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

Abstract

To provide an additive for a lithium secondary battery, capable of suppressing an increase in DC resistance even when a lithium secondary battery is stored for a long period of time in a high temperature environment.SOLUTION: An additive for a lithium secondary battery of the present disclosure includes a compound (I) represented by the following formula (I). In the formula (I), R11 and R12 each independently represent a C1-10 alkyl group, a C2-10 alkenyl group, a C2-10 alkynyl group, a benzyl group, or an aryl group, or R11 is integrated with R12 and represents an alkylene group forming a 3- to 8-membered ring structure together with a nitrogen atom in the formula (I), and R13 represents a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group or the aryl group.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This disclosure relates to additives for lithium secondary batteries, non-aqueous electrolytes for lithium secondary batteries, lithium secondary battery precursors, lithium secondary batteries, lithium sulfate compounds, and methods for producing lithium secondary batteries. [Background technology]

[0002] Lithium-ion batteries are attracting attention as high-energy-density batteries. Patent Document 1 discloses a non-aqueous electrolyte for energy storage devices (e.g., lithium secondary batteries) (hereinafter referred to as "non-aqueous electrolyte for lithium secondary batteries"). In the non-aqueous electrolyte for lithium secondary batteries disclosed in Patent Document 1, an electrolyte salt is dissolved in a non-aqueous solvent. The non-aqueous electrolyte for lithium secondary batteries disclosed in Patent Document 1 contains a specific zwitterion. Patent Document 1 specifically discloses a non-aqueous electrolyte for lithium secondary batteries containing 2-(triethylammonio)ethylsulfate as the specific zwitterion.

[0003] Patent Document 2 discloses a non-aqueous electrolyte secondary battery (hereinafter also referred to as a "lithium secondary battery"). The lithium secondary battery disclosed in Patent Document 2 comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte (hereinafter referred to as "non-aqueous electrolyte for lithium secondary batteries"). The positive electrode has a positive electrode active material capable of intercalating and releasing metal ions. The positive electrode active material contains a specific compound. The negative electrode has a negative electrode active material capable of intercalating and releasing metal ions. The non-aqueous electrolyte for lithium secondary batteries contains a specific compound. Patent Document 2 specifically discloses a non-aqueous electrolyte for lithium secondary batteries containing 2-(trimethylammonium)ethylsulfate.

[0004] The 2-(trimethylammonio)ethyl sulfate disclosed in Patent Document 2 is represented by the following formula (C-1). The 2-(triethylammonio)ethyl sulfate disclosed in Patent Document 1 is represented by the following formula (C-2).

[0005] [ka] [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2020 / 017318 [Patent Document 2] International Publication No. 2021 / 187625 [Overview of the project] [Problems that the invention aims to solve]

[0007] In lithium secondary batteries equipped with a non-aqueous electrolyte for lithium secondary batteries disclosed in Patent Documents 1 and 2, the ability to suppress the increase in DC resistance may be insufficient when stored for a long period of time (e.g., 14 days) in a high-temperature environment (e.g., 60°C).

[0008] In view of the above circumstances, this disclosure aims to provide an additive for lithium secondary batteries, a non-aqueous electrolyte for lithium secondary batteries, a lithium secondary battery precursor, a lithium secondary battery, a lithium sulfate compound, and a method for manufacturing a lithium secondary battery that can further suppress the increase in DC resistance even when lithium secondary batteries are stored for a long period of time in a high-temperature environment. [Means for solving the problem]

[0009] The following embodiments are included as means for solving the above problems. <1> An additive for lithium secondary batteries, comprising compound (I) represented by the following formula (I).

[0010] [ka]

[0011] [In formula (I), R 11 and R 12is, independently of each other, 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 or, R 11 and R 12 together represent an alkylene group that forms a 3- to 8-membered cyclic structure together with the nitrogen atom in the formula (I) (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), R 13 represents a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group, or the aryl group. ]] <2> The R 11 and R 12 are 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 or, R 11 and R 12 together represent an alkylene group that forms a 5- to 6-membered cyclic structure together with the nitrogen atom in the formula (I), The R 13 represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group, the additive for a lithium secondary battery according to <1> above. <3> The compound (I) includes at least one selected from the group consisting of compound (I-1) represented by the following formula (I-1), compound (I-2) represented by the following formula (I-2), compound (I-3) represented by the following formula (I-3), compound (I-4) represented by the following formula (I-4), compound (I-5) represented by the following formula (I-5), and compound (I-6) represented by the following formula (I-6). <1> or <2> Additives for lithium secondary batteries as described above.

[0012] [ka]

[0013] <4> The aforementioned <1> ~ <3> A non-aqueous electrolyte for lithium secondary batteries, comprising an additive for lithium secondary batteries as described in any one of the following. <5> The above further comprises at least one compound selected from the group consisting of compound (II), which is at least one of lithium monofluorophosphate and lithium difluorophosphate, compound (III), which is represented by the following formula (III), and compound (IV), which is represented by the following formula (IV). <4> Non-aqueous electrolyte for lithium secondary batteries as described above.

[0014] [ka]

[0015] [In formula (III), M is an alkali metal, Y is a transition element, a group 13, group 14, or group 15 element of the periodic table. b is an integer between 1 and 3. m is an integer between 1 and 4. n is an integer between 0 and 8. q is either 0 or 1, R 31This is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain substituents or heteroatoms in their structure, and when q is 1 and m is 2 to 4, there are m R 31 They may be joined together.) R 32 This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, or C6-C20 halogenated aryl groups (these groups may contain substituents or heteroatoms in their structure, and if n is 2-8, there are n R 32 They may each be joined together to form a ring. Q 1 , and Q 2 These are, independently, either an oxygen atom or a carbon atom. In formula (IV), R 41 This is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms. R 42 This is an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (iv-1), or a group represented by formula (iv-2). * indicates the bonding position. In formula (iv-1), R 43 This is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group. In formula (iv-2), R 44 This is an alkyl group having 1 to 6 carbon atoms, or an alkenyl group having 2 to 6 carbon atoms. <6> The content of compound (I) is 0.01% by mass to 5% by mass relative to the total amount of the non-aqueous electrolyte for lithium secondary batteries. <4> or <5> Non-aqueous electrolyte for lithium secondary batteries as described above. <7> The case and The case contains a positive electrode, a negative electrode, a separator, and an electrolyte, Equipped with, The positive electrode is a positive electrode capable of intercalating and releasing lithium ions. The aforementioned negative electrode is a negative electrode capable of intercalating and releasing lithium ions. The electrolyte, <4> ~ <6> A lithium secondary battery precursor, which is a non-aqueous electrolyte for lithium secondary batteries as described in any one of the following. <8> The positive electrode contains a lithium-containing composite oxide represented by the following formula (P1) as the positive electrode active material. <7> A lithium secondary battery precursor as described above. LiRing a Co b Mn c O2… Formula (P1) [In equation (P1), a, b, and c are each independently greater than 0 and less than 1, and the sum of a, b, and c is between 0.99 and 1.00.] <9> The aforementioned <7> or <8> The process of preparing the lithium secondary battery precursor described above, The process involves charging and discharging the lithium secondary battery precursor. A method for manufacturing lithium secondary batteries, including [the specified component]. <10> The aforementioned <7> or <8> A lithium secondary battery obtained by subjecting the lithium secondary battery precursor described above to charging and discharging. <11> A lithium sulfate compound represented by the following formula (I).

[0016] [ka]

[0017] [In formula (I), R 11 and R 12Each 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, R 11 and R 12 Together with the nitrogen atom in formula (I), it represents an alkylene group that forms a 3-8 membered ring 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). R 13 This represents a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group, or the aryl group. <12> The aforementioned R 11 and R 12 teeth, Each independently represents an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, or a benzyl group. Or, R 11 and R 12 This represents an alkylene group that, together with the nitrogen atom in formula (I), forms a 5-6 membered ring cyclic structure. R 13 This represents a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group, or the aryl group. <1> Lithium sulfate compounds as described above. <13> The aforementioned compound (I) is one selected from the group consisting of compound (I-1) represented by the following formula (I-1), compound (I-2) represented by the following formula (I-2), compound (I-3) represented by the following formula (I-3), compound (I-4) represented by the following formula (I-4), compound (I-5) represented by the following formula (I-5), and compound (I-6) represented by the following formula (I-6). <11> or <12> Lithium sulfate compounds as described above.

[0018] [ka] [Effects of the Invention]

[0019] According to this disclosure, an additive for lithium secondary batteries, a non-aqueous electrolyte for lithium secondary batteries, a lithium secondary battery precursor, a lithium secondary battery, a lithium sulfate compound, and a method for manufacturing a lithium secondary battery are provided that can suppress the increase in DC resistance even when the lithium secondary battery is stored for a long period of time in a high-temperature environment. [Brief explanation of the drawing]

[0020] [Figure 1] This is a schematic cross-sectional view showing a laminate-type battery, which is an example of a lithium secondary battery precursor of the present disclosure. [Figure 2] This is a schematic cross-sectional view showing a coin-type battery, which is another example of a lithium secondary battery precursor in this disclosure. [Modes for carrying out the invention]

[0021] In this specification, a numerical range represented by "~" means a range that includes the numbers written before and after "~" as the lower and upper limits, respectively. In this specification, the term "process" includes not only independent processes but also processes that cannot be clearly distinguished from other processes, provided that their intended purpose is achieved.

[0022] Hereinafter, embodiments of the lithium secondary battery additive, non-aqueous electrolyte for lithium secondary batteries, lithium secondary battery precursor, lithium secondary battery, lithium sulfate compound, and method for manufacturing a lithium secondary battery according to this disclosure will be described with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals and will not be repeated in the description.

[0023] [Additives for lithium secondary batteries] The lithium secondary battery additives described herein (hereinafter referred to as "additives") will be explained below.

[0024] The additives of this disclosure are suitably used as additives added to the non-aqueous electrolyte for lithium secondary batteries (hereinafter referred to as "non-aqueous electrolyte") contained in lithium secondary batteries. Details of lithium secondary batteries will be described later with reference to Figures 1 and 2.

[0025] The additives of this disclosure include compound (I) represented by the following formula (I) (hereinafter referred to as "lithium sulfate compound (I)").

[0026] [ka]

[0027] In formula (I), R 11 and R 12 teeth, Each independently represents an alkyl group having 1 to 10 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), an alkenyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 10 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), a benzyl group (at least one hydrogen atom in the benzyl group may be substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms), Or, R 11 and R 12 Together with the nitrogen atom in formula (I), it represents an alkylene group that forms a 3-8 membered ring 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). R 13 This represents a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group, or the aryl group.

[0028] Because the additive of this disclosure has the above configuration, it can suppress the increase in DC resistance even when a lithium secondary battery is stored in a high-temperature environment (e.g., 60°C) for a long period of time (e.g., 14 days). This effect is presumed to be due to, but is not limited to, the following reasons. When manufacturing a lithium secondary battery using the additives of this disclosure, it is believed that reaction products are 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 that components that are decomposition products of the reaction products are further generated. The reaction products are those produced by the reaction between lithium sulfate compound (I) and a compound derived from the electrolyte (for example, LiF). Such reaction products adhere to the negative electrode surface and form an SEI (Solid Electrolyte Interphase) film (hereinafter referred to as the "negative electrode SEI film"). It is believed that this component moves near the positive electrode surface during the manufacturing process, adheres to the positive electrode surface, and forms an SEI film (hereinafter referred to as the "positive electrode SEI film"). This enhances the stability of the lithium secondary battery in high-temperature environments. For example, the leaching of metal elements in the positive electrode active material is suppressed. Furthermore, lithium secondary batteries using the additives of this disclosure exhibit excellent stability even in high-temperature environments. In other words, even if lithium secondary batteries are stored in high-temperature environments, side reactions that are not part of the primary battery reaction are less likely to occur. The battery reaction involves the intercalation of lithium ions between the positive and negative electrodes. Side reactions include the reductive decomposition of the electrolyte by the negative electrode, the oxidative decomposition of the electrolyte by the positive electrode, and the elution of metal elements from the positive electrode active material. As a result, the progress of the decomposition reaction of the non-aqueous electrolyte is suppressed. As a result, it is presumed that the additives of this disclosure can suppress the increase in DC resistance even when lithium secondary batteries are stored in a high-temperature environment (e.g., 60°C) for a long period of time (e.g., 14 days).

