Lithium pyrrolidium bis(sulfate) compound, additive for lithium secondary battery, non-aqueous electrolyte for lithium secondary battery, precursor for lithium secondary battery, method for manufacturing lithium secondary battery, and lithium secondary battery

Abstract

To provide a lithium pyrrolidinium bis(sulfate) compound capable of suppressing decrease of discharge capacity, increase of DC resistance and an increase rate of the DC resistance relative to before long time storage, when a lithium ion secondary battery is stored for a long time under a high temperature environment.SOLUTION: A lithium pyrrolidinium bis(sulfate) compound is represented by the following formula (I). In the formula (I), R1 and R2 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), etc., or, together with a nitrogen atom in the formula (I), an alkylene group that forms a 3- to 8-membered ring structure (at least one hydrogen atom in the alkylene group may be substituted with a halogen atom, or an alkyl group with 1 to 10 carbon atoms).SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a lithium pyrrolidium bis(sulfate) compound, an additive for a lithium secondary battery, a nonaqueous electrolyte for a lithium secondary battery, a lithium secondary battery precursor, a lithium secondary battery, 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 secondary battery (hereinafter referred to as "lithium secondary battery"). The lithium secondary battery disclosed in Patent Document 1 includes a positive electrode, a negative electrode, and a non-aqueous electrolyte. The negative electrode is made of lithium or a negative electrode material capable of absorbing and releasing lithium. The non-aqueous electrolyte is made of an organic solvent and a solute. The organic solvent contains at least one of lithium monofluorophosphate and lithium difluorophosphate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 3439085 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). In cold regions, the battery performance of lithium secondary batteries may be degraded. Therefore, there is a demand for a lithium secondary battery that suppresses the decrease in discharge capacity, the increase in DC resistance, and the increase rate of DC resistance compared to before long-term storage when the lithium secondary battery is stored for a long period of time (e.g., 14 days) in a high-temperature environment (e.g., 60°C).

[0005] In view of the above circumstances, an object of the present disclosure is to provide a lithium pyrrolidium bis(sulfate) compound, an additive for a lithium secondary battery, a nonaqueous electrolyte for a lithium secondary battery, a lithium secondary battery precursor, a method for producing a lithium secondary battery, and a lithium secondary battery, which are capable of suppressing a decrease in discharge capacity, an increase in DC resistance, and a rate of increase in DC resistance compared to before long-term storage when a lithium secondary battery is stored for a long period of time in a high-temperature environment. [Means for solving the problem]

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

[0007] <1> A lithium pyrrolidium bis(sulfate) compound represented by the following formula (I):

[0008] [ka]

[0009] [In formula (I), R 1 and R 2 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, it represents an alkylene group which, together with the nitrogen atom in the formula (I), forms a 3- to 8-membered ring 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). <2> R 1 and R 2 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 an alkylene group which, taken together with the nitrogen atom in the formula (I), forms a 5- to 6-membered ring structure. <1> The lithium pyrrolidium bis(sulfate) compound according to claim 1. <3> The lithium pyrrolidium bis(sulfate) compound is represented by the following formula (I-1) or the following formula (I-2): <1> or <2> The lithium pyrrolidium bis(sulfate) compound according to claim 1.

[0010] [ka]

[0011] <4> The above <1> ~ <3> 13. An additive for lithium secondary batteries, comprising the lithium pyrrolidium bis(sulfate) compound according to any one of claims 1 to 12. <5> The above <1> ~ <3> 2. A non-aqueous electrolyte for a lithium secondary battery, comprising the lithium pyrrolidium bis(sulfate) compound according to any one of 1 to 11. <6> The compound represented by the following formula (II) is contained in the above-mentioned <5> The non-aqueous electrolyte for a lithium secondary battery according to claim 1.

[0012] [ka]

[0013] [In formula (II), M is an alkali metal; Y is a transition element, an element of 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 3 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 3 may be bonded to each other. R 4 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 4 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. <7> The compound represented by the following formula (III) is contained in the above-mentioned <5> or <6> The non-aqueous electrolyte for a lithium secondary battery according to claim 1.

[0014] [ka]

[0015] [In formula (III), R 5 represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms, R 6 represents an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (iii-1), or a group represented by formula (iii-2), * indicates the bond position, In formula (iii-1), R 61represents 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 (iii-2), R 62 is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms. <8> The compound (IV) is at least one selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate. <5> ~ <7> 10. The nonaqueous electrolyte for a lithium secondary battery according to claim 9, <9> The content of the lithium pyrrolidium bis(sulfate) compound is 0.01% by mass or more and 5% by mass or less based on the total amount of the non-aqueous electrolyte for a lithium secondary battery. <5> ~ <8> 10. The nonaqueous electrolyte for a lithium secondary battery according to claim 9, <10> Case and a positive electrode, a negative electrode, a separator, and an electrolyte solution contained in the case; Equipped with The positive electrode is a positive electrode capable of absorbing and releasing lithium ions, The negative electrode is capable of absorbing and releasing lithium ions, The electrolyte solution is <5> ~ <9> 10. A lithium secondary battery precursor, which is the nonaqueous electrolyte solution for a lithium secondary battery according to claim 9. <11> The positive electrode contains a lithium-containing composite oxide represented by the following formula (C1) as a positive electrode active material. <10> The lithium secondary battery precursor according to claim 1. LiNi a Co b Mn c O2… Formula (C1) (In formula (C1), 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.) <12> The above <10> or <11> 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: <13> The above <10> or <11> 2. A lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor according to claim 1. Effect of the Invention

[0016] According to the present disclosure, there are provided a lithium pyrrolidium bis(sulfate) compound, an additive for a lithium secondary battery, a nonaqueous electrolyte for a lithium secondary battery, a lithium secondary battery precursor, a method for producing a lithium secondary battery, and a lithium secondary battery, which are capable of suppressing an increase in DC resistance and a rate of increase in DC resistance compared to before long-term storage when a lithium secondary battery is stored for a long period of time in a high-temperature environment. [Brief description of the drawings]

[0017] [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. [Diagram 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 PREFERRED EMBODIMENTS

[0018] 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" refers not only to an independent process, but also to a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved.

[0019] Hereinafter, with reference to the drawings, the lithium pyrrolidium bis(sulfate) compound, the additive for lithium secondary battery, the non-aqueous electrolyte for lithium secondary battery, the lithium secondary battery precursor, the manufacturing method of the lithium secondary battery, and the lithium secondary battery according to the present disclosure will be described. In addition, in the drawings, the same or corresponding parts are designated by the same reference symbols, and the description will not be repeated.

[0020] [Lithium pyrrolidium bis(sulfate) compounds] The lithium pyrrolidium bis(sulfate) compounds of the present disclosure are described.

[0021] The lithium pyrrolidium bis(sulfate) compound of the present disclosure is a novel compound represented by the following formula (I):

[0022] [ka]

[0023] In formula (I), R 1 and R 2 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, it represents an alkylene group which, together with the nitrogen atom in the formula (I), forms 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).

[0024] Hereinafter, the lithium pyrrolidium bis(sulfate) compound represented by formula (I) will be referred to as "lithium pyrrolidium bis(sulfate) compound (I)".

[0025] The lithium pyrrolidium bis(sulfate) compound (I) of the present disclosure is represented by the following formula (I), and when added to a nonaqueous electrolyte solution for a lithium secondary battery (hereinafter, may be referred to as a "nonaqueous electrolyte solution") for use, it is possible to suppress a decrease in discharge capacity, an increase in DC resistance, and an increase rate of DC resistance compared to before long-term storage when the lithium secondary battery is stored for a long period of time in a high-temperature environment. The lithium secondary battery will be described in detail later with reference to FIGS.

[0026] The reason why the above effect is achieved is presumed to be as follows. When a lithium secondary battery is manufactured using a nonaqueous electrolyte to which the lithium pyrrolidium bis(sulfate) compound (I) of the present disclosure is added, it is considered that a reaction product is generated near the surface of the negative electrode of the lithium secondary battery during the manufacturing process (for example, the aging process described later), and further, a component that is a decomposition product of the reaction product is generated. The reaction product indicates a product of the reaction between the lithium pyrrolidium bis(sulfate) compound (I) and a compound (for example, LiF) generated from the electrolyte. Such a reaction product adheres to the negative electrode surface to form an SEI (Solid Electrolyte Interphase) film (hereinafter referred to as "negative electrode SEI film"). It is considered that this component migrates to the vicinity of the positive electrode surface during the manufacturing process, adheres to the positive electrode surface, and forms an SEI film (hereinafter referred to as "positive electrode SEI film"). This enhances the stability of the lithium secondary battery in a high-temperature environment. For example, the elution of metal elements in the positive electrode active material is suppressed. As a result, it is believed that when the lithium secondary battery is stored in a high-temperature environment, an increase in the DC resistance of the lithium secondary battery and an increase rate of the DC resistance compared to before long-term storage are suppressed. In addition, it is believed that the formation of the positive electrode SEI film continues to progress even during the storage period of the lithium secondary battery, and therefore, it is believed that the rate of increase in the DC resistance of the lithium secondary battery with respect to the storage period of the lithium secondary battery is reduced during storage of the lithium secondary battery.

[0027] Furthermore, as described above, the stability of the lithium secondary battery using the lithium pyrrolidium bis(sulfate) compound (I) of the present disclosure is excellent even in a high-temperature environment. In other words, it is considered that even if the lithium secondary battery is stored in a high-temperature environment, side reactions that are not the original battery reaction are unlikely to proceed. The battery reaction indicates a reaction in which lithium ions enter and leave (intercalate) the positive electrode and the negative electrode. The 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 in the positive electrode active material. This suppresses the progress of the decomposition reaction of the non-aqueous electrolyte. As a result, it is considered that even if the lithium secondary battery is stored in a high-temperature environment, the discharge capacity of the lithium secondary battery is unlikely to decrease.

