JP5034224B2 - Non-aqueous electrolyte and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte capable of forming a lithium secondary battery excellent in electric capacity, low temperature battery characteristics, and long-term cycle characteristics, and a lithium secondary battery using the same.

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. The desired electrochemical reaction is inhibited, resulting in 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.

Examples of the non-aqueous electrolyte that improves battery characteristics of the lithium secondary battery include a non-aqueous electrolyte containing an ether bond-containing acyclic carbonate compound (see Patent Documents 1 to 3) and a carbon-carbon triple bond-containing compound. Nonaqueous electrolyte solution (see Patent Documents 4 to 5), Nonaqueous electrolyte solution containing an S—O bond-containing compound such as a sulfite ester compound (see Patent Documents 6 to 9), Nonaqueous electrolyte solution containing a formate ester compound ( Patent Documents 10 to 11) have been proposed.
Although these non-aqueous electrolytes have improved battery characteristics to some extent, non-aqueous electrolytes and lithium secondary batteries having further excellent low-temperature battery characteristics and long-term cycle characteristics are required.

JP 2000-228216 A JP 2002-237328 A JP 2003-331914 A JP 2000-195545 A JP 2001-313072 A JP-A-11-162511 JP 9-167635 A JP 2000-294282 A JP 2000-124297 A JP-A-9-306538 JP-A-6-20719

  An object of this invention is to provide the non-aqueous electrolyte which can form the lithium secondary battery excellent in an electrical capacity, a low temperature battery characteristic, and a long-term cycle characteristic, and a lithium secondary battery using the same.

The inventors of the present invention have improved battery characteristics at low temperatures by using an ester solution having an alkyleneoxy group and a carbon-carbon triple bond, a formyl group, or a haloalkyl group in the electrolytic solution, and used the electrolytic solution. The secondary battery was found to have a high capacity and good cycle characteristics over a long period of time, and the present invention was completed.
That is, the present invention provides the following (1) to (3).
(1) In a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, the nonaqueous electrolytic solution contains at least one ester compound represented by the following general formulas (I) to (IV). A non-aqueous electrolyte characterized in that

(In the formula, R ¹ represents an alkenyloxy group having 2 to 8 carbon atoms, an alkynyloxy group having 3 to 8 carbon atoms, or an alkynyl group having 2 to 8 carbon atoms which may be substituted with a halogen atom; The alkynyl group of ¹ may be substituted with an ester group, and R ² is an alkyl group having 1 to 8 carbon atoms, an alkoxyalkyl group having 3 to 12 carbon atoms, or 6 carbon atoms that may be substituted with a halogen atom. -18 aryl group, aralkyl group having 7-18 carbon atoms, alkenyl group having 2-8 carbon atoms, alkynyl group having 3-8 carbon atoms, acetyl group, propynyl group, butyryl group, isobutyryl group, methoxyacetyl group, pivaloyl Group, benzoyl group, toluoyl group, methanesulfonyl group, ethanesulfonyl group, butanesulfonyl group, isopropylsulfonyl group, benzenesulfonyl group, p-toluenes Honiru group, a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, or phenoxycarbonyl group, R ¹ and R ² may be a good ring structure be branched .X is a halogen atom An optionally substituted alkylene group having 2 to 6 carbon atoms or an arylene group having 6 to 18 carbon atoms, which may be branched or a ring structure, Y represents —C (═O )-, -S (= O)-, -S (= O) _2- , or -C (= O) C (= O)-, wherein a represents an integer of 1 to 12. Show.)

(In the formula, X and a are the same as above, and R ³ is an alkyl group having 1 to 8 carbon atoms, an alkoxyalkyl group having 3 to 12 carbon atoms, and 6 to 6 carbon atoms which may be substituted with a halogen atom. 18 aryl groups, C 7-18 aralkyl groups, C 2-8 alkenyl groups, C 3-8 alkynyl groups, acetyl groups, propynyl groups, butyryl groups, isobutyryl groups, methoxyacetyl groups, pivaloyl groups , Benzoyl group, toluoyl group, methanesulfonyl group, ethanesulfonyl group, butanesulfonyl group, isopropylsulfonyl group, benzenesulfonyl group, p-toluenesulfonyl group, methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, phenoxycarbonyl group, or Only when a is 2 or more, it represents a formyl group and may be branched. It may be.)

(In the formula, Y is the same as defined above, and R ⁴ represents an alkenyloxy group having 2 to 8 carbon atoms, an alkynyloxy group having 3 to 8 carbon atoms, or an oxygen atom which may be substituted with a halogen atom. R 2 represents an alkynyl group having 2 to 8 carbon atoms which may be contained, and the alkynyl group of R ⁴ may be substituted with an ester group, and R ⁵ represents 1 carbon atom substituted with at least one halogen atom. An alkyl group having 6 to 6 carbon atoms, an aryl group having 6 to 18 carbon atoms, an aralkyl group having 7 to 18 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or an alkynyl group having 3 to 8 carbon atoms, R ⁴ and R ⁵ May be branched or a ring structure.)

(In the formula, R ⁶ is an alkyl group having 1 to 6 carbon atoms, an aralkyl group having 7 to 18 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or 3 carbon atoms substituted with at least one halogen atom. -8 alkynyl groups, which may be branched or cyclic.)
(2) In a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, 0.01 to 10 wt.% Of the ester compound represented by the general formula (II) or (IV) is contained in the nonaqueous electrolytic solution. And a non-aqueous electrolyte containing at least one selected from vinylene carbonate, 1,3-propane sultone, glycol sulfite, 1,4-butanediol dimethanesulfonate and divinylsulfone.
(3) A lithium secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte according to (1) or (2).

  The lithium secondary battery using the non-aqueous electrolyte of the present invention is excellent in electric capacity, battery characteristics at low temperature, etc., and exhibits excellent cycle characteristics over a long period of time.

