JP6749088B2 - Non-aqueous electrolyte for lithium secondary battery and lithium secondary battery - Google Patents

Description

TECHNICAL FIELD The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery, and a rechargeable lithium secondary battery used for a power source of a portable electronic device, a vehicle, an electric power storage, and the like.

In recent years, a lithium secondary battery has been widely used as an electronic device such as a mobile phone or a notebook computer, an electric vehicle, or a power source for power storage. Particularly in recent years, there has been a rapid increase in demand for batteries with high capacity, high output, and high energy density that can be mounted on hybrid vehicles and electric vehicles.
The lithium secondary battery is mainly composed of a positive electrode and a negative electrode containing a material capable of inserting and extracting lithium, and a non-aqueous electrolyte solution for a battery containing a lithium salt and a non-aqueous solvent.
As the positive electrode active material used for the positive electrode, for example, a lithium metal oxide such as LiCoO ₂ , LiMnO ₂ , LiNiO ₂ , or LiFePO ₄ is used.
Further, as the non-aqueous electrolyte, a mixed solvent of carbonates such as ethylene carbonate, propylene carbonate, dimethyl carbonate, and ethyl methyl carbonate (non-aqueous solvent), LiPF ₆ , LiBF ₄ , LiN(SO ₂ CF ₃ ) ₂ , LiN A solution in which a Li electrolyte such as (SO ₂ CF ₂ CF ₃ ) ₂ is mixed is used.
On the other hand, as the negative electrode active material used for the negative electrode, metallic lithium, metallic compounds capable of occluding and releasing lithium (metal simple substance, oxide, alloy with lithium, etc.) and carbon materials are known. Lithium secondary batteries that use coke, artificial graphite, and natural graphite that can store and release are put into practical use.

As an attempt to improve the battery performance, it has been proposed to incorporate various additives into the non-aqueous electrolyte for batteries.
For example, it is known that a boric acid compound is added to a non-aqueous electrolyte to improve battery performance such as suppression of initial (pre-storage) electrode interface resistance, improvement of charge/discharge cycle characteristics, and improvement of storage characteristics. (For example, patent documents 1-3).

JP, 2003-132946, A JP, H11-3728, A JP, H09-120825, A

As disclosed in Patent Documents 1 to 3, it is known to add a boric acid compound to a non-aqueous electrolyte in order to improve battery performance, but further improvement in battery performance is required. In particular, a non-aqueous electrolytic solution for a battery containing a boric acid compound as an additive and a battery using such a non-aqueous electrolytic solution for a battery are known to be useful in improving cycle characteristics, but after storage at high temperature, In terms of reducing the battery resistance of, it is still not sufficient and further improvement is necessary.
The present invention has been made in order to meet the challenges, it is an object of the present invention is to provide a non-aqueous electrolyte and a lithium secondary battery for a lithium secondary battery capable of reducing the battery resistance after high-temperature storage is there.

As a result of intensive studies, the present inventor has found that the nonaqueous electrolyte for a lithium secondary battery contains a boron compound having a specific basic skeleton, whereby the battery resistance after high temperature storage can be reduced, and the present invention has been completed. Let
In other words, means for solving the above problems is Ru der below.

< 1 > A non-aqueous electrolyte for a lithium secondary battery containing a boron compound represented by the following general formula (1) or the following general formula (2).

In (formula ^{(1), R 11} and ^{R 12,} adjacent turned and ^{R 11} and ^{R 12} are integrated, the general formula (1) boron atoms in ^an oxygen atom adjacent to ^{R 11,} and the ^{R 12} Represents a group forming a ring having 2 to 12 carbon atoms together with the oxygen atom, and n in formula (1) represents 1 or 2.
In the general formula (1), R ^{13 to} R ¹⁵ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl having 6 to 12 carbon atoms. Represents a group. However, in the general formula (1), when n is 2, two R ¹⁴ may be the same or different, and two R ¹⁵ may be the same or different.
In the general formula (2), R ²¹ and R ²² are adjacent to the boron atom, the oxygen atom adjacent to R ²¹ and the R ^{22 in} the general formula (2), together with R ²¹ and R ²² . It represents a group forming a ring having 2 to 12 carbon atoms together with an oxygen atom.
In formula (2), R ^{23 to} R ²⁵ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. to table to the group.

< 2 > The non-aqueous electrolyte for a lithium secondary battery according to < 1 >, which contains the boron compound represented by the general formula (2).

< 3 > In the general formula (1), R ¹¹ and R ¹² are integrated to form a boron atom in the general formula (1), an oxygen atom adjacent to R ^11, and an oxygen atom adjacent to R ^12. And a group forming a ring having 2 to 12 carbon atoms is a group represented by the following formula (a), and in the general formula (2), R ²¹ and R ²² are integrated to form a general formula The group forming a ring having 2 to 12 carbon atoms with the boron atom in (2), the oxygen atom adjacent to R ²¹ and the oxygen atom adjacent to R ²² is a group represented by the following formula (a). < 1 > or the non-aqueous electrolyte solution for lithium secondary batteries as described in < 2 >.

< 4 > Further containing at least one compound selected from the group consisting of a carbonate compound having a carbon-carbon unsaturated bond or a fluorine atom, a fluorophosphoric acid compound, an oxalato compound and a cyclic sulfonic acid ester, <1> or <2> The nonaqueous electrolytic solution for a lithium secondary battery according to 2> .

< 5 > Metal or alloy capable of alloying with the positive electrode and metallic lithium, lithium-containing alloy, lithium, oxide capable of doping/dedoping lithium ion, transition metal capable of doping/dedoping lithium ion A negative electrode containing at least one selected from the group consisting of a nitride and a carbon material capable of doping/dedoping lithium ions as a negative electrode active material, and any one of <1> , <2>, and < 4 > And a non-aqueous electrolyte solution for a lithium secondary battery according to item.

< 6 > A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to < 5 >.

< 7 > The method according to < 3 >, further containing at least one compound selected from the group consisting of a carbonate compound having a carbon-carbon unsaturated bond or a fluorine atom, a fluorophosphoric acid compound, an oxalato compound, and a cyclic sulfonic acid ester. Non-aqueous electrolyte for lithium secondary batteries.

< 8 > Metal or alloy capable of alloying with the positive electrode and metallic lithium, lithium-containing alloy, lithium, oxide capable of doping/dedoping lithium ion, transition metal capable of doping/dedoping lithium ion For a lithium secondary battery according to < 3 > or < 7 >, a negative electrode containing, as a negative electrode active material, at least one selected from the group consisting of a nitride and a carbon material capable of doping/dedoping lithium ions. A lithium secondary battery containing a non-aqueous electrolyte.

< 9 > A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to < 8 >.

According to the present invention, it is possible to provide a non-aqueous electrolyte and a lithium secondary battery for a lithium secondary battery capable of reducing the battery resistance after high-temperature storage.

FIG. 3 is a schematic cross-sectional view of a coin-type battery showing an example of the lithium secondary battery of the present invention.

Hereinafter, embodiments of the present invention will be described.
In the present specification, the numerical range represented by "to" means a range including the numerical values before and after "to" as the lower limit value and the upper limit value.

