JP4961714B2 - Pentafluorophenyloxy compound, non-aqueous electrolyte using the same, and lithium secondary battery - Google Patents

Description

  The present invention relates to a novel pentafluorophenyloxy compound useful as an intermediate raw material for various materials or a battery material, a method for producing the compound, a non-aqueous electrolyte containing the compound, and a lithium secondary battery.

In recent years, lithium secondary batteries have been widely used as power sources for driving small electronic devices and the like. The lithium secondary battery is mainly composed of a positive electrode made of a lithium composite oxide, a negative electrode made of a carbon material or lithium metal, and a non-aqueous electrolyte. As the non-aqueous electrolyte, carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) are used.
Lithium secondary batteries using, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO _2, etc. as the positive electrode are partially decomposed by oxidation of the solvent in the non-aqueous electrolyte during charging. Inhibiting the desired electrochemical reaction of the battery causes a decrease in battery performance. This is considered to be due to the electrochemical oxidation of the solvent at the interface between the positive electrode material and the non-aqueous electrolyte.
In addition, as a negative electrode, for example, a lithium secondary battery using a highly crystallized carbon material such as natural graphite or artificial graphite, the solvent in the non-aqueous electrolyte undergoes reductive decomposition on the negative electrode surface during charging, and the non-aqueous electrolyte solvent As for EC which is widely used as a part, reductive decomposition occurs partly during repeated charge and discharge, resulting in a decrease in battery performance.

For improving the battery performance of this lithium secondary battery, for example, Patent Documents 1 to 6 are known.
Patent Document 1 discloses a lithium secondary battery to which a pentafluorobenzene compound having an electron donating group such as pentafluoroanisole is added. This coin battery has a discharge capacity maintenance rate of about 80% after 200 cycles. And the cycle characteristics are not sufficient.
Patent Document 2 describes that pentafluoroanisole can be used as a redox reagent as a chemical overcharge protection means for a non-aqueous electrolyte secondary battery, but there is no description regarding cycle characteristics.
Patent Document 3 suggests a nonaqueous electrolytic solution containing 2-propynylphenyl carbonate, and Patent Document 4 suggests a nonaqueous electrolytic solution containing 2-propynylphenyl oxalate.
Example 5 of Patent Document 5 describes a nonaqueous electrolytic solution containing pentafluorophenyl methyl carbonate, and Patent Document 6 discloses pentafluorophenyl methanesulfonate and the like, vinylene carbonate and / or 1,3-propane sultone. Non-aqueous electrolytes containing are described.
These non-aqueous electrolytes have improved batteries to some extent, but demands for high capacity and long life are increasing, and further performance improvements are required.

US Patent Application Publication No. 2002/110735 JP-A-7-302614 JP 2000-195545 A JP 2002-124297 A International Publication No. 03/77351 Pamphlet International Publication No. 05/29631 Pamphlet

  The present invention provides a novel pentafluorophenyl compound useful as an intermediate raw material of various materials or a battery material, a method for producing the same, and a lithium secondary battery excellent in battery characteristics such as electric capacity, cycle characteristics, and storage characteristics. An object of the present invention is to provide a non-aqueous electrolyte and a lithium secondary battery that can be used.

The present inventors can provide a lithium secondary battery having excellent cycle characteristics and the like by synthesizing a novel pentafluorophenyloxy compound such as pentafluorophenylmethyl oxalate and including it in a non-aqueous electrolyte. The present invention has been completed.
That is, the present invention provides the following (1) to (4).
(1) A pentafluorophenyloxy compound represented by the following general formula (I).

(In the formula, R ¹ represents a —COCO— group, an S═O group, or an S (═O) ₂ group, and R ² represents an alkyl group having 1 to 12 carbon atoms and a cycloalkyl having 3 to 12 carbon atoms. Group, an alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 3 to 12 carbon atoms, an aryl group having 6 to 18 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms, provided that the hydrogen atom of R ² has One or more may be substituted with a halogen atom, and when R ¹ is a —COCO— group, R ² does not contain an aryl group.)
(2) Pentafluorophenol and an acid halide or halogen represented by the general formula R ² O—R ¹ —X (wherein X represents a halogen atom, and R ¹ and R ² are the same as above). A method for producing a pentafluorophenyloxy compound represented by the following general formula (I), wherein thionyl chloride is reacted in the presence of a base.
(3) In a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, the non-aqueous electrolyte solution contains a pentafluorophenyloxy compound represented by the following general formula (II) or (III) A feature of non-aqueous electrolyte.

(In the formula, R ³ represents a —COCO— group, a C═O group, an S═O group, or S (═O) ₂ , and R ⁴ represents an alkyl group having 1 to 12 carbon atoms and 3 to 3 carbon atoms. A cycloalkyl group having 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 3 to 12 carbon atoms, an aryl group having 6 to 18 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms, provided that R ⁴ represents One or more hydrogen atoms may be substituted with a halogen atom, and when R ³ is a C═O group, R ⁴ is an alkenyl group having 2 to 12 carbon atoms or 3 to 12 carbon atoms. An alkynyl group.)

（式中、Ｙは、アルカリ金属又はアルカリ土類金属を示し、ｎは１又は２を示す。）
（４）正極、負極及び非水溶媒に電解質塩が溶解されている非水電解液からなるリチウム二次電池において、該非水電解液中に前記一般式（II）又は（III）で表されるペンタフルオロフェニルオキシ化合物を含有することを特徴とするリチウム二次電池。

(In the formula, Y represents an alkali metal or an alkaline earth metal, and n represents 1 or 2.)
(4) In a lithium secondary battery comprising a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a non-aqueous solvent, the non-aqueous electrolyte solution is represented by the general formula (II) or (III). A lithium secondary battery comprising a pentafluorophenyloxy compound.

ADVANTAGE OF THE INVENTION According to this invention, the novel pentafluorophenyloxy compound useful as intermediate raw materials, such as a pharmaceutical, an agricultural chemical, an electronic material, a polymeric material, or a battery material, and its manufacturing method can be provided.
In addition, by including the pentafluorophenyloxy compound represented by the general formula (II) or (III) as an additive in the non-aqueous electrolyte, battery characteristics such as electric capacity, cycle characteristics, and storage characteristics can be obtained. It is possible to provide a lithium secondary battery that can exhibit excellent battery performance over a long period of time.

[New pentafluorophenyloxy compound]
The novel pentafluorophenyloxy compound of the present invention is represented by the following general formula (I).

