JP7681482B2 - Nonaqueous electrolyte, nonaqueous secondary battery precursor, nonaqueous secondary battery, and method for manufacturing nonaqueous secondary battery - Google Patents

Description

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

Lithium-ion secondary batteries have been attracting attention as batteries with high energy density.
Patent Document 1 discloses a nonaqueous electrolyte secondary battery (hereinafter referred to as "nonaqueous secondary battery"). The nonaqueous secondary battery disclosed in Patent Document 1 includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The negative electrode is made of lithium or a negative electrode material capable of absorbing and releasing lithium. The nonaqueous electrolyte is made of an organic solvent and a solute. The organic solvent contains at least one of lithium monofluorophosphate and lithium difluorophosphate as a solute.

Patent No. 3439085

Non-aqueous secondary batteries require a non-aqueous electrolyte that is unlikely to increase in direct current resistance or decrease in discharge capacity even when stored for a long period of time (e.g., 14 days) in a high-temperature environment (e.g., 60°C).

In view of the above circumstances, the present disclosure provides a nonaqueous electrolyte, a nonaqueous secondary battery precursor, a nonaqueous secondary battery, and a method for manufacturing a nonaqueous secondary battery that can suppress an increase in DC resistance and a decrease in discharge capacity even when the nonaqueous secondary battery is stored for a long period of time in a high-temperature environment.

Means for solving the above problems include the following aspects.
<1> A nonaqueous electrolyte solution containing a compound (I) represented by formula (I).

(In formula (I), R represents an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms.)
<2> The nonaqueous electrolyte solution according to <1>, wherein R is an alkoxy group having 1 to 6 carbon atoms.
<3> The nonaqueous electrolyte according to <1> or <2>, wherein the content of the compound (I) is 0.01% by mass or more and 10% by mass or less with respect to a total amount of the nonaqueous electrolyte.
<4> The nonaqueous electrolyte solution according to any one of <1> to <3>, further comprising a compound represented by the following formula (II):

(In formula (II), ^R1 and ^R2 each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group.)
<5> The nonaqueous electrolyte solution according to any one of <1> to <4>, further comprising at least one compound (III) selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate.
<6> The nonaqueous electrolyte solution according to any one of <1> to <5>, further comprising a compound represented by the following formula (IV):

[In formula (IV),
M is an alkali metal;
Y is a transition element, an element of Group 13, 14, or 15 of the periodic table;
b is an integer from 1 to 3;
m is an integer from 1 to 4,
n is an integer from 0 to 8,
q is 0 or 1;
R ³ is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain a substituent or a heteroatom in the structure, and when q is 1 and m is 2 to 4, m R ^3s may each be bonded to each other);
R ⁴ is a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms (these groups may contain a substituent or a heteroatom in the structure, and when n is 2 to 8, n R ^4s may be bonded to each other to form a ring);
Q ¹ and Q ² each independently represent an oxygen atom or a carbon atom.
<7> The nonaqueous electrolyte solution according to any one of <1> to <6>, further comprising a compound represented by the following formula (V):

[In formula (V),
^R5 represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 1 to 6 carbon atoms, or a vinylene group;
^R6 represents an alkylene group having 1 to 6 carbon atoms, a group represented by the above formula (v-1), or a group represented by the above formula (v-2).
* indicates the bond position.
In formula (v-1), R ⁶¹ represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group.
In formula (v-2), R ⁶² is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms.
<8> The nonaqueous electrolyte according to any one of <1> to <7>,
A positive electrode and
and a negative electrode.
<9> The nonaqueous secondary battery precursor according to <8>, wherein the positive electrode active material contained in the positive electrode contains a lithium-containing composite oxide.
<10> The nonaqueous secondary battery precursor according to <8> or <9>, wherein the negative electrode active material included in the negative electrode includes at least one selected from the group consisting of a material capable of absorbing and releasing lithium, a metal material capable of forming an alloy with lithium, and an oxide material.
<11> A preparation step of preparing a nonaqueous secondary battery precursor according to any one of <8> to <10>;
and an aging step of charging and discharging the nonaqueous secondary battery precursor.
<12> A nonaqueous secondary battery obtained by charging and discharging the nonaqueous secondary battery precursor according to any one of <8> to <10>.

The present disclosure provides a nonaqueous electrolyte, a nonaqueous secondary battery precursor, a nonaqueous secondary battery, and a method for manufacturing a nonaqueous secondary battery that can suppress an increase in DC resistance and a decrease in discharge capacity even when the nonaqueous secondary battery is stored for a long period of time in a high-temperature environment.

FIG. 1 is a schematic perspective view showing an example of a laminate type battery, which is an example of a nonaqueous secondary battery precursor or a nonaqueous 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. 2 is a schematic cross-sectional view showing an example of a coin-type battery, which is another example of the nonaqueous secondary battery precursor or the nonaqueous secondary battery of the present disclosure.

In this specification, a numerical range expressed using "to" means a range that includes the numerical values before and after "to" as the lower and upper limits.
In this specification, the amount of each component in a composition means, when a plurality of substances corresponding to each component are present in the composition, the total amount of the plurality of substances present in the composition, unless otherwise specified.

(Non-aqueous electrolyte)
The nonaqueous electrolyte of the present disclosure will now be described.

The nonaqueous electrolyte of the present disclosure is suitable for use as an electrolyte for nonaqueous secondary batteries. Nonaqueous secondary batteries include lithium secondary batteries. Details of nonaqueous secondary batteries will be described later with reference to Figures 1 to 3.

<Compound (I)>
The non-aqueous electrolyte of the present disclosure contains a compound (I) represented by the following general formula (I): The details of compound (I) will be described later.

Since the nonaqueous electrolyte solution of the present disclosure has the above-mentioned configuration, even if a nonaqueous secondary battery is stored for a long period of time in a high-temperature environment, an increase in DC resistance and a decrease in discharge capacity can be suppressed more than in a configuration that does not contain compound (I).
The reason why the increase in DC resistance and the decrease in discharge capacity can be suppressed more than in a configuration not containing compound (I) even when the nonaqueous secondary battery is stored for a long period of time in a high-temperature environment is presumably mainly due to the following reasons.
When a nonaqueous secondary battery using the nonaqueous electrolyte solution of the present disclosure is charged or discharged (hereinafter, sometimes referred to as "charging and discharging"), it is believed that a solid electrolyte interphase (SEI) film (hereinafter, referred to as an "SEI film") is formed on the surface of the negative electrode and the surface of the positive electrode.
Hereinafter, the negative electrode SEI film and the positive electrode SEI film may be simply referred to as "SEI film".
The SEI film is considered to be formed mainly by lithium ions in the nonaqueous electrolyte and decomposition products of the nonaqueous electrolyte that are decomposed during charging and discharging of the nonaqueous secondary battery.
It is believed that when the SEI film is formed, side reactions that are not the original battery reaction are less likely to proceed during the charge/discharge cycle of the nonaqueous secondary battery. The battery reaction is a reaction in which lithium ions enter and leave (intercalate) the positive electrode and the negative electrode. The side reactions include a reductive decomposition reaction of the nonaqueous electrolyte by the negative electrode, an oxidative decomposition reaction of the nonaqueous electrolyte by the positive electrode, and the elution of metal elements in the positive electrode active material.
On the other hand, the SEI film of the negative electrode tends to thicken with each charge and discharge. Lithium ions in the non-aqueous electrolyte are consumed to thicken the SEI film of the negative electrode. Therefore, the thickening of the SEI film of the negative electrode is considered to be one of the factors that increase the DC resistance of the non-aqueous secondary battery. In particular, the thickening of the SEI film of the negative electrode becomes more pronounced when the non-aqueous secondary battery is exposed to a high temperature environment. In addition, when the metal component of the positive electrode dissolves into the non-aqueous electrolyte, the metal component of the positive electrode is deposited on the surface of the negative electrode, promoting the decomposition reaction of the non-aqueous electrolyte. Therefore, the dissolution of the metal component from the positive electrode is also considered to be one of the factors that increase the DC resistance of the non-aqueous secondary battery. In particular, the dissolution of the metal component from the positive electrode becomes more pronounced when the non-aqueous secondary battery is exposed to a high temperature environment. The metal component of the positive electrode includes a transition metal that is a positive electrode active material.
In order to suppress the dissolution of the metal components of the positive electrode, an additive (compound (I)) that coordinates with the transition metal of the positive electrode active material is added to the non-aqueous electrolyte, thereby suppressing the dissolution of the metal components of the positive electrode. The additive (compound (I)) that can coordinate with the transition metal of the positive electrode active material can stabilize the metal on the surface of the positive electrode active material by coordinating with the transition metal of the positive electrode active material.
The nonaqueous electrolyte of the present disclosure can prevent the DC resistance from increasing even when the nonaqueous secondary battery is stored for a long period of time in a high-temperature environment. This is presumably because compound (I) suppresses the elution of the transition metal, which is the positive electrode active material, and thereby prevents the eluted transition metal from accumulating on the negative electrode and decomposing the solvent of the nonaqueous electrolyte, thereby suppressing the thickening of the SEI film of the negative electrode.
Furthermore, the nonaqueous electrolyte of the present disclosure can prevent the discharge capacity from decreasing even when the nonaqueous secondary battery is stored for a long period of time in a high-temperature environment. This is presumably because, as described above, compound (I) prevents the SEI film of the negative electrode from thickening, thereby suppressing the progression of side reactions and preventing the discharge capacity from decreasing even when the nonaqueous secondary battery is exposed to a high-temperature environment.

