JP2023142129A - Nonaqueous electrolyte for battery, lithium secondary battery precursor, lithium secondary battery, and method for manufacturing lithium secondary battery - Google Patents

Abstract

To provide a nonaqueous electrolyte for a battery, capable of suppressing an increase in DC resistance even when a charge/discharge cycle of a lithium secondary battery is repeated.SOLUTION: The nonaqueous electrolyte for a battery contains a compound represented by formula (I) and a compound (A). The compound (A) contains at least one selected from the group consisting of cyclic sulfone compounds, lithium monofluorophosphate and the like, cyclic dicarbonyl compounds, and sulfonimide lithium salt compounds. In the formula (I), R11, R12 and R13 are each independently a group represented by an optionally substituted C1-20 hydrocarbon group.SELECTED DRAWING: None

Description

The present disclosure relates to a nonaqueous electrolyte for batteries, a lithium secondary battery precursor, a lithium secondary battery, and a method for manufacturing a lithium secondary battery.

Lithium ion secondary batteries are attracting attention as batteries with high energy density.

Patent Document 1 discloses a non-aqueous electrolyte for lithium ion secondary batteries (hereinafter referred to as "non-aqueous electrolyte for batteries"). Specifically, the nonaqueous electrolyte for batteries disclosed in Patent Document 1 contains any one of compounds represented by the following formulas (I-1) to (I-4) as an additive.

International Publication No. 2020/184690

However, there is a need for a nonaqueous electrolyte for batteries that can further suppress deterioration of battery characteristics of lithium secondary batteries due to repeated charging and discharging. More specifically, a non-aqueous electrolyte for batteries that can suppress an increase in DC resistance even when a lithium secondary battery is repeatedly charged and discharged in an environment that promotes deterioration of electrical characteristics (e.g., 45°C) is developed. It may be required.

In view of the above circumstances, the present disclosure provides a non-aqueous electrolyte for batteries, a lithium secondary battery precursor, and a lithium secondary battery that can suppress an increase in DC resistance even when the lithium secondary battery is repeatedly charged and discharged. An object of the present invention is to provide a method for manufacturing a lithium secondary battery.

Means for solving the above problems include the following embodiments.
<1> Comprising a compound (I) represented by the following formula (I) and a compound (A),
The compound (A) comprises a compound (II) represented by the following formula (II), a compound (III) which is at least one of lithium monofluorophosphate and lithium difluorophosphate, and a compound represented by the following formula (IV). A non-aqueous electrolyte for a battery, comprising at least one selected from the group consisting of a compound (IV) represented by the following formula (IV) and a compound (V) represented by the following formula (V).

[In formula (I),
R ¹¹ , R ¹² and R ¹³ are each independently a group represented by a hydrocarbon group having 1 to 20 carbon atoms which may have a substituent.
In formula (II),
R ²¹ is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms,
R ²² is an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (ii-1), or a group represented by formula (ii-2),
* indicates the bonding position,
In formula (ii-1), R ²³ 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 (ii-2), R ²⁴ is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms.
In formula (IV),
M is an alkali metal,
Y is a transition element, a group 13 element, a group 14 element, or a group 15 element of the periodic table,
b is an integer from 1 to 3,
m is an integer from 1 to 4,
n is an integer from 0 to 8,
q is 0 or 1,
R ⁴¹ 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 are The structure may contain a substituent or a heteroatom, and when q is 1 and m is 2 to 4, each of the m R ^41s may be bonded.)
R ⁴² is a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms (these The group may contain a substituent or a heteroatom in its structure, and when n is 2 to 8, each of the n R ^42s may be bonded together to form a ring.) ,
Q ¹ and Q ² are each independently an oxygen atom or a carbon atom.
In formula (V),
R ⁵¹ and R ⁵² each independently represent a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group. ]
<2> In the formula (I),
R ¹¹ , R ¹² and R ¹³ are each independently an alkyl group having 1 to 4 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), or an alkyl group having 1 to 4 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom); 4 alkenyl group (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 4 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), ), or an aryl group (at least one hydrogen atom in the aryl group is substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms); The non-aqueous electrolyte for batteries according to <1> above, which is a group represented by the following.
<3> R ¹¹ , R ¹² and R ¹³ in the formula (I) each independently represent a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group , tert-butyl group, vinyl group, allyl group, ethynyl group, phenyl group, or 4-fluorophenyl group, the nonaqueous electrolyte for batteries according to <1> or <2> above.
<4> The compound (I) is a compound represented by the following formula (I-1), the following formula (I-2), the following formula (I-3), or the following formula (I-4), The nonaqueous electrolyte for batteries according to any one of <1> to <3> above.

<5> Any one of <1> to <4> above, wherein the content of the compound (I) is 0.01% by mass or more and 5% by mass or less based on the total amount of the nonaqueous electrolyte for batteries. A non-aqueous electrolyte for batteries as described in .
<6> Any one of <1> to <5> above, wherein the content of the compound (A) is 0.01% by mass or more and 5% by mass or less based on the total amount of the nonaqueous electrolyte for batteries. A non-aqueous electrolyte for batteries as described in .
<7> Case and
A positive electrode, a negative electrode, a separator, and an electrolytic solution housed in the case;
Equipped with
The positive electrode is a positive electrode capable of intercalating and deintercalating lithium ions,
The negative electrode is a negative electrode capable of intercalating and deintercalating lithium ions,
A lithium secondary battery precursor, wherein the electrolyte is the non-aqueous battery electrolyte according to any one of <1> to <6>.
<8> The lithium secondary battery precursor according to <7>, wherein the positive electrode contains a lithium-containing composite oxide represented by the following formula (X) as a positive electrode active material.
_LiNia Co _b Mn _c O ₂ ... Formula (X)
[In formula (X), a, b and c are each independently greater than 0 and less than 1, and the sum of a, b and c is 0.99 or more and 1.00 or less. ]
<9> Preparing the lithium secondary battery precursor according to <7> or <8>;
A method for manufacturing a lithium secondary battery, comprising the steps of charging and discharging the lithium secondary battery precursor.
<10> A lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor according to <7> or <8>.

According to the present disclosure, there is provided a non-aqueous electrolyte for a battery, a lithium secondary battery precursor, a lithium secondary battery, and a lithium secondary battery that can suppress an increase in DC resistance even after repeated charge/discharge cycles of a lithium secondary battery. A method of manufacturing a secondary battery is provided.

FIG. 1 is a schematic perspective view showing an example of a laminate type battery, which is an example of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure. 2 is a schematic cross-sectional view in the thickness direction of a laminated electrode body housed in the laminated battery shown in FIG. 1. FIG. FIG. 2 is a schematic cross-sectional view showing an example of a coin-type battery, which is another example of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure.

In this specification, a numerical range expressed using "~" means a range that includes the numerical values written before and after "~" as lower and upper limits.
In this specification, if there are multiple substances corresponding to each component in the composition, unless otherwise specified, the amount of each component in the composition refers to the total amount of the multiple substances present in the composition. means.
In this specification, the term "process" is used not only to refer to an independent process, but also to include any process that is not clearly distinguishable from other processes as long as the intended purpose of the process is achieved. It will be done.

[Non-aqueous electrolyte for batteries]
The non-aqueous electrolyte for batteries of the present disclosure (hereinafter also simply referred to as "non-aqueous electrolyte") is a compound (I) represented by the following formula (I) (hereinafter referred to as "lithium borate compound (I)"). ) and a compound (A), and the compound (A) is a compound (II) represented by the following formula (II) (hereinafter also referred to as a "cyclic sulfone compound (II)"). , a compound (III) which is at least one of lithium monofluorophosphate and lithium difluorophosphate (hereinafter also referred to as "lithium fluorophosphate compound (III)"), and a compound represented by the following formula (IV) ( IV) (hereinafter also referred to as "cyclic dicarbonyl compound (IV)"), and a compound (V) represented by the following formula (V) (hereinafter also referred to as "sulfonimide lithium salt compound (V)"). and at least one selected from the group consisting of.
Details of the lithium borate compound (I), the cyclic sulfone compound (II), the fluorophosphate lithium compound (III), the cyclic dicarbonyl compound (IV), and the sulfonimide lithium salt compound (V) will be described later.