In the formula, R ¹ represents a —COCO— group, an S═O group, or an S (═O) ₂ group, and R ² represents an alkyl group having 1 to 12 carbon atoms and a cycloalkyl group having 3 to 12 carbon atoms. , An alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 3 to 12 carbon atoms, an aryl group having 6 to 18 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms. However, one or more hydrogen atoms of R ² may be substituted with a halogen atom such as a fluorine atom or a chlorine atom, and when R ¹ is a —COCO— group, R ² does not contain an aryl group. .

In R ² of the general formula (I), the alkyl group having 1 to 12 carbon atoms includes methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, nonyl group, decyl group. And a dodecyl group. In these, a C1-C6 alkyl group is preferable and C1-C4 alkyl groups, such as a methyl group, an ethyl group, a propyl group, a butyl group, are especially preferable. These may be branched alkyl groups such as isopropyl group and tert-butyl group.
Examples of the cycloalkyl group having 3 to 12 carbon atoms, preferably 3 to 7 carbon atoms, include a cyclopropyl group and a cyclohexyl group, and the alkenyl group having 2 to 12 carbon atoms, preferably 2 to 6 carbon atoms. Are vinyl group, 2-propenyl group, 2-butenyl group, 3-butenyl group, 4-pentenyl group and the like. As the alkynyl group having 3 to 12 carbon atoms, preferably 3 to 7 carbon atoms, 2- A propynyl group, a 2-butynyl group, a 3-butynyl group, a 4-pentynyl group, a 5-hexynyl group, and the like. Examples of the aryl group having 6 to 18 carbon atoms include a pentafluorophenyl group, a heptafluoronaphthyl group, and a perfluoro group. A biphenyl group etc. are mentioned, As a C7-C20 aralkyl group, a benzyl group, a trityl group, etc. are mentioned.

Preferable examples of the compound in which R ¹ is a —COCO— group include pentafluorophenylmethyl oxalate, pentafluorophenylethyl oxalate, pentafluorophenylbutyl oxalate, pentafluorophenylcyclohexyl oxalate and the like.
Among these, from the viewpoint of applicability to various substances and materials, pentafluorophenylmethyl oxalate or pentafluorophenylethyl oxalate having an alkyl group is particularly preferable.

Preferable examples of the compound in which R ¹ is an S═O group include pentafluorophenyl methyl sulfite, pentafluorophenyl ethyl sulfite, pentafluorophenyl butyl sulfite, pentafluorophenyl cyclohexyl sulfite, and 2-propenyl pentafluorophenyl. Examples thereof include sulfite, 2-propynyl pentafluorophenyl sulfite, and bis (pentafluorophenyl) sulfite.
Among these, pentafluorophenyl methyl sulfite, pentafluorophenyl ethyl sulfite, 2-propynyl pentafluorophenyl sulfite, and bis (pentafluorophenyl) sulfite are preferable from the viewpoint of applicability to various substances and materials. .

Preferable examples of the compound in which R ¹ is S (═O) ₂ group include pentafluorophenyl methyl sulfate, pentafluorophenyl ethyl sulfate, pentafluorophenyl butyl sulfate, pentafluorophenyl cyclohexyl sulfate, and 2-propenyl. Examples thereof include pentafluorophenyl sulfate, 2-propynyl pentafluorophenyl sulfate, and bis (pentafluorophenyl) sulfate.
Among these, from the viewpoint of applicability to various substances and materials, pentafluorophenyl methyl sulfate, pentafluorophenyl ethyl sulfate, and bis (pentafluorophenyl) sulfate are preferable.

[Method for producing novel pentafluorophenyloxy compound]
Although there is no restriction | limiting in particular in the manufacturing method of the pentafluorophenyloxy compound represented by general formula (I), According to the method of this invention, it can manufacture efficiently. That is, an acid halide or halogenation represented by pentafluorophenol and a general formula R ² O—R ¹ —X (wherein X represents a halogen atom, and R ¹ and R ² are the same as described above). It is preferable to react with thionyl in the presence of a base.
The acid halide represented by the general formula R ² O—R ¹ —X is preferably an acid chloride represented by the general formula R ² O—R ¹ —Cl, for example, methyl chloroglyoxylate, ethyl chloroglyoxylate, chloro Examples thereof include propynyl glyoxylate and propynyl chloroformate. Further, as the thionyl halide, thionyl chloride is preferable.
In this reaction, acid halide or thionyl halide is usually used in an amount of 0.5 to 2 mol, preferably 0.8 to 1.5 mol, per 1 mol of pentafluorophenol.

Examples of the base used in the method of the present invention include amines such as pyridine, picoline, lutidine, dimethylaminopyridine, trimethylamine, triethylamine and diisopropylethylamine, alkali metal carbonates such as potassium carbonate, sodium carbonate and sodium hydrogencarbonate, sodium hydroxide Alkali metal hydroxides such as potassium hydroxide, alkaline earth metal hydroxides such as calcium hydroxide, alkali metal alkoxides such as sodium methoxide, sodium ethoxide and potassium tert-butoxide. Among these, amines such as pyridine, picoline and triethylamine are particularly preferable.
The usage-amount of a base is 0.01-0.2 mol normally with respect to 1 mol of pentafluorophenol, Preferably it is 0.02-0.15 mol. The reaction is preferably carried out in a solvent such as a halogenated hydrocarbon such as dichloromethane, dichloroethane or chloroform, an aromatic hydrocarbon such as benzene or toluene, or an ether such as diethyl ether, tetrahydrofuran or dioxane.
The reaction temperature is generally −10 ° C. to 80 ° C., preferably −5 ° C. to 50 ° C., particularly preferably 0 ° C. to 40 ° C.

[Non-aqueous electrolyte]
The nonaqueous electrolytic solution of the present invention contains a pentafluorophenyloxy compound represented by the following general formula (II) or (III) in a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent. It is characterized by.

(In the formula, R ³ represents a —COCO— group, a C═O group, an S═O group, or S (═O) ₂ , and R ⁴ represents an alkyl group having 1 to 12 carbon atoms and 3 to 3 carbon atoms. A cycloalkyl group having 12 carbon atoms, an alkenyl group having 2 to 12 carbon atoms, an alkynyl group having 3 to 12 carbon atoms, an aryl group having 6 to 18 carbon atoms, or an aralkyl group having 7 to 20 carbon atoms, provided that R ⁴ represents One or more hydrogen atoms may be substituted with a halogen atom, and when R ³ is a C═O group, R ⁴ is an alkenyl group having 2 to 12 carbon atoms or 3 to 12 carbon atoms. An alkynyl group.)

（式中、Ｙは、アルカリ金属又はアルカリ土類金属を示し、ｎは１又は２を示す。）

(In the formula, Y represents an alkali metal or an alkaline earth metal, and n represents 1 or 2.)