[0029] Hereafter, when the negative electrode SEI film and the positive electrode SEI film are not distinguished, the negative electrode SEI film or the positive electrode SEI film will simply be referred to as the "SEI film".

[0030] For details, see formula (I), R 13This represents a hydrogen atom, a C1-C10 alkyl group (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), a C2-C10 alkenyl group (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), a C2-C10 alkynyl group (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, a C1-C6 alkoxy group, or a C1-C6 alkyl group), or an aryl group (at least one hydrogen atom in the aryl group may be substituted with a halogen atom, a C1-C6 alkoxy group, or a C1-C6 alkyl group).

[0031] In formula (I), R 11 , R 12 and R 13 Each of the independently expressed "C1-C10 alkyl groups" is a linear or branched alkyl group having 1 to 10 carbon atoms. Examples of "C1-C10 alkyl groups" include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, 2-methylbutyl, 1-methylpentyl, neopentyl, 1-ethylpropyl, hexyl, 3,3-dimethylbutyl, heptyl, octyl, nonyl, and decyl groups. Among these, C1-C6 alkyl groups are preferred, and C1-C3 alkyl groups are more preferred. At least one hydrogen atom in the "C1-C10 alkyl group" may be substituted with a halogen atom. The halogen atom in the "C1-C10 alkyl 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, even more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the "alkyl group having 1 to 10 carbon atoms," the number of hydrogen atoms substituted for the halogen atom is not particularly limited and can be appropriately selected according to the number of carbon atoms in the alkyl group, with 1 to 7 being preferred.

[0032] In formula (I), R 11 , R 12 and R 13 Each of the independently expressed "alkenyl group having 2 to 10 carbon atoms" is a linear or branched alkenyl group having 2 to 10 carbon atoms. Examples of "alkenyl groups having 2 to 10 carbon atoms" include vinyl group, 2-propenyl group, 2-butenyl group, 3-butenyl group, 2-pentenyl group, 3-pentenyl group, 4-pentenyl group, and 5-hexenyl group. Among these, alkenyl groups having 2 to 6 carbon atoms are preferred, and alkenyl groups having 2 to 3 carbon atoms are more preferred. 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, even more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the "alkenyl group having 2 to 10 carbon atoms," the number of hydrogen atoms substituted by halogen atoms is not particularly limited and can be appropriately selected according to the number of carbon atoms in the alkenyl group, with 1 to 7 being preferred.

[0033] In formula (I), R 11 , R 12 and R 13 Each of the independently expressed "alkynyl group having 2 to 10 carbon atoms" is a linear or branched alkynyl group having 2 to 10 carbon atoms. Examples of "alkynyl groups having 2 to 10 carbon atoms" include ethynyl group, propargyl group (2-propynyl group), 2-butynyl group, 3-butynyl group, 2-pentynyl group, 3-pentynyl group, 4-pentynyl group, and 5-hexynyl group. Among these, "alkynyl groups having 2 to 10 carbon atoms" are preferably alkynyl groups having 2 to 6 carbon atoms, and more preferably alkynyl groups 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, even more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the "alkynyl group having 2 to 10 carbon atoms," the number of hydrogen atoms substituted for halogen atoms is not particularly limited and can be appropriately selected according to the number of carbon atoms in the alkynyl group, with 1 to 7 being preferred.

[0034] In formula (I), R 11 , R 12 and R 13 At least one hydrogen atom of each independently represented "benzyl group" may be substituted with a halogen atom, a carbon-1 to carbon-6 alkoxy group, or a carbon-1 to carbon-6 alkyl group. 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, even more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. The number of hydrogen atoms substituted for the halogen atom in the "benzyl group" is not particularly limited, but is preferably 1 to 7. The alkoxy group having 1 to 6 carbon atoms in the "benzyl group" may have a linear, branched, or cyclic alkyl group. Examples of alkoxy groups having 1 to 6 carbon atoms in the "benzyl group" include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, t-butoxy, and pentyloxy groups. Among these, the alkoxy group having 1 to 3 carbon atoms in the "benzyl group" is preferred, with methoxy and ethoxy groups being more preferred. The number of hydrogen atoms substituted by the alkoxy group having 1 to 6 carbon atoms in the "benzyl group" is not particularly limited, but 1 to 3 is preferred. The C1-C6 alkyl group in the "benzyl group" may be linear, branched, or cyclic. Examples of C1-C6 alkyl groups in the "benzyl group" include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, n-hexyl, and cyclohexyl groups. Among these, the C1-C6 alkyl group in the "benzyl group" is preferably a C1-C3 alkyl group, with methyl and ethyl groups being more preferred. The number of hydrogen atoms substituted by the C1-C6 alkyl group in the "benzyl group" is not particularly limited, but is preferably 1 to 3.

[0035] In formula (I), R 11 , R 12 and R 13 At least one hydrogen atom of each independently represented "aryl group" may be substituted with a halogen atom, a carbon-1 to carbon-6 alkoxy group, or a carbon-1 to carbon-6 alkyl group. 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, even more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. The number of hydrogen atoms substituted for the halogen atom in the "aryl group" is not particularly limited, but is preferably 1 to 5. The alkoxy group having 1 to 6 carbon atoms in the "aryl group" may have a linear, branched, or cyclic alkyl group. Examples of alkoxy groups having 1 to 6 carbon atoms in the "aryl group" include methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, t-butoxy, and pentyloxy groups. Among these, the alkoxy group having 1 to 3 carbon atoms in the "aryl group" is preferred, with methoxy and ethoxy groups being more preferred. The number of hydrogen atoms substituted by the alkoxy group having 1 to 6 carbon atoms in the "aryl group" is not particularly limited, but 1 to 3 is preferred. The C1-C6 alkyl group in the "aryl group" may be linear, branched, or cyclic. Examples of C1-C6 alkyl groups in the "aryl group" include methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, t-butyl, n-pentyl, n-hexyl, and cyclohexyl groups. Among these, the C1-C6 alkyl group in the "aryl group" is preferably a C1-C3 alkyl group, with methyl and ethyl groups being more preferred. The number of hydrogen atoms substituted by the C1-C6 alkyl group in the "aryl group" is not particularly limited, but is preferably 1 to 3.

[0036] In formula (I), R 11 and R 12 The "alkylene group that forms a 3- to 8-membered ring cyclic structure with a nitrogen atom" is an alkylene group that forms a cyclic structure with 3 to 8 ring members including the nitrogen atom in formula (I). Among these, the alkylene group that forms a 3- to 8-membered ring cyclic structure with a nitrogen atom is preferably an alkylene group that forms a cyclic structure with 5 to 6 ring members including the nitrogen atom in formula (I). At least one hydrogen atom in the alkylene group that forms a 3-8 membered ring cyclic structure with a nitrogen atom may be substituted with a halogen atom or an alkyl group having 1 to 10 carbon atoms. In the alkylene group that forms a 3-8 membered ring cyclic structure with a nitrogen atom, the halogen atom is preferably a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom, more preferably a fluorine atom, a chlorine atom, or a bromine atom, even more preferably a fluorine atom or a chlorine atom, and particularly preferably a fluorine atom. In the alkylene group that forms a 3-8 membered ring cyclic structure with a nitrogen atom, the number of hydrogen atoms substituted by the halogen atom is appropriately selected according to the number of ring members. When the number of ring members including the nitrogen atom in formula (I) is 5, the halogen atoms are substituted. The number of hydrogen atoms is not particularly limited, but 1 to 8 is preferred. The C1-C10 alkyl group in the "alkylene group that forms a 3-8 membered ring cyclic structure with a nitrogen atom" is a linear or branched alkyl group having 1-10 carbon atoms. Examples of C1-C10 alkyl groups in the "alkylene group that forms a 3-8 membered ring cyclic structure with a nitrogen atom" include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl, tert-butyl, pentyl, 2-methylbutyl, 1-methylpentyl, neopentyl, 1-ethylpropyl, hexyl, 3,3-dimethylbutyl, heptyl, octyl, nonyl, and decyl groups. Among these, the C1-C10 alkyl group in the "alkylene group that forms a 3-8 membered ring cyclic structure with a nitrogen atom" is preferably a C1-C6 alkyl group, and more preferably a C1-C3 alkyl group. In the alkylene group that forms a 3- to 8-membered ring cyclic structure with a nitrogen atom, the number of hydrogen atoms substituted by the C1- to C10 alkyl group is appropriately selected according to 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 by the C1- to C10 alkyl group is not particularly limited, but 1 to 3 is preferred.

[0037] In formula (I), R 11 and R 12 Each of these 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 R 11 and R 12 Regarding this, together with the nitrogen atom in formula (I), it represents an alkylene group that forms a 5-6 membered ring cyclic structure, and R 13 This preferably represents a hydrogen atom, a C1-C6 alkyl group, a C2-C6 alkenyl group, or a benzyl group, more preferably a C1-C6 alkyl group, and even more preferably a propyl group. This makes it possible to further suppress the increase in DC resistance in high-temperature environments, even when lithium secondary batteries are stored for long periods in high-temperature environments.

[0038] The lithium sulfate compound (I) preferably contains at least one compound selected from the group consisting of compound (I-1) represented by the following formula (I-1), compound (I-2) represented by the following formula (I-2), compound (I-3) represented by the following formula (I-3), compound (I-4) represented by the following formula (I-4), compound (I-5) represented by the following formula (I-5), and compound (I-6) represented by the following formula (I-6). This further suppresses the increase in DC resistance even when lithium secondary batteries are stored for long periods in high-temperature environments. Hereinafter, the compound represented by formula (I-1) (I-1) may be referred to as "lithium 2-(dimethylamino)ethyl sulfate (I-1)". The compound represented by formula (I-2) (I-2) may be referred to as "lithium 2-(diethylamino)ethyl sulfate (I-2)". The compound represented by formula (I-3) (I-3) may be referred to as "lithium 2-(piperidine-1-yl)ethyl sulfate (I-3)". The compound represented by formula (I-4) (I-4) may be referred to as "lithium 2-(pyrrolidine-1-yl)ethyl sulfate (I-4)". The compound represented by formula (I-5) (I-5) may be referred to as "lithium 1-(dimethylamino)pentan-2-yl sulfate (I-5)". The compound (I-6) represented by formula (I-6) is sometimes called "lithium 1-(pyrrolidine-1-yl)pentan-2-yl sulfate (I-6)".

[0039] [ka]

[0040] [Non-aqueous electrolyte] The non-aqueous electrolyte described herein is explained below.

[0041] The non-aqueous electrolyte of this disclosure is used as an electrolyte for lithium secondary batteries.

[0042] The non-aqueous electrolyte of this disclosure includes the additives of this disclosure. Since the non-aqueous electrolyte of this disclosure contains the additives of this disclosure, it is possible to suppress the increase in DC resistance even when the lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0043] Furthermore, when analyzing the non-aqueous electrolyte collected from disassembled lithium secondary batteries, the amount of lithium sulfate compound (I) was found to be lower compared to the amount added to the non-aqueous electrolyte. There is a possibility of this occurring. Even in this case, if even a small amount of lithium sulfate compound (I) is detected in the non-aqueous electrolyte extracted from the lithium secondary battery, the electrolyte of that lithium secondary battery is included in the scope of the non-aqueous electrolyte of this disclosure.

[0044] The content of lithium sulfate compound (I) is not particularly limited, but is preferably 0.01% to 5% by mass relative to the total amount of the non-aqueous electrolyte. This allows the lithium secondary battery to operate without the SEI film impairing the conductivity of lithium cations. The SEI film contains a sufficient amount of structure derived from lithium sulfate compound (I). This facilitates the formation of thermally and chemically stable inorganic salt or polymer structures. Therefore, at high temperatures, the elution of SEI film components that impair the durability of the SEI film, and the deterioration of the SEI film, are less likely to occur. As a result, the durability of the SEI film and the high-temperature storage characteristics of the lithium secondary battery are improved. The content of lithium sulfate compound (I) is more preferably 0.05% to 3.0% by mass, even more preferably 0.10% to 2.0% by mass, particularly preferably 0.20% to 2.0% by mass, and even more preferably 0.40% to 2.0% by mass, relative to the total amount of the non-aqueous electrolyte.