Since the non-aqueous electrolyte of the present disclosure has the above-described configuration, it is possible to suppress an increase in DC resistance more than before even when the charge-discharge cycle of a lithium secondary battery is repeated (hereinafter referred to as "charge-discharge cycle characteristics"). (It can be improved.)
This effect is presumed to be due to the following reasons, but is not limited thereto.
When the lithium secondary battery of the present disclosure is charged or discharged (hereinafter referred to as "charging and discharging"), a solid electrolyte interphase (SEI) film (hereinafter referred to as "SEI film") is formed on the surface of the negative electrode and the surface of the positive electrode. ) is thought to be formed.
Hereinafter, when the SEI film of the negative electrode and the SEI film of the positive electrode are not distinguished, the SEI film of the negative electrode and the SEI film of the positive electrode may be simply referred to as "SEI film".
The SEI film is considered to be mainly formed by a reaction product between lithium ions in the nonaqueous electrolyte and decomposed products of the nonaqueous electrolyte decomposed by charging and discharging a lithium secondary battery. The reaction product is thought to include a decomposition product of lithium borate compound (I) and a decomposition product of compound (A).
It is thought that when the SEI film is formed, side reactions that are not the original battery reactions are difficult to proceed during the charge/discharge cycle of the lithium secondary battery. A battery reaction is a reaction in which lithium ions move in and out (intercalate) between the positive electrode and the negative electrode. The side reactions include a reductive decomposition reaction of the non-aqueous electrolyte by the negative electrode, an oxidative decomposition reaction of the non-aqueous electrolyte by the positive electrode, elution of metal elements in the positive electrode active material, and the like.
In the lithium secondary battery using the non-aqueous electrolyte of the present disclosure, the SEI film is difficult to thicken even if charge/discharge cycles are repeated. Therefore, lithium ions in the non-aqueous electrolyte are not easily consumed.
For the above reasons, it is presumed that the non-aqueous electrolyte of the present disclosure can improve charge-discharge cycle characteristics.

<Lithium borate compound (I)>
The non-aqueous electrolyte contains a lithium borate compound (I) represented by the following formula (I).

In formula (I), R ¹¹ , R ¹² and R ¹³ are each independently a group represented by a hydrocarbon group having 1 to 20 carbon atoms which may have a substituent.

"Substituent" means an atom or atomic group substituting a hydrogen atom of a hydrocarbon.
The term "hydrocarbon group having 1 to 20 carbon atoms" means that the number of carbon atoms in the skeleton consisting only of hydrocarbon groups without substituents is 1 to 20.

Examples of the hydrocarbon group having 1 to 20 carbon atoms which may have a substituent represented by R ¹¹ to R ¹³ include an aliphatic group having 1 to 20 carbon atoms which may have a substituent, and a substituent. Examples include aryl groups having 6 to 20 carbon atoms which may have .

In formula (I), R ¹¹ , R ¹² and R ¹³ are substitutions in which two or more of R ¹¹ , R ¹² and R ¹³ are the same, from the viewpoint of further improving the charge/discharge cycle characteristics of the lithium secondary battery. It is preferably a hydrocarbon group having 1 to 20 carbon atoms which may have a group, and all three of R ¹¹ , R ¹² and R ¹³ may have the same substituent. More preferably, it is a hydrocarbon group.

In a hydrocarbon group having 1 to 20 carbon atoms which may have a substituent, a substituent which the hydrocarbon group having 1 to 20 carbon atoms may have (hereinafter, "substituent which may be included in formula (I)") halogen atoms, unsubstituted alkyl groups (i.e., alkyl groups in which the hydrogen atom is not substituted with a substituent), halogenated alkyl groups, and unsubstituted alkoxy groups (i.e., in which the hydrogen atom is not substituted with a substituent). (unsubstituted alkoxy group), halogenated alkoxy group, unsubstituted alkenyl group (i.e., alkenyl group in which the hydrogen atom is not substituted with a substituent), halogenated alkenyl group, unsubstituted alkynyl group (i.e., hydrogen atom is not substituted with a substituent), and halogenated alkynyl groups. Among the above, as a substituent that may be included in formula (I), a halogen atom is preferable from the viewpoint of further improving charge/discharge cycle characteristics.

In formula (I), R ¹¹ , R ¹² and R ¹³ are each independently an alkyl group having 1 to 4 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom). ), an alkenyl group having 2 to 4 carbon atoms (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 4 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), (at least one hydrogen atom in the aryl group may be substituted with a halogen atom), or an aryl group (at least one hydrogen atom in the aryl group is a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms), (may be substituted with an alkyl group) is preferable. Thereby, the nonaqueous electrolyte can further improve the charge/discharge cycle characteristics.

In formula (I), the "alkyl group having 1 to 4 carbon atoms" each independently represented by R ¹¹ , R ¹² and R ¹³ is a linear or branched alkyl group having 1 to 4 carbon atoms. It is preferable that Examples of the "alkyl group having 1 to 4 carbon atoms" include methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, sec-butyl group, tert-butyl group, and the like. Among these, the "alkyl group having 1 to 4 carbon atoms" is more preferably an alkyl group having 1 to 3 carbon atoms.
At least one hydrogen atom of the "alkyl group having 1 to 4 carbon atoms" may be substituted with a halogen atom. The halogen atom in the "alkyl group having 1 to 4 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; More preferred is a fluorine atom, particularly preferred.
In the "alkyl group having 1 to 4 carbon atoms", the number of hydrogen atoms substituted by the halogen atom is not particularly limited, and is appropriately selected depending on the number of carbon atoms in the alkyl group, and is preferably 1 to 7.

In formula (I), the "alkenyl group having 2 to 4 carbon atoms" each independently represented by R ¹¹ , R ¹² and R ¹³ is a linear or branched alkenyl group having 2 to 4 carbon atoms. It is preferable that Examples of the "alkenyl group having 2 to 4 carbon atoms" include vinyl group, 2-propenyl group, 2-butenyl group, and 3-butenyl group. Among these, the "alkenyl group having 2 to 4 carbon atoms" is more preferably an alkenyl group having 2 to 3 carbon atoms.
At least one hydrogen atom of the "alkenyl group having 2 to 4 carbon atoms" may be substituted with a halogen atom. The halogen atom in the "alkenyl group having 2 to 4 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; More preferred is a fluorine atom, particularly preferred.
In the "alkenyl group having 2 to 4 carbon atoms", the number of hydrogen atoms substituted by the halogen atom is not particularly limited, and is appropriately selected depending on the number of carbon atoms in the alkenyl group, and is preferably 1 to 7.

In formula (I), the "alkynyl group having 2 to 4 carbon atoms" each independently represented by R ¹¹ , R ¹² and R ¹³ is a linear or branched alkynyl group having 2 to 4 carbon atoms. It is preferable that Examples of the "alkynyl group having 2 to 4 carbon atoms" include ethynyl group, propargyl group (2-propynyl group), 2-butynyl group, and 3-butynyl group. Among these, the "alkynyl group having 2 to 4 carbon atoms" is more preferably an alkynyl group having 2 to 3 carbon atoms.
At least one hydrogen atom of the "alkynyl group having 2 to 4 carbon atoms" may be substituted with a halogen atom. The halogen atom in the "alkynyl group having 2 to 4 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; More preferred is a fluorine atom, particularly preferred.
In the "alkynyl group having 2 to 4 carbon atoms", the number of hydrogen atoms substituted by the halogen atom is not particularly limited, and is appropriately selected depending on the number of carbon atoms in the alkynyl group, and is preferably 1 to 7.

In formula (I), at least one hydrogen atom of the "aryl group" independently represented by R ¹¹ , R ¹² and R ¹³ is a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms. 6 may be substituted with an 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 a fluorine atom is Particularly preferred. In the "aryl group", the number of hydrogen atoms substituted by halogen atoms is not particularly limited, and is preferably 1 to 5.
The alkyl group in the alkoxy group having 1 to 6 carbon atoms in the "aryl group" may be linear, branched, or cyclic. Examples of the alkoxy group having 1 to 6 carbon atoms in the "aryl group" include methoxy group, ethoxy group, n-propoxy group, isopropoxy group, n-butoxy group, t-butoxy group, pentyloxy group, and the like. Among these, the alkoxy group having 1 to 6 carbon atoms in the "aryl group" is preferably an alkoxy group having 1 to 3 carbon atoms, and more preferably a methoxy group or an ethoxy group. In the "aryl group", the number of hydrogen atoms substituted by the alkoxy group having 1 to 6 carbon atoms is not particularly limited, and is preferably 1 to 3.
The alkyl group having 1 to 6 carbon atoms in the "aryl group" may be linear, branched, or cyclic. Examples of the alkyl group having 1 to 6 carbon atoms in the "aryl group" include methyl group, ethyl group, n-propyl group, i-propyl group, n-butyl group, i-butyl group, t-butyl group, n-pentyl group. group, n-hexyl group, cyclohexyl group, etc. Among these, the alkyl group having 1 to 6 carbon atoms in the "aryl group" is preferably an alkyl group having 1 to 3 carbon atoms, and more preferably a methyl group and an ethyl group. In the "aryl group", the number of hydrogen atoms substituted by the alkyl group having 1 to 6 carbon atoms is not particularly limited, and is preferably 1 to 3.