[Non-aqueous electrolyte for batteries]
The non-aqueous electrolytic solution for a lithium secondary battery of the present embodiment (hereinafter, also simply referred to as “non-aqueous electrolytic solution”) is a basic compound represented by the general formula ( 1 ) or the general formula ( 2 ) as an additive. It contains a skeleton-containing boron compound (hereinafter, also referred to as “specific boron compound”).
According to the present invention, a nonaqueous electrolytic solution for lithium secondary battery can be reduced battery resistance after high-temperature storage and a lithium secondary battery obtained.

The reason why the above effects are obtained by the nonaqueous electrolytic solution of the present invention is presumed as follows.
The specific boron compound in the present embodiment has three B-O bonds, and at least one of the three B-O bonds (hereinafter referred to as "specific B-O bond") has a carbon atom. It has a basic skeleton linked to the carbonyl group via one or two. It is considered that the specific boron compound forms a structure in which the oxygen of the carbonyl group linked to the specific B-O bond via one or two carbon atoms is intramolecularly coordinated with the boron atom. It is considered that such a structure contributes to reduction of battery resistance after storage at high temperature.
Specifically, the above-mentioned coordination structure facilitates cleavage of the remaining B-O bond, that is, the B-O bond other than the specific B-O bond. Thereby, a film derived from a boron compound is likely to be formed on the electrode surface by the initial charge. As a result, solvent decomposition at the electrode is suppressed. It is presumed that the battery resistance after storage can be reduced by preventing the solvent decomposition products from accumulating on the electrode surface.
In addition, although the boron compound is described as an additive of the nonaqueous electrolyte solution for secondary batteries in the above-mentioned patent documents 1-3, in any boron compound, a specific B-O bond has 1 carbon atom. It does not have a structure linked to a carbonyl group via one or two. For example, Patent Document 1 describes a boron compound in which an allyl group is linked to a specific B—O bond, and Patent Document 2 describes a boron compound in which an acyloxy group is linked to a specific B—O bond. There is. However, in these boron compounds, an allyl group or an acyloxy group is directly linked to a specific B-O bond, and the boron compound is not linked to a carbonyl group through one or two carbon atoms. Different from the specific boron compound.

According to the non-aqueous electrolyte solution of the present invention, as described above, the battery resistance after high temperature storage can be reduced. Therefore, the non-aqueous electrolyte solution of the present invention is expected to have the effect of extending the life of the battery.

Hereinafter, the components of the non-aqueous electrolyte solution of this embodiment will be specifically described.

<Specific boron compound>
The nonaqueous electrolytic solution for a battery of the present embodiment contains a specific boron compound as an additive.

(Basic skeleton)
The specific boron compound in the present embodiment has a basic skeleton represented by the following general formula (1S) or general formula (2S).

In the general formula (1S), n represents 1 or 2.

The boron compound having a basic skeleton represented by the general formula (1S) may be used alone or in combination of two or more.
The boron compound having a basic skeleton represented by the general formula (2S) may be used alone or in combination of two or more kinds.
Further, in the present embodiment, at least one kind of the boron compound having the basic skeleton represented by the general formula (1S) and at least one kind of the boron compound having the basic skeleton represented by the general formula (2S) are combined. You may use it.

(Boron compound represented by the general formula (1))
The boron compound having the basic skeleton represented by the general formula (1S) is preferably the boron compound represented by the general formula (1).

In formula (1), R ¹¹ and R ¹² are each independently a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a general formula a group represented by (1A), or represent a group represented by the general formula (2A), ^{or, R 11} and ^{R 12} and together form a boron atom in the formula ^{(1), R 11} Represents a group forming a ring having 2 to 12 carbon atoms with an oxygen atom adjacent to R ¹² and an oxygen atom adjacent to R ¹² . In the general formula (1), n represents 1 or 2.
In the general formula (1), R ^{13 to} R ¹⁵ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl having 6 to 12 carbon atoms. Represents a group. However, in the general formula (1), when n is 2, two R ¹⁴ may be the same or different, and two R ¹⁵ may be the same or different.
In formula (1A), R ^{13A to} R ^15A each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Represents a group. In the general formula (1A), n _A represents 1 or 2. However, in the general formula (1A), when n _A is 2, two R ^14A may be the same or different, and two R ^15A may be the same or different. In the general formula (1A), * represents a bonding position.
In formula (2A), R ^{23A to} R ^25A are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Represents a group. In general formula (2A), * represents a bonding position.

Specifically, when n is 1, the boron compound represented by the general formula (1) is represented by the following general formula (1-1).

When n is 2, the boron compound represented by the general formula (1) is specifically represented by the following general formula (1-2).

In the general formula (1), the alkyl group having 1 to 12 carbon atoms represented by R ¹¹ and R ¹² is more preferably an alkyl group having 1 to 10 carbon atoms, and further preferably an alkyl group having 1 to 8 carbon atoms. , An alkyl group having 1 to 6 carbon atoms is more preferable, and an alkyl group having 1 to 4 carbon atoms is further preferable. The alkyl group may be linear or branched.
Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group. , Tert-pentyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, n-heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, n-octyl group, isooctyl group, Examples thereof include sec-octyl group and tert-octyl group.
In the general formula (1), the alkyl group having 1 to 12 carbon atoms represented by R ¹¹ and R ¹² may be unsubstituted or may be substituted with a halogen atom (eg, fluorine atom, chlorine atom) or the like. ..

In the general formula (1), the alkenyl group having 2 to 12 carbon atoms represented by R ¹¹ and R ¹² is more preferably an alkenyl group having 2 to 10 carbon atoms, and further preferably an alkenyl group having 2 to 8 carbon atoms. , C 2-6 alkenyl groups are more preferred, and C 2-4 alkenyl groups are more preferred. The alkenyl group may be linear or branched.
Examples of the alkenyl group include an ethenyl group, a propenyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group and an octenyl group.
In the general formula (1), the alkenyl group having 2 to 12 carbon atoms represented by R ¹¹ and R ¹² may be unsubstituted or may be substituted with a halogen atom (eg, fluorine atom, chlorine atom) or the like. ..

In the general formula (1), the aryl group having 6 to 20 carbon atoms represented by R ¹¹ and R ¹² is more preferably an aryl group having 6 to 12 carbon atoms, and further preferably an aryl group having 6 to 10 carbon atoms. ..
Examples of the aryl group include a phenyl group; a group in which one hydrogen atom is removed from an alkylbenzene (eg, a benzyl group, a tolyl group, a xylyl group, a methicyl group, etc.); a naphthyl group; And the like.
In the general formula (1), the aryl group having 6 to 20 carbon atoms represented by R ¹¹ and R ¹² may be unsubstituted or may be substituted with a halogen atom (eg, fluorine atom, chlorine atom) or the like. ..

In the general formula (1), R ¹¹ and R ¹² are integrated to form a carbon atom having 2 to 2 carbon atoms in addition to the boron atom in the general formula (1), the oxygen atom adjacent to R ^11, and the oxygen atom adjacent to R ¹² . The group forming a ring of 12 is preferably a group forming a ring of 2 to 6 carbon atoms, and more preferably a group represented by the following formula (a), (b) or formula (c). * In the formulas (a), (b) or (c) represents a bonding position with the adjacent oxygen atom. The ring formed by the group represented by formula (a) is a ring having an oxalato structure.

