Non-aqueous electrolyte for batteries, lithium secondary battery precursor, lithium secondary battery, and method for manufacturing a lithium secondary battery

Abstract

To provide a non-aqueous electrolyte for battery capable of improving storage characteristics and cycle characteristics of a battery by reducing resistance of the battery.SOLUTION: A non-aqueous electrolyte for battery contains: an electrolyte containing fluorine-containing lithium salt; a non-aqueous solvent; an additive A which is specific sulfuric ester (A); an additive B which is at least one selected from between specific carbonate and specific sulfuric ester (B3); a specific additive C which is a specific boron compound; a specific sultone compound and a specific phosphate compound.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to a non-aqueous electrolyte for batteries, a lithium secondary battery precursor, a lithium secondary battery, and a method for manufacturing a lithium secondary battery. [Background technology]

[0002] Conventionally, non-aqueous electrolytes for batteries (i.e., non-aqueous electrolytes used in batteries) have been formulated to contain various additives. For example, Patent Documents 1 to 8 disclose non-aqueous electrolytes for lithium secondary batteries that contain specific cyclic sulfate esters as additives. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Patent No. 5524347 [Patent Document 2] Japanese Patent Publication No. 2020-38783 [Patent Document 3] International Publication No. 2020 / 022452 [Patent Document 4] Patent No. 6017697 [Patent Document 5] Japanese Patent Publication No. 2019-102183 [Patent Document 6] Japanese Patent Publication No. 2019-179609 [Patent Document 7] Japanese Patent Publication No. 2019-175577 [Patent Document 8] International Publication No. 2020 / 026853 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, there are times when it is necessary to further reduce the resistance of the battery and to improve its storage and cycle characteristics. An object of one aspect of this disclosure is to provide a non-aqueous electrolyte for batteries that can reduce the resistance of a battery and improve its storage characteristics and cycle characteristics, a lithium secondary battery with reduced resistance and excellent storage characteristics and cycle characteristics, and a lithium secondary battery precursor and a method for manufacturing the lithium secondary battery that are suitable for the manufacture of the lithium secondary battery. [Means for solving the problem]

[0005] The means for solving the above problems include the following embodiments.

[0006] <1> An electrolyte containing a fluorine-containing lithium salt, Non-aqueous solvents and Additive A is at least one compound selected from the group consisting of compounds represented by the following formula (A), Additive B is at least one compound selected from the group consisting of compounds represented by the following formulas (B1) to (B3), Additive C is at least one selected from the group consisting of compounds represented by the following formulas (C1) to (C8), tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, and tris(trimethylsilyl) sulfate. A non-aqueous electrolyte for batteries containing the following:

[0007] [ka]

[0008] In formula (A), R 1 R represents a group represented by formula (II) or formula (III), 2 R represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a group represented by formula (II), or a group represented by formula (III). In formula (II), R 3represents 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 (IV). The wavy lines in Formula (II), Formula (III), and Formula (IV) represent the bonding positions. When the compound represented by Formula (A) contains two groups represented by Formula (II), the two groups represented by Formula (II) may be the same as or different from each other. In Formula (B1), R b11 and R b12 each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group. In Formula (B2), R b21 to R b24 each independently represent an alkyl group having 1 to 3 carbon atoms which may be substituted with a fluorine atom, a hydrogen atom, a fluorine atom, or a chlorine atom. Provided that not all of R in Formula (B2) b21 to R b24 are hydrogen atoms. In Formula (B3), R b31 and R b32 each independently represent an alkyl group having 1 to 3 carbon atoms which may be substituted with a fluorine atom, a hydrogen atom, a fluorine atom, or a chlorine atom. In Formula (C1), M represents an alkali metal, Y represents a transition element, or an element of Group 13, Group 14, or Group 15 of the periodic table, b represents an integer of 1 to 3, m represents an integer of 1 to 4, n represents an integer of 0 to 8, and q represents 0 or 1. In Formula (C1), R c11 is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain a substituent or a heteroatom in their structure, and when q is 1 and m is 2 to 4, the m number of R c11 may each be bonded to each other.), and R c12 is a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, a halogenated aryl group having 6 to 20 carbon atoms (these groups may contain a substituent or a heteroatom in their structure, and when n is 2 to 8, the n number of R c12They may each be joined together to form a ring. ), or -Q 3 R c13 This represents Q 1 Q 2 and Q 3 These are, independently, O, S, or NR. c14 Represents R c13 and R c14 Each of these independently comprises a hydrogen atom, a C1-C10 alkyl group, a C1-C10 alkyl halide, a C6-C20 aryl group, or a C6-C20 aryl halide (these groups may contain substituents or heteroatoms in their structure, R c13 or R c14 If multiple instances exist, they may combine to form a ring. In formula (C2), R c21 ~R c24 Each of these independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 3 carbon atoms, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms. In formula (C3), R c31 ~R c33 Each of these independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms, L c31 This represents a single bond or an oxygen atom. In formula (C4), R c41 ~R c43 Each of these independently represents a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. In formula (C5), R c51 R represents a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. c52 n represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms, and n represents an integer from 1 to 3.

[0009] <2> The aforementioned additive A contains the following compound (A-1): <1> Non-aqueous electrolyte for batteries as described above.

[0010] [ka]

[0011] <3> The fluorine-containing lithium salt comprises lithium hexafluoride phosphate and a compound represented by the following formula (D1). <1> or <2> Non-aqueous electrolyte for batteries as described above.

[0012] [ka]

[0013] In formula (D1), R d11 and R d12 Each of these independently represents either a fluorine atom or a fluorinated hydrocarbon group having 1 to 6 carbon atoms.

[0014] <4> Positive electrode and, The negative electrode and, <1> ~ <3> A non-aqueous electrolyte for batteries as described in any one of the following, A lithium secondary battery precursor, including... <5> The positive electrode includes a positive electrode active material containing a compound represented by the following formula (X), <4> A lithium secondary battery precursor as described above. LiRing a Mn b Co c O2… (X) [In equation (X), a, b, and c are each independently greater than 0 and less than 1.00, and the sum of a, b, and c is between 0.99 and 1.00.] <6> The positive electrode active material contains a single crystal of the compound represented by formula (X), <5> A lithium secondary battery precursor as described above. <7> <4> ~ <6> A lithium secondary battery obtained by charging and discharging a lithium secondary battery precursor described in any one of the above. <8> The operating potential of the positive electrode exceeds 4.30V, based on the standard oxidation-reduction potential of Li metal. <7> Lithium secondary batteries as described above. <9> <4> ~ <6> A step of preparing a lithium secondary battery precursor as described in one of the following, The lithium secondary battery precursor is subjected to a charging and discharging process, A method for manufacturing lithium secondary batteries, including [the specified component]. [Effects of the Invention]

[0015] According to one aspect of this disclosure, a non-aqueous electrolyte for batteries that can reduce the resistance of a battery and improve its storage characteristics and cycle characteristics, a lithium secondary battery with reduced resistance and excellent storage characteristics and cycle characteristics, and a lithium secondary battery precursor and a method for manufacturing the lithium secondary battery are provided. [Brief explanation of the drawing]

[0016] [Figure 1] This is a schematic perspective view showing an example of a laminated battery, which is an example of a lithium secondary battery according to this disclosure. [Figure 2] Figure 1 is a schematic cross-sectional view in the thickness direction of a stacked electrode body housed in a laminate-type battery. [Figure 3] This is a schematic cross-sectional view showing an example of a coin-type battery, which is another example of a lithium secondary battery of the present disclosure. [Modes for carrying out the invention]

[0017] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. In this specification, the amount of each component in a composition means the total amount of any multiple substances present in the composition, unless otherwise specified. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their intended purpose is achieved.

[0018] [Nonaqueous electrolyte for batteries] The non-aqueous electrolyte for batteries disclosed herein (hereinafter also simply referred to as "non-aqueous electrolyte") An electrolyte containing a fluorine-containing lithium salt, Non-aqueous solvents and Additive A is at least one compound selected from the group consisting of compounds represented by the following formula (A), Additive B is at least one compound selected from the group consisting of compounds represented by the following formulas (B1) to (B3), Additive C is at least one selected from the group consisting of compounds represented by the following formulas (C1) to (C8), tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, and tris(trimethylsilyl) sulfate. It contains.

[0019] [ka]

[0020] In formula (A), R 1 R represents a group represented by formula (II) or formula (III), 2 R represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a group represented by formula (II), or a group represented by formula (III). In formula (II), R 3 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 (IV). The wavy lines in formulas (II), (III), and (IV) indicate the bond position. If a compound represented by formula (A) contains two groups represented by formula (II), the two groups represented by formula (II) may be the same or different from each other. In formula (B1), R b11 and R b12 Each of these independently represents a hydrogen atom, a methyl group, an ethyl group, or a propyl group. In formula (B2), R b21 ~R b24 Each of these independently represents a C1-C3 alkyl group which may be substituted with a fluorine atom, a hydrogen atom, a fluorine atom, or a chlorine atom. However, R in formula (B2) b21 ~R b24 Not all of them are hydrogen atoms. In formula (B3), R b31 and R b32Each of these independently represents a C1-C3 alkyl group, a hydrogen atom, a fluorine atom, or a chlorine atom, which may be substituted with a fluorine atom. In formula (C1), M represents alkali metals, Y represents transition elements or elements from groups 13, 14, or 15 of the periodic table, b represents an integer from 1 to 3, m represents an integer from 1 to 4, n represents an integer from 0 to 8, and q represents 0 or 1. In formula (C1), R c11 This is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain substituents or heteroatoms in their structure, and when q is 1 and m is 2 to 4, there are m R c11 These can be joined together.) and R c12 This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, and C6-C20 halogenated aryl groups (these groups may contain substituents or heteroatoms in their structure, and if n is 2-8, there are n R c12 They may each be joined together to form a ring. ), or -Q 3 R c13 This represents Q 1 Q 2 and Q 3 These are, independently, O, S, or NR. c14 Represents R c13 and R c14 Each of these independently comprises a hydrogen atom, a C1-C10 alkyl group, a C1-C10 alkyl halide, a C6-C20 aryl group, or a C6-C20 aryl halide (these groups may contain substituents or heteroatoms in their structure, R c13 or R c14 If multiple instances exist, they may combine to form a ring. In formula (C2), R c21 ~R c24 Each of these independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 3 carbon atoms, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms. In formula (C3), R c31 ~Rc33 Each of these independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms, L c31 This represents a single bond or an oxygen atom. In formula (C4), R c41 ~R c43 Each of these independently represents a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. In formula (C5), R c51 R represents a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. c52 n represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms, and n represents an integer from 1 to 3.