Among them, R ¹¹ , R ¹² and R ¹³ in formula (I) each independently represent a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, Preferably, it is a tert-butyl group, a vinyl group, an allyl group, an ethynyl group, a phenyl group, or a 4-fluorophenyl group.
Thereby, the nonaqueous electrolyte can further improve the charge/discharge cycle characteristics.

Specific examples of the lithium borate compound (I) include compounds represented by the following formulas (I-1) to (I-4). Hereinafter, the compound represented by formula (I-1) will be referred to as "lithium borate compound (I-1)," and the compound represented by formula (I-2) will be referred to as "lithium borate compound (I-2)." ", the compound represented by formula (I-3) is called "lithium borate compound (I-3)", and the compound represented by formula (I-4) is called "lithium borate compound (I-3)". 4).

The lithium borate compound (I) may be a compound represented by the above formula (I-1), the above formula (I-2), the above formula (I-3), or the above formula (I-4). preferable.
Thereby, the nonaqueous electrolyte can further improve the charge/discharge cycle characteristics.

The content of the lithium borate compound (I) is not particularly limited, and is preferably 0.01% by mass or more and 5% by mass or less based on the total amount of the nonaqueous electrolyte. As a result, a suitable SEI film is easily formed on the surface of the negative electrode and the surface of the positive electrode, and the charge/discharge cycle characteristics are further improved.
The content of the lithium borate compound (I) is more preferably 0.1% by mass or more based on the total amount of the non-aqueous electrolyte from the viewpoint of improving the charge/discharge cycle characteristics and the characteristics after high temperature storage of the lithium secondary battery. 3% by weight, more preferably 0.3% to 2% by weight, particularly preferably 0.5% to 1.5% by weight, even more preferably 0.5% to 1.0% by weight.

<Compound (A)>
The nonaqueous electrolyte contains compound (A).
Compound (A) is at least one selected from the group consisting of a cyclic sulfone compound (II), a fluorolithium phosphate compound (III), a cyclic dicarbonyl compound (IV), and a sulfonimide lithium salt compound (V). Contains one type.

The content of compound (A) is not particularly limited, and is preferably 0.01% by mass or more and 5% by mass or less based on the total amount of the nonaqueous electrolyte. As a result, a suitable SEI film is easily formed on the surface of the negative electrode and the surface of the positive electrode, and the charge/discharge cycle characteristics are further improved.
The content of compound (A) is more preferably 0.05% by mass to 5.0% by mass based on the total amount of the nonaqueous electrolyte from the viewpoint of improving the charge/discharge cycle characteristics and the characteristics after high temperature storage of the lithium secondary battery. The amount is preferably 0.10% to 3.0% by weight, particularly preferably 0.20% to 2.0% by weight.

Each of the cyclic sulfone compound (II), fluorophosphate lithium compound (III), cyclic dicarbonyl compound (IV), and sulfonimide lithium salt compound (V) will be described below.

(Cyclic sulfone compound (II))
The cyclic sulfone compound (II) is represented by the following formula (II).

In formula (II), R ²¹ is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms. R ²² 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 ²³ 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 ²⁴ is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms.

When the nonaqueous electrolyte further contains a cyclic sulfone compound (II) in addition to the lithium borate compound (I), the charge/discharge cycle characteristics are further improved.
This effect is presumed to be due to the following reasons.
When manufacturing a lithium secondary battery using a nonaqueous electrolyte, in the manufacturing process (e.g., the aging process described below), the reaction product is a cyclic sulfone compound (II) and a compound generated from the electrolyte (e.g., LiF). This further improves the stability of the lithium secondary battery. As a result, it is estimated that the charge/discharge cycle characteristics will be further improved.

In formula (II), R ²¹ is preferably an alkylene group having 2 to 3 carbon atoms, a vinylene group, or an oxygen atom, more preferably a trimethylene group, a vinylene group, or an oxygen atom; It is particularly preferable that there be.

In the cyclic sulfone compound (II), R ²¹ is preferably an oxygen atom. This facilitates the formation of a thermally and chemically stable inorganic salt structure. Therefore, under charge/discharge cycles and/or in a high-temperature environment, elution of components of the SEI film, etc. that 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 the SEI film and the like and the battery characteristics of the lithium secondary battery are improved.

In formula (II), R ²² is preferably a group represented by formula (ii-1) or a group represented by formula (ii-2).
In formula (ii-1), R ²³ 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 (ii-2), R ²⁴ 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.

Specific examples of the cyclic sulfone compound (II) include compounds represented by formulas (II-1) to (II-8).
Hereinafter, the compound represented by formula (II-1) may be referred to as "cyclic sulfone compound (II-1)".

The nonaqueous electrolyte may contain only one type of cyclic sulfone compound (II), or may contain two or more types of cyclic sulfone compound (II).

When the nonaqueous electrolyte contains a cyclic sulfone compound (II), the content of the cyclic sulfone compound (II) is preferably 0.10% by mass or more and 5.0% by mass or less based on the total amount of the nonaqueous electrolyte. , more preferably 0.20 mass% or more and 5.0 mass% or less, further preferably 0.30 mass% or more and 3.0 mass% or less, particularly preferably 0.30 mass% or more and 2.0 mass% or less. .
If the content of the cyclic sulfone compound (II) is within the above range, it is possible to suppress the decomposition of the nonaqueous solvent on the positive electrode or the negative electrode, and to suppress the increase in the film thickness of the SEI film. As a result, the charge/discharge cycle characteristics and the characteristics after high temperature storage of the lithium secondary battery are improved. When the content of the cyclic sulfone compound (II) is within the above range, an SEI film having a thickness that can suppress decomposition of the nonaqueous solvent in the nonaqueous electrolyte is formed. As a result, the charge/discharge cycle characteristics and the characteristics after high temperature storage of the lithium secondary battery are improved.

(Lithium fluorophosphate compound (III))
The lithium fluorophosphate compound (III) is at least one of lithium monofluorophosphate and lithium difluorophosphate.
Lithium difluorophosphate is represented by the following formula (III-1), and lithium monofluorophosphate is represented by the following formula (III-2). Hereinafter, lithium difluorophosphate is also referred to as "lithium difluorophosphate (III-1)."

When the non-aqueous electrolyte contains the lithium fluorophosphate compound (III) in addition to the lithium borate compound (I), the charge-discharge cycle characteristics are further improved.

The nonaqueous electrolyte may contain only one of lithium monofluorophosphate and lithium difluorophosphate, or may contain lithium monofluorophosphate and lithium difluorophosphate.

When the nonaqueous electrolyte contains the lithium fluorophosphate compound (III), the content of the lithium fluorophosphate compound (III) is preferably 0.001% by mass to 5% by mass based on the total amount of the nonaqueous electrolyte. % by weight, more preferably 0.01% by weight to 3% by weight, still more preferably 0.05% to 2% by weight, particularly preferably 0.1% to 0.5% by weight.
If the content of the lithium fluorophosphate compound (III) is within the above range, the solubility of the lithium fluorophosphate compound (III) in the nonaqueous solvent can be ensured. As a result, the DC resistance of the lithium secondary battery can be further reduced.

(Cyclic dicarbonyl compound (IV))
The cyclic dicarbonyl compound (IV) is represented by the following formula (IV).

In formula (IV), M represents an alkali metal, Y is a transition element, a group 13 element, a group 14 element, or a group 15 element of the periodic table, b is an integer of 1 to 3, and m is 1 n is an integer of 0 to 8, and q represents 0 or 1. R ⁴¹ 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 are may contain a substituent or a heteroatom in the structure, and when q is 1 and m is 2 to 4, each of the m R ^41s may be bonded.), and R ⁴² is a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms (these groups are , may contain a substituent or a heteroatom in the structure, and when n is 2 to 8, each of the n R ^42s may be bonded to form a ring.), and Q ¹ and Q ² each independently represent an oxygen atom or a carbon atom.

The non-aqueous electrolyte can further improve charge-discharge cycle characteristics by containing a cyclic dicarbonyl compound (IV) in addition to the lithium borate compound (I).
This effect is presumed to be due to the following reasons.
The non-aqueous electrolyte contains the cyclic dicarbonyl compound (IV) in addition to the lithium borate compound (I), so that the SEI membrane contains the cyclic dicarbonyl compound (IV) in addition to the above-mentioned reaction products. It may contain a bond derived from compound (IV). This facilitates the formation of a thermally and chemically stable polymer structure. Therefore, under charge/discharge cycles and/or in a high-temperature environment, elution of components of the SEI film and deterioration of the SEI film that impair the durability of the SEI film are unlikely to occur. As a result, it is estimated that the charge/discharge cycle characteristics will be further improved.