[0028] For the above reasons, when the lithium pyrrolidium bis(sulfate) compound (I) of the present disclosure is added to a non-aqueous electrolyte solution and used, the decrease in discharge capacity, the increase in direct current resistance, and the increase rate of direct current resistance compared to before the long-term storage can be suppressed when a lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0029] Hereinafter, when there is no need to distinguish between the negative electrode SEI film and the positive electrode SEI film, they will simply be referred to as "SEI film".

[0030] In formula (I), R 1 and R 2 The "alkyl group having 1 to 10 carbon atoms" represented by each of the above independently 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" 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, further 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.

[0031] In formula (I), R 1 and R 2 The "alkenyl group having 2 to 10 carbon atoms" represented by each independently 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, further 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.

[0032] In formula (I), R 1 and R 2The "alkynyl group having 2 to 10 carbon atoms" represented by each of the above independently is a straight-chain or branched-chain alkynyl group having from 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 in 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, further 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.

[0033] In formula (I), R 1 and R 2 At least one hydrogen atom of each independently represented "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. 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 linear, 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 any of linear, branched, and 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.

[0034] In formula (I), R 1 and R 2 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 linear, 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 methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, n-hexyl, and cyclohexyl. 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.

[0035] In formula (I), R 1 and R 2 The "alkylene group which forms a 3- to 8-membered cyclic structure together with the nitrogen atom" represented by these formulas taken together 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 atom in the "alkylene group forming a 3- to 8-membered ring structure together with the nitrogen atom" is preferably a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, more preferably a fluorine atom, a chlorine atom, or a bromine atom, further 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 forming 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 forming 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 forming a 3- to 8-membered ring structure together with the nitrogen atom" is preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms. In the "alkylene group forming a 3- to 8-membered cyclic structure together with the nitrogen atom", the number of hydrogen atoms substituted with the alkyl group 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 the alkyl group having 1 to 10 carbon atoms is not particularly limited, and is preferably 1 to 3.

[0036] In formula (I), R 1 and R 2 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 preferably represents an alkylene group which, taken together with the nitrogen atom in the formula (I), forms a 5- to 6-membered ring structure.

[0037] This can further suppress the decrease in discharge capacity, the increase in DC resistance, and the rate of increase in DC resistance compared to before long-term storage when the lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0038] The lithium pyrrolidium bis(sulfate) compound (I) is preferably represented by the following formula (I-1) or (I-2), which can further suppress the decrease in discharge capacity, the increase in DC resistance, and the increase rate of DC resistance compared to before the long-term storage when the lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0039] [ka]

[0040] Specific examples of the lithium pyrrolidium bis(sulfate) compound (I) include the compounds represented by the following formulas (I-1) to (I-7). Hereinafter, the compound represented by formula (I-1) may be referred to as "lithium 1,1-dimethylpyrrolidin-1-ium-3,4-diyl bissulfate (I-1)." The compound represented by formula (I-2) may be referred to as "lithium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2)." The compound represented by formula (I-3) may be referred to as "lithium 1,1-diethylpyrrolidin-1-um-3,4-diyl bisulfate (I-3)". The compound represented by formula (I-4) may be referred to as "lithium 1,1-di-n-propylpyrrolidin-1-um-3,4-diyl bisulfate (I-4)". The compound represented by formula (I-5) may be referred to as "lithium 1,1-di-i-propylpyrrolidin-1-um-3,4-diyl bisulfate (I-5)". The compound represented by formula (I-6) may be referred to as "lithium 1,1-dibenzylpyrrolidin-1-um-3,4-diyl bisulfate (I-6)". The compound represented by formula (I-7) may be referred to as "lithium 5-azaspiro[4.5]-decane-5-ium-2,3-diyl bissulfate (I-7)".

[0041] [ka]

[0042] [Additives for lithium secondary batteries] The additive for lithium secondary batteries according to the present disclosure (hereinafter, sometimes simply referred to as the "additive") will be described.

[0043] The additive of the present disclosure includes a lithium pyrrolidium bis(sulfate) compound represented by formula (I):

[0044] [ka]

[0045] In formula (I), R 1 and R 2 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, it represents an alkylene group which, together with the nitrogen atom in the formula (I), forms 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).

[0046] The additive of the present disclosure contains the lithium pyrrolidium bis(sulfate) compound (I), and when added to a non-aqueous electrolyte solution for use, it is possible to suppress a decrease in discharge capacity, an increase in direct current resistance, and an increase rate of direct current resistance compared to before long-term storage when a lithium secondary battery is stored for a long period of time in a high-temperature environment. The reason why the above-mentioned effect is exhibited is presumably the same as the reason why, when the lithium pyrrolidium bis(sulfate) compound (I) of the present disclosure is added to a non-aqueous electrolyte and used, the decrease in discharge capacity, the increase in direct current resistance, and the increase rate of direct current resistance compared to before the long-term storage can be suppressed when a lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0047] The additive of the present disclosure is suitable as an additive for non-aqueous electrolytes of lithium secondary batteries.

[0048] R 1 and R 2 As the R of the lithium pyrrolidium bis(sulfate) compound (I) described above, 1 and R2 Examples of the above-mentioned examples include those similar to those given as examples.

[0049] [Nonaqueous electrolyte for lithium secondary batteries] The nonaqueous electrolyte for a lithium secondary battery according to the present disclosure will now be described.

[0050] The nonaqueous electrolyte of the present disclosure is used as an electrolyte for a lithium secondary battery.

[0051] The nonaqueous electrolyte of the present disclosure contains a lithium pyrrolidium bis(sulfate) compound represented by the following formula (I):

[0052] [ka]

[0053] In formula (I), R 1 and R 2 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, it represents an alkylene group which, together with the nitrogen atom in the formula (I), forms 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).

[0054] Since the nonaqueous electrolyte solution of the present disclosure contains the lithium pyrrolidium bis(sulfate) compound (I), it is possible to suppress a decrease in discharge capacity, an increase in direct current resistance, and an increase rate of direct current resistance compared to before long-term storage when a lithium secondary battery is stored for a long period of time in a high-temperature environment. The reason why the above-mentioned effect is exhibited is presumably the same as the reason why, when the lithium pyrrolidium bis(sulfate) compound (I) of the present disclosure is added to a non-aqueous electrolyte and used, the decrease in discharge capacity, the increase in direct current resistance, and the increase rate of the direct current resistance compared to before the long-term storage can be suppressed when a lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0055] Examples of the lithium pyrrolidium bis(sulfate) compound (I) contained in the nonaqueous electrolyte solution of the present disclosure include the same compounds as those exemplified as the lithium pyrrolidium bis(sulfate) compound (I) contained in the additive of the present disclosure.

[0056] Specific examples of the lithium pyrrolidium bis(sulfate) compound (I) include the compounds represented by the above formulas (I-1) to (I-7).

[0057] In addition, when the non-aqueous electrolyte solution collected by disassembling the lithium secondary battery is actually analyzed, the amount of the lithium pyrrolidium bis(sulfate) compound (I) may be decreased compared to the amount added to the non-aqueous electrolyte solution. Even in this case, if even a small amount of the lithium pyrrolidium bis(sulfate) compound (I) is detected in the non-aqueous electrolyte solution taken out of 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.

[0058] The upper limit of the content of the lithium pyrrolidium bis(sulfate) compound (I) is preferably 5.0 mass % or less, more preferably 3.0 mass % or less, and further preferably 2.0 mass % or less, based on the total amount of the nonaqueous electrolyte. If the upper limit of the content of the lithium pyrrolidium bis(sulfate) compound (I) is within the above range, the SEI film does not impair the conductivity of lithium cations, and the lithium secondary battery can operate. Furthermore, since the SEI film contains a phosphoric acid structure, the battery characteristics of the lithium secondary battery are improved. The lower limit of the content of the lithium pyrrolidium bis(sulfate) compound (I) is preferably 0.01 mass% or more, more preferably 0.05 mass% or more, even more preferably 0.10 mass% or more, particularly preferably 0.20 mass% or more, and even more preferably 0.40 mass% or more, based on the total amount of the nonaqueous electrolyte. If the lower limit of the content of the lithium pyrrolidium bis(sulfate) compound (I) is within the above range, the SEI film contains a sufficient amount of the structure derived from the lithium pyrrolidium bis(sulfate) compound (I). This makes it easier to form a thermally and chemically stable inorganic salt or polymer structure. Therefore, the elution of the components of the SEI film that impair the durability of the SEI film and the deterioration of the SEI film are unlikely to occur at high temperatures. As a result, the durability of the SEI film and the characteristics of the lithium secondary battery after high-temperature storage are improved.

[0059] (Cyclic dicarbonyl compounds (II)) The nonaqueous electrolyte solution of the present disclosure preferably contains a compound represented by the following formula (II) (hereinafter referred to as "cyclic dicarbonyl compound (II)").

[0060] [ka]

[0061] In formula (II), M is an alkali metal; Y is a transition element, an element of 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 3represents 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 3 may be bonded to each other. R 4 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 4 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.