Specific embodiments of the boron compound represented by the general formula (1) include the following embodiments 1), 2) or 3).
1) In the general formula (1), R ¹¹ and R ¹² are integrated together to form a carbon atom together with the boron atom in the general formula (1), the oxygen atom adjacent to R ^11, and the oxygen atom adjacent to R ^12. The embodiment which is a group forming 2 to 12 rings.
2) One of R ¹¹ and R ¹² is represented by a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an aryl group having 6 to 20 carbon atoms, or general formula (1A). Represents a group or a group represented by the general formula (2A), the other of R ¹¹ and R ¹² is an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or 6 to 20 carbon atoms. The embodiment which is an aryl group.
3) A mode in which R ¹¹ and R ¹² are each independently a group represented by the general formula (1A) or a group represented by the general formula (2A).
Among the above aspects 1), the group forming a ring having 2 to 12 carbon atoms is preferably a group forming a ring having 2 to 6 carbon atoms. The ring formed by the group represented by formula (a) is a ring having an oxalato structure.

In the general formula (1), examples of the halogen atom represented by R ^{13 to} R ¹⁵ include a fluorine atom, a chlorine atom and a bromine atom, and a fluorine atom is preferable.

In the general formula (1), the alkyl group having 1 to 12 carbon atoms represented by R ^{13 to} R ¹⁵ is more preferably an alkyl group having 1 to 10 carbon atoms, and further preferably an alkyl group having 1 to 8 carbon atoms. , An alkyl group having 1 to 6 carbon atoms is more preferable, an alkyl group having 1 to 4 carbon atoms is more preferable, and an alkyl group having 1 to 3 carbon atoms is further preferable. The alkyl group may be linear or branched.
Examples of the alkyl group include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, tert-butyl group, n-pentyl group, isopentyl group, neopentyl group. , Tert-pentyl group, n-hexyl group, isohexyl group, sec-hexyl group, tert-hexyl group, n-heptyl group, isoheptyl group, sec-heptyl group, tert-heptyl group, n-octyl group, isooctyl group, Examples thereof include sec-octyl group and tert-octyl group.
In the general formula (1), the alkyl group having 1 to 12 carbon atoms represented by R ^{13 to} R ¹⁵ may be unsubstituted or may be substituted with a halogen atom (eg, fluorine atom, chlorine atom) or the like. ..

In the general formula (1), the alkenyl group having 2 to 12 carbon atoms represented by R ^{13 to} R ¹⁵ is more preferably an alkenyl group having 2 to 10 carbon atoms, and further preferably an alkenyl group having 2 to 8 carbon atoms. , C 2-6 alkenyl groups are more preferred, and C 2-4 alkenyl groups are more preferred. The alkenyl group may be linear or branched.
Examples of the alkenyl group include an ethenyl group, a propenyl group, a butenyl group, a pentenyl group, a hexenyl group, a heptenyl group and an octenyl group.
In the general formula (1), the alkenyl group having 2 to 12 carbon atoms represented by R ^{13 to} R ¹⁵ may be unsubstituted or may be substituted with a halogen atom (eg, fluorine atom, chlorine atom) or the like. ..

In the general formula (1), the aryl group having 6 to 12 carbon atoms represented by R ^{13 to} R ¹⁵ is more preferably an aryl group having 6 to 10 carbon atoms.
Examples of the aryl group include a phenyl group; a group in which one hydrogen atom is removed from an alkylbenzene (eg, a benzyl group, a tolyl group, a xylyl group, a methicyl group, etc.); a naphthyl group; And the like.
In the general formula (1), the aryl group having 6 to 12 carbon atoms represented by R ^{13 to} R ¹⁵ may be unsubstituted or may be substituted with a halogen atom (eg, fluorine atom, chlorine atom) or the like. ..

In the general formula ^(1), at least one of R 13 ^{to R 15} is an alkyl group, preferably an alkenyl group, or an aryl ^group, at least two R 13 ^{to R 15} is an alkyl group, an alkenyl group, Alternatively, it is more preferably an aryl group. In this case, preferred embodiments of the alkyl group, alkenyl group, and aryl group are as described above, and the alkyl group is preferred among the alkyl group, alkenyl group, and aryl group.

In the general formula ^(1A), R 13A ^{to R 15A} has the same meaning as ^R 13 ^{to R 15} in the general formula (1), and preferred ranges are also the same.

In formula (2A), R ^{23A to} R ^25A have the same meanings as R ^{13 to} R ¹⁵ in formula (1), and the preferred ranges are also the same.

The boron compound represented by the general formula (1) may be used alone or in combination of two or more kinds.

(Boron compound represented by the general formula (2))
The boron compound having the basic skeleton represented by the general formula (2S) is preferably the boron compound represented by the general formula (2).

In the general formula (2), R ²¹ and R ²² each independently represent a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a general formula Represents a group represented by formula (1A) or a group represented by formula (2A), or R ²¹ and R ²² are integrated to form a boron atom in formula (2), R ^21; Represents a group forming a ring having 2 to 12 carbon atoms together with an oxygen atom adjacent to R ²² and an oxygen atom adjacent to R ²² .
In formula (2), R ^{23 to} R ²⁵ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Represents a group.
In formula (1A), R ^{13A to} R ^15A each independently represent a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Represents a group. In the general formula (1A), n _A represents 1 or 2. However, in the general formula (1A), when n _A is 2, two R ^14A may be the same or different, and two R ^15A may be the same or different. In the general formula (1A), * represents a bonding position.
In formula (2A), R ^{23A to} R ^25A are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Represents a group. In general formula (2A), * represents a bonding position.

In the general formula (2), R ²¹ has the same meaning as R ¹¹ in the general formula (1), and the preferred range is also the same.
In the general formula (2), R ²² has the same meaning as R ¹² in the general formula (1), and the preferred range is also the same.

In the general formula (2), R ²¹ and R ²² are integrated, and the number of carbon atoms is 2 with the boron atom in the general formula (2), the oxygen atom adjacent to R ^21, and the oxygen atom adjacent to R ²² . The group forming a ring of 12 is preferably a group forming a ring of 2 to 6 carbon atoms, and more preferably a group represented by the following formula (a), (b) or formula (c). * In the formulas (a), (b) or (c) represents a bonding position with the adjacent oxygen atom. The ring formed by the group represented by formula (a) is a ring having an oxalato structure.

Specific embodiments of the boron compound represented by the general formula (2) include the following embodiments 1), 2) or 3).
1) In the general formula (2), R ²¹ and R ²² are integrated together to form a carbon atom together with the boron atom, the oxygen atom adjacent to R ²¹ and the oxygen atom adjacent to R ^{22 in} the general formula (2). The embodiment which is a group forming 2 to 12 rings.
2) One of R ²¹ and R ²² is represented by a hydrogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an aryl group having 6 to 20 carbon atoms, or general formula (1A). Represents a group or a group represented by the general formula (2A), and the other of R ²¹ and R ²² is an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an alkyl group having 6 to 20 carbon atoms. The embodiment which is an aryl group.
3) A mode in which R ²¹ and R ²² are each independently a group represented by the general formula (1A) or a group represented by the general formula (2A).
Among the above aspects 1), the group forming a ring having 2 to 12 carbon atoms is preferably a group forming a ring having 2 to 6 carbon atoms. The ring formed by the group represented by formula (a) is a ring having an oxalato structure.

In the general formula (2), R ^{23 to} R ²⁵ have the same meanings as R ^{13 to} R ¹⁵ in the general formula (1), and the preferred ranges are also the same.

In the general formula ^(1A), R 13A ^{to R 15A} has the same meaning as ^R 13 ^{to R 15} in the general formula (1), and preferred ranges are also the same.