<Compound (I)>
The non-aqueous electrolyte contains a compound (I) represented by the following formula (I).
The non-aqueous electrolyte may contain one type of compound (I) alone or two or more types of compound (I).

In formula (I), R represents an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms.

In formula (I), the alkyl group having 1 to 6 carbon atoms represented by R may be a straight-chain alkyl group or an alkyl group having a branched and/or cyclic structure.
In formula (I), examples of the alkyl group having 1 to 6 carbon atoms represented by R include a methyl group, an ethyl group, an n-propyl group, an isopropyl group, a 1-ethylpropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a 2-methylbutyl group, a 3,3-dimethylbutyl group, an n-pentyl group, an isopentyl group, a neopentyl group, a 1-methylpentyl group, an n-hexyl group, an isohexyl group, a sec-hexyl group, and a tert-hexyl group.
In formula (I), the number of carbon atoms in the alkyl group having 1 to 6 carbon atoms represented by R is preferably 1 to 3, more preferably 1 or 2, and even more preferably 1.

In formula (I), the alkoxy group having 1 to 6 carbon atoms represented by R may be a linear alkoxy group or an alkoxy group having a branched and/or cyclic structure.
In formula (I), examples of the alkoxy group having 1 to 6 carbon atoms represented by R include a methoxy group, an ethoxy group, an n-propoxy group, an isopropoxy group, a 1-ethylpropoxy group, an n-butoxy group, an isobutoxy group, a sec-butoxy group, a tert-butoxy group, a 2-methylbutoxy group, a 3,3-dimethylbutoxy group, an n-pentoxy group, an isopentoxy group, a neopentoxy group, a 1-methylpentoxy group, an n-hexoxy group, an isohexoxy group, a sec-hexoxy group, and a tert-hexoxy group. In formula (I), the number of carbon atoms of the alkoxy group having 1 to 6 carbon atoms represented by R is preferably 1 to 3, more preferably 1 or 2, and even more preferably 1.

In particular, in formula (I), R is preferably an alkoxy group having 1 to 6 carbon atoms.
When R is an alkoxy group having 1 to 6 carbon atoms, the nonaqueous electrolyte can further suppress an increase in direct current resistance and a decrease in discharge capacity even when the nonaqueous secondary battery is stored for a long period of time in a high-temperature environment.
The main reason for this effect is presumed to be as follows.
The electron density of the carbonyl group (C=O) in the molecule of compound (I) where R is an alkoxy group having 1 to 6 carbon atoms is higher than that in the case where R is an alkyl group having 1 to 6 carbon atoms. Therefore, in a non-aqueous secondary battery, compound (I) is considered to be more likely to be coordinated to the transition metal that is the positive electrode active material. As a result, it is presumed that the non-aqueous electrolyte can further suppress the increase in direct current resistance and the decrease in discharge capacity even if the non-aqueous secondary battery is stored for a long period of time in a high-temperature environment.

Specific examples of compound (I) include compounds represented by the following formulas (I-1) to (I-12).
Hereinafter, the compound represented by formula (I-1) may be referred to as "compound (I-1)."

The content of compound (I) is preferably 0.01% by mass or more and 10% by mass or less based on the total amount of the nonaqueous electrolyte.
When the content of compound (I) is within the above range, the nonaqueous electrolyte can further suppress an increase in DC resistance and a decrease in discharge capacity even when the nonaqueous secondary battery is stored for a long period of time in a high-temperature environment.
The upper limit of the content of compound (I) is preferably 10 mass% or less, more preferably 5.0 mass% or less, even more preferably 3.0 mass% or less, particularly preferably 2.0 mass% or less, and most preferably 1.0 mass% or less, based on the total amount of the nonaqueous electrolyte.
The lower limit of the content of compound (I) is preferably 0.01 mass % or more, more preferably 0.03 mass % or more, still more preferably 0.1 mass % or more, and even more preferably 0.3 mass % or more, based on the total amount of the nonaqueous electrolyte.

<Compound (II)>
The nonaqueous electrolyte solution of the present disclosure preferably contains a compound (II) represented by the following formula (II) (hereinafter referred to as "cyclic carbonate compound (II)").

In formula (II), R ¹ and R ² each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group.

The nonaqueous electrolyte solution of the present disclosure contains a cyclic carbonate ester compound (II) in addition to compound (I), and thus the increase in direct current resistance and the decrease in discharge capacity of the nonaqueous secondary battery are further suppressed even during charge-discharge cycles after long-term storage in a high-temperature environment.
This effect is presumably due to the following reasons.
The cyclic carbonate compound (II) is easily reductively decomposed by the negative electrode to form an SEI film before the electrolyte is reductively decomposed on the negative electrode, even during charge-discharge cycles after long-term storage in a high-temperature environment. This suppresses the decomposition of the electrolyte at the negative electrode. As a result, the increase in direct current resistance and the decrease in discharge capacity of the nonaqueous secondary battery are further suppressed.

Specific examples of the cyclic carbonate ester compound (II) include compounds represented by the following formulas (II-1) to (II-7).

When the non-aqueous electrolyte contains a cyclic carbonate ester (II), the upper limit of the content of the cyclic carbonate ester (II) is preferably 10.0 mass% or less, more preferably 5.0 mass% or less, and even more preferably 3.0 mass% or less, based on the total amount of the non-aqueous electrolyte. If the upper limit of the content of the cyclic carbonate ester (II) is within the above range, the decomposition of the non-aqueous solvent on the positive electrode or the negative electrode can be suppressed while suppressing an increase in the thickness of the SEI film. The non-aqueous solvent will be described later. As a result, the characteristics of the non-aqueous secondary battery after high-temperature storage are improved.
The lower limit of the content of the cyclic carbonate (II) is preferably 0.10 mass% or more, more preferably 0.20 mass% or more, and even more preferably 0.30 mass% or more, based on the total amount of the nonaqueous electrolyte. If the lower limit of the content of the cyclic carbonate (II) is within the above range, an SEI film having a thickness capable of suppressing decomposition of the nonaqueous solvent in the nonaqueous electrolyte is formed. As a result, the characteristics of the nonaqueous secondary battery after high-temperature storage are improved.

<Compound (III)>
The nonaqueous electrolyte solution of the present disclosure preferably contains at least one compound (III) selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate (hereinafter, sometimes referred to as “lithium fluorophosphate compound (III)”).
Lithium difluorophosphate is represented by the following formula (III-1), and lithium monofluorophosphate is represented by the following formula (III-2).