  The non-aqueous electrolyte for a lithium secondary battery of the present invention is a non-aqueous electrolyte in which an electrolyte salt is dissolved in a non-aqueous solvent, and the non-aqueous electrolyte is represented by the general formulas (I) to (IV). It is characterized in that it contains at least one kind of ester compound. By containing at least one of these ester compounds in the electrolytic solution, the coating film formed on the electrode surface has a good ion conductivity, suppresses the decomposition of the solvent, and improves the battery characteristics at low temperatures. A secondary battery using this electrolytic solution is considered to have a high capacity and good cycle characteristics over a long period of time.

  One type of ester compound used in the present invention is represented by the following general formula (I).

(In the formula, R ¹ represents an alkenyloxy group having 2 to 8 carbon atoms, an alkynyloxy group having 3 to 8 carbon atoms, or an alkynyl group having 2 to 8 carbon atoms which may be substituted with a halogen atom; The alkynyl group of ¹ may be substituted with an ester group, and R ² is an alkyl group having 1 to 8 carbon atoms, an alkoxyalkyl group having 3 to 12 carbon atoms, or 6 carbon atoms that may be substituted with a halogen atom. -18 aryl group, aralkyl group having 7-18 carbon atoms, alkenyl group having 2-8 carbon atoms, alkynyl group having 3-8 carbon atoms, acetyl group, propynyl group, butyryl group, isobutyryl group, methoxyacetyl group, pivaloyl Group, benzoyl group, toluoyl group, methanesulfonyl group, ethanesulfonyl group, butanesulfonyl group, isopropylsulfonyl group, benzenesulfonyl group, p-toluenes Honiru group, a methoxycarbonyl group, an ethoxycarbonyl group, a propoxycarbonyl group, or phenoxycarbonyl group, R ¹ and R ² may be a good ring structure be branched .X is a halogen atom An optionally substituted alkylene group having 2 to 6 carbon atoms or an arylene group having 6 to 18 carbon atoms, which may be branched or a ring structure, Y represents —C (═O )-, -S (= O)-, -S (= O) _2- , or -C (= O) C (= O)-, wherein a represents an integer of 1 to 12. Show.)

  Specific examples of the ester compound represented by the general formula (I) in the case where Y is a carbonic acid ester represented by —C (═O) — include, for example, 2-propynyl 2-methoxyethyl carbonate, 2-propynyl. 2-ethoxyethyl carbonate, 2-propynyl 2-propoxyethyl carbonate, 2-propynyl 2-butoxyethyl carbonate, 2-propynyl 2-hexyloxyethyl carbonate, 2-propynyl 2-isopropoxyethyl carbonate, 2-propynyl 2-iso Butoxyethyl carbonate, 2-propynyl 2-t-butyloxyethyl carbonate, 2-propynyl 2- (2-ethylhexyloxy) ethyl carbonate, 2-propynyl 2- (2-fluoroethoxy) ethyl carbonate, 2-propynyl 2- ( 2-K Roethoxy) ethyl carbonate, 2-propynyl 3-methoxypropyl carbonate, 2-propynyl 4-methoxybutyl carbonate, 2-propynyl 1-methoxy-2-propyl carbonate, 2-propynyl 1-ethoxy-2-propyl carbonate, 2-propynyl 1-propoxy-2-propyl carbonate, 2-propynyl 1-butoxy-2-propyl carbonate, 2-propynyl 3-methoxybutyl carbonate, 2-propynyl 3-methoxy-3-methylbutyl carbonate, 2-propynyl 4-methoxy- 4-methyl-2-pentyl carbonate, 2-propynyl 2- (2-methoxyethoxy) ethyl carbonate, 2-propynyl 2- (2-ethoxyethoxy) ethyl carbonate, 2-propynyl 2- (2- ( -Fluoroethoxy) ethoxy) ethyl carbonate, 2-propynyl 2- (2- (2-chloroethoxy) ethoxy) ethyl carbonate, 2-propynyl 2- (2-butoxyethoxy) ethyl carbonate, 2-propynyl 2- (2- Isobutoxyethoxy) ethyl carbonate, 2-propynyl 2- (2- (2-methoxyethoxy) ethoxy) ethyl carbonate, 2-propynyl 2- (2- (2-butoxyethoxy) ethoxy) ethyl carbonate, 2-propynyl 2- (2- (2- (2-methoxyethoxy) ethoxy) ethoxy) ethyl carbonate, 2-propynyl 2-phenoxyethyl carbonate, 2-propynyl 2- (benzyloxy) ethyl carbonate, 2-propynyl 2- (2- (benzyl Oxy) ethoxy) ethyl Carbonate, 2-propynyl 2-methoxyphenyl carbonate, 2-propynyl 3-methoxyphenyl carbonate, 2-propynyl 4-methoxyphenyl carbonate, 2-propynyl 2-ethoxyphenyl carbonate, 2-propynyl 3-ethoxyphenyl carbonate, 2-propynyl 2-methoxy-4-methylphenyl carbonate, 2-propynyl 3-methoxy-5-methylphenyl carbonate, 2-propynyl 4- (2-methoxyethyl) phenyl carbonate, 2-propynyl 4-propoxyphenyl carbonate, 2-propynyl 4 -Butoxyphenyl carbonate, 2-propynyl 4-methoxy-1-naphthyl carbonate, 2-propynyl 7-methoxy-2-naphthyl carbonate, 2-propynyl 2-methoxy 2-propynyl 3-methoxybenzyl carbonate, 2-propynyl 4-methoxybenzyl carbonate, 2-propynyl 2- (4-methoxyphenyl) ethyl carbonate, 2-propynyl (±) -glycidyl carbonate, 2-propynyl tetrahydro Examples include furfuryl carbonate and 2-propynyl (2-tetrahydropyranyl) methyl carbonate.

