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

Abstract

To provide a nonaqueous electrolyte for a lithium secondary battery, capable of reducing a normal temperature resistance increasing rate when a lithium secondary battery is stored at high temperatures.SOLUTION: A nonaqueous electrolyte for a lithium secondary battery contains a compound (I) represented by formula (I), a compound (II) of lithium monofluorophosphate and / or lithium difluorophosphate, and a compound (III) represented by formula (III). In the formulae (I) and (III), L represents a single bond or an oxygen atom, R represents a hydrocarbon group that may be substituted with a halogen atom, or the like, M represents an alkali metal, Y represents a transition element or a group 13-15 element, b represents 1-3, m represents 1-4, n represents 0-8, q represents 0 or 1, R31 and R32 each independently represent a coupling group, and Q1 and Q2 each independently represent S or C.SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a non-aqueous electrolyte for a lithium secondary battery, a lithium secondary battery precursor, a lithium secondary battery, and a method for manufacturing a lithium secondary battery.

Background Art

[0002] In recent years, various studies have been made on lithium secondary batteries. For example, in Example 1 of Patent Document 1, a non-aqueous electrolyte for a battery containing lithium trifluoromethanesulfonate (TFMSLi), lithium difluorophosphate (LiDFP), and lithium bis(oxalato)borate (LiBOB) is disclosed. This Patent Document 1 also discloses that the resistance of the lithium secondary battery at -10°C after storage was reduced by the non-aqueous electrolyte for a battery of Example 1.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, there are cases where it is required to further reduce the increase rate of the normal temperature resistance of a lithium secondary battery when the lithium secondary battery is stored at a high temperature (hereinafter, also referred to as "the increase rate of the normal temperature resistance of the lithium secondary battery during high temperature storage"). An object of one aspect of the present disclosure is to provide a non-aqueous electrolyte for a battery, a lithium secondary battery precursor, a lithium secondary battery, and a method for manufacturing a lithium secondary battery that can reduce the increase rate of the normal temperature resistance of the lithium secondary battery during high temperature storage.

Means for Solving the Problems

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

[0006] <1> Compound (I) represented by the following formula (I), a compound (II) which is at least one of lithium monofluorophosphate and lithium difluorophosphate, compound (III) represented by the following formula (III), A non-aqueous electrolyte for a lithium secondary battery containing the same.

[0007]

Chemical formula

[0008] In formula (I), L is a single bond or an oxygen atom, R is a hydrocarbon group having 1 to 10 carbon atoms which may be substituted with a halogen atom, or a group having a structure in which at least one of the carbon atoms in the hydrocarbon group is replaced by an oxygen atom, a nitrogen atom, a sulfur atom, or a sulfonyl group. In formula (III), M is an alkali metal, Y is a transition element, a Group 13 element, a Group 14 element, or a Group 15 element of the periodic table, b is an integer of 1 to 3, m is an integer of 1 to 4, n is an integer of 0 to 8, [[ID=3,8]] q is 0 or 1, R 31 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 the structure, and when q is 1 and m is 2 to 4, m R 31 may be bonded to each other.), R 32This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, or 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 32 They may each be joined together to form a ring. Q 1 and Q 2 Each of these is independently either an oxygen atom or a carbon atom.

[0009] <2> In the above formula (I), L is a single bond. <1> Non-aqueous electrolyte for lithium secondary batteries as described above. <3> In formula (I) above, L is an oxygen atom. <1> Non-aqueous electrolyte for lithium secondary batteries as described above. <4> The content of compound (I) is 0.01% by mass or more and 5.0% by mass or less, relative to the total amount of the non-aqueous electrolyte for the battery. <1> ~ <3> A non-aqueous electrolyte for lithium secondary batteries as described in any one of the following. <5> The content of compound (II) is 0.01% by mass or more and 5.0% by mass or less, relative to the total amount of the non-aqueous electrolyte for the battery. <1> ~ <4> A non-aqueous electrolyte for lithium secondary batteries as described in any one of the following. <6> The content of compound (III) is 0.01% by mass or more and 5.0% by mass or less, relative to the total amount of the non-aqueous electrolyte for the battery. <1> ~ <5> A non-aqueous electrolyte for lithium secondary batteries as described in any one of the following. <7> The case and The case contains a positive electrode, a negative electrode, a separator, and an electrolyte, Equipped with, The positive electrode is a positive electrode capable of intercalating and releasing lithium ions. The aforementioned negative electrode is a negative electrode capable of intercalating and releasing lithium ions. The aforementioned electrolyte, <1> ~ <6> A lithium secondary battery precursor, which is a non-aqueous electrolyte as described in any one of the following. <8> The positive electrode contains a lithium-containing composite oxide represented by the following formula (P1) as the positive electrode active material. <7> A lithium secondary battery precursor as described above. LiRinga Co b Mn c O2… Formula (P1) 〔In formula (P1), a, b, and c are each independently greater than 0 and less than 1, and the sum of a, b, and c is 0.99 or more and 1.00 or less.〕 <9> A step of preparing the lithium secondary battery precursor according to <7> or <8>, A step of charging and discharging the lithium secondary battery precursor A method for manufacturing a lithium secondary battery, comprising: <10> A lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor according to <7> or <8>.

Advantages of the Invention

[0010] According to the present disclosure, there are provided a non-aqueous electrolyte for a battery, a lithium secondary battery precursor, a lithium secondary battery, and a method for manufacturing a lithium secondary battery, which can reduce the rate of increase in normal temperature resistance during high-temperature storage of the lithium secondary battery.

Brief Description of the Drawings

[0011] [Figure 1] It is a schematic cross-sectional view showing a laminate-type battery which is an example of the lithium secondary battery precursor of the present disclosure. [Figure 2] It is a schematic cross-sectional view showing a coin-type battery which is another example of the lithium secondary battery precursor of the present disclosure.

Modes for Carrying Out the Invention

[0012] In this specification, a numerical range represented by "~" means a range including the numerical values described before and after "~" as the lower limit value and the upper limit value. In this specification, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. In 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.