M is an alkali metal. Examples of alkali metals include lithium, sodium, potassium, and the like. Among these, M is preferably lithium.
Y is a transition element, a group 13 element, a group 14 element, or a group 15 element of the periodic table. Y is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb; , B or P is more preferable. When Y is Al, B or P, the anionic compound can be synthesized relatively easily and manufacturing costs can be reduced.
b represents the valence of anion and the number of cations. b is an integer from 1 to 3, preferably 1. When b is 3 or less, the salt of the anionic compound is easily dissolved in the mixed organic solvent.
Each of m and n is a value related to the number of ligands. Each of m and n is determined by the type of M. m is an integer from 1 to 4. n is an integer from 0 to 8.
q represents 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 ⁴¹ represents an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. These alkylene groups, halogenated alkylene groups, arylene groups, or halogenated arylene groups may contain a substituent or a heteroatom in their structure. Specifically, these groups may contain a substituent instead of a hydrogen atom. Examples of the substituent include a halogen atom, a chain or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, or a hydroxyl group. It will be done. A structure in which a nitrogen atom, a sulfur atom, or an oxygen atom is introduced instead of the carbon element in these groups may be used. When q is 1 and m is 2 to 4, each of the m R ^41s may be bonded. Such an example may include a ligand such as ethylenediaminetetraacetic acid.
R ⁴² represents a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms. These alkyl groups, halogenated alkyl groups, aryl groups, or halogenated aryl groups may contain substituents and heteroatoms in their structures, and when n is 2 to 8 ^, n R ⁴² may be bonded to each other to form a ring. R ⁴² is preferably an electron-withdrawing group, particularly preferably a fluorine atom.
Q ¹ and Q ² each independently represent an oxygen atom (O) or a carbon atom (C). In other words, the ligand will be bonded to Y via these heteroatoms.

Specific examples of the cyclic dicarbonyl compound (IV) include compounds represented by the following formula (IV-1) or (IV-2). The compound represented by formula (IV-1) is referred to as a "cyclic dicarbonyl compound (IV-1)."

The nonaqueous electrolyte may contain only one type of cyclic dicarbonyl compound (IV), or may contain two or more types of cyclic dicarbonyl compound (IV).

When the nonaqueous electrolyte contains a cyclic dicarbonyl compound (IV), the content of the cyclic dicarbonyl compound (IV) is preferably 0.01% by mass to 5.0% by mass based on the total amount of the nonaqueous electrolyte. %, more preferably 0.05% to 5.0% by weight, even more preferably 0.10% to 3.0% by weight, particularly preferably 0.30% to 2.0% by weight, even more preferably is 0.30% by mass to 1.0% by mass.
If the content of the cyclic dicarbonyl compound (IV) is within the above range, the lithium secondary battery can operate without the SEI film impairing the conductivity of lithium cations. Furthermore, since the SEI film includes a cyclic dicarbonyl structure, the battery characteristics of the lithium secondary battery are improved. If the content of the cyclic dicarbonyl compound (IV) is within the above range, the SEI film will contain a sufficient amount of a structure mainly composed of cyclic dicarbonyl. This facilitates the formation of a thermally and chemically stable inorganic salt or polymer structure. Therefore, in a high-temperature environment, the components of the SEI film that impair the durability of the SEI film are less likely to be eluted and the SEI film is less likely to undergo deterioration. As a result, the durability of the SEI film and the charge/discharge cycle characteristics and high-temperature storage characteristics of the lithium secondary battery are improved.

<Sulfonimide lithium salt compound (V)>
The sulfonimide lithium salt compound (V) is represented by the following formula (VI).

In formula (V), R ⁵¹ and R ⁵² each independently represent a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group.

When the nonaqueous electrolyte further contains a sulfonimide lithium salt compound (V) in addition to the lithium borate compound (I), the charge/discharge cycle characteristics are further improved.
This effect is presumed to be due to the following reasons.
After the lithium secondary battery is stored, the sulfonimide lithium salt compound (V) is easily oxidized and decomposed by the positive electrode to form an SEI film before the non-aqueous electrolyte is reductively decomposed on the negative electrode. This suppresses decomposition of the non-aqueous electrolyte at the positive electrode. As a result, it is estimated that the charge/discharge cycle characteristics will be further improved.

Specific examples of the sulfonimide lithium salt compound (V) include compounds represented by the following formulas (V-1) to (V-3). The compound represented by formula (V-1) is referred to as a "sulfonimide lithium salt compound (V-1)."

When the non-aqueous electrolyte contains the sulfonimide lithium salt compound (V), the content of the sulfonimide lithium salt compound (V) is preferably 0.1% by mass to 5.0% by mass based on the total amount of the non-aqueous electrolyte. 0% by weight, more preferably 0.2% to 5.0% by weight, even more preferably 0.3% to 3.0% by weight, particularly preferably 0.3% to 2.0% by weight, even more Preferably it is 0.3% by mass to 1.0% by mass.
If the content of the sulfonimide lithium salt compound (V) is within the above range, the lithium secondary battery can operate without the SEI film impairing the conductivity of lithium cations. Furthermore, since the SEI film includes a structure mainly composed of sulfonimide, the battery characteristics of the lithium secondary battery are improved. If the content of the sulfonimide lithium salt compound (V) is within the above range, the SEI film will contain a sufficient amount of a structure mainly composed of sulfonimide. This facilitates the formation of a thermally and chemically stable polymer structure. Therefore, under charge/discharge cycles and/or in a high-temperature environment, the components of the SEI film that impair the durability of the SEI film are unlikely to be eluted, and the SEI film is unlikely to change in quality. As a result, the durability of the SEI film is improved. Furthermore, an increase in the DC resistance of a lithium secondary battery can be further suppressed even if charge/discharge cycles are repeated or the battery is stored for a long period of time in a high temperature environment.

<Non-aqueous solvent>
A non-aqueous electrolyte generally contains a non-aqueous solvent. As the non-aqueous solvent, various known ones can be appropriately selected. The number of nonaqueous solvents may be one, or two or more.

Examples of the nonaqueous solvent include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, and γ-lactones. , fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, fluorine-containing chain ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide , dimethyl sulfoxide phosphoric acid, and the like.

Examples of cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate (BC).
Examples of the fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), trifluoropropylene carbonate, and the like.
Examples of chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylmethyl carbonate (EMC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), dipropyl carbonate (DPC), and the like. can be mentioned.
Examples of the fluorine-containing chain carbonates include methyl 2,2,2-trifluoroethyl carbonate.
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 trimethyl. Examples include ethyl butyrate.
Examples of the fluorine-containing aliphatic carboxylic acid esters include methyl difluoroacetate, methyl 3,3,3-trifluoropropionate, ethyl difluoroacetate, and 2,2,2-trifluoroethyl acetate.
Examples of γ-lactones include γ-butyrolactone and γ-valerolactone.
Examples of the cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and the like. .
Examples of chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, and 1,2-dibutoxyethane.
Examples of the fluorine-containing chain ethers include HCF ₂ CF ₂ CH ₂ OCF ₂ CF ₂ H, CF _{3 CF 2} CH ₂ OCF 2 CF ₂ H, HCF ₂ CF ₂ CH ₂ OCF ₂ CFHCF ₃ , CF ₃ CF _{2 CH2OCF2CFHCF3 , C6F13OCH3 , C6F13OC2H5 , C8F17OCH3 , C8F17OC2H5 , CF3CFHCF2CH ( CH3 ) OCF2 _ _ _ _ _ _ CFHCF3 , HCF2CF2OCH ( C2H5 ) 2 , HCF2CF2OC4H9 , HCF2CF2OCH2CH ( C2H5 ) 2 , HCF2CF2OCH2CH ( CH3 _} ) ₂ , etc.
Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, and the like.
Examples of amides include N,N-dimethylformamide.
Examples of the lactams include N-methylpyrrolidinone, N-methyloxazolidinone, and N,N'-dimethylimidazolidinone.

The nonaqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates. In this case, the total proportion of the cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates is preferably 50% by mass to 100% by mass, based on the total amount of the nonaqueous solvent, More preferably 60% to 100% by weight, still more preferably 80% to 100% by weight.

It is preferable that the non-aqueous solvent contains at least one selected from the group consisting of cyclic carbonates and chain carbonates. In this case, the total proportion of cyclic carbonates and chain carbonates in the nonaqueous solvent is preferably 50% by mass to 100% by mass, more preferably 60% by mass to the total amount of the nonaqueous solvent. The amount is 100% by weight, more preferably 80% to 100% by weight.

The content of the nonaqueous solvent is preferably 60% to 99% by mass, more preferably 70% to 97% by mass, and even more preferably 70% to 90% by mass, based on the total amount of the nonaqueous electrolyte. be.