Among these, R ¹ is an alkenyloxy group having 2 to 4 carbon atoms, an alkynyloxy group having 3 to 5 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms, and R ² is substituted with a halogen atom. An ester compound which is an optionally substituted alkyl group having 1 to 4 carbon atoms, X is an alkylene group having 2 to 3 carbon atoms, and a is an integer of 1 to 4, particularly 2-propynyl 2-methoxyethyl. One or more selected from carbonate, 2-propynyl 2- (2-fluoroethoxy) ethyl carbonate, 2-propynyl 2- (2-chloroethoxy) ethyl carbonate, 2-propynyl 2- (2-methoxyethoxy) ethyl carbonate It is preferable to contain it from a viewpoint of improving a low-temperature battery characteristic and a long-term cycle characteristic.

  In the ester compound represented by the general formula (I), among carboxylic acid esters in which Y is represented by —C (═O) —, specific examples of propiolic acid ester include, for example, 2-methoxyethyl pro Piolate, 2-ethoxyethyl propiolate, 2-propoxyethyl propiolate, 2-propynyl 2-butoxyethyl propiolate, 2-isopropoxyethyl propiolate, 2-isobutoxyethyl propiolate, 2- t-butyloxyethyl propiolate, 2- (2-fluoroethoxy) ethyl propiolate, 2- (2-chloroethoxy) ethyl propiolate, 2- (2-methoxyethoxy) ethyl propiolate, 2- (2-Ethoxyethoxy) ethyl propiolate, 2- (2- (2-fluoroethoxy) ethoxy Ethyl propiolate, 2- (2- (2-chloroethoxy) ethoxy) ethyl propiolate, 2- (2-butoxyethoxy) ethyl propiolate, 2- (2-isobutoxyethoxy) ethyl propiolate, 2-phenoxyethyl propiolate, 2- (benzyloxy) ethyl propiolate, 4-methoxyphenyl propiolate, 4-methoxybenzyl propiolate, 2- (4-methoxyphenyl) ethyl propiolate, (±)- Glycidyl propiolate, tetrahydrofurfuryl propiolate, 2-methoxyethyl methyl acetylenedicarboxylate, bis (2-methoxyethyl) acetylenedicarboxylate, bis (3-methoxypropyl) acetylenedicarboxylate, bis (4-acetylene dicarboxylate) Methoxybutyl), acetyl Examples thereof include bis (2-ethoxyethyl) rangecarboxylate. Other examples include acetate esters such as 2- (2-propynyloxy) ethyl acetate and 4- (2-propynyloxy) phenyl acetate.

Among these, R ¹ is an alkenyloxy group having 2 to 4 carbon atoms, an alkynyloxy group having 3 to 5 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms, and R ² is substituted with a halogen atom. An ester compound having 1 to 4 carbon atoms, X being an alkylene group having 2 to 3 carbon atoms, and a being an integer of 1 to 4, particularly 2-methoxyethyl propiolate. , 2-ethoxyethyl propiolate, 2- (2-fluoroethoxy) ethyl propiolate, 2-methoxyethyl methyl acetylenedicarboxylate, or bis (2-methoxyethyl) acetylenedicarboxylate Is preferable from the viewpoint of improving low-temperature battery characteristics and long-term cycle characteristics.

  In the ester compound represented by the general formula (I), specific examples of the sulfite ester in which Y is represented by -S (= O)-include, for example, 2-propynyl 2-methoxyethyl sulfite, 2- Propynyl 2-ethoxyethyl sulfite, 2-propynyl 2-propoxyethyl sulfite, 2-propynyl 2-butoxyethyl sulfite, 2-propynyl 2-hexyloxyethyl sulfite, 2-propynyl 2-isopropoxyethyl sulfite, 2-propynyl 2-isobutoxyethyl sulfite, 2-propynyl 2-t-butyloxyethyl sulfite, 2-propynyl 2- (2-ethylhexyloxy) ethyl sulfite, 2-propynyl 2- (2-fluoroethoxy) Ethyl sulfite, 2-propynyl 2- (2- Loroethoxy) ethyl sulfite, 2-propynyl 3-methoxypropyl sulfite, 2-propynyl 4-methoxybutyl sulfite, 2-propynyl 1-methoxy-2-propyl sulfite, 2-propynyl 1-ethoxy-2-propyl sulfite Phyto, 2-propynyl 1-propoxy-2-propyl sulfite, 2-propynyl 1-butoxy-2-propyl sulfite, 2-propynyl 3-methoxybutyl sulfite, 2-propynyl 3-methoxy-3-methylbutyl sulfite Phyto, 2-propynyl 4-methoxy-4-methyl-2-pentyl sulfite, 2-propynyl 2- (2-methoxyethoxy) ethyl sulfite, 2-propynyl 2- (2-ethoxyethoxy) ethyl sulfite, 2 -Propynyl 2- (2- 2-fluoroethoxy) ethoxy) ethyl sulfite, 2-propynyl 2- (2- (2-chloroethoxy) ethoxy) ethyl sulfite, 2-propynyl 2- (2-butoxyethoxy) ethyl sulfite, 2-propynyl 2 -(2-isobutoxyethoxy) ethyl sulfite, 2-propynyl 2- (2- (2-methoxyethoxy) ethoxy) ethyl sulfite, 2-propynyl 2- (2- (2-butoxyethoxy) ethoxy) ethyl sulfite Phyto, 2-propynyl 2- (2- (2- (2-methoxyethoxy) ethoxy) ethoxy) ethyl sulfite, 2-propynyl 2-phenoxyethyl sulfite, 2-propynyl 2- (benzyloxy) ethyl sulfite, 2-propynyl 2- (2- (benzyloxy) ethoxy) eth Rusulfite, 2-propynyl 2-methoxyphenyl sulfite, 2-propynyl 3-methoxyphenyl sulfite, 2-propynyl 4-methoxyphenyl sulfite, 2-propynyl 2-ethoxyphenyl sulfite, 2-propynyl 3-ethoxy Phenylsulfite, 2-propynyl 2-methoxy-4-methylphenyl sulfite, 2-propynyl 3-methoxy-5-methylphenyl sulfite, 2-propynyl 4- (2-methoxyethyl) phenyl sulfite, 2-propynyl 4-propoxyphenyl sulfite, 2-propynyl 4-butoxyphenyl sulfite, 2-propynyl 4-methoxy-1-naphthyl sulfite, 2-propynyl 7-methoxy-2-naphthyl sulfite, 2-propynyl 2-meth Benzyl sulfite, 2-propynyl 3-methoxybenzyl sulfite, 2-propynyl 4-methoxybenzyl sulfite, 2-propynyl 2- (4-methoxyphenyl) ethyl sulfite, 2-propynyl (±) -glycidyl sulfite, Examples include 2-propynyltetrahydrofurfuryl sulfite, 2-propynyl (2-tetrahydropyranyl) methyl sulfite, and allyl 2-methoxyethyl sulfite.