By containing the lithium fluorophosphate compound (III) in addition to the compound (I) in the nonaqueous electrolyte solution of the present disclosure, the increase in direct current resistance and the decrease in discharge capacity of the nonaqueous secondary battery are further suppressed even during charge-discharge cycles after long-term storage in a high-temperature environment.

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

<Compound (IV)>
The nonaqueous electrolyte solution of the present disclosure preferably contains a compound represented by the following formula (IV) (hereinafter referred to as "cyclic dicarbonyl compound (IV)").

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

By including a cyclic dicarbonyl compound (IV) in addition to compound (I) in the nonaqueous electrolyte solution of the present disclosure, the increase in direct current resistance and the decrease in discharge capacity of the nonaqueous secondary battery are further suppressed even during charge-discharge cycles after long-term storage in a high-temperature environment.
The non-aqueous electrolyte contains a cyclic dicarbonyl compound (IV) in addition to the compound (I), so that the SEI film may contain bonds derived from the cyclic dicarbonyl compound (IV) in addition to the above-mentioned reaction products. This makes it easier to form a thermally and chemically stable inorganic salt or polymer structure. Therefore, at high temperatures, the components of the SEI film that impair the durability of the SEI film are less likely to dissolve, and the SEI film is less likely to degrade. As a result, the increase in direct current resistance and the decrease in discharge capacity of the non-aqueous secondary battery are more suppressed even in charge-discharge cycles after long-term storage in a high-temperature environment.

M is an alkali metal. Examples of the alkali metal include lithium, sodium, and potassium. Among them, M is preferably lithium.
Y is a transition element, a group 13 element, a group 14 element, or a group 15 element of the periodic table. Y is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb, and more preferably Al, B, or P. When Y is Al, B, or P, the synthesis of the anion compound becomes relatively easy, and the production cost can be reduced.
b represents the valence of the anion and the number of cations. b is an integer of 1 to 3, and is preferably 1. When b is 3 or less, the salt of the anion compound is easily dissolved in the mixed organic solvent.
Each of m and n is a value related to the number of ligands. Each of m and n is determined depending on the type of M. m is an integer of 1 to 4. n is an integer of 0 to 8.
q is 0 or 1. When q is 0, the chelate ring is a five-membered ring, and when q is 1, the chelate ring is a six-membered ring.
R ³ represents an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. These alkylene groups, halogenated alkylene groups, arylene groups, or halogenated arylene groups may contain a substituent or a heteroatom in their structure. Specifically, these groups may contain a substituent instead of a hydrogen atom. Examples of the substituent include a halogen atom, a linear or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, or a hydroxyl group. In addition, the structure may have a nitrogen atom, a sulfur atom, or an oxygen atom introduced instead of the carbon element of these groups. In addition, when q is 1 and m is 2 to 4, m R ^3s may be bonded to each other. An example of such a ligand is ethylenediaminetetraacetic acid.
R ⁴ represents a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms. As with R ³ , these alkyl groups, halogenated alkyl groups, aryl groups, and halogenated aryl groups may contain a substituent or a heteroatom in the structure, and when n is 2 to 8, n R ^4s may be bonded to each other to form a ring. As R ⁴ , an electron-withdrawing group is preferable, and a fluorine atom is particularly preferable.
Q ¹ and Q ² each independently represent O or S. That is, the ligand bonds to Y via these heteroatoms.

Specific examples of cyclic dicarbonyl compounds (IV) include compounds represented by the following formulas (IV-1) to (IV-2).

When the non-aqueous electrolyte contains a cyclic dicarbonyl compound (IV), the upper limit of the content of the cyclic dicarbonyl compound (IV) is preferably 10% by mass or less, more preferably 5.0% by mass or less, even more preferably 3.0% by mass or less, and particularly preferably 2.0% by mass or less, based on the total amount of the non-aqueous electrolyte. If the upper limit of the content of the cyclic dicarbonyl compound (IV) is within the above range, the non-aqueous secondary battery can operate without the SEI film impairing the conductivity of lithium cations. Furthermore, the battery characteristics of the non-aqueous secondary battery are improved due to the SEI film containing a cyclic dicarbonyl structure.
The lower limit of the content of the cyclic dicarbonyl compound (IV) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more, based on the total amount of the non-aqueous electrolyte. If the lower limit of the content of the cyclic dicarbonyl compound (IV) is within the above range, the SEI film contains a sufficient amount of a structure mainly composed of a cyclic dicarbonyl structure. This makes it easier to form a thermally and chemically stable inorganic salt or polymer structure. Therefore, at high temperatures, the elution of the components of the SEI film that impair the durability of the SEI film and the deterioration of the SEI film are unlikely to occur. As a result, the durability of the SEI film and the characteristics of the non-aqueous secondary battery after high-temperature storage are improved.

<Compound (V)>
The nonaqueous electrolyte solution of the present disclosure preferably contains a compound represented by the following formula (V) (hereinafter referred to as "cyclic sulfur-containing ester compound (V)").

In formula (V),
^R5 is an oxygen atom, an alkylene group having 1 to 6 carbon atoms, or an alkenylene group having 2 to 6 carbon atoms;
R ⁶ is an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, a group represented by formula (v-1), or a group represented by formula (v-2),
* indicates the bond position,
In formula (v-1), R ⁶¹ represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group.
In formula (v-2), R ⁶² is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms.

By including the cyclic sulfur-containing ester compound (V) in addition to compound (I) in the nonaqueous electrolyte solution of the present disclosure, the increase in direct current resistance and the decrease in discharge capacity of the nonaqueous secondary battery are further suppressed even during charge-discharge cycles after long-term storage in a high-temperature environment.
This effect is presumably due to the following reasons.
When a non-aqueous secondary battery is manufactured using the non-aqueous electrolyte of the present disclosure, in the manufacturing process (for example, the aging step described below), the reaction product includes a product of the reaction between the cyclic sulfur-containing ester compound (IV) and a compound (for example, LiF) generated from the electrolyte. This further enhances the stability of the non-aqueous secondary battery in a high-temperature environment. As a result, even in the charge-discharge cycle after long-term storage in a high-temperature environment, the increase in direct current resistance and the decrease in discharge capacity of the non-aqueous secondary battery are further suppressed.

In formula (V), R ⁵ is preferably an alkylene group having 2 to 3 carbon atoms, a vinylene group, or an oxygen atom, more preferably a trimethylene group, a vinylene group, or an oxygen atom, and particularly preferably an oxygen atom.

In the cyclic sulfur-containing ester compound (V), R ⁵ is preferably an oxygen atom. This makes it easier to form a thermally and chemically stable inorganic salt structure. Therefore, at high temperatures, the components of the SEI film that impair the durability of the SEI film are unlikely to be eluted, and the SEI film is unlikely to be altered. As a result, the durability of the SEI film and the battery characteristics of the non-aqueous secondary battery are improved.

In formula (V), R ⁶ is preferably a group represented by formula (v-1) or a group represented by formula (v-2).
In formula (v-1), R ⁶¹ is preferably an alkylene group having 1 to 3 carbon atoms, an alkenylene group having 1 to 3 carbon atoms, or an oxymethylene group, and more preferably an oxymethylene group.
In formula (v-2), R ⁶² is preferably an alkyl group having 1 to 3 carbon atoms or an alkenyl group having 2 to 3 carbon atoms, and more preferably a propyl group.

Specific examples of the cyclic sulfur-containing ester compound (V) include compounds represented by formulas (V-1) to (V-7).

The nonaqueous electrolyte may contain only one type of cyclic sulfur-containing ester compound (V), or may contain two or more types.