In formula (2A), R ^{23A to} R ^25A have the same meanings as R ^{13 to} R ¹⁵ in formula (1), and the preferred ranges are also the same.

The boron compound represented by the general formula (2) may be used alone or in combination of two or more kinds.

In the present embodiment, at least one kind of the boron compound represented by the general formula (1) and at least one kind of the boron compound represented by the general formula (2) may be used in combination.

Specific examples of the specific boron compound include the following exemplary compounds (1) to (26). However, the specific boron compound is not limited to these.
In the structures of the exemplified compounds below, “tBu” represents a tertiary butyl group, “Ph” represents a phenyl group, and “OiPr” represents an isopropoxy group.

The specific boron compound in the present embodiment can be synthesized, for example, by the method described in Chemische Berichte, Volume 68, Issue 6, Pages 1949-55, 1965.

The specific boron compound contained in the non-aqueous electrolytic solution of the present embodiment may be only one kind or two or more kinds.
The content of the specific boron compound (the total content in the case of two or more kinds) in the present embodiment is preferably 0.01% by mass to 10% by mass, and 0.05% by mass with respect to the total amount of the non-aqueous electrolytic solution. % To 5 mass% is more preferable, 0.1 mass% to 5 mass% is further preferable, 0.5 mass% to 5 mass% is further preferable, 0.5 mass% to 3 mass% is further preferable, and 0. 5 mass% to 2 mass% is more preferable, and 0.5 mass% to 1 mass% is further preferable.

<Other additives>
The nonaqueous electrolytic solution of the present embodiment is composed of a carbonate compound having a carbon-carbon unsaturated bond or a fluorine atom, a fluorophosphoric acid compound, an oxalato compound, and a cyclic sulfonic acid ester, in addition to the specific boron compound described above. It is preferable to contain at least one compound selected from the group (hereinafter, also referred to as “other additive”). The effects of the present invention described above are more effectively exhibited by the non-aqueous electrolyte solution of the present embodiment containing other additives.

(Carbonate compound having a carbon-carbon unsaturated bond)
Examples of the carbonate compound having a carbon-carbon unsaturated bond include methyl vinyl carbonate, ethyl vinyl carbonate, divinyl carbonate, methyl propynyl carbonate, ethyl propynyl carbonate, dipropynyl carbonate, methylphenyl carbonate, ethylphenyl carbonate, and diphenyl carbonate. Carbonates; vinylene carbonate, methylvinylene carbonate, 4,4-dimethylvinylene carbonate, 4,5-dimethylvinylene carbonate, vinylethylene carbonate, 4,4-divinylethylene carbonate, 4,5-divinylethylene carbonate, ethynylethylene carbonate, Cyclic carbonates such as 4,5-diethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, propynyl ethylene carbonate, 4,5-dipropynyl ethylene carbonate and 4,5-dipropynyl ethylene carbonate; Among these, preferably, methylphenyl carbonate, ethylphenyl carbonate, diphenyl carbonate, vinylene carbonate, vinyl ethylene carbonate, 4,4-divinylethylene carbonate, 4,5-divinylethylene carbonate, more preferably vinylene carbonate, It is vinyl ethylene carbonate.

(Carbonate compound having a fluorine atom)
Examples of the carbonate compound having a fluorine atom include methyl trifluoromethyl carbonate, ethyl trifluoromethyl carbonate, bis(trifluoromethyl)carbonate, methyl(2,2,2-trifluoroethyl)carbonate, ethyl(2,2,2). -Chain carbonates such as trifluoroethyl)carbonate and bis(2,2,2-trifluoroethyl)carbonate; 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4 -Cyclic carbonates such as trifluoromethylethylene carbonate; and the like. Of these, 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate and 4,5-difluoroethylene carbonate are preferable.

(Fluorophosphate compound)
Examples of the fluorophosphate compound include lithium difluorophosphate, lithium monofluorophosphate, difluorophosphoric acid, monofluorophosphoric acid, methyl difluorophosphate, ethyl difluorophosphate, dimethyl fluorophosphate, diethyl fluorophosphate and the like. .. Of these, lithium difluorophosphate and lithium monofluorophosphate are preferable.

(Oxalato compound)
Examples thereof include lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium tris(oxalato)phosphate, lithium difluoro(oxalato)borate, and lithium bisoxalatoborate. Of these, lithium difluorobis(oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, and lithium bisoxalatoborate are preferable.

(Cyclic sulfonic acid ester)
Examples of the cyclic sulfonic acid ester include 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1-methyl-1,3-propene sultone, 2-methyl-1,3-propene sultone, and 3 -Sulfones such as methyl-1,3-propene sultone. Of these, 1,3-propane sultone and 1,3-propene sultone are preferable.

The above-mentioned other additives are vinylene carbonate, vinyl ethylene carbonate, 4-fluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,5-difluoroethylene carbonate, lithium monofluorophosphate, lithium difluorophosphate, difluorobissulfate. Lithium (oxalato)phosphate, lithium tetrafluoro(oxalato)phosphate, lithium tris(oxalato)phosphate, lithium difluoro(oxalato)borate, lithium bisoxalatoborate, 1,3-propanesultone, 1,3-propene Particularly preferred is at least one selected from the group consisting of sultone.

When the non-aqueous electrolyte in the present embodiment contains another additive, the other additive contained may be only one kind or two or more kinds.
When the non-aqueous electrolyte in the present embodiment contains other additives, the content thereof (total content in the case of two or more kinds) is not particularly limited, but the effect of the present invention is more effective. From the viewpoint of the above, it is preferably 0.001% by mass to 10% by mass, more preferably 0.05% by mass to 5% by mass, and more preferably 0% by mass with respect to the total amount of the non-aqueous electrolytic solution. It is more preferably in the range of 1% by mass to 4% by mass, further preferably in the range of 0.1% by mass to 2% by mass, and in the range of 0.1% by mass to 1% by mass. Particularly preferred.

Moreover, the non-aqueous electrolyte in the present invention may contain a specific boron compound and an additive other than the other additive.
Specific boron compounds and additives other than the other additives include, for example, difluorophosphate salts other than the above-mentioned lithium difluorophosphate, monofluorophosphate salts other than lithium monofluorophosphate, and fluorosulfonates. Is mentioned.
In addition, additives other than the above are, for example, International Publication No. 2012/053644, Japanese Patent No. 4033074, Japanese Patent No. 4819409, Japanese Patent Laid-Open No. 2012-226878, Japanese Patent No. 5353923, Japanese Patent No. 4424895. It can be appropriately selected and used from the additives described in the above.

Next, other components of the non-aqueous electrolyte will be described.
The non-aqueous electrolytic solution generally contains an electrolyte and a non-aqueous solvent.

<Non-aqueous solvent>
As the non-aqueous solvent in the present embodiment, various known ones can be appropriately selected, but it is preferable to use a cyclic aprotic solvent and/or a chain aprotic solvent.
In order to improve the flash point of the solvent in order to improve the safety of the battery, it is preferable to use a cyclic aprotic solvent as the non-aqueous solvent.