[0062] By including the cyclic dicarbonyl compound (II) in addition to the lithium pyrrolidium bis(sulfate) compound (I) in the nonaqueous electrolyte solution of the present disclosure, even during charge-discharge cycles after storage in a high-temperature environment, the decrease in discharge capacity, the increase in DC resistance in a 25°C environment and a -10°C environment, and the rate of increase in DC resistance compared to before long-term storage in a 25°C environment and a -10°C environment can be further suppressed. This effect is presumably due to the following reasons. The non-aqueous electrolyte contains a cyclic dicarbonyl compound (II) in addition to the lithium pyrrolidium bis(sulfate) compound (I), so that the SEI film and the like may contain bonds derived from the cyclic dicarbonyl compound (II) in addition to the above-mentioned reaction products and the like. This makes it easier to form a thermally and chemically stable inorganic salt or polymer structure. Therefore, at high temperatures, the components of the SEI film and the like that impair the durability of the SEI film and the like are less likely to dissolve, and the SEI film and the like are less likely to degrade. As a result, even in charge-discharge cycles after long-term storage in a high-temperature environment, the decrease in discharge capacity, the increase in direct current resistance in a 25°C environment and a -10°C environment, the increase rate of direct current resistance compared to before long-term storage in a 25°C environment, and the increase rate of resistance in a 25°C environment and a -10°C environment are more suppressed.

[0063] 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, a group 13 element, a group 14 element, or a group 15 element 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 the production cost can be reduced. b represents the valence of the anion and the number of cations, and is an integer of 1 to 3, and is preferably 1. When b is 3 or less, the salt of the anion 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 3represents 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, these groups may contain a substituent instead of a hydrogen atom. 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. In addition, the structure may have a nitrogen atom, a sulfur atom, or an oxygen atom introduced instead of a carbon element of these groups. In addition, when q is 1 and m is 2 to 4, m R 3 may be bonded to each other. An example of such a ligand is ethylenediaminetetraacetic acid. R 4 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 3 Similarly, the structure may contain a substituent or a heteroatom, and when n is 2 to 8, n R 4 may be bonded to each other to form a ring. 4 As the group, an electron-withdrawing group is preferable, and a fluorine atom is particularly preferable. Q 1 , and Q 2 each independently represents O or S. That is, the ligand bonds to Y via these heteroatoms.

[0064] Specific examples of the cyclic dicarbonyl compound (II) include compounds represented by the following formulas (II-1) to (II-2). Hereinafter, the compound represented by formula (II-1) may be referred to as "lithium bis(oxalato)borate (II-1)".

[0065] [ka]

[0066] When the non-aqueous electrolyte contains a cyclic dicarbonyl compound (II), the upper limit of the content of the cyclic dicarbonyl compound (II) 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 (II) is within the above range, the lithium secondary battery can operate without the SEI film or the like impairing the conductivity of lithium cations. Furthermore, the battery characteristics of the lithium secondary battery are improved as the SEI film or the like contains a cyclic dicarbonyl structure. The lower limit of the content of the cyclic dicarbonyl compound (II) 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 non-aqueous electrolyte. If the lower limit of the content of the cyclic dicarbonyl compound (II) is within the above range, the SEI film etc. contains a sufficient amount of a structure mainly composed of a cyclic dicarbonyl structure. This makes it easier to form a thermally and chemically stable inorganic salt or polymer structure. Therefore, at high temperatures, the elution of components of the SEI film etc., which impairs the durability of the SEI film etc., and the deterioration of the SEI film etc., are unlikely to occur. As a result, the durability of the SEI film etc. and the characteristics of the lithium secondary battery after high-temperature storage are improved.

[0067] (Cyclic sulfur-containing ester compound (III)) The nonaqueous electrolyte solution of the present disclosure preferably contains a compound represented by the following formula (III) (hereinafter referred to as "cyclic sulfur-containing ester compound (III)").

[0068] [ka]

[0069] In formula (III), R 5 represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms, R 6 represents an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (iii-1), or a group represented by formula (iii-2), * indicates the bond position, In formula (iii-1), R 61 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 (iii-2), R 62 is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms.

[0070] By including the cyclic sulfur-containing ester compound (III) in addition to the lithium pyrrolidium bis(sulfate) compound (I) in the nonaqueous electrolyte solution of the present disclosure, even when stored for a long period of time in a high temperature environment, the decrease in discharge capacity, the increase in DC resistance in a 25°C environment and a -10°C environment, and the increase rate of DC resistance compared to before long-term storage in a 25°C environment and a -10°C environment can be further suppressed. This effect is presumably due to the following reasons. When a lithium secondary battery is manufactured using the nonaqueous electrolyte of the present disclosure, in the manufacturing process (for example, the aging step described later), the reaction product includes a product of the reaction between the cyclic sulfur-containing 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 if the lithium secondary battery is stored in a high-temperature environment, it is considered that the increase in the DC resistance of the lithium secondary battery in a 25°C environment and a -10°C environment, and the increase rate of the DC resistance in a 25°C environment and a -10°C environment compared to before long-term storage are further suppressed. Furthermore, the progress of the decomposition reaction of the nonaqueous electrolyte is further suppressed. As a result, it is considered that the discharge capacity of the lithium secondary battery is less likely to decrease even if the lithium secondary battery is stored in a high-temperature environment.

[0071] In formula (III), R 5is 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.

[0072] The cyclic sulfur-containing ester compound (III) is R 5 is preferably an oxygen atom. This makes it easier to form a thermally and chemically stable inorganic salt structure. Therefore, at high temperatures, the components of the SEI film and the like that impair the durability of the SEI film and the like are less likely to dissolve, and the SEI film and the like are less likely to degrade. As a result, the durability of the SEI film and the like and the battery characteristics of the lithium secondary battery are improved.

[0073] In formula (III), R 6 is preferably a group represented by formula (iii-1) or a group represented by formula (iii-2). In formula (iii-1), R 61 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 (iii-2), R 62 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.

[0074] Specific examples of the cyclic sulfur-containing ester compound (III) include the compounds represented by the formulae (III-1) to (III-7). Hereinafter, the compound represented by formula (III-1) may be referred to as "cyclic sulfur-containing ester compound (III-1)".

[0075] [ka]

[0076] The non-aqueous electrolyte may contain only one type of cyclic sulfur-containing ester compound (III), or may contain two or more types.

[0077] The upper limit of the content of the cyclic sulfur-containing ester compound (III) 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. If the upper limit of the content of the cyclic sulfur-containing ester compound (III) is within the above range, the SEI film etc. does not impair the conductivity of lithium ions, and the lithium secondary battery can operate. Furthermore, the battery characteristics of the lithium secondary battery are improved as the SEI film etc. contains a cyclic sulfur-containing ester structure. The lower limit of the content of the cyclic sulfur-containing ester 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. If the lower limit of the content of the cyclic sulfur-containing ester compound (III) is within the above range, the SEI film or the like contains a sufficient amount of cyclic sulfur-containing ester structure. This makes it easier to form a thermally and chemically stable inorganic salt or polymer structure. Therefore, at high temperatures, the elution of components of the SEI film or the like that impairs the durability of the SEI film or the like, and the 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.

[0078] (Lithium fluorophosphate compound (IV)) The nonaqueous electrolyte solution of the present disclosure preferably contains at least one compound (IV) selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate (hereinafter, sometimes referred to as "lithium fluorophosphate compound (IV)"). Lithium difluorophosphate is represented by the following formula (IV-1), and lithium monofluorophosphate is represented by the following formula (IV-2).

[0079] [ka]

[0080] By containing the lithium fluorophosphate compound (IV) in addition to the lithium lithium pyrrolidinium bis(sulfate) compound (I) in the nonaqueous electrolyte solution of the present disclosure, it is possible to further suppress the decrease in discharge capacity of the lithium secondary battery, the increase in DC resistance in a 25°C environment and a -10°C environment, and the increase rate of DC resistance compared to before long-term storage in a 25°C environment, even during charge-discharge cycles after storage in a high-temperature environment.

[0081] When the non-aqueous electrolyte contains a lithium fluorophosphate compound (IV), the upper limit of the content of the lithium fluorophosphate compound (IV) is preferably 5 mass % or less, more preferably 3 mass % or less, and further 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 (IV) is within the above range, the solubility of lithium fluorophosphate in the non-aqueous solvent can be ensured. The lower limit of the content of the lithium fluorophosphate compound (IV) is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more, based on the total amount of the nonaqueous electrolyte. When the lower limit of the content of the lithium fluorophosphate compound (IV) is within the above range, the direct current resistance of the lithium secondary battery can be further reduced.

[0082] <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, the additives described in paragraphs 0042 to 0055 of JP 2019-153443 A can be used.

[0083] <Non-aqueous solvent> The non-aqueous electrolyte generally contains a non-aqueous solvent. As the non-aqueous solvent, various known ones can be appropriately selected. The non-aqueous solvent may be one kind or two or more kinds.

[0084] 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 carboxylate 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. The amides include, for example, N,N-dimethylformamide. Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

[0085] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates. In this case, the total proportion of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates is preferably 50 mass% or more and 100 mass% or less, more preferably 60 mass% or more and 100 mass% or less, and even more preferably 80 mass% or more and 100 mass% or less, based on the total amount of the non-aqueous solvent.

[0086] 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.

[0087] 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 more preferably 70 mass% or more, based on the total amount of the nonaqueous electrolyte.

[0088] The intrinsic viscosity of the nonaqueous 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.

[0089] <Electrolytes> The non-aqueous electrolyte generally contains an electrolyte.

[0090] 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.

[0091] 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 them, lithium hexafluorophosphate (LiPF6) is particularly preferable as the fluorine-containing lithium salt.

[0092] Fluorine-free lithium salts include lithium perchlorate (LiClO4), lithium aluminium tetrachloride (LiAlCl4), and lithium decachlorodecaborate (Li2B 10 Cl 10 ) etc.

[0093] When the electrolyte contains a fluorine-containing lithium salt, the content of the fluorine-containing lithium salt is preferably 50 mass % or more and 100 mass % or less, more preferably 60 mass % or more and 100 mass % or less, and even more preferably 80 mass % or more and 100 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 mass% or more and 100 mass% or less, more preferably 60 mass% or more and 100 mass% or less, and even more preferably 80 mass% or more and 100 mass% or less, based on the total amount of the electrolyte.