Among these, R ¹ is an alkenyloxy group having 2 to 4 carbon atoms, an alkynyloxy group having 3 to 5 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms, and R ² is substituted with a halogen atom. An ester compound which is an optionally substituted alkyl group having 1 to 4 carbon atoms, X is an alkylene group having 2 to 3 carbon atoms, and a is an integer of 1 to 4, particularly 2-propynyl 2-methoxyethyl. It is preferable from the viewpoint of improving low-temperature battery characteristics and long-term cycle characteristics that it contains at least one selected from sulfite, 2-propynyl 2- (2-fluoroethoxy) ethyl sulfite, and allyl 2-methoxyethyl sulfite. .

Specific examples of the ester compound represented by the general formula (I) in the case where Y is a sulfate ester represented by —S (═O) ₂ — include, for example, 2-propynyl 2-methoxyethyl sulfate, 2- Propynyl 2-ethoxyethyl sulfate, 2-propynyl 2-propoxyethyl sulfate, 2-propynyl 2-butoxyethyl sulfate, 2-propynyl 2-hexyloxyethyl sulfate, 2-propynyl 2-isopropoxyethyl sulfate, 2-propynyl 2- Isobutoxyethyl sulfate, 2-propynyl 2-t-butyloxyethyl sulfate, 2-propynyl 2- (2-ethylhexyloxy) ethyl sulfate, 2-propynyl 2- (2-fluoroethoxy) ethyl sulfate, 2-propynyl 2- (2- Loroethoxy) ethyl sulfate, 2-propynyl 3-methoxypropyl sulfate, 2-propynyl 4-methoxybutyl sulfate, 2-propynyl 1-methoxy-2-propyl sulfate, 2-propynyl 1-ethoxy-2-propyl sulfate, 2-propynyl 1-propoxy-2-propyl sulfate, 2-propynyl 1-butoxy-2-propyl sulfate, 2-propynyl 3-methoxybutyl sulfate, 2-propynyl 3-methoxy-3-methylbutyl sulfate, 2-propynyl 4-methoxy- 4-methyl-2-pentyl sulfate, 2-propynyl 2- (2-methoxyethoxy) ethyl sulfate, 2-propynyl 2- (2-ethoxyethoxy) ethyl sulfate, 2-propynyl 2- (2- 2-fluoroethoxy) ethoxy) ethyl sulfate, 2-propynyl 2- (2- (2-chloroethoxy) ethoxy) ethyl sulfate, 2-propynyl 2- (2-butoxyethoxy) ethyl sulfate, 2-propynyl 2- (2 -Isobutoxyethoxy) ethyl sulfate, 2-propynyl 2- (2- (2-methoxyethoxy) ethoxy) ethyl sulfate, 2-propynyl 2- (2- (2-butoxyethoxy) ethoxy) ethyl sulfate, 2-propynyl 2 -(2- (2- (2-methoxyethoxy) ethoxy) ethoxy) ethyl sulfate, 2-propynyl 2-phenoxyethyl sulfate, 2-propynyl 2- (benzyloxy) ethyl sulfate, 2-propynyl 2- (2- ( Benzyloxy) ethoxy) eth Rusulfate, 2-propynyl 2-methoxyphenyl sulfate, 2-propynyl 3-methoxyphenyl sulfate, 2-propynyl 4-methoxyphenyl sulfate, 2-propynyl 2-ethoxyphenyl sulfate, 2-propynyl 3-ethoxyphenyl sulfate, 2- Propynyl 2-methoxy-4-methylphenyl sulfate, 2-propynyl 3-methoxy-5-methylphenyl sulfate, 2-propynyl 4- (2-methoxyethyl) phenyl sulfate, 2-propynyl 4-propoxyphenyl sulfate, 2-propynyl 4-butoxyphenyl sulfate, 2-propynyl 4-methoxy-1-naphthyl sulfate, 2-propynyl 7-methoxy-2-naphthyl sulfate, 2-propynyl 2-meth Benzyl sulfate, 2-propynyl 3-methoxybenzyl sulfate, 2-propynyl 4-methoxybenzyl sulfate, 2-propynyl 2- (4-methoxyphenyl) ethyl sulfate, 2-propynyl (±) -glycidyl sulfate, 2-propynyl tetrahydrofur Examples include furyl sulfate and 2-propynyl (2-tetrahydropyranyl) methyl sulfate.

Among these, R ¹ is an alkenyloxy group having 2 to 4 carbon atoms, an alkynyloxy group having 3 to 5 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms, and R ² is substituted with a halogen atom. An ester compound which is an optionally substituted alkyl group having 1 to 4 carbon atoms, X is an alkylene group having 2 to 3 carbon atoms, and a is an integer of 1 to 4, particularly 2-propynyl 2-methoxyethyl. From the viewpoint of improving low-temperature battery characteristics and long-term cycle characteristics, it is preferable to contain one or more selected from sulfate, 2-propynyl 2-ethoxyethyl sulfate, and 2-propynyl 2- (2-fluoroethoxy) ethyl sulfate.