[0045] <Compound (A)> The non-aqueous electrolyte preferably further contains at least one compound (hereinafter referred to as "compound (A)") selected from the group consisting of compound (II) (hereinafter referred to as "lithium fluorophosphate compound (II)"), compound (III) (hereinafter referred to as "cyclic dicarbonyl compound (III)"), and compound (IV) (hereinafter referred to as "cyclic sulfonic acid ester compound (IV)"). Lithium fluorophosphate compound (II) is at least one of lithium monofluorophosphate and lithium difluorophosphate. Cyclic dicarbonyl compound (III) is represented by the following formula (III). Cyclic sulfonic acid ester compound (IV) is represented by the following formula (IV). Details of lithium fluorophosphate compound (II), cyclic dicarbonyl compound (III), and cyclic sulfonic acid ester compound (IV) will be described later.

[0046] [ka]

[0047] By further including compound (A) in addition to lithium sulfate compound (I), the non-aqueous electrolyte can suppress the increase in DC resistance even when lithium secondary batteries are stored for long periods in high-temperature environments.

[0048] When the non-aqueous electrolyte contains compound (A), the content of compound (A) is preferably 0.01% to 10.0% by mass, more preferably 0.05% to 5.0% by mass, even more preferably 0.10% to 3.0% by mass, and particularly preferably 0.20% to 2.0% by mass, relative to the total amount of the non-aqueous electrolyte, from the viewpoint of improving the high-temperature storage characteristics of the lithium secondary battery.

[0049] The following describes each of the following: lithium fluorophosphate compounds (II), cyclic dicarbonyl compounds (III), and cyclic sulfonic acid ester compounds (IV).

[0050] (Lithium fluorophosphate compound (II)) The non-aqueous electrolyte preferably contains lithium fluorophosphate compound (II). Lithium fluorophosphate compound (II) is at least one of lithium monofluorophosphate and lithium difluorophosphate. Lithium difluorophosphate is represented by the following formula (II-1), and lithium monofluorophosphate is represented by the following formula (II-2). Hereinafter, the compound represented by formula (II-1) may be referred to as "lithium fluorophosphate compound (II-1)". The compound represented by formula (II-2) may be referred to as "lithium fluorophosphate compound (II-2)".

[0051] [ka]

[0052] By including lithium fluorophosphate compound (II) in addition to lithium sulfate compound (I) in the non-aqueous electrolyte, the increase in DC resistance can be further suppressed even when lithium secondary batteries are stored for long periods in high-temperature environments.

[0053] The non-aqueous electrolyte may contain only lithium monofluorophosphate and lithium difluorophosphate, or it may contain both lithium monofluorophosphate and lithium difluorophosphate.

[0054] When the non-aqueous electrolyte contains lithium fluorophosphate compound (II), the content of lithium fluorophosphate compound (II) is preferably 0.001% to 5% by mass, more preferably 0.01% to 3% by mass, and even more preferably 0.1% to 2% by mass, relative to the total amount of the non-aqueous electrolyte. If the upper limit of the content of lithium fluorophosphate compound (II) is within the above range, the solubility of lithium fluorophosphate compound (II) in the non-aqueous solvent can be ensured, and the DC resistance of the lithium secondary battery can be further reduced.

[0055] (Cyclic dicarbonyl compound (III)) The non-aqueous electrolyte of this disclosure preferably contains a cyclic dicarbonyl compound (III) represented by the following formula (III).

[0056] [ka]

[0057] In formula (III), M is an alkali metal, Y is a transition element, a group 13, group 14, or group 15 element of the periodic table. b is an integer between 1 and 3. m is an integer between 1 and 4. n is an integer between 0 and 8. q is either 0 or 1, R 31 This is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain substituents or heteroatoms in their structure, and when q is 1 and m is 2 to 4, there are m R 31 They may be joined together.) R 32 This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, or C6-C20 halogenated aryl groups (these groups may contain substituents or heteroatoms in their structure, and if n is 2-8, there are n R 32 They may each be joined together to form a ring. Q 1 , and Q 2 These are, independently, either an oxygen atom or a carbon atom.

[0058] The non-aqueous electrolyte of this disclosure contains a cyclic dicarbonyl compound (III) in addition to a lithium sulfate compound (I), which further suppresses the increase in DC resistance even when the lithium secondary battery is stored for a long period of time in a high-temperature environment. This effect is presumed to be due to the following reasons: The non-aqueous electrolyte contains a cyclic dicarbonyl compound (III) in addition to the lithium sulfate compound (I), so that the SEI film and the like may contain bonds derived from the cyclic dicarbonyl compound (III) in addition to the reaction products mentioned above. This makes it easier to form thermally and chemically stable inorganic salt or polymer structures. Therefore, at high temperatures, the elution of components of the SEI film and the like, which would impair the durability of the SEI film and the like, and the deterioration of the SEI film and the like are less likely to occur. As a result, even if lithium secondary batteries are stored for a long period of time in a high-temperature environment, the increase in DC resistance can be further suppressed.

[0059] M is an alkali metal. Examples of alkali metals include lithium, sodium, and potassium. Of these, M is preferably lithium. Y is a transition element, a group 13, group 14, or group 15 element of the periodic table. Preferably, Y is Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb, and more preferably Al, B, or P. When Y is Al, B, or P, the synthesis of the anionic compound becomes relatively easy, and manufacturing costs can be reduced. b represents the valency of the anion and the number of cations. b is an integer between 1 and 3, and is preferably 1. If b is 3 or less, the salt of the anionic compound is easily soluble in the mixed organic solvent. m and n are values ​​related to the number of ligands. Each of m and n is determined by the type of M. m is an integer from 1 to 4. n is an integer from 0 to 8. q is either 0 or 1. When q is 0, the chelate ring is a five-membered ring, and when q is 1, the chelate ring is a six-membered ring. R 31 R represents an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. These alkylene groups, halogenated alkylene groups, arylene groups, or halogenated arylene groups may contain substituents or heteroatoms in their structure. Specifically, R 31These groups may contain substituents instead of hydrogen atoms. Substituents include halogen atoms, linear or cyclic alkyl groups, aryl groups, alkenyl groups, alkoxy groups, aryloxy groups, sulfonyl groups, amino groups, cyano groups, carbonyl groups, acyl groups, amide groups, or hydroxyl groups. These groups may also have structures in which nitrogen atoms, sulfur atoms, or oxygen atoms are introduced instead of the carbon element. When q is 1 and m is 2-4, there are m R 31 These components may be bonded together. An example of such a ligand is ethylenediaminetetraacetic acid. R 32 R represents a halogen atom, an alkyl group having 1 to 10 carbon atoms, an alkyl halide having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or an aryl halide having 6 to 20 carbon atoms. These alkyl groups, alkyl halides, aryl groups, or aryl halides are R 31 Similarly, the structure may contain substituents and heteroatoms, and when n is 2 to 8, there are n R 32 These may each be joined to form a ring. 32 As such, electron-withdrawing groups are preferred, and fluorine atoms are particularly preferred. Q 1 , and Q 2 These elements independently represent either O or C. Therefore, the ligand will bond to Y via these heteroatoms.

[0060] Specific examples of cyclic dicarbonyl compounds (III) include the compounds represented by the following formulas (III-1) to (III-2). Hereinafter, compounds represented by formula (III-1) may be referred to as "cyclic dicarbonyl compounds (III-1)".

[0061] [ka]

[0062] When the non-aqueous electrolyte contains cyclic dicarbonyl compound (III), the content of cyclic dicarbonyl compound (III) is preferably 0.01% to 10% by mass, more preferably 0.05% to 5.0% by mass, even more preferably 0.10% to 3.0% by mass, and particularly preferably 0.10% to 2.0% by mass, relative to the total amount of the non-aqueous electrolyte. If the content of cyclic dicarbonyl compound (III) is within the above range, the lithium secondary battery can operate without the SEI film, etc., impairing the conductivity of the lithium cation. Furthermore, as the SEI film, etc., contains a cyclic dicarbonyl structure, the battery characteristics of the lithium secondary battery are improved. If the content of cyclic dicarbonyl compound (III) 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 thermally and chemically stable inorganic salt or polymer structures. Therefore, at high temperatures, the leaching of components of the SEI film and other materials that impair its durability, as well as the deterioration of the SEI film and other materials, are less likely to occur. As a result, the durability of the SEI film and other materials, and the characteristics of lithium secondary batteries after high-temperature storage, are improved.

[0063] (Cyclic sulfonic acid ester compound (IV)) The non-aqueous electrolyte of this disclosure preferably contains a cyclic sulfonic acid ester compound (IV) represented by the following formula (IV).

[0064] [ka]

[0065] In formula (IV), R 41 This is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms. R 42 This is an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (iv-1), or a group represented by formula (iv-2). * indicates the bonding position. In formula (iv-1), R 43This is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group. In formula (iv-2), R 44 This is an alkyl group having 1 to 6 carbon atoms, or an alkenyl group having 2 to 6 carbon atoms.

[0066] The non-aqueous electrolyte of this disclosure contains a cyclic sulfonic acid ester compound (IV) in addition to a lithium sulfate compound (I), which further suppresses the increase in DC resistance even when the lithium secondary battery is stored for a long period of time in a high-temperature environment. This effect is presumed to be due to the following reasons: When a lithium secondary battery is manufactured using the non-aqueous electrolyte of this disclosure, the reaction products in the manufacturing process (for example, the aging process described later) include products resulting from the reaction between a cyclic sulfonic acid ester compound (IV) and a compound derived from the electrolyte (for example, LiF). This further enhances the stability of the lithium secondary battery under high-temperature conditions. As a result, even when the lithium secondary battery is stored under high-temperature conditions, the increase in the DC resistance of the lithium secondary battery is expected to be more suppressed.

[0067] In formula (IV), R 41 It is preferably an alkylene group, vinylene group, or oxygen atom having 2 to 3 carbon atoms, more preferably a trimethylene group, vinylene group, or oxygen atom, and particularly preferably an oxygen atom.

[0068] In cyclic sulfonic acid ester compounds (IV), R 41 However, it is preferable that the atom be an oxygen atom. This facilitates the formation of a thermally and chemically stable inorganic salt structure. Therefore, at high temperatures, the elution of components of the SEI film, which impairs the durability of the SEI film, and the deterioration of the SEI film are less likely to occur. As a result, the durability of the SEI film and the battery characteristics of the lithium secondary battery are improved.

[0069] In formula (IV), R 42 It is preferable that the group is represented by formula (iv-1) or formula (iv-2). In formula (iv-1), R 43 The group is preferably an alkylene group having 1 to 3 carbon atoms, an alkenylene group having 1 to 3 carbon atoms, or an oxymethylene group, and more preferably an oxymethylene group. In formula (iv-2), R 44 It 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.

[0070] Specific examples of cyclic sulfonic acid ester compounds (IV) include the compounds represented by formulas (IV-1) to (IV-8). Hereinafter, compounds represented by formula (IV-1) may be referred to as "cyclic sulfonic acid ester compounds (IV-1)".

[0071] [ka]

[0072] The non-aqueous electrolyte may contain only one cyclic sulfonic acid ester compound (IV), or it may contain two or more.

[0073] When the non-aqueous electrolyte contains a cyclic sulfonic acid ester compound (IV), the content of the cyclic sulfonic acid ester compound (IV) is preferably 0.01% to 5.0% by mass, more preferably 0.05% to 3.0% by mass, and even more preferably 0.10% to 2.0% by mass, relative to the total amount of the non-aqueous electrolyte. If the content of the cyclic sulfonic acid ester compound (IV) is within the above range, the lithium secondary battery can operate without the SEI film, etc., impairing the conductivity of lithium ions. Furthermore, as the SEI film, etc., contains a cyclic sulfur-containing ester structure, the battery characteristics of the lithium secondary battery are improved. If the content of the cyclic sulfonic acid ester compound (IV) is within the above range, the SEI film, etc., contains a sufficient amount of cyclic sulfur-containing ester structure. This makes it easier to form thermally and chemically stable inorganic salt or polymer structures. Therefore, at high temperatures, elution of components of the SEI film, etc., that would impair the durability of the SEI film, etc., and deterioration of the SEI film, etc., are unlikely to occur. As a result, the durability of SEI films and other components, as well as the battery characteristics of lithium secondary batteries, are improved.

[0074] <Other additives> The non-aqueous electrolyte of this disclosure may contain other additives. Other additives are not particularly limited, and any known additives can be used as desired. Other additives that can be used include, for example, those described in paragraphs 0042 to 0055 of Japanese Patent Publication No. 2019-153443.