[0094] 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.

[0095] 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.

[0096] <Other ingredients> The non-aqueous electrolyte may contain other components as necessary. Other components include acid anhydrides.

[0097] [Lithium secondary battery precursor] Next, the lithium secondary battery precursor of the present disclosure will be described.

[0098] 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, the negative electrode, the separator, and the electrolyte are housed in the case. The positive electrode is a positive electrode capable of absorbing and releasing lithium ions. The negative electrode is a negative electrode capable of absorbing and releasing lithium ions. The electrolyte is the nonaqueous electrolyte of the present disclosure.

[0099] 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.

[0100] <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, a case consisting of a battery can and a battery can lid, etc.

[0101] <Positive electrode> The positive electrode is capable of absorbing and releasing lithium ions. The positive electrode preferably contains at least one positive electrode active material capable of absorbing and releasing lithium ions.

[0102] 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.

[0103] Examples of the material of the positive electrode current collector include metals and alloys. More specifically, examples of the material of the positive electrode current collector include aluminum, nickel, stainless steel (SUS), and copper. Among them, aluminum is preferred from the viewpoint of the balance between high conductivity and cost. Here, "aluminum" means pure aluminum or an aluminum alloy. As the positive electrode current collector, aluminum foil is preferred. The material of the aluminum foil is not particularly limited, and examples thereof include A1085 material, A3003 material, and the like.

[0104] The positive electrode mixture layer contains a positive electrode active material and a binder.

[0105] The positive electrode active material is not particularly limited as long as it is a material capable of absorbing and releasing lithium ions, and can be appropriately adjusted depending on the application of the lithium secondary battery precursor, etc.

[0106] Examples of the positive electrode active material include a first oxide and a second oxide. The first oxide includes lithium (Li) and nickel (Ni) as constituent metal elements. The second oxide includes Li, Ni, and at least one metal element other than Li and Ni as constituent metal elements. Examples of the metal elements other than Li and Ni include transition metal elements and typical metal elements. The second oxide preferably includes the metal elements other than Li and Ni at a ratio equal to or less than Ni in terms of atomic number. The metal elements other than Li and Ni may be at least one selected from the group consisting of Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. These positive electrode active materials may be used alone or in a mixture of two or more.

[0107] The positive electrode active material preferably contains a lithium-containing composite oxide (hereinafter, sometimes referred to as "NCM") represented by the following formula (C1). The lithium-containing composite oxide (C1) has the advantages of high energy density per unit volume and excellent thermal stability. LiNi a Co b Mn c O2… Formula (C1) In formula (C1), a, b and c each independently represent more than 0 and less than 1, and the sum of a, b and c is 0.99 or greater and 1.00 or less. 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.

[0108] The positive electrode active material may contain a lithium-containing composite oxide (hereinafter sometimes referred to as "NCA") represented by the following formula (C2). Li t Ni 1-x-y Co x Al y O2… Formula (C2) In formula (C2), 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.

[0109] 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 mass% or more, more preferably 30 mass% or more, even more preferably 50 mass% or more, and particularly preferably 70 mass% or more, based on 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 mass% or less, more preferably 99 mass% or less, based on the total amount of the positive electrode mixture layer.

[0110] Examples of the binder include polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesin, and rubber particles. Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of the 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 necessary. 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 with respect to the total amount of the positive electrode mixture layer, from the viewpoint of balancing the physical properties of the positive electrode mixture layer (e.g., electrolyte permeability, peel strength, etc.) and battery performance. When the content of the binder is 0.1% by mass or more, the adhesion of the positive electrode mixture layer to the positive electrode current collector and the binding of the positive electrode active materials themselves are further improved. When the content of the binder is 4% by mass or less, the amount of the positive electrode active material in the positive electrode mixture layer can be increased, and thus the discharge capacity is further improved.

[0111] The positive electrode mixture layer preferably contains a conductive additive. As the material of the conductive assistant, a known conductive assistant can be used. As the known conductive assistant, a conductive carbon material is preferable. As the conductive carbon material, graphite, carbon black, conductive carbon fiber, fullerene, etc. can be mentioned. These can be used alone or in combination of two or more kinds. As the conductive carbon fiber, carbon nanotube, carbon nanofiber, carbon fiber, etc. can be mentioned. As the graphite, for example, artificial graphite, natural graphite, etc. can be mentioned. As the natural graphite, for example, flake graphite, lump graphite, earthy graphite, etc. can be mentioned. The conductive additive may be a commercially available product. Examples of commercially available carbon black products 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, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975ULTRA, etc., 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 of such blacks include LITX-50, LITX-200 (furnace black, manufactured by Cabot Corporation), Ensaco 250G, Ensaco 260G, Ensaco 350G, Super-P (manufactured by TIMCAL Corporation), Ketjen Black EC-300J, EC-600JD (manufactured by Akzo Corporation), Denka Black, Denka Black HS-100, FX-35 (acetylene black, manufactured by Denka Corporation).

[0112] The positive electrode mixture layer may contain other components such as a thickener, a surfactant, a dispersant, a wetting agent, and a defoamer.

[0113] <Negative electrode> The negative electrode is capable of absorbing and releasing lithium ions, and preferably contains at least one negative electrode active material capable of absorbing and releasing lithium ions.

[0114] More preferably, the negative electrode includes a negative electrode current collector and a negative electrode mixture layer. The negative electrode mixture layer is provided on at least a portion of the surface of the negative electrode current collector.

[0115] The material of the negative electrode current collector is not particularly limited and can be any known material, for example, metal or alloy. More 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 preferable as the material of the negative electrode current collector from the viewpoint of workability. Copper foil is preferable as the negative electrode current collector.

[0116] The negative electrode mixture layer contains a negative electrode active material and a binder.

[0117] 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 selected from the group consisting of, for example, 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").

[0118] 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 thereof include fibrous, spherical, potato, and flake 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) calcined at 1500° C. or less, and mesophase pitch carbon fiber (MCF). Examples of the graphite material include natural graphite and artificial graphite. Examples of the 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 the metal material that coats the graphite material include gold, platinum, silver, copper, and tin. The graphite material may be a mixture of amorphous carbon and graphite.

[0119] The negative electrode mixture layer preferably contains a conductive assistant. Examples of the conductive assistant include the same conductive assistants as those exemplified as the conductive assistants that can be contained in the positive electrode mixture layer.

[0120] The negative electrode mixture layer may contain other components in addition to the above components, such as a thickener, a surfactant, a dispersant, a wetting agent, and a defoamer.

[0121] <separator> The separator may be, for example, a porous resin plate. The material of the porous resin plate may be a resin, a nonwoven fabric containing the resin, etc. The resin may be polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, polyamide, etc. In particular, the separator is preferably a porous resin sheet having a single layer or a multilayer structure. The material of 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.

[0122] [An example of a 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.

[0123] 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.

[0124] As shown in Fig. 1, the battery element 10 is formed by laminating a positive electrode 11, a separator 13, and a negative electrode 12. The positive electrode 11 is formed by forming a positive electrode mixture layer 11B on both main surfaces of a positive electrode current collector 11A. The negative electrode 12 is formed by forming a negative electrode mixture layer 12B on both main surfaces of a negative electrode current collector 12A. The positive electrode mixture layer 11B formed on one main surface of the positive electrode current collector 11A of the positive electrode 11 and the negative electrode mixture layer 12B formed on one main surface of the negative electrode current collector 12A of the negative electrode 12 adjacent to the positive electrode 11 face each other via the separator 13.

[0125] The nonaqueous electrolyte solution of the present disclosure is injected into the interior of the exterior body 30 of the lithium secondary battery precursor 1. The nonaqueous electrolyte solution of the present disclosure permeates the positive electrode mixture layer 11B, the separator 13, and the negative electrode mixture layer 12B. In the lithium secondary battery precursor 1, one single cell layer 14 is formed by the adjacent positive electrode mixture layer 11B, the separator 13, and the negative electrode mixture layer 12B. Note that the positive electrode and the negative electrode may each have an active material layer formed on one side of each current collector.

[0126] 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 in layers. The wound type includes a cylindrical type and a rectangular type.

[0127] 1, the directions in which the positive electrode lead and the negative electrode lead each protrude from the inside of the exterior body 30 to the outside 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 each protrude from the inside of the exterior body 30 to the outside may be the same direction relative to the exterior body 30.

[0128] 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 mixture layer 11B and the negative electrode mixture layer 12B in the lithium secondary battery precursor 1 by charging and discharging the lithium secondary battery precursor 1.

[0129] 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 disk-shaped negative electrode 42, a separator 45 filled with a non-aqueous electrolyte, a disk-shaped positive electrode 41, and, if necessary, spacer plates 47, 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 a "battery can") and a sealing plate 44 (hereinafter also referred to as a "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 .

[0130] [Lithium secondary battery] Next, a lithium secondary battery according to an embodiment of the present disclosure will be described.

[0131] The lithium secondary battery according to the present embodiment includes a case, a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode, the negative electrode, the separator, and the electrolyte are housed in a case. The positive electrode is a positive electrode capable of absorbing and releasing lithium ions. The negative electrode is a negative electrode capable of absorbing and releasing 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.

[0132] The lithium secondary battery according to this embodiment differs from the lithium secondary battery precursor according to this embodiment 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 according to this embodiment is similar to the lithium secondary battery precursor according to this embodiment except for the first and second points. Therefore, hereinafter, a description of the components of the lithium secondary battery according to this embodiment other than the first and second points will be omitted.

