lithium difluorophosphate is particularly preferred.

[0044] The total content of at least one fluorophosphate selected from the group consisting of monofluorophosphate and difluorophosphate in the non-aqueous electrolyte is usually 0.01% by mass or more and 5.0% by mass or less, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more as the lower limit value, and preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, particularly preferably 1.5% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). When the total content of these compounds is within the above range, it becomes easier to control the capacity retention rate and the resistance increase rate after charge and discharge cycles to good values.

[0045] (Non-aqueous solvent) The non-aqueous electrolyte generally contains a non-aqueous solvent. Various known non-aqueous solvents can be appropriately selected. The non-aqueous solvent may be only one kind or two or more kinds.

[0046] Examples of the non-aqueous solvent include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, γ-lactones, fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, fluorine-containing chain ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, and the like. Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. Examples of the fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC), and the like. 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), and the like. 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, ethyl trimethylbutyrate, and the like. Examples of γ-lactones include γ-butyrolactone, γ-valerolactone, and the like. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and the like. Examples of chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, 1,2-dibutoxyethane, and the like. Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, and the like. Examples of amides include N,N-dimethylformamide, and the like. Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, and the like.

[0047] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates. In this case, the total proportion of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain 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 still more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the non-aqueous solvent.

[0048] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and chain carbonates. In this case, the total proportion of cyclic carbonates and chain 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 still more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the non-aqueous solvent.

[0049] The upper limit of the content of the non-aqueous solvent is preferably 99% by mass, more preferably 97% by mass, and still more preferably 90% by mass, based on the total amount of the non-aqueous electrolyte. The lower limit of the content of the non-aqueous solvent is preferably 60% by mass or more, more preferably 70% by mass or more, based on the total amount of the non-aqueous electrolyte.

[0050] From the viewpoint of further improving the dissociation property of the electrolyte and the mobility of ions, the intrinsic viscosity of the non-aqueous solvent is preferably 10.0 mPa·s or less at 25°C.

[0051] (Electrolyte) The non-aqueous electrolyte generally contains an electrolyte.

[0052] The electrolyte preferably contains at least one of a lithium salt containing fluorine (hereinafter sometimes referred to as "fluorine-containing lithium salt") and a lithium salt not containing fluorine.

[0053] Examples of the fluorine-containing lithium salt include inorganic acid anion salts, organic acid anion salts, and the like. Examples of the inorganic acid anion salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluorotantalate (LiTaF6), and the like. Examples of the organic acid anion salts include lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), lithium bis(pentafluoroethanesulfonyl)imide (Li(C2F5SO2)2N), and the like. Among them, as the fluorine-containing lithium salt, lithium hexafluorophosphate (LiPF6) is more preferable.

[0054] Examples of the lithium salts containing no fluorine include lithium perchlorate (LiClO4), lithium aluminum tetrachloride (LiAlCl4), lithium decachlorodecaborate (Li2B 10 Cl 10 ), and the like.

[0055] When the electrolyte contains a fluorine-containing lithium salt, the content ratio of the fluorine-containing lithium salt 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 still more preferably 80% by mass or more and 100% by mass or less based on the total amount of the electrolyte. When the fluorine-containing lithium salt contains lithium hexafluorophosphate (LiPF6), the content ratio of lithium hexafluorophosphate (LiPF6) 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 still more preferably 80% by mass or more and 100% by mass or less based on the total amount of the electrolyte.

[0056] 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, and more preferably 0.5 mol / L or more and 2 mol / L or less.

[0057] When the non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF6), the concentration of lithium hexafluorophosphate (LiPF6) in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less.

[0058] <Negative electrode> A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is a non-aqueous electrolyte secondary battery including a "positive electrode", a "negative electrode", a "non-aqueous electrolyte", and a "separator", wherein the "negative electrode" includes a "current collector" and a "negative electrode composite material layer formed on the current collector and containing a negative electrode active material", and the "negative electrode active material" includes at least one selected from the group consisting of "silicon single particles", "silicon oxide particles", and "silicon carbide particles". Usually, the negative electrode is prepared by dispersing a negative electrode active material, a binder, a conductive assistant, and a thickener in a solvent to form a slurry, applying the slurry to a current collector, drying, and compressing it to form a negative electrode composite material layer (also referred to as a "negative electrode active material layer") on the current collector. Hereinafter, the "negative electrode active material" and the like will be described in detail.