  In the nonaqueous electrolytic solution of the present invention, if the content of the pentafluorophenyloxy compound represented by the general formula (II) or (III) is excessively large, battery performance may be deteriorated, and excessively small. The expected battery performance cannot be obtained. Therefore, the content of the pentafluorophenyloxy compound is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and most preferably 0.3% by weight or more based on the weight of the non-aqueous electrolyte. The upper limit thereof is preferably 10% by weight or less, more preferably 5% by weight or less, and most preferably 3% by weight or less based on the weight of the non-aqueous electrolyte.

Among R ^{3 in} the general formula (II), from the viewpoint of improving battery characteristics such as cycle characteristics, a —COCO— group, a C═O group, or a S═O group is preferable, a —COCO— group or a S═O group. Is particularly preferred.
R ^{4 in the} general formula (II) may be a fluorophenyl group or a pentafluorophenyl group in which at least one of the hydrogen atoms of R ⁴ is substituted with a halogen atom such as a fluorine atom or a chlorine atom. When R ³ is a C═O group, R ⁴ is an alkenyl group having 2 to 12 carbon atoms, preferably 3 to 6 carbon atoms, or 3 to 12 carbon atoms, preferably 3 to 7 carbon atoms. It is.
R ⁴ is an alkyl group having 1 to 12 carbon atoms, preferably 1 to 6 carbon atoms, 3 to 12 carbon atoms, preferably a cycloalkyl group having 3 to 7 carbon atoms, 2 to 12 carbon atoms, preferably carbon atoms. Examples of the alkenyl group having 2 to 6 carbon atoms and the alkynyl group having 3 to 12 carbon atoms, preferably 3 to 7 carbon atoms include those described above as R ^{2 in the} general formula (I).
In addition, examples of the aryl group having 6 to 18 carbon atoms include a phenyl group, a fluorophenyl group, and a pentafluorophenyl group, and examples of the aralkyl group having 7 to 20 carbon atoms include a benzyl group and a trityl group.

Preferable examples of the compound in which R ³ is a —COCO— group include pentafluorophenylmethyl oxalate, pentafluorophenylethyl oxalate, pentafluorophenylbutyl oxalate, pentafluorophenylcyclohexyl oxalate, and 2-propenylpentaoxalate. Examples thereof include fluorophenyl, 2-propynylpentafluorophenyl oxalate, pentafluorophenylphenyl oxalate, bis (pentafluorophenyl) oxalate, and pentafluorophenylbenzyl oxalate.
Among these, from the viewpoint of improving battery characteristics such as cycle characteristics, pentafluorophenylmethyl oxalate or pentafluorophenylethyl oxalate having an alkyl group, or 2-propynylpentafluorophenyl oxalate having an alkynyl group is particularly preferable. .

Preferred examples of the compound in which R ³ is a C═O group include vinyl pentafluorophenyl carbonate, 2-propenyl pentafluorophenyl carbonate, 3-propenyl pentafluorophenyl carbonate, 2-propynyl pentafluorophenyl carbonate, and 2-butynyl. Examples include pentafluorophenyl carbonate, 3-butynyl pentafluorophenyl carbonate, and 4-pentynyl pentafluorophenyl carbonate.
Among these, 2-propynylpentafluorophenyl carbonate is particularly preferable from the viewpoint of improving battery characteristics such as cycle characteristics.

Preferable examples of the compound in which R ³ is an S═O group include pentafluorophenyl methyl sulfite, pentafluorophenyl ethyl sulfite, pentafluorophenyl butyl sulfite, pentafluorophenyl cyclohexyl sulfite, and 2-propenyl pentafluorophenyl. Examples thereof include sulfite, 2-propynyl pentafluorophenyl sulfite, pentafluorophenyl phenyl sulfite, bis (pentafluorophenyl) sulfite, and pentafluorophenyl benzyl sulfite.
Among these, from the viewpoint of improving battery characteristics such as cycle characteristics, pentafluorophenyl methyl sulfite, pentafluorophenyl ethyl sulfite, 2-propynyl pentafluorophenyl sulfite, and bis (pentafluorophenyl) sulfite are preferable. Bis (pentafluorophenyl) sulfite is particularly preferred.

Preferable examples of the compound in which R ³ is S (═O) ₂ group include pentafluorophenyl methyl sulfate, pentafluorophenyl ethyl sulfate, pentafluorophenyl butyl sulfate, pentafluorophenyl cyclohexyl sulfate, and 2-propenyl. Examples include pentafluorophenyl sulfate, 2-propynyl pentafluorophenyl sulfate, pentafluorophenyl phenyl sulfate, bis (pentafluorophenyl) sulfate, and pentafluorophenyl benzyl sulfate.
Among these, from the viewpoint of improving battery characteristics such as cycle characteristics, pentafluorophenyl methyl sulfate, pentafluorophenyl ethyl sulfate, and bis (pentafluorophenyl) sulfate are particularly preferable.

In the general formula (III), Y is an alkali metal such as Li, Na, or K, or an alkaline earth metal such as Ma, Ca, or Ba.
Preferable examples of the pentafluorophenyloxy compound represented by the general formula (III) include lithium pentafluorophenoxide, sodium pentafluorophenoxide, potassium pentafluorophenoxide, magnesium bispentafluorophenoxide, calcium bispentafluorophenoxide, barium bispenta Examples thereof include fluorophenoxide. Among these, lithium pentafluorophenoxide is particularly preferable from the viewpoint of improving battery characteristics such as cycle characteristics.

[Other additives]
The non-aqueous electrolyte of the present invention includes vinylene carbonate (VC) and 1,3-propane sultone together with a pentafluorophenyloxy compound represented by the general formula (II) or (III) from the viewpoint of improving charge / discharge characteristics. It is preferable to use one or more selected from (PS) and triple bond-containing compounds.
If the content of vinylene carbonate and 1,3-propane sultone is excessively large, battery performance may be deteriorated, and sufficient battery performance expected to be excessively small cannot be obtained. Therefore, the content of vinylene carbonate is preferably 0.1% by volume or more, more preferably 0.5% by volume or more, and most preferably 1% by volume or more with respect to the capacity of the nonaqueous electrolytic solution. Further, the upper limit is preferably 10% by volume or less, more preferably 5% by volume or less, and most preferably 3% by volume or less with respect to the capacity of the non-aqueous electrolyte.
Further, the content of 1,3-propane sultone is preferably 0.1% by volume or more, more preferably 0.5% by volume or more, and most preferably 1% by volume or more with respect to the capacity of the nonaqueous electrolytic solution. Further, the upper limit is preferably 10% by volume or less, more preferably 5% by volume or less, and most preferably 3% by volume or less with respect to the capacity of the non-aqueous electrolyte.

