Additive for lithium secondary battery, non-aqueous electrolyte for lithium secondary battery, precursor for lithium secondary battery, lithium secondary battery, lithium sulfonate compound, and method for manufacturing lithium secondary battery

Abstract

To provide an additive agent for a lithium secondary battery, which can suppress increase DC resistance even in the case of a lithium secondary battery being stored for a long time under a high-temperature environment.SOLUTION: An additive agent for a lithium secondary battery according to a disclosure hereof comprises a compound (I) represented by a formula below. In the formula (I), R11 and R12 independently represent an alkyl group with 1-10 carbon atoms, an alkenyl group with 2-10 carbon atoms, an alkynyl group with 2-10 carbon atoms, a benzyl group or an aryl group, otherwise an alkylene group which forms a 3- to 8-membered cyclic structure together with nitrogen atoms in the formula (I) integrally; a wavy line represents that the component is a trans or cis isomer.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present disclosure relates to an additive for a lithium secondary battery, a nonaqueous electrolyte for a lithium secondary battery, a lithium secondary battery precursor, a lithium secondary battery, a lithium sulfonate compound, and a method for producing a lithium secondary battery. [Background technology]

[0002] Lithium secondary batteries have been attracting attention as batteries with high energy density. Patent Document 1 discloses a non-aqueous electrolyte for an electricity storage device (e.g., a lithium secondary battery). In the non-aqueous electrolyte disclosed in Patent Document 1, an electrolyte salt is dissolved in a non-aqueous solvent. The non-aqueous electrolyte disclosed in Patent Document 1 contains a specific zwitterion. Patent Document 1 specifically discloses a non-aqueous electrolyte containing 2-(triethylammonio)ethyl sulfate, 2-dodecyldimethyl(carboxylatomethyl)ammonium, trimethyl(carboxylatomethyl)ammonium, or triethyl(sulfopropyl)ammonium as the specific zwitterion. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2020 / 017318 Summary of the Invention [Problem to be solved by the invention]

[0004] Lithium secondary batteries are sometimes used not only in warm regions (e.g., 25°C) but also in cold regions (e.g., -10°C), where the battery performance of the lithium secondary battery may be reduced. When a lithium secondary battery including the nonaqueous electrolyte solution disclosed in Patent Document 1 is stored in a high-temperature environment (e.g., 60°C) for a long period of time (e.g., 14 days), the DC resistance may increase in environments of 25°C and -10°C.

[0005] In view of the above circumstances, an object of the present disclosure is to provide an additive for a lithium secondary battery, a nonaqueous electrolyte solution for a lithium secondary battery, a lithium secondary battery precursor, a lithium secondary battery, a lithium sulfonate compound, and a method for producing a lithium secondary battery, which are capable of suppressing an increase in DC resistance even when the lithium secondary battery is stored in a high-temperature environment for a long period of time. [Means for solving the problem]

[0006] The means for solving the above problems include the following embodiments.

[0007] <1> An additive for a lithium secondary battery, comprising a compound (I) represented by the following formula (I):

[0008] [ka]

[0009] [In formula (I), R 11 and R 12 teeth, each independently represents an alkyl group having 1 to 10 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), an alkenyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), a benzyl group (at least one hydrogen atom in the benzyl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), or an aryl group (at least one hydrogen atom in the aryl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), Alternatively, they represent alkylene groups which together with the nitrogen atom in formula (I) form a 3- to 8-membered cyclic structure (at least one hydrogen atom in the alkylene group may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms). The wavy line indicates a trans or cis form.] <2> R 11 and R 12 teeth, each independently represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group; or represents an alkylene group which together with the nitrogen atom in formula (I) form a 5- to 6-membered ring structure, <1> The additive for a lithium secondary battery according to claim 1. <3> The compound (I) is a compound (I-1) represented by the following formula (I-1) or a compound (I-2) represented by the following formula (I-2): <1> or <2> The additive for a lithium secondary battery according to claim 1.

[0010] [ka]

[0011] <4> The aforementioned <1> ~ <3> 10. A non-aqueous electrolyte solution for a lithium secondary battery, comprising the additive for a lithium secondary battery according to any one of claims 1 to 9. <5> The compound (II) is at least one of lithium monofluorophosphate and lithium difluorophosphate, and further contains at least one selected from the group consisting of a compound (III) represented by the following formula (III) and a compound (IV) represented by the following formula (IV): <4> The nonaqueous electrolyte for a lithium secondary battery according to claim 1.

[0012] [ka]

[0013] [In formula (III), M is an alkali metal; Y is a transition element, an element in Group 13, 14, or 15 of the periodic table; b is an integer from 1 to 3, m is an integer from 1 to 4, n is an integer from 0 to 8, q is 0 or 1; R 31 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 groups may contain a substituent or a heteroatom in the structure, and when q is 1 and m is 2 to 4, m R 31 may be bonded to each other. 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 heteroatom in the structure, and when n is 2 to 8, n R 32 may be bonded to each other to form a ring; Q 1 , and Q 2 are each independently an oxygen atom or a carbon atom. In formula (IV), R 41 represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms, R 42 represents an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (iv-1), or a group represented by formula (iv-2), * indicates the bond position, In formula (iv-1), R 43 represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group, In formula (iv-2), R 44 is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms. <6> The content of the compound (I) is 0.01% by mass or more and 5% by mass or less with respect to the total amount of the non-aqueous electrolyte solution. <4> or <5> The nonaqueous electrolyte for a lithium secondary battery according to claim 1. <7> Case and a positive electrode, a negative electrode, a separator, and an electrolyte solution housed in the case; Equipped with the positive electrode is a positive electrode capable of absorbing and desorbing lithium ions, the negative electrode is capable of absorbing and desorbing lithium ions, The electrolyte solution <4> ~ <6> 1. A lithium secondary battery precursor, which is the nonaqueous electrolyte solution according to any one of 1 to 8. <8> The positive electrode contains, as a positive electrode active material, a lithium-containing composite oxide represented by the following formula (P1): <7> The lithium secondary battery precursor according to claim 1. LiNi a Co b Mn c O2… Formula (P1) [In formula (P1), a, b, and c each independently represent a number greater than 0 and less than 1, and the sum of a, b, and c represents a number greater than or equal to 0.99 and less than or equal to 1.00.] <9> The aforementioned <7> or <8> preparing a lithium secondary battery precursor according to the present invention; charging and discharging the lithium secondary battery precursor; A method for producing a lithium secondary battery, comprising: <10> The aforementioned <7> or <8> A lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor according to claim 1. <11> A lithium sulfonate compound represented by the following formula (I):

[0014] [ka]

[0015] [In formula (I), R 11 and R 12 teeth, each independently represents an alkyl group having 1 to 10 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), an alkenyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), a benzyl group (at least one hydrogen atom in the benzyl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), or an aryl group (at least one hydrogen atom in the aryl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), Alternatively, they represent alkylene groups which together with the nitrogen atom in formula (I) form a 3- to 8-membered cyclic structure (at least one hydrogen atom in the alkylene group may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms). The wavy line indicates a trans or cis form.] <12> R 11 and R 12 teeth, each independently represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group; or represents an alkylene group which together with the nitrogen atom in formula (I) form a 5- to 6-membered ring structure, <11> The lithium sulfonate compound according to claim 1. <13> The compound (I-1) is one selected from the group consisting of a compound (I-1) represented by the following formula (I-1), a compound (I-2) represented by the following formula (I-2), and a compound (I-3) represented by the following formula (I-3). <11> or <12> The lithium sulfonate compound according to claim 1.

[0016] [ka] [Effects of the Invention]

[0017] According to the present disclosure, there are provided an additive for a lithium secondary battery, a nonaqueous electrolyte solution for a lithium secondary battery, a lithium secondary battery precursor, a lithium secondary battery, a lithium sulfonate compound, and a method for producing a lithium secondary battery, which are capable of suppressing an increase in DC resistance even when the lithium secondary battery is stored in a high-temperature environment for a long period of time. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic cross-sectional view showing a laminated battery, which is an example of a lithium secondary battery precursor according to the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view showing a coin-type battery, which is another example of a lithium secondary battery precursor according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0019] In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits. In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0020] Hereinafter, embodiments of the additive for a lithium secondary battery, the nonaqueous electrolyte for a lithium secondary battery, the lithium secondary battery precursor, the lithium secondary battery, the lithium sulfonate compound, and the method for manufacturing a lithium secondary battery according to the present disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference symbols, and description thereof will not be repeated.

[0021] [Additives for lithium secondary batteries] The additive for lithium secondary batteries (hereinafter referred to as "additive") of the present disclosure will be described.

[0022] The additive of the present disclosure is suitably used as an additive to be added to a non-aqueous electrolyte solution contained in a lithium secondary battery. Details of the lithium secondary battery will be described later with reference to FIGS.

[0023] The additive of the present disclosure contains a compound (I) represented by the following formula (I) (hereinafter referred to as "lithium sulfonate compound (I)").

[0024] [ka]

[0025] In formula (I), R 11 and R 12 teeth, each independently represents an alkyl group having 1 to 10 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), an alkenyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), a benzyl group (at least one hydrogen atom in the benzyl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), or an aryl group (at least one hydrogen atom in the aryl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), Alternatively, they represent alkylene groups which together with the nitrogen atom in formula (I) form a 3- to 8-membered cyclic structure (at least one hydrogen atom in the alkylene group may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms). The wavy line indicates a trans or cis form.

[0026] The additive of the present disclosure has the above-described structure, and therefore can suppress an increase in DC resistance even when the lithium secondary battery is stored in a high-temperature environment (for example, 60°C) for a long period of time (for example, 14 days). This effect is presumably due to, but not limited to, the following reasons. When a lithium secondary battery is manufactured using the additive of the present disclosure, it is believed that during the manufacturing process (e.g., the aging process described below), a reaction product is generated near the surface of the negative electrode of the lithium secondary battery, and further, components that are decomposition products of the reaction product are generated. The reaction product refers to a product resulting from the reaction between the lithium sulfonate compound (I) and a compound (e.g., LiF) generated from the electrolyte. Such reaction products adhere to the negative electrode surface to form an SEI (Solid Electrolyte Interphase) film (hereinafter referred to as the "negative electrode SEI film"). It is believed that these components migrate to the vicinity of the positive electrode surface during the manufacturing process, adhere to the positive electrode surface, and form an SEI film (hereinafter referred to as the "positive electrode SEI film"). This improves the stability of the lithium secondary battery in high-temperature environments. For example, the elution of metal elements in the positive electrode active material is suppressed. Furthermore, as described above, the stability of lithium secondary batteries using the additives of the present disclosure is excellent even in high-temperature environments. In other words, it is believed that even when a lithium secondary battery is stored in a high-temperature environment, side reactions that are not the original battery reaction are less likely to proceed. The battery reaction involves the movement of lithium ions between the positive electrode and the negative electrode (intercalation). Side reactions include a reductive decomposition reaction of the electrolyte by the negative electrode, an oxidative decomposition reaction of the electrolyte by the positive electrode, and elution of metal elements from the positive electrode active material. This suppresses the progress of the decomposition reaction of the non-aqueous electrolyte. As a result, it is believed that an increase in the DC resistance of the lithium secondary battery is suppressed even when the lithium secondary battery is stored in a high-temperature environment for a long period of time. For the above reasons, it is presumed that the additive of the present disclosure can suppress an increase in DC resistance even when a lithium secondary battery is stored in a high-temperature environment for a long period of time.

[0027] Hereinafter, when there is no need to distinguish between the negative electrode SEI film and the positive electrode SEI film, the negative electrode SEI film or the positive electrode SEI film will simply be referred to as the "SEI film."

[0028] In formula (I), R 11 and R 12The "alkyl group having 1 to 10 carbon atoms" represented independently by the formulas above is a straight-chain or branched-chain alkyl group having from 1 to 10 carbon atoms. Examples of the "alkyl group having 1 to 10 carbon atoms" include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a 2-methylbutyl group, a 1-methylpentyl group, a neopentyl group, a 1-ethylpropyl group, a hexyl group, a 3,3-dimethylbutyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. Among these, the "alkyl group having 1 to 10 carbon atoms" is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms. At least one hydrogen atom in the "alkyl group having 1 to 10 carbon atoms" may be substituted with a halogen atom. The halogen atom in the "alkyl group having 1 to 10 carbon atoms" 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, still more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the "alkyl group having 1 to 10 carbon atoms", the number of hydrogen atoms substituted with halogen atoms is not particularly limited and is appropriately selected depending on the number of carbon atoms in the alkyl group, with 1 to 7 being preferred.