[0013] [Nonaqueous electrolyte for batteries] The non-aqueous electrolyte for batteries disclosed herein (hereinafter also simply referred to as "non-aqueous electrolyte") Compound (I) represented by the following formula (I), Compound (II) which is at least one of lithium monofluorophosphate and lithium difluorophosphate, Compound (III) represented by the following formula (III), A non-aqueous electrolyte for lithium secondary batteries containing the following:

[0014] [ka]

[0015] In formula (I), L is a single bond or an oxygen atom. R represents a hydrocarbon group having 1 to 10 carbon atoms, which may be substituted with halogen atoms, or a group having a structure in which at least one carbon atom in the hydrocarbon group is replaced with an oxygen atom, a nitrogen atom, a sulfur atom, or a sulfonyl group. In formula (III), M is an alkali metal, Y is a transition element, a group 13, group 14, or group 15 element of the periodic table. b is an integer between 1 and 3. m is an integer between 1 and 4. n is an integer between 0 and 8. q is either 0 or 1, R 31 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 31They may be joined together.) R 32 This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, or 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 32 They may each be joined together to form a ring. Q 1 and Q 2 Each of these is independently either an oxygen atom or a carbon atom.

[0016] The non-aqueous electrolyte of this disclosure can reduce the rate of resistance increase at room temperature when lithium secondary batteries are stored at high temperatures. In this disclosure, room temperature resistance means resistance under room temperature conditions (for example, 25°C). In this disclosure, the rate of increase in room temperature resistance when a lithium secondary battery is stored at high temperatures means the rate of increase in the room temperature resistance of a lithium secondary battery when it is stored at high temperatures. In this disclosure, the rate of increase in room temperature resistance of a lithium secondary battery during high-temperature storage is determined as the ratio of the room temperature resistance of the lithium secondary battery after high-temperature storage to the room temperature resistance of the lithium secondary battery before high-temperature storage (i.e., the ratio [room temperature resistance of the lithium secondary battery after high-temperature storage / room temperature resistance of the lithium secondary battery before high-temperature storage]).

[0017] The above-mentioned effects of the non-aqueous electrolyte of this disclosure are thought to be the effects brought about by the combination of compound (I), compound (II), and compound (III). The reason for the above effects is thought to be that the combination of compound (I), compound (II), and compound (III) efficiently forms a coating on the electrodes (i.e., the positive electrode and / or negative electrode) in the lithium secondary battery, and this coating suppresses side reactions such as the decomposition of the electrolyte or non-aqueous solvent in the non-aqueous electrolyte during charging and discharging.

[0018] <Compound (I)> The non-aqueous electrolyte of this disclosure contains compound (I) represented by the following formula (I). The non-aqueous electrolyte of this disclosure may contain only one compound (I) or two or more compounds.

[0019] [ka]

[0020] In formula (I), L is a single bond or an oxygen atom. R represents a hydrocarbon group having 1 to 10 carbon atoms that may be substituted with halogen atoms (hereinafter also referred to as a "specific hydrocarbon group"), or a group having a structure in which at least one carbon atom in the specific hydrocarbon group is replaced with an oxygen atom, a nitrogen atom, a sulfur atom, or a sulfonyl group.

[0021] The halogen atom in the specific hydrocarbon group represented by R (i.e., a hydrocarbon group having 1 to 10 carbon atoms that may be substituted with a halogen atom) is preferably a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, more preferably a fluorine atom, a chlorine atom, or a bromine atom, and even more preferably a fluorine atom.

[0022] Represented by R, "a group having a structure in which at least one carbon atom in a specific hydrocarbon group is replaced by an oxygen atom, a nitrogen atom, a sulfur atom, or a sulfonyl group," Preferably, the group has a structure in which one carbon atom in the specific hydrocarbon group is replaced by an oxygen atom, a nitrogen atom, a sulfur atom, or a sulfonyl group. A more preferable group is one having a structure in which one carbon atom in a specific hydrocarbon group is replaced by a sulfonyl group.

[0023] When L is a single bond, R is as follows: Preferably, it is an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, or a halogenated alkylsulfonylmethyl group having 1 to 9 carbon atoms. More preferably, an alkyl group having 1 to 6 carbon atoms, a halogenated alkyl group having 1 to 6 carbon atoms, or a halogenated alkylsulfonylmethyl group having 1 to 5 carbon atoms. More preferably, the group is an alkyl group having 1 to 4 carbon atoms, a halogenated alkyl group having 1 to 4 carbon atoms, or a halogenated alkylsulfonylmethyl group having 1 to 3 carbon atoms.

[0024] When L is an oxygen atom (i.e., -O-), R is: Preferably, it is an alkyl group having 1 to 10 carbon atoms, an alkyl halogenated group having 1 to 10 carbon atoms, an alkylsulfonylmethyl halogenated group having 1 to 9 carbon atoms, or an alkylsulfonyl halogenated group having 1 to 9 carbon atoms. More preferably, an alkyl group having 1 to 6 carbon atoms, an alkyl halogenated group having 1 to 6 carbon atoms, an alkylsulfonylmethyl halogenated group having 1 to 5 carbon atoms, or an alkylsulfonyl halogenated group having 1 to 5 carbon atoms. More preferably, the group is an alkyl group having 1 to 3 carbon atoms, an alkyl halogenated group having 1 to 3 carbon atoms, or an alkylsulfonyl halogenated group having 1 to 3 carbon atoms.

[0025] The following are examples of compound (I), but compound (I) is not limited to these examples. Of the following example compounds, Compounds (I-1) to (I-3), (I-6), (I-9), and (I-10) are examples in which L in formula (I) is a single bond. Compounds (I-4), (I-5), (I-7), and (I-8) are examples in which L in formula (I) is an oxygen atom.

[0026] [ka]

[0027] Of the compounds (I-1) to (I-5) described above, when compounds (I-1), (I-2), (I-4), and (I-5) are used, not only can the rate of resistance increase at room temperature during high-temperature storage of lithium secondary batteries (e.g., the rate of resistance increase at 25°C) be reduced, but the rate of resistance increase at low temperatures during high-temperature storage of lithium secondary batteries (e.g., the rate of resistance increase at -10°C) can also be reduced (see Table 1 below).

[0028] The content of compound (I) relative to the total amount of the non-aqueous electrolyte of this disclosure is preferably 0.01% by mass or more and 5.0% by mass or less, more preferably 0.1% by mass or more and 3.0% by mass or less, and even more preferably 0.2% by mass or more and 2.0% by mass or less.