  Specific examples of the ester compound represented by the general formula (I) in the case where Y is an oxalate ester represented by —C (═O) C (═O) — include, for example, 2-propynyl 2-methoxy Ethyl oxalate, 2-propynyl 2-ethoxyethyl oxalate, 2-propynyl 2-propoxyethyl oxalate, 2-propynyl 2-butoxyethyl oxalate, 2-propynyl 2-hexyloxyethyl oxalate, 2-propynyl 2-isopropoxyethyl oxalate, 2-propynyl 2-isobutoxyethyl oxalate, 2-propynyl 2-t-butyloxyethyl oxalate, 2-propynyl 2- (2-ethylhexyloxy) ethyl Oxalate, 2-propynyl 2- (2-fluoroethoxy) ethyl oxalate, 2-propiyl Nyl 2- (2-chloroethoxy) ethyl oxalate, 2-propynyl 3-methoxypropyl oxalate, 2-propynyl 4-methoxybutyl oxalate, 2-propynyl 1-methoxy-2-propyl oxalate, 2-propynyl 1-ethoxy-2-propyl oxalate, 2-propynyl 1-propoxy-2-propyl oxalate, 2-propynyl 1-butoxy-2-propyl oxalate, 2-propynyl 3-methoxybutyl oxate Zalate, 2-propynyl 3-methoxy-3-methylbutyl oxalate, 2-propynyl 4-methoxy-4-methyl-2-pentyl oxalate, 2-propynyl 2- (2-methoxyethoxy) ethyl oxa 2-propynyl 2- (2-ethoxyethoxy) ethyl oxalate, 2-propiyl 2- (2- (2-fluoroethoxy) ethoxy) ethyl oxalate, 2-propynyl 2- (2- (2-chloroethoxy) ethoxy) ethyl oxalate, 2-propynyl 2- (2-butoxyethoxy) ) Ethyl oxalate, 2-propynyl 2- (2-isobutoxyethoxy) ethyl oxalate, 2-propynyl 2- (2- (2-methoxyethoxy) ethoxy) ethyl oxalate, 2-propynyl 2- ( 2- (2-butoxyethoxy) ethoxy) ethyl oxalate, 2-propynyl 2- (2- (2- (2-methoxyethoxy) ethoxy) ethoxy) ethyl oxalate, 2-propynyl 2-phenoxyethyl oxa 2-propynyl 2- (benzyloxy) ethyl oxalate, 2-propynyl 2- (2- (benzyloxy) Ethoxy) ethyl oxalate, 2-propynyl 2-methoxyphenyl oxalate, 2-propynyl 3-methoxyphenyl oxalate, 2-propynyl 4-methoxyphenyl oxalate, 2-propynyl 2-ethoxyphenyl oxalate 2-propynyl 3-ethoxyphenyl oxalate, 2-propynyl 2-methoxy-4-methylphenyl oxalate, 2-propynyl 3-methoxy-5-methylphenyl oxalate, 2-propynyl 4- (2- Methoxyethyl) phenyl oxalate, 2-propynyl 4-propoxyphenyl oxalate, 2-propynyl 4-butoxyphenyl oxalate, 2-propynyl 4-methoxy-1-naphthyl oxalate, 2-propynyl 7-methoxy 2-naphthyl oxalate, 2-pro Pinyl 2-methoxybenzyl oxalate, 2-propynyl 3-methoxybenzyl oxalate, 2-propynyl 4-methoxybenzyl oxalate, 2-propynyl 2- (4-methoxyphenyl) ethyl oxalate, 2-propynyl (±) -glycidyl oxalate, 2-propynyltetrahydrofurfuryl oxalate, 2-propynyl (2-tetrahydropyranyl) methyl oxalate and the like.

Among these, R ¹ is an alkenyloxy group having 2 to 4 carbon atoms, an alkynyloxy group having 3 to 5 carbon atoms, or an alkynyl group having 2 to 4 carbon atoms, and R ² is substituted with a halogen atom. An ester compound which is an optionally substituted alkyl group having 1 to 4 carbon atoms, X is an alkylene group having 2 to 3 carbon atoms, and a is an integer of 1 to 4, particularly 2-propynyl 2-methoxyethyl. Containing one or more selected from oxalate, 2-propynyl 2-ethoxyethyl oxalate, and 2-propynyl 2- (2-fluoroethoxy) ethyl oxalate has low-temperature battery characteristics and long-term cycle characteristics. It is preferable from the viewpoint of improvement.

  Another type of ester compound used in the present invention is represented by the following general formula (II).

(In the formula, X and a are the same as above, and R ³ is an alkyl group having 1 to 8 carbon atoms, an alkoxyalkyl group having 3 to 12 carbon atoms, and 6 to 6 carbon atoms which may be substituted with a halogen atom. 18 aryl groups, C 7-18 aralkyl groups, C 2-8 alkenyl groups, C 3-8 alkynyl groups, acetyl groups, propynyl groups, butyryl groups, isobutyryl groups, methoxyacetyl groups, pivaloyl groups , Benzoyl group, toluoyl group, methanesulfonyl group, ethanesulfonyl group, butanesulfonyl group, isopropylsulfonyl group, benzenesulfonyl group, p-toluenesulfonyl group, methoxycarbonyl group, ethoxycarbonyl group, propoxycarbonyl group, phenoxycarbonyl group, or Only when a is 2 or more, it represents a formyl group and may be branched. It may be.)