(Cyclic aprotic solvent)
As the cyclic aprotic solvent, cyclic carbonate, cyclic carboxylic acid ester, cyclic sulfone and cyclic ether can be used.
The cyclic aprotic solvent may be used alone or in combination of two or more.
The mixing ratio of the cyclic aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass. With such a ratio, the conductivity of the electrolytic solution related to the charge/discharge characteristics of the battery can be increased.
Specific examples of the cyclic carbonate include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, and 2,3-pentylene carbonate. Of these, ethylene carbonate and propylene carbonate, which have a high dielectric constant, are preferably used. In the case of a battery using graphite as the negative electrode active material, ethylene carbonate is more preferable. Moreover, you may use these cyclic carbonates in mixture of 2 or more types.

Specific examples of the cyclic carboxylic acid ester include γ-butyrolactone, δ-valerolactone, or alkyl-substituted compounds such as methyl γ-butyrolactone, ethyl γ-butyrolactone, and ethyl δ-valerolactone.
The cyclic carboxylic acid ester has a low vapor pressure, a low viscosity, and a high dielectric constant, and can reduce the viscosity of the electrolytic solution without reducing the flash point of the electrolytic solution and the dissociation degree of the electrolyte. Therefore, since it has a feature that the conductivity of the electrolyte, which is an index related to the discharge characteristics of the battery, can be increased without increasing the flammability of the electrolyte, when aiming to improve the flash point of the solvent, It is preferable to use a cyclic carboxylic acid ester as the cyclic aprotic solvent. Among the cyclic carboxylic acid esters, γ-butyrolactone is most preferable.
The cyclic carboxylic acid ester is preferably used as a mixture with another cyclic aprotic solvent. For example, a mixture of cyclic carboxylic acid ester and cyclic carbonate and/or chain carbonate may be mentioned.

Examples of the cyclic sulfone include sulfolane, 2-methylsulfolane, 3-methylsulfolane, dimethylsulfone, diethylsulfone, dipropylsulfone, methylethylsulfone, methylpropylsulfone and the like.
Dioxolane may be mentioned as an example of a cyclic ether.

(Chain aprotic solvent)
As the chain-like aprotic solvent, chain carbonate, chain carboxylic acid ester, chain ether, chain phosphoric acid ester and the like can be used.
The mixing ratio of the chain aprotic solvent in the non-aqueous solvent is 10% by mass to 100% by mass, more preferably 20% by mass to 90% by mass, and particularly preferably 30% by mass to 80% by mass.
Specifically as a chain carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, ethyl butyl carbonate, dibutyl carbonate, methyl pentyl carbonate, Examples thereof include 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, and methyl trifluoroethyl carbonate. You may use these chain carbonates in mixture of 2 or more types.

Specific examples of the chain carboxylic acid ester include methyl pivalate.
Specific examples of the chain ether include dimethoxyethane and the like.
Specific examples of the chain phosphoric acid ester include trimethyl phosphate.

(Combination of solvent)
The non-aqueous solvent used in the non-aqueous electrolytic solution in the present embodiment may be one kind or a mixture of plural kinds. Further, even if only one kind or a plurality of kinds of cyclic aprotic solvent is used, one kind or a plurality of kinds of chain aprotic solvent alone is used, or a cyclic aprotic solvent and chain protic solvent are used. You may mix and use a solvent. When it is particularly intended to improve the load characteristics and low temperature characteristics of the battery, it is preferable to use a cyclic aprotic solvent and a chain aprotic solvent in combination as the non-aqueous solvent.
Further, in view of electrochemical stability of the electrolytic solution, it is particularly preferable to apply a cyclic carbonate to the cyclic aprotic solvent and a chain carbonate to the chain aprotic solvent. Further, the conductivity of the electrolytic solution relating to the charge/discharge characteristics of the battery can be increased also by combining the cyclic carboxylic acid ester with the cyclic carbonate and/or the chain carbonate.

As a combination of a cyclic carbonate and a chain carbonate, specifically, ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, propylene carbonate and methyl ethyl carbonate, and propylene carbonate. Diethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and methyl ethyl carbonate and diethyl carbonate Ethylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate, methyl ethyl carbonate and diethyl Carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, etc. are mentioned.
The mixing ratio of the cyclic carbonate and the chain carbonate is expressed by mass ratio, and the cyclic carbonate:chain carbonate is 5:95 to 80:20, more preferably 10:90 to 70:30, and particularly preferably 15:85. ~55:45. With such a ratio, an increase in the viscosity of the electrolytic solution can be suppressed and the dissociation degree of the electrolyte can be increased, so that the conductivity of the electrolytic solution related to the charge/discharge characteristics of the battery can be increased. In addition, the solubility of the electrolyte can be further increased. Therefore, the electrolytic solution having excellent electric conductivity at room temperature or low temperature can be obtained, and thus the load characteristics of the battery at room temperature to low temperature can be improved.

Specific examples of the combination of cyclic carboxylic acid ester and cyclic carbonate and/or chain carbonate include γ-butyrolactone and ethylene carbonate, γ-butyrolactone and ethylene carbonate and dimethyl carbonate, γ-butyrolactone and ethylene carbonate and methyl ethyl. Carbonate, γ-butyrolactone and ethylene carbonate and diethyl carbonate, γ-butyrolactone and propylene carbonate, γ-butyrolactone and propylene carbonate and dimethyl carbonate, γ-butyrolactone and propylene carbonate and methyl ethyl carbonate, γ-butyrolactone and propylene carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate and propylene carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate and dimethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, dimethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate and dimethyl carbonate And methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate and methyl ethyl carbonate, γ-butyrolactone, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate, γ-butyrolactone, ethylene carbonate and propylene carbonate And methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and ethylene carbonate, propylene carbonate, dimethyl carbonate, methyl ethyl carbonate and diethyl carbonate, γ-butyrolactone and sulfolane, γ-butyrolactone and ethylene carbonate and sulfolane, γ-butyrolactone and propylene carbonate Sulfolane, γ-butyrolactone, ethylene carbonate, propylene carbonate and sulfolane, γ-butyro Examples include lolactone, sulfolane, and dimethyl carbonate.

(Other solvents)
The non-aqueous electrolyte solution of the present embodiment may contain a solvent other than the above as the non-aqueous solvent. Specific examples of the other solvent include amides such as dimethylformamide, chain carbamates such as methyl-N,N-dimethylcarbamate, cyclic amides such as N-methylpyrrolidone, and N,N-dimethylimidazolidinone. Examples include boron compounds such as cyclic urea, trimethyl borate, triethyl borate, tributyl borate, trioctyl borate, and trimethylsilyl borate, and polyethylene glycol derivatives represented by the following general formula.
HO(CH ₂ CH ₂ O) _a H
HO[CH ₂ CH(CH ₃ )O] _b H
CH ₃ O(CH ₂ CH ₂ O) _c H
CH ₃ O[CH ₂ CH(CH ₃ )O] _d H
_{CH 3 O (CH 2 CH 2} O) e CH 3
_{CH 3 O [CH 2 CH (} CH 3) O] f CH 3
_{C 9 H 19 PhO (CH 2} CH 2 O) g [CH (CH 3) O] h CH 3
(Ph is a phenyl group)
_{CH 3 O [CH 2 CH (} CH 3) O] i CO [OCH (CH 3) CH 2] j OCH 3
In the above formula, a to f are integers from 5 to 250, g to j are integers from 2 to 249, and 5≦g+h≦250 and 5≦i+j≦250.