[0029] Furthermore, when analyzing non-aqueous electrolytes collected from disassembled batteries, the amount of compound (I) may be less than the amount added to the non-aqueous electrolyte. Even in this case, if even a small amount of compound (I) is detected in the non-aqueous electrolyte collected from the battery, the non-aqueous electrolyte of that battery is included within the scope of non-aqueous electrolytes of this disclosure. The same applies to the other compounds described below (compound (II), etc.).

[0030] <Compound (II)> The non-aqueous electrolyte of this disclosure contains compound (II), which is at least one of lithium monofluorophosphate and lithium difluorophosphate. The non-aqueous electrolyte of this disclosure may contain only one compound (II) or two or more compounds. Here, lithium difluorophosphate is compound (II-1) below, and lithium monofluorophosphate is compound (II-2) below.

[0031] [ka]

[0032] Compound (II) may be lithium monofluorophosphate and lithium difluorophosphate alone, or both lithium monofluorophosphate and lithium difluorophosphate.

[0033] The content of compound (II) relative to the total amount of the non-aqueous electrolyte of this disclosure is preferably 0.01% by mass or more and 5.0% by mass or less, more preferably 0.1% by mass or more and 3.0% by mass or less, and even more preferably 0.2% by mass or more and 2.0% by mass or less.

[0034] In the non-aqueous electrolyte of this disclosure, the mass ratio of the content of compound (II) to the content of compound (I) (hereinafter also referred to as the content mass ratio [(II) / (I)]) is preferably 0.5 to 4.0, more preferably 1.0 to 3.0, even more preferably 1.2 to 3.0, and even more preferably 1.5 to 2.5.

[0035] <Compound (III)> The non-aqueous electrolyte of this disclosure contains compound (III) represented by the following formula (III). The non-aqueous electrolyte of this disclosure may contain only one compound (III) or two or more compounds.

[0036] [ka]

[0037] In formula (III), M is an alkali metal, Y is a transition element, a group 13, group 14, or group 15 element of the periodic table. b is an integer between 1 and 3. m is an integer between 1 and 4. n is an integer between 0 and 8. q is either 0 or 1, R 31This 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 31 They may be joined together.) R 32 This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, or 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 32 They may each be joined together to form a ring. Q 1 , and Q 2 These are, independently, either an oxygen atom or a carbon atom.

[0038] M is an alkali metal. Examples of alkali metals include lithium, sodium, and potassium. Of these, M is preferably lithium. Y is a transition element, a group 13, group 14, or group 15 element of the periodic table. Preferably, Y is 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 represents the valency of the anion and the number of cations. b is an integer between 1 and 3, and is preferably 1. If b is 3 or less, the salt of the anionic compound is easily soluble in the mixed organic solvent. m and n are values ​​related to the number of ligands. Each of m and n is determined by the type of M. m is an integer from 1 to 4. n is an integer from 0 to 8. q is either 0 or 1. When q is 0, the chelate ring is a five-membered ring, and when q is 1, the chelate ring is a six-membered ring. R 31R 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, R 31 These groups may contain substituents instead of hydrogen atoms. Substituents include 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. These groups may also have structures in which nitrogen atoms, sulfur atoms, or oxygen atoms are introduced instead of the carbon element. When q is 1 and m is 2-4, there are m R 31 These components may be bonded together. An example of such a ligand is ethylenediaminetetraacetic acid. R 32 R represents a halogen atom, an alkyl group having 1 to 10 carbon atoms, an alkyl halide having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aryl halide having 6 to 20 carbon atoms. These alkyl groups, alkyl halides, aryl groups, or aryl halides are R 31 Similarly, the structure may contain substituents and heteroatoms, and when n is 2 to 8, there are n R 32 These may each be joined to form a ring. 32 As such, electron-withdrawing groups are preferred, and fluorine atoms are particularly preferred. Q 1 and Q 2 Each of these elements independently represents either O or C. Therefore, the ligand will bond to Y via these heteroatoms.

[0039] Specific examples of compound (III) include the following compounds (III-1) and (III-2).

[0040] [ka]

[0041] The content of compound (III) relative to the total amount of the non-aqueous electrolyte of this disclosure is preferably 0.01% by mass or more and 5.0% by mass or less, more preferably 0.1% by mass or more and 3.0% by mass or less, and even more preferably 0.2% by mass or more and 2.0% by mass or less.

[0042] In the non-aqueous electrolyte of this disclosure, the mass ratio of the content of compound (III) to the content of compound (I) (hereinafter also referred to as the content mass ratio [(III) / (I)]) is preferably 0.1 to 3.0, more preferably 0.2 to 2.5, even more preferably 0.3 to 2.0, and even more preferably 0.5 to 1.5.

[0043] <Compound (IV)> The non-aqueous electrolyte of this disclosure may contain compound (IV) represented by the following formula (IV). In this case, the non-aqueous electrolyte of the present disclosure may contain only one compound (IV) or two or more compounds.

[0044] [ka]

[0045] In formula (IV), R 1 and R 2 Each of these independently represents a hydrogen atom, a methyl group, an ethyl group, or a propyl group.

[0046] In formula (IV), R 1 and R 2 Each 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 compound (IV) represented by formula (IV) include vinylene carbonate (hereinafter also referred to as "VC"), methyl vinylene carbonate, and dimethyl vinylene carbonate, with vinylene carbonate being particularly preferred.

[0047] The content of compound (IV) relative to the total amount of the non-aqueous electrolyte of this disclosure is preferably 0.01% by mass or more and 5.0% by mass or less, more preferably 0.1% by mass or more and 3.0% by mass or less, and even more preferably 0.2% by mass or more and 2.0% by mass or less.

[0048] In the non-aqueous electrolyte of this disclosure, the mass ratio of the content of compound (IV) to the content of compound (I) (hereinafter also referred to as the content mass ratio [(IV) / (I)]) is preferably 0.1 to 3.0, more preferably 0.2 to 2.5, even more preferably 0.3 to 2.0, and even more preferably 0.5 to 1.5.

[0049] <Other additives> The non-aqueous electrolyte of this disclosure may contain other additives. Other additives are not particularly limited, and any known additives can be used as desired. Other additives that can be used include, for example, those described in paragraphs 0042 to 0055 of Japanese Patent Publication No. 2019-153443.