[0133] Regarding the first point, "the negative electrode includes a negative electrode SEI film" includes a first negative electrode form and a second negative electrode form when the negative electrode includes a negative electrode current collector and a negative electrode composite layer. The first negative electrode form refers to a form in which the negative electrode SEI film is formed on at least a part 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.

[0134] Regarding the second point, "the positive electrode includes a positive electrode SEI film" includes a first positive electrode form and a second positive electrode form when the positive electrode includes a positive electrode current collector and a positive electrode mixture layer. The first positive electrode form refers to a form in which a positive electrode SEI film is formed on at least a part of the surface of the positive electrode mixture 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 that is a constituent material of the positive electrode mixture layer.

[0135] The SEI film contains, for example, at least one selected from the group consisting of a decomposition product of the lithium pyrrolidium bis(sulfate) compound (I), a reaction product of the lithium pyrrolidium bis(sulfate) compound (I) with an electrolyte, and a decomposition product of the reaction product.

[0136] 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.

[0137] 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 carrying out the aging step described below.

[0138] [Method for producing lithium pyrrolidium bis(sulfate) compounds] Next, a method for producing the lithium pyrrolidium bis(sulfate) compound (I) of the present disclosure will be described.

[0139] The method for producing the lithium pyrrolidium bis(sulfate) compound (I) includes a first step described below and a second step described below. The first step and the second step are carried out in this order. This allows the lithium pyrrolidium bis(sulfate) compound (I) of the present disclosure to be obtained.

[0140] <First step> In the first step, a cyclic sulfur-containing ester compound (III-1) is reacted with an amine compound in an organic solvent, and the resulting mixture is washed to obtain a pyrrolidium bis(sulfate) compound.

[0141] The amine compound is appropriately selected depending on the type of the lithium pyrrolidium bis(sulfate) compound (I) that is the product. Examples of the amine compound include monoamines, cyclic amines, and polyamines having two or more amino groups in the molecule. Examples of monoamines include methylamine, dimethylamine, ethylamine, diethylamine, n-propylamine, di-n-propylamine, i-propylamine, di-i-propylamine, n-butylamine, di-n-butylamine, i-butylamine, di-i-butylamine, sec-butylamine, di-sec-butylamine, tert-butylamine, di-tert-butylamine, allylamine, diallylamine, triallylamine, cyclohexylamine, dicyclohexylamine, n-Octylamine, di-n-octylamine, benzylamine, dibenzylamine, bis(trifluoromethyl)amine, bis(perfluoroethyl)amine, bis(perfluoropropyl)amine, bis(perfluoropropan-2-yl)amine, bis(perfluorobutan-2-yl)amine, bis(1,1,1,3,3,3-hexafluoro-2-(trifluoromethyl)propyl)amine, bis(1,1,2,3,3,3-hexafluoro-2-(trifluoromethyl)propan-2-yl )amine, 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-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 pyridine. 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, ethylbenzene, butylbenzene, pentylbenzene, hexylbenzene, heptylbenzene, propylbenzene, isopropylbenzene (also known as cumene), cyclohexylbenzene, tetralin, mesitylene, methylcyclopentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, cyclononane, etc. Xylene includes ortho-xylene, meta-xylene, and para-xylene.

[0142] The above reaction in the first step can be carried out either under normal pressure or under reduced pressure. The reaction temperature in the first step is preferably -20°C or higher and 60°C or lower, more preferably 0°C or higher and 40°C or lower, and further preferably 10°C or higher and 30°C or lower. The reaction time in the first step is preferably from 30 minutes to 12 hours, more preferably from 1 hour to 6 hours, from the viewpoint of efficiently progressing the reaction.

[0143] <Second process> In the second step, the pyrrolidium bis(sulfate) compound is reacted with a lithium salt compound in a solvent to obtain the lithium pyrrolidium bis(sulfate) compound (I).

[0144] 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 more preferably lithium carbonate.

[0145] The above reaction in the second step can be carried out either under normal pressure or under reduced pressure. The reaction temperature in the second step is preferably from -20°C to 60°C, more preferably from 0°C to 40°C, and further preferably from 10°C to 30°C. The reaction time in the second step is preferably from 30 minutes to 12 hours, more preferably from 1 hour to 6 hours, from the viewpoint of efficiently progressing the reaction.

[0146] The method of extracting the lithium pyrrolidium bis(sulfate) compound (I) from the product is not particularly limited, and can be appropriately adjusted depending on the state of the product obtained. When only the lithium pyrrolidium bis(sulfate) compound (I) is obtained, the lithium pyrrolidium bis(sulfate) compound (I) is extracted without any special treatment. When the product is a slurry in which the lithium pyrrolidium bis(sulfate) compound (I) is dispersed in a solvent, the lithium pyrrolidium bis(sulfate) compound (I) is extracted by separating the solvent from the slurry and drying it. When the product is a solution in which the lithium pyrrolidium bis(sulfate) compound (I) is dissolved in a solvent, the lithium pyrrolidium bis(sulfate) compound (I) is extracted by distilling off the solvent from the solution by heating and concentrating it. In addition, when the product is a solution in which the lithium pyrrolidium bis(sulfate) compound (I) is dissolved in a solvent, a solvent in which the lithium pyrrolidium bis(sulfate) compound (I) is not soluble is added to the solution to precipitate the lithium pyrrolidium bis(sulfate) compound (I), and then the solvent is separated from the solution and dried, whereby the lithium pyrrolidium bis(sulfate) compound (I) is extracted.

[0147] [Method for producing non-aqueous electrolyte] Next, a method for producing the nonaqueous electrolyte solution of the present disclosure will be described.

[0148] 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.

[0149] In the synthesis step, a lithium pyrrolidium bis(sulfate) compound (I) is synthesized. The synthesis process can be carried out in the same manner as the above-mentioned method for producing the lithium pyrrolidium bis(sulfate) compound (I).

[0150] 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 the addition of the lithium pyrrolidium bis(sulfate) compound (I).

[0151] In the mixing step, the lithium pyrrolidium bis(sulfate) compound (I) and, if necessary, other additives are added to the solution and mixed. This results in a non-aqueous electrolyte. The non-aqueous electrolyte obtained by the method for producing a non-aqueous electrolyte according to the present embodiment is more effective in reducing the DC resistance in a lithium secondary battery.

[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, but the present disclosure is not limited thereto.

[0153] [Method for producing lithium secondary battery precursor] Next, a method for producing a lithium secondary battery precursor according to the present disclosure will be described.

[0154] 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 housing step, and an injection step. The housing 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 housing step.

[0155] 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 of 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 of drying the positive electrode mixture slurry is not particularly limited, and examples thereof include drying with warm air, hot air, and low-humidity air; vacuum drying; and drying by irradiation with infrared rays (e.g., far-infrared rays). The drying time is not particularly limited, and is preferably 1 minute or more and 30 minutes or less. The drying temperature is not particularly limited, and is preferably 40°C or more and 80°C or less. The cathode mixture slurry is applied to the 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 the pressure treatment method include a die press and a roll press.

[0156] 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 liquid media compatible with water. When the solvent contained in the negative electrode mixture slurry includes a liquid medium compatible with water, the coating property on the negative electrode current collector can be improved. Examples of the liquid medium compatible with water include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, phosphoric acid esters, ethers, and nitriles. Examples of the method for applying, drying, and pressurizing the negative electrode mixture slurry include the same methods as those exemplified as the method for applying, drying, and pressurizing the positive electrode mixture slurry.

[0157] In the third preparation step, a non-aqueous electrolyte solution is prepared by the same method as that described in the above-mentioned method for producing a non-aqueous electrolyte solution.

[0158] 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 made of a positive electrode, a negative electrode, and a separator. Next, the positive electrode current collector and the positive electrode lead of the positive electrode are electrically connected, and the negative electrode current collector and the negative electrode lead of the negative electrode are electrically connected. 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.

[0159] Hereinafter, the state in which the positive electrode, negative electrode, and separator are housed in the case will be referred to as an "assembly."

[0160] In the injection step, the nonaqueous electrolyte solution of the present disclosure is injected into the inside of 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.

[0161] [Method for manufacturing lithium secondary battery] Next, a method for producing the lithium secondary battery of the present disclosure will be described.

[0162] The method for producing a lithium secondary battery according to the present disclosure includes a fourth preparation step and an aging step, which are performed in this order.

[0163] 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 the lithium secondary battery precursor.

[0164] In the aging step, the lithium secondary battery precursor is subjected to an 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. or higher and 70° C. or lower. In detail, 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.

[0165] 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. EXAMPLES

[0166] Hereinafter, the embodiments of the present disclosure will be described in detail with reference to examples. Note that the present disclosure is not limited to the description of these examples.

[0167] [Synthesis of lithium pyrrolidium bis(sulfate) compound (I)] The compounds represented by the following formulas (I-1) to (I-7) were synthesized as follows.

[0168] [Synthesis Example 1] Lithium 1,1-dimethylpyrrolidin-1-ium-3,4-diyl bissulfate (I-1) represented by the following formula (I-1) was synthesized as follows.