[0059] (Negative electrode active material) The single substance or compound serving as the negative electrode active material can be classified into (1) carbon single substances and carbon compounds capable of doping / dedoping lithium ions, (2) metals and alloys capable of alloying with lithium, and (3) oxides, nitrides, carbides, etc. capable of doping / dedoping lithium ions. When the negative electrode active material is silicon single substance or the like, usually a single substance or compound in the form of particles (powders) is used. Also, the negative electrode active material used is not limited to one type, and two or more types may be mixed and used.

[0060] In a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, the negative electrode active material contains at least one selected from the group consisting of silicon single crystal particles, silicon oxide particles, and silicon carbide particles. However, it is preferable that the negative electrode active material contains single carbon particles and at least one selected from the group consisting of silicon single crystal particles, silicon oxide particles, and silicon carbide particles. Examples of the single carbon particles include graphite (natural graphite, artificial graphite) particles, carbon black particles, activated carbon particles, amorphous carbon particles, etc. Examples of artificial graphite include graphitized MCMB, graphitized MCF, etc. Examples of amorphous carbon materials include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 °C or lower, mesophase pitch carbon fiber (MCF), etc.

[0061] When the single substance or compound serving as the negative electrode active material is in the form of particles (powder), specific shapes include fibrous, spherical, potato-shaped, and flake-shaped.

[0062] When the negative electrode active material contains single carbon particles, the median diameter D50 of the single carbon is usually 1 μm to 30 μm, preferably 10 μm or more, more preferably 15 μm or more, preferably 25 μm or less, and more preferably 20 μm or less.

[0063] When the negative electrode active material contains single carbon particles, the BET specific surface area of the single carbon is usually 1.0 m 2 / g to 5.0 m 2 / g, preferably 2.0 m 2 / g or more, more preferably 3.0 m 2 / g or more, preferably 4.5 m 2 / g or less, more preferably 4.0 m 2 / g or less.

[0064] Silicon oxide is SiO xIt can be represented by, where x is a variable. That is, the oxygen atom content in silicon oxide is not particularly limited, but x is usually 0 ≦ x < 2. As the lower limit value of x, it is preferably 0.2 or more, more preferably 0.4 or more, and even more preferably 0.6 or more. As the upper limit value of x, it is preferably 1.8 or less, more preferably 1.6 or less, and even more preferably 1.4 or less.

[0065] The median diameter D50 of the single silicon particles, silicon oxide particles, or silicon carbide particles is usually 0.5 μm to 20 μm, preferably 1.0 μm or more, more preferably 3.0 μm or more, preferably 15 μm or less, and more preferably 10 μm or less.

[0066] The BET specific surface area of the single silicon particles, silicon oxide particles, or silicon carbide particles is usually 1.0 m 2 / g to 5.0 m 2 / g, preferably 1.5 m 2 / g or more, more preferably 2.0 m 2 / g or more, preferably 4.5 m 2 / g or less, more preferably 4.0 m 2 / g or less.

[0067] When the negative electrode active material contains at least one selected from the group consisting of single carbon particles and single silicon particles, silicon oxide particles, and silicon carbide particles, the total content of the single silicon particles, silicon oxide particles, and silicon carbide particles in the negative electrode active material is usually 1% by mass to 20% by mass when the entire negative electrode active material is 100% by mass, preferably 3% by mass or more, more preferably 5% by mass or more, preferably 18% by mass or less, and more preferably 15% by mass or less.

[0068] When the negative electrode active material contains carbon single particles and at least one selected from the group consisting of silicon single particles, silicon oxide particles, and silicon carbide particles, the content of carbon single particles in the negative electrode active material is usually 70% by mass to 99% by mass, preferably 80% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, when the entire negative electrode active material is 100% by mass. When the total content of silicon single particles or the like and the content of carbon single particles are within the above ranges, it becomes easier to secure the balance between the energy density and the capacity retention rate of the lithium ion secondary battery.

[0069] The total content of the negative electrode active material in the negative electrode binder layer is usually 70% by mass to 99.5% by mass, preferably 75% by mass or more, preferably 99% by mass or less, when the entire negative electrode binder layer is 100% by mass.