[0050] <Non-aqueous solvent> Non-aqueous electrolytes generally contain a non-aqueous solvent. Various known non-aqueous solvents can be appropriately selected. There may be only one non-aqueous solvent or two or more.

[0051] Examples of non-aqueous solvents include cyclic carbonates, fluorinated cyclic carbonates, linear carbonates, fluorinated linear carbonates, aliphatic carboxylic acid esters, fluorinated aliphatic carboxylic acid esters, γ-lactones, fluorinated γ-lactones, cyclic ethers, fluorinated cyclic ethers, linear ethers, fluorinated linear ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolanes, trimethyl phosphate, dimethyl sulfoxide, and dimethyl sulfoxide phosphate. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC). Examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC). Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, and ethyl trimethylbutyrate. Examples of γ-lactones include γ-butyrolactone and γ-valerolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane. Examples of linear ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile. Examples of amides include N,N-dimethylformamide. Examples of lactam compounds include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

[0052] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, linear carbonates, and fluorine-containing linear carbonates. In this case, the total proportion of cyclic carbonates, fluorinated cyclic carbonates, linear carbonates, and fluorinated linear carbonates is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, relative to the total amount of the non-aqueous solvent.

[0053] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and linear carbonates. In this case, the total proportion of cyclic carbonates and linear carbonates in the non-aqueous solvent is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, relative to the total amount of the non-aqueous solvent.

[0054] The upper limit of the non-aqueous solvent content is preferably 99% by mass, preferably 97% by mass, and more preferably 90% by mass, relative to the total amount of the non-aqueous electrolyte. The lower limit of the non-aqueous solvent content is preferably 60% by mass or more, more preferably 70% by mass or more, relative to the total amount of the non-aqueous electrolyte.

[0055] The intrinsic viscosity of the non-aqueous solvent is preferably 10.0 mPa·s or less at 25°C, from the viewpoint of further improving the dissociation of the electrolyte and the mobility of ions.

[0056] <Electrolytes> Non-aqueous electrolytes generally contain electrolytes.

[0057] The electrolyte preferably contains at least one of a lithium salt containing fluorine (hereinafter sometimes referred to as "fluorinated lithium salt") and a lithium salt that does not contain fluorine.

[0058] Examples of fluorinated lithium salts include inorganic acid anionic salts and organic acid anionic salts. Examples of inorganic acid anionic salts include lithium hexafluoride phosphate (LiPF6), lithium borate tetrafluoride (LiBF4), lithium arsenate hexafluoride (LiAsF6), and lithium tantalate hexafluoride (LiTaF6). Examples of organic acid anionic salts include lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), and lithium bis(pentafluoroethanesulfonyl)imide (Li(C2F5SO2)2N). Among these, lithium hexafluoride phosphate (LiPF6) is even more preferred as the fluorinated lithium salt.

[0059] Lithium salts that do not contain fluorine include lithium perchlorate (LiClO4), lithium aluminate tetrachloride (LiAlCl4), and lithium decachlorodecaborate (Li2B 10 Cl 10 ) are some examples.

[0060] When the electrolyte contains a fluorinated lithium salt, the content of the fluorinated lithium salt is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass, relative to the total amount of the electrolyte. When the fluorinated lithium salt contains lithium hexafluoride phosphate (LiPF6), the content of lithium hexafluoride phosphate (LiPF6) is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass, relative to the total amount of the electrolyte.

[0061] When the non-aqueous electrolyte contains an electrolyte, the concentration of the electrolyte in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less.

[0062] When the non-aqueous electrolyte contains lithium hexafluoride phosphate (LiPF6), the concentration of lithium hexafluoride phosphate (LiPF6) in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less.

[0063] <Other ingredients> The non-aqueous electrolyte may contain other components as needed. Other components include acid anhydrides.

[0064] [Precursor for lithium secondary batteries] The lithium secondary battery precursor of this disclosure is The case and The positive electrode, negative electrode, separator, and electrolyte were repurposed for the case. It is equipped with. Here, The positive electrode is a positive electrode capable of intercalating and releasing lithium ions. The negative electrode is a negative electrode capable of intercalating and releasing lithium ions. The electrolyte is the non-aqueous electrolyte of this disclosure.

[0065] In this disclosure, a lithium secondary battery precursor refers to a lithium secondary battery before it has been charged and discharged.

[0066] According to the lithium secondary battery precursor of this disclosure, in a lithium secondary battery obtained by charging and discharging this lithium secondary battery precursor, the rate of resistance increase at room temperature during high-temperature storage can be reduced.

[0067] <Case> The shape of the case is not particularly limited and can be appropriately selected depending on the application of the lithium secondary battery precursor described herein. Examples of cases include cases containing laminate film, and cases consisting of a battery can and a battery can lid.

[0068] <Positive electrode> The positive electrode is a positive electrode capable of intercalating and releasing lithium ions. The positive electrode preferably includes at least one positive electrode active material capable of intercalating and releasing lithium ions.

[0069] The positive electrode preferably comprises a positive electrode current collector and a positive electrode composite layer provided on at least a portion of the surface of the positive electrode current collector.

[0070] Examples of materials for the positive electrode current collector include metal or alloy. More specifically, suitable materials for the positive electrode current collector include aluminum, nickel, stainless steel (SUS), and copper. Among these, aluminum is preferred from the viewpoint of balancing high conductivity with cost. Here, "aluminum" refers to pure aluminum or aluminum alloy. Aluminum foil is preferred as the positive electrode current collector. The material of the aluminum foil is not particularly limited, and examples include A1085 and A3003.

[0071] The positive electrode composite layer contains a positive electrode active material and a binder.

[0072] The positive electrode active material is not particularly limited as long as it is a material capable of intercalating and releasing lithium ions, and can be appropriately adjusted depending on the application of the lithium secondary battery precursor.

[0073] Examples of positive electrode active materials include primary oxides and secondary oxides. Primary oxides consist of lithium (Li) and nickel (Ni) as constituent metal elements. Secondary oxides contain Li, Ni, and at least one other metal element as constituent metal elements. Examples of metal elements other than Li and Ni include transition metal elements and typical metal elements. Preferably, the secondary oxide contains the metal element other than Li and Ni in an amount equivalent to or less than Ni in terms of atomic number. The metal element other than Li and Ni may be at least one selected from the group consisting of Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. These positive electrode active materials may be used individually or in combination.