[0169] [ka]

[0170] <First step: synthesis of 4-((((dimethylamino)oxy)sulfonyl)oxy)-1,1-dimethylpyrrolidin-1-um-3-yl sulfate> In a 200mL four-neck flask purged with nitrogen, [4,4'-bi(1,3,2-dioxathiolane)] 2,2,2',2'-tetraoxide (7.39g, 30mmol) and tetrahydrofuran (100mL) as a solvent were charged, and kept at 0℃. Dimethylamine 2M tetrahydrofuran solution (18mL, 36mmol) was added and reacted with stirring at room temperature (25℃). After 16 hours, n-hexane (50mL) was added, and the reaction was stopped after stirring for 2 hours. The reaction product was then washed. That is, the reaction solution was filtered and then washed twice with n-hexane (50 mL). This gave a white solid of 4-((((dimethylamino)oxy)sulfonyl)oxy)-1,1-dimethylpyrrolidin-1-um-3-yl sulfate (I-1') (6.65 g, 19.77 mmol, yield 66%). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ2.61(s,6H), 3.21(s,3H), 3.31(s,3H), 3.85-4.03(m,4H), 5.15-5.23(m,2H)

[0171] <Second step: Synthesis of lithium 1,1-dimethylpyrrolidin-1-ium-3,4-diyl bissulfate (I-1)> 4-((((dimethylamino)oxy)sulfonyl)oxy)-1,1-dimethylpyrrolidin-1-um-3-yl sulfate (I-1') (1.68 g, 5.0 mmol), tetrahydrofuran (20 mL) as a solvent, and pure water (20 mL) were charged into a 200 mL eggplant flask, kept at room temperature, lithium carbonate (0.26 g, 3.50 mL) was added, and the mixture was stirred for 6 hours, after which the reaction was stopped. The reaction solution was filtered to remove insoluble matter, and then concentrated under reduced pressure to remove tetrahydrofuran and water components. This gave white solid lithium 1,1-dimethylpyrrolidin-1-ium-3,4-diyl bissulfate (I-1) (1.39 g, 4.67 mmol, yield 93%). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ3.20(s,3H), 3.30(s,3H), 3.83-4.03(m,4H), 5.15-5.23(m,2H)

[0172] As described above, based on the results of Synthesis Example 1, lithium 1,1-dimethylpyrrolidin-1-ium-3,4-diyl bissulfate (I-1) was obtained according to the following reaction scheme.

[0173] [ka]

[0174] [Synthesis Example 2] Lithium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2) represented by the following formula (I-2) was synthesized as follows.

[0175] [ka]

[0176] <First step: Synthesis of pyrrolidin-1-ium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2')> The compound was synthesized in the same manner as in the first step of Synthesis Example 1 (Synthetic Compound (I-1)), except that in the first step of Synthesis Example 1, [4,4'-bi(1,3,2-dioxathiolane)] 2,2,2',2'-tetraoxide (2.46 g, 10 mmol) was used and the dimethylamine solution was changed to pyrrolidine (0.71 g, 10 mmol). This gave a white solid of pyrrolidin-1-ium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2') (3.65 g, 9.4 mmol, yield 94%). In addition, the white solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ1.75-1.95(m,4H), 2.00-2.25(m,4H), 3.10-3.25(m,4H), 3.52-3.62 (m,2H), 3.62-3.72(m,4H), 3.83-3.93(m,4H)

[0177] <Second step: Synthesis of lithium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2)> The raw materials were pyrrolidin-1-ium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2') (3.65 g, 9.42 mmol) and lithium carbonate (0.42 g, 5.65 mmol), and the synthesis was carried out in the same manner as in the second step of Synthesis Example 1. This gave white solid lithium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2) (2.87 g, 8.88 mmol, yield 94%). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ2.00-2.20(m,4H), 3.48-3.60(m,2H), 3.60-3.72(m,2H), 3.80-3.92(m,2H), 3.77-4.05(m,4H), 5.10-5.22(m,2H)

[0178] [Synthesis Example 3] Lithium 1,1-diethylpyrrolidin-1-ium-3,4-diyl bissulfate (I-3) represented by the following formula (I-3) was synthesized as follows.

[0179] [ka]

[0180] <First step: synthesis of 4-((((diethylamino)oxy)sulfonyl)oxy)-1,1-diethylpyrrolidin-1-um-3-yl sulfate (I-3')> The compound was synthesized in the same manner as in the first step of Synthesis Example 1 (Synthetic Compound (I-1)), except that in the first step of Synthesis Example 1, [4,4'-bi(1,3,2-dioxathiolane)] 2,2,2',2'-tetraoxide (5.91 g, 24 mmol) was used and the dimethylamine solution was changed to diethylamine (1.46 g, 20 mmol). This gave a white solid of 4-((((diethylamino)oxy)sulfonyl)oxy)-1,1-diethylpyrrolidin-1-um-3-yl sulfate (I-3') (3.63 g, 9.3 mmol, yield 46.3%). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ1.41(d,J=7.2Hz,3H), 1.19-1.33(m,3H), 2.94(q,J=7.6Hz,4H), 3.38(q,J=7.0Hz,2H), 3.52(q,J=7.0Hz,2H), 3.73-3.97(m, 4H), 5.05-5.20(m,2H)

[0181] <Second step: Synthesis of lithium 1,1-diethylpyrrolidin-1-ium-3,4-diyl bissulfate (I-3)> The raw materials used were 4-((((diethylamino)oxy)sulfonyl)oxy)-1,1-diethylpyrrolidin-1-um-3-yl sulfate (I-3') (3.63 g, 9.25 mmol) and lithium carbonate (0.38 g, 5.09 mmol), and the compound was synthesized in the same manner as in the second step of Synthesis Example 1 (Synthetic Compound (I-1)). This gave white solid lithium 1,1-diethylpyrrolidin-1-ium-3,4-diyl bissulfate (I-3) (2.92 g, 8.98 mmol, yield 97%). White solid1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ1.17-1.27(m,6H), 3.37(q,J=7.3Hz,2H), 3.52(q,J=7.2Hz,2H), 3.73-3.91(m, 4H), 5.05-5.15(m,2H)

[0182] [Synthesis Example 4] Lithium 1,1-di-n-propylpyrrolidin-1-ium-3,4-diyl bissulfate (I-4) represented by the following formula (I-4) was synthesized as follows.

[0183] [ka]

[0184] <First step: synthesis of 4-((((di-n-propylamino)oxy)sulfonyl)oxy)-1,1-di-n-propylpyrrolidin-1-um-3-yl sulfate (I-4')> The synthesis was performed in the same manner as in the first step of Synthesis Example 1, except that in the first step of Synthesis Example 1, [4,4'-bi(1,3,2-dioxathiolane)] 2,2,2',2'-tetraoxide (9.85 g, 40 mmol) was used and the dimethylamine solution was changed to di-n-propylamine (4.05 g, 40 mmol). This gave a white solid of 4-((((di-n-propylamino)oxy)sulfonyl)oxy)-1,1-di-n-propylpyrrolidin-1-um-3-yl sulfate (I-4') (12.0 g, 26.8 mmol, yield 66.9%). In addition, the white solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR:δ0.85-1.10 (m, 12H), 1.55-1.90(m,3H), 2.82-3.05(m,4H), 3.25-3.42(m,2H), 3.42-3.70(m,2H), 3.80-4.12(m, 4H), 5.05-5.20(m,2H)

[0185] <Second step: Synthesis of lithium 1,1-di-n-propylpyrrolidin-1-ium-3,4-diyl bissulfate (I-4)> The raw materials used were 4-((((di-n-propylamino)oxy)sulfonyl)oxy)-1,1-di-n-propylpyrrolidin-1-um-3-yl sulfate (I-4') (12.0 g, 26.8 mmol) and lithium carbonate (1.09 g, 14.8 mmol), and the synthesis was carried out in the same manner as in the second step of Synthesis Example 1. This gave white solid lithium 1,1-di-n-propylpyrrolidin-1-ium-3,4-diyl bissulfate (I-4) (6.88 g, 19.5 mmol, yield 73%). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ0.80-0.92(m,6H), 1.55-1.77(m,4H), 3.20-3.32(m,2H), 3.33-3.45(m,2H), 3.78-3.96(m, 4H), 5.05-5.17(m,2H)

[0186] [Synthesis Example 5] Lithium 1,1-di-i-propylpyrrolidin-1-ium-3,4-diyl bissulfate (I-5) represented by the following formula (I-5) was synthesized as follows.

[0187] [ka]

[0188] <First step: synthesis of 4-((((di-i-propylamino)oxy)sulfonyl)oxy)-1,1-di-i-propylpyrrolidin-1-um-3-yl sulfate (I-5')> The synthesis was performed in the same manner as in the first step of Synthesis Example 1, except that in the first step of Synthesis Example 1, [4,4'-bi(1,3,2-dioxathiolane)] 2,2,2',2'-tetraoxide (24.62 g, 100 mmol) was used and the dimethylamine solution was changed to di-i-propylamine (10.12 g, 100 mmol). This gave a white solid of 4-((((di-i-propylamino)oxy)sulfonyl)oxy)-1,1-di-i-propylpyrrolidin-1-um-3-yl sulfate (I-5') (3.69 g, 8.2 mmol, yield 8.2%). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ1.18(d,J=6.5Hz,12H), 1.30(d,J=6.5Hz,6H), 1.36(d,J=6.5Hz,6H), 3.30-3.50 (m, 2H), 3.62-3.85(m,4H), 3.86-4.05(m,4H), 4.95-5.10(m,2H)

[0189] <Second step: Synthesis of lithium 1,1-di-i-propylpyrrolidin-1-ium-3,4-diyl bissulfate (I-5)> The raw materials used were 4-((((di-i-propylamino)oxy)sulfonyl)oxy)-1,1-di-i-propylpyrrolidin-1-um-3-yl sulfate (I-5') (3.24 g, 7.3 mmol) and lithium carbonate (0.32 g, 4.4 mmol), and the synthesis was carried out in the same manner as in the second step of Synthesis Example 1. This gave white solid lithium 1,1-di-i-propylpyrrolidin-1-ium-3,4-diyl bissulfate (I-5) (2.34 g, 6.6 mmol, yield 91%). White solid 1 The results of H-NMR (CD3OD) are shown below. 1H-NMR: δ1.30(d,J=6.5Hz,6H), 1.36(d,J=6.5Hz,6H), 3.70-3.80(m,4H), 3.85-4.05(m,2H), 4.96-5.06(m,2H)

[0190] [Synthesis Example 6] Lithium 1,1-dibenzylpyrrolidin-1-ium-3,4-diyl bissulfate (I-6) represented by the following formula (I-6) was synthesized as follows.