The upper limit of the content of the cyclic sulfur-containing ester compound (V) is preferably 5.0 mass% or less, more preferably 3.0 mass% or less, and even more preferably 2.0 mass% or less, based on the total amount of the nonaqueous electrolyte. If the upper limit of the content of the cyclic sulfur-containing ester compound (V) is within the above range, the SEI film does not impair the conductivity of lithium ions, and the nonaqueous secondary battery can operate. Furthermore, the battery characteristics of the nonaqueous secondary battery are improved as the SEI film contains a cyclic sulfur-containing ester structure.
The lower limit of the content of the cyclic sulfur-containing ester compound (V) is preferably 0.01% by mass or more, more preferably 0.05% by mass or more, and even more preferably 0.10% by mass or more, based on the total amount of the nonaqueous electrolyte. If the lower limit of the content of the cyclic sulfur-containing ester compound (V) is within the above range, the SEI film contains a sufficient amount of cyclic sulfur-containing ester structure. This makes it easier to form a thermally and chemically stable inorganic salt or polymer structure. Therefore, at high temperatures, the elution of the components of the SEI film that impair the durability of the SEI film and the deterioration of the SEI film are unlikely to occur. As a result, the durability of the SEI film and the battery characteristics of the nonaqueous secondary battery are improved.

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

<Non-aqueous solvent>
The non-aqueous electrolyte of the present disclosure may contain a non-aqueous solvent.

As the non-aqueous solvent, various known ones can be appropriately selected.
As the non-aqueous solvent, for example, the non-aqueous solvents described in paragraphs 0069 to 0087 of JP-A-2017-45723 can be used.

The non-aqueous solvent preferably contains a cyclic carbonate compound and a chain carbonate compound.
The cyclic carbonate compound and the chain carbonate compound may each be used alone or in combination of two or more kinds.

Examples of the cyclic carbonate compound include ethylene carbonate (hereinafter sometimes referred to as "EC"), propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate.
Among these, ethylene carbonate, which has a high dielectric constant, is preferable. In particular, when the negative electrode active material of the nonaqueous secondary battery contains graphite, it is more preferable that the nonaqueous solvent contains ethylene carbonate.

Examples of chain carbonate compounds include dimethyl carbonate (hereinafter sometimes referred to as "DMC"), ethyl methyl carbonate (hereinafter sometimes referred to as "EMC"), diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl carbonate, ethyl pentyl carbonate, dipentyl carbonate, methyl heptyl carbonate, ethyl heptyl carbonate, diheptyl carbonate, methyl hexyl carbonate, ethyl hexyl carbonate, dihexyl carbonate, methyl octyl carbonate, ethyl octyl carbonate, dioctyl carbonate, etc.

The combination of the cyclic carbonate and the chain carbonate is not particularly limited.The non-aqueous electrolyte preferably contains EC, DMC, and EMC as non-aqueous solvents.
When the negative electrode active material of a non-aqueous secondary battery contains graphite, the non-aqueous solvent contains EC, so that the SEI film of the negative electrode in which lithium ions can move smoothly and efficiently can be formed. EC is a solid at room temperature, so it has a high viscosity even when melted. By mixing EC with DMC and EMC, which have low viscosity, the non-aqueous solvent has a moderate viscosity. It is believed that this makes it easier for lithium ions in the non-aqueous electrolyte to move at high speed. As a result, the battery performance of the non-aqueous secondary battery is improved.

The mixing ratio of the cyclic carbonate compound and the chain carbonate compound is, for example, 5:95 to 80:20, preferably 10:90 to 70:30, and more preferably 15:85 to 55:45, expressed as a mass ratio of the cyclic carbonate compound to the chain carbonate compound. By setting such a ratio, the increase in viscosity of the non-aqueous electrolyte can be suppressed and the degree of dissociation of the electrolyte, which will be described later, can be increased, thereby increasing the conductivity of the non-aqueous electrolyte, which is related to the charge-discharge characteristics of the non-aqueous secondary battery. In addition, the solubility of the electrolyte can be further increased. Therefore, a non-aqueous electrolyte with excellent electrical conductivity at room temperature or low temperature can be obtained, and the load characteristics of the non-aqueous secondary battery at room temperature to low temperature can be improved.

The non-aqueous solvent may contain compounds other than the cyclic carbonate compound and the chain carbonate compound.
In this case, the other compound contained in the non-aqueous solvent may be only one type, or may be two or more types.
Other compounds include cyclic carboxylate compounds (e.g., gamma-butyrolactone), cyclic sulfone compounds, cyclic ether compounds, chain carboxylate compounds, chain ether compounds, chain phosphate compounds, amide compounds, chain carbamate compounds, cyclic amide compounds, cyclic urea compounds, boron compounds, polyethylene glycol derivatives, and the like.
For these compounds, the descriptions in paragraphs 0069 to 0087 of JP-A-2017-45723 can be appropriately referred to.

The proportion of the cyclic carbonate compound and the chain carbonate compound in the non-aqueous solvent is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more.
The proportion of the cyclic carbonate compound and the chain carbonate compound in the non-aqueous solvent may be 100% by mass.

When the non-aqueous solvent contains EC, DMC, and EMC, the mixing ratio of EC, DMC, and EMC is not particularly limited, but is preferably 30:35:35 by volume.

The proportion of the nonaqueous solvent in the nonaqueous electrolyte is preferably 60% by mass or more, and more preferably 70% by mass or more.
The upper limit of the proportion of the nonaqueous solvent in the nonaqueous electrolyte solution varies depending on the contents of other components (electrolyte, additives, etc.), but is, for example, 99 mass %, preferably 97 mass %, and more preferably 90 mass %.

<Electrolyte>
The nonaqueous electrolyte solution of the present disclosure preferably contains an electrolyte.
The electrolyte preferably comprises a lithium salt.
The lithium salt preferably comprises _LiPF6 .
When the electrolyte contains LiPF ₆ , the ratio of LiPF ₆ in the electrolyte is preferably 10% by mass to 100% by mass, more preferably 50% by mass to 100% by mass, and further preferably 70% by mass to 100% by mass.

The concentration of the electrolyte in the non-aqueous electrolyte solution is preferably 0.1 mol/L to 3 mol/L, and more preferably 0.5 mol/L to 2 mol/L.

When the electrolyte contains LiPF ₆ , the electrolyte may contain compounds other than LiPF ₆ .
Compounds other than _LiPF6 include:
tetraalkylammonium salts such as (C ₂ H ₅ ) ₄ NPF ₆ , (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₄ NClO ₄ , (C ₂ H ₅ ) ₄ NAsF ₆ , (C ₂ H ₅ ) ₄ N ₂ SiF ₆ , (C ₂ H ₅ ) ₄ NOSO ₂ C _k F _(2k+1) (k = an integer from 1 to 8), (C ₂ H ₅ ) ₄ NPF _n [C _k F _(2k+1) ] _(6-n) (n = 1 to 5, k = an integer from 1 to 8);
Lithium salts such as LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li ₂ SiF ₆ , LiOSO ₂ C _k F _(2k+1) (k = an integer from 1 to 8), LiPF _n [C _k F _(2k+1) ] _(6-n) (n = 1 to 5, k = an integer from 1 to 8), LiC(SO ₂ R ⁷ ) (SO ₂ R ⁸ ) (SO _{2 R} ⁹ ), LiN(SO ₂ ^{OR 10 )} (SO ₂ OR ¹¹ ), LiN(SO ₂ R ¹² ) (SO 2 R 13 ) (wherein R ⁷ to R ¹³ may be the same or different and are a fluorine atom or a perfluoroalkyl group having 1 to 8 carbon atoms) (i.e., lithium salts other than LiPF ₆ );
etc.

<Other additives>
The nonaqueous electrolyte solution of the present disclosure preferably contains other additives.
By including other additives in the non-aqueous electrolyte, the progression of side reactions during the charge-discharge cycle of the non-aqueous secondary battery can be suppressed, and as a result, the battery performance of the non-aqueous secondary battery is improved.
The non-aqueous electrolyte may contain one type of other additive alone or two or more types of additives.

The other additives are not particularly limited, and any known additives can be used.
As other additives, for example, additives described in paragraphs 0042 to 0055 of JP-A-2019-153443 can be used.