The intrinsic viscosity of the nonaqueous solvent is preferably 10.0 mPa·s or less at 25° C. from the viewpoint of further improving the dissociation properties of the electrolyte and the mobility of ions.

<Electrolyte>
A non-aqueous electrolyte generally contains an electrolyte.

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

Examples of the fluorine-containing lithium salt include inorganic acid anion salts and organic acid anion salts.
Examples of inorganic acid anion salts include lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium hexafluoroarsenate (LiAsF ₆ ), and lithium hexafluorotantalate ( LiTaF ₆ ), and the like.
Examples of the organic acid anion salt include lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ). Among these, LiPF ₆ is particularly preferred as the fluorine-containing lithium salt.
Examples of fluorine-free lithium salts include lithium perchlorate (LiClO ₄ ), lithium aluminum tetrachloride (LiAlCl ₄ ), and lithium decachlorodecaborate (Li ₂ B ₁₀ Cl ₁₀ ).

When the electrolyte contains a fluorine-containing lithium salt, the content of the fluorine-containing lithium salt is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and even more preferably It is 80% by mass to 100% by mass.

When the fluorine-containing lithium salt contains lithium hexafluorophosphate (LiPF ₆ ), the content of lithium hexafluorophosphate (LiPF ₆ ) is preferably 50% by mass to 100% by mass based on the total amount of the electrolyte. , more preferably 60% by mass to 100% by mass, still more preferably 80% by mass to 100% by mass.

When the nonaqueous electrolyte contains an electrolyte, the concentration of the electrolyte in the nonaqueous electrolyte is preferably 0.1 mol/L to 3 mol/L, more preferably 0.5 mol/L to 2 mol/L.

When the non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF ₆ ), the concentration of lithium hexafluorophosphate (LiPF ₆ ) in the non-aqueous electrolyte is preferably 0.1 mol/L to 3 mol/L, More preferably, it is 0.5 mol/L to 2 mol/L.

<Other ingredients>
The non-aqueous electrolyte may contain other components as necessary.

Other components include acid anhydrides and the like.

[Lithium secondary battery precursor]

The lithium secondary battery precursor of the present disclosure includes a case, a positive electrode, a negative electrode, a separator, and an electrolyte. The case houses a positive electrode, a negative electrode, a separator, and an electrolyte. The positive electrode is capable of intercalating and deintercalating lithium ions. The negative electrode is capable of intercalating and deintercalating lithium ions. The separator separates the positive and negative electrodes. The electrolyte is a non-aqueous electrolyte of the present disclosure.

A lithium secondary battery precursor refers to a lithium secondary battery before being charged and discharged. That is, in the lithium secondary battery precursor, the negative electrode does not contain an SEI film, and the positive electrode does not contain an SEI film.

<Case>
The shape of the case is not particularly limited, and is appropriately selected depending on the use of the lithium secondary battery precursor of the present disclosure. Examples of the case include a case containing a laminate film and a case consisting of a battery can and a battery can lid.

<Positive electrode>
The positive electrode preferably contains at least one positive electrode active material. The positive electrode active material is capable of intercalating and deintercalating lithium ions.

The positive electrode of the present disclosure includes a positive electrode current collector and a positive electrode composite material layer. The positive electrode composite material layer is provided on at least a portion of the surface of the positive electrode current collector.

Examples of the material of the positive electrode current collector include metals and alloys. Specifically, examples of the material of the positive electrode current collector include aluminum, nickel, stainless steel (SUS), copper, and the like. Among these, from the viewpoint of a balance between high conductivity and cost, the material of the positive electrode current collector is preferably aluminum. Here, "aluminum" means pure aluminum or aluminum alloy. As the positive electrode current collector, aluminum foil is preferable. The material of the aluminum foil is not particularly limited, and examples include A1085 material and A3003 material.

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

The positive electrode active material is not particularly limited as long as it is a material that can insert and release lithium ions, and can be adjusted as appropriate depending on the use of the lithium secondary battery precursor.

Examples of the positive electrode active material include a first oxide, a second oxide, and the like.
The first oxide includes lithium (Li) and nickel (Ni) as constituent metal elements.
The second oxide contains Li, Ni, and at least one metal element other than Li and Ni as constituent metal elements. Examples of metal elements other than Li and Ni include transition metal elements and typical metal elements. The second oxide preferably contains a metal element other than Li and Ni in a proportion equal to or smaller than Ni in terms of the number of atoms. Metal elements other than Li and Ni include, for example, Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, and La. and Ce. These positive electrode active materials may be used alone or in combination.

The positive electrode active material preferably includes a lithium-containing composite oxide (hereinafter sometimes referred to as "NCM") represented by the following formula (X). The lithium-containing composite oxide (X) has the advantage of having a high energy density per unit volume and excellent thermal stability.

_LiNia Co _b Mn _c O ₂ ... Formula (X)

In formula (X), 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 O ₂ , LiNi _0.5 Co _0.3 Mn _0.2 O ₂ , LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , LiNi _0.6 Co _0.2 Mn _0.2 O ₂ , LiNi _0.8 Co _0.1 Mn _0.1 O ₂ and the like.

The positive electrode active material may include a lithium-containing composite oxide (hereinafter sometimes referred to as "NCA") represented by the following formula (Y).

Li _t Ni _1-x-y Co _x Al _y O ₂ ... Formula (Y)

In formula (Y), t is 0.95 to 1.15, x is 0 to 0.3, y is 0.1 to 0.2, and the sum of x and y is It is less than 0.5.

Specific examples of NCAs include LiNi _0.8 Co _0.15 Al _0.05 O ₂ and the like.

When the positive electrode includes 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 material layer is based on the total amount of the positive electrode composite material layer. The content is preferably 10% to 99.9% by weight, more preferably 30% to 99% by weight, even more preferably 50% to 99% by weight, particularly preferably 70% to 99% by weight.

Examples of the binder include polyvinyl acetate, polymethyl methacrylate, nitrocellulose, fluororesin, and rubber particles.
Examples of the fluororesin include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), vinylidene fluoride-hexafluoropropylene copolymer, and the like.
Examples of the rubber particles include styrene-butadiene rubber particles and acrylonitrile rubber particles.
Among these, from the viewpoint of improving the oxidation resistance of the positive electrode composite layer, the binder is preferably a fluororesin. One type of binder can be used alone, or two or more types can be used in combination as necessary.

The binder content in the positive electrode composite layer is determined based on the total amount of the positive electrode composite layer, from the viewpoint of achieving both physical properties of the positive electrode composite layer (e.g., electrolyte permeability, peel strength, etc.) and battery performance. Preferably it is 0.1% by mass to 4% by mass. When the content of the binder is within the above range, the adhesion of the positive electrode composite layer to the positive electrode current collector and the binding property between positive electrode active materials are further improved, and the positive electrode active material in the positive electrode composite layer is further improved. Since the amount of can be increased, the capacity can be further improved.

The positive electrode composite material layer preferably contains a conductive additive.

As the material of the conductive aid, a known conductive aid can be used. As the known conductive aid, a carbon material having conductivity is preferable. Examples of the carbon material having conductivity include graphite, carbon black, conductive carbon fiber, and fullerene. These can be used alone or in combination of two or more. Examples of the conductive carbon fiber include carbon nanotubes, carbon nanofibers, and carbon fibers. Examples of graphite include artificial graphite and natural graphite. Examples of natural graphite include scaly graphite, lumpy graphite, and earthy graphite.

The material of the conductive aid may be a commercially available material. Commercially available carbon blacks include, for example, Toka Black #4300, #4400, #4500, #5500 (manufactured by Tokai Carbon Co., Ltd., Furnace Black), Printex L, etc. (manufactured by Degussa Corporation, Furnace Black), Raven 7000, 5750. , 5250, 5000ULTRAIII, 5000ULTRA, etc., Conductex SC ULTRA, Conductex 975ULTRA, etc., PUER BLACK100, 115, 205, etc. (manufactured by Columbian, furnace black), #2350, #2400B, #2600B, #30050B, #3030B, #3230B, #3350B, #3400B, #5400B, etc. (manufactured by Mitsubishi Chemical Corporation, furnace black), MONARCH1400, 1300, 900, VulcanXC-72R, BlackPearls2000, LITX-50, LITX-200, etc. (manufactured by Cabot Corporation, furnace black), Ensaco25 0G, Ensaco260G, Ensaco350G, Super-P (manufactured by TIMCAL), Ketjen Black EC-300J, EC-600JD (manufactured by Akzo), Denka Black, Denka Black HS-100, FX-35 (manufactured by Denka, acetylene black), etc. can be mentioned.

The positive electrode composite material layer may contain other components. Other components include thickeners, surfactants, dispersants, wetting agents, antifoaming agents, and the like.