[0021] The non-aqueous electrolyte for batteries of this disclosure can reduce the resistance of the battery and improve its storage characteristics and cycle characteristics. The effects described above will be explained in more detail below.

[0022] The above effects are thought to be brought about by the formation of a low-resistance protective film (hereinafter also referred to as an SEI (Solid Electrolyte Interface) film) on the battery electrodes (i.e., the negative electrode and / or positive electrode) through the combination of additives A, B, and C. Additive A (i.e., the compound represented by formula (A)) is a cyclic sulfate ester compound that contains at least one cyclic sulfate ester group in one molecule, and a total of two or more sulfate ester groups and sulfonic acid ester groups (hereinafter collectively referred to as "S-containing ester groups") in one molecule. Additive A is thought to be a compound that, when contained in a non-aqueous electrolyte, forms a low-resistance SEI film on the electrode surface due to multiple mutually bonded S-containing ester groups. As a result, the battery's resistance is reduced, and the decomposition reaction of the non-aqueous electrolyte on the electrode surface is suppressed, thereby improving the battery's storage characteristics and cycle characteristics. Additive B is thought to be a compound that, when contained in a non-aqueous electrolyte, forms an SEI film on the negative electrode surface and suppresses the decomposition reaction of the non-aqueous electrolyte occurring on the negative electrode surface. When additives A and B are used together, it is thought that additive B penetrates into the SEI film of the negative electrode formed by additive A, reinforcing the SEI film to compensate for areas where the protection of the negative electrode is insufficient. As a result, it is thought that the protective effect of the negative electrode is further enhanced while maintaining the resistance-reducing effect of additive A. Additive C is thought to be a compound that, when contained in a non-aqueous electrolyte, suppresses the decomposition reaction of the non-aqueous electrolyte on the positive electrode surface by forming an SEI film on the positive electrode surface and / or coordinating to active sites on the positive electrode surface. When additives A and C are used in combination, it is thought that additive C penetrates into the SEI film of the positive electrode formed by additive A, reinforcing the SEI film to reinforce areas where the positive electrode is not adequately protected. As a result, it is thought that the protective effect of the positive electrode is further enhanced while maintaining the resistance-reducing effect of additive A. When the non-aqueous electrolyte of this disclosure is used in a battery, as described above, additives A, B, and C work together to form a low-resistance and highly protective SEI film on the negative electrode and positive electrode, and as a result, the above-mentioned effects (i.e., the effect of reducing the battery's resistance and improving the battery's storage characteristics and cycle characteristics) are expected to be achieved.

[0023] The following describes the components that may be contained in the non-aqueous electrolyte of this disclosure.

[0024] <Electrolytes> The non-aqueous electrolyte of this disclosure contains at least one electrolyte. The electrolyte contains a fluorine-containing lithium salt. The electrolyte contained in the non-aqueous electrolyte of this disclosure may be one type or two or more types. The fluorine-containing lithium salt contained as an electrolyte in the non-aqueous electrolyte of this disclosure may be one type or two or more types.

[0025] (Fluorine-containing lithium salt) Examples of fluorine-containing lithium salts used as electrolytes include LiPF6 (i.e., lithium hexafluoride phosphate), LiBF4, LiClO4, LiAsF6, Li2SiF6, and LiiOSO2C. k F (2k+1) (k = integers from 1 to 8), LiPF n [C k F (2k+1) ] (6-n) (n=integer from 1 to 5, k=integer from 1 to 8), LiC(SO2R 7 )(SO2R 8 )(SO2R 9 )(R here 7 ~R 9 These elements may be the same or different from each other, and include a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms, lithium sulfate imide compounds, and the like. Examples of lithium sulfate imide compounds include, LiN(SO2OR 10 )(SO2OR 11 )(R here 10 and R 11 Examples include compounds represented by the following formula (D1), where the atoms are either the same or different, and are a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms. Lithium sulfate imide compounds include, A compound represented by the following formula (D1) is preferred. LiN(SO2F)2 (i.e., lithium bis(fluorosulfonyl)imide; hereinafter also referred to as "LiFSi") or LiN(SO2CF3)2 is preferred. LiFSi is particularly preferred.

[0026] From the viewpoint of more effectively achieving the above-mentioned effects with the non-aqueous electrolyte of this disclosure, fluorine-containing lithium salts are used as electrolytes. It is preferable to include lithium hexafluoride phosphate and a lithium sulfate imide compound. It is more preferable to include lithium hexafluoride phosphate and a compound represented by the following formula (D1). When the fluorine-containing lithium salt as the electrolyte contains lithium hexafluorophosphate and a lithium sulfonylimide compound, the diffusibility of lithium ions in the non-aqueous electrolytic solution and in the SEI film is further improved, and as a result, the initial increase in battery resistance and the increase in battery resistance during storage and / or cycles are further suppressed.

[0027]

Chemical Formula

[0028] In formula (D1), R d11 and R d12 each independently represent a fluorine atom or a fluorinated hydrocarbon group having 1 to 6 carbon atoms.

[0029] R d11 and R d12 each independently are preferably a fluorine atom or a perfluoroalkyl group having 1 to 6 carbon atoms, more preferably a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group, still more preferably a fluorine atom or a trifluoromethyl group, particularly preferably a fluorine atom.

[0030] As the compound represented by formula (D1), LiN(SO2F)2 (i.e., lithium bis(fluorosulfonyl)imide; hereinafter also referred to as "LiFSI") or LiN(SO2CF3)2 is preferred, and LiFSI is particularly preferred.

[0031] When the fluorine-containing lithium salt as the electrolyte contains LiPF6 and the compound represented by formula (D1), the proportion of the content of LiPF6 relative to the total content of LiPF6 and the compound represented by formula (D1) is preferably 20 mass% to 99 mass%, and more preferably 40 mass% to 95 mass%. When the LiPF6 content is 20% by mass or more, oxidation of the positive electrode (for example, oxidative corrosion of the aluminum in the positive electrode current collector) can be further suppressed. When the LiPF6 content is 99% by mass or less, the low-temperature characteristics of the battery can be further improved.

[0032] When the fluorine-containing lithium salt as an electrolyte contains LiPF6 and a compound represented by formula (D1), the total content of LiPF6 and the compound represented by formula (D1) relative to the total amount of the fluorine-containing lithium salt is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. The total content of LiPF6 and the compound represented by formula (D1) relative to the total amount of the fluorine-containing lithium salt may be 100% by mass. Furthermore, when the fluorine-containing lithium salt as the electrolyte contains LiPF6 and a compound represented by formula (D1), the total content of LiPF6 and the compound represented by formula (D1) relative to the total amount of the electrolyte is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. The total content of LiPF6 and LiFSi relative to the total amount of the electrolyte may be 100% by mass.

[0033] The content of fluorine-containing lithium salt as an electrolyte relative to the total amount of electrolyte is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 80% by mass or more. The content of fluorine-containing lithium salt as an electrolyte relative to the total amount of electrolyte may be 100% by mass.

[0034] The content of fluorine-containing lithium salt as an electrolyte relative to the total amount of the non-aqueous electrolyte is preferably 5% to 30% by mass, more preferably 8% to 25% by mass, and even more preferably 10% to 20% by mass. When the content of fluorine-containing lithium salt as an electrolyte is 5% by mass or more, the ionic conductivity of the non-aqueous electrolyte is further improved. When the content of the fluorine-containing lithium salt as the electrolyte is 30 mass% or less, the viscosity of the non-aqueous electrolyte solution is further reduced, and the injectability into empty cells during battery production is further improved.

[0035] (Compounds other than fluorine-containing lithium salts) The electrolyte may contain at least one compound other than the fluorine-containing lithium salt. Examples of the compound other than the fluorine-containing lithium salt as the electrolyte include tetraalkylammonium salts. Examples of the tetraalkylammonium salts include, for example, (C2H5)4NPF6, (C2H5)4NBF4, (C2H5)4NClO4, (C2H5)4NAsF6, (C2H5)4N2SiF6, (C2H5)4NOSO2C k F (2k+1) (k is an integer of 1 to 8), (C2H5)4NPF n [C k F (2k+1) (6-n) (n is an integer of 1 to 5, k is an integer of 1 to 8), and the like.

[0036] (Preferable content of electrolyte) The content of the electrolyte relative to the total amount of the non-aqueous electrolyte solution is preferably 5 mass% to 30 mass%, more preferably 8 mass% to 25 mass%, and still more preferably 10 mass% to 20 mass%. When the content of the electrolyte is 5 mass% or more, the ionic conductivity of the non-aqueous electrolyte solution is further improved. When the content of the electrolyte is 30 mass% or less, the viscosity of the non-aqueous electrolyte solution is further reduced, and the injectability into empty cells (that is, cells before the non-aqueous electrolyte solution is injected) during battery production is further improved.