[0075] <Non-aqueous solvent> Non-aqueous electrolytes generally contain a non-aqueous solvent. Various known non-aqueous solvents can be appropriately selected. There may be only one non-aqueous solvent or two or more.

[0076] Examples of non-aqueous solvents include cyclic carbonates, fluorinated cyclic carbonates, linear carbonates, fluorinated linear carbonates, aliphatic carboxylic acid esters, fluorinated aliphatic carboxylic acid esters, γ-lactones, fluorinated γ-lactones, cyclic ethers, fluorinated cyclic ethers, linear ethers, fluorinated linear ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolanes, trimethyl phosphate, dimethyl sulfoxide, and dimethyl sulfoxide phosphate. Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC). Examples of fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC). Examples of linear carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), and dipropyl carbonate (DPC). Examples of aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, and ethyl trimethylbutyrate. Examples of γ-lactones include γ-butyrolactone and γ-valerolactone. Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, and 1,4-dioxane. Examples of linear ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane. Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, and 3-methoxypropionitrile. Examples of amides include N,N-dimethylformamide. Examples of lactam compounds include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

[0077] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, linear carbonates, and fluorine-containing linear carbonates. In this case, the total proportion of cyclic carbonates, fluorinated cyclic carbonates, linear carbonates, and fluorinated linear carbonates is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass, relative to the total amount of the non-aqueous solvent.

[0078] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and linear carbonates. In this case, the total proportion of cyclic carbonates and linear carbonates in the non-aqueous solvent is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass, relative to the total amount of the non-aqueous solvent.

[0079] The content of the non-aqueous solvent is preferably 60% to 99% by mass, more preferably 70% to 97% by mass, and even more preferably 70% to 90% by mass, relative to the total amount of the non-aqueous electrolyte.

[0080] The intrinsic viscosity of the non-aqueous solvent is preferably 10.0 mPa·s or less at 25°C, from the viewpoint of further improving the dissociation of the electrolyte and the mobility of ions.

[0081] <Electrolyte> Non-aqueous electrolytes generally contain electrolytes.

[0082] The electrolyte preferably contains at least one of a lithium salt containing fluorine (hereinafter sometimes referred to as "fluorine-containing lithium salt") and a lithium salt that does not contain fluorine.

[0083] Examples of fluorinated lithium salts include inorganic acid anionic salts and organic acid anionic salts. Examples of inorganic acid anionic salts include lithium hexafluoride phosphate (LiPF6), lithium borate tetrafluoride (LiBF4), lithium arsenate hexafluoride (LiAsF6), and lithium tantalate hexafluoride (LiTaF6). Examples of organic acid anionic salts include lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(fluorosulfonyl)imide (Li(FSO2)2N), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), and lithium bis(pentafluoroethanesulfonyl)imide (Li(C2F5SO2)2N). Among the fluorinated lithium salts, lithium hexafluoride phosphate (LiPF6) is particularly preferred.

[0084] Lithium salts that do not contain fluorine include lithium perchlorate (LiClO4), lithium aluminate tetrachloride (LiAlCl4), and lithium decachlorodecaborate (Li2B 10 Cl 10 ) are some examples.

[0085] When the electrolyte contains a fluorinated lithium salt, the content of the fluorinated lithium salt is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass, relative to the total amount of the electrolyte. When the fluorinated lithium salt contains lithium hexafluoride phosphate (LiPF6), the content of lithium hexafluoride phosphate (LiPF6) is preferably 50% to 100% by mass, more preferably 60% to 100% by mass, and even more preferably 80% to 100% by mass, relative to the total amount of the electrolyte.

[0086] When the non-aqueous electrolyte contains an electrolyte, the concentration of the electrolyte in the non-aqueous electrolyte is preferably 0.1 mol / L to 3 mol / L, more preferably 0.5 mol / L to 2 mol / L.

[0087] When the non-aqueous electrolyte contains lithium hexafluoride phosphate (LiPF6), the concentration of lithium hexafluoride phosphate (LiPF6) in the non-aqueous electrolyte is preferably 0.1 mol / L to 3 mol / L, more preferably 0.5 mol / L to 2 mol / L.

[0088] <Other ingredients> The non-aqueous electrolyte may contain other components as needed. Other components include acid anhydrides.

[0089] [Precursor for lithium secondary batteries] Next, the lithium secondary battery precursor of this disclosure will be described.

[0090] The lithium secondary battery precursor of this disclosure comprises a case, a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode, negative electrode, separator, and electrolyte are housed in the case. The positive electrode is a positive electrode capable of intercalating and releasing lithium ions. The negative electrode is a negative electrode capable of intercalating and releasing lithium ions. The electrolyte is a non-aqueous electrolyte of this disclosure.

[0091] A lithium secondary battery precursor refers to a lithium secondary battery before charging and discharging. In other words, in a lithium secondary battery precursor, the negative electrode does not contain a negative electrode SEI film, and the positive electrode does not contain a positive electrode SEI film.

[0092] <Case> The shape of the case is not particularly limited and can be appropriately selected depending on the application of the lithium secondary battery precursor disclosed herein. Examples of cases include cases including a laminate film, and cases consisting of a battery can and a battery can lid.

[0093] <Positive electrode> The positive electrode is a positive electrode capable of intercepting and releasing lithium ions. Preferably, the positive electrode contains at least one positive electrode active material capable of intercepting and releasing lithium ions.

[0094] The positive electrode comprises a positive electrode current collector and a positive electrode composite layer. The positive electrode composite layer is provided on at least a portion of the surface of the positive electrode current collector.

[0095] Examples of materials for the positive electrode current collector include metals and alloys. More specifically, examples of positive electrode current collector materials include aluminum, nickel, stainless steel (SUS), and copper. Among these, aluminum is preferred from the viewpoint of balancing high conductivity and cost. Here, "aluminum" means pure aluminum or aluminum alloy. Aluminum foil is preferred as the positive electrode current collector. The material of the aluminum foil is not particularly limited, and examples include A1085 material and A3003 material.

[0096] The positive electrode composite layer contains a positive electrode active material and a binder.

[0097] The positive electrode active material is not particularly limited as long as it is a material capable of intercalating and releasing lithium ions, and can be appropriately adjusted depending on the application of the lithium secondary battery precursor.

[0098] Examples of the positive electrode active material include, for example, a first oxide, a second oxide, etc. The first oxide has lithium (Li) and nickel (Ni) as constituent metal elements. The second oxide contains Li, Ni, and at least one metal element other than Li and Ni as constituent metal elements. Examples of the metal element other than Li and Ni include, for example, a transition metal element, a typical metal element, etc. The second oxide preferably contains the metal element other than Li and Ni at a ratio preferably comparable to or less than Ni in terms of the number of atoms. The metal element other than Li and Ni may be, for example, at least one selected from the group consisting of Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce. These positive electrode active materials may be used alone or in combination of a plurality.

[0099] It is preferable that the positive electrode contains a lithium-containing composite oxide represented by the following formula (P1) (hereinafter sometimes referred to as "NCM") as the positive electrode active material. The lithium-containing composite oxide (P1) has the advantages of high energy density per unit volume and excellent thermal stability. LiNi a Co b Mn c O2… Formula (P1) In formula (P1), a, b, and c are each independently greater than 0 and less than 1, and the sum of a, b, and c is 0.99 to 1.00. Specific examples of NCM include LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.

[0100] The positive electrode active material may contain a lithium-containing composite oxide represented by the following formula (P2) (hereinafter sometimes referred to as "NCA"). Li t Ni 1-x-y Co x Al y O2… Formula (P2) In equation (P2), t is between 0.95 and 1.15, x is between 0 and 0.3, y is between 0.1 and 0.2, and the sum of x and y is less than 0.5. A specific example of NCA is Li Ni 0.8 Co 0.15 Al 0.05 Examples include O2.

[0101] In the lithium secondary battery precursor of the present disclosure, if the positive electrode comprises a positive electrode current collector and a positive electrode composite layer containing a positive electrode active material and a binder, the content of the positive electrode active material in the positive electrode composite layer is preferably 10% to 99.9% by mass, more preferably 30% to 99% by mass, even more preferably 50% to 99% by mass, and particularly preferably 70% to 99% by mass, based on the total amount of the positive electrode composite layer.

[0102] Examples of binders include polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesins, and rubber particles. Examples of fluororesins include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and vinylidene fluoride-hexafluoropropylene copolymer. Examples of rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles. Among these, fluororesins are preferred from the viewpoint of improving the oxidation resistance of the positive electrode composite layer. One type of binder can be used alone, and two or more types can be used in combination as needed. The binder content in the positive electrode composite layer is preferably 0.1% to 4% by mass relative to the total amount of the positive electrode composite layer, from the viewpoint of balancing the physical properties of the positive electrode composite layer (e.g., electrolyte permeability, peel strength, etc.) and battery performance. If the binder content is 0.1% by mass or more, the adhesion of the positive electrode composite layer to the positive electrode current collector and the bonding of the positive electrode active materials to each other are further improved. If the binder content is 4% by mass or less, the amount of positive electrode active material in the positive electrode composite layer can be increased, thus further improving the discharge capacity.

[0103] The positive electrode composite layer preferably contains a conductive additive. As the material for the conductive additive, known conductive additives can be used. Among the known conductive additives, conductive carbon materials are preferred. Examples of conductive carbon materials include graphite, carbon black, conductive carbon fibers, and fullerenes. These can be used alone or in combination of two or more types. Examples of conductive carbon fibers include carbon nanotubes, carbon nanofibers, and carbon fibers. Examples of graphite include artificial graphite and natural graphite. Examples of natural graphite include flake graphite, lump graphite, and earthy graphite. The material of the conductive additive may be a commercially available product. Examples of commercially available carbon blacks include Tokai Carbon #4300, #4400, #4500, #5500, etc. (Tokai Carbon Co., Ltd., Furnace Black), Printex L, etc. (Degussa Co., Ltd., Furnace Black), Raven 7000, 5750, 5250, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975ULTRA, etc., PUER BLACK100, 115, 205 etc. (Columbian brand, Furnace Black), #2350, #2400B, #2600B, #30050B, #3030B, #3230B, #3350B, #3400B, #5400B etc. (Mitsubishi Chemical Corporation, Furnace Black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, Examples include LITX-50, LITX-200 (Cabot Furnace Black), Ensaco 250G, Ensaco 260G, Ensaco 350G, Super-P (TIMCAL), Ketjenblack EC-300J, EC-600JD (Akzo), Denka Black, Denka Black HS-100, FX-35 (Denka Acetylene Black).

[0104] The positive electrode composite layer may contain other components. These other components include thickeners, surfactants, dispersants, wetting agents, and defoaming agents.

[0105] <Negative electrode> The negative electrode is a negative electrode capable of intercepting and releasing lithium ions. Preferably, the negative electrode contains at least one negative electrode active material capable of intercepting and releasing lithium ions.

[0106] The negative electrode more preferably comprises a negative electrode current collector and a negative electrode composite layer. The negative electrode composite layer is provided on at least a portion of the surface of the negative electrode current collector.

[0107] There are no particular restrictions on the material of the negative electrode current collector; any known material can be used, such as metal or alloy. Specifically, examples of materials for the negative electrode current collector include aluminum, nickel, stainless steel (SUS), nickel-plated steel, and copper. Among these, copper is preferred as the material for the negative electrode current collector from the viewpoint of processability. Copper foil is preferred as the negative electrode current collector.

[0108] The negative electrode composite layer contains a negative electrode active material and a binder.

[0109] The negative electrode active material is not particularly limited as long as it is a material capable of intercalating and releasing lithium ions. Preferably, the negative electrode active material is at least one selected from the group consisting of, for example, metallic lithium, lithium-containing alloys, metals or alloys that can be alloyed with lithium, oxides that can be doped and dedoped with lithium ions, transition metal nitrides that can be doped and dedoped with lithium ions, and carbon materials that can be doped and dedoped with lithium ions. Among these, the negative electrode active material is preferably a carbon material capable of doping and dedoping with lithium ions (hereinafter referred to as "carbon material").