[0191] [ka]

[0192] <First step: synthesis of 4-((((dibenzylamino)oxy)sulfonyl)oxy)-1,1-dibenzylpyrrolidin-1-um-3-yl sulfate (I-6')> The synthesis was performed in the same manner as in the first step of Synthesis Example 1, except that in the first step of Synthesis Example 1, [4,4'-bi(1,3,2-dioxathiolane)] 2,2,2',2'-tetraoxide (7.39 g, 30 mmol) was used and the dimethylamine solution was changed to dibenzylamine (5.92 g, 30 mmol). This gave a white solid of 4-((((dibenzylamino)oxy)sulfonyl)oxy)-1,1-dibenzylpyrrolidin-1-um-3-yl sulfate (I-6') (12.9 g, 20.1 mmol, yield 67.1%). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ3.98(dd,J=13.2Hz, 4.3Hz, 2H), 4.23(dd,J=13.2Hz, 4.3Hz, 2H), 4.26(s,4H), 4.49(s,2H), 4.52-4.64(m,2H), 4.93(s,2H), 7.35-7.60(m,18H), 7.72-7.81(m,2H)

[0193] <Second step: Synthesis of lithium 1,1-dibenzylpyrrolidine-1-ium-3,4-diyl bissulfate (I-6)> The raw materials used were 4-((((dibenzylamino)oxy)sulfonyl)oxy)-1,1-dibenzylpyrrolidin-1-um-3-yl sulfate (I-6') (12.9 g, 20.1 mmol) and lithium carbonate (0.89 g, 12.1 mmol), and the synthesis was carried out in the same manner as in the second step of Synthesis Example 1. This gave white solid lithium 1,1-dibenzylpyrrolidin-1-ium-3,4-diyl bissulfate (I-6) (3.56 g, 7.92 mmol, yield 39%). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ3.91(dd,J=13.5Hz, 4.1Hz, 2H), 4.04(dd,J=14.0Hz, 4.1Hz, 2H), 4.42(s,4H), 4.75(s,2H), 7.33-7.62(m,10H)

[0194] [Synthesis Example 7] Lithium 5-azaspiro[4.5]-decane-5-ium-2,3-diyl bissulfate (I-7) represented by the following formula (I-7) was synthesized as follows.

[0195] [ka]

[0196] <First step: Synthesis of pyrrolidin-1-ium 5-azaspiro[4.5]decane-5-ium-2,3-diyl bissulfate (I-7')> The synthesis was performed in the same manner as in the first step of Synthesis Example 1, except that in the first step of Synthesis Example 1, [4,4'-bi(1,3,2-dioxathiolane)] 2,2,2',2'-tetraoxide' (7.39 g, 30 mmol) was used and the dimethylamine solution was changed to piperidine (2.55 g, 30 mmol). This gave a white solid of piperidine-1-nium 5-azaspiro[4.5]-decane-5-nium-2,3-diyl bissulfate (I-7') (10.3 g, 24.8 mmol, 83% yield). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ1.45-1.90(m,6H), 2.98-3.10(m,4H), 3.30-3.45(m,2H), 3.45-3.60(m,2H), 3.86-4.00(m,4H), 5.08-5.18(m,2H)

[0197] <Second step: Synthesis of lithium 5-azaspiro[4.5]-decane-5-ium-2,3-diyl bissulfate (I-7)> The raw materials were piperidin-1-ium 5-azaspiro[4.5]-decane-5-ium-2,3-diyl bissulfate (I-7') (10.3 g, 24.9 mmol) and lithium carbonate (1.10 g, 14.9 mmol), and the synthesis was carried out in the same manner as in the second step of Synthesis Example 1. This gave white solid lithium 5-azaspiro[4.5]-decane-5-ium-2,3-diyl bissulfate (I-7) (6.49 g, 19.2 mmol, 77% yield). White solid 1 The results of H-NMR (CD3OD) are shown below. 1 H-NMR: δ1.45-1.65(m,2H), 1.70-1.90(m,4H), 3.30-3.45(m,2H), 3.45-3.60(m,2H), 3.77-4.05(m,4H), 5.08-5.18(m,2H)

[0198] Example 1 A non-aqueous electrolyte was prepared as follows.

[0199] <Preparation of non-aqueous electrolyte> Ethylene carbonate (hereinafter, EC), dimethyl carbonate (hereinafter, DMC), and methyl ethyl carbonate (hereinafter, 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 resulting mixed solvent so that the concentration in the finally obtained non-aqueous electrolyte solution was 1 mol / L, to obtain an electrolyte solution.

[0200] Hereinafter, the obtained electrolyte solution will be referred to as the "base electrolyte solution."

[0201] As an additive, lithium 5-azaspiro[4.4]nonane-5-um-2,3-diyl bissulfate (I-2) synthesized in Synthesis Example 2 and represented by the following formula (I-2) was added to the base electrolyte so that the content relative to the total amount of the finally obtained nonaqueous electrolyte was the content (mass%) shown in Table 1. Thus, a nonaqueous electrolyte was obtained.

[0202] [ka]

[0203] A coin-type battery (hereinafter, simply referred to as a "battery") was fabricated as a lithium secondary battery precursor in the following manner.

[0204] <Preparation of positive electrode> Li(Ni 0.5 Co 0.2 Mn 0.3 A mixture was obtained by adding O2 (94 mass%) as an electroconductive assistant, carbon black (3 mass%) as a conductive assistant, and polyvinylidene fluoride (PVDF) (3 mass%) as a binder. The mixture was dispersed in N-methylpyrrolidone solvent to obtain a positive electrode mixture slurry. An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector. The obtained positive electrode mixture slurry was applied onto 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.

[0205] <Preparation of negative electrode> Graphite (96 mass%) was used as the negative electrode active material, carbon black (1 mass%) was used as a conductive assistant, 1 mass% of sodium carboxymethylcellulose dispersed in pure water as a thickener in terms of solid content, and 2 mass% of styrene-butadiene rubber (SBR) dispersed in pure water as a binder in terms of solid content were mixed together to obtain a negative electrode mixture slurry. A copper foil having 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.

[0206] The nonaqueous electrolyte obtained by the above-mentioned production of the nonaqueous electrolyte was prepared.

[0207] As a separator, a porous polyethylene film was prepared.

[0208] <Making a coin-type battery> The negative electrode was punched out into a disk shape with a diameter of 14 mm, the positive electrode into a disk shape with a diameter of 13 mm, and the separator into a disk shape with a diameter of 17 mm, thereby obtaining a coin-shaped negative electrode, a coin-shaped positive electrode, and a coin-shaped separator. 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 size). 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 can lid was crimped via a polypropylene gasket to seal the battery. In this manner, a coin-type lithium secondary battery precursor was obtained having the structure shown in Fig. 2. The size of the lithium secondary battery precursor was 20 mm in diameter and 3.2 mm in height.

[0209] Comparative Example 1 In the preparation of the non-aqueous electrolyte described above, a lithium secondary battery precursor was obtained in the same manner as in Example 1, except that lithium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2) was not added to the basic electrolyte as an additive.

[0210] Example 2 In the preparation of the non-aqueous electrolyte solution described above, in addition to lithium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2), lithium bis(oxalato)borate (II-1) represented by the following formula (II-1) was added to the base electrolyte solution as an additive so that the content relative to the total amount of the non-aqueous electrolyte solution finally obtained was the content (mass%) shown in Table 3. A lithium secondary battery precursor was obtained in the same manner as in Example 1.

[0211] [ka]

[0212] Example 3 In the preparation of the non-aqueous electrolyte solution described above, in addition to lithium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2), a cyclic sulfur-containing ester compound (III-1) represented by the following formula (III-1) was added to the base electrolyte solution as an additive so that the content of the cyclic sulfur-containing ester compound (III-1) relative to the total amount of the non-aqueous electrolyte solution finally obtained was the content (mass%) shown in Table 1. A lithium secondary battery precursor was obtained in the same manner as in Example 1.

[0213] [ka]

[0214] Example 4 In the preparation of the non-aqueous electrolyte solution described above, in addition to lithium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2), lithium difluorophosphate (IV-1) represented by the following formula (IV-1) was added to the basic electrolyte solution as an additive so that the content relative to the total amount of the non-aqueous electrolyte solution finally obtained was the content (mass%) shown in Table 3. A lithium secondary battery precursor was obtained in the same manner as in Example 1.

[0215] [ka]

[0216] [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 described below (25°C) to obtain a third battery. The obtained third battery was subjected to the second DC resistance evaluation treatment described below (-10°C) 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 described below (25°C) to obtain a seventh battery. The obtained seventh battery was subjected to the second DC resistance evaluation treatment described below (-10°C) to obtain an eighth battery. The resulting first to eighth batteries were used to measure the capacity after high temperature storage, the resistance after high temperature storage (25°C), the resistance after high temperature storage (-10°C), the resistance increase rate (25°C), and the resistance increase rate (-10°C) by the following measurement methods. The measurement results are shown in Table 1.

[0217] <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.

[0218] 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.

[0219] <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.

[0220] The first battery was kept 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 was repeated for 3 cycles 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 4.2 V, then rested for 30 minutes, and then discharged at a constant current (1C-CC) at a discharge rate of 1C up to 2.5 V. This produced a second battery.

[0221] <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.

[0222] 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 charging at a charge rate of 0.2 C. "CC10s discharge" means discharging at a constant current for 10 seconds. "CC10s charging" 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.