[0074] The positive electrode active material preferably contains a lithium-containing composite oxide (hereinafter sometimes referred to as "NCM") represented by the following formula (P1). The lithium-containing composite oxide (P1) has the advantage of having a high energy density per unit volume and excellent thermal stability. LiRing a Co b Mn c O2… Formula (P1) In equation (P1), a, b, and c are each independently greater than 0 and less than 1, and the sum of a, b, and c is between 0.99 and 1.00. A specific example of NCM is LiNi 0.33 Co 0.33 Mn 0.33 O2, LiLiLi 0.5 Co 0.3 Mn 0.2 O2, LiLiLi 0.5 Co 0.2 Mn 0.3 O2, LiLiLi 0.6 Co 0.2 Mn 0.2 O2, LiLiLi 0.8 Co 0.1 Mn 0.1 Examples include O2.

[0075] The positive electrode active material may contain a lithium-containing composite oxide represented by the following formula (P2) (hereinafter sometimes referred to as "NCA"). Li t Ni 1-x-y Co x Al y O2… Formula (P2) In equation (P2), t is between 0.95 and 1.15, x is between 0 and 0.3, y is between 0.1 and 0.2, and the sum of x and y is less than 0.5. A specific example of NCA is Li Ni 0.8 Co 0.15 Al 0.05 Examples include O2.

[0076] In the lithium secondary battery precursor of this disclosure, when the positive electrode comprises a positive electrode current collector and a positive electrode composite layer containing a positive electrode active material and a binder, the content of the positive electrode active material in the positive electrode composite layer is preferably 10% by mass or more, more preferably 30% by mass or more, even more preferably 50% by mass or more, and particularly preferably 70% by mass or more, based on the total amount of the positive electrode composite layer. The content of the positive electrode active material in the positive electrode composite layer is preferably 99.9% by mass or less, more preferably 99% by mass or less, based on the total amount of the positive electrode composite layer.

[0077] 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 composite layer. One type of binder can be used alone, and two or more types can be used in combination as needed. The binder content in the positive electrode composite layer is preferably 0.1% by mass or more and 4% by mass or less relative to the total amount of the positive electrode composite layer, from the viewpoint of balancing the physical properties of the positive electrode composite layer (e.g., electrolyte permeability, peel strength, etc.) and battery performance. When the binder content is 0.1% by mass or more, the adhesion of the positive electrode composite layer to the positive electrode current collector and the bonding of the positive electrode active materials to each other are further improved. When the binder content is 4% by mass or less, the amount of positive electrode active material in the positive electrode composite layer can be increased, thus further improving the discharge capacity.

[0078] The positive electrode composite layer preferably contains a conductive additive. As the material for the conductive additive, known conductive additives can be used. Among the known conductive additives, conductive carbon materials are preferred. Examples of conductive carbon materials include graphite, carbon black, conductive carbon fibers, and fullerenes. These can be used alone or in combination of two or more types. Examples of conductive carbon fibers include carbon nanotubes, carbon nanofibers, and carbon fibers. Examples of graphite include artificial graphite and natural graphite. Examples of natural graphite include flake graphite, lump graphite, and earthy graphite. The material of the conductive additive may be a commercially available product. Examples of commercially available carbon blacks include Tokai Carbon #4300, #4400, #4500, #5500, etc. (Tokai Carbon Co., Ltd., Furnace Black), Printex L, etc. (Degussa Co., Ltd., Furnace Black), Raven 7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975ULTRA, etc., PUER BLACK100, 115, 205 etc. (Columbian brand, Furnace Black), #2350, #2400B, #2600B, #30050B, #3030B, #3230B, #3350B, #3400B, #5400B etc. (Mitsubishi Chemical Corporation, Furnace Black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, Examples include LITX-50, LITX-200 (Cabot Furnace Black), Ensaco 250G, Ensaco 260G, Ensaco 350G, Super-P (TIMCAL), Ketjenblack EC-300J, EC-600JD (Akzo), Denka Black, Denka Black HS-100, FX-35 (Denka Acetylene Black).

[0079] The positive electrode composite layer may contain other components. These other components include thickeners, surfactants, dispersants, wetting agents, and defoaming agents.

[0080] <Negative electrode> The negative electrode is a negative electrode capable of intercalating and releasing lithium ions. The negative electrode preferably includes at least one negative electrode active material capable of intercalating and releasing lithium ions.

[0081] The negative electrode preferably comprises a negative electrode current collector and a negative electrode composite material layer provided on at least a portion of the surface of the negative electrode current collector.

[0082] There are no particular restrictions on the material of the negative electrode current collector; any known material can be used, such as metal or alloy. Specifically, examples of materials for the negative electrode current collector include aluminum, nickel, stainless steel (SUS), nickel-plated steel, and copper. Among these, copper is preferred as the material for the negative electrode current collector from the viewpoint of processability. Copper foil is preferred as the negative electrode current collector.

[0083] The negative electrode composite layer contains a negative electrode active material and a binder.

[0084] The negative electrode active material is not particularly limited as long as it is a material capable of intercalating and releasing lithium ions. Preferably, the negative electrode active material is at least one selected from the group consisting of, for example, metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped and dedoped with lithium ions, transition metal nitrides that can be doped and dedoped with lithium ions, and carbon materials that can be doped and dedoped with lithium ions. Among these, the negative electrode active material is preferably a carbon material capable of doping and dedoping with lithium ions (hereinafter also simply referred to as "carbon material").

[0085] Examples of carbon materials include carbon black, activated carbon, graphite materials, and amorphous carbon materials. These carbon materials may be used individually or in mixtures of two or more. The form of the carbon material is not particularly limited and can be fibrous, spherical, potato-shaped, or flake-shaped. The particle size of the carbon material is not particularly limited, but is preferably 5 μm to 50 μm, and more preferably 20 μm to 30 μm. Examples of amorphous carbon materials include hard carbon, coke, mesocarbon microbeads (MCMB) fired at temperatures below 1500°C, and mesophase pitch carbon fiber (MCF). Examples of graphite materials include natural graphite and artificial graphite. Examples of artificial graphite include graphitized MCMB and graphitized MCF. Graphite materials may also contain boron. Graphite materials may be coated with metal or amorphous carbon. Examples of metals used to coat graphite materials include gold, platinum, silver, copper, and tin. Graphite materials may also be mixtures of amorphous carbon and graphite.