[0110] Examples of carbon materials include carbon black, activated carbon, graphite materials, and amorphous carbon materials. These carbon materials may be used individually or in mixtures of two or more types. The form of the carbon material is not particularly limited and can be fibrous, spherical, potato-shaped, or flake-shaped. The particle size of the carbon material is not particularly limited, but is preferably 5 μm to 50 μm, and more preferably 20 μm to 30 μm. Examples of amorphous carbon materials include hard carbon, coke, mesocarbon microbeads (MCMB) fired at temperatures below 1500°C, and mesophase pitch carbon fiber (MCF). Examples of graphite materials include natural graphite and artificial graphite. Examples of artificial graphite include graphitized MCMB and graphitized MCF. Graphite materials may also contain boron. Graphite materials may be coated with metal or amorphous carbon. Examples of metals used to coat graphite materials include gold, platinum, silver, copper, and tin. Graphite materials may also be mixtures of amorphous carbon and graphite.

[0111] The negative electrode composite layer preferably contains a conductive additive. Examples of conductive additives include those similar to those exemplified as conductive additives that may be included in the positive electrode composite layer.

[0112] The negative electrode composite layer may contain other components in addition to the above-mentioned components. Examples of other components include thickeners, surfactants, dispersants, wetting agents, and defoaming agents.

[0113] <Separator> Examples of separators include porous resin plates. Materials for the porous resin plates include resin, nonwoven fabrics containing this resin, and others. Examples of resins include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, and polyamide. In particular, the separator is preferably a porous resin sheet with a single-layer or multi-layer structure. The porous resin sheet is mainly made of one or more types of polyolefin resin. The thickness of the separator is preferably 5 μm to 30 μm. The separator is preferably placed between the positive electrode and the negative electrode.

[0114] [An example of a lithium secondary battery precursor] An example of a lithium secondary battery precursor 1 according to an embodiment of this disclosure will be specifically described with reference to Figure 1. Figure 1 is a cross-sectional view of a lithium secondary battery precursor 1 according to an embodiment of this disclosure.

[0115] The lithium secondary battery precursor 1 is of the stacked type. As shown in Figure 1, in the lithium secondary battery precursor 1, the battery element 10 is sealed inside the outer casing 30. The outer casing 30 is made of laminate film. The battery element 10 is fitted with a positive electrode lead 21 and a negative electrode lead 22. The positive electrode lead 21 and the negative electrode lead 22 are led out in opposite directions from the inside to the outside of the outer casing 30.

[0116] As shown in Figure 1, the battery element 10 is made up of a stack of a positive electrode 11, a separator 13, and a negative electrode 12. The positive electrode 11 has a positive electrode composite layer 11B formed on both main surfaces of the positive electrode current collector 11A. The negative electrode 12 has a negative electrode composite layer 12B formed on both main surfaces of the negative electrode current collector 12A. The positive electrode composite layer 11B formed on one main surface of the positive electrode current collector 11A of the positive electrode 11 and the negative electrode composite layer 12B formed on one main surface of the negative electrode current collector 12A of the negative electrode 12 adjacent to the positive electrode 11 face each other via the separator 13.

[0117] The non-aqueous electrolyte of this disclosure is injected into the exterior casing 30 of the lithium secondary battery precursor 1. The non-aqueous electrolyte of this disclosure permeates the positive electrode composite layer 11B, the separator 13, and the negative electrode composite layer 12B. In the lithium secondary battery precursor 1, a single cell layer 14 is formed by the adjacent positive electrode composite layer 11B, the separator 13, and the negative electrode composite layer 12B. The positive electrode and negative electrode may be formed with their respective active material layers on one side of their respective current collectors.

[0118] In this embodiment, the lithium secondary battery precursor 1 is of the stacked type, but the disclosure is not limited thereto, and for example, it may be of the wound type. The wound type is formed by stacking a positive electrode, a separator, a negative electrode, and a separator in that order and winding them in layers. The wound type includes cylindrical or rectangular shapes.

[0119] In this embodiment, as shown in Figure 1, the direction in which each of the positive lead and the negative lead protrudes from the inside to the outside of the casing 30 is opposite to the direction of the casing 30, but the disclosure is not limited thereto. For example, the way in which each of the positive lead and the negative lead protrudes from the inside to the outside of the casing 30 is the same direction with respect to the casing 30.

[0120] An example of a lithium secondary battery according to the embodiments of the present disclosure described below is a lithium secondary battery in which an SEI film is formed on the respective surfaces of the positive electrode composite layer 11B and the negative electrode composite layer 12B of the lithium secondary battery precursor 1 by charging and discharging the lithium secondary battery precursor 1.

[0121] Another example of a lithium secondary battery precursor in this disclosure is a coin cell. Figure 2 is a schematic perspective view showing an example of a coin cell battery, which is another example of a lithium secondary battery precursor of the present disclosure. In the coin-type battery shown in Figure 2, a disc-shaped negative electrode 42, a separator 45 injected with a non-aqueous electrolyte, a disc-shaped positive electrode 41, and, if necessary, spacer plates 47 and 48 made of stainless steel or aluminum are stacked in this order and housed between the positive electrode can 43 (hereinafter also referred to as the "battery can") and the sealing plate 44 (hereinafter also referred to as the "battery can lid"). The positive electrode can 43 and the sealing plate 44 are crimped and sealed via a gasket 46. In this example, the non-aqueous electrolyte of this disclosure is used as the non-aqueous electrolyte injected into the separator 45.

[0122] [Lithium-ion secondary battery] Next, the lithium secondary battery of this disclosure will be described.

[0123] The lithium secondary battery of this disclosure comprises a case, a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode, negative electrode, separator, and electrolyte are housed in the case. The positive electrode is a positive electrode capable of intercalating and releasing lithium ions. The negative electrode is a negative electrode capable of intercalating and releasing lithium ions. The electrolyte is a non-aqueous electrolyte of this disclosure. The negative electrode includes a negative electrode SEI film. The positive electrode includes a positive electrode SEI.

[0124] The lithium secondary battery of this disclosure differs from the lithium secondary battery precursor of this disclosure primarily in two ways: the negative electrode includes a negative electrode SEI film (point 1), and the positive electrode includes a positive electrode SEI film (point 2). In other words, the lithium secondary battery of this disclosure is the same as the lithium secondary battery precursor of this disclosure except for points 1 and 2. Therefore, the description of the components of the lithium secondary battery of this disclosure other than points 1 and 2 will be omitted below.

[0125] Regarding the first point, "the negative electrode includes a negative electrode SEI film" means that when the negative electrode comprises a negative electrode current collector and a negative electrode composite layer, it includes a first negative electrode form and a second negative electrode form. The first negative electrode form refers to a form in which a negative electrode SEI film is formed on at least a portion of the surface of the negative electrode composite layer. The second negative electrode form refers to a form in which a 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.

[0126] Regarding the second point, "the positive electrode includes a positive electrode SEI film" means that when the positive electrode comprises a positive electrode current collector and a positive electrode composite layer, it includes a first positive electrode form and a second positive electrode form. The first positive electrode form refers to a form in which a positive electrode SEI film is formed on at least a portion of the surface of the positive electrode composite layer. The second positive electrode form refers to a form in which a positive electrode SEI film is formed on the surface of the positive electrode active material, which is a constituent material of the positive electrode composite layer.

[0127] The SEI film includes, for example, at least one selected from the group consisting of a decomposition product of a lithium sulfate compound (I), a reaction product of a lithium sulfate compound (I) and an electrolyte, and a decomposition product of the reaction product.

[0128] The components of the negative electrode SEI film and the positive electrode SEI film may be the same or different. The thickness of the negative electrode SEI film and the thickness of the positive electrode SEI film may be the same or different.

[0129] The lithium secondary battery of this disclosure is obtained by charging and discharging the lithium secondary battery precursor of this disclosure. In other words, the lithium secondary battery of this disclosure is obtained by subjecting it to an aging process described later.

[0130] [Lithium sulfate compounds] The lithium sulfate compounds of this disclosure are represented by the following formula (I).

[0131] [ka]

[0132] In formula (I), R 11 and R 12 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, R 11 and R 12 Together with the nitrogen atom in formula (I), it represents an alkylene group that forms a 3-8 membered ring 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). R13 This represents a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group, or the aryl group.

[0133] Because the lithium sulfate compound of this disclosure has the above configuration, when used by being added to a non-aqueous electrolyte, it can suppress the increase in DC resistance even when the lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0134] Examples of lithium sulfate compounds in this disclosure include those similar to those exemplified as lithium sulfate compound (I).

[0135] In formula (I), the R 11 and R 12 teeth, Each independently represents an alkyl group with 1 to 6 carbon atoms, an alkenyl group with 2 to 6 carbon atoms, or a benzyl group. Or, R 11 and R 12 This represents an alkylene group that, together with the nitrogen atom in formula (I), forms a 5-6 membered ring cyclic structure. R 13 It is preferable that represents a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group, or the aryl group.

[0136] As a result, when the lithium sulfate compound of this disclosure is added to a non-aqueous electrolyte and used, the increase in DC resistance can be further suppressed even when the lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0137] The lithium sulfate compound (I) of this disclosure is preferably one selected from the group consisting of a compound (I-1) represented by the following formula (I-1), a compound (I-2) represented by the following formula (I-2), a compound (I-3) represented by the following formula (I-3), a compound (I-4) represented by the following formula (I-4), a compound (I-5) represented by the following formula (I-5), and a compound (I-6) represented by the following formula (I-6).

[0138] [ka]

[0139] If the lithium sulfate compound (I) of the present disclosure is one selected from the group consisting of compound (I-1), compound (I-2), compound (I-3), compound (I-4), compound (I-5), and compound (I-6), then when the lithium sulfate compound of the present disclosure is added to a non-aqueous electrolyte, the increase in DC resistance can be further suppressed even when the lithium secondary battery is stored for a long period of time in a high-temperature environment.

[0140] [Method for producing lithium sulfate compounds] Next, a method for producing the lithium sulfate compound (I) of this disclosure will be described.

[0141] A method for producing lithium sulfate compound (I) comprises a first step and a second step, which will be described later. The first and second steps are performed in this order. This yields lithium sulfate compound (I) of the present disclosure.

[0142] <First step> In the first step, 1,3,2-dioxathiolane 2,2-dioxide represented by formula (IV-2) or 4-propyl-1,3,2-dioxathiolane 2,2-dioxide represented by formula (IV-8) is reacted with a specific amine compound in an organic solvent and washed. This yields the ammonium sulfate compound (I') represented by formula (I') below.

[0143] [ka]

[0144] R in equation (I') 11 , R 12 and R 13 Each of these is R in equation (I). 11 , R 12 and R 13This is the same as the examples given for each of them.

[0145] The specific amine compound is either a secondary amine or a cyclic amine, and is appropriately selected depending on the type of lithium sulfate compound (I) produced. Examples of secondary amines include dimethylamine, diethylamine, di-n-propylamine, di-i-propylamine, di-n-butylamine, di-i-butylamine, di-sec-butylamine, di-tert-butylamine, diallylamine, dicyclohexylamine, di-n-octylamine, dibenzylamine, methylethylamine, methyl-n-propylamine, methyl-i-propylamine, methyl-n-butylamine, methyl-i-butylamine, methyl-sec-butylamine, methyl-tert-butylamine, ethyl-n-propylamine, ethyl-i-propylamine, ethyl-n-butylamine, ethyl-i-butylamine, ethyl Examples include s-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, sec-butyl-tert-butylamine, and the like. Examples of cyclic amines include pyrrolidine, piperidine, pyrrole, and morpholine. Examples of organic solvents include tetrahydrofuran, diethyl ether, dimethoxyethane, 1,4-dioxane, acetone, ethyl acetate, acetonitrile, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, pentane, hexane, heptane, octane, nonane, decane, toluene, xylene (e.g., orthoxylene, metaxylene, paraxylene, etc.), ethylbenzene, butylbenzene, pentylbenzene, hexylbenzene, heptylbenzene, propylbenzene, isopropylbenzene (also known as cumene), cyclohexylbenzene, tetralin, mesitylene, methylcyclopentane, cyclohexane, methylcyclohexane, cycloheptane, cyclooctane, and cyclononane.

[0146] The reaction between 1,3,2-dioxathiolane 2,2-dioxide or 4-propyl-1,3,2-dioxathiolane 2,2-dioxide and certain amine compounds can be carried out under either atmospheric pressure or reduced pressure. The reaction temperature is preferably -40°C to 60°C, more preferably -40°C to 40°C, and even more preferably -40°C to 25°C. From the viewpoint of ensuring the reaction proceeds efficiently, the reaction time is preferably 2 to 30 hours, and more preferably 4 to 8 hours.