[0029] In formula (I), R 11 and R 12 The "alkenyl group having 2 to 10 carbon atoms" represented independently by the formula (I) above is a straight-chain or branched-chain alkenyl group having 2 to 10 carbon atoms. Examples of the "alkenyl group having 2 to 10 carbon atoms" include a vinyl group, a 2-propenyl group, a 2-butenyl group, a 3-butenyl group, a 2-pentenyl group, a 3-pentenyl group, a 4-pentenyl group, and a 5-hexenyl group. Among these, the "alkenyl group having 2 to 10 carbon atoms" is preferably an alkenyl group having 2 to 6 carbon atoms, and more preferably an alkenyl group having 2 to 3 carbon atoms. At least one hydrogen atom in the "alkenyl group having 2 to 10 carbon atoms" may be substituted with a halogen atom. The halogen atom in the "alkenyl group having 2 to 10 carbon atoms" 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, still more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the "alkenyl group having 2 to 10 carbon atoms", the number of hydrogen atoms substituted with halogen atoms is not particularly limited and is appropriately selected depending on the number of carbon atoms in the alkenyl group, with 1 to 7 being preferred.

[0030] In formula (I), R 11 and R 12 The "alkynyl group having 2 to 10 carbon atoms" represented independently by the formula (I) above is a straight-chain or branched-chain alkynyl group having 2 to 10 carbon atoms. Examples of the "alkynyl group having 2 to 10 carbon atoms" include an ethynyl group, a propargyl group (2-propynyl group), a 2-butynyl group, a 3-butynyl group, a 2-pentynyl group, a 3-pentynyl group, a 4-pentynyl group, and a 5-hexynyl group. Among these, the "alkynyl group having 2 to 10 carbon atoms" is preferably an alkynyl group having 2 to 6 carbon atoms, and more preferably an alkynyl group having 2 to 3 carbon atoms. At least one hydrogen atom of the "alkynyl group having 2 to 10 carbon atoms" may be substituted with a halogen atom. The halogen atom in the "alkynyl group having 2 to 10 carbon atoms" 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, still more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the "alkynyl group having 2 to 10 carbon atoms", the number of hydrogen atoms substituted with halogen atoms is not particularly limited and is appropriately selected depending on the number of carbon atoms in the alkynyl group, with 1 to 7 being preferred.

[0031] In formula (I), R 11 and R 12 At least one hydrogen atom of the "benzyl group" represented independently by the formula (I) may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms. The halogen atom in the "benzyl group" 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, further preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the "benzyl group", the number of hydrogen atoms substituted with halogen atoms is not particularly limited, and is preferably 1 to 7. In the "benzyl group", the alkyl group in the alkoxy group having 1 to 6 carbon atoms may be straight-chain, branched, or cyclic. Examples of the alkoxy group having 1 to 6 carbon atoms in the "benzyl group" include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a t-butoxy group, and a pentyloxy group. Among these, the alkoxy group having 1 to 6 carbon atoms in the "benzyl group" is preferably an alkoxy group having 1 to 3 carbon atoms, and more preferably a methoxy group or an ethoxy group. In the "benzyl group", the number of hydrogen atoms substituted by the alkoxy group having 1 to 6 carbon atoms is not particularly limited, and is preferably 1 to 3. The alkyl group having 1 to 6 carbon atoms in the "benzyl group" may be linear, branched, or cyclic. Examples of the alkyl group having 1 to 6 carbon atoms in the "benzyl group" include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, and a cyclohexyl group. Among these, the alkyl group having 1 to 6 carbon atoms in the "benzyl group" is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group or an ethyl group. In the "benzyl group", the number of hydrogen atoms substituted by the alkyl group having 1 to 6 carbon atoms is not particularly limited, and is preferably 1 to 3.

[0032] In formula (I), R 11 and R 12 At least one hydrogen atom of the "aryl group" represented independently by the formula (I) may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms. The halogen atom in the "aryl group" 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, further preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the "aryl group", the number of hydrogen atoms substituted with halogen atoms is not particularly limited, and is preferably 1 to 5. In the "aryl group", the alkyl group in the alkoxy group having 1 to 6 carbon atoms may be straight-chain, branched, or cyclic. Examples of the alkoxy group having 1 to 6 carbon atoms in the "aryl group" include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, an n-butoxy group, a t-butoxy group, and a pentyloxy group. Among these, the alkoxy group having 1 to 6 carbon atoms in the "aryl group" is preferably an alkoxy group having 1 to 3 carbon atoms, and more preferably a methoxy group or an ethoxy group. In the "aryl group", the number of hydrogen atoms substituted by the alkoxy group having 1 to 6 carbon atoms is not particularly limited, and is preferably 1 to 3. The alkyl group having 1 to 6 carbon atoms in the "aryl group" may be linear, branched, or cyclic. Examples of the alkyl group having 1 to 6 carbon atoms in the "aryl group" include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, an n-butyl group, an i-butyl group, a t-butyl group, an n-pentyl group, an n-hexyl group, and a cyclohexyl group. Among these, the alkyl group having 1 to 6 carbon atoms in the "aryl group" is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group or an ethyl group. In the "aryl group", the number of hydrogen atoms substituted by the alkyl group having 1 to 6 carbon atoms is not particularly limited, and is preferably 1 to 3.

[0033] In formula (I), R 11 and R 12 The "alkylene group which forms a 3- to 8-membered cyclic structure together with the nitrogen atom" represented by these formulas is an alkylene group which forms a cyclic structure having 3 to 8 ring members including the nitrogen atom in formula (I). Among these, the "alkylene group which forms a 3- to 8-membered cyclic structure together with the nitrogen atom" is preferably an alkylene group which forms a cyclic structure having 5 to 6 ring members including the nitrogen atom in formula (I). At least one hydrogen atom in the "alkylene group forming a 3- to 8-membered ring structure together with the nitrogen atom" may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms. The halogen atoms in the "alkylene group forming a 3- to 8-membered ring structure together with the nitrogen atom" are 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, still more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the "alkylene group forming a 3- to 8-membered ring structure together with the nitrogen atom", the number of hydrogen atoms substituted with halogen atoms is appropriately selected depending on the number of ring members. When the number of ring members including the nitrogen atom in formula (I) is 5, the number of hydrogen atoms substituted with halogen atoms is not particularly limited, and is preferably 1 to 8. The alkyl group having 1 to 10 carbon atoms in the "alkylene group which forms a 3- to 8-membered ring structure together with the nitrogen atom" is a straight-chain or branched-chain alkyl group having 1 to 10 carbon atoms. Examples of the alkyl group having 1 to 10 carbon atoms in the "alkylene group which forms a 3- to 8-membered ring structure together with the nitrogen atom" include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a pentyl group, a 2-methylbutyl group, a 1-methylpentyl group, a neopentyl group, a 1-ethylpropyl group, a hexyl group, a 3,3-dimethylbutyl group, a heptyl group, an octyl group, a nonyl group, and a decyl group. Among these, the alkyl group having 1 to 10 carbon atoms in the "alkylene group which forms a 3- to 8-membered ring structure together with the nitrogen atom" is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 3 carbon atoms. In the "alkylene group forming a 3- to 8-membered ring structure together with the nitrogen atom," the number of hydrogen atoms substituted with alkyl groups having 1 to 10 carbon atoms is appropriately selected depending on the number of ring members. When the number of ring members including the nitrogen atom in formula (I) is 5, the number of hydrogen atoms substituted with alkyl groups having 1 to 10 carbon atoms is not particularly limited, and is preferably 1 to 3.

[0034] The wavy line preferably indicates a cis form.

[0035] In formula (I), R 11 and R 12 teeth, each independently represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group; Alternatively, it is preferable that they together represent alkylene groups which form a 5- to 6-membered ring structure together with the nitrogen atom in the formula (I).

[0036] This makes it possible to further suppress an increase in DC resistance even when the lithium secondary battery is stored in a high-temperature environment for a long period of time.

[0037] Specific examples of the lithium sulfonate compound (I) include compounds represented by the following formulas (I-1) to (I-3). Hereinafter, the compound (I-1) represented by formula (I-1) may be referred to as "lithium (Z)-3-(dimethylamino)prop-1-ene-1-sulfonate (I-1)." The compound (I-2) represented by formula (I-2) may be referred to as "lithium (Z)-3-(diethylamino)prop-1-ene-1-sulfonate (I-2)." The compound (I-3) represented by formula (I-3) may be referred to as "lithium (Z)-3-(dibenzylamino)prop-1-ene-1-sulfonate (I-3)."

[0038] [ka]

[0039] The lithium sulfonate compound (I) is preferably a compound (I-1) represented by the following formula (I-1) or a compound (I-2) represented by the following formula (I-2), which can further suppress an increase in DC resistance even when the lithium secondary battery is stored in a high-temperature environment for a long period of time.

[0040] [ka]

[0041] [Non-aqueous electrolyte for lithium secondary batteries] The nonaqueous electrolyte for lithium secondary batteries (hereinafter referred to as "nonaqueous electrolyte") of the present disclosure will be described.

[0042] The nonaqueous electrolyte solution of the present disclosure is suitable for use as an electrolyte solution in lithium secondary batteries.

[0043] The nonaqueous electrolyte of the present disclosure includes the additive of the present disclosure.

[0044] The nonaqueous electrolyte solution of the present disclosure contains the additive of the present disclosure, and therefore can suppress an increase in DC resistance even when the lithium secondary battery is stored in a high-temperature environment for a long period of time.

[0045] In addition, when the non-aqueous electrolyte solution collected by disassembling a lithium secondary battery is actually analyzed, the amount of lithium sulfonate compound (I) may be found to be reduced compared to the amount added to the non-aqueous electrolyte solution. Even in this case, if even a small amount of lithium sulfonate compound (I) is detected in the non-aqueous electrolyte solution removed from the lithium secondary battery, the electrolyte solution of the lithium secondary battery is included in the scope of the non-aqueous electrolyte solution of the present disclosure.

[0046] The content of the lithium sulfonate compound (I) is not particularly limited, but is preferably 0.01% by mass or more and 5% by mass or less based on the total amount of the nonaqueous electrolyte. This allows the SEI film to operate without impairing the lithium cation conductivity, enabling the lithium secondary battery to function. The SEI film contains a sufficient amount of a structure derived from the lithium sulfonate compound (I). This facilitates the formation of a thermally and chemically stable inorganic salt or polymer structure. Therefore, elution of SEI film components, which impair the durability of the SEI film, and deterioration of the SEI film are less likely to occur at high temperatures. As a result, the durability of the SEI film and the performance of the lithium secondary battery after high-temperature storage are improved. The upper limit of the content of the lithium sulfonate compound (I) is more preferably 3.0 mass % or less, and even more preferably 2.0 mass % or less, based on the total amount of the non-aqueous electrolyte solution. The lower limit of the content of the lithium sulfonate compound (I) is more preferably 0.05% by mass or more, even more preferably 0.10% by mass or more, particularly preferably 0.20% by mass or more, and even more preferably 0.40% by mass or more, based on the total amount of the nonaqueous electrolyte.

[0047] <Compound (A)> It is preferable that the non-aqueous electrolyte solution further contains at least one compound (hereinafter referred to as "compound (A)") selected from the group consisting of compound (II) (hereinafter referred to as "lithium fluorophosphate compound (II)"), compound (III) (hereinafter referred to as "cyclic dicarbonyl compound (III)"), and compound (IV) (hereinafter referred to as "cyclic sulfonate ester compound (IV)"). The lithium fluorophosphate compound (II) is at least one of lithium monofluorophosphate and lithium difluorophosphate. The cyclic dicarbonyl compound (III) is represented by the following formula (III). The cyclic sulfonate compound (IV) is represented by the following formula (IV). Details of the lithium fluorophosphate compound (II), the cyclic dicarbonyl compound (III), and the cyclic sulfonate compound (IV) will be described later.

[0048] [ka]

[0049] By further containing the compound (A) in addition to the lithium sulfonate compound (I), the nonaqueous electrolyte solution can further suppress an increase in DC resistance even when the lithium secondary battery is stored in a high-temperature environment for a long period of time.