In addition, when the electrode mixture density of the battery is increased in a high-capacity battery, a decrease in cycle characteristics is generally observed. However, the use of a triple bond-containing compound is preferable because the cycle characteristics are improved.
Examples of triple bond-containing compounds include methyl propargyl carbonate (MPC), ethyl propargyl carbonate (EPC), dipropargyl carbonate (DPC), dipropargyl oxalate (DPO), propargyl methanesulfonate, dipropargyl sulfite, and methyl propargyl sulfite. And ethyl propargyl sulfite.
The content of the triple bond-containing compound is preferably 0.01% by volume or more, more preferably 0.1% by volume or more, and most preferably 0.5% by volume or more with respect to the capacity of the nonaqueous electrolytic solution. Further, the upper limit is preferably 10% by volume or less, more preferably 5% by volume or less, and most preferably 3% by volume or less with respect to the capacity of the non-aqueous electrolyte.

[Nonaqueous solvent]
Examples of the nonaqueous solvent used in the nonaqueous electrolytic solution of the present invention include cyclic carbonates, chain carbonates, chain esters, ethers, amides, phosphate esters, sulfones, lactones, and nitriles. , S═O-containing compounds and the like.
Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, fluoroethylene carbonate, dimethyl vinylene carbonate, vinyl ethylene carbonate, etc., and most preferably contains EC having a high dielectric constant. preferable.
Examples of chain carbonates include asymmetric chain carbonates such as methyl ethyl carbonate (MEC), methyl propyl carbonate, methyl butyl carbonate, and ethyl propyl carbonate, dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate, and dibutyl carbonate. Symmetric chain carbonates such as

Examples of the chain esters include methyl propionate, methyl pivalate, butyl pivalate, hexyl pivalate, octyl pivalate, dimethyl oxalate, ethyl methyl oxalate, diethyl oxalate and the like. , Tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane and the like. Examples of amides include dimethylformamide, phosphoric esters such as trimethyl phosphate and trioctyl phosphate, sulfones include divinyl sulfone, lactones include γ-butyrolactone, γ-valerolactone, α-angelica lactone, and the like. Examples of nitriles include acetonitrile and adiponitrile.
S = O-containing compounds include 1,4-propane sultone, divinyl sulfone, 1,4-butanediol dimethane sulfonate, glycol sulfite, propylene sulfite, glycol sulfate, propylene sulfate, dipropargyl sulfite, methyl propargyl sulfite Phyto, ethyl propargyl sulfite, divinyl sulfone and the like.

The above non-aqueous solvents are usually used as a mixture in order to achieve appropriate physical properties. The combination is, for example, a combination of cyclic carbonates and chain carbonates, a combination of cyclic carbonates and lactones, a combination of lactones and chain esters, a combination of cyclic carbonates, lactones and chain esters, Combinations of cyclic carbonates, chain carbonates and lactones, combinations of cyclic carbonates and ethers, combinations of cyclic carbonates, chain carbonates and ethers, cyclic carbonates, chain carbonates and chains Various combinations such as combinations with esters can be mentioned, and the mixing ratio is not particularly limited.
Among these, combinations of cyclic carbonates and chain carbonates are preferable, and specifically, combinations of cyclic carbonates such as EC and PC and chain carbonates such as MEC and DEC are particularly preferable. The ratio of cyclic carbonates to chain carbonates is preferably 20:80 to 40:60, particularly preferably 25:75 to 35:65, as cyclic carbonates: chain carbonates (volume ratio).

Examples of the electrolyte salt used in the present invention include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (SO ₂ CF ₃ ) ₂ , LiN (SO ₂ C ₂ F ₅ ) ₂ , LiCF ₃ SO ₃ , LiC (SO _{2 CF 3) 3, LiPF 4} (CF 3) 2, LiPF 3 (C 2 F 5) 3, LiPF 3 (CF 3) 3, LiPF 3 (iso-C 3 F 7) 3, LiPF 5 (iso-C ₃ Lithium salt containing a chain alkyl group such as F ₇ ) or a cyclic alkylene chain such as (CF ₂ ) ₂ (SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi A lithium salt is mentioned.
Among these, particularly preferable electrolyte salts are LiPF ₆ , LiBF ₄ , and LiN (SO ₂ CF ₃ ) ₂ , and the most preferable electrolyte salt is LiPF ₆ . These electrolyte salts can be used singly or in combination of two or more.

Suitable combinations of these electrolyte salts include combinations of LiPF ₆ and LiBF ₄ , combinations of LiPF ₆ and LiN (SO ₂ CF ₃ ) ₂ , combinations of LiBF ₄ and LiN (SO ₂ CF ₃ ) _2, and the like. Is mentioned. Particularly preferred is a combination of LiPF ₆ and LiBF ₄ , with LiPF ₆ : LiBF ₄ (capacity ratio) of preferably 80:20 to 99: 1, particularly preferably 90:10 to 98: 2.
The electrolyte salt can be mixed in an arbitrary ratio, but the ratio (molar ratio) of the other electrolyte salt in the total electrolyte salt when used in combination with LiPF ₆ is preferably 0.01 to 45%, more Preferably it is 0.03 to 20%, more preferably 0.05 to 10%, and most preferably 0.05 to 5%.
The concentration used by dissolving all the electrolyte salts is usually preferably 0.3M or more, more preferably 0.5M or more, and most preferably 0.7M or more with respect to the non-aqueous solvent. Further, the upper limit is preferably 3M or less, more preferably 2.5M or less, and most preferably 2M or less.

The electrolytic solution of the present invention is prepared, for example, by mixing the above non-aqueous solvent, dissolving the above electrolyte salt and pentafluorophenyloxy compound, and further, if necessary, vinylene carbonate (VC), 1,3-propane. It can be obtained by dissolving at least one selected from sultone (PS) and triple bond-containing compounds.
At this time, the non-aqueous solvent, pentafluorophenyloxy compound, VC, PS, triple bond-containing compound, and other additives to be used should be purified in advance within a range that does not significantly reduce the productivity and have as few impurities as possible. It is preferable to use it.

By including air or carbon dioxide in the non-aqueous electrolyte of the present invention, for example, gas generation due to decomposition of the electrolyte can be suppressed, and battery characteristics such as long-term cycle characteristics and charge storage characteristics can be improved. .
As a method of containing (dissolving) air or carbon dioxide in the non-aqueous electrolyte, (1) a method of bringing the non-aqueous electrolyte into contact with air or a carbon dioxide-containing gas before injecting it into the battery in advance. (2) After pouring, before or after sealing the battery, a method of incorporating air or carbon dioxide-containing gas into the battery can be employed. The air or carbon dioxide-containing gas preferably contains as little water as possible, preferably has a dew point of −40 ° C. or lower, and particularly preferably has a dew point of −50 ° C. or lower.
In the present invention, it is particularly preferable to use an electrolytic solution in which carbon dioxide is dissolved in a nonaqueous electrolytic solution from the viewpoint of improving charge / discharge characteristics at high temperatures. The amount of carbon dioxide dissolved is preferably 0.001% by weight or more, more preferably 0.05% by weight or more, more preferably 0.2% by weight or more, based on the weight of the non-aqueous electrolyte. Most preferably, the carbon dioxide is dissolved until saturation.