When the non-aqueous electrolyte contains other additives, the content of the other additives is preferably 0.001% by mass to 10% by mass, more preferably 0.005% by mass to 5% by mass, even more preferably 0.01% by mass to 2% by mass, particularly preferably 0.1% by mass to 2% by mass, and even more preferably 0.1% by mass to 1% by mass, based on the total amount of the non-aqueous electrolyte.

[Non-aqueous secondary battery precursor]
The nonaqueous secondary battery precursor of the present disclosure includes the nonaqueous electrolyte of the present disclosure, a positive electrode, and a negative electrode.

The nonaqueous secondary battery precursor refers to a nonaqueous secondary battery before it is charged and discharged. That is, in the nonaqueous secondary battery precursor, the negative electrode does not include an SEI film, and the positive electrode does not include an SEI film.

(positive electrode)
The nonaqueous secondary battery precursor of the present disclosure includes a positive electrode.
The positive electrode includes a positive electrode active material.

Examples of the positive electrode active material include a lithium-containing composite oxide, a lithium-containing oxide, a transition metal oxide, a transition metal sulfide, a conductive polymer material, etc. The positive electrode active material may be used alone or in combination of two or more kinds.
The lithium-containing composite oxide will be described later.
Examples of lithium-containing oxides include lithium-containing oxides such as _LiNiO2 , _LiCoO2 , _LiMnO2 , _LiMn2O4 , and _LiNiO2 , and lithium _- containing phosphate compounds such as LiFePO4 _{and LiMnPO4} .
Examples of transition metal oxides include _MnO2 , _{V2O5 , and the like} .
Examples of transition metal sulfides include _MoS2 and _TiS2 .
Examples of the conductive polymer material include polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline complexes.
Among these, it is preferable that the positive electrode active material contains a lithium-containing composite oxide from the viewpoints of battery capacity, life specification, availability, and the like.

The lithium-containing composite oxide contains Li, Ni, and at least one metal element other than Li and Ni. Examples of metal elements other than Li and Ni include transition metal elements and typical metal elements. It is preferable that the metal elements other than Li and Ni are contained in an amount equivalent to or less than Ni in terms of atomic number. The metal elements other than Li and Ni may be, for example, at least one selected from the group consisting of Co, Mn, Al, Cr, Fe, V, Mg, Ca, Na, Ti, Zr, Nb, Mo, W, Cu, Zn, Ga, In, Sn, La, and Ce.

The lithium-containing composite oxide preferably contains a lithium-containing composite oxide (hereinafter, sometimes referred to as "NCM") represented by the following formula (C1): The lithium-containing composite oxide (C1) has a high energy density per unit volume and excellent thermal stability.
LiNi _a Co _b Mn _c O ₂ ... Formula (C1)
In formula (C1), a, b, and c each independently represent greater than 0 and less than 1, and the sum of a, b, and c is 0.99 or greater and 1.00 or less.
_{Specific examples of NCM include LiNi0.33Co0.33Mn0.33O2 , LiNi0.5Co0.3Mn0.2O2 , LiNi0.5Co0.2Mn0.3O2 , LiNi0.6Co0.2Mn0.2O2 , LiNi0.8Co0.1Mn0.1O2 , and the like . ​}

The lithium-containing composite oxide may contain a lithium-containing composite oxide (hereinafter, sometimes referred to as "NCA") represented by the following formula (C2).
Li _t Ni _1-x-y Co _x Al _y O ₂ ... Formula (C2)
In formula (C2), t is 0.95 or more and 1.15 or less, x is 0 or more and 0.3 or less, y is 0.1 or more and 0.2 or less, and the sum of x and y is less than 0.5.
_Specific examples of NCAs _{include LiNi0.8Co0.15Al0.05O2 .}

The positive electrode may include a positive electrode current collector.
The material of the positive electrode current collector is not particularly limited, and any known material can be used.
Specific examples of the positive electrode current collector include metal materials, carbon materials, etc. Metal materials for the positive electrode current collector include aluminum, aluminum alloys, stainless steel, nickel, titanium, tantalum, etc. Carbon materials for the positive electrode current collector include carbon cloth, carbon paper, etc.

The positive electrode may include a positive electrode current collector and a positive electrode active material layer provided on at least a portion of the surface of the positive electrode current collector.
The positive electrode active material layer contains at least one positive electrode active material, which preferably contains a lithium-containing composite oxide.
The content of the lithium-containing composite oxide is preferably 70% by mass or more, and more preferably 80% by mass or more, based on the total amount of the positive electrode active material layer.
The positive electrode active material layer may further contain at least one conductive additive, such as graphite, carbon black, conductive carbon fiber, and fullerene.
The positive electrode active material layer may further contain at least one binder.
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, acrylonitrile rubber particles, etc. Among these, fluororesin is preferred from the viewpoint of improving the oxidation resistance of the positive electrode active material layer.
The content of the binder is preferably 1% by mass to 20% by mass, and more preferably 1% by mass to 10% by mass, based on the total amount of the positive electrode active material layer.

(Negative electrode)
The nonaqueous secondary battery precursor of the present disclosure includes a negative electrode.
The negative electrode includes a negative electrode active material.

Examples of the negative electrode active material include metallic lithium, materials capable of absorbing and releasing lithium, metal materials capable of forming an alloy with lithium, oxide materials, etc. Lithium includes lithium ions.
Examples of materials capable of absorbing and releasing lithium include carbon materials, oxides, transition metal nitrides, and the like. Examples of carbon materials include graphite materials, carbon black, activated carbon, and amorphous carbon materials. Examples of graphite materials include artificial graphite and natural graphite. Examples of artificial graphite include graphitized mesocarbon microbeads (MCMB: Meso Carbon Micro Beads) and graphitized mesocarbon fiber (MCF: Meso Carbon Fiber). In addition, graphite materials containing boron can also be used. In addition, graphite materials can be those coated with metals such as gold, platinum, silver, copper, and tin, those coated with amorphous carbon, and those mixed with amorphous carbon and graphite. The form of the carbon material may be any of fibrous, spherical, potato, and flake-like. Examples of oxides include lithium titanate (Li(Li _1/3 Ti _5/3 )O ₄ ). The transition metal nitride may be an amorphous lithium-containing transition metal nitride.
Metal materials capable of forming an alloy with lithium can form an alloy with lithium, for example, when a non-aqueous secondary battery is charged. Metal materials capable of forming an alloy with lithium include metals and alloys. Metals include Si, Zn, Sn, Al, Zn, Ge, Cd, Pb, Bi, Sb, etc. Alloys include Si alloys, Zn alloys, Sn alloys, Al alloys, Zn alloys, Ge alloys, Cd alloys, Pb alloys, Bi alloys, Sb alloys, etc.
Examples of oxide materials include oxides containing at least one of silicon and tin, lithium titanate (Li ₂ TiO ₃ ), and the like.
In particular, from the viewpoint of the safety of the resulting nonaqueous secondary battery, it is preferable that the negative electrode active material contains at least one selected from the group consisting of a material capable of absorbing and releasing lithium, a metal material capable of forming an alloy with lithium, and an oxide material.
Among these, carbon materials capable of absorbing and releasing lithium are preferred from the viewpoints of further improving the formability of the SEI film of the negative electrode and further reducing the DC resistance of the nonaqueous secondary battery at the initial stage and/or after long-term storage at high temperature.

The negative electrode may include a negative electrode current collector.
Examples of the material of the negative electrode current collector include metal materials. Examples of the metal material of the negative electrode current collector include copper, nickel, stainless steel, nickel-plated steel, etc. Among them, copper is particularly preferable as the material of the negative electrode current collector from the viewpoint of ease of processing.