[0070] (Binder) Examples of the binder for the negative electrode include styrene-butadiene rubber (SBR). The content of the binder in the negative electrode binder layer is usually 0.1% by mass to 5% by mass, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, preferably 3% by mass or less, more preferably 2% by mass or less, when the entire negative electrode binder layer is 100% by mass.

[0071] (Conductive aid) The negative electrode binder layer preferably further contains a conductive aid. Examples of the conductive aid for the negative electrode include carbon black (for example, acetylene black), carbon nanotubes, amorphous whiskers, graphite, and the like.

[0072] The total content of the conductive aid in the negative electrode binder layer is usually 0.01% by mass to 3% by mass, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, preferably 2% by mass or less, more preferably 1% by mass or less, when the entire negative electrode binder layer is 100% by mass.

[0073] (Thickener) The negative electrode composite material layer preferably further contains a thickening agent. By including a thickening agent, it becomes easier to adjust the viscosity of the slurry, improving productivity. Examples of the thickening agent for the negative electrode include cellulose derivatives such as carboxymethyl cellulose (CMC), carboxyethyl cellulose, and hydroxyethyl cellulose; polyoxyethylene and its modified products; polyvinyl alcohol and its modified products; polysaccharides; and the like.

[0074] When the total content of the thickening agent in the negative electrode composite material layer is based on 100% by mass of the entire negative electrode composite material layer, it is usually 0.1% to 5% by mass, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, preferably 3% by mass or less, and more preferably 2% by mass or less.

[0075] The slurry may contain a solvent. Examples of the solvent include water, acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, and the like. Note that the solvent may be a mixed solvent in which the aforementioned solvents are mixed.

[0076] Examples of the material of the current collector of the negative electrode include copper, nickel, stainless steel, nickel-plated steel, and the like.

[0077] <Positive Electrode> The non-aqueous electrolyte secondary battery according to one aspect of the present invention is a non-aqueous electrolyte secondary battery including a "positive electrode", a "negative electrode", a "non-aqueous electrolyte", and a "separator". Usually, the positive electrode is prepared by dispersing a positive electrode active material, a binder, a conductive aid and a thickening agent as needed in a solvent to form a slurry, applying this slurry to a current collector, drying, and compressing it to form a positive electrode composite material layer (also referred to as a "positive electrode active material layer") on the current collector.

[0078] Examples of the positive electrode active material include Transition metal oxides or transition metal sulfides such as MoS2, TiS2, MnO2, and V2O5; LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiNiX Co (1-X) O2 (0 < X < 1), LiNi x Co y Mn z O2 (x, y, and z are each independently greater than 0 and less than 1.00, and the sum of x, y, and z is between 0.99 and 1.00.) (so-called "NCM"; for example, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2) and other composite oxides composed of lithium and transition metals; Li t Ni 1-x-y Co x Al y O2 (t is between 0.95 and 1.15, x is between 0 and 0.3, y is between 0.1 and 0.2, and the sum of x and y is less than 0.5.) (so-called "NCA"; for example, LiNi 0.8 Co 0.15 Al 0.05 O2) and other composite oxides composed of lithium, transition metals, and typical metals; Conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline composites; Lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium manganese iron phosphate (LiMn x Fe 1-x PO4; 0 < x < 1), lithium cobalt phosphate (LiCoPO4), lithium nickel phosphate (LiNiPO4), and other lithium metal phosphates; etc. can be mentioned.

[0079] (Binder, etc.) Examples of the binder for the positive electrode include polyvinylidene fluoride. Examples of the conductive assistant for the positive electrode include carbon black (e.g., acetylene black), amorphous whiskers, graphite, etc. Examples of the thickening agent for the positive electrode include carboxymethyl cellulose, etc. Examples of the solvent for the slurry for forming the positive electrode include organic solvents such as N-methylpyrrolidone.

[0080] The total content of the positive electrode active material in the positive electrode composite layer is usually 70% by mass to 97% by mass, preferably 75% by mass or more and preferably 95% by mass or less when the total content of the positive electrode composite layer is 100% by mass.

[0081] Examples of the material of the current collector of the positive electrode include aluminum, aluminum alloy, stainless steel, nickel, titanium, tantalum, carbon cloth, carbon paper, etc.