In the electrolytic solution of the present invention, the safety of the battery during overcharge can be ensured by further containing an aromatic compound.
Examples of the aromatic compound include the following (a) to (c).
(A) cyclohexylbenzene, fluorocyclohexylbenzene compound (1-fluoro-2-cyclohexylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-4-cyclohexylbenzene), biphenyl.
(B) tert-butylbenzene, 1-fluoro-4-tert-butylbenzene, tert-amylbenzene, 4-tert-butylbiphenyl, 4-tert-amylbiphenyl.
(C) Terphenyl (o-, m-, p-form), diphenyl ether, 2-fluorodiphenyl ether, 4-diphenyl ether, fluorobenzene, difluorobenzene (o-, m-, p-form), 2-fluorobiphenyl, 4-fluorobiphenyl, 2,4-difluoroanisole, terphenyl partially hydride (1,2-dicyclohexylbenzene, 2-phenylbicyclohexyl, 1,2-diphenylcyclohexane, o-cyclohexylbiphenyl).
Among these, (a) and (b) are preferable, and at least one selected from cyclohexylbenzene, fluorocyclohexylbenzene compounds (1-fluoro-4-cyclohexylbenzene, etc.), tert-butylbenzene, and tert-amylbenzene is used. Most preferred.
The total content of the aromatic compound is preferably 0.1 to 5% by weight with respect to the weight of the non-aqueous electrolyte.

[Lithium secondary battery]
The lithium secondary battery of the present invention comprises a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a positive electrode, a negative electrode, and a nonaqueous solvent. Components other than the non-aqueous electrolyte, such as a positive electrode and a negative electrode, can be used without particular limitation.
For example, a composite metal oxide with lithium containing cobalt, manganese, or nickel is used as the positive electrode active material. These positive electrode active materials can be used individually by 1 type or in combination of 2 or more types.
Examples of such composite metal oxides include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , LiCo _1-x Ni _x O ₂ (0.01 <x <1), LiCo _1/3 Ni _1/3 Mn. Examples thereof include _1/3 O ₂ and LiNi _1/2 Mn _3/2 O ₄ . Further, LiCoO ₂ and LiMn ₂ O ₄ , LiCoO ₂ and LiNiO ₂ , LiMn ₂ O ₄ and LiNiO ₂ may be used in combination. Among these, lithium composite metal oxides such as LiCoO ₂ , LiMn ₂ O ₄ , and LiNiO ₂ that can be used at a charged potential of the positive electrode in a fully charged state of 4.3 V or more on the basis of Li are preferable, and LiCo _1/3 A lithium composite oxide that can be used at 4.4 V or higher, such as Ni _1/3 Mn _1/3 O ₂ and LiNi _1/2 Mn _3/2 O ₄ , is more preferable. Further, a part of the lithium composite oxide may be substituted with another element. For example, a part of Co in LiCoO ₂ may be replaced with Sn, Mg, Fe, Ti, Al, Zr, Cr, V, Ga, Zn, Cu Etc. may be substituted.

Moreover, a lithium containing olivine type phosphate can also be used as a positive electrode active material. Specific examples thereof include LiFePO ₄ , LiCoPO ₄ , LiNiPO ₄ , LiMnPO ₄ , LiFe _1-x M _x PO ₄ (M is at least one selected from Co, Ni, Mn, Cu, Zn, and Cd, x is 0 ≦ x ≦ 0.5). Among these, LiFePO ₄ or LiCoPO ₄ is preferable as the positive electrode active material for high voltage.
Lithium-containing olivine-type phosphate can also be used by mixing with other positive electrode active materials.

  The conductive agent for the positive electrode is not particularly limited as long as it is an electron conductive material that does not cause a chemical change. Examples thereof include graphites such as natural graphite (eg, scaly graphite) and artificial graphite, and carbon blacks such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. Further, graphites and carbon blacks may be appropriately mixed and used. The amount of the conductive agent added to the positive electrode mixture is preferably 1 to 10% by weight, particularly preferably 2 to 5% by weight.

  For the positive electrode, the positive electrode active material is a conductive agent such as acetylene black or carbon black, and polytetrafluoroethylene, polyvinylidene fluoride, a copolymer of styrene and butadiene, a copolymer of acrylonitrile and butadiene, carboxymethyl cellulose, ethylene propylene dienter After mixing with a binder such as a polymer and adding a high boiling point solvent such as 1-methyl-2-pyrrolidone to knead to make a positive electrode mixture, the positive electrode material is used as an aluminum foil or stainless steel as a current collector. It can be produced by rolling to a glass plate and heat-treating at a temperature of about 50 ° C. to 250 ° C. for about 2 hours under vacuum.

Negative electrodes (negative electrode active materials) include lithium metals and lithium alloys, and carbon materials that can occlude and release lithium (pyrolytic carbons, cokes, graphite (artificial graphite, natural graphite, etc.), organic polymer compound combustion Body, carbon fiber], tin, tin compound, silicon, silicon compound and the like can be used singly or in combination of two or more.
Among these, a carbon material is preferable, and a carbon material having a graphite-type crystal structure in which the plane spacing (d ₀₀₂ ) of the lattice plane ( ₀₀₂ ) is 0.340 nm or less, particularly 0.335 to 0.340 nm is more preferable.
The negative electrode can be produced by the same method using the same binder and high-boiling solvent as those for the positive electrode.

In the present invention, in order to increase the effect of adding the pentafluorophenyloxy compound represented by the general formula (II) or (III), it is preferable to increase the electrode mixture density of the battery. In particular, the density is 3.2 g / cm ³ or more preferably a positive electrode (positive electrode mixture layer) formed on the aluminum foil, 3.3 g / cm ³ or more, more preferably, 3.4 g / cm ^3, most preferably at least . The upper limit thereof, since there is a case where substantially produced exceeds 4.0 g / cm ³ is difficult, preferably 4.0 g / cm ³ or less, more preferably 3.9 g / cm ^3, 3.8 g / Cm ³ or less is most preferable.
On the other hand, the density of the negative electrode (negative electrode mixture layer) formed on the copper foil, 1.3 g / cm ³ or more, more preferably ^{1.4g / cm 3, 1.5g / cm} 3 is most preferred. If the upper limit exceeds 2.0 g / cm ³ , production may be substantially difficult, so 2.0 g / cm ³ or less is preferable, 1.9 g / cm ³ or less is more preferable, and 1.8 g / cm ³ is more preferable. Most preferred is cm ³ or less.