[0147] <Second process> In the second step, the ammonium sulfate compound (I') is reacted with the lithium salt compound in a solvent. This yields the lithium sulfate compound (I).

[0148] Examples of lithium salt compounds include lithium carbonate, lithium bis(trimethylsilyl)amide, lithium chloride, lithium hydroxide, lithium methoxide, lithium ethoxide, and lithium-t-butoxide. Among these, lithium carbonate, lithium bis(trimethylsilyl)amide, lithium chloride, or lithium hydroxide are preferred lithium salt compounds, with lithium carbonate being more preferred.

[0149] The above reaction in the second step can be carried out under either atmospheric pressure or reduced pressure. The reaction temperature in the second step is preferably -20°C to 60°C, more preferably 0°C to 40°C, and even more preferably 10°C to 30°C. The reaction time in the second step is preferably 30 minutes to 12 hours, and more preferably 1 hour to 6 hours, from the viewpoint of efficiently carrying out the reaction.

[0150] [Method for producing non-aqueous electrolyte] Next, a method for producing the non-aqueous electrolyte according to this disclosure will be described.

[0151] The method for producing a non-aqueous electrolyte according to this 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.

[0152] In the synthesis process, lithium sulfate compound (I) is synthesized. The synthesis process can be carried out in the same manner as the method for producing lithium sulfate compound (I) described above.

[0153] In the dissolution step, the electrolyte is dissolved in a non-aqueous solvent to obtain a solution. It is preferable that the electrical conductivity of the resulting non-aqueous electrolyte is reduced compared to the electrical conductivity of the solution before the addition of lithium sulfate compound (I).

[0154] In the mixing step, lithium sulfate compound (I) and, if necessary, other additives are added to the solution and mixed. This yields a non-aqueous electrolyte. The non-aqueous electrolyte obtained by the method for producing a non-aqueous electrolyte according to this embodiment exhibits a more effective effect in reducing DC resistance in lithium secondary batteries.

[0155] The method for producing a non-aqueous electrolyte described herein includes, but is not limited to, a synthesis step, a dissolution step, and a mixing step.

[0156] [Method for manufacturing lithium secondary battery precursors] Next, a method for manufacturing a lithium secondary battery precursor of the present disclosure will be described.

[0157] The method for manufacturing 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 executed in this order. Each of the first preparation step, the second preparation step, and the third preparation step is executed before the housing step.

[0158] In the first preparation step, a positive electrode is prepared. Examples of the method for preparing the positive electrode include, for example, a method of applying a positive electrode composite material slurry to the surface of a positive electrode current collector and drying it. The positive electrode composite material slurry contains a positive electrode active material and a binder. As the solvent contained in the positive electrode composite material slurry, an organic solvent is preferable. Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP). The method for applying the positive electrode composite material slurry is not particularly limited, and examples thereof include slot die coating, slide coating, curtain coating, gravure coating, etc. The method for drying the positive electrode composite material slurry is not particularly limited, and examples thereof include drying with warm air, hot air, low humidity air; vacuum drying; drying by infrared ray (for example, far infrared ray) irradiation; etc. The drying time is not particularly limited, and preferably it is 1 minute to 30 minutes. The drying temperature is not particularly limited, and preferably it is 40°C to 80°C. It is preferable that the dried product obtained by applying and drying the positive electrode composite material slurry on the positive electrode current collector is subjected to a pressure treatment. Thereby, the porosity of the positive electrode active material layer is reduced. Examples of the method for the pressure treatment include die pressing, roll pressing, etc.

[0159] In the second preparation step, a negative electrode is prepared. Examples of the method for preparing the negative electrode include, for example, a method of applying a negative electrode composite material slurry to the surface of a negative electrode current collector and drying it. The negative electrode composite material slurry contains a negative electrode active material and a binder. Examples of solvents included in the negative electrode mixture slurry include water and liquid media that are compatible with water. Including a liquid media that is compatible with water in the solvent of the negative electrode mixture slurry can improve the coating properties on the negative electrode current collector. Examples of liquid media that are compatible with water include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphate amides, sulfoxides, carboxylic acid esters, phosphate esters, ethers, and nitriles. The methods for applying, drying, and pressurizing the negative electrode mixture slurry are the same as those exemplified for applying, drying, and pressurizing the positive electrode mixture slurry.

[0160] In the third preparation step, a non-aqueous electrolyte is prepared. The method for preparing the non-aqueous electrolyte is the same as the method described in the non-aqueous electrolyte manufacturing method above.

[0161] In the housing process, the positive electrode, negative electrode, and separator are housed in the case. For example, in the housing process, a battery element is created using a positive electrode, a negative electrode, and a separator. Next, the positive electrode current collector and the positive electrode lead are electrically connected, and the negative electrode current collector and the negative electrode lead are electrically connected. Then, the battery element is housed in a case and fixed in place. The method for electrically connecting the positive electrode current collector and the positive electrode lead is not particularly limited and includes, for example, ultrasonic welding and resistance welding. The method for electrically connecting the negative electrode current collector and the negative electrode lead is not particularly limited and includes, for example, ultrasonic welding and resistance welding.

[0162] Hereinafter, the state in which the positive electrode, negative electrode, and separator are housed in the case will be referred to as the "assembly."

[0163] In the injection process, the non-aqueous electrolyte of this disclosure is injected into the interior of the assembly. This allows the non-aqueous electrolyte to permeate the positive electrode composite layer, the separator, and the negative electrode composite layer. As a result, a lithium secondary battery precursor is obtained.

[0164] [Method of manufacturing lithium secondary batteries] Next, a method for manufacturing the lithium secondary battery of this disclosure will be described.

[0165] The method for manufacturing a lithium secondary battery according to this disclosure includes a fourth preparation step and an aging step. The fourth preparation step and the aging step are performed in this order.

[0166] In the fourth preparation step, the lithium secondary battery precursor is prepared. The method for preparing the lithium secondary battery precursor is the same as the method described in the section on the manufacturing method of the lithium secondary battery precursor.

[0167] In the aging process, the lithium secondary battery precursor is subjected to an aging treatment. This forms the negative electrode SEI film and the positive electrode SEI film. In other words, a lithium secondary battery is obtained. The aging process includes charging and discharging the lithium secondary battery precursor in an environment of 25°C to 70°C. In the charging and discharging process, it is preferable to perform one or more combinations of charging and discharging on the lithium secondary battery precursor in an environment of 25°C to 70°C.

[0168] The lithium secondary battery obtained by the lithium secondary battery manufacturing method of this disclosure can suppress the increase in DC resistance even when the lithium secondary battery is stored for a long period of time in a high-temperature environment. [Examples]

[0169] The embodiments relating to this disclosure will be described in detail below with reference to the examples. However, this disclosure is not limited in any way to the descriptions of these examples.

[0170] [Synthesis of lithium sulfate compound (I) and ammonium sulfate (C)] Compounds (I-1) to (I-6), compound (C-1), and compound (C-2) were synthesized as follows.

[0171] [Synthesis Example 1] Lithium 2-(dimethylamino)ethyl sulfate (I-1) represented by the following formula (I-1) was synthesized as follows.

[0172] [Chemical Formula]

[0173] <First Step: Synthesis of 2-(dimethylammonio)ethyl sulfate (I-1’)> A 200 mL four-necked flask purged with nitrogen was charged with 1,3,2-dioxathiolane 2,2-dioxide (1.0 g, 8.06 mmol) and tetrahydrofuran (THF) (80 mL) as a solvent, maintained at -40 °C, and a dimethylamine solution (2 M tetrahydrofuran solution, 4 mL, 8.06 mmol) was added, followed by stirring reaction at -40 °C. Four hours after the start of the stirring reaction, acetone (50 mL) was added, and the resulting reaction solution was filtered. The filtrate (i.e., white solid) was washed twice with acetone (50 mL). Thereby, white solid 2-(dimethylammonio)ethyl sulfate (I-1’) (1.30 g, 7.45 mmol, yield 92%, purity 97%) was obtained. 1 H-NMR: δ2.79(s,6H), 3.28 - 3.35(m, 2H), 4.00 - 4.07(m, 2H), 9.30(br, 1H)

[0174] <Second Step: Synthesis of Lithium 2-(dimethylamino)ethyl sulfate (I-1)> A 200 mL eggplant-shaped flask was charged with 2-(dimethylammonio)ethyl sulfate (I-1') (0.90 g, 5.32 mmol) and pure water (50 mL) as a solvent, maintained at room temperature, and lithium carbonate (0.24 g, 3.19 mmol) was added. After stirring for 4 hours, the reaction was stopped to obtain a reaction solution. The reaction solution was filtered to remove insoluble matter and then concentrated under reduced pressure. That is, the water component was removed from the reaction solution. Methanol (20 mL) was added to the resulting white solid to obtain a slurry-like reaction solution. The resulting reaction mixture was filtered to obtain a solution from which the salt had been removed, and then the solution was concentrated under reduced pressure. This yielded lithium 2-(dimethylamino)ethyl sulfate (I-1) (0.72 g, 4.07 mmol, yield 77%) as a transparent, viscous liquid. Transparent viscous liquid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ2.30(s,6H), 2.63(t, J=5.8Hz, 2H), 3.18(t, J=5.8Hz, 2H)

[0175] As described above, based on the results of Synthesis Example 1, lithium 2-(dimethylamino)ethylsulfate (I-1) was obtained by the following reaction scheme.

[0176] [ka]

[0177] [Synthesis Example 2] Lithium 2-(diethylamino)ethylsulfate (I-2), represented by the following formula (I-2), was synthesized as described below.

[0178] [ka]

[0179] <Step 1: Synthesis of 2-(diethylammonio)ethylsulfate (I-2')> The synthesis was carried out in the same manner as in Synthesis Example 1, except that 1,3,2-dioxathione 2,2-dioxide (2.0 g, 16.11 mmol) was used and the dimethylamine solution was replaced with diethylamine (0.98 g, 13.43 mmol). This yielded a white solid 2-(diethylammonio)ethylsulfate (I-2') (2.56 g, 12.6 mmol, yield 78%, purity 97%). White solid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ1.19(t,J=7.2Hz,6H), 3.16(q,J=7.2Hz,4H), 3.27-3.40(m, 2H), 4.01-4.08(m, 2H), 6.50(dt, J=11.4Hz, 1.4Hz, 1H), 9.07(br,1H)

[0180] <Second step: Synthesis of lithium 2-(diethylamino)ethylsulfate (I-2)> The compound was synthesized using the same method as in Synthesis Example 1, except that lithium carbonate (0.27 g, 3.69 mmol) was used and 2-(dimethylammonio)ethyl sulfate was replaced with 2-(diethylammonio)ethyl sulfate (1.25 g, 6.15 mmol). This yielded lithium 2-(diethylamino)ethylsulfate (I-2) (1.27 g, 5.67 mmol, yield 92%, purity 91%) as a transparent, viscous liquid. Transparent viscous liquid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ1.10(t,J=7.2Hz,6H), 2.92(q,J=7.2Hz, 4H), 3.06(t,J=5.4Hz, 2H), 3.94(t,J=5.6Hz, 2H)

[0181] [Synthesis Example 3] Lithium 2-(piperidine-1-yl)ethylsulfate (I-3), represented by the following formula (I-3), was synthesized as described below.

[0182] [ka]

[0183] <Step 1: Synthesis of 2-(piperidine-1-ium-1-yl)ethylsulfate (I-3')> The compound was synthesized using the same method as in Synthesis Example 1, except that 1,3,2-dioxathione 2,2-dioxide (2.0 g, 16.11 mmol) was used, the dimethylamine solution was replaced with piperidine (1.65 g, 19.34 mmol), and the reaction temperature was changed to room temperature. This yielded a white solid 2-(piperidine-1-ium-1-yl)ethyl sulfate (I-3') (2.88 g, 13.35 mmol, yield 83%, purity 97%). White solid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ1.10-1.90(m,6H), 2.70-3.15(m,2H), 3.22-3.37(m,2H), 3.37-3.65(m,2H), 4.00-4.12(m,2H), 9.20(br,1H)

[0184] <Second step: Synthesis of lithium 2-(piperidine-1-yl)ethylsulfate (I-3)> The compound was synthesized using the same method as in Synthesis Example 1, except that lithium carbonate (0.35 g, 4.79 mmol) was used and 2-(dimethylammonio)ethyl sulfate was replaced with 2-(piperidine-1-ium-1-yl)ethyl sulfate (1.67 g, 7.98 mmol). This yielded lithium 2-(piperidine-1-yl)ethyl sulfate (I-3) (1.66 g, 7.64 mmol, yield 96%, purity 99%) as a clear, viscous liquid. Transparent viscous liquid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ1.35-1.48(m,2H), 1.52-1.66(m,2H), 2.72-2.89(m,4H), 2.90-2.97(m,2H), 3.93(t,J=5.4Hz, 2H)

[0185] [Synthesis Example 4] Lithium 2-(pyrrolidine-1-yl)ethylsulfate (I-4), represented by the following formula (I-4), was synthesized as described below.