<Electrolyte>
The non-aqueous electrolyte solution of this embodiment may contain various known electrolytes. As the electrolyte, any of those generally used as an electrolyte for a non-aqueous electrolyte can be used.
Specific examples of the electrolyte in the present embodiment include (C ₂ H ₅ ) ₄ NPF ₆ , (C ₂ H ₅ ) ₄ NBF ₄ , (C ₂ H ₅ ) ₄ NClO ₄ , and (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 = 1~8 _{integer), (C 2 H 5)} 4 NPF n [C k _{F (2k + 1)] (} 6-n) (n = 1~5, k = 1~8 integer) tetraalkylammonium salts, such _{as, LiPF 6, LiBF 4, LiClO} 4, LiAsF 6, Li 2 SiF 6, LiOSO Lithium such as ₂ C _k F _(2k+1) (k=1 to 8 integer), LiPF _n [C _k F _(2k+1) ] _(6-n) (n=1 to 5 and k=1 to 8 integer). Examples include salt. Further, a lithium salt represented by the following general formula can also be used.

_{^{LiC (SO 2 R 27) (}} SO 2 R 28) (SO 2 R 29), LiN (SO 2 OR 30) (SO 2 OR 31), LiN (SO 2 R 32) (SO 2 R 33) ( where R ^{27 to} R ^{33, which} may be the same or different, are perfluoroalkyl groups having 1 to 8 carbon atoms). These electrolytes may be used alone or in combination of two or more.
Of these, a lithium salt is particularly preferable, and further, LiPF ₆ , LiBF ₄ , LiOSO ₂ C _k F _(2k+1) (k=1 to 8), LiClO ₄ , LiAsF ₆ , LiNSO ₂ [C _k F _{( 2k+1)} ] ₂ (k=1 to 8 integer) and LiPF _n [C _k F _(2k+1) ] _(6-n) (n=1 to 5 and k=1 to 8 integer) are preferable.
The electrolyte in the present embodiment is usually contained in the non-aqueous electrolyte at a concentration of 0.1 mol/L to 3 mol/L, preferably 0.5 mol/L to 2 mol/L.

In the non-aqueous electrolytic solution of the present embodiment, when a cyclic carboxylic acid ester such as γ-butyrolactone is also used as the non-aqueous solvent, it is particularly desirable to contain LiPF ₆ . Since LiPF ₆ has a high dissociation degree, it can increase the conductivity of the electrolytic solution and further has an action of suppressing the reductive decomposition reaction of the electrolytic solution on the negative electrode. LiPF ₆ may be used alone, or LiPF ₆ and an electrolyte other than that may be used. As the electrolyte other than that, any of those generally used as an electrolyte for a non-aqueous electrolyte can be used, but among the specific examples of the above-mentioned lithium salt, a lithium salt other than LiPF ₆ is preferable. ..
Specific examples, LiPF ₆ and LiBF _4, LiPF ₆ and _{LiN [SO 2 C k F (} 2k + 1)] 2 (k = 1~8 integer), LiPF ₆ and LiBF ₄ and LiN _{[SO 2} C k _{F ( 2k+1)} ] (k is an integer of 1 to 8) and the like.

The ratio of LiPF _{6 in} the lithium salt is 1% by mass to 100% by mass, preferably 10% by mass to 100% by mass, and more preferably 50% by mass to 100% by mass. Such an electrolyte is preferably contained in the non-aqueous electrolyte at a concentration of 0.1 mol/L to 3 mol/L, preferably 0.5 mol/L to 2 mol/L.

Further, the non-aqueous electrolytic solution of the present embodiment can also contain an overcharge preventing agent.
Examples of the overcharge inhibitor include biphenyl, alkylbiphenyl, terphenyl (o-, m-, p-form) and terphenyl (o-, m-, p-form) partially hydrogenated products (for example, 1, 2 -Dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl), cyclohexylbenzene, t-butylbenzene, 1,3-di-t-butylbenzene, t-amylbenzene, diphenylether, dibenzofuran Aromatic compounds such as fluorotoluene (o-, m-, p-form), difluorotoluene, trifluorotoluene, tetrafluorotoluene, pentafluorotoluene, fluorobenzene, difluorobenzene (o-, m-, p-form) ), 1-fluoro-4-t-butylbenzene, 2-fluorobiphenyl, fluorocyclohexylbenzene (for example, 1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene. And fluorinated anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole.
Of these, the aromatic compounds exemplified above are preferable.
The overcharge preventing agent may be used alone or in combination of two or more kinds.
In the case of using two or more kinds in combination, in particular, a combination of cyclohexylbenzene and t-butylbenzene or t-amylbenzene, biphenyl, alkylbiphenyl, terphenyl, a partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, It is desirable to use at least one selected from oxygen-free aromatic compounds such as t-amylbenzene and at least one selected from oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran in combination with overcharge prevention characteristics and high-temperature storage characteristics. Is preferable from the standpoint of balance.

When the non-aqueous electrolytic solution of the present embodiment contains an overcharge inhibitor, the content of the overcharge inhibitor is not particularly limited, for example, 0.1 mass% or more, preferably 0.2 mass% or more, It is more preferably 0.3% by mass or more, and particularly preferably 0.5% by mass or more.
The content of the overcharge inhibitor is, for example, 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 2% by mass or less.

The non-aqueous electrolyte solution of the present embodiment may contain at least one compound other than the above-mentioned compounds as an additive as long as the object of the present invention is not impaired.
Specific examples of other compounds include sulfuric acid esters such as dimethyl sulfate, diethyl sulfate, ethylene sulfate, propylene sulfate, butene sulfate, penten sulfate, and vinylene sulfate; and sulfur compounds such as sulfolane, 3-sulfolene, and divinylsulfone. Can be mentioned.
These compounds may be used alone or in combination of two or more.
Of these, ethylene sulfate, propylene sulfate, butene sulfate, and pentene sulfate are preferable.

[Lithium secondary battery]
The lithium secondary battery of the present embodiment includes a negative electrode, a positive electrode, and the nonaqueous electrolytic solution of the present embodiment.
Usually, a separator is provided between the negative electrode and the positive electrode.

(Negative electrode)
The negative electrode active material constituting the negative electrode is metallic lithium, a lithium-containing alloy, a metal or an alloy capable of alloying with lithium, an oxide capable of doping/dedoping with lithium ions, and a doping/dedoping of lithium ions. At least one selected from the group consisting of possible transition metal nitrides and carbon materials capable of doping/dedoping lithium ions (may be used alone, or a mixture containing two or more of these may be used). May be used) can be used.

Examples of metals or alloys that can be alloyed with lithium (or lithium ions) include silicon, silicon alloys, tin, and tin alloys. Alternatively, lithium titanate may be used.
Among these, carbon materials capable of doping/dedoping lithium ions are preferable. Examples of such carbon materials include carbon black, activated carbon, graphite materials (artificial graphite, natural graphite), amorphous carbon materials, and the like. The form of the carbon material may be any of fibrous, spherical, potato-like and flake-like forms.

Specific examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) calcined at 1500° C. or lower, and meso-paze bitch carbon fiber (MCF).
Examples of the graphite material include natural graphite and artificial graphite. As the artificial graphite, graphitized MCMB, graphitized MCF or the like is used. As the graphite material, a material containing boron can be used. As the graphite material, a material coated with a metal such as gold, platinum, silver, copper or tin, a material coated with amorphous carbon, or a material mixed with amorphous carbon and graphite can be used.