The negative electrode may include a negative electrode current collector and a negative electrode active material layer provided on at least a portion of the surface of the negative electrode current collector.
The negative electrode active material layer contains at least one negative electrode active material, which preferably contains the above-mentioned carbon material.
From the viewpoints of further improving the formability of the SEI film of the negative electrode and further reducing the direct current resistance of the nonaqueous secondary battery at the initial stage and/or after long-term storage at high temperature, the content of the carbon material is preferably 70 mass % or more, more preferably 80 mass % or more, and even more preferably 90 mass % or more, relative to the total amount of the negative electrode active material layer.
The negative electrode active material layer may further contain at least one binder.
The binder is preferably at least one selected from the group consisting of styrene butadiene (SBR) rubber (e.g., SBR latex), acrylonitrile-butadiene rubber, acrylonitrile-butadiene-styrene rubber, carboxymethyl cellulose (CMC), hydroxypropyl methyl cellulose, polyvinyl alcohol, hydroxypropyl cellulose, and diacetyl cellulose. The binder preferably contains SBR latex and carboxymethyl cellulose.
The content of the binder in the negative electrode active material layer is preferably 1 mass % to 20 mass %, more preferably 1 mass % to 10 mass %, and even more preferably 1 mass % to 5 mass %, based on the total amount of the negative electrode active material layer.

The Si content is preferably 5 mass % or less based on the total amount of the negative electrode.
When the Si content is 5 mass % or less, the formability of the SEI film in the negative electrode is further improved, and the DC resistance of the nonaqueous secondary battery at the initial stage and/or after long-term storage at high temperature is further reduced.

(Separator)
The non-aqueous secondary battery precursor of the present disclosure may include a separator disposed between the negative electrode and the positive electrode.
The separator is a membrane that electrically insulates the positive electrode from the negative electrode and is permeable to lithium ions, and examples of the separator include a porous membrane and a polymer electrolyte.
As the porous membrane, a microporous polymer film is preferably used, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, polyester, and the like.
In particular, the material of the porous membrane is preferably a porous polyolefin. Specifically, the porous membrane may be a porous polyethylene film, a porous polypropylene film, or a multi-layer film of a porous polyethylene film and a porous polypropylene film. The porous polyolefin film may be coated with another resin having excellent thermal stability.
Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved, and a polymer swollen with an electrolytic solution.
The nonaqueous electrolyte solution of the present disclosure may be used for the purpose of swelling a polymer to obtain a polymer electrolyte.

(case)
The nonaqueous secondary battery precursor of the present disclosure may include a case that houses, for example, a positive electrode, a negative electrode, a nonaqueous electrolyte, and a separator.
The shape of the case is not particularly limited and may be appropriately selected depending on the application of the nonaqueous secondary battery, etc. Examples of the case include a case including a laminate film and a case consisting of a battery can and a battery can lid.

<Configuration of non-aqueous secondary battery precursor>
The nonaqueous secondary battery precursor of the present disclosure can have various known shapes, and can be formed into any shape such as a cylinder, a coin, a square, a laminate, a film, etc. The basic structure of the nonaqueous secondary battery precursor is the same regardless of the shape, and the design can be modified according to the purpose.

[Non-aqueous secondary battery]
The nonaqueous secondary battery of the present disclosure is obtained by charging and discharging a nonaqueous secondary battery precursor.
In particular, the nonaqueous secondary battery of the present disclosure includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. The negative electrode includes an SEI film. The positive electrode includes an SEI film.

A nonaqueous secondary battery differs from a nonaqueous secondary battery precursor mainly in the first point that the negative electrode includes an SEI film, and in the second point that the positive electrode includes an SEI film. In other words, a nonaqueous secondary battery is similar to a nonaqueous secondary battery precursor except for the first and second points. Therefore, hereinafter, a description of the components of a nonaqueous secondary battery other than the first and second points will be omitted.

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 active material layer. The first negative electrode form refers to a form in which an SEI film is formed on at least a portion of the surface of the negative electrode active material layer. The second negative electrode form refers to a form in which an SEI film is formed on the surface of the negative electrode active material, which is a constituent material of the negative electrode active material layer.

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

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

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

For the basic structure of the nonaqueous secondary battery of the present disclosure, refer to the basic structure of the nonaqueous secondary battery precursor of the present disclosure.

An example of the nonaqueous secondary battery precursor or the nonaqueous 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 a nonaqueous secondary battery precursor or a nonaqueous secondary battery of the present disclosure, and FIG. 2 is a schematic cross-sectional view in the thickness direction of a stacked electrode body housed in the laminated battery shown in FIG.
The laminated battery 1 includes a laminated exterior body 8. The laminated exterior body 8 contains a nonaqueous electrolyte solution (not shown in FIG. 1) and a laminated electrode body (not shown in FIG. 1) of the present disclosure. The periphery of the laminated exterior body 8 is sealed. In other words, the inside of the laminated exterior body 8 is airtight. The laminated exterior body 8 is made of a material such as aluminum.
2, the laminated electrode body is formed by alternately stacking positive electrode plates 5 and negative electrode plates 6 with separators 7 interposed therebetween. The positive electrode plates 5, the negative electrode plates 6, and the separators 7 are impregnated with the nonaqueous electrolyte of the present disclosure.
Each of the multiple 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 protrudes outward from the peripheral edge of the laminated exterior body 8 (see FIG. 1 ). The portion of the peripheral edge of the laminated exterior body 8 from which the positive electrode terminal 2 protrudes is sealed with an insulating seal 4.
Similarly, each of the 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 portion of this negative electrode terminal 3 protrudes outward from the peripheral edge of the laminated exterior body 8 (see FIG. 1 ). The portion of the peripheral edge of the laminated exterior body 8 from which the negative electrode terminal 3 protrudes is sealed with an insulating seal 4.
In the laminated battery according to the above example, the number of positive plates 5 is five and the number of negative plates 6 is six, and the positive plates 5 and the negative plates 6 are laminated with separators 7 interposed between them in an arrangement in which the outermost layers on both sides are negative plates 6. However, it goes without saying that the number and arrangement of positive and negative plates in the laminated battery are not limited to this example, and various modifications may be made.

Another example of the nonaqueous secondary battery precursor or the nonaqueous 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, which is another example of the nonaqueous secondary battery precursor or the nonaqueous secondary battery of the present disclosure.
3, a disk-shaped negative electrode 12, a separator 15 filled with a nonaqueous electrolyte, a disk-shaped positive electrode 11, and, if necessary, spacer plates 17, 18 made of stainless steel, aluminum, or the like are stacked in this order and housed between a positive electrode can 13 (hereinafter also referred to as a "battery can") and a sealing plate 14 (hereinafter also referred to as a "battery can lid"). The positive electrode can 13 and the sealing plate 14 are crimped and sealed with a gasket 16 interposed therebetween.
In this example, the nonaqueous electrolyte of the present disclosure is used as the nonaqueous electrolyte injected into separator 15 .

The use of the nonaqueous secondary battery precursor or the nonaqueous secondary battery disclosed herein is not particularly limited, and the battery can be used for various known uses. For example, the battery can be widely used in notebook computers, mobile computers, mobile phones, headphone stereos, video movie players, liquid crystal televisions, handy cleaners, electronic organizers, calculators, radios, backup power supplies, motors, automobiles, electric automobiles, motorcycles, electric motorcycles, bicycles, electric bicycles, lighting equipment, game machines, watches, power tools, cameras, and the like, regardless of whether the device is small portable or large.

[Method for manufacturing non-aqueous secondary battery]
The method for producing a nonaqueous secondary battery according to the present disclosure includes a preparation step, which will be described later, and an aging step, which will be described later, thereby obtaining a nonaqueous secondary battery.

(Preparation process)
In the preparation step, a non-aqueous secondary battery precursor is prepared.

The nonaqueous secondary battery precursor comprises a nonaqueous electrolyte solution containing compound (I), a positive electrode, and a negative electrode.

The structure of the nonaqueous secondary battery precursor is the same as that of a nonaqueous secondary battery, except that an SEI film is not formed. Therefore, a description of the structure of the nonaqueous secondary battery precursor is omitted.

The method for preparing the non-aqueous secondary battery precursor is not particularly limited, and the non-aqueous secondary battery precursor may be assembled by a known method.