[0082] <Separator> The non-aqueous electrolyte secondary battery which is one aspect of the present disclosure is a non-aqueous electrolyte secondary battery including a "positive electrode", a "negative electrode", a "non-aqueous electrolyte", and a "separator". Examples of the separator include a porous resin flat plate. Examples of the material of the porous resin flat plate include resin, non-woven fabric containing this resin, etc. Examples of the resin include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, polyamide, etc. Among them, the separator is preferably a porous resin sheet having a single-layer or multi-layer structure. The material of the porous resin sheet is mainly composed of one or two or more polyolefin resins. The thickness of the separator is preferably 5 μm or more and 30 μm or less. The separator is preferably disposed between the positive electrode and the negative electrode.

[0083] <Case> The shape of the case etc. is not particularly limited and is appropriately selected according to the use etc. of the non-aqueous electrolyte secondary battery which is one aspect of the present disclosure. Examples of the case include a case containing a laminate film, a case composed of a battery can and a battery can lid, and the like.

[0084] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure is obtained by subjecting a non-aqueous electrolyte secondary battery precursor, which is a non-aqueous electrolyte secondary battery before charging and discharging, to charging and discharging. The non-aqueous electrolyte lithium secondary battery precursor represents a non-aqueous electrolyte lithium secondary battery before charging and discharging. Specific examples of the non-aqueous electrolyte secondary battery precursor include a lithium-ion secondary battery precursor that performs charge and discharge by the movement of lithium ions.

[0085] <Specific examples of lithium-ion secondary battery precursors> FIG. 1 is a schematic cross-sectional view showing a laminated lithium-ion secondary battery precursor, which is an example of a lithium-ion secondary battery precursor.

[0086] As shown in FIG. 1, the lithium-ion secondary battery precursor 1 is a laminated battery precursor. Specifically, in the lithium secondary battery precursor 1, the battery element 10 is enclosed inside the exterior body 30. The exterior body 30 is formed of a laminate film. Each of a positive electrode lead 21 and a negative electrode lead 22 is attached to the battery element 10. Each of the positive electrode lead 21 and the negative electrode lead 22 is led out in opposite directions from inside the exterior body 30 toward the outside.

[0087] As shown in FIG. 1, the battery element 10 is formed by laminating a positive electrode 11, a separator 13, and a negative electrode 12. The positive electrode 11 is formed by forming a positive electrode mixture layer 11B on both main surfaces of a positive electrode current collector 11A. The negative electrode 12 is formed by forming a negative electrode mixture layer 12B on both main surfaces of a negative electrode current collector 12A. The positive electrode mixture layer 11B formed on one main surface of the positive electrode current collector 11A of the positive electrode 11 and the negative electrode mixture layer 12B formed on one main surface of the negative electrode current collector 12A of the negative electrode 12 adjacent to the positive electrode 11 face each other with the separator 13 interposed therebetween.

[0088] Inside the exterior body 30 of the lithium-ion secondary battery precursor 1, a non-aqueous electrolyte is injected. The non-aqueous electrolyte has penetrated into the positive electrode composite material layer 11B, the separator 13, and the negative electrode composite material layer 12B. In the lithium secondary battery precursor 1, one single battery layer 14 is formed by the adjacent positive electrode composite material layer 11B, separator 13, and negative electrode composite material layer 12B. Note that the positive electrode and the negative electrode may be those in which each active material layer is formed on one side of each current collector.

[0089] Note that the lithium-ion secondary battery precursor 1 is a laminated lithium secondary battery precursor, but the lithium-ion secondary battery precursor is not limited thereto. For example, it may be a wound lithium-ion secondary battery precursor. The wound lithium secondary battery precursor is formed by stacking a positive electrode, a separator, a negative electrode, and a separator in this order and winding them in a layered manner. The wound lithium-ion secondary battery precursor includes a cylindrical lithium-ion secondary battery precursor and a rectangular lithium-ion secondary battery precursor.

[0090] As shown in FIG. 1, in the lithium-ion secondary battery precursor 1, the directions in which each of the positive electrode lead and the negative electrode lead protrude from the inside of the exterior body 30 toward the outside are opposite to each other with respect to the exterior body 30, but the present disclosure is not limited thereto. For example, the methods in which each of the positive electrode lead and the negative electrode lead protrude from the inside of the exterior body 30 toward the outside may be the same direction with respect to the exterior body 30.