Further, the thickness of the positive electrode layer (per collector surface) is 30 μm or more because if the electrode material layer is too thin, the amount of active material in the electrode material layer decreases and the battery capacity decreases. Preferably, 50 μm or more is more preferable. On the other hand, if the thickness is too thick, the charge / discharge cycle characteristics and rate characteristics deteriorate, which is not preferable. Accordingly, the thickness of the positive electrode layer is preferably 120 μm or less, and more preferably 100 μm or less.
If the thickness of the electrode layer of the negative electrode (per collector surface) is too thin, the amount of active material in the electrode material layer decreases and the battery capacity decreases, so that it is preferably 1 μm or more, more preferably 3 μm. On the other hand, if the thickness is too thick, the charge / discharge cycle characteristics and rate characteristics deteriorate, which is not preferable. Accordingly, the thickness of the negative electrode layer is preferably 100 μm or less, and more preferably 70 μm or less.

The structure of the lithium secondary battery is not particularly limited, and a coin battery, a cylindrical battery, a square battery, a laminate battery, or the like having a single-layer or multi-layer separator can be applied.
As the battery separator, a single layer or laminated porous film of polyolefin such as polypropylene and polyethylene, woven fabric, non-woven fabric and the like can be used.
The battery separator varies depending on the production conditions, but if the air permeability is too high, the lithium ion conductivity is lowered and the function as a battery separator is not sufficient. Therefore, the air permeability is preferably 1000 seconds / 100 cc or less, more preferably 800 seconds / 100 cc or less, and most preferably 500 seconds / 100 cc or less. On the other hand, if the air permeability is too low, the mechanical strength is lowered. Therefore, it is preferably 50 seconds / 100 cc or more, more preferably 100 seconds / 100 cc or more, and most preferably 300 seconds / 100 cc or more. The porosity is preferably 30 to 60%, more preferably 35 to 55%, and most preferably 40 to 50% from the viewpoint of improving battery capacity characteristics.
Further, the thickness of the battery separator is preferably 50 μm or less, more preferably 40 μm or less, and most preferably 25 μm or less because a thinner separator can increase the energy density. From the viewpoint of mechanical strength, the thickness is preferably 5 μm or more, more preferably 10 μm or more, and most preferably 15 μm or more.

  The lithium secondary battery of the present invention has excellent cycle characteristics over a long period of time even when the end-of-charge voltage is 4.2 V or higher, particularly 4.3 V or higher. Further, even at 4.4 V, the cycle characteristics are It is good. The end-of-discharge voltage can be 2.5 V or higher, and further 2.8 V or higher. Although it does not specifically limit about an electric current value, Usually, it is used by 0.1-3C constant current discharge. Moreover, the lithium secondary battery in this invention can be charged / discharged at -40-100 degreeC, Preferably it is 0-80 degreeC.

In the present invention, as a countermeasure against an increase in the internal pressure of the lithium secondary battery, a method of providing a safety valve on the sealing plate or cutting a member such as a battery can or a gasket can be employed.
The lithium secondary battery in the present invention is stored in a battery pack by assembling a plurality of lithium secondary batteries in series and / or in parallel. In addition to overcurrent prevention elements such as PTC elements, thermal fuses, bimetals, etc., the battery pack has a safety circuit (the function of monitoring the voltage, temperature, current, etc. of each battery and / or the entire assembled battery and cutting off the current) Circuit).

  Examples of the cylindrical battery and comparative examples will be described with respect to the present invention, but the present invention is not limited to the following examples, and is not particularly limited to combinations of solvents.

Example 1 (Synthesis of pentafluorophenyl methyl oxalate)
10 g (54 mmol) of pentafluorophenol and 5 ml (61 mmol) of pyridine were dissolved in 35 ml of toluene, and 7.2 g (59 mmol) of methyl chloroglyoxylate was added dropwise and reacted under ice cooling. After stirring at room temperature for 1 hour, the reaction solution was filtered and concentrated. The obtained crude product was purified by distillation to obtain 10.1 g of pentafluorophenylmethyl oxalate. The melting point of this compound was 34-35 ° C.
About the obtained pentafluorophenyl methyl oxalate, mass spectrometry (manufactured by Hitachi, Ltd., model: using M80B) and infrared spectroscopic analysis (IR) (manufactured by Varian USA, model: using FTS7000E) were measured. The structure was confirmed. The results are shown below.
(1) Mass spectrometry: CI-MS, m / e = 271 (M + 1)
(2) IR: 1805, 1766, 1522, 1308, 1149, 1123, 999 cm ⁻¹

Example 2 (Synthesis of pentafluorophenylethyl oxalate)
16.5 g (90 mmol) of pentafluorophenol and 8 ml (99 mmol) of pyridine were dissolved in 50 ml of toluene, and 12.9 g (94 mmol) of ethyl chloroglyoxylate was added dropwise and reacted under ice cooling. After stirring at room temperature for 1 hour, the reaction solution was filtered and concentrated. The resulting crude product was purified by distillation to obtain 13.5 g (colorless liquid) of pentafluorophenylethyl oxalate. The boiling point of this compound was 70-71 ° C./2 mmHg.
The obtained pentafluorophenylethyl oxalate was subjected to mass spectrometry and IR measurement in the same manner as in Synthesis Example 1 to confirm the structure. The results are shown below.
(1) Mass spectrometry: CI-MS, m / e = 285 (M + 1)
(2) IR: 2992, 1805, 1761, 1521, 1473, 1305, 1149, 1122, 991, 859 cm ⁻¹

Example 3 (Synthesis of 2-propynylpentafluorophenyl oxalate)
10 g (79 mmol) of oxalyl chloride was dissolved in 100 ml of methylene chloride, and 4.4 g (79 mmol) of propargyl alcohol and 6.4 ml (79 mmol) of pyridine dissolved in 30 ml of methylene chloride were slowly added dropwise over 1 hour under ice cooling. The mixture was stirred at room temperature for 30 minutes to produce propynyl chloroglyoxylate in the reaction system. Subsequently, a solution prepared by dissolving 14.5 g (79 mmol) of pentafluorophenol and 6.4 ml (79 mmol) of pyridine in 30 ml of methylene chloride was slowly added dropwise under ice cooling. After stirring at room temperature for 1 hour, the reaction product was filtered, washed with water, dried over anhydrous magnesium sulfate and concentrated. The obtained crude product was purified by crystallization to obtain 2.1 g of 2-propynylpentafluorophenyl oxalate.
About the obtained 2-propynylpentafluorophenyl oxalate, ¹ H-NMR (manufactured by JEOL Ltd., model: use of AL300) and the IR measurement were performed, and the structure was confirmed. The results are shown below.
(1) ¹ H-NMR (CDCl _{3 /} TMS): 2.59 ppm (s, 1H, C≡CH), 4.89 ppm (s, 2H, —CH ₂ —)
(2) IR: 3249, 1744, 1182, 943, 729, 715 cm ⁻¹