[0050] When the non-aqueous electrolyte solution contains the compound (A), the content of the compound (A) is preferably in the following range from the viewpoint of improving the characteristics of the lithium secondary battery after high-temperature storage. The upper limit of the content of the compound (A) is preferably 10.0 mass % or less, more preferably 5.0 mass % or less, and even more preferably 3.0 mass % or less, based on the total amount of the non-aqueous electrolyte solution. The lower limit of the content of the compound (A) is preferably 0.10% by mass or more, more preferably 0.20% by mass or more, and even more preferably 0.30% by mass or more, based on the total amount of the non-aqueous electrolyte solution.

[0051] The lithium fluorophosphate compound (II), the cyclic dicarbonyl compound (III), and the cyclic sulfonate compound (IV) will be described below.

[0052] (Lithium fluorophosphate compound (II)) The non-aqueous electrolyte preferably contains a lithium fluorophosphate compound (II). The lithium fluorophosphate compound (II) is at least one of lithium monofluorophosphate and lithium difluorophosphate. Lithium difluorophosphate is represented by the following formula (II-1), and lithium monofluorophosphate is represented by the following formula (II-2). Hereinafter, the compound represented by formula (II-1) may be referred to as "lithium fluorophosphate compound (II-1)." The compound represented by formula (II-2) may be referred to as "lithium fluorophosphate compound (II-2)."

[0053] [ka]

[0054] By including the lithium fluorophosphate compound (II) in addition to the lithium sulfonate compound (I), the nonaqueous electrolyte solution can further suppress an increase in the DC resistance of the lithium secondary battery even during charge-discharge cycles after storage in a high-temperature environment.

[0055] The non-aqueous electrolyte may contain only one of lithium monofluorophosphate and lithium difluorophosphate, or may contain both lithium monofluorophosphate and lithium difluorophosphate.

[0056] When the non-aqueous electrolyte contains the lithium fluorophosphate compound (II), the content of the lithium fluorophosphate compound (II) is preferably in the following range. The upper limit of the content of the lithium fluorophosphate compound (II) is preferably 5 mass % or less, more preferably 3 mass % or less, and even more preferably 2 mass % or less, based on the total amount of the non-aqueous electrolyte. When the upper limit of the content of the lithium fluorophosphate compound (II) is within the above range, the solubility of the lithium fluorophosphate compound (II) in the non-aqueous solvent can be ensured. The lower limit of the content of the lithium fluorophosphate compound (II) is preferably 0.001 mass % or more, more preferably 0.01 mass % or more, and even more preferably 0.1 mass % or more, based on the total amount of the non-aqueous electrolyte. When the lower limit of the content of the lithium fluorophosphate compound (II) is within the above range, the DC resistance of the lithium secondary battery can be further reduced.

[0057] (Cyclic dicarbonyl compound (III)) The nonaqueous electrolyte solution of the present disclosure preferably contains a cyclic dicarbonyl compound (III) represented by the following formula (III).

[0058] [ka]

[0059] In formula (III), M is an alkali metal; Y is a transition element, an element in Group 13, 14, or 15 of the periodic table; b is an integer from 1 to 3, m is an integer from 1 to 4, n is an integer from 0 to 8, q is 0 or 1; R 31 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 groups may contain a substituent or a heteroatom in the structure, and when q is 1 and m is 2 to 4, m R 31 may be bonded to each other. R 32is 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 heteroatom in the structure, and when n is 2 to 8, n R 32 may be bonded to each other to form a ring; Q 1 , and Q 2 are each independently an oxygen atom or a carbon atom.

[0060] By including the cyclic dicarbonyl compound (III) in addition to the lithium sulfonate compound (I) in the nonaqueous electrolyte solution of the present disclosure, the decrease in discharge capacity and the increase in DC resistance can be further suppressed even during charge-discharge cycles after storage in a high-temperature environment. This effect is presumably due to the following reasons. The nonaqueous electrolyte solution contains a cyclic dicarbonyl compound (III) in addition to the lithium sulfonate compound (I). This allows the SEI film and other components to contain bonds derived from the cyclic dicarbonyl compound (III) within the film, in addition to the reaction products described above. This facilitates the formation of a thermally and chemically stable inorganic salt or polymer structure. Therefore, leaching of components of the SEI film and other components, which impair the durability of the SEI film and other components, and deterioration of the SEI film and other components, are unlikely to occur at high temperatures. As a result, even during charge-discharge cycles after long-term storage in a high-temperature environment, the decrease in discharge capacity and the increase in DC resistance are further suppressed.

[0061] M is an alkali metal. Examples of the alkali metal include lithium, sodium, and potassium. Among these, M is preferably lithium. Y is a transition element, or an element in 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 anion compound becomes relatively easy, and production costs can be reduced. b represents the valence of the anion and the number of cations, and is an integer of 1 to 3, preferably 1. When b is 3 or less, the salt of the anionic compound is easily dissolved in the mixed organic solvent. Each of m and n is a value related to the number of ligands. Each of m and n is determined depending on the type of M. m is an integer of 1 to 4. n is an integer of 0 to 8. q is 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 31 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 a substituent or a heteroatom in their structure. Specifically, R 31 may contain a substituent in place of the hydrogen atom of these groups. Examples of the substituent include a halogen atom, a linear or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, or a hydroxyl group. The carbon element of these groups may be replaced by a nitrogen atom, a sulfur atom, or an oxygen atom. When q is 1 and m is 2 to 4, m R 31 may be bonded to each other. An example of such a ligand is ethylenediaminetetraacetic acid. R 32 represents 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 alkyl groups, halogenated alkyl groups, aryl groups, and halogenated aryl groups are represented by R 31 Similarly, the structure may contain a substituent or a heteroatom, and when n is 2 to 8, n R 32 may be bonded to each other to form a ring. 32 As the group, an electron-withdrawing group is preferred, and a fluorine atom is particularly preferred. Q1 , and Q 2 each independently represents O or C. That is, the ligand bonds to Y via these hetero atoms.

[0062] Specific examples of the cyclic dicarbonyl compound (III) include compounds represented by the following formulae (III-1) and (III-2). Hereinafter, the compound represented by formula (III-1) may be referred to as "cyclic dicarbonyl compound (III-1)".

[0063] [ka]

[0064] When the non-aqueous electrolyte contains the cyclic dicarbonyl compound (III), the content of the cyclic dicarbonyl compound (III) is preferably in the following range. The upper limit of the content of the cyclic dicarbonyl compound (III) is preferably 10% by mass or less, more preferably 5.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less, based on the total amount of the non-aqueous electrolyte. If the upper limit of the content of the cyclic dicarbonyl compound (III) is within the above range, the SEI film and the like do not impair the conductivity of lithium cations, and the lithium secondary battery can operate. Furthermore, since the SEI film and the like contain a cyclic dicarbonyl structure, the battery characteristics of the lithium secondary battery are improved. The lower limit of the content of the cyclic dicarbonyl compound (III) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more, based on the total amount of the nonaqueous electrolyte. When the lower limit of the content of the cyclic dicarbonyl compound (III) is within the above range, the SEI film or the like contains a sufficient amount of a structure mainly composed of a cyclic dicarbonyl structure. This facilitates the formation of a thermally and chemically stable inorganic salt or polymer structure. Therefore, at high temperatures, elution of components of the SEI film or the like, which impairs the durability of the SEI film or the like, and deterioration of the SEI film or the like, are unlikely to occur. As a result, the durability of the SEI film or the like and the characteristics of the lithium secondary battery after high-temperature storage are improved.

[0065] (Cyclic sulfonate ester compound (IV)) The nonaqueous electrolyte solution of the present disclosure preferably contains a cyclic sulfonate ester compound (IV) represented by the following formula (IV).

[0066] [ka]

[0067] In formula (IV), R 41 represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms, R 42 represents an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (iv-1), or a group represented by formula (iv-2), * indicates the bond position, In formula (iv-1), R 43 represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group, In formula (iv-2), R 44 is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms.

[0068] By including the cyclic sulfonate ester compound (IV) in addition to the lithium sulfonate compound (I) in the nonaqueous electrolyte solution of the present disclosure, a decrease in discharge capacity and an increase in DC resistance can be further suppressed even when the battery is stored for a long period of time in a high-temperature environment. This effect is presumably due to the following reasons. When a lithium secondary battery is manufactured using the nonaqueous electrolyte solution of the present disclosure, the reaction product during the manufacturing process (for example, the aging step described below) includes a product resulting from the reaction between the cyclic sulfonate ester compound (IV) and a compound (for example, LiF) generated from the electrolyte. This further enhances the stability of the lithium secondary battery in a high-temperature environment. As a result, even when the lithium secondary battery is stored in a high-temperature environment, it is believed that an increase in the DC resistance of the lithium secondary battery is further suppressed. Furthermore, the progress of the decomposition reaction of the nonaqueous electrolyte solution is further suppressed. As a result, even when the lithium secondary battery is stored in a high-temperature environment, it is believed that the discharge capacity of the lithium secondary battery is less likely to decrease.

[0069] In formula (IV), R 41 is preferably an alkylene group having 2 to 3 carbon atoms, a vinylene group, or an oxygen atom, more preferably a trimethylene group, a vinylene group, or an oxygen atom, and particularly preferably an oxygen atom.

[0070] In the cyclic sulfonate compound (IV), R 41 is preferably an oxygen atom. This facilitates the formation of a thermally and chemically stable inorganic salt structure. Therefore, at high temperatures, elution of components of the SEI film and the like, which impair the durability of the SEI film and the like, and deterioration of the SEI film and the like, are unlikely to occur. As a result, the durability of the SEI film and the like and the battery characteristics of the lithium secondary battery are improved.

[0071] In formula (IV), R 42 is preferably a group represented by formula (iv-1) or a group represented by formula (iv-2). In formula (iv-1), R 43 is preferably an alkylene group having 1 to 3 carbon atoms, an alkenylene group having 1 to 3 carbon atoms, or an oxymethylene group, and more preferably an oxymethylene group. In formula (iv-2), R 44 is preferably an alkyl group having 1 to 3 carbon atoms or an alkenyl group having 2 to 3 carbon atoms, and more preferably a propyl group.

[0072] Specific examples of the cyclic sulfonate compound (IV) include compounds represented by formulae (IV-1) to (IV-8). Hereinafter, the compound represented by formula (IV-1) may be referred to as "cyclic sulfonate compound (IV-1)".

[0073] [ka]

[0074] The non-aqueous electrolyte may contain only one type of cyclic sulfonate compound (IV), or may contain two or more types.

[0075] When the non-aqueous electrolyte contains the cyclic sulfonate compound (IV), the content of the cyclic sulfonate compound (IV) is preferably in the following range. The upper limit of the content of the cyclic sulfonate compound (IV) is preferably 5.0 mass% or less, more preferably 3.0 mass% or less, and even more preferably 2.0 mass% or less, based on the total amount of the non-aqueous electrolyte. When the upper limit of the content of the cyclic sulfonate compound (IV) is within the above range, the SEI film and the like do not impair the lithium ion conductivity, and the lithium secondary battery can operate. Furthermore, since the SEI film and the like contain a cyclic sulfur-containing ester structure, the battery characteristics of the lithium secondary battery are improved. The lower limit of the content of the cyclic sulfonate ester compound (IV) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more, based on the total amount of the nonaqueous electrolyte. When the lower limit of the content of the cyclic sulfonate ester compound (IV) is within the above range, the SEI film or the like contains a sufficient amount of cyclic sulfur-containing ester structure. This facilitates the formation of a thermally and chemically stable inorganic salt or polymer structure. Therefore, at high temperatures, elution of components of the SEI film or the like, which impairs the durability of the SEI film or the like, and deterioration of the SEI film or the like, are unlikely to occur. As a result, the durability of the SEI film or the like and the battery characteristics of the lithium secondary battery are improved.

[0076] <Other additives> The nonaqueous electrolyte of the present disclosure may contain other additives. The other additives are not particularly limited, and any known additives can be used. As other additives, for example, additives described in paragraphs 0042 to 0055 of JP-A-2019-153443 can be used.

[0077] <Non-aqueous solvent> The non-aqueous electrolyte generally contains a non-aqueous solvent. Various known non-aqueous solvents can be appropriately selected as the non-aqueous solvent. The non-aqueous solvent may be one type or two or more types.

[0078] Examples of non-aqueous solvents include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, γ-lactones, fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, fluorine-containing chain ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, 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 chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC). Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, and ethyl trimethylbutyrate. Examples of γ-lactones include γ-butyrolactone and γ-valerolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane. Examples of chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile. Examples of amides include N,N-dimethylformamide. Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

[0079] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates. In this case, the total proportion of the cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the non-aqueous solvent.