[0037] <Non-aqueous Solvent> The non-aqueous electrolyte solution of the present disclosure contains at least one non-aqueous solvent. The non-aqueous solvent is not particularly limited, and for example, the non-aqueous solvents described in paragraphs 0069 to 0087 of Japanese Patent Application Laid-Open No. 2017-45723 can be used. The non-aqueous electrolyte solution is​ It is preferable that it contains a carbonate compound. It is more preferable to include cyclic carbonate compounds and linear carbonate compounds. The cyclic carbonate compounds and linear carbonate compounds that may be included in the other non-aqueous solvents may be one or more of each.

[0038] Examples of cyclic carbonate compounds include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate.

[0039] Examples of chain-like carbonate compounds include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl carbonate, ethyl pentyl carbonate, dipentyl carbonate, methylheptyl carbonate, ethylheptyl carbonate, diheptyl carbonate, methylhexyl carbonate, ethylhexyl carbonate, dihexyl carbonate, methyl octyl carbonate, ethyl octyl carbonate, dioctyl carbonate, and the like.

[0040] Specifically, combinations of cyclic carbonates and linear carbonates include: ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methyl ethyl carbonate, propylene carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate and methyl ethyl carbonate, ethylene carbonate, propylene carbonate and diethyl carbonate, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, and ethylene carbonate and dimethyl carbonate. Examples include diethyl carbonate, ethylene carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate, and ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate and diethyl carbonate.

[0041] The mixing ratio of the cyclic carbonate compound to the linear carbonate compound is expressed as a mass ratio, where the ratio of cyclic carbonate compound to linear carbonate compound is, for example, 5:95 to 80:20, preferably 10:90 to 70:30, and more preferably 15:85 to 55:45.

[0042] The total proportion of cyclic carbonate compounds and linear carbonate compounds in the non-aqueous solvent is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more. The total proportion of cyclic carbonate compounds and linear carbonate compounds in the non-aqueous solvent may be 100% by mass.

[0043] The proportion of the non-aqueous solvent in the total amount of the non-aqueous electrolyte of this disclosure is preferably 60% by mass or more, and more preferably 70% by mass or more. The upper limit of the proportion of non-aqueous solvent in the non-aqueous electrolyte depends on the content of other components (electrolytes, additives, etc.), but the upper limit is, for example, 99% by mass, preferably 97% by mass, and more preferably 90% by mass.

[0044] <Additional A> The non-aqueous electrolyte of this disclosure contains additive A. Additive A is at least one compound selected from the group consisting of compounds represented by the following formula (A). The function of additive A is as described above.

[0045] [ka]

[0046] In formula (A), R 1 R represents a group represented by formula (II) or formula (III), 2 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a group represented by formula (II), or a group represented by formula (III). In formula (II), R 3 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 (IV). The wavy lines in formulas (II), (III), and (IV) indicate the bond position. If a compound represented by formula (A) contains two groups represented by formula (II), the two groups represented by formula (II) may be identical or different from each other.

[0047] In formula (A), "halogen atoms" can be specifically fluorine, chlorine, bromine, or iodine atoms. As the halogen atom, a fluorine atom is preferred.

[0048] In formula (A), "C1-C6 alkyl group" refers to a linear or branched alkyl group having 1 to 6 carbon atoms, and specific examples include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, pentyl group, 2-methylbutyl group, 1-methylpentyl group, neopentyl group, 1-ethylpropyl group, hexyl group, and 3,3-dimethylbutyl group. Among alkyl groups having 1 to 6 carbon atoms, alkyl groups having 1 to 3 carbon atoms are more preferred.

[0049] In formula (A), "C1-C6 halogenated alkyl group" refers to a linear or branched halogenated alkyl group having 1 to 6 carbon atoms, and specific examples include fluoromethyl group, difluoromethyl group, trifluoromethyl group, 2,2,2-trifluoroethyl group, perfluoroethyl group, perfluoropropyl group, perfluorobutyl group, perfluoropentyl group, perfluorohexyl group, perfluoroisopropyl group, perfluoroisobutyl group, chloromethyl group, chloroethyl group, chloropropyl group, bromomethyl group, bromoethyl group, bromopropyl group, methyl iodide group, ethyl iodide group, and propyl iodide group. Among the alkyl halides having 1 to 6 carbon atoms, alkyl halides having 1 to 3 carbon atoms are more preferred.

[0050] In formula (A), "alkoxy group having 1 to 6 carbon atoms" refers to a linear or branched alkoxy group having 1 to 6 carbon atoms, and specific examples include methoxy group, ethoxy group, propoxy group, isopropoxy group, butoxy group, isobutoxy group, sec-butoxy group, tert-butoxy group, pentyloxy group, 2-methylbutoxy group, 1-methylpentyloxy group, neopentyloxy group, 1-ethylpropoxy group, hexyloxy group, and 3,3-dimethylbutoxy group. Among alkoxy groups having 1 to 6 carbon atoms, alkoxy groups having 1 to 3 carbon atoms are more preferred.

[0051] R in equation (A) 1Preferably, a base represented by formula (II) (in formula (II), R 3 It is preferably a fluorine atom, a C1-C3 alkyl group, a C1-C3 halogenated alkyl group, a C1-C3 alkoxy group, or a group represented by formula (IV), or a group represented by formula (III). R in equation (A) 2 Preferably, a hydrogen atom, an alkyl group having 1 to 3 carbon atoms, and a group represented by formula (II) (in formula (II), R 3 It is preferably a fluorine atom, a C1-C3 alkyl group, a C1-C3 halogenated alkyl group, a C1-C3 alkoxy group, or a group represented by formula (IV). It is more preferably a hydrogen atom or a methyl group, and particularly preferably a hydrogen atom.

[0052] R in equation (A) 1 If is a group represented by formula (II), then R in formula (II) 3 As mentioned above, R is a halogen atom, an alkyl group having 1 to 6 carbon atoms, an alkyl halide having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, or a group represented by formula (IV), but R 3 More preferably, the group is a fluorine atom, a C1-C3 alkyl group, a C1-C3 halogenated alkyl group, a C1-C3 alkoxy group, or a group represented by formula (IV). Even more preferably, the group is a fluorine atom, a methyl group, an ethyl group, a methoxy group, an ethoxy group, or a group represented by formula (IV). R in equation (A) 2 If is a group represented by formula (II), then R in formula (II) 3 For the preferred range of R in equation (A), 1 When R is a group represented by formula (II), 3 This is similar to the preferred range.

[0053] R in equation (A) 1 and R 2 A preferred combination is R 1 However, the base represented by formula (II) (in formula (II), R 3(preferably a fluorine atom, a C1-C3 alkyl group, a C1-C3 halogenated alkyl group, a C1-C3 alkoxy group, or a group represented by formula (IV), or a group represented by formula (III), R 2 However, hydrogen atoms, alkyl groups having 1 to 3 carbon atoms, and groups represented by formula (II) (in formula (II), R 3 It is preferable that is a fluorine atom, a C1-C3 alkyl group, a C1-C3 halogenated alkyl group, a C1-C3 alkoxy group, or a group represented by formula (IV), or a combination of a group represented by formula (III). R in equation (A) 1 and R 2 A more preferred combination is R 1 The base is represented by equation (II) (where R 3 (preferably a fluorine atom, a methyl group, an ethyl group, a methoxy group, an ethoxy group, or a group represented by formula (IV) or a group represented by formula (III), R 2 This is a combination in which the atom is either a hydrogen atom or a methyl group. R in equation (A) 1 and R 2 A particularly preferred combination is, in equation (A), R 1 The base is represented by formula (III), and R 2 This is a combination in which the atom is a hydrogen atom (i.e., compound (A-1) described later).

[0054] Preferred embodiments and specific examples of the compound represented by formula (A) can be appropriately referenced in paragraphs 0054 to 0070 of the aforementioned Patent Document 1 (i.e., International Publication No. 2012 / 053644).

[0055] Particularly preferred examples of the compound represented by formula (A) are the following compound (A-1) or the following compound (A-2), with compound (A-1) being the particularly preferred example.

[0056] [ka]

[0057] The compound represented by formula (A) is particularly preferably compound (A-1). When the compound represented by formula (A) contains compound (A-1), the proportion of compound (A) in the total amount of the compound represented by formula (A) is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass.

[0058] The preferred range for the content of additive A relative to the total volume of the non-aqueous electrolyte will be described later.

[0059] <Additive B> The non-aqueous electrolyte of this disclosure contains additive B. Additive B is at least one compound selected from the group consisting of compounds represented by the following formulas (B1) to (B3). The function of additive B is as described above.

[0060] [ka]

[0061] In formula (B1), R b11 and R b12 Each of these independently represents a hydrogen atom, a methyl group, an ethyl group, or a propyl group. In formula (B2), R b21 ~R b24 Each of these independently represents a C1-C3 alkyl group which may be substituted with a fluorine atom, a hydrogen atom, a fluorine atom, or a chlorine atom. However, R in formula (B2) b21 ~R b24 Not all of them are hydrogen atoms. In formula (B3), R b31 and R b32 Each of these independently represents a C1-C3 alkyl group, a hydrogen atom, a fluorine atom, or a chlorine atom, which may be substituted with a fluorine atom.

[0062] In formula (B1), R b11 and R b12Each of these is preferably independently a hydrogen atom, a methyl group, or an ethyl group, more preferably a hydrogen atom or a methyl group, and even more preferably a hydrogen atom. Examples of compounds represented by formula (B1) include vinylene carbonate (hereinafter also referred to as "VC"), methylvinylene carbonate, and dimethylvinylene carbonate, with vinylene carbonate being particularly preferred.