[0091] As an example of the lithium-ion secondary battery described later, there is a lithium-ion secondary battery obtained by charging and discharging the lithium-ion secondary battery precursor 1.

[0092] FIG. 2 is a schematic cross-sectional view showing a coin-type lithium secondary battery precursor which is another example of the lithium-ion secondary battery precursor.

[0093] In the coin-type lithium-ion secondary battery precursor shown in Fig. 2, a disk-shaped negative electrode 42, a separator 45 filled with a non-aqueous electrolyte, a disk-shaped positive electrode 41, and, if necessary, spacer plates 47 and 48 made of stainless steel or aluminum are stacked in this order and housed between a positive electrode can 43 (hereinafter also referred to as "battery can") and a sealing plate 44 (hereinafter also referred to as "battery can lid"). The positive electrode can 43 and the sealing plate 44 are caulked and sealed via a gasket 46. In this example, the non-aqueous electrolyte used above is used as the non-aqueous electrolyte injected into the separator 45.

[0094] As an example of the lithium-ion secondary battery described below, there is also a lithium-ion secondary battery obtained by charging and discharging the coin-type lithium-ion secondary battery precursor shown in Fig. 2.

[0095] 〔Lithium-ion secondary battery and method for manufacturing the same〕 A method for manufacturing a lithium-ion secondary battery, which is a preferred embodiment of the non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, includes a step of preparing the above-described lithium-ion secondary battery precursor (hereinafter also referred to as "preparation step"), and a step of charging and discharging the above lithium-ion secondary battery precursor. The lithium-ion secondary battery is a lithium secondary battery obtained by charging and discharging the above-described lithium-ion secondary battery precursor.

[0096] According to the non-aqueous electrolyte secondary battery and the method for manufacturing the same according to one aspect of the present disclosure, it is possible to improve the capacity retention rate and the resistance increase rate after the charge-discharge cycle of the non-aqueous electrolyte secondary battery.

[0097] The preparation step may be simply a step of preparing a pre-manufactured lithium-ion secondary battery precursor for use in the step of charging and discharging, or may be a step of manufacturing the lithium-ion secondary battery precursor. The lithium secondary battery precursor is as described above.

[0098] ​ In the process of charging and discharging, the charging and discharging of the lithium-ion secondary battery precursor can be carried out according to known methods. In this process, the charging and discharging cycles may be repeated a plurality of times for the lithium-ion secondary battery precursor. As described above, preferably, a SEI (Solid Electrolyte Interface) film is formed on the surface of the positive electrode (especially the positive electrode active material) and / or the negative electrode (especially the negative electrode active material) in the lithium-ion secondary battery precursor by this charging and discharging.

[0099] The process of charging and discharging is preferably carried out by applying a combination of charging and discharging one or more times to the lithium-ion secondary battery precursor in an environment of 25°C to 70°C.

Example

[0100] Examples of the present disclosure are shown below, but the present disclosure is not limited to the following examples. Hereinafter, “%” means “mass %” unless otherwise specified.

[0101] 〔Example 1〕 <Preparation of non-aqueous electrolyte> Ethylene carbonate (hereinafter, “EC”), dimethyl carbonate (hereinafter, “DMC”), and ethyl methyl carbonate (hereinafter, “EMC”) were mixed at EC:DMC:EMC = 30:35:35 (volume ratio). Thereby, a mixed solvent was obtained as a non-aqueous solvent. To the obtained mixed solvent, LiPF6 as an electrolyte was dissolved so that the concentration in the finally obtained non-aqueous electrolyte became 1.0 mol / L to obtain an electrolyte (hereinafter, also referred to as “basic electrolyte”). A phosphoric acid triester compound represented by the following formula (I-1) was blended so that the content in the finally obtained non-aqueous electrolyte with respect to the total amount of the non-aqueous electrolyte became 1.0 mass % to obtain a non-aqueous electrolyte.

[0102]

Chemical formula

[0103] <Fabrication of the positive electrode> LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (94% by mass), carbon black (3% by mass) as a conductive assistant, and polyvinylidene fluoride (PVdF) (3% by mass) as a binder were mixed to obtain a mixture. The obtained mixture was dispersed in an N-methylpyrrolidone solvent to obtain a positive electrode composite slurry. An aluminum foil with a thickness of 20 μm was prepared as the positive electrode current collector. The obtained positive electrode composite slurry was coated on the aluminum foil, dried, and then rolled with a press to obtain a sheet-like positive electrode. The positive electrode consists of a positive electrode current collector and a positive electrode active material layer.