[0080] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and chain carbonates. In this case, the total proportion of cyclic carbonates and chain carbonates in the non-aqueous solvent is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the non-aqueous solvent.

[0081] The upper limit of the content of the nonaqueous solvent is preferably 99 mass %, more preferably 97 mass %, and even more preferably 90 mass %, based on the total amount of the nonaqueous electrolyte. The lower limit of the content of the nonaqueous solvent is preferably 60 mass % or more, and even more preferably 70 mass % or more, based on the total amount of the nonaqueous electrolyte.

[0082] 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 property of the electrolyte and the mobility of ions.

[0083] <Electrolytes> The non-aqueous electrolyte generally contains an electrolyte.

[0084] The electrolyte preferably contains at least one of a fluorine-containing lithium salt (hereinafter sometimes referred to as a "fluorine-containing lithium salt") and a fluorine-free lithium salt.

[0085] Examples of the fluorine-containing lithium salt include inorganic acid anion salts and organic acid anion salts. Examples of inorganic acid anion salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), and lithium hexafluorotantalate (LiTaF6). Examples of organic acid anion salts include lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (Li(FSO2)2N), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), and lithium bis(pentafluoroethanesulfonyl)imide (Li(C2F5SO2)2N). Among these, lithium hexafluorophosphate (LiPF6) is particularly preferred as the fluorine-containing lithium salt.

[0086] Fluorine-free lithium salts include lithium perchlorate (LiClO4), lithium tetrachloroaluminate (LiAlCl4), and lithium decachlorodecaborate (Li2B 10 Cl 10 ) etc.

[0087] When the electrolyte contains a fluorine-containing lithium salt, the content of the fluorine-containing lithium salt is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the electrolyte. When the fluorine-containing lithium salt contains lithium hexafluorophosphate (LiPF6), the content of lithium hexafluorophosphate (LiPF6) is preferably 50% by mass or more and 100% by mass or less, more preferably 60% by mass or more and 100% by mass or less, and even more preferably 80% by mass or more and 100% by mass or less, based on the total amount of the electrolyte.

[0088] When the non-aqueous electrolyte contains an electrolyte, the concentration of the electrolyte in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, and more preferably 0.5 mol / L or more and 2 mol / L or less.

[0089] When the non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF6), the concentration of lithium hexafluorophosphate (LiPF6) in the non-aqueous electrolyte is preferably 0.1 mol / L or more and 3 mol / L or less, more preferably 0.5 mol / L or more and 2 mol / L or less.

[0090] <Other ingredients> The non-aqueous electrolyte may contain other components as needed. Other components include acid anhydrides.

[0091] [Lithium secondary battery precursor] Next, the lithium secondary battery precursor of the present disclosure will be described.

[0092] The lithium secondary battery precursor of the present disclosure includes a case, a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode, negative electrode, separator, and electrolyte are housed in the case. The positive electrode is a positive electrode capable of absorbing and desorbing lithium ions. The negative electrode is a negative electrode capable of absorbing and desorbing lithium ions. The electrolyte is the nonaqueous electrolyte of the present disclosure.

[0093] The lithium secondary battery precursor refers to a lithium secondary battery before charging and discharging. That is, in the lithium secondary battery precursor, the negative electrode does not include a negative electrode SEI film, and the positive electrode does not include a positive electrode SEI film.

[0094] <Case> The shape of the case is not particularly limited and may be appropriately selected depending on the application of the lithium secondary battery precursor of the present disclosure, etc. Examples of the case include a case including a laminate film and a case consisting of a battery can and a battery can lid.

[0095] <Positive electrode> The positive electrode is a positive electrode capable of absorbing and desorbing lithium ions, and preferably contains at least one positive electrode active material capable of absorbing and desorbing lithium ions.

[0096] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer. The positive electrode mixture layer is provided on at least a portion of the surface of the positive electrode current collector.

[0097] Examples of the material for the positive electrode current collector include metals and alloys. Specifically, examples of the material for the positive electrode current collector include aluminum, nickel, stainless steel (SUS), and copper. Among these, aluminum is preferred from the viewpoint of the balance between high conductivity and cost. Here, "aluminum" refers to pure aluminum or an aluminum alloy. Aluminum foil is preferred as the positive electrode current collector. The material for the aluminum foil is not particularly limited, and examples include A1085 material, A3003 material, and the like.

[0098] The positive electrode mixture layer includes a positive electrode active material and a binder.

[0099] The positive electrode active material is not particularly limited as long as it is a material that can absorb and release lithium ions, and can be adjusted appropriately depending on the application of the lithium secondary battery precursor.

[0100] Examples of positive electrode active materials include a first oxide and a second oxide. The first oxide contains lithium (Li) and nickel (Ni) as constituent metal elements. The second oxide contains Li, Ni, and at least one metal element other than Li and Ni as constituent metal elements. Examples of metal elements other than Li and Ni include transition metal elements and typical metal elements. The second oxide preferably contains the metal elements other than Li and Ni in an amount equivalent to or less than Ni in atomic number terms. The metal element other than Li and Ni may be, for example, 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 alone or in combination.

[0101] 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 advantages of high energy density per unit volume and excellent thermal stability. LiNi a Cob Mn c O2… Formula (P1) In formula (P1), a, b, and c each independently represent a number greater than 0 and less than 1, and the sum of a, b, and c represents a number greater than or equal to 0.99 and less than or equal to 1.00. A specific example of NCM is LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2.

[0102] The positive electrode active material may contain a lithium-containing composite oxide (hereinafter, sometimes referred to as "NCA") represented by the following formula (P2). Li t Ni 1-x-y Co x Al y O2… Formula (P2) In formula (P2), t is 0.95 or more and 1.15 or less, x is 0 or more and 0.3 or less, y is 0.1 or more and 0.2 or less, and the sum of x and y is less than 0.5. A specific example of NCA is LiNi 0.8 Co 0.15 Al 0.05 Examples include O2.

[0103] When the positive electrode in the lithium secondary battery precursor of the present disclosure includes a positive electrode current collector and a positive electrode mixture layer containing a positive electrode active material and a binder, the content of the positive electrode active material in the positive electrode mixture 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, relative to the total amount of the positive electrode mixture layer. The content of the positive electrode active material in the positive electrode mixture layer is preferably 99.9% by mass or less, more preferably 99% by mass or less, relative to the total amount of the positive electrode mixture layer.

[0104] Examples of binders include polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesin, and rubber particles. Examples of fluororesin 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, fluororesin is preferred from the viewpoint of improving the oxidation resistance of the positive electrode mixture layer. One type of binder can be used alone, or two or more types can be used in combination as needed. The content of the binder in the positive electrode mixture layer is preferably 0.1% by mass or more and 4% by mass or less, based on the total amount of the positive electrode mixture layer, from the viewpoint of achieving both the physical properties of the positive electrode mixture 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 mixture layer to the positive electrode current collector and the binding strength between the positive electrode active materials are further improved. When the binder content is 4% by mass or less, the amount of positive electrode active material in the positive electrode mixture layer can be increased, thereby further improving the discharge capacity.

[0105] The positive electrode mixture layer preferably contains a conductive additive. Known conductive additives can be used as the material for the conductive additive. As known conductive additives, conductive carbon materials are preferred. Examples of conductive carbon materials include graphite, carbon black, conductive carbon fiber, and fullerene. These can be used alone or in combination of two or more. 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 amorphous graphite. The material of the conductive additive may be a commercially available product. Examples of commercially available carbon black include Toka Black #4300, #4400, #4500, #5500, etc. (furnace black manufactured by Tokai Carbon Co., Ltd.), Printex L, etc. (furnace black manufactured by Degussa Corporation), Raven 7000, 5750, 5250, 5000ULTRA III, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975ULTRA, etc., and PUER BLACK100, 115, 205, etc. (Columbian Furnace Black), #2350, #2400B, #2600B, #30050B, #3030B, #3230B, #3350B, #3400B, #5400B, etc. (Mitsubishi Chemical Furnace Black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, Examples include LITX-50, LITX-200 (furnace black, manufactured by Cabot Corporation), Ensaco250G, Ensaco260G, Ensaco350G, Super-P (manufactured by TIMCAL), Ketjenblack EC-300J, EC-600JD (manufactured by Akzo), Denkablack, Denkablack HS-100, FX-35 (acetylene black, manufactured by Denka Co., Ltd.), and the like.

[0106] The positive electrode mixture layer may contain other components such as a thickener, a surfactant, a dispersant, a wetting agent, and an antifoaming agent.

[0107] <Negative electrode> The negative electrode is capable of absorbing and desorbing lithium ions, and preferably contains at least one negative electrode active material capable of absorbing and desorbing lithium ions.

[0108] More preferably, the negative electrode includes a negative electrode current collector and a negative electrode mixture layer, the negative electrode mixture layer being provided on at least a portion of the surface of the negative electrode current collector.

[0109] The material of the negative electrode current collector is not particularly limited and any known material can be used, for example, a metal or alloy. Specifically, the material of the negative electrode current collector can be aluminum, nickel, stainless steel (SUS), nickel-plated steel, copper, etc. Among them, copper is preferred as the material of the negative electrode current collector from the viewpoint of workability. Copper foil is preferred as the negative electrode current collector.

[0110] The negative electrode mixture layer contains a negative electrode active material and a binder.

[0111] The negative electrode active material is not particularly limited as long as it is a material capable of absorbing and releasing lithium ions. The negative electrode active material is preferably at least one material selected from the group consisting of metallic lithium, lithium-containing alloys, metals or alloys capable of alloying with lithium, oxides capable of doping and dedoping lithium ions, transition metal nitrides capable of doping and dedoping lithium ions, and carbon materials capable of doping and dedoping lithium ions. Among these, the negative electrode active material is preferably a carbon material capable of doping and dedoping lithium ions (hereinafter referred to as "carbon material").

[0112] Examples of carbon materials include carbon black, activated carbon, graphite materials, and amorphous carbon materials. These carbon materials may be used alone or in combination of two or more. The form of the carbon material is not particularly limited, and examples include fibrous, spherical, potato-like, and flake-like forms. The particle size of the carbon material is not particularly limited, and is preferably 5 μm to 50 μm, more preferably 20 μm to 30 μm. Examples of amorphous carbon materials include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500° C. or less, 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. The graphite material may contain boron. The graphite material may be coated with a metal or amorphous carbon. Examples of metal materials that coat the graphite material include gold, platinum, silver, copper, and tin. The graphite material may be a mixture of amorphous carbon and graphite.

[0113] The negative electrode mixture layer preferably contains a conductive additive. Examples of the conductive additive include the same conductive additives as those exemplified as the conductive additives that can be contained in the positive electrode mixture layer.

[0114] In addition to the above components, the negative electrode mixture layer may contain other components such as a thickener, a surfactant, a dispersant, a wetting agent, and an antifoaming agent.

[0115] <separator> The separator may be, for example, a porous resin plate. Materials for the porous resin plate include resin and nonwoven fabric containing the resin. Examples of resin include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, and polyamide. In particular, the separator is preferably a porous resin sheet having a single layer or a multilayer structure. The porous resin sheet is mainly made of one or more polyolefin resins. The thickness of the separator is preferably 5 μm or more and 30 μm or less. The separator is preferably disposed between the positive electrode and the negative electrode.

[0116] [Example of lithium secondary battery precursor] An example of a lithium secondary battery precursor 1 according to an embodiment of the present disclosure will be specifically described with reference to Fig. 1. Fig. 1 is a cross-sectional view of a lithium secondary battery precursor 1 according to an embodiment of the present disclosure.

[0117] The lithium secondary battery precursor 1 is a laminated type. As shown in FIG. 1, in the lithium secondary battery precursor 1, a battery element 10 is enclosed inside an exterior body 30. The exterior body 30 is formed of a laminate film. A positive electrode lead 21 and a negative electrode lead 22 are attached to the battery element 10. 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 exterior body 30.

[0118] As shown in FIG. 1 , battery element 10 is formed by laminating positive electrode 11, separator 13, and negative electrode 12. Positive electrode 11 has positive electrode composite layer 11B formed on both main surfaces of positive electrode current collector 11A. Negative electrode 12 has negative electrode composite layer 12B formed on both main surfaces of negative electrode current collector 12A. Positive electrode composite layer 11B formed on one main surface of positive electrode current collector 11A of positive electrode 11 and negative electrode composite layer 12B formed on one main surface of negative electrode current collector 12A of negative electrode 12 adjacent to positive electrode 11 face each other with separator 13 interposed therebetween.