[0063] In formula (B2), R b21 ~R b24 It is preferable that each atom is not entirely a hydrogen atom, but rather independently a C1-C3 alkyl group, a hydrogen atom, or a fluorine atom, which may be substituted with a fluorine atom; more preferably a C1-C3 alkyl fluoride group, a hydrogen atom, or a fluorine atom; and even more preferably a hydrogen atom or a fluorine atom.

[0064] In this disclosure, if "alkyl group which may be substituted with a fluorine atom" is an alkyl group that is substituted with a fluorine atom (i.e., a fluorinated alkyl group), then the alkyl group that is substituted with a fluorine atom (i.e., a fluorinated alkyl group) is not limited to being a perfluoroalkyl group, and only if the alkyl group is substituted with at least one fluorine atom.

[0065] Examples of compounds represented by formula (B2) include 4-fluoroethylene carbonate (hereinafter also referred to as "FEC"), 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, and 4-trifluoromethylethylene carbonate, with 4-fluoroethylene carbonate being particularly preferred.

[0066] In formula (B3), R b31 and R b32 Each of these is preferably independently a hydrogen atom, a methyl group, an ethyl group, or a propyl group. In formula (B3), R b31 and R b32A more preferable configuration is one in which one is a hydrogen atom, a methyl group, an ethyl group, or a propyl group, and the other is a hydrogen atom. Examples of compounds represented by formula (B3) include: Examples include ethylene sulfate (hereinafter also referred to as "DTD"), 1,2-propylene sulfate, 1,3-propylene sulfate, 1,2-butylene sulfate, 2,3-butylene sulfate, 1,2-pentylene sulfate, and 2,3-pentylene sulfate. Of these, ethylene sulfate, 1,2-propylene sulfate, 1,2-butylene sulfate, or 1,2-pentylene sulfate are preferred.

[0067] The preferred range for the content of additive B relative to the total volume of the non-aqueous electrolyte will be described later.

[0068] <Additive C> The non-aqueous electrolyte of this disclosure contains additive C. Additive C is at least one compound selected from the group consisting of compounds represented by the following formulas (C1) to (C8), tris(trimethylsilyl) phosphate, tris(trimethylsilyl) borate, and tris(trimethylsilyl) sulfate. The function of additive C is as described above.

[0069] [ka]

[0070] In formula (C1), M represents alkali metals, Y represents transition elements or elements from groups 13, 14, or 15 of the periodic table, b represents an integer from 1 to 3, m represents an integer from 1 to 4, n represents an integer from 0 to 8, and q represents 0 or 1. In formula (C1), R c11 This is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain substituents or heteroatoms in their structure, and when q is 1 and m is 2 to 4, there are m R c11These can be joined together.) and R c12 This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, and C6-C20 halogenated aryl groups (these groups may contain substituents or heteroatoms in their structure, and if n is 2-8, there are n R c12 They may each be joined together to form a ring. ), or -Q 3 R c13 This represents Q 1 Q 2 and Q 3 These are, independently, O, S, or NR. c14 Represents R c13 and R c14 Each of these independently comprises a hydrogen atom, a C1-C10 alkyl group, a C1-C10 alkyl halide, a C6-C20 aryl group, or a C6-C20 aryl halide (these groups may contain substituents or heteroatoms in their structure, R c13 or R c14 If multiple instances exist, they may combine to form a ring. In formula (C2), R c21 ~R c24 Each of these independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 3 carbon atoms, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms. In formula (C3), R c31 ~R c33 Each of these independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms, L c31 This represents a single bond or an oxygen atom. In formula (C4), R c41 ~R c43 Each of these independently represents a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. In formula (C5), R c51 R represents a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. c52n represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms, and n represents an integer from 1 to 3.

[0071] (The compound represented by formula (C1)) In formula (C1), M is an alkali metal, and Y is a transition metal, or an element from group 13, 14, or 15 of the periodic table. Y is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb, and more preferably Al, B, or P. When Y is Al, B, or P, the synthesis of the anionic compound becomes relatively easy, and manufacturing costs can be reduced. b, which represents the valence of the anion and the number of cations, is an integer from 1 to 3, and is preferably 1. If b is greater than 3, the salt of the anionic compound tends to be less soluble in the mixed organic solvent, which is undesirable. The constants m and n are values ​​related to the number of ligands and are determined by the type of M; m is an integer from 1 to 4, and n is an integer from 0 to 8. The constant q is 0 or 1. When q is 0, the chelate ring becomes a five-membered ring, and when q is 1, the chelate ring becomes a six-membered ring.

[0072] R c11 represents an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. These alkylene groups, halogenated alkylene groups, arylene groups, or halogenated arylene groups may contain substituents or heteroatoms in their structure. Specifically, instead of hydrogen atoms in these groups, halogen atoms, linear or cyclic alkyl groups, aryl groups, alkenyl groups, alkoxy groups, aryloxy groups, sulfonyl groups, amino groups, cyano groups, carbonyl groups, acyl groups, amide groups, or hydroxyl groups may be included as substituents. Furthermore, instead of carbon atoms in these groups, nitrogen atoms, sulfur atoms, or oxygen atoms may be introduced into the structure. Also, when q is 1 and m is 2 to 4, there are m R c11These components may be bonded together. An example of such a ligand is ethylenediaminetetraacetic acid.

[0073] R c12 This includes halogen atoms, C1-C10 alkyl groups, C1-C10 alkyl halides, C6-C20 aryl groups, C6-C20 aryl halides, or -Q 3 R c13 (Q 3 and R c13 This will be explained later.) R c12 In these alkyl groups, halogenated alkyl groups, aryl groups, or halogenated aryl groups, R 91 Similarly, the structure may contain substituents and heteroatoms, and when n is 2 to 8, there are n R c12 These may each be joined to form a ring. c12 As such, electron-withdrawing groups are preferred, and fluorine atoms are particularly preferred.

[0074] Q 1 Q 2 and Q 3 These are, independently, O, S, or NR. c14 This represents the ligands bonding to Y via these heteroatoms.

[0075] R c13 and R c14 Each of these independently represents a hydrogen atom, a C1-C10 alkyl group, a C1-C10 alkyl halide, a C6-C20 aryl group, or a C6-C20 aryl halide. These alkyl groups, alkyl halides, aryl groups, or aryl halides are R c11 Similarly, its structure may contain substituents and heteroatoms. Also, R c13 and R c14 If there are multiple such elements, they may combine to form a ring.

[0076] Examples of alkali metals represented by M include lithium, sodium, and potassium. Of these, lithium is particularly preferred. For n, an integer between 0 and 4 is preferable.

[0077] The compound represented by formula (C1) is more preferably at least one selected from the group consisting of the compound represented by formula (C1A), the compound represented by formula (C1B), the compound represented by formula (C1C), the compound represented by formula (C1D), and the compound represented by formula (C1E).

[0078] [ka]

[0079] In equations (C1A) to (C1E), M is the same as M in equation (C1), and the preferred embodiment is also the same.

[0080] The compound represented by formula (C1) is particularly preferably a compound represented by formula (C1A) in which M is lithium (more specifically, "BOB" described later), or a compound represented by formula (C1B) in which M is lithium (more specifically, "DFOB" described later).

[0081] (The compound represented by formula (C2)) In formula (C2), R c21 ~R c24 Each of these independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 3 carbon atoms, or a fluorinated hydrocarbon group having 1 to 3 carbon atoms. R c21 ~R c24 The number of carbon atoms in the hydrocarbon group having 1 to 3 carbon atoms, represented by , is preferably 1 or 2, and more preferably 1. R c21 ~R c24 The carbon number of the fluorinated hydrocarbon group having 1 to 3 carbon atoms, represented by , is preferably 1 or 2, and more preferably 1.

[0082] For specific examples of compounds represented by formula (C2), see, for example, paragraph 0029 of Japanese Patent Application Publication No. 2021-22525. The compound represented by formula (C2) is particularly preferably 1,3-propensultone (PRS).

[0083] (The compound represented by formula (C3)) In formula (C3), R c31 ~R c33 Each of these independently represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms, L c31 This represents a single bond or an oxygen atom (i.e., -O-). For preferred embodiments of the compound represented by formula (C3), see, for example, paragraphs 0064 to 0066 of Japanese Patent Application Publication No. 2017-091687 and paragraphs 0039 to 0049 of Japanese Patent Application Publication No. 2021-22525.

[0084] The following are specific examples of compounds represented by formula (C3), but the compounds represented by formula (C3) are not limited to these examples.

[0085] [ka]

[0086] (The compound represented by formula (C4)) In formula (C4), R c41 ~R c43 Each of these independently represents a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. For preferred embodiments of the compound represented by formula (C4), see, for example, paragraphs 0051 to 0057 of Japanese Patent Application Publication No. 2021-22525.

[0087] The following are specific examples of compounds represented by formula (C4), but compounds represented by formula (C4) are not limited to these examples.

[0088] [ka]

[0089] (The compound represented by formula (C5)) In formula (C5), R c51 R represents a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms. c52 n represents a hydrogen atom, a fluorine atom, a hydrocarbon group having 1 to 6 carbon atoms, or a fluorinated hydrocarbon group having 1 to 6 carbon atoms, and n represents an integer from 1 to 3. For preferred embodiments of the compound represented by formula (C5), see, for example, paragraphs 0058 to 0065 of Japanese Patent Application Publication No. 2021-22525.

[0090] The following are specific examples of compounds represented by formula (C5), but the compounds represented by formula (C5) are not limited to these examples.