  Specific examples of the formate compound represented by the general formula (II) include, for example, 2-methoxyethyl formate, 2-ethoxyethyl formate, 2-propoxyethyl formate, 2-butoxyethyl formate, 2 -Hexyloxyethyl formate, 2-isopropoxyethyl formate, 2-isobutoxyethyl formate, 2-t-butyloxyethyl formate, 2- (2-ethylhexyloxy) ethyl formate, 2- (2- Fluoroethoxy) ethyl formate, 2- (2-chloroethoxy) ethyl formate, 3-methoxypropyl formate, 4-methoxybutyl formate, 1-methoxy-2-propyl formate, 1-ethoxy-2-propyl Formate, 1-propoxy-2-propylformate, 1-butoxy 2-propylformate, 3-methoxybutylformate, 3-methoxy-3-methylbutylformate, 4-methoxy-4-methyl-2-pentylformate, 2- (2-methoxyethoxy) ethylformate, 2- (2-ethoxyethoxy) ethyl formate, 2- (2- (2-fluoroethoxy) ethoxy) ethyl formate, 2- (2- (2-chloroethoxy) ethoxy) ethyl formate, 2- (2 -Butoxyethoxy) ethyl formate, 2- (2-isobutoxyethoxy) ethyl formate, 2- (2- (2-methoxyethoxy) ethoxy) ethyl formate, 2- (2- (2-butoxyethoxy) ethoxy ) Ethyl formate, 2- (2- (2- (2-methoxyethoxy) ethoxy) ethoxy) ethyl formate, 2-Fe Noxyethyl formate, 2- (benzyloxy) ethyl formate, 2- (2- (benzyloxy) ethoxy) ethyl formate, 2-methoxyphenyl formate, 3-methoxyphenyl formate, 4-methoxyphenyl formate Mate, 2-ethoxyphenylformate, 3-ethoxyphenylformate, 2-methoxy-4-methylphenylformate, 3-methoxy-5-methylphenylformate, 4- (2-methoxyethyl) phenylformate, 4-propoxyphenyl formate, 4-butoxyphenyl formate, 4-methoxy-1-naphthyl formate, 7-methoxy-2-naphthyl formate, 2-methoxybenzyl formate, 3-methoxybenzyl formate, 4- Methoxybenzylformate, 2- (4-methoxyphe E) Ethyl formate, (±) -glycidyl formate, tetrahydrofurfuryl formate, (2-tetrahydropyranyl) methyl formate, diethylene glycol diformate, triethylene glycol diformate, tetraethylene glycol diformate, etc. Is mentioned.

Among these, R ³ is an alkyl group, or an alkoxyalkyl group having 3 to 6 carbon atoms, methoxycarbonyl group, ethoxycarbonyl group, or a propoxycarbonyl group having 1 to 4 carbon atoms, carbon atoms X is 2-4 An ester group in which a is an integer of 1 to 4, in particular, containing at least one selected from 2-methoxyethyl formate, 2-ethoxyethyl formate and diethylene glycol diformate is a low temperature. It is preferable from the viewpoint of improving battery characteristics and long-term cycle characteristics.

  Another type of ester compound used in the present invention is represented by the following general formula (III).

(In the formula, Y is the same as defined above, and R ⁴ represents an alkenyloxy group having 2 to 8 carbon atoms, an alkynyloxy group having 3 to 8 carbon atoms, or an oxygen atom which may be substituted with a halogen atom. R 2 represents an alkynyl group having 2 to 8 carbon atoms which may be contained, and the alkynyl group of R ⁴ may be substituted with an ester group, and R ⁵ represents 1 carbon atom substituted with at least one halogen atom. An alkyl group having 6 to 6 carbon atoms, an aryl group having 6 to 18 carbon atoms, an aralkyl group having 7 to 18 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or an alkynyl group having 3 to 8 carbon atoms, R ⁴ and R ⁵ May be branched or a ring structure.)

  Specific examples of the ester compound represented by the general formula (III) include, for example, 2-propynyl 2-fluoroethyl carbonate, 2-propynyl 2-chloroethyl carbonate, 2-propynyl 2,2,2-trifluoroethyl. Carbonate, 2-propynyl pentafluorophenyl carbonate, 2-propynyl 2-fluoroethyl sulfite, 2-propynyl 2-chloroethyl sulfite, 2-propynyl 2,2,2-trifluoroethyl sulfite, 2-propynyl pentafluoro Phenylsulfite, 2-propynyl 2-fluoroethyl sulfate, 2-propynyl 2-chloroethyl sulfate, 2-propynyl 2,2,2-trifluoroethyl sulfate, 2-propynyl pentafluorophenyl sulfate, methoxy Ethyl propiolate, tetrahydropyran-2-ylmethyl propiolate, 2-fluoroethyl propiolate, 2-chloroethyl propiolate, 2-bromoethyl propiolate, 2,2,2-trifluoroethyl pro Piolate, pentafluorophenylpropiolate, acetylenedicarboxylate bis (2-fluoroethyl), acetylenedicarboxylate bis (3-fluoropropyl), acetylenedicarboxylate bis (2-chloroethyl), acetylenedicarboxylate bis (3-chloropropyl) Bis (2-bromoethyl) acetylenecarboxylate, bis (3-bromopropyl) acetylenecarboxylate, bis (2,2,2-trifluoroethyl) acetylenecarboxylate, bis (3,3,3-trifluoro) acetylene dicarboxylate Propyl), bis (2,2,3,3,3-pentafluoropropyl) acetylenedicarboxylate, 1,2-ethanediol dipropiolate, 1,3-propanediol dipropiolate, 1,4-butanediol dipro Piolate, 1,5-pentanediol dipropiolate, 2,2-bischloromethyl-3-propinoyloxypropyl propiolate, 3-phenylcyclohexylpropiolate, 2-propynyl 2-fluoroethyl oxalate, Examples include 2-propynyl 2-chloroethyl oxalate, 2-propynyl 2,2,2-trifluoroethyl oxalate, and 2-propynyl pentafluorophenyl oxalate.