[0119] The nonaqueous electrolyte solution of the present disclosure is poured into the interior of the exterior housing 30 of the lithium secondary battery precursor 1. The nonaqueous electrolyte solution of the present 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, one unit cell layer 14 is formed by the adjacent positive electrode composite layer 11B, the separator 13, and the negative electrode composite layer 12B. Note that the positive electrode and the negative electrode may each have an active material layer formed on one side of the respective current collectors.

[0120] In this embodiment, the lithium secondary battery precursor 1 is a laminated type, but the present disclosure is not limited thereto and may be, for example, a wound type. The wound type is formed by stacking a positive electrode, a separator, a negative electrode, and a separator in this order and winding them into a layered shape. The wound type includes a cylindrical type and a rectangular type.

[0121] 1 , the directions in which the positive electrode lead and the negative electrode lead protrude from the inside to the outside of the exterior body 30 are opposite directions relative to the exterior body 30, but the present disclosure is not limited thereto. For example, the directions in which the positive electrode lead and the negative electrode lead protrude from the inside to the outside of the exterior body 30 may be the same direction relative to the exterior body 30.

[0122] An example of the lithium secondary battery according to the embodiment of the present disclosure described below is a lithium secondary battery in which an SEI film is formed on each surface of the positive electrode composite layer 11B and the negative electrode composite layer 12B in the lithium secondary battery precursor 1 by charging and discharging the lithium secondary battery precursor 1.

[0123] Another example of the lithium secondary battery precursor of the present disclosure is a coin-type battery. FIG. 2 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. 2, a disc-shaped negative electrode 42, a separator 45 filled with a non-aqueous electrolyte, a disc-shaped positive electrode 41, and, if necessary, spacer plates 47 and 48 made of stainless steel, aluminum, or the like, are stacked in this order and housed between a positive electrode can 43 (hereinafter also referred to as the "battery can") and a 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 with a gasket 46 interposed therebetween. In this example, the nonaqueous electrolyte of the present disclosure is used as the nonaqueous electrolyte injected into separator 45 .

[0124] [Lithium secondary battery] Next, the lithium secondary battery of the present disclosure will be described.

[0125] The lithium secondary battery of the present disclosure includes a case, a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode, negative electrode, separator, and electrolyte are housed in a case. The positive electrode is a positive electrode capable of absorbing and desorbing lithium ions. The negative electrode is a negative electrode capable of absorbing and desorbing lithium ions. The electrolyte is the nonaqueous electrolyte of the present disclosure. The negative electrode includes a negative electrode SEI film. The positive electrode includes a positive electrode SEI.

[0126] The lithium secondary battery of the present disclosure differs from the lithium secondary battery precursor of the present disclosure mainly in the first point that the negative electrode includes a negative electrode SEI film and the second point that the positive electrode includes a positive electrode SEI film. That is, the lithium secondary battery of the present disclosure is similar to the lithium secondary battery precursor of the present disclosure except for the first and second points. Therefore, hereinafter, a description of the components of the lithium secondary battery of the present disclosure other than the first and second points will be omitted.

[0127] Regarding the first point, when the negative electrode includes a negative electrode current collector and a negative electrode composite layer, the phrase "the negative electrode includes a negative electrode SEI film" includes a first negative electrode form and a second negative electrode form. The first negative electrode form refers to a form in which the negative electrode SEI film is formed on at least a portion of the surface of the negative electrode composite layer. The second negative electrode form refers to a form in which the negative electrode SEI film is formed on the surface of the negative electrode active material, which is a constituent material of the negative electrode composite layer.

[0128] Regarding the second point, when the positive electrode includes a positive electrode current collector and a positive electrode composite layer, the phrase "the positive electrode includes a positive electrode SEI film" includes a first positive electrode form and a second positive electrode form. The first positive electrode form refers to a form in which a positive electrode SEI film is formed on at least a portion of the surface of the positive electrode composite layer. The second positive electrode form refers to a form in which a positive electrode SEI film is formed on the surface of a positive electrode active material, which is a constituent material of the positive electrode composite layer.

[0129] The SEI film contains, for example, at least one selected from the group consisting of a decomposition product of the lithium sulfonate compound (I), a reaction product of the lithium sulfonate compound (I) with an electrolyte, and a decomposition product of the reaction product.

[0130] The components of the negative electrode SEI film and the positive electrode SEI film may be the same or different, and the thicknesses of the negative electrode SEI film and the positive electrode SEI film may be the same or different.

[0131] The lithium secondary battery of the present disclosure is obtained by charging and discharging the lithium secondary battery precursor of the present disclosure. In other words, the lithium secondary battery of the present disclosure is obtained by performing the aging step described below.

[0132] [Lithium sulfonate compounds] The lithium sulfonate compound of the present disclosure is represented by the following formula (I):

[0133] [ka]

[0134] In formula (I), R 11 and R 12 teeth, each independently represents an alkyl group having 1 to 10 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), an alkenyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), a benzyl group (at least one hydrogen atom in the benzyl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), or an aryl group (at least one hydrogen atom in the aryl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), Alternatively, they represent alkylene groups which together with the nitrogen atom in formula (I) form a 3- to 8-membered cyclic structure (at least one hydrogen atom in the alkylene group may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms). The wavy line indicates a trans or cis form.

[0135] The lithium sulfonate compound of the present disclosure has the above-described structure, and therefore, when added to a nonaqueous electrolyte solution of a lithium secondary battery, an increase in DC resistance can be suppressed even when the lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0136] Examples of the lithium sulfonate compound of the present disclosure include the same compounds as those exemplified as the lithium sulfonate compound (I).

[0137] In formula (I), the R 11 and R 12 teeth, each independently represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group; Alternatively, it is preferable that they together represent alkylene groups which form a 5- to 6-membered ring structure together with the nitrogen atom in the formula (I).

[0138] As a result, when the lithium sulfonate compound of the present disclosure is added to a nonaqueous electrolyte solution of a lithium secondary battery, an increase in DC resistance can be further suppressed even when the lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0139] The lithium sulfonate compound of the present disclosure is preferably one selected from the group consisting of a compound (I-1) represented by the following formula (I-1), a compound (I-2) represented by the following formula (I-2), and a compound (I-3) represented by the following formula (I-3).

[0140] [ka]

[0141] When the lithium sulfonate compound of the present disclosure is one selected from the group consisting of compound (I-1), compound (I-2), and compound (I-3), and the lithium sulfonate compound of the present disclosure is added to a nonaqueous electrolyte solution of a lithium secondary battery for use, an increase in DC resistance can be further suppressed even when the lithium secondary battery is stored in a high-temperature environment for a long period of time.

[0142] [Method for producing lithium sulfonate compound] Next, a method for producing the lithium sulfonate compound (I) of the present disclosure will be described.

[0143] The method for producing the lithium sulfonate compound (I) includes a first step (described later) and a second step (described later). The first step and the second step are carried out in this order. This allows the lithium sulfonate compound (I) of the present disclosure to be obtained.

[0144] <First step> In the first step, 5H-1,2-oxathiol 2,2-dioxide represented by the following formula (IV-4) is reacted with a specific amine compound in an organic solvent and washed, thereby obtaining ammonium sulfonate compound (I') represented by the following formula (I').

[0145] [ka]

[0146] The specific amine compound is either a secondary amine or a cyclic amine, and is appropriately selected depending on the type of the lithium sulfonate compound (I) that is the product. Examples of secondary amines include dimethylamine, diethylamine, di-n-propylamine, di-i-propylamine, di-n-butylamine, di-i-butylamine, di-sec-butylamine, di-tert-butylamine, diallylamine, dicyclohexylamine, di-n-octylamine, dibenzylamine, methylethylamine, methyl-n-propylamine, methyl-i-propylamine, methyl-n-butylamine, methyl-i-butylamine, methyl-sec-butylamine, methyl-tert-butylamine, ethyl-n-propylamine, ethyl-i-propylamine, ethyl-n-butylamine, ethyl-i-butylamine, ethyl n-propyl-sec-butylamine, ethyl-tert-butylamine, n-propyl-i-propylamine, n-propyl-n-butylamine, n-propyl-i-butylamine, n-propyl-sec-butylamine, n-propyl-tert-butylamine, i-propyl-n-butylamine, i-propyl-i-butylamine, i-propyl-sec-butylamine, i-propyl-tert-butylamine, n-butyl-i-butylamine, n-butyl-sec-butylamine, n-butyl-tert-butylamine, i-butyl-sec-butylamine, i-butyl-tert-butylamine, and sec-butyl-tert-butylamine. Examples of cyclic amines include pyrrolidine, piperidine, pyrrole, and morpholine. Examples of organic solvents include tetrahydrofuran, diethyl ether, dimethoxyethane, 1,4-dioxane, acetone, ethyl acetate, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, pentane, hexane, heptane, octane, nonane, decane, toluene, xylene (e.g., ortho-xylene, meta-xylene, para-xylene, etc.), ethylbenzene, butylbenzene, pentylbenzene, hexylbenzene, heptylbenzene, propylbenzene, isopropylbenzene (also known as cumene), cyclohexylbenzene, tetralin, mesitylene, methylcyclopentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, and cyclononane.

[0147] The reaction of 5H-1,2-oxathiol 2,2-dioxide with a specific amine compound can be carried out either under normal pressure or under reduced pressure. The reaction temperature is preferably from -20°C to 60°C, more preferably from 0°C to 40°C, and even more preferably from 10°C to 30°C. The reaction time is preferably 3 hours or more and 30 hours or less, more preferably 10 hours or more and 20 hours or less, from the viewpoint of efficiently progressing the reaction.

[0148] <Second process> In the second step, the ammonium sulfonate compound (I') is reacted with a lithium salt compound in a solvent to obtain the lithium sulfonate compound (I).

[0149] Examples of the lithium salt compound include lithium carbonate, lithium bis(trimethylsilyl)amide, lithium chloride, lithium hydroxide, lithium methoxide, lithium ethoxide, lithium t-butoxide, etc. Among these, the lithium salt compound is preferably lithium carbonate, lithium bis(trimethylsilyl)amide, lithium chloride, or lithium hydroxide, and more preferably lithium carbonate.

[0150] The reaction in the second step can be carried out under either normal pressure or reduced pressure. The reaction in the second step is preferably carried out under an inert atmosphere to prevent the inclusion of components (e.g., moisture) that inhibit the production of the lithium sulfonate compound (I). Examples of the inert atmosphere include a nitrogen atmosphere and an argon atmosphere. The reaction temperature in the second step is preferably -20°C or higher and 60°C or lower, more preferably 0°C or higher and 40°C or lower, and even more preferably 10°C or higher and 30°C or lower. The reaction time in the second step is preferably 30 minutes to 12 hours, more preferably 1 hour to 6 hours, from the viewpoint of efficiently progressing the reaction.

[0151] [Method for producing non-aqueous electrolyte] Next, a method for producing the nonaqueous electrolyte solution of the present disclosure will be described.

[0152] The method for producing a nonaqueous electrolyte solution according to the present disclosure includes a synthesis step, a dissolution step, and a mixing step. The dissolution step and the mixing step are performed in this order. The synthesis step may be performed before the mixing step.

[0153] In the synthesis step, a lithium sulfonate compound (I) is synthesized. The synthesis step can be carried out in the same manner as the above-mentioned method for producing the lithium sulfonate compound (I).

[0154] In the dissolving step, an electrolyte is dissolved in a non-aqueous solvent to obtain a solution. It is preferable that the electrical conductivity of the obtained non-aqueous electrolyte solution is reduced compared to the electrical conductivity of the solution before adding the lithium sulfonate compound (I).

[0155] In the mixing step, the lithium sulfonate compound (I) and, if necessary, other additives are added to the solution and mixed. This results in a nonaqueous electrolyte solution. The nonaqueous electrolyte solution obtained by the method for producing a nonaqueous electrolyte solution according to this embodiment more effectively exhibits the effect of reducing DC resistance in lithium secondary batteries.

[0156] The method for producing a nonaqueous electrolyte solution according to the present disclosure includes a synthesis step, a dissolution step, and a mixing step, but the present disclosure is not limited thereto.