[0091] [ka]

[0092] <Preferred content of additives A-C> The content of additive A is preferably 0.001% to 10% by mass, more preferably 0.003% to 5% by mass, even more preferably 0.03% to 3% by mass, even more preferably 0.1% to 3% by mass, even more preferably 0.2% to 3% by mass, and even more preferably 0.3% to 2% by mass, based on the total amount of the non-aqueous electrolyte.

[0093] The content of additive B is preferably 0.001% to 10% by mass, more preferably 0.003% to 5% by mass, even more preferably 0.003% to 3% by mass, even more preferably 0.03% to 3% by mass, even more preferably 0.1% to 3% by mass, and even more preferably 0.1% to 2% by mass, based on the total amount of the non-aqueous electrolyte.

[0094] The content of additive C is preferably 0.001% to 10% by mass, more preferably 0.003% to 5% by mass, even more preferably 0.003% to 3% by mass, even more preferably 0.03% to 3% by mass, even more preferably 0.1% to 3% by mass, and even more preferably 0.1% to 2% by mass, based on the total amount of the non-aqueous electrolyte.

[0095] In the non-aqueous electrolyte of this disclosure, from the viewpoint of more effectively achieving the effects of the non-aqueous electrolyte of this disclosure, the ratio of the content of additive A to the total content of additives A to C is preferably 0.3 or more, more preferably 0.4 or more, and even more preferably 0.5 or more. The ratio of the content of additive A to the total content of additives A to C should be less than 1.0, preferably 0.9 or less, and more preferably 0.8 or less.

[0096] In the non-aqueous electrolyte of the present disclosure, from the viewpoint of more effectively achieving the effects of the non-aqueous electrolyte of the present disclosure, the ratio of the content of additive B to the total content of additive B and additive C is preferably 0.1 to 0.9, more preferably 0.2 to 0.8, even more preferably 0.3 to 0.7, and even more preferably 0.4 to 0.6.

[0097] The non-aqueous electrolyte of this disclosure may contain other components besides those described above, as necessary.

[0098] [Lithium secondary battery precursor, lithium secondary battery] The lithium secondary battery precursor of this disclosure comprises a positive electrode, a negative electrode, and the non-aqueous electrolyte of this disclosure described above.

[0099] The lithium secondary battery of this disclosure is a lithium secondary battery obtained by subjecting the lithium secondary battery precursor of this disclosure to charging and discharging (hereinafter also referred to as "charging and discharging").

[0100] In this disclosure, a lithium secondary battery precursor means a lithium secondary battery that has been manufactured but has not undergone charging or discharging. In other words, in this disclosure, a lithium secondary battery means a battery in which a lithium secondary battery precursor has been subjected to charging and discharging.

[0101] The lithium secondary battery precursor of this disclosure includes the non-aqueous electrolyte of this disclosure as described above. Therefore, the lithium secondary battery precursor and the non-aqueous electrolyte of this disclosure produce the same effects as those described above for the non-aqueous electrolyte of this disclosure.

[0102] The following describes the various components that may be included in the lithium secondary battery precursor of this disclosure. Each component that may be included in the lithium secondary battery of this disclosure is essentially the same as each component that may be included in the lithium secondary battery precursor of this disclosure as described below. In the lithium secondary battery of this disclosure, a Solid Electrolyte Interface (SEI) film is preferably formed on the surface of the positive electrode (preferably the positive electrode active material) and / or the negative electrode (preferably the negative electrode active material). The SEI film is a coating that can be formed by charging and discharging the lithium secondary battery precursor. The SEI film contains components in the non-aqueous electrolyte and / or products derived from the above components (e.g., decomposition products).

[0103] <Negative electrode> The negative electrode preferably contains at least one negative electrode active material. The negative electrode active material preferably includes a carbon material capable of intercalating and releasing lithium ions. Including the above carbon material in the negative electrode active material improves the stability of the SEI film formed by charging and discharging. In particular, the above carbon material is advantageous in terms of SEI film stability because it undergoes less morphological change during charging and discharging compared to other negative electrode active materials (e.g., metallic Li, metallic Si, silicon oxide). The negative electrode active material may include both the carbon material and other negative electrode active materials (e.g., metallic Li, metallic Si, silicon oxide). From the viewpoint of suppressing morphological changes during charging and discharging and improving the energy density of the negative electrode, the negative electrode active material may include the carbon material and at least one of metallic Si and silicon oxide. In this case, the ratio of the total amount of metallic Si and silicon oxide to the total amount of carbon material, metallic Si, and silicon oxide may be 0.5% to 50% by mass, 1% to 20% by mass, or 2% to 20% by mass.

[0104] The combination of the carbon material as the negative electrode active material and the non-aqueous electrolyte of this disclosure described above improves the stability of the SEI film formed on the negative electrode, thereby more significantly enhancing the effects of improved storage and cycling properties described above.

[0105] Examples of carbon materials used as negative electrode active materials include hard carbon, soft carbon, MCMB, natural graphite, and artificial graphite. Natural graphite and artificial graphite may each be coated with amorphous carbon. Of these, natural graphite coated with hard carbon, MCMB, or amorphous carbon, or artificial graphite coated with amorphous carbon, is preferred because the SEI film formed on the negative electrode has high stability and high lithium ion storage capacity.

[0106] The negative electrode preferably includes a negative electrode current collector. There are no particular restrictions on the material of the negative electrode current collector; any known material can be used. Specific examples of negative electrode current collectors include metal materials such as copper, nickel, stainless steel, and nickel-plated steel. Among these, copper is particularly preferred due to its ease of processing.

[0107] The negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on at least a portion of the surface of the negative electrode current collector. The negative electrode active material layer contains at least one type of negative electrode active material. The negative electrode active material in the negative electrode active material layer contains the carbon material described above. The carbon material content in the negative electrode active material layer is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, relative to the total amount of the negative electrode active material layer, from the viewpoint of further improving the film formation properties on the negative electrode and further reducing the resistance of the battery in its initial state and / or after storage.

[0108] The negative electrode active material layer may further contain at least one binder. The binder is preferably at least one selected from the group consisting of styrene-butadiene (SBR) rubber (e.g., SBR latex), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, carboxymethylcellulose (CMC), hydroxypropylmethylcellulose, polyvinyl alcohol, hydroxypropylcellulose, and diacetylcellulose. The binder preferably contains SBR latex and carboxymethylcellulose. The binder content in the negative electrode active material layer is preferably 1% to 20% by mass, more preferably 1% to 10% by mass, and even more preferably 1% to 5% by mass, relative to the total amount of the negative electrode active material layer.

[0109] <Positive electrode> The positive electrode preferably contains at least one positive electrode active material. There are no particular limitations on the positive electrode active material; known positive electrode active materials can be used. Lithium transition metal oxides or metallic lithium phosphate are preferred as the positive electrode active material. Examples of lithium transition metal oxides include, Lithium cobalt oxide (LiCoO2) Lithium manganese oxide (LiMnO2 or LiMn2O4) Lithium nickel oxide (LiNiO2) Lithium nickel cobalt oxide, Lithium nickel manganese cobalt oxide (hereinafter also referred to as "NMC"), Lithium nickel cobalt aluminum oxide (hereinafter also referred to as "NCA"), These are some examples. Examples of metallic lithium phosphate include, Lithium iron phosphate (LiFePO4), Lithium manganese phosphate (LiMnPO4), Lithium iron manganese phosphate (LiMn (1-X) Fe X PO4;0 <X<1)、 These are some examples.

[0110] The positive electrode active material is selected from the viewpoint of achieving a more effective effect with the non-aqueous electrolyte of this disclosure. It is preferable that it contains a lithium transition metal oxide. It is more preferable to contain NMC. It is even more preferable that the compound is represented by the following formula (X).

[0111] LiRing a Mn b Co c O2… (X) [In equation (X), a, b, and c are each independently greater than 0 and less than 1.00, and the sum of a, b, and c is between 0.99 and 1.00.]

[0112] A specific example of a compound represented by formula (X) is, for example, LiNi 0.33 Mn 0.33 Co 0.33 O2, LiLiLi 0.5 Mn 0.2 Co 0.3 O2, LiLiLi 0.5 Mn 0.3 Co 0.2 Examples include O2.

[0113] In formula (X), a is preferably 0.20 or greater, more preferably 0.30 or greater, even more preferably 0.40 or greater, even more preferably 0.50 or greater, and even more preferably 0.70 or greater. A larger value of 'a' (i.e., a higher Ni content) is advantageous because it increases the battery's capacity (energy density). On the other hand, generally speaking, the larger a is (i.e., the higher the Ni content), the lower the high-temperature storage characteristics and high-temperature cycling characteristics may be. However, when using the non-aqueous electrolyte of this disclosure, the combined effect of additives A, B, and C suppresses the deterioration of high-temperature storage characteristics and high-temperature cycling characteristics, even when a is large (for example, 0.40 or more).

[0114] In formula (X), a is preferably 0.95 or less, and more preferably 0.90 or less. In formula (X), b is preferably 0.05 or greater, and more preferably 0.10 or greater. In formula (X), b is preferably 0.90 or less, more preferably 0.50 or less, and even more preferably 0.40 or less. In formula (X), c is preferably 0.05 or greater, and more preferably 0.10 or greater. In formula (X), c is preferably 0.90 or less, more preferably 0.50 or less, and even more preferably 0.40 or less.