(Aging process)
In the aging step, the nonaqueous secondary battery precursor is charged or discharged (hereinafter referred to as "aging treatment"), whereby an SEI film is formed, that is, a nonaqueous secondary battery is obtained.

The aging process includes charging and discharging the non-aqueous secondary battery precursor in an environment of 25°C or higher and 70°C or lower. In detail, the aging process includes a first charging phase, a first holding phase, a second charging phase, a second holding phase, and a charge/discharge phase.

In the first charging phase, the nonaqueous secondary battery precursor is charged in an environment of 25°C or higher and 70°C or lower. In the first holding phase, the nonaqueous secondary battery precursor after the first charging phase is held in an environment of 25°C or higher and 70°C or lower. In the second charging phase, the nonaqueous secondary battery precursor after the first holding phase is charged in an environment of 25°C or higher and 70°C or lower. In the second holding phase, the nonaqueous secondary battery precursor after the second charging phase is held in an environment of 25°C or higher and 70°C or lower. In the charge/discharge phase, the nonaqueous secondary battery precursor after the second holding phase is subjected to a combination of charging and discharging one or more times in an environment of 25°C or higher and 70°C or lower.

The nonaqueous secondary battery obtained by the method for producing a nonaqueous secondary battery disclosed herein exhibits the effect of suppressing the increase in direct current resistance and the decrease in discharge capacity more effectively than a configuration that does not contain compound (I), even when stored at high temperature for a long period of time.

Embodiments of the present disclosure will be described in detail below 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 secondary battery precursor was prepared as follows.

<Preparation of non-aqueous electrolyte>
Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed in a ratio of EC:DMC:EMC=30:35:35 (volume ratio) to obtain a mixed solvent as a non-aqueous solvent.
_LiPF6 as an electrolyte was dissolved in the resulting mixed solvent so that the concentration in the final non-aqueous electrolyte solution was 1 mol/L to obtain an electrolyte solution. Hereinafter, the obtained electrolyte solution is referred to as the "base electrolyte solution."

As compound (I), compound (I-1) shown below in (I-1) was used.
The compound (I-1) was added to the base electrolyte so that the content relative to the total amount of the finally obtained nonaqueous electrolyte was the content (mass%) shown in Table 1. In this way, a nonaqueous electrolyte was obtained.

<Preparation of Positive Electrode>
_{A mixture} was obtained by adding _{LiNi0.5Co0.2Mn0.3O2} (94 mass%) as a positive _electrode active material, carbon black (3 mass%) as a conductive assistant, and polyvinylidene fluoride (PVdF) (3 mass%) as a binder, and the mixture was dispersed in an N-methylpyrrolidone solvent to obtain a positive electrode mixture slurry.
An aluminum foil having a thickness of 20 μm was prepared as a positive electrode current collector.
The obtained positive electrode mixture slurry was applied onto an aluminum foil, dried, and then rolled with a press to obtain a sheet-shaped positive electrode, which was composed of a positive electrode current collector and a positive electrode active material layer.

<Preparation of negative electrode>
A negative electrode mixture slurry was obtained by mixing 96 mass % of natural graphite as a negative electrode active material, 1 mass % of carbon black as a conductive assistant, 1 mass % of sodium carboxymethylcellulose dispersed in pure water as a thickener in terms of solid content, and 2 mass % of styrene-butadiene rubber (SBR) dispersed in pure water as a binder.
A copper foil having 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, dried, and then rolled with a press to obtain a sheet-shaped negative electrode, which was composed of a negative electrode current collector and a negative electrode active material layer.

<Preparing the separator>
As a separator, a porous polyethylene film was prepared.

<Preparation of coin-type battery>
The negative electrode was punched out into a disk shape with a diameter of 14 mm, the positive electrode was punched out into a disk shape with a diameter of 13 mm, and the separator was punched out into a disk shape with a diameter of 17 mm, thereby obtaining a coin-shaped negative electrode, a coin-shaped positive electrode, and a coin-shaped separator.
The obtained coin-shaped negative electrode, coin-shaped separator, and coin-shaped positive electrode were stacked in this order in a stainless steel battery can (size: 2032 size). Next, 20 μL of non-aqueous electrolyte was poured into the battery can, and the separator, positive electrode, and negative electrode were immersed in the non-aqueous electrolyte.
Next, an aluminum plate (thickness: 1.2 mm, diameter: 16 mm) and a spring were placed on the positive electrode, and the battery can lid was crimped via a polypropylene gasket to seal the battery.
In this manner, a coin-shaped nonaqueous secondary battery precursor was obtained having the structure shown in Fig. 3. The coin-shaped nonaqueous secondary battery precursor had a diameter of 20 mm and a height of 3.2 mm.

Comparative Example 1
A coin-type non-aqueous secondary battery precursor was obtained in the same manner as in Example 1, except that the compound (I-1) was not added.

[Examples 2 to 6]
In the preparation of the nonaqueous electrolyte solution described above, in addition to compound (I-1), compounds represented by the following formulas (II-1), (III-1), (IV-1), (V-1), and (V-2) were added as additives to the base electrolyte solution so that the contents of the compounds and contents (mass %) relative to the total amount of the nonaqueous electrolyte solution finally obtained were those shown in Table 1. A coin-shaped nonaqueous secondary battery precursor was obtained in the same manner as in Example 1.

[Evaluation test]
The obtained nonaqueous secondary battery precursor was subjected to the aging treatment described below to obtain a first battery. The obtained first battery was subjected to the initial charge/discharge treatment described below to obtain a second battery. The obtained second battery was subjected to the treatment for evaluating DC resistance described below to obtain a third battery. The obtained third battery was subjected to a high-temperature storage treatment to obtain a fourth battery. The obtained fourth battery was subjected to the later charge/discharge treatment described below to obtain a fifth battery.
The resistance increase rate and capacity retention rate of the first to fifth batteries thus obtained were measured by the following measurement methods. The measurement results are shown in Table 1.
The evaluation results are shown in Table 1.

<Aging treatment>
The nonaqueous secondary battery precursor was subjected to the following aging treatment to obtain a first battery.
The nonaqueous secondary battery precursor was charged at a temperature range of 25 to 60° C. with an end voltage range of 1.5 V to 3.5 V, and then rested for a range of 5 to 50 hours. Next, the nonaqueous secondary battery precursor was charged at a temperature range of 25 to 60° C. with an end voltage range of 3.5 V to 4.2 V, and held for a range of 5 to 50 hours. Next, the nonaqueous secondary battery precursor was charged to 4.2 V at a temperature range of 25 to 60° C., and then discharged to 2.5 V. This produced a first battery.

<Initial charge/discharge treatment>
The first battery was subjected to the following initial charge/discharge treatment to obtain a second battery.
The first battery was kept in a temperature environment of 25°C for 12 hours. Next, the first battery was charged at a constant current and constant voltage (0.2C-CCCV) at a charge rate of 0.2C to 4.2V (SOC (State Of Charge): 100%), then rested for 30 minutes, and then discharged at a constant current (0.2C-CC) at a discharge rate of 0.2C to 2.5V. This was repeated for three cycles to stabilize the battery. Thereafter, the first battery was charged at a constant current and constant voltage (0.5C-CCCV) at a charge rate of 0.2C to 4.2V, then rested for 30 minutes, and then discharged at a constant current (1C-CC) at a discharge rate of 1C to 2.5V. This produced a second battery.

<Processing for evaluating DC resistance>
The second battery was subjected to the following treatment for evaluating DC resistance to obtain a third battery.
The process for evaluating DC resistance was performed in a temperature environment of 25° C. The second battery was CC discharged to 2.5 V at a discharge rate of 0.2 C, and CCCV charged to 3.7 V at a charge rate of 0.2 C. “CCCV charging” means charging at a constant current and constant voltage.
Next, the second battery was subjected to CC10s discharge at a discharge rate of 0.2 C and CC10s charging at a charge rate of 0.2 C. "CC10s discharge" means discharging at a constant current for 10 seconds. "CC10s charging" means charging at a constant current for 10 seconds.
Next, the second battery was subjected to CC10s discharge at a discharge rate of 0.5 C and CC25s charge at a charge rate of 0.2 C. Next, the second battery was subjected to CC10s discharge at a discharge rate of 1 C and CC50s charge at a charge rate of 0.2 C. Next, the second battery was subjected to CC10s discharge at a discharge rate of 2 C and CC100s charge at a charge rate of 0.2 C. This produced a third battery.