Example 4 (Synthesis of bis (pentafluorophenyl) sulfite)
10 g (54 mmol) of pentafluorophenol and 5 ml (61 mmol) of pyridine were dissolved in 35 ml of toluene, and 3.3 g (28 mmol) of thionyl chloride was added dropwise and reacted under ice cooling. Thereafter, distillation purification was performed to obtain 7.6 g (colorless liquid) of bis (pentafluorophenyl) sulfite. The boiling point of this compound was 95-95.5 ° C./2 mmHg.
The obtained bis (pentafluorophenyl) sulfite was subjected to mass spectrometry and IR measurement in the same manner as in Synthesis Example 1 to confirm the structure. The results are shown below.
(1) Mass spectrometry: CI-MS, m / e = 415 (M + 1)
(2) IR: 1517, 1467, 1313, 1252, 1140, 997, 984 cm ⁻¹

Example 5 (Synthesis of 2-propynylpentafluorophenyl carbonate)
Dissolve 7.3 g (25 mmol) of triphosgene in 100 ml of methylene chloride, and slowly dissolve a solution of 4.2 g (74 mmol) of propargyl alcohol and 6.0 ml (74 mmol) of pyridine in 30 ml of methylene chloride over 1 hour. The solution was added dropwise, stirred at room temperature for 30 minutes, and propynyl chloroformate was produced in the reaction system. Subsequently, 13.7 g (74 mmol) of pentafluorophenol and 6.0 ml (74 mmol) of pyridine dissolved in 30 ml of methylene chloride were slowly added dropwise under ice cooling to cause a reaction. After stirring at room temperature for 1 hour, the reaction product was filtered, washed with water, dried over anhydrous magnesium sulfate and concentrated. The obtained crude product was purified by crystallization to obtain 7.5 g of 2-propynylpentafluorophenyl carbonate. The melting point of this compound was 66-67 ° C.
About the obtained 2-propynyl pentafluorophenyl carbonate, it carried out similarly to the synthesis example 1, and performed the mass spectrometry and IR measurement, and confirmed the structure. The results are shown below.
(1) Mass spectrometry: CI-MS, m / e = 267 (M + 1)
(2) IR: 3286, 1783, 1524, 1439, 1377, 1278, 1234, 1162, 1007, 993, 977, 941, 910, 774, 723, 659 cm ⁻¹

Example 6
(Preparation of non-aqueous electrolyte)
Under an atmosphere of dry nitrogen, ethylene carbonate (EC): vinylene carbonate (VC): methyl ethyl carbonate (MEC) (volume ratio) = 30: 2: A non-aqueous solvent to prepare a 68, LiPF ₆ and as the electrolyte salt After preparing a non-aqueous electrolyte by dissolving LiBF ₄ to a concentration of 0.95 M and 0.05 M, respectively, pentafluorophenyl methyl oxalate is 1% by weight with respect to the non-aqueous electrolyte. Added as follows.
[Production of lithium secondary battery]
The positive electrode was prepared by 94% by weight of LiNi _1/3 Mn _1/3 Co _1/3 O ₂ (positive electrode active material), 3% by weight of acetylene black (conductive agent), and 3% of polyvinylidene fluoride (binder). The mixture was mixed at a ratio of% by weight, mixed with 1-methyl-2-pyrrolidone solvent added thereto, applied onto an aluminum foil, dried, pressure-molded, and heat-treated.
The negative electrode was prepared by adding 95% by weight of artificial graphite (negative electrode active material) having a graphite type crystal structure with a lattice plane (002) spacing (d ₀₀₂ ) of 0.335 nm and polyvinylidene fluoride (binder). The mixture was mixed at a ratio of 5% by weight, a 1-methyl-2-pyrrolidone solvent was added thereto, the mixture was applied onto a copper foil, dried, pressure-molded, and heat-treated.
Using a polyethylene microporous film separator, after injecting the non-aqueous electrolyte obtained above, carbon dioxide having a dew point of −60 ° C. was saturated until the non-aqueous electrolyte was saturated, and the battery was sealed. A cylindrical battery (diameter 18 mm, height 65 mm) was produced. The battery was provided with a pressure release port and an internal current interrupt device (PTC element). At this time, the electrode density of the positive electrode was 3.5 g / cm ³ , and the electrode density of the negative electrode was 1.6 g / cm ³ . The thickness of the positive electrode layer (per collector side) was 70 μm, and the thickness of the negative electrode layer (per collector side) was 60 μm.
[Measurement of battery characteristics]
The obtained 18650 battery was charged to 4.2 V at a constant current of 2.2 A (1 C) at room temperature (25 ° C.), and then charged at a constant voltage as a final voltage of 4.2 V for a total of 3 hours. Next, the battery was discharged to a final voltage of 3.0 V under a constant current of 2.2 A (1 C), and this charge / discharge was repeated. When the initial charge / discharge capacity is 0.95M LiPF ₆ + 0.05M LiBF ₄ −EC: VC: MEC (capacity ratio) = 30: 2: 68 without adding pentafluorophenylmethyl oxalate as the non-aqueous electrolyte It was almost the same as (Comparative Example 1), and when the battery characteristics after 300 cycles were measured, the discharge capacity retention rate was 81% when the initial discharge capacity was 100%.
Table 1 shows the results of battery fabrication conditions and battery characteristics.

Example 7
In Example 6, a cylindrical battery was produced in the same manner as in Example 6 except that 2-propynylpentafluorophenyl oxalate was used instead of pentafluorophenylmethyl oxalate, and battery characteristics were measured. The results are shown in Table 1.
Example 8
A cylindrical battery was prepared in the same manner as in Example 6 except that bis (pentafluorophenyl) sulfite was used in place of pentafluorophenylmethyl oxalate in Example 6, and battery characteristics were measured. The results are shown in Table 1.
Example 9
In Example 6, a cylindrical battery was produced in the same manner as in Example 6 except that 2-propynylpentafluorophenyl carbonate was used instead of pentafluorophenylmethyl oxalate, and battery characteristics were measured. The results are shown in Table 1.