Among the ester compounds represented by the general formula (III), R ⁴ is an alkenyloxy group having 2 to 4 carbon atoms, an alkynyloxy group having 3 to 6 carbon atoms, or an alkynyl group having 2 to 6 carbon atoms, R ⁵ is an alkyl group having 1 to 3 carbon atoms, an alkenyl group having 2 to 4 carbon atoms, or an alkynyl group having 3 to 6 carbon atoms substituted with at least one halogen atom, particularly a fluorine atom, and Y is Ester compounds which are —C (═O) — or —S (═O) — are preferred, particularly 2-propynyl 2-fluoroethyl carbonate, 2-propynyl 2,2,2-trifluoroethyl carbonate, 2-propynyl pentane. Fluorophenyl carbonate, methoxyethyl propiolate, acetylenedicarboxylic acid bis (2,2,2-trifluoroethyl), 1,2-ethanediol dipropiolate 1,3-propanediol dipropiolate, 2-propynyl 2-fluoroethyl sulfite, 2-propynyl 2,2,2-trifluoroethyl sulfite, 2-propynyl pentafluorophenyl sulfite, 2-fluoroethyl propio A low-temperature battery characteristic that contains at least one selected from a rate, 2,2,2-trifluoroethyl propiolate, 2-propynyl 2-fluoroethyl oxalate, and 2-propynyl pentafluorophenyl oxalate; It is preferable from the viewpoint of improving long-term cycle characteristics.

  Another type of ester compound used in the present invention is represented by the following general formula (IV).

(In the formula, R ⁶ is an alkyl group having 1 to 6 carbon atoms, an aralkyl group having 7 to 18 carbon atoms, an alkenyl group having 2 to 8 carbon atoms, or 3 carbon atoms substituted with at least one halogen atom. -8 alkynyl groups, which may be branched or cyclic.)

Specific examples of the formate compound represented by the general formula (IV) include, for example, 2-fluoroethyl formate, 2-chloroethyl formate, 2,2,2-trifluoroethyl formate, 2,2 , 3,3-tetrafluorobutanediol diformate, 2,3,5,6-tetrafluorohydroquinone diformate, and the like.
Among the ester compounds represented by the general formula (IV), an ester compound in which R ⁶ is an alkyl group having 1 to 3 carbon atoms substituted with at least one halogen atom, particularly a fluorine atom, is particularly preferable. From the viewpoint of improving low-temperature battery characteristics and long-term cycle characteristics, it is preferable to contain at least one selected from -fluoroethyl formate and 2,2,2-trifluoroethyl formate.

  The content of the ester compounds represented by the general formulas (I) to (IV) contained in the non-aqueous electrolyte is such as sufficient electric capacity, low temperature battery characteristics, long-term cycle characteristics, etc. If the battery performance is not obtained and is excessively large, the battery performance may be deteriorated. The content is preferably 0.01% by weight or more, particularly preferably 0.05% by weight or more, and most preferably 0.1% by weight, based on the weight of the non-aqueous electrolyte. Further, the upper limit is preferably 10% by weight or less, particularly preferably 5% by weight or less, and most preferably 3% by weight or less.

[Nonaqueous solvent]
Nonaqueous solvents used in the present invention include cyclic carbonates, chain carbonates, esters, sulfur acid ester compounds, ethers, amides, phosphate esters, sulfones, lactones, nitriles, and the like. Can be mentioned.
Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), vinylene carbonate (VC), butylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, and particularly include EC having a high dielectric constant. Is most preferred.
Examples of the chain carbonates include asymmetric chain carbonates such as methyl ethyl carbonate (MEC), methyl propyl carbonate, methyl butyl carbonate, and ethyl propyl carbonate, and symmetric chain carbonates such as dimethyl carbonate (DMC) and diethyl carbonate (DEC). Can be mentioned. In particular, the asymmetric chain carbonate has a low melting point and is effective for low temperature characteristics of the battery, and MEC is most preferable.

Examples of the esters include methyl propionate, methyl pivalate, butyl pivalate, hexyl pivalate, octyl pivalate, and the like, and examples of the sulfur acid ester compound include 1,3-propane sultone, 1,4-butanediol diester. Examples thereof include methane sulfonate, glycol sulfite, propylene sulfite, glycol sulfate, and propylene sulfate.
The ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1,2-dibutoxyethane, and the amides include dimethyl. Phosphoric esters such as formamide, trimethyl phosphate, trioctyl phosphate, etc., sulfones such as divinyl sulfone, lactones such as γ-butyrolactone, nitriles such as acetonitrile, adiponitrile, etc. .

Among the above non-aqueous solvents, cyclic carbonates, chain carbonates, esters, and sulfur acid ester compounds are preferable, and these can be used alone or in combination of two or more. Among these, it is more preferable to include cyclic carbonates and / or chain carbonates.
More specifically, a combination of cyclic carbonates such as EC, PC, and VC and chain carbonates such as MEC, DMC, and DEC is particularly preferable.
The volume ratio of cyclic carbonates: chain carbonates is 10:90 to 40:60, preferably 20:80 to 40:60, and more preferably 25:75 to 45:55.

Moreover, it is preferable to use a sulfur acid ester compound and / or divinyl sulfone in combination with the cyclic carbonates and the chain carbonates. In particular, the combined use with at least one sulfur acid ester compound selected from 1,3-propane sultone, glycol sulfite, and 1,4-butanediol dimethanesulfonate and / or divinylsulfone is most preferable in terms of charge / discharge characteristics.
In particular, when the ester compound represented by the general formula (II) or (IV) is used, the ester compound is contained in an amount of 0.01 to 10% by weight, and vinylene carbonate, 1,3-propane sultone, glycol salt. It is preferable to contain at least one selected from phyto, 1,4-butanediol dimethanesulfonate and divinylsulfone.

[Electrolyte salt]
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.
Preferable combinations include a combination of LiPF ₆ and LiBF ₄ , a combination of LiPF ₆ and LiN (SO ₂ CF ₃ ) ₂ , a combination of LiBF ₄ and LiN (SO ₂ CF ₃ ) _2, and the like. A combination of ₆ and LiBF ₄ is particularly preferred.