[0186] [ka]

[0187] <Step 1: Synthesis of 2-(pyrrolidine-1-ium-1-yl)ethylsulfate (I-4')> The compound was synthesized using the same method as in Synthesis Example 1, except that 1,3,2-dioxathione 2,2-dioxide (1.0 g, 8.06 mmol) was used and the dimethylamine solution was replaced with pyrrolidine (0.57 g, 8.06 mmol). This yielded a white solid 2-(pyrrolidine-1-ium-1-yl)ethyl sulfate (I-4') (0.83 g, 4.25 mmol, 53% yield). White solid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ1.85-1.97(m,4H), 3.20-3.45(m,6H), 3.98-4.08(m,2H), 9.49(br,1H)

[0188] <Second step: Synthesis of lithium 2-(pyrrolidine-1-yl)ethylsulfate (I-4)> The compound was synthesized using the same method as in Synthesis Example 1, except that lithium carbonate (0.15 g, 1.97 mmol) was used and 2-(dimethylammonio)ethyl sulfate was replaced with 2-(pyrrolidine-1-ium-1-yl)ethyl sulfate (0.64 g, 3.28 mmol). This yielded lithium 2-(pyrrolidine-1-yl)ethyl sulfate (I-4) (0.45 g, 1.99 mmol, yield 61%, purity 99%) as a clear, viscous liquid. Transparent viscous liquid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ1.70-1.85(m,4H), 2.82-2.96(m,4H), 3.02(t, J=5.6Hz, 2H)

[0189] [Synthesis Example 5] Lithium 1-(dimethylamino)pentan-2-ylsulfate (I-5), represented by the following formula (I-5), was synthesized as described below.

[0190] [ka]

[0191] <Step 1: Synthesis of 1-(dimethylammonio)pentan-2-yl sulfate (I-5')> The synthesis was carried out in the same manner as in Synthesis Example 1, except that 1,3,2-dioxathiolane 2,2-dioxide was replaced with 4-propyl-1,3,2-dioxathiolane 2,2-dioxide (3.0 g, 18.05 mmol) and the solution was changed to dimethylamine solution (2 M tetrahydrofuran solution, 9 mL, 18.05 mmol). This yielded a white solid 1-(dimethylammonio)pentan-2-yl sulfate (I-5') (3.14 g, 14.86 mmol, 82% yield). White solid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ0.88(t,J=7.2Hz, 3H), 1.34(sext, J=7.6Hz, 2H), 1.43-1.54(m, 1H), 1.55-1.67(m, 1H), 2.85(s,6H), 3.15-3.27(m, 2H), 4.50-4.60(m, 1H), 9.08(br, 1H)

[0192] <Second step: Synthesis of lithium 1-(dimethylamino)pentan-2-ylsulfate (I-5)> In a 200 mL round-bottom flask, 1.0 g (4.73 mmol) of 1-(dimethylammonium)pentan-2-yl sulfate, 50 mL of tetrahydrofuran (as solvent), and 50 mL of pure water were added. The mixture was kept at room temperature, and lithium carbonate (0.21 g (2.84 mmol) was added. After stirring for 4 hours, the reaction was stopped to obtain the reaction solution. The reaction solution was filtered to remove insoluble matter, and then concentrated under reduced pressure. In other words, the organic solvent and water components were removed from the reaction solution. To the resulting white solid, 20 mL of hexane was added to obtain a slurry-like reaction solution. A white solid was obtained by filtering the resulting reaction solution. This yielded lilithium 1-(dimethylamino)pentan-2-ylsulfate (I-5) (0.18 g, 0.85 mmol, yield 18%) as a white solid. White solid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR:δ0.85(t, J=7.2Hz, 3H), 1.25-1.48(m, 4H), 2.12(s,6H), 2.35(dd, J=12.0, 7.2Hz, 1H), 2.45-2.51(m, 1H), 4.10-4.18(m, 1H)

[0193] [Synthesis Example 6] Lithium 1-(pyrrolidine-1-yl)pentan-2-yl sulfate (I-6), represented by the following formula (I-6), was synthesized as described below.

[0194] [ka]

[0195] <Step 1: Synthesis of 1-(pyrrolidine-1-ium-1-yl)pentan-2-yl sulfate (I-6')> The compound was synthesized using the same method as in Synthesis Example 1, except that 1,3,2-dioxathiolane 2,2-dioxide was replaced with 4-propyl-1,3,2-dioxathiolane 2,2-dioxide (2.0 g, 12.03 mmol) and the dimethylamine solution was replaced with pyrrolidine (0.86 g, 12.03 mmol). This yielded a white solid 1-(pyrrolidine-1-ium-1-yl)pentan-2-yl sulfate (I-6') (2.28 g, 9.57 mmol, 79% yield). White solid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ0.87(t, J=7.2Hz, 3H), 1.33(sext, J=7.6Hz, 2H), 1.42-1.63(m, 2H), 1.72-2.08(m, 4H), 2.90-3.15(m, 2H), 3.23-3.28(m, 2H), 3.55-3.85(m, 2H), 4.35-4.43(m, 1H), 9.17(br, 1H)

[0196] <Second step: Synthesis of lithium 1-(pyrrolidin-1-yl)pentan-2-yl sulfate (I-6)> The compound was synthesized in the same manner as in Synthesis Example 5, except that lithium carbonate (0.15 g, 2.12 mmol) was used and 1-(dimethylammonio)pentan-2-yl sulfate was replaced with 1-(pyrrolidine-1-ium-1-yl)pentan-2-yl sulfate (0.84 g, 3.54 mmol). This yielded a white solid lithium 1-(pyrrolidine-1-yl)pentan-2-yl sulfate (I-6) (0.71 g, 2.92 mmol, yield 83%). White solid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR:δ0.87(t,J=7.2Hz, 3H), 1.25-1.40(m, 2H), 1.45-1.57(m, 2H), 1.75-1.87(m, 4H), 2.85-3.12(m, 2H), 4.25-4.35(m, 1H)

[0197] [Synthesis Example 7] 2-(trimethylammonio)ethylsulfate (C-1), represented by the following formula (C-1), was synthesized as described below.

[0198] [ka]

[0199] In a nitrogen-purged 200 mL four-necked flask, 1,3,2-dioxathiolane 2,2-dioxide (1.0 g, 8.06 mmol) and ethanol (40 mL) as solvent were added and maintained at 0°C. Trimethylamine solution (2 M tetrahydrofuran solution, 4.8 mL, 9.67 mmol) was added, and after the addition of the trimethylamine solution was complete, the temperature was raised to 80°C and the reaction was stirred. After 4 hours from the start of the stirring reaction, the mixture was returned to room temperature, acetone (50 mL) was added, and the mixture was stirred for 1 hour. The reaction was then stopped to obtain the reaction solution. After filtering the resulting reaction solution, the filtrate (i.e., a white solid) was washed twice with acetone (50 mL). This yielded 2-(trimethylammonio)ethylsulfate (C-1) (0.37 g, 2.02 mmol, yield 25%) as a white solid. White solid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ3.11(s, 9H), 3.55-3.61(m, 2H), 4.12-4.18(m, 2H)

[0200] As described above, based on the results of Synthesis Example 11, 2-(trimethylammonio)ethylsulfate (C-1) was obtained by the following reaction scheme.

[0201] [ka]

[0202] [Synthesis Example 8] 2-(triethylammonio)ethylsulfate (C-2), represented by the following formula (C-2), was synthesized as described below.

[0203] [ka]

[0204] The synthesis was carried out in the same manner as in Synthesis Example 11, except that the dimethylamine solution was replaced with triethylamine (0.82 g, 8.06 mmol). This yielded a white solid 2-(triethylammonio)ethylsulfate (C-2) (0.76 g, 3.35 mmol, 42% yield). White solid 1 The measurement results by 1H-NMR (DMSO-d6) are shown below. 1 H-NMR: δ1.19(t,J=6.8Hz, 9H), 3.31(q,J=6.8Hz, 6H), 3.11(s, 9H), 3.45-3.51(m, 2H), 4.07-4.14(m, 2H)

[0205] [Example 1] A non-aqueous electrolyte was obtained as described below.

[0206] <Preparation of non-aqueous electrolyte> Ethylene carbonate (hereinafter referred to as "EC"), dimethyl carbonate (hereinafter referred to as "DMC"), and ethyl methyl carbonate (hereinafter referred to as "EMC") were mixed in a volume ratio of EC:DMC:EMC = 30:35:35. This yielded a mixed solvent as a non-aqueous solvent. LiPF6, used as the electrolyte, was dissolved in the resulting mixed solvent so that its concentration in the final non-aqueous electrolyte was 1 mole / liter, thereby obtaining the electrolyte solution.

[0207] Hereafter, the obtained electrolyte will be referred to as the "basic electrolyte."

[0208] As an additive, lithium 2-(dimethylamino)ethyl sulfate (I-1), represented by the following formula (I-1) and synthesized in Synthesis Example 1, was added to the basic electrolyte solution in such a way that its content relative to the total volume of the final non-aqueous electrolyte solution was as shown in Table 1 (mass %). This resulted in the acquisition of a non-aqueous electrolyte solution.

[0209] [ka]

[0210] A coin-type battery (hereinafter also simply referred to as "battery") was fabricated as a precursor for lithium secondary batteries in the following manner.

[0211] <Fabrication of the positive electrode> Li(Ni) is used as the positive electrode active material. 0.5 Co 0.2 Mn 0.3 A mixture was obtained by adding 94% by mass of O2, carbon black (3% by mass) as a conductive additive, and polyvinylidene fluoride (PVdF) (3% by mass) as a binder. The obtained mixture was dispersed in N-methylpyrrolidone solvent to obtain a cathode composite slurry. A 20 μm thick aluminum foil was prepared as the positive electrode current collector. The obtained positive electrode slurry was applied to aluminum foil, dried, and then rolled in a press to obtain a sheet-like positive electrode. The positive electrode consists of a positive electrode current collector and a positive electrode active material layer.

[0212] <Fabrication of the negative electrode> A negative electrode slurry was obtained by mixing graphite (96% by mass) as the negative electrode active material, carbon black (1% by mass) as a conductive additive, 1% by mass of carboxymethylcellulose sodium dispersed in pure water as a thickener, and 2% by mass of styrene-butadiene rubber (SBR) dispersed in pure water as a binder. A 10 μm thick copper foil was prepared as the negative electrode current collector. The obtained slurry was applied to copper foil, dried, and then rolled in a press to obtain a sheet-like negative electrode. The negative electrode consists of a negative electrode current collector and a negative electrode active material layer.

[0213] The non-aqueous electrolyte obtained from the production of the non-aqueous electrolyte described above was prepared.

[0214] A porous polyethylene film was prepared as a separator.

[0215] <Preparation of lithium secondary battery precursors> The negative electrode was punched out in a disc shape with a diameter of 14 mm, the positive electrode in a disc shape with a diameter of 13 mm, and the separator in a disc shape with a diameter of 17 mm. This resulted in coin-shaped negative electrodes, coin-shaped positive electrodes, and coin-shaped separators. The obtained coin-shaped negative electrode, coin-shaped separator, and coin-shaped positive electrode were stacked in this order inside a stainless steel battery case (size: 2032). Next, 20 μL of non-aqueous electrolyte was poured into the battery case, immersing the separator, positive electrode, and negative electrode in the non-aqueous electrolyte. Next, an aluminum plate (1.2 mm thick, 16 mm in diameter) and a spring were placed on the positive electrode, and the battery was sealed by closing the battery can lid via a polypropylene gasket. Based on the above, a coin-shaped lithium secondary battery precursor having the configuration shown in Figure 2 was obtained. The size of the lithium secondary battery precursor was 20 mm in diameter and 3.2 mm in height.