[0157] [Method for producing a lithium secondary battery precursor] Next, a method for producing a lithium secondary battery precursor according to the present disclosure will be described.

[0158] The method for producing a lithium secondary battery precursor of the present disclosure includes a first preparation step, a second preparation step, a third preparation step, a containing step, and an injection step. The containing step and the injection step are performed in this order. Each of the first preparation step, the second preparation step, and the third preparation step is performed before the containing step.

[0159] In the first preparation step, a positive electrode is prepared. The positive electrode can be prepared, for example, by applying a positive electrode mixture slurry to the surface of a positive electrode current collector and drying the slurry. The positive electrode mixture slurry contains a positive electrode active material and a binder. The solvent contained in the positive electrode mixture slurry is preferably an organic solvent, such as N-methyl-2-pyrrolidone (NMP). The method for applying the positive electrode mixture slurry is not particularly limited, and examples thereof include slot die coating, slide coating, curtain coating, and gravure coating. The method for drying the positive electrode mixture slurry is not particularly limited, and examples thereof include drying with warm air, hot air, or low-humidity air; vacuum drying; and drying by infrared (e.g., far-infrared) irradiation. The drying time is not particularly limited, and is preferably 1 minute to 30 minutes. The drying temperature is not particularly limited, and is preferably 40°C to 80°C. The cathode composite slurry is applied to a cathode current collector, and the dried product is preferably subjected to a pressure treatment. This reduces the porosity of the cathode active material layer. Examples of pressure treatment methods include die pressing and roll pressing.

[0160] In the second preparation step, a negative electrode is prepared. The negative electrode can be prepared, for example, by applying a negative electrode mixture slurry to the surface of a negative electrode current collector and drying the slurry. The negative electrode mixture slurry contains a negative electrode active material and a binder. Examples of the solvent contained in the negative electrode mixture slurry include water and a liquid medium compatible with water. When the solvent contained in the negative electrode mixture slurry includes a liquid medium compatible with water, the coating properties on the negative electrode current collector can be improved. Examples of the liquid medium compatible with water include alcohols, glycols, cellosolves, aminoalcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers, and nitriles. The method for applying, drying, and pressurizing the negative electrode composite slurry may be the same as the methods exemplified for applying, drying, and pressurizing the positive electrode composite slurry.

[0161] In the third preparation step, a non-aqueous electrolyte solution is prepared by the same method as described above in the method for producing a non-aqueous electrolyte solution.

[0162] In the housing step, the positive electrode, the negative electrode, and the separator are housed in a case. For example, in the housing step, a battery element is formed from a positive electrode, a negative electrode, and a separator. Next, the positive electrode current collector of the positive electrode is electrically connected to the positive electrode lead, and the negative electrode current collector of the negative electrode is electrically connected to the negative electrode lead. Next, the battery element is housed and fixed in a case. The method for electrically connecting the positive electrode current collector and the positive electrode lead is not particularly limited, and examples thereof include ultrasonic welding, resistance welding, etc. The method for electrically connecting the negative electrode current collector and the negative electrode lead is not particularly limited, and examples thereof include ultrasonic welding, resistance welding, etc.

[0163] Hereinafter, the state in which the positive electrode, negative electrode, and separator are housed in the case will be referred to as an "assembly."

[0164] In the injection step, the nonaqueous electrolyte solution of the present disclosure is injected into the assembly, thereby allowing the nonaqueous electrolyte solution to permeate the positive electrode mixture layer, the separator, and the negative electrode mixture layer, thereby obtaining a lithium secondary battery precursor.

[0165] [Method for manufacturing lithium secondary battery] Next, a method for producing the lithium secondary battery of the present disclosure will be described.

[0166] The method for manufacturing a lithium secondary battery according to the present disclosure includes a fourth preparation step and an aging step, which are carried out in this order.

[0167] In the fourth preparation step, a lithium secondary battery precursor is prepared. The method for preparing the lithium secondary battery precursor is the same as the method described in the method for producing a lithium secondary battery precursor.

[0168] In the aging step, the lithium secondary battery precursor is subjected to aging treatment, whereby a negative electrode SEI film and a positive electrode SEI film are formed, that is, a lithium secondary battery is obtained. The aging treatment includes charging and discharging the lithium secondary battery precursor in an environment of 25° C. to 70° C. Specifically, the aging treatment includes a first charging phase, a first holding phase, a second charging phase, a second holding phase, and a charge / discharge phase. In the first charging phase, the lithium secondary battery precursor is charged in an environment of 25°C or higher and 70°C or lower. In the first holding phase, the lithium secondary battery precursor after the first charging phase is held in an environment of 25°C or higher and 70°C or lower. In the second charging phase, the lithium secondary battery precursor after the first holding phase is charged in an environment of 25°C or higher and 70°C or lower. In the second holding phase, the lithium secondary battery precursor after the second charging phase is held in an environment of 25°C or higher and 70°C or lower. In the charge / discharge phase, the lithium secondary battery precursor after the second holding phase is subjected to a combination of charging and discharging one or more times in an environment of 25°C or higher and 70°C or lower.

[0169] The lithium secondary battery obtained by the method for producing a lithium secondary battery according to the present disclosure more effectively exhibits the effect of suppressing an increase in DC resistance and a decrease in discharge capacity even when stored in a high-temperature environment. [Example]

[0170] Hereinafter, embodiments of the present disclosure will be described in detail with reference to examples, but the present disclosure is not limited to the descriptions of these examples.

[0171] [Synthesis of lithium sulfonate compound (I)] Compounds (I-1) to (I-3), compound (C-1) and compound (C-2) were synthesized as follows.

[0172] [Synthesis Example 1] Lithium (Z)-3-(dimethylamino)prop-1-ene-1-sulfonate (I-1) represented by the following formula (I-1) was synthesized as follows.

[0173] [ka]

[0174] <First step: (Z)-3-(dimethyl-λ 4 Synthesis of (Azanil)prop-1-ene-1-sulfonate (I-1') A 200 mL four-neck flask was charged with 5H-1,2-oxathiol 2,2-dioxide (5.0 g, 41.6 mmol) and tetrahydrofuran (100 mL) as a solvent, maintained at 0°C, and a dimethylamine solution (2 M tetrahydrofuran solution, 25 mL, 49.9 mmol) was added. After the addition of the dimethylamine solution was completed, the temperature was raised and the reaction was stirred at room temperature (25°C). After 16 hours from the start of the reaction, n-hexane (50 mL) was added, and the reaction was stopped after stirring for 2 hours, to obtain a reaction solution. The resulting reaction solution was filtered, and the residue (i.e., white solid) was washed twice with n-hexane (50 mL). 4 -azaneil)prop-1-ene-1-sulfonate (I-1') (6.02 g, 36.4 mmol, 88% yield) was obtained. White solid 1 The results of H-NMR (DMSO-d) are shown below. 1 H-NMR: δ2.76(s,6H), 4.15(dd, J=7.0Hz, 1.4Hz, 2H), 5.68(dt, J=11.4Hz, 7.2Hz, 1H), 6.51(dt, J=11.2Hz, 1.4Hz, 1H)

[0175] <Second Step: Synthesis of Lithium (Z)-3-(dimethylamino)prop-1-ene-1-sulfonate (I-1)> In a 200 mL eggplant-shaped flask, add (Z)-3-(dimethyl-λ4 (-azaneil)prop-1-ene-1-sulfonate (I-1') (6.02 g, 36.4 mmol), tetrahydrofuran (50 mL) as a solvent, and pure water (50 mL) were charged and kept at room temperature. Lithium carbonate (1.62 g, 21.9 mmol) was added, and after stirring for 3 hours, the reaction was stopped to obtain a reaction solution. The reaction solution was filtered to remove insoluble matter, and then concentrated under reduced pressure. In other words, tetrahydrofuran and water components were removed from the reaction solution. This gave lithium (Z)-3-(dimethylamino)prop-1-ene-1-sulfonate (I-1) (4.45 g, 26.0 mmol, 71% yield) as a yellow solid. Yellow solid 1 The results of H-NMR (DMSO-d) are shown below. 1 H-NMR: δ2.38(s,6H), 3.64(dd, J=6.8Hz, 1.4Hz, 2H), 5.59(dt, J=11.4Hz, 6.4Hz, 1H), 6.26(dt, J=11.6Hz, 1.8Hz, 1H)

[0176] As described above, based on the results of Synthesis Example 1, lithium (Z)-3-(dimethylamino)prop-1-ene-1-sulfonate (I-1) was obtained according to the following reaction scheme.

[0177] [ka]

[0178] [Synthesis Example 2] Lithium (Z)-3-(diethylamino)prop-1-ene-1-sulfonate (I-2) represented by the following formula (I-2) was synthesized as follows.

[0179] [ka]

[0180] <First step: (Z)-3-(diethyl-λ 4Synthesis of (Azanil)prop-1-ene-1-sulfonate (I-2') The synthesis was carried out in the same manner as in the first step of Synthesis Example 1, except that 5H-1,2-oxathiol 2,2-dioxide (10.0 g, 83 mmol) was used in the first step of Synthesis Example 1, and the dimethylamine solution was changed to diethylamine (6.09 g, 83 mmol). This resulted in the formation of a white solid, (Z)-3-(diethyl-λ 4 -azaneil)prop-1-ene-1-sulfonate (I-2') (6.12 g, 31.7 mmol, yield 38.0%) was obtained. White solid 1 The results of H-NMR (DMSO-d) are shown below. 1 H-NMR: δ1.20(t,J=7.2Hz,6H), 3.11(q,J=7.2Hz,4H), 4.21(dd, J=7.0Hz, 1.4Hz, 2H), 5.69(dt, J=11.6Hz, 7.0Hz, 1H), 6.50(dt, J=11.4Hz, 1.4Hz, 1H), 9.15(br,1H)

[0181] <Second Step: Synthesis of Lithium (Z)-3-(diethylamino)prop-1-ene-1-sulfonate (I-2)> In a 200 mL eggplant-shaped flask, add (Z)-3-(diethyl-λ 4 (-azaneil)prop-1-ene-1-sulfonate (I-2') (1.32 g, 6.8 mmol), tetrahydrofuran (50 mL) as a solvent, and pure water (50 mL) were charged and kept at room temperature. Lithium carbonate (0.28 g, 3.8 mmol) was added, and after stirring for 3 hours, the reaction was stopped to obtain a reaction solution. The reaction solution was filtered to remove insoluble matter, and then concentrated under reduced pressure. In other words, tetrahydrofuran and water components were removed from the reaction solution. This gave lithium (Z)-3-(diethylamino)prop-1-ene-1-sulfonate (I-2) (1.24 g, 6.2 mmol, yield 91%) as a yellow viscous liquid. Yellow viscous liquid 1 The results of H-NMR (DMSO-d) are shown below. 1 H-NMR: δ1.02(t, J=7.6Hz, 6H), 2.55-2.75(m, 4H), 3.62-3.72(m, 2H), 5.58(dt, J=11.6Hz, 6.4Hz, 1H), 6.19(d, J=11.2Hz, 2H)

[0182] [Synthesis Example 3] Lithium (Z)-3-(dibenzylamino)prop-1-ene-1-sulfonate (I-3) represented by the following formula (I-3) was synthesized as follows.