<High temperature storage treatment>
The third battery was subjected to the following high-temperature storage treatment to obtain a fourth battery.
The third battery was charged at a constant current of 0.2 C at a charge rate up to 4.2 V in a temperature environment of 25° C. The charged battery was then left to stand for 14 days in an atmosphere at 60° C. Thus, a fourth battery was obtained.

<Late-stage charge/discharge treatment>
The fourth battery was subjected to the following later charge-discharge treatment to obtain a fifth battery.
The fourth battery was allowed to cool in a temperature environment of 25°C, and was subjected to a first discharge, a first charge, and a second discharge. The first discharge indicates constant current discharge (1C-CC) to 2.5V at a discharge rate of 1C. The first charge indicates constant current constant voltage charge (0.2C-CCCV) to 4.2V at a charge rate of 0.2C. The second discharge indicates constant current discharge (1C-CC) to 2.5V at a discharge rate of 1C. In this way, the fifth battery was obtained.

<Method for measuring capacity retention rate>
As shown in the following formula (X1), the relative value of the discharge capacity of the fourth battery of each Example to the discharge capacity of the fourth battery of Comparative Example 1 was defined as the "capacity maintenance rate [%]." The discharge capacity indicates the capacity obtained when the second discharge was performed in the above-mentioned later charge-discharge treatment.

Capacity retention rate [relative value; %] = (discharge capacity of the fourth battery [mAh/g] / discharge capacity of the fourth battery of Comparative Example 1 [mAh/g]) x 100... (X1)

<Method for measuring resistance increase rate>
As shown in the following formula (X2), the relative value of the resistance increase rate of each Example to the resistance increase rate of Comparative Example 1 was taken as "resistance increase rate [%]".

Resistance increase rate [relative value; %] = (resistance increase rate / resistance increase rate of comparative example 1) x 100 ... (X2)

In formula (X2), the resistance increase rate is the DC resistance (Ω) of the fourth battery divided by the DC resistance (Ω) of the second battery.

The DC resistance (Ω) of the fourth battery was measured by the following method.
The fourth battery was subjected to a DC resistance evaluation process similar to the DC resistance evaluation process described above. The DC resistance (Ω) of the fourth battery was calculated based on the voltage drop (=voltage before the start of discharge-voltage 10 seconds after the start of discharge) due to "CC10s discharge" at discharge rates of 0.2C to 1C and each current value (i.e., each current value corresponding to discharge rates of 0.2C to 1C).

The DC resistance (Ω) of the second battery was measured in the same manner as the DC resistance (Ω) of the fourth battery.

In Table 1, "content" indicates the content [mass %] of compound (I) relative to the total amount of the finally obtained nonaqueous electrolyte.
In Table 1, "NCM523" represents _{" LiNi0.5Co0.2Mn0.3O2} ." In Table 1, _" (I-1)" represents "compound (I-1 ₎ ."
In Table 1, "-" in the non-aqueous secondary battery section indicates that the corresponding component is not contained.

The above relative value of the DC resistance of the fifth battery after the high-temperature storage test corresponds to the increase rate (%) of DC resistance due to storage in an atmosphere at 60° C. (hereinafter, also simply referred to as the “resistance increase rate”). The increase rate referred to here is an increase rate in a mode in which neither increase nor decrease is expressed as 100%, an increase is expressed as more than 100%, and a decrease is expressed as less than 100%.
The reason for focusing on the rate of increase in resistance is that, although a low resistance value itself is an important performance factor in battery performance, reducing the rate of increase in resistance due to deterioration during storage is also an extremely important performance factor.

The nonaqueous electrolyte solutions of Examples 1 to 6 contain compound (I-1). Therefore, in the nonaqueous secondary batteries of Examples 1 to 6, the resistance increase rate was 98% or less, and the capacity retention rate was 102% or more. As a result, it was found that the nonaqueous secondary batteries of Examples 1 to 6 suppressed the increase in DC resistance and the decrease in discharge capacity even when stored for a long period of time in a high-temperature environment. In other words, it was found that the nonaqueous electrolyte solutions of Examples 1 to 6 can suppress the increase in DC resistance and the decrease in discharge capacity even when the nonaqueous secondary batteries are stored for a long period of time in a high-temperature environment.

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

Claims (12)

A non-aqueous electrolyte solution comprising a compound (I) represented by formula (I).

(In formula (I), R represents an alkyl group having 1 to 6 carbon atoms or an alkoxy group having 1 to 6 carbon atoms.) The nonaqueous electrolyte according to claim 1, wherein R is an alkoxy group having 1 to 6 carbon atoms. The nonaqueous electrolyte according to claim 1 or 2, wherein the content of the compound (I) is 0.01% by mass or more and 10% by mass or less with respect to the total amount of the nonaqueous electrolyte. The nonaqueous electrolyte solution according to any one of claims 1 to 3, comprising a compound represented by the following formula (II):

(In formula (II), ^R1 and ^R2 each independently represent a hydrogen atom, a methyl group, an ethyl group, or a propyl group.) The nonaqueous electrolyte according to any one of claims 1 to 4, comprising at least one compound (III) selected from the group consisting of lithium monofluorophosphate and lithium difluorophosphate. The nonaqueous electrolyte solution according to any one of claims 1 to 5, comprising a compound represented by the following formula (IV):

[In formula (IV),
M is an alkali metal;
Y is a transition element, an element of Group 13, 14, or 15 of the periodic table;
b is an integer from 1 to 3;
m is an integer from 1 to 4,
n is an integer from 0 to 8,
q is 0 or 1;
R ³ is an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (these groups may contain a substituent or a heteroatom in the structure, and when q is 1 and m is 2 to 4, m R ^3s may each be bonded to each other);
R ⁴ is a halogen atom, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms (these groups may contain a substituent or a heteroatom in the structure, and when n is 2 to 8, n R ^4s may be bonded to each other to form a ring);
Q ¹ and Q ² each independently represent an oxygen atom or a carbon atom. The nonaqueous electrolyte solution according to any one of claims 1 to 6, comprising a compound represented by the following formula (V):

[In formula (V),
^R5 represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 1 to 6 carbon atoms, or a vinylene group;
^R6 represents an alkylene group having 1 to 6 carbon atoms, a group represented by the above formula (v-1), or a group represented by the above formula (v-2).
* indicates the bond position.
In formula (v-1), R ⁶¹ represents an oxygen atom, an alkylene group having 1 to 6 carbon atoms, an alkenylene group having 2 to 6 carbon atoms, or an oxymethylene group.
In formula (v-2), R ⁶² is an alkyl group having 1 to 6 carbon atoms or an alkenyl group having 2 to 6 carbon atoms. The nonaqueous electrolyte according to any one of claims 1 to 7,
A positive electrode and
and a negative electrode. The nonaqueous secondary battery precursor according to claim 8, wherein the positive electrode active material contained in the positive electrode includes a lithium-containing composite oxide. The nonaqueous secondary battery precursor according to claim 8 or 9, wherein the negative electrode active material contained in the negative electrode includes at least one selected from the group consisting of a material capable of absorbing and releasing lithium, a metal material capable of forming an alloy with lithium, and an oxide material. A preparation step of preparing a nonaqueous secondary battery precursor according to any one of claims 8 to 10;
and an aging step of charging and discharging the nonaqueous secondary battery precursor. A non-aqueous secondary battery obtained by charging and discharging the non-aqueous secondary battery precursor according to any one of claims 8 to 10.