Example 10
In Example 6, instead of pentafluorophenyl methyl oxalate, bis (pentafluorophenyl) oxalate was used in the same manner as in Example 6 except that 0.1% by weight of non-aqueous electrolyte was used. A cylindrical battery was prepared and the battery characteristics were measured. The results are shown in Table 1.
Example 11
In Example 6, a cylindrical battery was prepared in the same manner as in Example 6 except that 0.5% by weight of pentafluorophenylmethyl oxalate was added and 0.5% by weight of methylpropargyl carbonate was added. Battery characteristics were measured. The results are shown in Table 1.

Comparative Example 1
A cylindrical battery was produced in the same manner as in Example 6 except that pentafluorophenylmethyl oxalate was not added in Example 6, and the battery characteristics were measured. The results are shown in Table 1.
Comparative Examples 2 and 3
In Example 6, a cylindrical battery was produced in the same manner as in Example 6 except that the compounds shown in Table 1 were used instead of pentafluorophenylmethyl oxalate, and the battery characteristics were measured. The results are shown in Table 1.

Example 12
Under a dry nitrogen atmosphere, a nonaqueous solvent of ethylene carbonate (EC): 1,3-propane sultone (PS): methyl ethyl carbonate (MEC) (volume ratio) = 30: 2: 68 was prepared, and an electrolyte salt was prepared therefor LiPF ₆ and LiBF ₄ were dissolved to a concentration of 0.95 M and 0.05 M, respectively, to prepare a non-aqueous electrolyte, and then pentafluorophenylethyl oxalate was used for the non-aqueous electrolyte. A cylindrical battery was produced in the same manner as in Example 6 and the battery characteristics were measured. The results are shown in Table 1.
Example 13
In Example 12, a cylindrical battery was produced in the same manner as in Example 12 except that 0.05% by weight of lithium pentafluorophenoxide was used instead of pentafluorophenylmethyl oxalate, and battery characteristics were measured. The results are shown in Table 1.

Comparative Example 4
A cylindrical battery was produced in the same manner as in Example 12 except that pentafluorophenylmethyl oxalate was not added in Example 12, and the battery characteristics were measured. The results are shown in Table 1.

  Compared with the lithium secondary battery of the comparative example which does not contain the pentafluorophenyloxy compound represented by the general formula (II) or (III), the lithium secondary battery of the above embodiment has longer cycle characteristics and charge storage characteristics. It turns out that it is excellent.

Claims (8)

A pentafluorophenyloxy compound represented by the following general formula (I).

(In the formula, R ¹ represents a —COCO— group or an S═O group, and R ² represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 7 carbon atoms, or a group having 2 to 6 carbon atoms. An alkenyl group or an alkynyl group having 3 to 7 carbon atoms, provided that one or more hydrogen atoms of R ² may be substituted with a halogen atom. In a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, the pentafluorophenyloxy compound represented by the following general formula (II) or (III) is added to the non-aqueous electrolyte in the weight of the non-aqueous electrolyte. A nonaqueous electrolytic solution characterized by containing 0.01 to 10% by weight.

(In the formula, R ³ represents a —COCO— group, a C═O group, or an S═O group, and R ⁴ represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 7 carbon atoms, and carbon. Represents an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 7 carbon atoms, or an aryl group having 6 to 18 carbon atoms, provided that one or more hydrogen atoms of R ⁴ may be substituted with a halogen atom. In addition, when R ³ is a C═O group, R ⁴ is an alkenyl group having 2 to 6 carbon atoms or an alkynyl group having 3 to 7 carbon atoms, and when R ³ is an S═O group, R ⁴ is an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 7 carbon atoms, a phenyl group, a fluorophenyl group, or a pentafluorophenyl group .

(In the formula, Y represents an alkali metal or an alkaline earth metal, and n represents 1 or 2.)   The pentafluorophenyloxy compound represented by the general formula (II) is pentafluorophenylmethyl oxalate, pentafluorophenylethyl oxalate, 2-propynylpentafluorophenyl oxalate, bis (pentafluorophenyl) oxalate; vinyl Pentafluorophenyl carbonate, 2-propenyl pentafluorophenyl carbonate, 3-propenyl pentafluorophenyl carbonate, 2-propynyl pentafluorophenyl carbonate, 2-butynyl pentafluorophenyl carbonate, 3-butynyl pentafluorophenyl carbonate, 4-penthi Nyl pentafluorophenyl carbonate; pentafluorophenyl methyl sulfite, pentafluorophenyl ethyl sulfite, 2-propynyl pen Fluorophenyl sulfite, and bis (pentafluorophenyl) non-aqueous electrolyte according to claim 2 is one or more selected from sulfite.   The nonaqueous electrolytic solution according to claim 2, wherein the pentafluorophenyloxy compound represented by the general formula (III) is lithium pentafluorophenoxide.   The nonaqueous electrolytic solution according to any one of claims 2 to 4, wherein the nonaqueous solvent contains cyclic carbonates and chain carbonates.   The nonaqueous electrolytic solution according to any one of claims 2 to 5, wherein the nonaqueous electrolytic solution further contains one or more selected from vinylene carbonate, 1,3-propane sultone, and a triple bond-containing compound.   The triple bond-containing compound contains one or more selected from methyl propargyl carbonate, ethyl propargyl carbonate, dipropargyl carbonate, dipropargyl oxalate, propargyl methanesulfonate, dipropargyl sulfite, methyl propargyl sulfite, and ethyl propargyl sulfite. The nonaqueous electrolytic solution according to any one of claims 2 to 6. In a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, pentafluorophenyl represented by the following general formula (II) or (III) in the non-aqueous electrolyte A lithium secondary battery, wherein the oxy compound is contained in an amount of 0.01 to 10% by weight based on the weight of the non-aqueous electrolyte.

(In the formula, R ³ represents a —COCO— group, a C═O group, or an S═O group, and R ⁴ represents an alkyl group having 1 to 6 carbon atoms, a cycloalkyl group having 3 to 7 carbon atoms, and carbon. Represents an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 7 carbon atoms, or an aryl group having 6 to 18 carbon atoms, provided that one or more hydrogen atoms of R ⁴ may be substituted with a halogen atom. In addition, when R ³ is a C═O group, R ⁴ is an alkenyl group having 2 to 6 carbon atoms or an alkynyl group having 3 to 7 carbon atoms, and when R ³ is an S═O group, R ⁴ is an alkyl group having 1 to 6 carbon atoms, an alkenyl group having 2 to 6 carbon atoms, an alkynyl group having 3 to 7 carbon atoms, a phenyl group, a fluorophenyl group, or a pentafluorophenyl group .

(In the formula, Y represents an alkali metal or an alkaline earth metal, and n represents 1 or 2.)