[0183] [ka]

[0184] <First step: (Z)-3-(dibenzyl-λ 4 Synthesis of (Azanil)prop-1-ene-1-sulfonate (I-3') The synthesis was carried out in the same manner as in the first step of Synthesis Example 1, except that 5H-1,2-oxathiol 2,2-dioxide (2.0 g, 16.7 mmol) was used in the first step of Synthesis Example 1, and the dimethylamine solution was changed to dibenzylamine (3.28 g, 16.7 mmol). This resulted in the formation of a white solid, (Z)-3-(dibenzyl-λ 4 -azaneil)prop-1-ene-1-sulfonate (I-3') (1.82 g, 5.7 mmol, 34% yield) was obtained. White solid 1 The results of H-NMR (DMSO-d) are shown below. 1 H-NMR: δ4.07-4.20(m,2H), 4.28(dd, J=13.4Hz, 5.2Hz, 2H), 4.38(dd, J=13.4Hz, 5.2Hz, 2H), 5.84(dt, J=11.6Hz, 6.4Hz, 1H), 6.53(d, J=11.6Hz, 1H), 7.42-7.46(m,10H), 10.20(br,1H)

[0185] <Second Step: Synthesis of Lithium (Z)-3-(dibenzylamino)prop-1-ene-1-sulfonate (I-3)> In a 200 mL eggplant-shaped flask, add (Z)-3-(dibenzyl-λ 4 (-azaneil)prop-1-ene-1-sulfonate (I-4') (0.70 g, 2.2 mmol), tetrahydrofuran (50 mL) as a solvent, and pure water (50 mL) were charged and kept at room temperature. Lithium carbonate (0.08 g, 1.1 mmol) was added, and after stirring for 3 hours, the reaction was stopped to obtain a reaction solution. The reaction solution was filtered to remove insoluble matter, and then concentrated under reduced pressure. In other words, tetrahydrofuran and water components were removed from the reaction solution. This gave white solid lithium (Z)-3-(dibenzylamino)prop-1-ene-1-sulfonate (I-3) (0.66 g, 2.1 mmol, 93% yield). White solid 1 The results of H-NMR (DMSO-d) are shown below. 1 H-NMR: δ3.40-3.47(m,2H), 3.50(s,4H), 5.67(dt, J=11.6Hz, 6.4Hz, 1H), 6.14(d, J=11.6Hz, 1H), 7.20-7.26(m,2H), 7.29-7.37(m,8H)

[0186] [Synthesis Example 4] 3-(trimethylammonio)propane-1-sulfonate 3-(Trimethylammonio)propane-1-sulfonate (C-1) represented by the following formula (C-1) was synthesized as follows.

[0187] [ka]

[0188] A 200 mL four-neck flask purged with nitrogen was charged with 5H-1,2-oxathiol 2,2-dioxide (5.91 g, 48.4 mmol) and ethanol (100 mL) as a solvent, and while maintaining the temperature at 0°C, 30% aqueous trimethylamine solution (9.53 g, 48.4 mmol) was added. After the addition of the aqueous trimethylamine solution was completed, the temperature was raised and the reaction was carried out with stirring at 80°C. After 8 hours had elapsed from the start of the reaction with stirring, the temperature was returned to room temperature, acetone (50 mL) was added, and the reaction was stopped after stirring for 1 hour, to obtain a reaction solution. The resulting reaction solution was filtered, and the residue (i.e., white solid) was washed twice with acetone (50 mL), thereby obtaining 3-(trimethylammonio)propane-1-sulfonate (C-1) (7.65 g, 42.2 mmol, yield 87%) as a white solid. White solid 1 The results of H-NMR (DMSO-d) are shown below. 1 H-NMR: δ1.95-2.03(m, 2H), 2.45(t, J=7.0Hz, 2H), 3.04(s, 9H), 3.37-3.44(m, 2H)

[0189] As described above, based on the results of Synthesis Example 4, 3-(trimethylammonio)propane-1-sulfonate (C-1) was obtained according to the following reaction scheme.

[0190] [ka]

[0191] [Synthesis Example 5] 3-(Triethylammonio)propane-1-sulfonate (C-2) represented by the following formula (C-2) was synthesized as follows.

[0192] [ka]

[0193] A 200 mL four-neck flask purged with nitrogen was charged with 5H-1,2-oxathiol 2,2-dioxide (2.0 g, 16.4 mmol) and ethanol (50 mL) as a solvent, and while maintaining the temperature at 0°C, triethylamine (1.66 g, 16.4 mmol) was added. After the addition of triethylamine was completed, the temperature was raised and the reaction was carried out with stirring at 80°C. After 6 hours had elapsed from the start of the reaction with stirring, the temperature was returned to room temperature, acetone (50 mL) was added, and the reaction was stopped after stirring for 1 hour, to obtain a reaction solution. The resulting reaction solution was filtered, and the residue (i.e., white solid) was washed twice with acetone (50 mL), thereby obtaining 3-(triethylammonio)propane-1-sulfonate (C-2) (1.77 g, 7.93 mmol, yield 48%) as a white solid. White solid 1 The results of H-NMR (DMSO-d) are shown below. 1 H-NMR: δ1.18(tt, J=7.2Hz, 1.8Hz,9H), 1.84-1.93(m, 2H), 2.48-2.52(m, 2H), 3.21(q, J=7.2Hz, 6H), 3.30-3.40(m, 2H)

[0194] Example 1 A non-aqueous electrolyte solution was prepared as follows.

[0195] <Preparation of non-aqueous electrolyte> Ethylene carbonate (hereinafter referred to as "EC"), dimethyl carbonate (hereinafter referred to as "DMC"), and ethyl methyl carbonate (hereinafter referred to as "EMC") were mixed in a volume ratio of EC:DMC:EMC = 30:35:35, thereby obtaining a mixed solvent as a non-aqueous solvent. LiPF6 as an electrolyte was dissolved in the obtained mixed solvent so that the concentration in the finally obtained non-aqueous electrolyte solution was 1 mol / L, to obtain an electrolyte solution.

[0196] Hereinafter, the obtained electrolyte solution will be referred to as the "basic electrolyte solution."

[0197] As an additive, lithium (Z)-3-(dimethylamino)prop-1-ene-1-sulfonate (I-1) represented by the following formula (I-1) synthesized in Synthesis Example 1 was added to the base electrolyte solution in an amount (mass %) relative to the total amount of the finally obtained nonaqueous electrolyte solution shown in Table 1. In this way, a nonaqueous electrolyte solution was obtained.

[0198] [ka]

[0199] A coin-type battery (hereinafter also simply referred to as "battery") was fabricated as a lithium secondary battery precursor in the following manner.

[0200] <Preparation of positive electrode> Li(Ni) as the positive electrode active material 0.5 Co 0.2 Mn 0.3 A mixture of 94% by mass of ZnO, 3% by mass of carbon black as a conductive additive, and 3% by mass of polyvinylidene fluoride (PVdF) as a binder was obtained. The mixture was dispersed in N-methylpyrrolidone solvent to obtain a positive electrode mixture slurry. An aluminum foil with a thickness of 20 μm was prepared as a positive electrode current collector. The resulting positive electrode mixture slurry was applied to an aluminum foil, dried, and then rolled with a press to obtain a sheet-shaped positive electrode. The positive electrode was composed of a positive electrode current collector and a positive electrode active material layer.

[0201] <Preparation of negative electrode> Graphite (96% by mass) was used as the negative electrode active material, carbon black (1% by mass) was used as a conductive additive, 1% by mass of sodium carboxymethyl cellulose dispersed in pure water as a thickener (solid content), and 2% by mass of styrene-butadiene rubber (SBR) dispersed in pure water as a binder (solid content) were mixed to obtain a negative electrode composite slurry. A copper foil with a thickness of 10 μm was prepared as a negative electrode current collector. The obtained slurry was applied onto a copper foil, dried, and then rolled with a press to obtain a sheet-shaped negative electrode, which was composed of a negative electrode current collector and a negative electrode active material layer.

[0202] The non-aqueous electrolyte obtained by the above-described non-aqueous electrolyte production was prepared.

[0203] A porous polyethylene film was prepared as a separator.

[0204] <Making a coin-type battery> The negative electrode was punched out into a disk shape with a diameter of 14 mm, the positive electrode was punched out into a disk shape with a diameter of 13 mm, and the separator was punched out into a disk shape with a diameter of 17 mm, thereby obtaining a coin-shaped negative electrode, coin-shaped positive electrode, and coin-shaped separator, respectively. The obtained coin-shaped negative electrode, coin-shaped separator, and coin-shaped positive electrode were stacked in this order in a stainless steel battery can (size: 2032). Next, 20 μL of non-aqueous electrolyte was poured into the battery can, and the separator, positive electrode, and negative electrode were immersed in the non-aqueous electrolyte. Next, an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring were placed on the positive electrode, and the battery case lid was crimped via a polypropylene gasket to seal the battery. As a result of the above, a coin-type lithium secondary battery precursor was obtained having the structure shown in Fig. 2. The lithium secondary battery precursor had a diameter of 20 mm and a height of 3.2 mm.

[0205] [Examples 2 to 5, Comparative Examples 1 to 3] A lithium secondary battery precursor was obtained in the same manner as in Example 1, except that the compound (I-1) represented by the following formula, the compound (I-2), 3-(trimethylammonio)propane-1-sulfonate (C-1), 3-(triethylammonio)propane-1-sulfonate (C-2), the lithium fluorophosphate compound (II-1), the cyclic dicarbonyl compound (III-1), and the cyclic sulfonate ester compound (IV-1) were added so that the contents (mass%) relative to the total amount of the non-aqueous electrolyte solution finally obtained would be the contents shown in Table 1.

[0206] [ka]

[0207] [Evaluation test] The obtained lithium secondary battery precursor was subjected to the aging treatment described below to obtain a first battery. The obtained first battery was subjected to the initial charge / discharge treatment described below to obtain a second battery. The obtained second battery was subjected to the first DC resistance evaluation treatment (25°C) described below to obtain a third battery. The obtained third battery was subjected to the second DC resistance evaluation treatment (-10°C) described below to obtain a fourth battery. The obtained fourth battery was subjected to the high-temperature storage treatment described below to obtain a fifth battery. The obtained fifth battery was subjected to the later charge / discharge treatment described below to obtain a sixth battery. The obtained sixth battery was subjected to the first DC resistance evaluation treatment (25°C) described below to obtain a seventh battery. The obtained seventh battery was subjected to the second DC resistance evaluation treatment (-10°C) described below to obtain an eighth battery. The discharge capacity after high-temperature storage, resistance after high-temperature storage (25°C), and resistance after high-temperature storage (-10°C) were measured using the obtained batteries Nos. 1 to 8 by the following measurement methods. The measurement results are shown in Table 1.

[0208] <Aging treatment> The lithium secondary battery precursor was subjected to the following aging treatment in a temperature environment of 25° C. to obtain a first battery. Specifically, the lithium secondary battery precursor was charged at a temperature range of 25°C to 70°C with a cut-off voltage range of 1.5V to 3.5V, and then rested for 5 to 50 hours. Next, the battery precursor was charged at a temperature range of 25°C to 70°C with a cut-off voltage range of 3.5V to 4.2V, and held for 5 to 50 hours. Next, the battery precursor was charged to 4.2V at a temperature range of 25°C to 70°C, and then discharged to 2.5V. This produced a first battery.

[0209] <Initial charge / discharge process> The first battery was subjected to the following initial charge-discharge treatment in a temperature environment of 25° C. to obtain a second battery. Specifically, the first battery was stored in a temperature environment of 25°C for 12 hours. Next, the first battery was charged at a constant current and constant voltage (0.2C-CCCV) at a charge rate of 0.2C to 4.2V (SOC (State of Charge) 100%), then rested for 30 minutes, and then discharged at a constant current (0.2C-CC) at a discharge rate of 0.2C to 2.5V. This cycle was repeated three times to stabilize the battery. Thereafter, the battery was charged at a constant current and constant voltage (0.5C-CCCV) at a charge rate of 0.2C up to 4.2V, then rested for 30 minutes, and then discharged at a constant current (1C-CC) at a discharge rate of 1C down to 2.5V, thereby obtaining a second battery.

[0210] <First DC Resistance Evaluation Process> The second battery was subjected to the following first DC resistance evaluation treatment in a temperature environment of 25° C. to obtain a third battery. Specifically, the second battery was CC discharged to 2.5 V at a discharge rate of 0.2 C, and CCCV charged to 3.7 V at a charge rate of 0.2 C. "CCCV charging" means charging at a constant current and constant voltage. Next, the second battery was subjected to CC10s discharge at a discharge rate of 0.2 C and CC10s charge at a charge rate of 0.2 C. "CC10s discharge" means discharging at a constant current for 10 seconds. "CC10s charge" means charging at a constant current for 10 seconds. Next, the second battery was subjected to CC10s discharge at a discharge rate of 0.5C and CC25s charge at a charge rate of 0.2C. Next, the second battery was subjected to CC10s discharge at a discharge rate of 1C and CC50s charge at a charge rate of 0.2C. Next, the second battery was subjected to CC10s discharge at a discharge rate of 2 C and CC100s charge at a charge rate of 0.2 C. In this way, a third battery was obtained.