[0086] The negative electrode composite layer preferably contains a conductive additive. Examples of conductive additives include those similar to those exemplified as conductive additives that may be included in the positive electrode composite layer.

[0087] The negative electrode composite layer may contain other components in addition to the above-mentioned components. Examples of other components include thickeners, surfactants, dispersants, wetting agents, and defoaming agents.

[0088] <Separator> Examples of separators include porous resin plates. Materials for the porous resin plates include resin, nonwoven fabrics containing this resin, and others. Examples of resins include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, and polyamide. In particular, the separator is preferably a porous resin sheet with a single-layer or multi-layer structure. The porous resin sheet is mainly made of one or more types of polyolefin resin. The thickness of the separator is preferably 5 μm to 30 μm. The separator is preferably placed between the positive electrode and the negative electrode.

[0089] <Specific examples of lithium secondary battery precursors> Figure 1 is a schematic cross-sectional view showing a stacked lithium secondary battery precursor, which is an example of a lithium secondary battery precursor according to this disclosure.

[0090] As shown in Figure 1, lithium secondary battery precursor 1 is a stacked battery precursor. In detail, in the lithium secondary battery precursor 1, the battery element 10 is enclosed inside the outer casing 30. The outer casing 30 is made of laminate film. The battery element 10 is fitted with a positive electrode lead 21 and a negative electrode lead 22. The positive electrode lead 21 and the negative electrode lead 22 are led out in opposite directions from the inside to the outside of the outer casing 30.

[0091] As shown in Figure 1, the battery element 10 is made up of a stack of a positive electrode 11, a separator 13, and a negative electrode 12. The positive electrode 11 has a positive electrode composite layer 11B formed on both main surfaces of the positive electrode current collector 11A. The negative electrode 12 has a negative electrode composite layer 12B formed on both main surfaces of the negative electrode current collector 12A. The positive electrode composite layer 11B formed on one main surface of the positive electrode current collector 11A of the positive electrode 11 and the negative electrode composite layer 12B formed on one main surface of the negative electrode current collector 12A of the negative electrode 12 adjacent to the positive electrode 11 face each other via the separator 13.

[0092] The non-aqueous electrolyte of this disclosure is injected into the exterior casing 30 of the lithium secondary battery precursor 1. The non-aqueous electrolyte of this disclosure permeates the positive electrode composite layer 11B, the separator 13, and the negative electrode composite layer 12B. In the lithium secondary battery precursor 1, a single cell layer 14 is formed by the adjacent positive electrode composite layer 11B, the separator 13, and the negative electrode composite layer 12B. The positive electrode and negative electrode may be formed with their respective active material layers on one side of their respective current collectors.

[0093] Although lithium secondary battery precursor 1 is a stacked lithium secondary battery precursor, the lithium secondary battery precursor of this disclosure is not limited to this, and may be, for example, a wound lithium secondary battery precursor. The wound lithium secondary battery precursor is formed by stacking a positive electrode, a separator, a negative electrode, and a separator in that order and winding them in layers. The wound lithium secondary battery precursor includes cylindrical lithium secondary battery precursors and prismatic lithium secondary battery precursors.

[0094] As shown in Figure 1, in the lithium secondary battery precursor 1, the directions in which the positive electrode lead and the negative electrode lead protrude from the inside to the outside of the outer casing 30 are opposite to the outer casing 30, but the disclosure is not limited thereto. For example, the way in which the positive electrode lead and the negative electrode lead protrude from the inside to the outside of the outer casing 30 is the same direction with respect to the outer casing 30.

[0095] An example of the lithium secondary battery of this disclosure described later is a lithium secondary battery obtained by subjecting a lithium secondary battery precursor 1 to charging and discharging.

[0096] Figure 2 is a schematic cross-sectional view showing a coin-type lithium secondary battery precursor, which is another example of a lithium secondary battery precursor of the present disclosure.

[0097] In the coin-type lithium secondary battery precursor shown in Figure 2, a disc-shaped negative electrode 42, a separator 45 injected with a non-aqueous electrolyte, a disc-shaped positive electrode 41, and, if necessary, spacer plates 47 and 48 made of stainless steel or aluminum are stacked in this order and housed between the positive electrode can 43 (hereinafter also referred to as the "battery can") and the sealing plate 44 (hereinafter also referred to as the "battery can lid"). The positive electrode can 43 and the sealing plate 44 are crimped and sealed via a gasket 46. In this example, the non-aqueous electrolyte of this disclosure is used as the non-aqueous electrolyte injected into the separator 45.

[0098] An example of the lithium secondary battery of this disclosure, as described later, is a lithium secondary battery obtained by charging and discharging a coin-type lithium secondary battery precursor shown in Figure 2.

[0099] [Lithium secondary battery and method for manufacturing the same] The method for manufacturing a lithium secondary battery disclosed herein is: The process for preparing the lithium secondary battery precursor described above (hereinafter also referred to as the "preparation process"), The above lithium secondary battery precursor is subjected to a charging and discharging process, Includes. The lithium secondary battery of this disclosure is a lithium secondary battery obtained by subjecting the lithium secondary battery precursor of this disclosure described above to charging and discharging.

[0100] According to the lithium secondary battery and its manufacturing method disclosed herein, the rate of increase in resistance at room temperature during high-temperature storage of the lithium secondary battery can be reduced.

[0101] The preparation step may simply be a step of preparing a pre-manufactured lithium secondary battery precursor of the present disclosure for use in a charging and discharging step, or it may be a step of manufacturing the lithium secondary battery precursor of the present disclosure. The lithium secondary battery precursor is as described above.

[0102] 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 (Solid Electrolyte Interface) film on the surface of the positive electrode (especially the positive electrode active material) and / or the negative electrode (especially the negative electrode active material) of the lithium secondary battery precursor.

[0103] The charging and discharging process preferably involves performing a combination of charging and discharging one or more times on the lithium secondary battery precursor in an environment of 25°C to 70°C. [Examples]

[0104] The following are examples of the embodiments of this disclosure, but this disclosure is not limited to the following embodiments. In the following, "%" refers to "mass%" unless otherwise specified.