[0104] <Fabrication of the negative electrode> Graphite 92.15% by mass and silicon monoxide (SiO x (x = 1), silicon monoxide) 4.85% by mass, sodium carboxymethyl cellulose dispersed in pure water as a thickening agent 1.5% by mass in solid content, and styrene-butadiene rubber (SBR) dispersed in pure water as a binder 1.5% by mass in solid content were mixed to obtain a negative electrode composite slurry. A copper foil with a thickness of 10 μm was prepared as the negative electrode current collector. The obtained negative electrode composite slurry was coated on the copper foil, dried, and then rolled with a press to obtain a sheet-like negative electrode. The negative electrode consists of a negative electrode current collector and a negative electrode active material layer.

[0105] <Preparation of the separator> A porous polyethylene film was prepared as the separator.

[0106] <Fabrication of the lithium-ion secondary battery precursor> The negative electrode was punched out into a disk shape with a diameter of 14 mm, the positive electrode was punched out into a disk shape with a diameter of 13 mm, and the separator was punched out into a disk shape with a diameter of 17 mm. As a result, a coin-shaped negative electrode, a coin-shaped positive electrode, and a coin-shaped separator were obtained respectively. The obtained coin-shaped negative electrode, coin-shaped separator, and coin-shaped positive electrode were stacked in this order inside a stainless steel battery can (size: 2032 size). Next, 20 μL of a non-aqueous electrolyte was injected into this battery can, and the separator, positive electrode, and negative electrode were impregnated with the non-aqueous electrolyte. Next, an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring were placed on the positive electrode, and the battery can lid was caulked through a polypropylene gasket to seal the battery. Thus, a coin-type lithium-ion secondary battery precursor (i.e., a lithium-ion secondary battery before charging and discharging) having the configuration shown in Fig. 2 was obtained. The size of the lithium-ion secondary battery precursor was 20 mm in diameter and 3.2 mm in height.

[0107] <Fabrication of Lithium-Ion Secondary Battery> The above lithium-ion secondary battery precursor was repeatedly charged up to 4.2 V and discharged up to 2.5 V three times in the temperature range of 25 °C to 70 °C to obtain a lithium-ion secondary battery.

[0108] <Measurement of Initial Discharge Capacity> The above lithium-ion secondary battery was charged up to 4.2 V in a thermostat at 25 °C, and then discharged up to 2.5 V, and the discharge capacity [mAh] (hereinafter also referred to as "initial discharge capacity") was measured.

[0109] <Measurement of Initial Resistance Value> After the measurement of the initial discharge capacity, the lithium-ion secondary battery was charged up to 3.7 V, and then in a thermostat at -20 °C, the voltage drop amount (= voltage before discharge start - voltage at the 10th second after discharge start) for each CC10s discharge at each discharge rate from 0.1C (Coulomb) to 1.0C was measured. Here, CC10s discharge means discharge performed for 10 seconds at a constant current (Constant Current). Based on the obtained voltage drop amounts and the respective current values (i.e., the respective current values corresponding to the discharge rates from 0.1C to 1.0C), the DC resistance [Ω] as the initial resistance value was measured.

[0110] <Charge and Discharge Cycle Test> Next, the lithium ion secondary battery after the initial resistance measurement was subjected to constant current charging up to 4.2 V at a charging rate of 0.5C in a thermostat at 25°C. Subsequently, it was discharged at a discharge rate of 0.5C until 2.5 V. The above charge and discharge cycle was repeated 50 times.