[0223] <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.

[0224] The third battery was left to stand in a temperature environment of -10°C for at least 3 hours. 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.

[0225] <High temperature preservation treatment> The fourth battery was subjected to the following high-temperature storage treatment to obtain a fifth battery.

[0226] The fourth battery was charged at a constant current of 4.2 V at a charge rate of 0.2 C in a temperature environment of 25° C. The charged battery was then left to stand for 14 days in an atmosphere of 60° C. Thus, the fifth battery was obtained.

[0227] <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.

[0228] The fifth battery was allowed to cool in a temperature environment of 25°C, and was 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. In this way, the sixth battery was obtained.

[0229] <First DC resistance evaluation treatment after high temperature storage> The sixth battery was subjected to the first DC resistance evaluation treatment described below in a temperature environment of 25° C. to obtain a seventh battery.

[0230] The sixth battery was CC discharged at a discharge rate of 0.2 C to 2.5 V, and CCCV charged at a charge rate of 0.2 C to 3.7 V. "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 charging at a charge rate of 0.2 C. "CC10s discharge" means discharging at a constant current for 10 seconds. "CC10s charging" 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.

[0231] <Treatment for evaluating the second DC resistance 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.

[0232] The seventh battery was left to stand in a temperature environment of -10°C for more than 3 hours. 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.

[0233] [Method for measuring 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 "capacity after high-temperature storage [%]." The capacity after high-temperature storage indicates the capacity obtained when the second discharge was performed in the above-mentioned later charge-discharge treatment.

[0234] 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)

[0235] [Method of measuring resistance after high temperature storage (25℃)] As shown in the following formula (X2), the relative value of the direct current 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.) [%]."

[0236] 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)

[0237] 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 voltage drop (= voltage before the start of discharge - voltage 10 seconds after the start of discharge) due to "CC10s discharge" at each discharge rate of 0.2C to 2C and each current value (i.e., each current value corresponding to the discharge rates of 0.2C to 2C).

[0238] [Method of measuring resistance after high temperature storage (-10℃)] As shown in the following formula (X3), the relative value of the DC resistance of the seventh battery to the DC resistance (DCIR) of the seventh battery of Comparative Example 1 was defined as "resistance after high-temperature storage (-10°C) [%]".

[0239] 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)

[0240] [Method of measuring resistance increase rate (25℃)] As shown in the following formula (X4), the relative value of the resistance increase rate (25° C.) of each Example to the resistance increase rate (25° C.) of Comparative Example 1 was defined as "resistance increase rate (25° C.) [%]."

[0241] Resistance increase rate (25°C) [relative value; %] = (resistance increase rate of each example (25°C) / resistance increase rate of comparative example 1 (25°C)) × 100 ... (X4)

[0242] In formula (X4), the resistance increase rate (25°C) is the DC resistance (Ω) of the sixth battery divided by the DC resistance (Ω) of the second battery. The DC resistance (Ω) of the sixth battery and the DC resistance (Ω) of the second battery are each measured in the same manner as in the measurement method of the DC resistance (Ω) of the sixth battery in the method of measuring resistance after high-temperature storage described above.

[0243] The relative value of the DC resistance of the sixth battery after the high-temperature storage test corresponds to the increase rate (%) of DC resistance due to storage (hereinafter also simply referred to as the "resistance increase rate"). The increase rate referred to here is an increase rate in a mode in which neither increase nor decrease is expressed as 100%, an increase is expressed as more than 100%, and a decrease is expressed as less than 100%.

[0244] [Method of measuring resistance increase rate (-10℃)] As shown in the following formula (X5), the relative value of the resistance increase rate (-10°C) of each example to the resistance increase rate (-10°C) of Comparative Example 1 was taken as "resistance increase rate (-10°C) [%]".

[0245] Resistance increase rate (-10°C) [relative value; %] = (resistance increase rate of each example (-10°C) / resistance increase rate of comparative example 1 (-10°C)) × 100 ... (X5)

[0246] In formula (X5), the resistance increase rate (-10°C) is the DC resistance (Ω) of the seventh battery divided by the DC resistance (Ω) of the second battery. The DC resistance (Ω) of the seventh battery and the DC resistance (Ω) of the second battery are each measured in the same manner as in the measurement method of the DC resistance (Ω) of the seventh battery in the method of measuring the resistance after high-temperature storage (-10°C) described above.

[0247] The above relative value of the DC resistance of the seventh battery after the high-temperature storage test corresponds to the increase rate (%) of DC resistance due to storage (hereinafter also simply referred to as the "resistance increase rate"). The increase rate referred to here is an increase rate in a mode in which neither increase nor decrease is expressed as 100%, an increase is expressed as more than 100%, and a decrease is expressed as less than 100%.

[0248] [Table 1]

[0249] In Table 1, "-" means 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 for lithium secondary batteries. "(I)" indicates the lithium pyrrolidium bis(sulfate) compound (I). "(I-2)" indicates lithium 5-azaspiro[4.4]nonane-5-ium-2,3-diyl bissulfate (I-2). "(II)" indicates the cyclic dicarbonyl compound (II). "(II-1)" indicates the lithium bisoxalatoborate (II-1). "(III)" indicates the cyclic sulfur-containing ester compound (III). "(III-1)" indicates the cyclic sulfur-containing ester compound (III-1). "(IV)" indicates the lithium fluorophosphate compound (IV). "(IV-1)" indicates the lithium difluorophosphate (IV-1).

[0250] Since the nonaqueous electrolyte solutions of Examples 1 to 4 contain the lithium pyrrolidium bis(sulfate) compound (I), the lithium secondary batteries of Examples 1 to 4 had a capacity after high-temperature storage of 101% or more, a resistance after high-temperature storage (measured at 25°C) of 94% or less, a resistance after high-temperature storage (measured at -10°C) of 93% or less, and a resistance increase rate (measured at 25°C) of 97% or less. That is, it was found that the nonaqueous electrolyte solutions of Examples 1 to 4 can suppress the decrease in discharge capacity, the increase in DC resistance, and the increase rate of DC resistance compared to before long-term storage when the lithium secondary batteries are stored for a long period of time in a high-temperature environment. Comparing Examples 2 to 4, the lithium secondary battery of Example 3 had a resistance increase rate (measured at 25°C) of 75%, which was lower than those of Examples 3 and 4, and a resistance increase rate (measured at -10°C) of 71%, which was lower than those of Examples 3 and 4. That is, it was found that the nonaqueous electrolyte solution containing the cyclic sulfur-containing ester compound (III) in addition to the lithium pyrrolidium bis(sulfate) compound (I) can further suppress the increase rate of DC resistance compared to before long-term storage in a 25°C environment and a -10°C environment. [Explanation of symbols]

[0251] 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 plate

Claims

1. A lithium pyrrolidium bis(sulfate) compound represented by the following formula (I): 【Chemistry 1】 [In formula (I), R １ and R ２ 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, it represents an alkylene group which, together with the nitrogen atom in the formula (I), forms a 3- to 8-membered ring 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).

2. The R １ and R ２ 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 an alkylene group which, taken together with the nitrogen atom in formula (I), forms a 5- to 6-membered ring structure.

3. The lithium pyrrolidium bis(sulfate) compound according to claim 1 or 2, wherein the lithium pyrrolidium bis(sulfate) compound is represented by the following formula (I-1) or the following formula (I-2): 【Chemistry 2】

4. An additive for lithium secondary batteries, comprising the lithium pyrrolidium bis(sulfate) compound according to any one of claims 1 to 3.

5. A non-aqueous electrolyte for a lithium secondary battery, comprising the lithium pyrrolidium bis(sulfate) compound according to any one of claims 1 to 3.

6. The nonaqueous electrolyte for a lithium secondary battery according to claim 5 , comprising a compound represented by the following formula (II): 【Chemistry 3】 [In formula (II), M is an alkali metal; Y is a transition element, an element of 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 ３ 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 ３ may be bonded to each other; R ４ 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 ４ 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.

7. The nonaqueous electrolyte for a lithium secondary battery according to claim 5 or 6, comprising a compound represented by the following formula (III): 【Chemistry 4】 [In formula (III), R ５ represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms, R ６ represents an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (iii-1), or a group represented by formula (iii-2), * indicates the bond position, In formula (iii-1), R ６１ 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 (iii-2), R ６２ is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms.

8. The nonaqueous electrolyte for a lithium secondary battery according to any one of claims 5 to 7, comprising at least one compound (IV) selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate.

9. The non-aqueous electrolyte solution for lithium secondary batteries according to any one of claims 5 to 8, wherein the content of the lithium pyrrolidium bis(sulfate) compound is 0.01 mass% or more and 5 mass% or less with respect to the total amount of the non-aqueous electrolyte solution for lithium secondary batteries.

10. Case and a positive electrode, a negative electrode, a separator, and an electrolyte solution contained in the case; Equipped with The positive electrode is a positive electrode capable of absorbing and releasing lithium ions, The negative electrode is capable of absorbing and releasing lithium ions, A lithium secondary battery precursor, wherein the electrolyte is the nonaqueous electrolyte for lithium secondary batteries according to any one of claims 5 to 9.

11. The lithium secondary battery precursor according to claim 10 , wherein the positive electrode contains a lithium-containing composite oxide represented by the following formula (C1) as a positive electrode active material: LiNi ａ Co ｂ Mn ｃ O ２ ... Formula (C1) [In formula (C1), 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.]

12. A step of preparing a lithium secondary battery precursor according to claim 10 or 11; charging and discharging the lithium secondary battery precursor; A method for producing a lithium secondary battery, comprising:

13. A lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor according to claim 10 or 11.

Images