[0105] [Example 1] <Preparation of non-aqueous electrolyte> Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of EC:DMC:EMC = 30:35:35. This yielded a mixed solvent as a non-aqueous solvent. To the resulting mixed solvent, LiPF6 was dissolved as an electrolyte so that the concentration in the final non-aqueous electrolyte solution was 1 mole / liter, thereby obtaining the electrolyte solution (hereinafter also referred to as the "basic electrolyte solution"). To the obtained basic electrolyte, Compound (I-1) as the above compound (I), The above compound (II) is the above compound (II-1) (i.e., lithium difluorophosphate), and The above compound (III-1) is used as the above compound (III), The non-aqueous electrolyte was obtained by adding the ingredients so that their content relative to the total volume of the final non-aqueous electrolyte was as shown in Table 1 (mass %).

[0106] <Fabrication of the positive electrode> LiNi as a positive electrode active material 0.5 Co 0.2 Mn 0.3 A mixture was obtained by mixing O2 (90% by mass), acetylene black (5% by mass) as a conductive additive, and polyvinylidene fluoride (PVdF) (5% by mass) as a binder. The obtained mixture was dispersed in N-methylpyrrolidone solvent to obtain a cathode composite slurry. A 20 μm thick aluminum foil was prepared as the positive electrode current collector. The obtained positive electrode slurry was applied onto aluminum foil, dried, and then rolled in a press to obtain a sheet-like positive electrode. The positive electrode consists of a positive electrode current collector and a positive electrode active material layer.

[0107] <Fabrication of the negative electrode> A negative electrode slurry was obtained by mixing natural graphite (98% by mass) as the negative electrode active material, 1% by mass of carboxymethylcellulose sodium dispersed in pure water as a thickener, and 1% by mass of styrene-butadiene rubber (SBR) dispersed in pure water as a binder. A 10 μm thick copper foil was prepared as the negative electrode current collector. The obtained negative electrode slurry was applied onto copper foil, dried, and then rolled in a press to obtain a sheet-like negative electrode. The negative electrode consists of a negative electrode current collector and a negative electrode active material layer.

[0108] <Preparing the separator> A porous polyethylene film was prepared as a separator.

[0109] <Preparation of lithium secondary battery precursors> The negative electrode was punched out in a disc shape with a diameter of 14 mm, the positive electrode in a disc shape with a diameter of 13 mm, and the separator in a disc shape with a diameter of 17 mm. This resulted in coin-shaped negative electrodes, coin-shaped positive electrodes, and coin-shaped separators. The obtained coin-shaped negative electrode, coin-shaped separator, and coin-shaped positive electrode were stacked in this order inside a stainless steel battery case (size: 2032). Next, 20 μL of non-aqueous electrolyte was poured into the battery case, immersing the separator, positive electrode, and negative electrode in the non-aqueous electrolyte. Next, an aluminum plate (1.2 mm thick, 16 mm in diameter) and a spring were placed on the positive electrode, and the battery was sealed by crimping the battery can lid via a polypropylene gasket. Based on the above, a coin-shaped lithium secondary battery precursor (i.e., a lithium secondary battery before charging and discharging) having the configuration shown in Figure 2 was obtained. The size of the lithium secondary battery precursor was 20 mm in diameter and 3.2 mm in height.

[0110] <Manufacturing of lithium secondary batteries> The lithium secondary battery precursor described above was subjected to the following processes in order: charging from 1.5V to 4.2V, holding for 5 to 50 hours, charging to 4.2V, and discharging to 2.5V, all within a temperature range of 25°C to 70°C, to obtain a lithium secondary battery.

[0111] <Initial charge / discharge process> The lithium secondary battery obtained above was charged to 4.2V in a constant temperature bath at 25°C, and then discharged to 2.5V.

[0112] <Measurement of initial resistance at 25°C> Next, the lithium secondary battery, after initial charge-discharge treatment, was charged to 3.7V and discharged at a constant current of 0.4mA. The DC resistance [Ω] of the lithium secondary battery was measured by measuring the potential drop during the first 10 seconds of discharge. The obtained measurement value was defined as the initial 25°C resistance (Ω). The initial 25°C resistance is an example of the resistance at room temperature (i.e., before high-temperature storage).

[0113] <Measurement of initial resistance at -10°C> Next, the lithium secondary battery, after its initial resistance measurement at 25°C, was charged to 3.7V, then cooled to -10°C in a constant temperature bath and left to stand for 3 hours to allow it to cool sufficiently. After that, the lithium secondary battery cooled to -10°C was discharged at -10°C with a constant current of 0.4mA, and the DC resistance [Ω] of the lithium secondary battery was measured by measuring the potential drop during the first 10 seconds from the start of discharge. The obtained measurement value was defined as the initial -10°C resistance (Ω). The initial -10°C resistance is an example of the low-temperature resistance at the initial stage (i.e., before high-temperature storage).

[0114] <High-temperature preservation treatment> Next, the lithium secondary batteries, after initial resistance measurement at -10°C, were charged to 4.2V, and the charged lithium secondary batteries were stored in a constant temperature bath at 80°C for 6 days (hereinafter referred to as "high-temperature storage").

[0115] <Measurement of resistance at 25°C after high-temperature storage> Next, the 25°C resistance of lithium secondary batteries after high-temperature storage was measured using the same method as for the initial 25°C resistance. Similarly, the 25°C resistance of the lithium secondary battery after high-temperature storage was measured for Comparative Example 1, described later.

[0116] <Measurement of resistance at -10°C after high-temperature storage> Next, the -10°C resistance of the lithium secondary battery, after measuring its resistance at 25°C following high-temperature storage, was measured using the same method as the initial -10°C resistance measurement. Similarly, for Comparative Example 1 described later, the resistance at -10°C was measured after measuring the resistance at 25°C following high-temperature storage.

[0117] <Evaluation of resistance increase rate at 25°C during high-temperature storage> The percentage increase in resistance at 25°C during high-temperature storage was calculated using the following formula. Resistance increase rate at 25°C during high-temperature storage (%) = (Resistance at 25°C after high-temperature storage / Initial resistance at 25°C) × 100

[0118] Similarly, the 25°C resistance increase rate (%) during high-temperature storage was calculated for Comparative Example 1, described later. The 25°C resistance increase rate (relative value) for Example 1 during high-temperature storage was determined, with the 25°C resistance increase rate for Comparative Example 1 during high-temperature storage set to 100. The results are shown in Table 1.