[0115] The positive electrode active material preferably contains a single crystal of the compound represented by formula (X). A single crystal of the compound represented by formula (X) as a positive electrode active material has a smaller surface area compared to a polycrystalline compound represented by formula (X) as a positive electrode active material. Therefore, the effects of using the above single crystal are expected to include suppressing the oxidative decomposition reaction of the non-aqueous electrolyte on the electrode surface, as well as improving the high-temperature storage characteristics and high-temperature cycle characteristics of the battery. On the other hand, when a single crystal of the compound represented by formula (X) is used as the positive electrode active material, the battery resistance may increase compared to when a polycrystalline compound represented by formula (X) is used. However, when the non-aqueous electrolyte of this disclosure is used, the combined effect of additives A, B, and C suppresses the increase in battery resistance, even when a single crystal of the compound represented by formula (X) is used as the positive electrode active material. The distinction between a single crystal of the compound represented by formula (X) and a polycrystalline compound represented by formula (X) can be made by X-ray structural analysis.

[0116] The positive electrode may contain at least one conductive additive. Examples of conductive additives include carbon materials such as carbon black, amorphous whiskers, and graphite.

[0117] The positive electrode preferably includes a positive electrode current collector. There are no particular restrictions on the material of the positive electrode current collector; any known material can be used. Specific examples of positive electrode current collectors include metallic materials such as aluminum, aluminum alloys, stainless steel, nickel, titanium, and tantalum; and carbon materials such as carbon cloth and carbon paper.

[0118] The positive electrode may include a positive electrode current collector and a positive electrode active material layer provided on at least a portion of the surface of the positive electrode current collector. The positive electrode active material layer contains at least one positive electrode active material. Preferred positive electrode active materials are as described above. The content of the positive electrode active material in the positive electrode active material layer is preferably 70% by mass or more, and more preferably 80% by mass or more, relative to the total amount of the positive electrode active material layer. The positive electrode active material layer may further contain at least one of the above-mentioned conductive additives. The positive electrode active material layer may further contain at least one binder. Examples of binders include polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesins, and rubber particles. Examples of fluororesins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles. Among these, fluororesins are preferred from the viewpoint of improving the oxidation resistance of the positive electrode active material layer. The binder content in the positive electrode active material layer is preferably 1% to 20% by mass, and more preferably 1% to 10% by mass, relative to the total amount of the positive electrode active material layer.

[0119] <Separator> The lithium secondary battery precursor of this disclosure preferably includes a separator between the negative electrode and the positive electrode. The separator is a membrane that electrically insulates the positive electrode and the negative electrode and is permeable to lithium ions, and examples include porous membranes and polymer electrolytes. Microporous polymer films are preferably used as porous membranes, and examples of materials include polyolefins, polyimides, polyvinylidene fluoride, and polyester. In particular, porous polyolefins are preferred, and specific examples include porous polyethylene films, porous polypropylene films, or multilayer films of porous polyethylene films and polypropylene films. The porous polyolefin film may be coated with other resins that have excellent thermal stability. Examples of polymer electrolytes include polymers in which lithium salts have been dissolved, and polymers swollen with an electrolyte solution. The non-aqueous electrolyte of this disclosure may be used for the purpose of swelling a polymer to obtain a polymer electrolyte.

[0120] <Composition of lithium secondary battery precursor> The lithium secondary battery precursor of this disclosure can take on various known shapes, and can be formed into cylindrical, coin-shaped, prismatic, laminated, film-shaped, or any other shape. However, the basic structure of the lithium secondary battery precursor is the same regardless of the shape, and the design can be modified according to the purpose. Furthermore, the basic structure of the lithium secondary battery described herein can also be referenced to the basic structure of the lithium secondary battery precursor described herein.

[0121] Examples of lithium secondary battery precursors or lithium secondary batteries of the present disclosure include laminated batteries. Figure 1 is a schematic perspective view showing an example of a laminated battery, which is an example of a lithium secondary battery precursor or lithium secondary battery of the present disclosure, and Figure 2 is a schematic cross-sectional view in the thickness direction of the stacked electrode body housed in the laminated battery shown in Figure 1. The laminated battery shown in Figure 1 comprises a laminated casing 1 that houses a non-aqueous electrolyte (not shown in Figure 1) and a stacked electrode body (not shown in Figure 1), and whose periphery is sealed to create an internally enclosed structure. For example, an aluminum laminated casing 1 may be used. The laminated electrode body housed in the laminated outer casing 1 comprises, as shown in Figure 2, a laminate in which positive electrode plates 5 and negative electrode plates 6 are alternately stacked with separators 7 in between, and a separator 8 surrounding this laminate. The positive electrode plate 5, negative electrode plate 6, separator 7, and separator 8 are impregnated with the non-aqueous electrolyte of this disclosure. In the above-described laminated electrode body, each of the multiple positive electrode plates 5 is electrically connected to a positive electrode terminal 2 via a positive electrode tab (not shown), and a portion of this positive electrode terminal 2 protrudes outward from the peripheral edge of the laminated casing 1 (Figure 1). The portion of the peripheral edge of the laminated casing 1 from which the positive electrode terminal 2 protrudes is sealed by an insulating seal 4. Similarly, each of the plurality of negative electrode plates 6 in the laminated electrode assembly is electrically connected to the negative electrode terminal 3 via a negative electrode tab (not shown), and a part of this negative electrode terminal 3 protrudes outward from the peripheral end portion of the laminate outer package 1 (Figure 1). The portion where the negative electrode terminal 3 protrudes at the peripheral end portion of the laminate outer package 1 is sealed by an insulating seal 4. Incidentally, in the laminate type battery according to the above example, the number of positive electrode plates 5 is 5, and the number of negative electrode plates 6 is 6, and the positive electrode plates 5 and the negative electrode plates 6 are laminated with the separator 7 interposed therebetween in an arrangement where the outermost layers on both sides are all the negative electrode plates 6. However, it goes without saying that the number of positive electrode plates, the number of negative electrode plates, and the arrangement in the laminate type battery are not limited to this example, and various modifications may be made.

[0122] As another example of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure, a coin-type battery may be mentioned. Figure 3 is a schematic perspective view showing an example of a coin-type battery which is another example of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure. In the coin-type battery shown in Figure 3, a disc-shaped negative electrode 12, a separator 15 injected with a non-aqueous electrolyte, a disc-shaped positive electrode 11, and optionally spacer plates 17, 18 made of stainless steel, aluminum or the like are accommodated in this sequentially laminated state between a positive electrode can 13 (hereinafter also referred to as "battery can") and a sealing plate 14 (hereinafter also referred to as "battery can lid"). The positive electrode can 13 and the sealing plate 14 are caulked and sealed via a gasket 16. In this example, the non-aqueous electrolyte of the present disclosure is used as the non-aqueous electrolyte injected into the separator 15.

[0123] In the lithium secondary battery of the present disclosure, the operating potential of the positive electrode is not particularly limited. In the lithium secondary battery of the present disclosure, the operating potential of the positive electrode preferably exceeds 4.30 V with reference to the standard oxidation-reduction potential of Li metal. It is advantageous in terms of the output and capacity of the battery that the operating potential of the positive electrode exceeds 4.30 V with reference to the standard oxidation-reduction potential of Li metal. On the other hand, in general, when the operating potential of the positive electrode exceeds 4.30 V with reference to the standard oxidation-reduction potential of lithium metal, the oxidative decomposition activity on the electrode surface increases, which may lead to an increase in battery resistance. However, when the non-aqueous electrolyte of the present disclosure is used, the combined effect of the combination of Additive A, Additive B, and Additive C suppresses an increase in battery resistance even when the operating potential of the positive electrode exceeds 4.30 V with reference to the standard oxidation-reduction potential of lithium metal.

[0124] The application of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure is not particularly limited, and can be widely used regardless of small portable devices or large-scale devices. Examples of applications of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure include notebook personal computers, mobile personal computers, mobile phones, headphone stereos, video movies, liquid crystal televisions, handy cleaners, electronic organizers, calculators, radios, backup power supplies, power storage power sources (e.g., power sources for storing nighttime electricity, power sources for storing surplus power from solar power generation, etc.), motors, automobiles, electric vehicles, hybrid vehicles, motorcycles, electric motorcycles, bicycles, electric bicycles, lighting fixtures, game machines, watches, electric tools, cameras, and the like.

[0125] [Method for Producing Lithium Secondary Battery] The method for producing a lithium secondary battery of the present disclosure includes: a step of preparing the above-described lithium secondary battery precursor of the present disclosure (hereinafter also referred to as "preparation step"), and a step of subjecting the lithium secondary battery precursor to charging and discharging.

[0126] The preparation step may be a step of merely preparing the pre-produced lithium secondary battery precursor of the present disclosure to be supplied to the step of performing charging and discharging, or may be a step of producing the lithium secondary battery precursor of the present disclosure. The lithium secondary battery precursor is as described above.

[0127] ​In the charging and discharging process, the charging and discharging of the lithium secondary battery precursor can be carried out according to known methods. In this process, the lithium secondary battery precursor may undergo multiple charging and discharging cycles. As described above, this charging and discharging process preferably forms an SEI film on the surface of the positive electrode (particularly the positive electrode active material) and / or the negative electrode (particularly the negative electrode active material) of the lithium secondary battery precursor. [Examples]

[0128] The following are examples of the present disclosure, but the present disclosure is not limited to these examples. In the following examples, "amount added" refers to the content relative to the total amount of the final non-aqueous electrolyte. Furthermore, unless otherwise specified, the "%" symbol used to indicate quantity refers to mass percentage.

[0129] [Examples 1-1 to 1-7, 2-1 to 2-7, and 3-1 to 3-7, and Comparative Examples 1-1 to 1-5, 2-1 to 2-5, and 3-1 to 3-5] Following the procedure below, NMC polycrystalline cathode batteries and NMC monocrystalline cathode batteries were fabricated as test batteries, which are lithium-ion secondary batteries.