These carbon materials may be used alone or in combination of two or more.
As the carbon material, a carbon material having a (002) plane spacing d(002) of 0.340 nm or less measured by X-ray analysis is particularly preferable. Further, as the carbon material, graphite having a true density of 1.70 g/cm ³ or more or a highly crystalline carbon material having a property close to that is also preferable. By using the above carbon materials, the energy density of the battery can be increased.

(Positive electrode)
Examples of the positive electrode active material forming the positive electrode include transition metal oxides or transition metal sulfides such as MoS ₂ , TiS ₂ , MnO ₂ , and V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiNi _X Co _(1-X) O ₂ [0<X<1], Li _1+α Me _1-α O ₂ (Me is a transition metal element containing Mn, Ni, and Co, having an α-NaFeO ₂ type crystal structure, 1.0≦(1+α)/(1-α)≦1.6), LiNi _x Co _y Mn _z O ₂ [x+y+z=1, 0<x<1, 0<y<1, 0<z<1] _{(e.g., LiNi 0.33 Co 0.33 Mn 0.33 O} 2, LiNi 0.5 Co 0.2 Mn 0.3 O 2 , _etc.), a composite consisting of lithium and transition metals such as LiFePO 4, LiMnPO ₄ Examples thereof include conductive polymer materials such as oxides, polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline complex. Among these, a composite oxide composed of lithium and a transition metal is particularly preferable. When the negative electrode is lithium metal or a lithium alloy, a carbon material can be used as the positive electrode. Alternatively, a mixture of a composite oxide of lithium and a transition metal and a carbon material can be used as the positive electrode.
The positive electrode active material may be used alone or in combination of two or more. When the positive electrode active material has insufficient conductivity, it can be used together with a conductive auxiliary agent to form a positive electrode. Examples of the conductive aid include carbon materials such as carbon black, amorphous whiskers, and graphite.

(Separator)
The separator is a film that electrically insulates the positive electrode and the negative electrode and allows lithium ions to pass therethrough, and examples thereof include a porous film and a polymer electrolyte.
A microporous polymer film is preferably used as the porous film, and examples of the material include polyolefin, polyimide, polyvinylidene fluoride, polyester and the like.
In particular, porous polyolefin is preferable, and specific examples thereof include a porous polyethylene film, a porous polypropylene film, and a multilayer film of a porous polyethylene film and a 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 non-aqueous electrolytic solution of this embodiment may be used for the purpose of swelling a polymer to obtain a polymer electrolyte.

(Battery configuration)
The lithium secondary battery of the present embodiment includes the above negative electrode active material, positive electrode active material and separator.
The lithium secondary battery of the present embodiment can take various known shapes, and can be formed in any shape such as a cylindrical shape, a coin shape, a square shape, and a film shape. However, the basic structure of the battery is the same regardless of the shape, and the design can be changed according to the purpose.
As an example of the lithium secondary battery (non-aqueous electrolyte secondary battery) of the present embodiment, the coin battery shown in FIG. 1 can be mentioned.
In the coin-type battery shown in FIG. 1, the disc-shaped negative electrode 2, the separator 5 injecting the non-aqueous electrolyte, the disc-shaped positive electrode 1, and, if necessary, the spacer plates 7 and 8 made of stainless steel or aluminum are arranged in this order. In the laminated state, the positive electrode can 3 (hereinafter, also referred to as “battery can”) and the sealing plate 4 (hereinafter, also referred to as “battery can lid”) are housed. The positive electrode can 3 and the sealing plate 4 are caulked and sealed via a gasket 6.
In this example, the nonaqueous electrolytic solution of the present embodiment can be used as the nonaqueous electrolytic solution injected into the separator 5.

The lithium secondary battery according to the present embodiment is a lithium secondary battery (a lithium secondary battery before charging/discharging) that includes a negative electrode, a positive electrode, and the nonaqueous electrolytic solution according to the present embodiment. It may be a lithium secondary battery obtained by the above.
That is, the lithium secondary battery of the present embodiment, first, to prepare a lithium secondary battery before charging and discharging including a negative electrode, a positive electrode, and the nonaqueous electrolytic solution of the present embodiment, and then this charging and discharging It may be a lithium secondary battery (charged and discharged lithium secondary battery) produced by charging and discharging the previous lithium secondary battery one or more times.

The application of the lithium secondary battery of the present embodiment is not particularly limited, and it can be used for various known applications. For example, laptops, mobile computers, cell phones, headphone stereos, video movies, LCD TVs, handy cleaners, electronic organizers, calculators, radios, backup power supplies, motors, automobiles, electric vehicles, motorcycles, electric motorcycles, bicycles, electric vehicles. It can be widely used for small portable devices and large devices such as bicycles, lighting equipment, game machines, watches, electric tools, and cameras.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.
In addition, in the following examples, "wt%" represents mass %.
In addition, in the following examples, the "addition amount" represents the content in the finally obtained non-aqueous electrolytic solution (that is, the amount based on the total amount of the finally obtained non-aqueous electrolytic solution).

[Example 1]
A lithium secondary battery was produced by the following procedure.
<Production of negative electrode>
20 parts by mass of artificial graphite, 80 parts by mass of natural graphite-based graphite, 1 part by mass of carboxymethyl cellulose and 2 parts by mass of SBR latex were kneaded with a water solvent to prepare a paste-like negative electrode mixture slurry.
Next, this negative electrode mixture slurry is applied to a negative electrode current collector made of strip-shaped copper foil having a thickness of 18 μm, dried, and then compressed by a roll press to form a sheet-shaped negative electrode composed of the negative electrode current collector and the negative electrode active material layer. Got At this time, the coating density of the negative electrode active material layer was 10 mg/cm ² , and the filling density was 1.5 g/ml.

<Production of positive electrode>
90 parts by mass of LiCoO ₂ , 5 parts by mass of acetylene black and 5 parts by mass of polyvinylidene fluoride were kneaded with N-methylpyrrolidinone as a solvent to prepare a paste-like positive electrode mixture slurry.
Next, the positive electrode mixture slurry is applied to a positive electrode current collector of a strip-shaped aluminum foil having a thickness of 20 μm, dried, and then compressed by a roll press to obtain a sheet-shaped positive electrode composed of the positive electrode current collector and the positive electrode active material. Obtained. At this time, the coating density of the positive electrode active material layer was 30 mg/cm ² and the filling density was 2.5 g/ml.

<Preparation of non-aqueous electrolyte>
Ethylene carbonate (EC), dimethyl carbonate (DMC), and methyl ethyl carbonate (EMC) were mixed at a ratio of 30:35:35 (mass ratio) as a non-aqueous solvent to obtain a mixed solvent.
LiPF ₆ , which is an electrolyte, was dissolved in the obtained mixed solvent so that the electrolyte concentration in the finally obtained non-aqueous electrolyte was 1 mol/liter.
The above-exemplified compound (1) (addition amount: 0.5 wt %) was added as an additive (specific boron compound) to the solution obtained above to obtain a non-aqueous electrolytic solution.