[0216] [Comparative Example 1, Comparative Example 2, Examples 2 to 9] A lithium secondary battery precursor was obtained in the same manner as in Example 1, except that the compounds (I-1), (I-2), (I-3), (I-4), (I-5), (I-6), (2-(trimethylammonio)ethylsulfate (C-1), (2-(triethylammonio)ethylsulfate (C-2)), (II-1) lithium fluorophosphate compound, (III-1) cyclic dicarbonyl compound, and (IV-1) cyclic sulfonic acid ester compound were added in such a manner that their content relative to the total amount of the final non-aqueous electrolyte was as shown in Table 1 (mass%).

[0217] [ka]

[0218] <Manufacturing of lithium secondary batteries> The lithium secondary battery precursor described above was subjected to the following processes in order: charging from 1.5V to 4.2V, holding for 5 to 50 hours, charging to 4.2V, and discharging to 2.5V, all within a temperature range of 25°C to 70°C, to obtain a lithium secondary battery.

[0219] <Initial charge / discharge process> The lithium secondary battery obtained above was charged to 4.2V in a constant temperature bath at 25°C, and then discharged to 2.5V.

[0220] <Measurement of initial resistance> Next, the lithium secondary battery, after initial charge-discharge treatment, was charged to 3.7V. Then, in a constant temperature bath at 25°C, the DC resistance [Ω] as the initial resistance value was measured based on the voltage drop (=voltage before discharge - voltage 10 seconds after discharge) and the current value (i.e., the current value corresponding to the discharge rates of 0.2C to 2.0C) during a "CC10s discharge" at each discharge rate from 0.2C to 2.0C.

[0221] <Measurement of resistance after high-temperature storage> Next, the lithium secondary battery, after initial resistance measurement, was charged to 4.2V, and the charged lithium secondary battery was stored in a constant temperature bath at 60°C for 14 days (hereinafter, this operation is referred to as "high-temperature storage"). The discharge capacity [mAh] of lithium secondary batteries after high-temperature storage was determined by discharging them to 2.5V in a constant temperature bath at 25°C, then charging them to 4.2V, and finally discharging them again to 2.5V. Next, lithium secondary batteries discharged to 2.5V were charged to 3.7V, and then, in a constant temperature bath at 25°C, the DC resistance [Ω] as the resistance value after high-temperature storage was measured based on the voltage drop (=voltage before discharge - voltage 10 seconds after discharge) and the current value (i.e., the current value corresponding to the discharge rates of 0.2C to 2.0C) for each discharge rate of 0.2C to 2.0C during a "CC10s discharge".

[0222] The resistance of Comparative Example 1, described later, after high-temperature storage was measured in the same manner as in Example 1.

[0223] [Method for evaluating resistance after high-temperature storage] As shown in the following formula (X1), the relative value of the resistance value of Example 1 after high-temperature storage to the resistance value of Comparative Example 1 after high-temperature storage was defined as "Resistance after high-temperature storage [%]". The acceptable range for Resistance after high-temperature storage [%] is 97% or less.

[0224] Resistance after high-temperature storage [relative value; %] = (Resistance value after high-temperature storage of Example 1 [Ω] / Resistance value after high-temperature storage of Comparative Example 1 [Ω]) × 100 … (X1)

[0225] [Table 1]

[0226] In Table 1, "-" indicates that the corresponding component is not present. "Content of each additive" indicates the content (mass %) of the additive relative to the total amount of the non-aqueous electrolyte. "(I)" indicates lithium sulfate compound (I). "(II)" indicates lithium fluorophosphate compound (II). "(III)" indicates cyclic dicarbonyl compound (III). "(IV)" indicates cyclic sulfonic acid ester compound (IV). "(I-1)" indicates lithium 2-(dimethylamino)ethyl sulfate (I-1). "(I-2)" indicates lithium 2-(diethylamino)ethyl sulfate (I-2). "(I-3)" indicates lithium 2-(piperidine-1-yl)ethyl sulfate (I-3). "(I-4)" indicates lithium 2-(pyrrolidine-1-yl)ethyl sulfate (I-4). "(I-5)" represents lithium 1-(dimethylamino)pentan-2-ylsulfate (I-5). "(I-6)" represents lithium 1-(pyrrolidine-1-yl)pentan-2-ylsulfate (I-6). "(C-1)" indicates 2-(trimethylammonio)ethylsulfate (C-1). "(C-2)" indicates 2-(triethylammonio)ethylsulfate (C-2). "(II-1)" indicates lithium fluorophosphate compound (II-1). "(III-1)" indicates cyclic dicarbonyl compound (III-1). "(IV-1)" indicates cyclic sulfonic acid ester compound (IV-1).

[0227] The non-aqueous electrolyte of Comparative Example 2 did not contain lithium sulfate compound (I). Therefore, the resistance [%] of Comparative Example 2 after high-temperature storage was 98% (acceptable range: 97% or less). From this result, it was found that the non-aqueous electrolyte of Comparative Example 2 could not suppress the increase in DC resistance even when the lithium secondary battery was stored for a long period of time in a high-temperature environment.

[0228] The non-aqueous electrolytes of Examples 1 to 9 contain ammonium sulfate compound (I). Therefore, the resistance [%] after high-temperature storage of Examples 1 to 9 was 93% or less (acceptable range: 97% or less). From these results, it was found that the non-aqueous electrolytes of Examples 1 to 9 can suppress the increase in DC resistance even when lithium secondary batteries are stored for a long period of time in a high-temperature environment.

[0229] The non-aqueous electrolyte of Example 3 is the same as the non-aqueous electrolyte of Example 2, except that it contains a lithium fluorophosphate compound (II-1). The non-aqueous electrolyte of Example 4 is the same as the non-aqueous electrolyte of Example 2, except that it contains a cyclic dicarbonyl compound (III-1). The non-aqueous electrolyte of Example 5 is the same as the non-aqueous electrolyte of Example 2, except that it contains a cyclic sulfonic acid ester compound (IV-1). Comparing Examples 3 to 5 with Example 2, the resistance after high-temperature storage in Examples 3 to 5 was lower than that of Example 2. From these results, it was found that by further including at least one compound selected from the group consisting of lithium fluorophosphate compound (II), cyclic dicarbonyl compound (III), and cyclic sulfonic acid ester compound (IV), in addition to lithium sulfate compound (I), the increase in DC resistance of the lithium secondary battery can be further suppressed even when stored for a long period of time in a high-temperature environment.

[0230] Comparing Example 4 with Examples 3 and 5, the resistance of Example 4 after high-temperature storage was lower than that of Examples 3 and 5. From these results, it was found that by including a cyclic dicarbonyl compound (III) in addition to the lithium sulfate compound (I) in the non-aqueous electrolyte, the increase in DC resistance can be further suppressed even when the lithium secondary battery is stored for a long period of time in a high-temperature environment, compared to when the electrolyte includes a lithium fluorophosphate compound (II) or a cyclic sulfonic acid ester compound (IV) in addition to the ammonium sulfate compound (I). [Explanation of Symbols]

[0231] 1. Lithium secondary battery precursor 10 Battery elements 11 Positive electrode 11A positive electrode current collector 11B Positive electrode composite layer 12 Negative electrode 12A negative electrode current collector 12B Negative electrode composite layer 13 Separator 14 single cell layers 21 Positive lead 22 Negative lead 30 Exterior 41 Positive electrode 42 Negative electrode 43 Positive electrode can 44 Sealing plate 45 Separator 46 Gasket 47, 48 Spacer plate

Claims

1. A non-aqueous electrolyte for lithium secondary batteries containing an additive for lithium secondary batteries comprising compound (I) represented by the following formula (I), A lithium secondary battery aqueous electrolyte in which the content of compound (I) is 0.4% by mass to 2.0% by mass relative to the total amount of the non-aqueous electrolyte for lithium secondary batteries. 【Chemistry 1】 [In formula (I), R １１ and R １２ 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, R １１ and R １２ Together with the nitrogen atom in formula (I), it represents an alkylene group that forms a 3- to 8-membered ring 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). R １３ This represents a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group, or the aryl group.

2. The aforementioned R １１ and R １２ teeth, Each independently represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group. or R １１ and R １２ together represent an alkylene group that forms a 5- to 6-membered ring structure together with the nitrogen atom in the formula (I), The aforementioned R １３ The aqueous electrolyte for lithium secondary batteries according to claim 1, wherein is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group.

3. The aqueous electrolyte for lithium secondary batteries according to claim 1 or claim 2, wherein the compound (I) comprises at least one selected from the group consisting of a compound (I-1) represented by the following formula (I-1), a compound (I-2) represented by the following formula (I-2), a compound (I-3) represented by the following formula (I-3), a compound (I-4) represented by the following formula (I-4), a compound (I-5) represented by the following formula (I-5), and a compound (I-6) represented by the following formula (I-6). 【Chemistry 2】

4. A non-aqueous electrolyte for a lithium secondary battery according to any one of claims 1 to 3, further comprising at least one selected from the group consisting of compound (II), which is at least one of lithium monofluorophosphate and lithium difluorophosphate; compound (III), which is represented by the following formula (III); and compound (IV), which is represented by the following formula (IV). 【Transformation 3】 [In formula (III), M is an alkali metal, Y is a transition element, a group 13, group 14, or group 15 element of the periodic table. b is an integer between 1 and 3. m is an integer between 1 and 4. n is an integer from 0 to 8. q is either 0 or 1, R ３１ This is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain substituents or heteroatoms in their structure, and when q is 1 and m is 2 to 4, there are m R ３１ They may be joined together.) R ３２ This includes halogen atoms, C1-C10 alkyl groups, C1-C10 halogenated alkyl groups, C6-C20 aryl groups, or C6-C20 halogenated aryl groups (these groups may contain substituents or heteroatoms in their structure, and when n is 2-8, there are n R ３２ They may each be joined together to form a ring. Q １ , and Q ２ These are, independently, either an oxygen atom or a carbon atom. In formula (IV), R ４１ This is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms. R ４２ This is an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (iv-1), or a group represented by formula (iv-2). * indicates the bonding position. In formula (iv-1), R ４３ This is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group. In formula (iv-2), R ４４ This is an alkyl group having 1 to 6 carbon atoms, or an alkenyl group having 2 to 6 carbon atoms.

5. The case and The case contains a positive electrode, a negative electrode, a separator, and an electrolyte, Equipped with, The positive electrode is a positive electrode capable of intercalating and releasing lithium ions. The aforementioned negative electrode is a negative electrode capable of intercalating and releasing lithium ions. A lithium secondary battery precursor wherein the electrolyte is the non-aqueous electrolyte for lithium secondary batteries described in any one of claims 1 to 4.

6. The lithium secondary battery precursor according to claim 5, wherein the positive electrode contains a lithium-containing composite oxide represented by the following formula (P1) as the positive electrode active material. LiNi ａ Co ｂ Mn ｃ O ２ … Formula (P1) [In formula (P1), a, b, and c are each independently greater than 0 and less than 1, and the sum of a, b, and c is between 0.99 and 1.00.]

7. A step of preparing a lithium secondary battery precursor according to claim 5 or claim 6, The process involves charging and discharging the lithium secondary battery precursor. A method for manufacturing lithium secondary batteries, including [the specified component].

8. A lithium secondary battery obtained by charging and discharging a lithium secondary battery precursor according to claim 5 or claim 6.

9. A lithium sulfate compound represented by the following formula (I). 【Chemistry 4】 [In formula (I), R １１ and R １２ 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, R １１ and R １２ Together with the nitrogen atom in formula (I), it represents an alkylene group that forms a 3- to 8-membered ring 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). R １３ This represents a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group, or the aryl group.

10. The aforementioned R １１ and R １２ teeth, Each independently represents an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, or a benzyl group. Or, R １１ and R １２ This represents an alkylene group that, together with the nitrogen atom in formula (I), forms a 5-6 membered ring cyclic structure. R １３ The lithium sulfate compound according to claim 9, wherein is a hydrogen atom, the alkyl group, the alkenyl group, the alkynyl group, the benzyl group, or the aryl group.

11. The lithium sulfate compound according to claim 9 or claim 10, which is one selected from the group consisting of a compound represented by the following formula (I-1) (I-1), a compound represented by the following formula (I-2) (I-2), a compound represented by the following formula (I-3) (I-3), a compound represented by the following formula (I-4) (I-4), a compound represented by the following formula (I-5) (I-5), and a compound represented by the following formula (I-6) (I-6). 【Transformation 5】

Images