[0130] <Fabrication of the negative electrode sheet> A paste-like anode mixture slurry was prepared by kneading artificial graphite (97 parts by mass) as the anode active material, carboxymethylcellulose (1 part by mass) as a thickener, and SBR latex (2 parts by mass) as a binder with an aqueous solvent. Next, this negative electrode mixture slurry was applied to one side of a negative electrode current collector, which was a strip of copper foil 10 μm thick, dried, and then compressed with a roll press. Based on the above, a negative electrode sheet (hereinafter also referred to as a "graphite negative electrode sheet") was obtained, having a structure in which a negative electrode active material layer is arranged on one side of the negative electrode current collector. Table 1 shows the coating density of the negative electrode active material layer and the packing density of the negative electrode active material in the graphite negative electrode sheet.

[0131] <Fabrication of the positive electrode sheet> As cathode sheets, NMC polycrystalline cathode sheets and NMC single-crystal sheets were fabricated, respectively.

[0132] (Fabrication of NMC polycrystalline cathode sheets) Lithium nickel manganese cobalt oxide (specifically, LiNi) as a positive electrode active material. 0.5 Mn 0.3 Co 0.2 A paste-like cathode mixture slurry was prepared by kneading polycrystalline O2 (90 parts by mass), acetylene black (5 parts by mass) as a conductive additive, and polyvinylidene fluoride (5 parts by mass) as a binder with N-methylpyrrolidinone as the solvent. Here, Li Limited 0.5 Mn 0.3 Co 0.2 As for polycrystalline O2, LiNi has a number-average particle size of 0.5 μm. 0.5 Mn 0.3 Co 0.2 A polycrystalline material with a structure in which primary O2 particles are aggregated was used. Next, this positive electrode mixture slurry was applied to both sides of the positive electrode current collector, which was a strip of aluminum foil 20 μm thick, dried, and then compressed with a roll press. Based on the above, an NMC polycrystalline positive electrode sheet was obtained, having a structure in which NMC polycrystalline positive electrode active material layers are arranged on both sides of the positive electrode current collector. Table 1 shows the coating density of the positive electrode active material layer and the packing density of the positive electrode active material on one side of the NMC polycrystalline positive electrode sheet.

[0133] (Fabrication of NMC single-crystal cathode sheets) LiRing 0.5 Mn 0.3 Co 0.2 A polycrystalline O2, with the same mass of LiNi 0.5 Mn 0.3 Co 0.2 The NMC single-crystal cathode sheet was fabricated in the same manner as the NMC polycrystalline cathode sheet, except that the material was changed to O2 single crystal. Table 1 shows the coating density of the positive electrode active material layer and the packing density of the positive electrode active material on one side of the NMC single crystal positive electrode sheet.

[0134] [Table 1]

[0135] <Preparation of Non-Aqueous Electrolyte> Each non-aqueous electrolyte having the composition shown in Table 2 below was prepared. The amount (%) of each component in the composition means the content (% by mass) relative to the total amount of the finally obtained non-aqueous electrolyte.

[0136] [Table 2]

[0137] -Description of Base Electrolytes in Table 2- Base electrolytes A and B each mean an electrolyte having the following composition composed of a non-aqueous solvent and an electrolyte. Base electrolyte A: LiPF6 / EC / EMC=14 / 28 / 58 (% by mass) Base electrolyte B: LiPF6 / LiFSI / EC / EMC=10 / 5 / 28 / 57 (% by mass) Here, LiPF6, LiFSI, EC, and EMC are respectively lithium hexafluorophosphate as an electrolyte, lithium bis(fluorosulfonyl)imide as an electrolyte which is a specific example of the compound represented by formula (D1), ethylene carbonate as a non-aqueous solvent, and ethyl methyl carbonate as a non-aqueous solvent . Each non-aqueous electrolyte is obtained by adding each additive of the type and content (% by mass) shown in Table 2 to base electrolyte A or B. The amount (%) of the additive means the content (% by mass) relative to the total amount of the finally obtained non-aqueous electrolyte.

[0138] -Description of Additives in Table 2- (A-1) and (A-2) are the following compounds (A-1) and (A-2), which are specific examples of additive A (more specifically, cyclic sulfate esters represented by formula (A)). DTD is the following compound, which is a specific example of additive B (more specifically, the compound represented by formula (B3)). VC is the following compound, which is a specific example of additive B (more specifically, the compound represented by formula (B1)). FEC is the following compound, which is a specific example of additive B (more specifically, the compound represented by formula (B2)). DFP is the following compound, which is additive C (specifically, the compound represented by formula (C7)). DFOB and BOB are the following compounds, which are specific examples of additive C (more specifically, compounds represented by formula (C1)), respectively. TMSB is a specific example of additive C, which is the following compound (tris(trimethylsilyl) borate).

[0139] [ka]

[0140] <Preparation of test batteries> Using a negative electrode sheet, a positive electrode sheet, and a non-aqueous electrolyte, test batteries (i.e., NMC polycrystalline positive electrode batteries and NMC monocrystalline positive electrode batteries), which are lithium-ion secondary batteries, were fabricated as follows.

[0141] (Preparation of test battery precursors (i.e., test batteries before charging and discharging)) The aforementioned negative electrode sheet was punched out into a rectangle measuring 53 mm vertically x 37 mm horizontally, leaving uncoated copper foil at the edges, to obtain a strip-shaped negative electrode. A negative electrode tab was ultrasonically welded to the uncoated copper foil portion of the obtained negative electrode. An adhesive resin layer was placed in the middle of this negative electrode tab. Furthermore, the aforementioned positive electrode sheet was punched out into a rectangle measuring 52 mm vertically x 36.5 mm horizontally, leaving uncoated aluminum foil at the edges, to obtain a strip-shaped positive electrode. A positive electrode tab was ultrasonically welded to the uncoated aluminum foil portion of the obtained positive electrode. An adhesive resin layer was also placed in the middle of this positive electrode tab. Furthermore, a 20 μm thick microporous polyethylene film was cut into a rectangle measuring 55 mm in length and 185 mm in width to obtain a separator for separating the positive and negative electrodes.

[0142] Next, (1) a negative electrode (coated on one side), (2) a separator, (3) a positive electrode (coated on both sides), (4) a separator (Note: the separator from (2) is folded and overlapped), and (5) a negative electrode (coated on one side) were stacked in this order to obtain a laminate. Next, the excess portion of the separator was used to wrap around the outer circumference of the laminate, and then the ends of the separators were fixed together with Kapton tape to obtain an integrated electrode including the negative electrode, separator, and positive electrode. Next, this integrated electrode was placed inside a rectangular cylindrical bag made of an aluminum laminate film sheet for battery casing, with the positive electrode tab and negative electrode tab protruding from one end of the cylindrical bag. In this state, the one end was heat-sealed to close the bag, and an empty battery was obtained. Next, 0.5 mL of non-aqueous electrolyte was injected into the empty battery at 85°C, then the inside of the empty battery was depressurized to 0.10 atmospheres for 5 seconds, and then the remaining end (i.e., the other end of the cylindrical bag) was heat-sealed. Based on the above, a film-type test battery precursor (i.e., a test battery before charging and discharging) with dimensions of 95 mm in length and 65 mm in width was obtained.

[0143] (Preparation of test batteries (charging and discharging)) The following charge and discharge processes were applied to the test battery precursors to complete film-type test batteries (i.e., NMC polycrystalline cathode batteries and NMC monocrystalline cathode batteries).

[0144] - Preparation of test batteries (charging and discharging) - (1) Charge the battery with a constant current of 0.05C until the battery voltage reaches 3.7V. (2) Let it stand for 6 hours. (3) Charge the battery with a constant current of 0.5C until the battery voltage reaches 4.20V. (4) Charge at a constant voltage of 4.20V until the current reaches 0.05C. (5) Discharge with a constant current of 0.5C until the voltage reaches 3.0V. (6) Repeat the charging and discharging operations in (3) to (5) twice.

[0145] <Evaluation of test batteries> The following evaluations were performed on the film-type test batteries obtained above. The results are shown in Table 3.

[0146] (DCIR (direct current resistance)) The DCIR (direct current resistance) of the test battery was measured as follows. The test battery was charged and adjusted to a state of charge (SOC) of 50%. Then, it was discharged at 25°C for 10 seconds, and the DCIR was measured from the voltage change during this time. DCIR was measured at discharge currents corresponding to 0.2C, 0.5C, 1.0C, and 2.0C, and the arithmetic mean of the four obtained measurements was determined as the DCIR of the test battery (hereinafter also referred to as "DCIR before high-temperature storage," "DCIR before high-temperature cycling," or "initial DCIR").

[0147] (High temperature storage characteristics) For the test batteries, in order to evaluate their high-temperature storage characteristics, the capacity retention rate (hereinafter also simply referred to as "retention rate") and capacity recovery rate (hereinafter also simply referred to as "recovery rate") after high-temperature storage, as well as the resistance increase rate during high-temperature storage, were measured as follows. In the following operation, the upper limit charging voltage was set to two conditions: 4.20V (normal voltage) and 4.35V (high voltage). Since the operating potential of the graphite negative electrode relative to the standard oxidation-reduction potential of Li metal is 0.10V, the operating potentials of the positive electrode relative to the standard oxidation-reduction potential of Li metal are 4.30V (normal potential) and 4.45V (high potential), respectively, under the above two conditions.

[0148] The test batteries were charged and adjusted to a state of charge (SOC) of 100%, then stored at 70°C for 10 days. Hereafter, this 10-day storage at 70°C will be referred to as high-temperature storage. For the test batteries after high-temperature storage, the remaining battery capacity after discharge at 1C (hereinafter also referred to as "1C remaining capacity after high-temperature storage") and the battery capacity recovered after recharging at 1C after this discharge (hereinafter also referred to as "1C recovered capacity after high-temperature storage") were measured. Based on the obtained 1C remaining capacity and 1C recovery capacity, and the discharge capacity at 1C before high-temperature storage (hereinafter also referred to as "1C capacity before high-temperature storage"), the remaining rate and recovery rate after high-temperature storage were calculated using the following formula. Subsequently, the SOC was adjusted to 50%, and the DCIR after high-temperature storage was measured in the same manner as before high-temperature storage. Based on the DCIR before and after high-temperature storage, the resistance increase rate during high-temperature storage was calculated using the following formula.