[0211] <Second DC Resistance Evaluation Process> The third battery was subjected to the second DC resistance evaluation treatment described below in a temperature environment of −10° C. to obtain a fourth battery. Specifically, the third battery was left standing in a temperature environment of −10° C. for 3 hours or more. Next, the third battery was subjected to CC10s discharge at a discharge rate of 0.1C and CC10s charge at a charge rate of 0.1C. Next, the third battery was subjected to CC10s discharge at a discharge rate of 0.2C and CC20s charge at a charge rate of 0.1C. Next, the third battery was subjected to CC10s discharge at a discharge rate of 0.4C and CC40s charge at a charge rate of 0.1C. Next, the third battery was subjected to CC10s discharge at a discharge rate of 0.6 C and CC60s charge at a charge rate of 0.1 C. This produced a fourth battery.

[0212] <High-temperature preservation treatment> The fourth battery was subjected to the following high-temperature storage treatment to obtain a fifth battery. Specifically, the fourth battery was charged at a constant current of 0.2 C to 4.2 V in a temperature environment of 25° C. The charged battery was then left to stand in an atmosphere of 60° C. for 14 days, thereby obtaining the fifth battery.

[0213] <Late-stage charge / discharge treatment> The fifth battery was subjected to the following later charge-discharge treatment in a temperature environment of 25° C. to obtain a sixth battery. Specifically, the fifth battery was cooled in a 25°C environment, and then subjected to a first discharge, a first charge, and a second discharge. The first discharge refers to a constant current discharge (1C-CC) to 2.5V at a discharge rate of 1C. The first charge refers to a constant current / constant voltage charge (0.2C-CCCV) to 4.2V at a charge rate of 0.2C. The second discharge refers to a constant current discharge (1C-CC) to 2.5V at a discharge rate of 1C. This resulted in the sixth battery.

[0214] <First DC resistance evaluation treatment after high-temperature storage> The sixth battery was subjected to the following first DC resistance evaluation treatment in a temperature environment of 25° C. to obtain a seventh battery. Specifically, the sixth battery was CC discharged to 2.5 V at a discharge rate of 0.2 C, and CCCV charged to 3.7 V at a charge rate of 0.2 C. "CCCV charging" means charging at a constant current and constant voltage. Next, the sixth battery was subjected to CC10s discharge at a discharge rate of 0.2 C and CC10s charge at a charge rate of 0.2 C. "CC10s discharge" means discharging at a constant current for 10 seconds. "CC10s charge" means charging at a constant current for 10 seconds. Next, the sixth battery was subjected to CC10s discharge at a discharge rate of 0.5C and CC25s charge at a charge rate of 0.2C. Next, the sixth battery was subjected to CC10s discharge at a discharge rate of 1C and CC50s charge at a charge rate of 0.2C. Next, the sixth battery was subjected to CC10s discharge at a discharge rate of 2 C and CC100s charge at a charge rate of 0.2 C. In this way, a seventh battery was obtained.

[0215] <Second DC resistance evaluation treatment after high-temperature storage> The seventh battery was subjected to the second DC resistance evaluation treatment described below in a temperature environment of −10° C. to obtain an eighth battery. Specifically, the seventh battery was left standing in a temperature environment of −10° C. for 3 hours or more. Next, the seventh battery was subjected to CC10s discharge at a discharge rate of 0.1C and CC10s charge at a charge rate of 0.1C. Next, the seventh battery was subjected to CC10s discharge at a discharge rate of 0.2C and CC20s charge at a charge rate of 0.1C. Next, the seventh battery was subjected to CC10s discharge at a discharge rate of 0.4C and CC40s charge at a charge rate of 0.1C. Next, the seventh battery was subjected to CC10s discharge at a discharge rate of 0.6 C and CC60s charge at a charge rate of 0.1 C. In this way, an eighth battery was obtained.

[0216] [Method for measuring discharge capacity after high-temperature storage] As shown in the following formula (X1), the relative value of the discharge capacity of the fifth battery of each Example to the discharge capacity of the fifth battery of Comparative Example 1 was defined as "discharge capacity after high-temperature storage [%]." The discharge capacity after high-temperature storage indicates the capacity obtained when the second discharge was performed in the above-mentioned later charge-discharge treatment.

[0217] Discharge capacity after high-temperature storage (25°C) [relative value; %] = (discharge capacity of the fifth battery [mAh / g] / discharge capacity of the fifth battery of Comparative Example 1 [mAh / g]) × 100 (X1)

[0218] [Method for measuring resistance after high temperature storage (25℃)] As shown in the following formula (X2), the relative value of the direct current internal resistance (DCIR) of the sixth battery to the direct current resistance of the sixth battery of Comparative Example 1 was defined as "resistance after high-temperature storage (25°C) [%]."

[0219] Resistance after high-temperature storage (25°C) [relative value; %] = (DC resistance of the sixth battery [Ω] / DC resistance of the sixth battery of Comparative Example 1 [Ω]) × 100 (X2)

[0220] The DC resistance of the sixth battery was measured by the following method. The DC resistance (Ω) of the sixth battery was calculated based on the amount of voltage drop (= voltage before discharge started - voltage 10 seconds after discharge started) due to "CC10s discharge" at each discharge rate of 0.2C to 2C and each current value (i.e., each current value corresponding to discharge rates of 0.2C to 2C).

[0221] [Method for measuring resistance after high temperature storage (-10℃)] As shown in the following formula (X3), the relative value of the DC resistance of Battery 7 to the DC resistance (DCIR) of Battery 7 of Comparative Example 1 was defined as "resistance after high-temperature storage (-10°C) [%]."

[0222] Resistance after high-temperature storage (-10°C) [relative value; %] = (DC resistance of the seventh battery [Ω] / DC resistance of the seventh battery of Comparative Example 1 [Ω]) × 100 (X3)

[0223] The DC resistance of the seventh battery was measured by the following method. The DC resistance (Ω) of the seventh battery was calculated based on the amount of voltage drop (= voltage before discharge started - voltage 10 seconds after discharge started) due to "CC10s discharge" at each discharge rate of 0.1C to 0.6C and each current value (i.e., each current value corresponding to discharge rates of 0.1C to 0.6C).

[0224] [Table 1]

[0225] In Table 1, "-" indicates that the corresponding component is not contained. "Content of each additive" indicates the content (mass%) of the additive relative to the total amount of the nonaqueous electrolyte. "(I)" indicates the lithium sulfonate compound (I). "(II)" indicates the lithium fluorophosphate compound (II). "(III)" indicates the cyclic dicarbonyl compound (III). "(IV)" indicates the cyclic sulfonate ester compound (IV). "(I-1)" indicates lithium (Z)-3-(dimethylamino)prop-1-ene-1-sulfonate (I-1). "(I-2)" indicates lithium (Z)-3-(diethylamino)prop-1-ene-1-sulfonate (I-2). "(C-1)" indicates 3-(trimethylammonio)propane-1-sulfonate (C-1). "(C-2)" refers to 3-(triethylammonio)propane-1-sulfonate (C-2). "(II-1)" refers to lithium fluorophosphate compound (II-1). "(III-1)" refers to cyclic dicarbonyl compound (III-1). "(IV-1)" refers to cyclic sulfonate ester compound (IV-1).

[0226] The additives of Comparative Examples 2 and 3 did not contain the lithium sulfonate compound (I). Therefore, in the lithium secondary batteries of Comparative Examples 2 and 3, the resistance after high-temperature storage (measured at 25°C) was 114% or more, and the resistance after high-temperature storage (measured at -10°C) was 111%. That is, when the lithium secondary batteries of Comparative Examples 2 and 3 were stored in a high-temperature environment for a long period of time, the increase in DC resistance was not suppressed. As a result, it was found that the additives of Comparative Examples 2 and 3 could not suppress the increase in DC resistance even when the lithium secondary batteries were stored in a high-temperature environment for a long period of time.

[0227] The additives of Examples 1 to 5 contain a lithium sulfonate compound (I). Therefore, in the lithium secondary batteries of Examples 1 to 5, the resistance after high-temperature storage (measured at 25°C) was 97% or less, and the resistance after high-temperature storage (measured at -10°C) was 97% or less. That is, even when the lithium secondary batteries of Examples 1 to 5 were stored in a high-temperature environment for a long period of time, an increase in DC resistance was suppressed. As a result, it was found that the additives of Examples 1 to 5 can suppress an increase in DC resistance even when the lithium secondary batteries are stored in a high-temperature environment for a long period of time. [Explanation of symbols]

[0228] 1. Lithium secondary battery precursor 10 Battery element 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 Cell layer 21 Positive lead 22 Negative lead 30 Exterior body 41 Positive electrode 42 Negative electrode 43 Positive electrode can 44 Sealing plate 45 Separator 46 Gasket 47, 48 Spacer plates

Claims

1. An additive for a lithium secondary battery, comprising a compound (I) represented by the following formula (I): 【Chemistry 1】 [In formula (I), R １１ and R １２ teeth, each independently represents an alkyl group having 1 to 10 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), an alkenyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), a benzyl group (at least one hydrogen atom in the benzyl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), or an aryl group (at least one hydrogen atom in the aryl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), or together with the nitrogen atom in formula (I) to form a 3- to 8-membered ring structure. and represents an alkylene group (at least one hydrogen atom in the alkylene group may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms). The wavy line indicates a trans or cis form.]

2. The R １１ and R １２ teeth, each independently represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group; or together with the nitrogen atom in formula (I) to form a 5- or 6-membered ring structure. The additive for a lithium secondary battery according to claim 1 , wherein the alkylene group is

3. 3. The additive for a lithium secondary battery according to claim 1 or 2, wherein the compound (I) is a compound (I-1) represented by the following formula (I-1) or a compound (I-2) represented by the following formula (I-2): 【Chemistry 2】

4. A non-aqueous electrolyte solution for a lithium secondary battery, comprising the additive for a lithium secondary battery according to any one of claims 1 to 3.

5. 5. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 4, further comprising at least one selected from the group consisting of compound (II) which is at least one of lithium monofluorophosphate and lithium difluorophosphate, compound (III) represented by the following formula (III), and compound (IV) represented by the following formula (IV): 【Transformation 3】 [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 from 1 to 3; m is an integer from 1 to 4, n is an integer from 0 to 8, q is 0 or 1; R ３１ 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 groups may contain a substituent or a heteroatom in the structure, and when q is 1 and m is 2 to 4, m R ３１ may be bonded to each other; R ３２ represents 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 heteroatom in the structure, and when n is 2 to 8, n R ３２ may be bonded to each other to form a ring; Q １ , and Q ２ are each independently an oxygen atom or a carbon atom. In formula (IV), R ４１ represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms, R ４２ represents an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (iv-1), or a group represented by formula (iv-2), * indicates the bond position, In formula (iv-1), R ４３ represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group, In formula (iv-2), R ４４ is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms.

6. The content of the compound (I) is 0.01% by mass or more and 5% by mass or less based on the total amount of the non-aqueous electrolyte.

6. The nonaqueous electrolyte solution for a lithium secondary battery according to claim 4 or claim 5, wherein:

7. Case and a positive electrode, a negative electrode, a separator, and an electrolyte solution housed in the case; Equipped with the positive electrode is a positive electrode capable of absorbing and desorbing lithium ions, the negative electrode is capable of absorbing and desorbing lithium ions, A lithium secondary battery precursor, wherein the electrolytic solution is the nonaqueous electrolytic solution according to any one of claims 4 to 6.

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

00.

9. A step of preparing a lithium secondary battery precursor according to claim 7 or claim 8; charging and discharging the lithium secondary battery precursor; A method for producing a lithium secondary battery, comprising:

10. A method for producing a lithium secondary battery, comprising the step of charging and discharging the lithium secondary battery precursor according to claim 7 or 8.

11. A lithium sulfonate compound represented by the following formula (I): 【Chemistry 4】 [In formula (I), R １１ and R １２ teeth, each independently represents an alkyl group having 1 to 10 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), an alkenyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), a benzyl group (at least one hydrogen atom in the benzyl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), or an aryl group (at least one hydrogen atom in the aryl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), or together with the nitrogen atom in formula (I) to form a 3- to 8-membered ring structure. and represents an alkylene group (at least one hydrogen atom in the alkylene group may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms). The wavy line indicates a trans or cis form.]

12. The R １１ and R １２ teeth, each independently represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group; or together with the nitrogen atom in formula (I) to form a 5- or 6-membered ring structure.

12. The lithium sulfonate compound of claim 11, wherein the alkylene group is

13. The lithium sulfonate compound according to claim 11 or 12, which is one selected from the group consisting of a compound (I-1) represented by the following formula (I-1), a compound (I-2) represented by the following formula (I-2), and a compound (I-3) represented by the following formula (I-3): 【Transformation 5】

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