<Preparation of coin type battery>
The above-mentioned negative electrode was punched into a disk shape with a diameter of 14 mm and the above-mentioned positive electrode with a diameter of 13 mm to obtain coin-shaped electrodes (negative electrode and positive electrode). Further, a 20 μm thick microporous polyethylene film was punched into a disc shape having a diameter of 17 mm to obtain a separator.
The obtained coin-shaped negative electrode, separator and coin-shaped positive electrode were laminated in this order in a stainless steel battery can (2032 size), and 20 μl of the non-aqueous electrolyte was injected to contain the separator, the positive electrode and the negative electrode. Let it soak.
Further, an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring are placed on the positive electrode, and the battery can lid is caulked through a polypropylene gasket to seal the battery, and the diameter is 20 mm and height. A coin type lithium secondary battery (hereinafter, referred to as a test battery) having a configuration of 3.2 mm and having the configuration shown in FIG. 1 was produced.
Each measurement was performed on the obtained coin type battery (test battery).

[Evaluation method]
<Battery resistance characteristics: Battery resistance after storage>
The coin type battery was charged at a constant voltage of 4.2 V, and then the charged coin type battery was stored in a thermostat at 80° C. for 2 days. The coin-type battery after storage is cooled to −20° C. in a constant temperature bath, discharged at −20° C. with a constant current of 0.2 mA, and the potential drop is measured for 10 seconds from the start of discharge to obtain a coin-type battery. DC resistance [Ω] (−20° C.) of was measured. The obtained value was set as a resistance value [Ω] (−20° C.) after storage.
The resistance value [Ω] (−20° C.) after storage was similarly measured for the coin-type battery of Comparative Example 1 described later.
From these results, the resistance value after storage (relative value; %) in Example 1 when the resistance value after storage [Ω] (−20° C.) in Comparative Example 1 was 100% was calculated by the following formula: "Battery resistance after storage [%]" was determined.
The results obtained are shown in Table 1.

Battery resistance after storage [%]
=(resistance value after storage [Ω] in Example 1/resistance value after storage [Ω] in Comparative Example 1)×100[%]

[Comparative Example 1]
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the exemplified compound (1) was not added (that is, no additive was added). The battery was manufactured and evaluated in the same manner as in Example 1. The results obtained are shown in Table 1.

[Example 2]
A non-aqueous electrolyte solution was prepared in the same manner as in Example 1 except that the amount of Exemplified Compound (1) was changed to that of Exemplified Compound (2). The battery was manufactured and evaluated in the same manner as in Example 1. The results obtained are shown in Table 1.

[Example 3]
A non-aqueous electrolyte solution was prepared in the same manner as in Example 1, except that the amount of Exemplified Compound (1) in Example 1 was changed to the same amount as Exemplified Compound (19). The battery was manufactured and evaluated in the same manner as in Example 1. The results obtained are shown in Table 1.

[Comparative Example 2]
A nonaqueous electrolytic solution was prepared in the same manner as in Example 1 except that the exemplified compound (1) was changed to the same addition amount of the trimethyl borate compound in Example 1. The battery was manufactured and evaluated in the same manner as in Example 1. The results obtained are shown in Table 1.

-Explanation of Table 1-
-"None" in the column of additive means that the additive was not used.
“Amount (wt %)” indicates the amount of additive (content in the finally obtained non-aqueous electrolyte) (mass %).

In Table 1, as is clear from the results of Examples 1 to 3 and Comparative Examples 1 and 2, a non-aqueous electrolytic solution containing no additive (Comparative Example 1) and a trimethyl borate compound as an additive were contained. In contrast to the non-aqueous electrolyte solution (Comparative Example 2), the non-aqueous electrolyte solution (Examples 1 to 3) containing an exemplary compound that is a specific boron compound as an additive was stored at high temperature (80° C. for 2 days). It can be seen that the battery resistance of the latter) is reduced.

1 Positive Electrode 2 Negative Electrode 3 Positive Electrode Can 4 Sealing Plate 5 Separator 6 Gasket 7, 8 Spacer Plate

Claims (9)

A non-aqueous electrolyte for a lithium secondary battery, containing a boron compound represented by the following general formula (1) or the following general formula (2).


(In the general formula (1), R ¹¹ and R ¹² are integrally formed with R ¹¹ and R ^12, and the boron atom, the oxygen atom adjacent to R ¹¹ and the adjacent R ^{12 in} the general formula (1) are adjacent to each other. Represents a group forming a ring having 2 to 12 carbon atoms together with the oxygen atom, and n in formula (1) represents 1 or 2.
In the general formula (1), R ^{13 to} R ¹⁵ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl having 6 to 12 carbon atoms. Represents a group. However, in the general formula (1), when n is 2, two R ¹⁴ may be the same or different, and two R ¹⁵ may be the same or different.
In formula ^{(2), R 21} and ^{R 22,} together with ^{R 21} and ^{R 22} has the general formula (2) boron atom ^in, adjacent to the ^{R 21} adjacent oxygen atoms, and the ^{R 22} It represents a group forming a ring having 2 to 12 carbon atoms together with an oxygen atom.
In formula (2), R ^{23 to} R ²⁵ are each independently a hydrogen atom, a halogen atom, an alkyl group having 1 to 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, or an aryl group having 6 to 12 carbon atoms. Represents a group. ) The non-aqueous electrolyte for a lithium secondary battery according to claim 1, which contains a boron compound represented by the general formula (2). In the general formula (1), R ¹¹ and R ¹² are integrated together to form a carbon atom together with the boron atom in the general formula (1), the oxygen atom adjacent to R ^11, and the oxygen atom adjacent to R ^12. The group forming a ring of 2 to 12 is a group represented by the following formula (a), and in the general formula (2), R ²¹ and R ²² are integrated to form the general formula (2). The group forming a ring having 2 to 12 carbon atoms together with the boron atom therein, the oxygen atom adjacent to R ²¹ and the oxygen atom adjacent to R ²² is a group represented by the following formula (a): Alternatively, the nonaqueous electrolytic solution for a lithium secondary battery according to claim 2.
The carbon-carbon unsaturated bond or a carbonate compound having a fluorine atom, a fluorophosphoric acid compound, an oxalato compound and at least one compound selected from the group consisting of cyclic sulfonates, further containing at least one compound. A non-aqueous electrolyte solution for a lithium secondary battery as described above. Positive electrode, metallic lithium, lithium-containing alloy, metal or alloy capable of alloying with lithium, oxide capable of doping/dedoping lithium ion, transition metal nitride capable of doping/dedoping of lithium ion, And a negative electrode containing, as a negative electrode active material, at least one selected from the group consisting of carbon materials capable of doping and dedoping lithium ions, and the negative electrode according to any one of claims 1, 2 and 4. lithium secondary battery comprising a non-aqueous, and electrolytic solution for a lithium secondary battery. A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to claim 5. 4. The lithium dioxide according to claim 3, further comprising at least one compound selected from the group consisting of a carbonate compound having a carbon-carbon unsaturated bond or a fluorine atom, a fluorophosphoric acid compound, an oxalato compound and a cyclic sulfonate ester. Non-aqueous electrolyte for secondary battery. Positive electrode, metallic lithium, lithium-containing alloy, metal or alloy capable of alloying with lithium, oxide capable of doping/dedoping lithium ion, transition metal nitride capable of doping/dedoping of lithium ion, And a negative electrode containing at least one selected from the group consisting of carbon materials capable of doping/dedoping lithium ions as a negative electrode active material, and the non-aqueous electrolysis for a lithium secondary battery according to claim 3 or 7. And a lithium secondary battery containing the liquid. A lithium secondary battery obtained by charging and discharging the lithium secondary battery according to claim 8.