[0119] <Evaluation of resistance increase rate at -10°C during high-temperature storage> The percentage increase in resistance at -10°C during high-temperature storage was calculated using the following formula. -10°C resistance increase rate during high-temperature storage (%) = (-10°C resistance after high-temperature storage / initial -10°C resistance) × 100

[0120] Similarly, the percentage increase in resistance at -10°C during high-temperature storage was calculated for Comparative Example 1, described later. The -10°C resistance increase rate (relative value) for Example 1 during high-temperature storage was determined, with the -10°C resistance increase rate for Comparative Example 1 during high-temperature storage set to 100. The results are shown in Table 1.

[0121] In Table 1, the values ​​listed in the column for each component indicate the content (mass %) relative to the total amount of the non-aqueous electrolyte, and "-" indicates that the component is not present.

[0122] [Example 2] The procedure was the same as in Example 1, except that vinylene carbonate (VC) as compound (IV) was added to the basic electrolyte so that its content relative to the total amount of the final non-aqueous electrolyte was as shown in Table 1 (mass %). The results are shown in Table 1.

[0123] [Examples 3-6] The procedure was the same as in Example 1, except that the type of compound (I) was changed as shown in Table 1. The results are shown in Table 1.

[0124] [Comparative Example 1] The procedure was the same as in Example 1, except that compound (I-1) as compound (I) was changed to comparative compound (C-1) described below. The results are shown in Table 1.

[0125] The compounds used in the examples and comparative examples are as follows:

[0126] [ka]

[0127] [Table 1]

[0128] As shown in Table 1, the lithium secondary batteries of Examples 1 to 6, which used a non-aqueous electrolyte containing compound (I), compound (II), and compound (III), showed a reduced rate of resistance increase at room temperature during high-temperature storage (i.e., resistance increase at 25°C) compared to the lithium secondary battery of Comparative Example 1, which used comparative compound (C-1) instead of compound (I). [Explanation of Symbols]

[0129] 1. Lithium secondary battery precursor 10 Battery elements 11 Positive electrode 11A positive electrode current collector 11B Positive electrode composite layer 12 Negative electrode 12A negative electrode current collector 12B Negative electrode composite layer 13 Separator 14 single cell layers 21 Positive lead 22 Negative lead 30 Exterior 41 Positive electrode 42 Negative electrode 43 Positive electrode can 44 Sealing plate 45 Separator 46 Gasket 47, 48 Spacer plate

Claims

1. Compound (I) represented by the following formula (I), Compound (II) which is at least one of lithium monofluorophosphate and lithium difluorophosphate, Compound (III) represented by the following formula (III), It contains, A non-aqueous electrolyte for lithium secondary batteries, wherein the mass ratio of the content of compound (II) to the content of compound (I) is 0.5 to 4.

0. 【Chemistry 1】 [In formula (I), L is a single bond, R represents a hydrocarbon group having 1 to 10 carbon atoms, which may be substituted with halogen atoms, or a group having a structure in which at least one of the carbon atoms in the hydrocarbon group is replaced with an oxygen atom, a nitrogen atom, a sulfur atom, or a sulfonyl group. In formula (III), M is an alkali metal, Y is B, b is an integer between 1 and 3. m is an integer between 1 and 4. n is an integer from 0 to 8. q is either 0 or 1, R ３１ 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 ３１ They may be joined together.) R ３２ This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, or 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 ３２ They may each be joined together to form a ring. Q １ and Q ２ Each of these is independently either an oxygen atom or a carbon atom.

2. Compound (I) represented by the following formula (I), Compound (II) which is at least one of lithium monofluorophosphate and lithium difluorophosphate, Compound (III) represented by the following formula (III), A non-aqueous electrolyte for lithium secondary batteries containing the following: 【Chemistry 2】 [In formula (I), L is an oxygen atom, R represents a hydrocarbon group having 1 to 10 carbon atoms, which may be substituted with halogen atoms, or a group having a structure in which at least one of the carbon atoms in the hydrocarbon group is replaced with an oxygen atom, a nitrogen atom, or a sulfur atom. In formula (III), M is an alkali metal, Y is B, b is an integer between 1 and 3. m is an integer between 1 and 4. n is an integer from 0 to 8. q is either 0 or 1, R ３１ 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 ３１ They may be joined together.) R ３２ 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, or a halogenated aryl group having 6 to 20 carbon atoms (these groups may contain a substituent or a hetero atom in the structure, and when n is 2 to 8, n R ３２ may each be bonded to form a ring.). Q １ and Q ２ Each of these is independently either an oxygen atom or a carbon atom.

3. The non-aqueous electrolyte for lithium secondary batteries according to claim 1 or claim 2, wherein the content of compound (I) is 0.01% by mass or more and 5.0% by mass or less based on the total amount of the non-aqueous electrolyte for batteries.

4. The non-aqueous electrolyte for lithium secondary batteries according to any one of claims 1 to 3, wherein the content of compound (II) is 0.01% by mass or more and 5.0% by mass or less based on the total amount of the non-aqueous electrolyte for batteries.

5. The non-aqueous electrolyte for lithium secondary batteries according to any one of claims 1 to 4, wherein the content of compound (III) is 0.01% by mass or more and 5.0% by mass or less based on the total amount of the non-aqueous electrolyte for batteries.

6. The case and, The case contains a positive electrode, a negative electrode, a separator, and an electrolyte, Equipped with, The positive electrode is a positive electrode capable of intercalating and releasing lithium ions. The aforementioned negative electrode is a negative electrode capable of intercalating and releasing lithium ions. A lithium secondary battery precursor wherein the electrolyte is the non-aqueous electrolyte described in any one of claims 1 to 5.

7. The lithium secondary battery precursor according to claim 6, wherein the positive electrode contains a lithium-containing composite oxide represented by the following formula (P1) as the positive electrode active material. LiNi ａ Co ｂ Mn ｃ O ２ ... Formula (P1) [In formula (P1), a, b, and c are each independently greater than 0 and less than 1, and the sum of a, b, and c is 0.99 or greater and 1.00 or less.]

8. A step of preparing a lithium secondary battery precursor according to claim 6 or claim 7, The process involves charging and discharging the lithium secondary battery precursor. A method for manufacturing lithium secondary batteries, including [the specified component].

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