<Negative electrode>
The negative electrode contains at least one negative electrode active material. The negative electrode active material is capable of intercalating and deintercalating lithium ions.

The negative electrode more preferably includes a negative electrode current collector and a negative electrode composite material layer. The negative electrode composite material layer is provided on at least a portion of the surface of the negative electrode current collector.

The material of the negative electrode current collector is not particularly limited and any known material can be used, such as metals or alloys. Specifically, examples of the material of the negative electrode current collector include aluminum, nickel, stainless steel (SUS), nickel-plated steel, copper, and the like. Among these, copper is preferable as the material for the negative electrode current collector from the viewpoint of workability. Copper foil is preferred as the negative electrode current collector.

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

The negative electrode active material is not particularly limited as long as it is a material that can insert and release lithium ions. The negative electrode active material is, for example, metallic lithium, a lithium-containing alloy, a metal or alloy that can be alloyed with lithium, an oxide that can dope and dedope lithium ions, and a transition material that can dope and dedope lithium ions. The material is preferably at least one selected from the group consisting of metal nitrides and carbon materials capable of doping and dedoping with lithium ions. Among these, the negative electrode active material is preferably a carbon material (hereinafter referred to as "carbon material") that can be doped and dedoped with lithium ions.

Examples of carbon materials include carbon black, activated carbon, graphite materials, and amorphous carbon materials. These carbon materials may be used alone or in combination of two or more. The shape of the carbon material is not particularly limited, and examples thereof include fibrous, spherical, and flaky shapes. The particle size of the carbon material is not particularly limited, and is preferably 5 μm to 50 μm, more preferably 20 μm to 30 μm.
Examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500° C. or lower, and mesophase pitch carbon fiber (MCF).
Examples of graphite materials include natural graphite and artificial graphite. Examples of the artificial graphite include graphitized MCMB and graphitized MCF. The graphite material may contain boron. The graphite material may be coated with metal or amorphous carbon. Examples of the metal material covering the graphite material include gold, platinum, silver, copper, and tin. The graphite material may be a mixture of amorphous carbon and graphite.

It is preferable that the negative electrode composite material layer contains a conductive additive. Examples of the conductive aid include the same conductive aids as those exemplified as conductive aids that may be included in the positive electrode composite layer.

The negative electrode composite material layer may contain other components in addition to the above-mentioned components. Other components include thickeners, surfactants, dispersants, wetting agents, antifoaming agents, and the like.

<Separator>
Examples of the separator include porous resin flat plates. Examples of the material for the porous resin flat plate include resin, nonwoven fabric containing this resin, and the like. Examples of the resin include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, and polyamide.

Among these, the separator is preferably a porous resin sheet with a single layer or multilayer structure. The material of the porous resin sheet is mainly composed 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.

[Lithium secondary battery]
The lithium secondary battery of the present disclosure is obtained by charging and discharging a lithium secondary battery precursor.
Specifically, the lithium secondary battery of the present disclosure includes a case, a positive electrode, a negative electrode, a separator, and an electrolyte. A positive electrode, a negative electrode, a separator, and an electrolyte are housed in a case. The positive electrode is capable of intercalating and deintercalating lithium ions. The negative electrode is capable of intercalating and deintercalating lithium ions. The electrolyte is a non-aqueous electrolyte of the present disclosure. The negative electrode includes an SEI film. The positive electrode includes an SEI film.

The lithium secondary battery of the present disclosure differs from the lithium secondary battery precursor of the present disclosure mainly in the first point that the negative electrode includes an SEI film, and the second point that the positive electrode includes an SEI film. That is, the lithium secondary battery of the present disclosure is the same as the lithium secondary battery precursor of the present disclosure except for the first and second points. Therefore, description of the constituent members other than the first and second points regarding the lithium secondary battery of the present disclosure will be omitted below.

Regarding the first point, "the negative electrode includes an SEI film" includes a first negative electrode form and a second negative electrode form when the negative electrode includes a negative electrode current collector and a negative electrode composite layer. The first negative electrode configuration is a configuration in which an SEI film is formed on at least a portion of the surface of the negative electrode composite material layer. The second negative electrode form shows a form in which an SEI film is formed on the surface of a negative electrode active material that is a constituent material of the negative electrode composite layer.

Regarding the second point, "the positive electrode includes an SEI film" includes the first positive electrode form and the second positive electrode form when the positive electrode includes a positive electrode current collector and a positive electrode composite material layer. The first positive electrode configuration is a configuration in which an SEI film is formed on at least a portion of the surface of the positive electrode composite material layer. The second positive electrode form shows a form in which an SEI film is formed on the surface of a positive electrode active material that is a constituent material of the positive electrode composite layer.

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

The components of the positive electrode SEI film and the negative electrode SEI film may be the same or different. Further, the thickness of the positive electrode SEI film and the negative electrode SEI film may be the same or different.

[Example of lithium secondary battery precursor or lithium secondary battery]
An example of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure is a laminate type battery.
FIG. 1 is a schematic perspective view showing an example of a laminated battery, which is an example of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure, and FIG. 2 is a schematic perspective view of the laminated battery shown in FIG. FIG. 2 is a schematic cross-sectional view in the thickness direction of a laminated electrode body housed in the .
The laminate type battery 1 includes a laminate exterior body 8. A non-aqueous electrolyte (not shown in FIG. 1) and a laminated electrode body (not shown in FIG. 1) of the present disclosure are housed inside the laminate exterior body 8. The periphery of the laminate exterior body 8 is sealed. That is, the inside of the laminate exterior body 8 is sealed. As the material of the laminate exterior body 8, aluminum is used, for example.
As shown in FIG. 2, the stacked electrode body is formed by alternately stacking positive electrode plates 5 and negative electrode plates 6 with separators 7 in between. The positive electrode plate 5, the negative electrode plate 6, and the separator 7 are impregnated with the non-aqueous electrolyte of the present disclosure.
Each of the plurality of positive electrode plates 5 in the laminated electrode body is electrically connected to a positive electrode terminal 2 via a positive electrode tab (not shown), and a part of this positive electrode terminal 2 is connected to the periphery of the laminate exterior body 8. It protrudes outward from the end (see Figure 1). A portion of the peripheral end of the laminate exterior body 8 from which the positive electrode terminal 2 protrudes is sealed with an insulating seal 4.
Similarly, each of the plurality of negative electrode plates 6 in the laminated electrode body is electrically connected to the negative electrode terminal 3 via a negative electrode tab (not shown), and a part of the negative electrode terminal 3 is connected to the laminate exterior. It protrudes outward from the peripheral end of the body 8 (see FIG. 1). A portion of the peripheral end of the laminate exterior body 8 from which the negative electrode terminal 3 protrudes is sealed with an insulating seal 4.
In addition, in the laminated battery according to the above example, the number of positive electrode plates 5 is five and the number of negative electrode plates 6 is six, and the positive electrode plates 5 and the negative electrode plates 6 are connected to the uppermost part of both sides with a separator 7 in between. The outer layers are laminated in such a manner that each of them becomes a negative electrode plate 6. However, it goes without saying that the number of positive electrode plates, the number of negative electrode plates, and their arrangement in the laminate type battery are not limited to this example, and various changes may be made.

Another example of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure includes a coin-type battery.
FIG. 3 is a schematic perspective view showing an example of a coin-type battery that is another example of the lithium secondary battery precursor of the present disclosure or the lithium secondary battery of the present disclosure.
In the coin-type battery shown in FIG. 3, a disc-shaped negative electrode 12, a separator 15 injected with a non-aqueous electrolyte, a disc-shaped positive electrode 11, and spacer plates 17 and 18 made of stainless steel or aluminum, if necessary, are arranged in this order. The stacked state is stored between the positive electrode can 13 (hereinafter also referred to as "battery can") and the sealing plate 14 (hereinafter also referred to as "battery can lid"). The positive electrode can 13 and the sealing plate 14 are caulked and sealed via a gasket 16.
In this example, the nonaqueous electrolyte of the present disclosure is used as the nonaqueous electrolyte injected into the separator 15.

[Method for producing lithium secondary battery precursor]
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 accommodation process and the injection process are performed in this order. Each of the first preparation step, the second preparation step, and the third preparation step is performed before the accommodation step.

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

In the second preparation step, a negative electrode is prepared.
Examples of the method for preparing the negative electrode include a method of applying a negative electrode composite material slurry to the surface of a negative electrode current collector and drying the slurry. The negative electrode composite slurry includes a negative electrode active material and a binder.
Examples of the solvent contained in the negative electrode composite material slurry include water and a liquid medium that is compatible with water. When the solvent contained in the negative electrode composite material slurry contains a liquid medium that is compatible with water, the coating properties on the negative electrode current collector can be improved. Liquid media that are compatible with water include alcohols, glycols, cellosolves, amino alcohols, amines, ketones, carboxylic acid amides, phosphoric acid amides, sulfoxides, carboxylic acid esters, and phosphoric acid esters. ethers, nitriles, etc.
Examples of the coating method, drying method, and pressure treatment of the negative electrode composite material slurry include the same methods as those exemplified as the coating method, drying method, and pressure treatment of the positive electrode composite material slurry.