[0111] <Measurement of Discharge Capacity Retention Rate after Charge and Discharge Cycles and Calculation of Relative Value> Next, the discharge capacity of the lithium ion secondary battery after the charge and discharge cycle test was measured in the same manner as the initial discharge capacity. Also for Comparative Example 1 described later, the discharge capacity of the lithium ion secondary battery after the charge and discharge cycle test was measured by the same method. When the discharge capacity retention rate after the charge and discharge cycle of Comparative Example 1 was set to 100, the discharge capacity retention rate after the charge and discharge cycle of Example 1 was calculated as a relative value (see the following formula). Discharge capacity retention rate (relative value) after charge and discharge cycles of Example 1 = (Discharge capacity retention rate after charge and discharge cycles of Example 1) / (Discharge capacity retention rate after charge and discharge cycles of Comparative Example 1) × 100

[0112] <Measurement of Resistance Increase Rate after Charge and Discharge Cycles and Calculation of Relative Value> Next, the resistance value of the lithium ion secondary battery after the charge and discharge cycle test was measured in the same manner as the initial resistance value. Also for Comparative Example 1 described later, the resistance value of the lithium ion secondary battery after the charge and discharge cycle test was measured by the same method. When the resistance increase rate after the charge and discharge cycle of Comparative Example 1 was set to 100, the resistance increase rate after the charge and discharge cycle of Example 1 was calculated as a relative value (see the following formula). Resistance increase rate (relative value) after charge and discharge cycles of Example 1 = (Resistance increase rate after charge and discharge cycles of Example 1) / (Resistance increase rate after charge and discharge cycles of Comparative Example 1) × 100

[0113] 〔Comparative Example 1〕 A non-aqueous electrolyte solution was prepared and a lithium-ion secondary battery was fabricated by the same procedure as in Example 1, except that the phosphoric acid triester compound represented by formula (I-1) was not added to the non-aqueous electrolyte solution. Further, by the same procedure as in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and the reference values of "discharge capacity retention rate (relative value) after charge-discharge cycles" and "resistance increase rate (relative value) after charge-discharge cycles" in Example 1 were used. The results are shown in Table 1.

[0114] [Example 2] A non-aqueous electrolyte solution was prepared and a lithium-ion secondary battery was fabricated by the same procedure as in Example 1, except that in addition to the phosphoric acid triester compound represented by formula (I-1), fluoroethylene carbonate (FEC) was added so that the content relative to the total mass of the non-aqueous electrolyte solution was 2.0% by mass. Further, by the same procedure as in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and relative values were calculated with the "discharge capacity retention rate after charge-discharge cycles" and "resistance increase rate after charge-discharge cycles" of the lithium-ion secondary battery in Comparative Example 1 set to 100, and used as the "discharge capacity retention rate (relative value) after charge-discharge cycles" and "resistance increase rate (relative value) after charge-discharge cycles". The results are shown in Table 1.

[0115] [Example 3] In addition to the triester phosphate compound represented by the formula (I-1), fluoroethylene carbonate (FEC) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 2.0% by mass, and further lithium difluorophosphate (LiPO2F2) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 1.0% by mass. Except for this, a non-aqueous electrolyte was prepared by the same operation as described in Example 1, and a lithium-ion secondary battery was prepared. Further, by the same operation as described in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and the relative values with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium-ion secondary battery of Comparative Example 1 being 100 were calculated, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0116] [Example 4] Instead of the triester phosphate compound represented by the formula (I-1), a triester borate compound represented by the following formula (III-1) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 1.0% by mass. Except for this, a non-aqueous electrolyte was prepared by the same operation as described in Example 1, and a lithium-ion secondary battery was prepared. Further, by the same operation as described in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and the relative values with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium-ion secondary battery of Comparative Example 1 being 100 were calculated, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0117] [Chemical formula]

[0118] [Example 5] In addition to the boric acid triester compound represented by the formula (III-1), a non-aqueous electrolyte was prepared by the same procedure as described in Example 4, except that fluoroethylene carbonate (FEC) was added so that its content relative to the total mass of the non-aqueous electrolyte was 2.0% by mass, and a lithium ion secondary battery was fabricated. Further, by the same procedure as described in Example 4, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and relative values were calculated with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium ion secondary battery of Comparative Example 1 set to 100, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0119] [Example 6] In addition to the boric acid triester compound represented by the formula (III-1), fluoroethylene carbonate (FEC) was added so that its content relative to the total mass of the non-aqueous electrolyte was 2.0% by mass, and further lithium difluorophosphate (LiPO2F2) was added so that its content relative to the total mass of the non-aqueous electrolyte was 1.0% by mass. Then, a non-aqueous electrolyte was prepared by the same procedure as described in Example 4, and a lithium ion secondary battery was fabricated. Further, by the same procedure as described in Example 4, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and relative values were calculated with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium ion secondary battery of Comparative Example 1 set to 100, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0120] [Example 7] Instead of the phosphoric acid triester compound represented by the formula (I-1), a non-aqueous electrolyte was prepared by the same procedure as described in Example 1, except that a phosphorous acid triester compound represented by the following formula (II-1) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 1.0% by mass, and a lithium ion secondary battery was fabricated. Further, by the same procedure as described in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and relative values were calculated with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium ion secondary battery of Comparative Example 1 set to 100, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0121]