[0149] Survival rate after high-temperature storage = (Remaining 1C volume after high-temperature storage / 1C volume before high-temperature storage) × 100 (%) Recovery rate after high-temperature storage = (1C recovery capacity after high-temperature storage / 1C capacity before high-temperature storage) × 100 (%) Resistivity increase rate during high-temperature storage = (DCIR after high-temperature storage (25°C) / DCIR before high-temperature storage (25°C)) × 100 (%)

[0150] (High-temperature cycle characteristics) For the test batteries, the maintenance rate after high-temperature cycling and the resistance increase rate during high-temperature cycling were determined as follows to evaluate their high-temperature cycling characteristics. In the following operation, the upper limit charging voltage was set to two conditions: 4.20V (normal voltage) and 4.35V (high voltage). Under these two conditions, the operating potential of the positive electrode, based on the standard oxidation-reduction potential of Li metal, was 4.30V (normal potential) and 4.45V (high potential), respectively.

[0151] The test batteries underwent the following high-temperature cycling test at 55°C. The discharge capacity at 1C (hereinafter also referred to as 1C capacity) of the test batteries was measured before and after this high-temperature cycling test. The retention rate after the high-temperature cycling was calculated from the obtained 1C capacity based on the following formula. Subsequently, the SOC was adjusted to 50%, and the DCIR after the high-temperature cycle was measured in the same manner as before the high-temperature cycle. Based on the DCIR before and after the high-temperature cycle, the resistance increase rate during the high-temperature cycle was calculated using the following formula.

[0152] Maintenance rate after high-temperature cycling = (1C capacity after high-temperature cycling test / 1C capacity before high-temperature cycling test) × 100 (%) Resistance increase rate during high-temperature cycling = (DCIR after high-temperature cycling (25°C) / DCIR before high-temperature cycling (25°C)) × 100 (%)

[0153] -High-temperature cycling test- (1) Charge the battery with a constant current of 1C until the battery voltage reaches the upper limit of the charge. (2) Charge at a constant voltage, which is the upper limit voltage for charging, until the current reaches 0.05C. (3) Discharge the battery with a constant current of 1C until the battery voltage reaches 3.0V. (4) The charging and discharging process described in (1) to (3) constitutes one cycle, and this charging and discharging process was repeated 300 times.

[0154] [Table 3]

[0155] As can be seen from the results in Table 3, the batteries in each example using a non-aqueous electrolyte containing all of additives A, B, and C have a reduced DCIR and superior high-temperature storage characteristics and high-temperature cycling characteristics compared to the batteries in each comparative example using a non-aqueous electrolyte containing only one or two of additives A, B, and C.

[0156] In general, when NMC polycrystalline material is used as the positive electrode active material, increasing the upper charge limit voltage from 4.20V to 4.35V tends to decrease the retention rate and recovery rate (see the comparison between Comparative Examples 1-1 to 1-5 and Comparative Examples 2-1 to 2-5 for specific details). In contrast to this trend, Examples 2-1 to 2-7, which use a non-aqueous electrolyte containing all of additives A, B, and C, show suppressed decreases in retention rate and recovery rate, as well as increases in resistance (see the comparison between Examples 1-1 to 1-7 and Examples 2-1 to 2-7 for specific details). Furthermore, when the charging upper limit voltage is 4.35V, changing from NMC polycrystalline to NMC monocrystalline improves the overall capacity retention rate, but tends to increase DCIR (i.e., initial DCIR) and the resistance increase rate (see the comparison between Comparative Examples 2-1 to 2-5 and Comparative Examples 3-1 to 3-5 for specifics). In contrast to this trend, it can be seen that the increase in DCIR and the resistance increase rate is suppressed when the non-aqueous electrolyte of the examples is used (see the comparison between Examples 2-1 to 2-7 and Examples 3-1 to 3-7 for specifics). From the above, it can be seen that the effects of the non-aqueous electrolyte of this disclosure are more effectively realized when the upper limit charging voltage exceeds 4.20V (i.e., when the operating potential of the positive electrode, based on the standard oxidation-reduction potential of Li metal, exceeds 4.30V), and when an NMC single crystal is used as the NMC active material of the positive electrode. [Explanation of Symbols]

[0157] 1. Laminated outer casing 2 Positive terminals 3 Negative terminal 4. Insulating seal 5 Positive plate 6. Negative plate 7, 8 Separators 11 Positive electrode 12 Negative electrode 13 Positive electrode can 14 Sealing plate 15 Separators 16 Gaskets 17, 18 Spacer plate

Claims

1. An electrolyte containing a fluorine-containing lithium salt, Non-aqueous solvents and Additive A is a compound represented by the following formula (A), Additive B is at least one compound selected from the group consisting of compounds represented by the following formulas (B1) to (B2), Additive C is at least one selected from the group consisting of the compound represented by the following formula (C7) and tris(trimethylsilyl) borate, It contains, The ratio of the content of additive A to the total content of additives A to C is 0.5 or more. Non-aqueous electrolyte for batteries. 【Chemistry 1】 [In formula (A), R １ R represents the group shown in formula (III), ２ This represents a hydrogen atom. In formula (B1), R ｂ１１ and R ｂ１２ Each of these independently represents a hydrogen atom, a methyl group, an ethyl group, or a propyl group. In formula (B2), R ｂ２１ ~R ｂ２４ Each of these independently represents a C1-C3 alkyl group which may be substituted with a fluorine atom, a hydrogen atom, a fluorine atom, or a chlorine atom. However, R in formula (B2) ｂ２１ ~R ｂ２４ Not all of them are hydrogen atoms.

2. An electrolyte containing a fluorine-containing lithium salt, Non-aqueous solvents and Additive A is a compound represented by the following formula (A), Additive B is at least one compound selected from the group consisting of compounds represented by the following formulas (B1) to (B2), Additive C is a compound represented by the following formula (C1), It contains, The ratio of the content of additive A to the total content of additives A to C is 0.5 or more. Non-aqueous electrolyte for batteries. 【Chemistry 2】 In formula (A), R １ represents a group represented by formula (III), and R ２ represents a hydrogen atom. In formula (B1), R ｂ１１ and R ｂ１２ Each of these independently represents a hydrogen atom, a methyl group, an ethyl group, or a propyl group. In formula (B2), R ｂ２１ ~R ｂ２４ Each of these independently represents a C1-C3 alkyl group which may be substituted with a fluorine atom, a hydrogen atom, a fluorine atom, or a chlorine atom. However, R in formula (B2) ｂ２１ ~R ｂ２４ Not all of them are hydrogen atoms. In formula (C1), M represents an alkali metal, Y represents a transition element or an element from group 13, 14, or 15 of the periodic table, b represents an integer from 1 to 3, m represents an integer from 1 to 4, n represents an integer from 0 to 8, and q represents 0 or 1. In formula (C1), R ｃ１１ This is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain substituents or heteroatoms in their structure, and when q is 1 and m is 2 to 4, there are m R ｃ１１ Each of these may be joined together.) Represents R ｃ１２ This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, and C6-C20 halogenated aryl groups (these groups may contain substituents or heteroatoms in their structure, and when n is 2-8, there are n R ｃ１２ They may each be joined together to form a ring. ), or -Q ３ R ｃ１３ This represents Q. In equation (C1), １ Q ２ and Q ３ These are, independently, O, S, or NR ｃ１４ Represents R ｃ１３ and R ｃ１４ Each of these independently comprises a hydrogen atom, a C1-C10 alkyl group, a C1-C10 alkyl halide, a C6-C20 aryl group, or a C6-C20 aryl halide (these groups may contain substituents or heteroatoms in their structure, R ｃ１３ or R ｃ１４ If multiple instances exist, they may combine to form a ring.

3. The non-aqueous electrolyte for a battery according to claim 1 or claim 2, wherein the fluorine-containing lithium salt comprises lithium hexafluoride phosphate and a compound represented by the following formula (D1). 【Transformation 3】 [In formula (D1), R ｄ１１ and R ｄ１２ Each of these independently represents either a fluorine atom or a fluorinated hydrocarbon group having 1 to 6 carbon atoms.

4. Positive electrode and, The negative electrode and, A non-aqueous electrolyte for a battery according to any one of claims 1 to 3, A lithium secondary battery precursor, including...

5. The lithium secondary battery precursor according to claim 4, wherein the positive electrode comprises a positive electrode active material containing a compound represented by the following formula (X). L)) ａ Mn ｂ Co ｃ O ２ … (X) [In equation (X), a, b, and c are each independently greater than 0 and less than 1.00, and the sum of a, b, and c is between 0.99 and 1.00.]

6. The lithium secondary battery precursor according to claim 5, wherein the positive electrode active material contains a single crystal of the compound represented by formula (X).

7. A lithium secondary battery obtained by charging and discharging a lithium secondary battery precursor according to any one of claims 4 to 6.

8. The lithium secondary battery according to claim 7, wherein the operating potential of the positive electrode exceeds 4.30 V, based on the standard oxidation-reduction potential of Li metal.

9. A step of preparing a lithium secondary battery precursor according to any one of claims 4 to 6, The lithium secondary battery precursor is subjected to a charging and discharging process, A method for manufacturing lithium secondary batteries, including [the specified component].

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