In the third preparation step, a non-aqueous electrolyte is prepared.
A method for preparing a non-aqueous electrolyte includes, for example, a step of dissolving an electrolyte in a non-aqueous solvent to obtain a solution, and adding and mixing a lithium borate compound (I) to the obtained solution. and a step of obtaining a non-aqueous electrolyte.

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

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

In the injection step, the non-aqueous electrolyte of the present disclosure is injected into the interior of the assembly. Thereby, the non-aqueous electrolyte is allowed to penetrate into the positive electrode mixture layer, the separator, and the negative electrode mixture layer. As a result, a lithium secondary battery precursor is obtained.

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

In the fourth preparation step, a lithium secondary battery precursor is prepared. The method for preparing the lithium secondary battery precursor is the same as the method described in the manufacturing method of the lithium secondary battery precursor.

In the aging step, the lithium secondary battery precursor is subjected to aging treatment. As a result, a negative electrode SEI film and a positive electrode SEI film are formed. In other words, a lithium secondary battery is obtained.
The aging treatment includes charging and discharging the lithium secondary battery precursor in an environment of 25°C to 70°C. In the step of charging and discharging, the lithium secondary battery precursor is preferably subjected to a combination of charging and discharging one or more times in an environment of 25° C. to 70° C.

The charge/discharge cycle characteristics of the lithium secondary battery obtained by the method for manufacturing a lithium secondary battery of the present disclosure are superior to those of the conventional ones.

Hereinafter, embodiments according to the present disclosure will be described in detail with reference to Examples. Note that the present disclosure is in no way limited to the description of these examples.

[Example 1]
A non-aqueous electrolyte was obtained in the following manner.

(Preparation of non-aqueous electrolyte)
Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed at EC:DMC:EMC=30:35:35 (volume ratio). Thereby, a mixed solvent (non-aqueous solvent) as a non-aqueous solvent was obtained.
LiPF ₆ (electrolyte) is dissolved in the obtained mixed solvent so that the concentration in the final non-aqueous electrolyte is 1 mol/liter, and the electrolyte (hereinafter referred to as "basic electrolyte") is dissolved. ) was obtained.

Add lithium borate compound (I) as an additive to the basic electrolyte so that the content based on the total amount of the non-aqueous electrolyte finally obtained is the content (mass%) listed in Table 1. did. Thereby, a non-aqueous electrolyte was obtained.
Lithium borate compound (I) is represented by the following formula (I-1).

<Preparation of lithium secondary battery precursor>
A coin-type battery as a lithium secondary battery precursor was produced in the following manner.

(First preparation step)
A positive electrode was prepared as follows.
Li (Ni _0.5 Co _0.2 Mn _0.3 O ₂ ) (94% by mass) as a positive electrode active material, carbon black (3% by mass) as a conductive aid, and polyvinylidene fluoride (PVDF) as a binder. (3% by mass) was obtained. The resulting mixture was dispersed in N-methylpyrrolidone solvent to obtain a positive electrode mixture slurry.
An aluminum foil with a thickness of 20 μm was prepared as a positive electrode current collector.
The obtained positive electrode mixture slurry was applied onto an aluminum foil (positive electrode current collector), dried, and then rolled in a press to obtain a positive electrode material. The obtained positive electrode material was punched out into a disk shape with a diameter of 13.0 mm to obtain a disk-shaped positive electrode. The positive electrode consists of a positive electrode current collector and a positive electrode active material layer.

(Second preparation process)
A negative electrode was prepared as follows.
Graphite (96% by mass) as a negative electrode active material, carbon black (1% by mass) as a conductive aid, 1% by mass of sodium carboxymethyl cellulose dispersed in pure water as a thickener, and pure as a binder. Styrene-butadiene rubber (SBR) dispersed in water was mixed with a solid content of 2% by mass to obtain a negative electrode mixture slurry.
A copper foil with a thickness of 10 μm was prepared as a negative electrode current collector.
The obtained negative electrode mixture slurry was applied onto a copper foil (negative electrode current collector), dried, and then rolled in a press to obtain a negative electrode material. The obtained negative electrode material was punched out into a disk shape with a diameter of 14.5 mm to obtain a disk-shaped negative electrode. The negative electrode consists of a negative electrode current collector and a negative electrode active material layer.

(Third preparation process)
A non-aqueous electrolyte obtained in the above-described production of a non-aqueous electrolyte was prepared.

(Accommodation process)
A porous polyethylene film punched into a disk shape with a diameter of 17 mm was prepared as a separator.
The disc-shaped negative electrode, disc-shaped separator, and disc-shaped positive electrode obtained in the above steps were stacked in this order in a stainless steel battery can (2032 size). Next, 14 μL of the above-mentioned nonaqueous electrolyte was injected into the battery can to impregnate the separator, positive electrode, and negative electrode.
Next, an aluminum plate (thickness: 1.2 mm, diameter: 16 mm) and a spring were placed on the positive electrode, and a battery can lid was caulked through a polypropylene gasket to seal the battery.
Through the above steps, a coin-shaped lithium secondary battery precursor (that is, a lithium secondary battery before being charged and discharged) having the configuration shown in FIG. 3 was obtained. The size of the lithium secondary battery precursor was 20 mm in diameter and 3.2 mm in height.

<Production of lithium secondary battery>
Lithium secondary battery precursors were charged at 1.5V to 4.2V, held for 5 to 50 hours, charged to 4.2V, and charged to 2.5V under a temperature range of 25°C to 70°C. Discharging was performed in this order to obtain a lithium secondary battery (coin type battery).

<Initial charge/discharge treatment>
The coin cell was charged to 4.2V and then discharged to 2.5V.

<Initial resistance evaluation process>
Next, the coin-type battery after the initial charging and discharging process was charged to 3.7V, then cooled to -10°C in a constant temperature bath, and subjected to "CC10s discharge" at each discharge rate of 0.1C to 0.6C. The initial Direct current resistance [Ω] as a resistance value was measured.
Regarding Comparative Example 1, which will be described later, the initial resistance of the coin-type battery was measured in the same manner.
From the above results, the resistance value (relative value) of the initial resistance of Example 1 was determined when the initial resistance of Comparative Example 1 was 100, and was defined as "initial resistance (relative value)".
The obtained "initial resistance (relative value)" is shown in Table 1.

<High temperature cycle treatment>
Next, the coin-type battery after the initial resistance measurement was charged at a constant current of 4.2 V at a charging rate of 1 C in a temperature environment of 45°C. Then, constant current discharge was performed to 2.5V at a discharge rate of 1C. The above charge/discharge cycle was repeated 100 times.

<Evaluation of resistance after cycle>
Next, the resistance value of the coin-shaped battery after the high-temperature cycle treatment was measured in the same manner as the initial resistance value.
Regarding Comparative Example 1, which will be described later, the resistance value of the coin-shaped battery after high-temperature cycle treatment was measured in the same manner.
From the above results, the resistance value (relative value) of the coin-type battery after the high-temperature cycle treatment of Example 1 was determined, assuming that the resistance value of the coin-type battery after the high-temperature cycle treatment of Comparative Example 1 was 100. Post-cycle resistance (relative value).
The obtained "post-cycle resistance (relative value)" is shown in Table 1. The acceptable range of post-cycle resistance (relative value) is 91% or less.

[Example 2 to Example 8, Comparative Example 1 to Comparative Example 4]
The following lithium borate compound (I-1), the following lithium borate compound (I-2), the following lithium borate compound (I-3), and the following lithium borate compound (I-4) as additives. , the following cyclic sulfone compound (II-1), the following lithium difluorophosphate (III-1), the following cyclic dicarbonyl compound (IV-1), and the following sulfonimide lithium salt compound (V-1). The same operation as in Example 1 was carried out except that the basic electrolyte was added so that the content based on the total amount of the non-aqueous electrolyte finally obtained was the content (mass%) listed in Table 1. went.
Table 1 shows the measurement results of the resistance increase rate (relative value) of Examples 2 to 8 and Comparative Examples 1 to 4.

In Table 1, "-" means that the corresponding component is not contained. "Content of each additive" indicates the content (mass%) of the additive with respect to the total amount of the non-aqueous electrolyte for batteries.