Chemical formula

[0122] 〔Example 8〕 A non-aqueous electrolyte was prepared by the same procedure as described in Example 7, except that in addition to the phosphorous acid triester compound represented by the formula (II-1), fluoroethylene carbonate (FEC) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 2.0% by mass, and a lithium ion secondary battery was fabricated. Further, by the same procedure as described in Example 7, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and relative values were calculated with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium ion secondary battery of Comparative Example 1 set to 100, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0123] 〔Example 9〕 In addition to the triester compound represented by the formula (II-1), fluoroethylene carbonate (FEC) was added so that the content with respect to the total mass of the non-aqueous electrolyte was 2.0% by mass, and further lithium difluorophosphate (LiPO2F2) was added so that the content with respect to the total mass of the non-aqueous electrolyte was 1.0% by mass. Except for this, a non-aqueous electrolyte was prepared by the same operation as described in Example 7, and a lithium-ion secondary battery was prepared. Further, by the same operation as described in Example 7, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and the relative values with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium-ion secondary battery of Comparative Example 1 being set to 100 were calculated, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0124]

Table 1

[0125] As is clear from Table 1, the non-aqueous electrolyte secondary batteries of Examples 1 to 9 using a non-aqueous electrolyte containing at least one triester compound selected from the group consisting of the triester compound represented by the formula (I), the triester compound represented by the formula (II), and the triester compound represented by the formula (III) have improved capacity retention rate and resistance increase rate after charge-discharge cycles. Also, it is clear that the non-aqueous electrolyte secondary batteries of Examples 2, 3, 5, 6, 8, and 9 using a non-aqueous electrolyte further containing fluoroethylene carbonate (FEC) or lithium difluorophosphate (LiPO2F2) have more effectively improved capacity retention rate and resistance increase rate after charge-discharge cycles.

Explanation of Symbols

[0126] 1 Lithium secondary battery precursor 10 Battery element 11 Positive electrode 11A Positive electrode current collector 11B Positive electrode composite material layer 12 Negative electrode 12A Negative electrode current collector 12B Negative electrode composite layer 13 Separator 14 Single cell layer 21 Positive electrode lead 22 Negative electrode lead 30 Outer package 41 Positive electrode 42 Negative electrode 43 Positive electrode can 44 Sealing plate 45 Separator 46 Gasket 47, 48 Spacer plates

Claims

1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and a separator, wherein the negative electrode includes a current collector and a negative electrode composite material layer containing a negative electrode active material formed on the current collector, the negative electrode active material includes at least one selected from the group consisting of silicon single crystal particles, silicon oxide particles, and silicon carbide particles, and the non-aqueous electrolyte secondary battery, wherein the non-aqueous electrolyte contains at least one triester compound selected from the group consisting of a phosphoric acid triester compound represented by the following formula (I), a phosphorous acid triester compound represented by the following formula (II), and a boric acid triester compound represented by the following formula (III). 【Chemical 1】 (In formulas (I) to (III), R １ each independently represents a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-).)

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte further contains a cyclic carbonate compound represented by the following formula (IV). [Chemical 2] (In formula (IV), X is a fluoro group (-F), a chloro group (-Cl), or a bromo group (-Br), and R ２ is, independently of one another, a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an oxa group (-O-), and h represents an integer of 0 to 3.)

3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte further contains at least one fluorophosphate selected from the group consisting of monofluorophosphate and difluorophosphate.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material includes single carbon particles and at least one selected from the group consisting of silicon single crystal particles, silicon oxide particles, and silicon carbide particles.

5. The non-aqueous electrolyte secondary battery according to claim 4, wherein the total content of the silicon single crystal particles, the silicon oxide particles, and the silicon carbide particles is 30% by mass or less when the total amount of the negative electrode active material is 100% by mass.

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