The non-aqueous electrolytes of Comparative Examples 1 to 4 contain a lithium borate compound (I), a cyclic sulfone compound (II), a lithium fluorophosphate compound (III), and a cyclic dicarbonyl compound (IV). and sulfonimide lithium salt compound (V) (ie, compound (A)). Therefore, the post-cycle resistance (relative value) of the lithium secondary batteries of Comparative Examples 1 to 4 was 92% or more (acceptable range: 91% or less).
As a result, it was found that the non-aqueous electrolytes of Comparative Examples 1 to 4 were unable to suppress the increase in DC resistance even when the lithium secondary battery was repeatedly charged and discharged.

The non-aqueous electrolytes of Examples 1 to 8 contain a lithium borate compound (I), and further contain a cyclic sulfone compound (II), a fluorolithium compound (III), and a cyclic dicarbonyl compound ( IV) and a sulfonimide lithium salt compound (V) (ie, compound (A)). Therefore, the post-cycle resistance (relative value) of the lithium secondary batteries of Examples 1 to 8 was 85% or less (acceptable range: 91% or less).
These results revealed that the non-aqueous electrolytes of Examples 1 to 8 were able to suppress an increase in DC resistance even when the lithium secondary battery was repeatedly charged and discharged.

The non-aqueous electrolyte of Example 1 is the same as Example 8 except that it contains the lithium borate compound (I-1) instead of the lithium borate compound (I-4). The nonaqueous electrolyte of Example 2 is the same as Example 8 except that it contains a lithium borate compound (I-2) instead of the lithium borate compound (I-4). The nonaqueous electrolyte of Example 7 is the same as Example 8 except that it contains a lithium borate compound (I-3) instead of the lithium borate compound (I-4).
Comparing Example 8 with Example 1, Example 2, or Example 7, the post-cycle resistance (relative value) of the lithium secondary battery of Example 8 is the same as that of Example 1, Example 2, or Example 7. was lower than the post-cycle resistance (relative value) of a lithium secondary battery.
From these results, when R ¹¹ , ^{R 12 and R 13 are} isopropyl groups, the lithium ^secondary battery It was found that the increase in DC resistance can be further suppressed even after repeated charge/discharge cycles.

The nonaqueous electrolyte of Example 2 is the same as Example 4 except that it contains a cyclic sulfone compound (II-1) instead of lithium difluorophosphate (III-1). The nonaqueous electrolyte of Example 3 is the same as Example 4 except that it contains a cyclic dicarbonyl compound (IV-1) instead of lithium difluorophosphate (III-1). The non-aqueous electrolyte of Example 5 is the same as Example 4 except that it contains a sulfonimide lithium salt compound (V-1) instead of lithium difluorophosphate (III-1).
Comparing Example 4 with Example 2, Example 3, or Example 5, each of the post-cycle resistance (relative value) and initial resistance (relative value) of the lithium secondary battery of Example 4 is the same as that of Example 4. 2. It was lower than each of the post-cycle resistance (relative value) and initial resistance (relative value) of the lithium secondary battery of Example 3 or Example 5.
From these results, the non-aqueous electrolyte of the present disclosure contains the fluorophosphate lithium compound (III), thereby combining the cyclic sulfone compound (II), the cyclic dicarbonyl compound (IV), and the sulfonimide lithium salt compound. It was found that the increase in DC resistance and initial resistance can be further suppressed even when the charge/discharge cycle of the lithium secondary battery is repeated than when one type selected from the group (V) is contained.

The nonaqueous electrolyte of Example 6 contains a lithium borate compound (I-2) and a cyclic sulfone compound (II-1) as additives, and further contains lithium difluorophosphate (III-1). The rest is the same as in Example 2.
Comparing Example 6 and Example 2, each of the post-cycle resistance (relative value) and initial resistance (relative value) of the lithium secondary battery of Example 6 is different from that of the lithium secondary battery of Example 2. It was lower than each of the post-resistance (relative value) and initial resistance (relative value).
From these results, the nonaqueous electrolyte of the present disclosure further contains a lithium fluorophosphate compound (III) in addition to the lithium borate compound (I) and the cyclic sulfone compound (II), so that lithium borate It was found that the increase in DC resistance and initial resistance of a lithium secondary battery can be further suppressed even after repeated charge/discharge cycles than when only compound (I) and cyclic sulfone compound (II) are contained.

1 Laminated battery 2 Positive electrode terminal 3 Negative electrode terminal 4 Insulating seal 5 Positive electrode plate 6 Negative electrode plate 7 Separator 8 Laminate exterior body 11 Positive electrode 12 Negative electrode 13 Positive electrode can 14 Sealing plate 15 Separator 16 Gasket 17, 18 Spacer plate

Claims (10)

Comprising a compound (I) represented by the following formula (I) and a compound (A),
The compound (A) comprises a compound (II) represented by the following formula (II), a compound (III) which is at least one of lithium monofluorophosphate and lithium difluorophosphate, and a compound represented by the following formula (IV). A non-aqueous electrolyte for a battery, comprising at least one selected from the group consisting of a compound (IV) represented by the following formula (IV) and a compound (V) represented by the following formula (V).

[In formula (I),
R ¹¹ , R ¹² and R ¹³ are each independently a group represented by a hydrocarbon group having 1 to 20 carbon atoms which may have a substituent.
In formula (II),
R ²¹ is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms,
R ²² is an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (ii-1), or a group represented by formula (ii-2),
* indicates the bonding position,
In formula (ii-1), R ²³ 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 (ii-2), R ²⁴ is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms.
In formula (IV),
M is an alkali metal,
Y is a transition element, a group 13 element, a group 14 element, or a group 15 element of the periodic table,
b is an integer from 1 to 3,
m is an integer from 1 to 4,
n is an integer from 0 to 8,
q is 0 or 1,
R ⁴¹ 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 are The structure may contain a substituent or a heteroatom, and when q is 1 and m is 2 to 4, each of the m R ^41s may be bonded.)
R ⁴² is a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms (these The group may contain a substituent or a heteroatom in its structure, and when n is 2 to 8, each of the n R ^42s may be bonded together to form a ring.) ,
Q ¹ and Q ² are each independently an oxygen atom or a carbon atom.
In formula (V),
R ⁵¹ and R ⁵² each independently represent a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group. ] In the formula (I),
R ¹¹ , R ¹² and R ¹³ are each independently an alkyl group having 1 to 4 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom), or an alkyl group having 1 to 4 carbon atoms (at least one hydrogen atom in the alkyl group may be substituted with a halogen atom); 4 alkenyl group (at least one hydrogen atom in the alkenyl group may be substituted with a halogen atom), an alkynyl group having 2 to 4 carbon atoms (at least one hydrogen atom in the alkynyl group may be substituted with a halogen atom), ), or an aryl group (at least one hydrogen atom in the aryl group is substituted with a halogen atom, an alkoxy group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms); The non-aqueous electrolyte for batteries according to claim 1, which is a group represented by the following. In the formula (I), R ¹¹ , R ¹² and R ¹³ each independently represent a methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert- The nonaqueous electrolyte for batteries according to claim 1 or 2, which is a butyl group, a vinyl group, an allyl group, an ethynyl group, a phenyl group, or a 4-fluorophenyl group. Claim 1, wherein the compound (I) is a compound represented by the following formula (I-1), the following formula (I-2), the following formula (I-3), or the following formula (I-4). - The non-aqueous electrolyte for batteries according to any one of claims 3 to 5.
The battery according to any one of claims 1 to 4, wherein the content of the compound (I) is 0.01% by mass or more and 5% by mass or less based on the total amount of the nonaqueous electrolyte for batteries. Non-aqueous electrolyte. The battery according to any one of claims 1 to 5, wherein the content of the compound (A) is 0.01% by mass or more and 5% by mass or less based on the total amount of the nonaqueous electrolyte for batteries. Non-aqueous electrolyte. case and
A positive electrode, a negative electrode, a separator, and an electrolytic solution housed in the case;
Equipped with
The positive electrode is a positive electrode capable of intercalating and deintercalating lithium ions,
The negative electrode is a negative electrode capable of intercalating and deintercalating lithium ions,
A lithium secondary battery precursor, wherein the electrolyte is the non-aqueous battery electrolyte according to any one of claims 1 to 6. The lithium secondary battery precursor according to claim 7, wherein the positive electrode contains a lithium-containing composite oxide represented by the following formula (X) as a positive electrode active material.
_LiNia Co _b Mn _c O ₂ ... Formula (X)
[In formula (X), a, b and c are each independently greater than 0 and less than 1, and the sum of a, b and c is 0.99 or more and 1.00 or less. ] A step of preparing a lithium secondary battery precursor according to claim 7 or claim 8;
A method for manufacturing a lithium secondary battery, comprising the steps of charging and discharging the lithium secondary battery precursor. A lithium secondary battery obtained by charging and discharging the lithium secondary battery precursor according to claim 7 or 8.