The electrolyte salt can be mixed in an arbitrary ratio. However, when LiPF ₆ is selected as the first electrolyte salt and other electrolyte salt, for example, LiBF ₄ is used in combination as the second electrolyte salt, the second electrolyte is used. The proportion of the salt in the total electrolyte salt is preferably 0.01 mol% or more, more preferably 0.03% or more, and most preferably 0.05% or more. The upper limit is preferably 45% or less, more preferably 20% or less, further preferably 10% or less, and most preferably 5% or less.
The concentration used by dissolving these total electrolyte salts is usually preferably 0.1 M or more, more preferably 0.5 M or more, still more preferably 0.7 M or more, relative to the nonaqueous solvent. 8M or more is most preferable. The upper limit is preferably 3M or less, more preferably 2.5M or less, further preferably 2.0M or less, and most preferably 1.4M or less.
The most preferable combination of the non-aqueous solvent and the electrolyte salt includes (i) EC and / or PC, (ii) VC, and (iii) one or more selected from MEC, DMC, and DEC, particularly MEC and DMC. An electrolytic solution containing a combination of LiPF ₆ and / or LiBF ₄ as an electrolyte salt in a mixed solvent composed of a combination or a combination of MEC and DEC can be used.
More specifically, the capacity ratio of one or more selected from (i) EC and / or PC: (ii) VC: (iii) MEC, DMC and DEC is 10: 0.2: 89.8-40. : 10: 50, preferably 20: 0.5: 79.5 to 35: 5: 60, more preferably 25: 1: 74 to 32: 3: 65, and LiPF ₆ : LiBF ₄ (mol) Ratio) = 100: 0 to 55:45, preferably 99.8: 0.2 to 75:25, more preferably 99.5: 0.5 to 85:15, most preferably 99: 1 to 90:10. It is preferable to combine the electrolyte salts.

[Production of non-aqueous electrolyte]
The electrolytic solution of the present invention is represented by the above general formulas (I) to (IV), for example, by mixing a nonaqueous solvent such as EC, PC, MEC, DMC, VC, etc., and dissolving the electrolyte salt therein. It can be obtained by dissolving the ester compound.
At this time, the non-aqueous solvent to be used, the ester compounds represented by the general formulas (I) to (IV), and other additives are 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 one.

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 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.

Examples of combinations when two or more aromatic compounds are used include the following (d) to (f).
(D) Biphenyl and tert-butylbenzene, biphenyl and tert-amylbenzene, cyclohexylbenzene and tert-amylbenzene, cyclohexylbenzene and 1-fluoro-4-tert-butylbenzene, tert-amylbenzene and 1-fluoro-4- A combination of tert-butylbenzene.
(E) A combination of biphenyl and cyclohexylbenzene, cyclohexylbenzene and tert-butylbenzene.
(F) Biphenyl and fluorobenzene, cyclohexylbenzene and fluorobenzene, 2,4-difluoroanisole and cyclohexylbenzene, cyclohexylbenzene and fluorocyclohexylbenzene compound, fluorocyclohexylbenzene compound and fluorobenzene, 2,4-difluoroanisole and fluorocyclohexylbenzene A combination of compounds.
In these, the combination of (d) and (e) is preferable, the combination of (d) is more preferable, and the combination containing a fluorine-containing compound is especially preferable in (d). The mixing ratio (weight ratio) of fluorine-free aromatic compound: fluorine-containing aromatic compound is preferably 50:50 to 10:90, more preferably 50:50 to 20:80, and 50:50 to 25:75. 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. The constituent members such as the positive electrode and the negative electrode other than the non-aqueous electrolyte are not particularly limited, and various known constituent members can be used.
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 of Co, Ni, Mn, Cu, Zn, and Cd, and 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. Battery capacity can be increased by replacing part or all of the carbon material with tin, a tin compound, silicon, or a silicon compound.
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, it is preferable to adjust the density of the electrode material layer in order to enhance the effect of adding the ester compounds represented by the general formulas (I) to (IV). 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.
Battery separators vary depending on manufacturing conditions. However, if the air permeability is too low, the mechanical strength is lowered, and if the air permeability is too high, the lithium ion conductivity is lowered and the function as a battery separator is sufficient. Disappear. 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 the present invention can be charged and discharged at -40 ° C or higher, preferably 0 ° C or higher. Moreover, it can charge / discharge at 100 degrees C or less, Preferably it is 80 degrees C or less.

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. Battery packs include overcurrent prevention elements such as PTC elements, thermal fuses, bimetals, and safety circuits (circuits that monitor the voltage, temperature, current, etc. of each battery and / or the entire battery pack, and cut off the current) It is preferable to provide at least one or more.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, this invention is not limited to these Examples, The various combination which can be easily guessed from the meaning of invention is possible. In particular, the combinations of solvents in the following examples are not limited.

Example 1
(Preparation of non-aqueous electrolyte)
In a dry nitrogen atmosphere, a nonaqueous solvent of ethylene carbonate (EC): vinylene carbonate (VC): dimethyl carbonate (DMC): methyl ethyl carbonate (MEC) (volume ratio) = 28: 2: 20: 50 was prepared, A non-aqueous electrolyte was prepared by dissolving LiPF ₆ as an electrolyte salt at a concentration of 0.95 M and LiBF ₄ at a concentration of 0.05 M, and then further adding 2-methoxyethyl formate to the non-aqueous electrolyte. [Compound represented by formula (II)] was added so as to be 1% by weight. The non-aqueous solvent, the electrolyte salt, and the ester compound were purified in advance.

[Production of lithium secondary battery]
The positive electrode was prepared by 94% by weight of LiCo _1/3 Ni _1/3 Mn _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, kneaded 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.
Then, using a polyethylene microporous film separator (thickness 20 μm), after injecting the non-aqueous electrolyte prepared above, air with a dew point of −60 ° C. was contained in the battery before sealing the battery, and the 18650 size cylinder A 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]
Using this 18650 battery, the battery was charged at a constant current of 2.2 A (1 C) at 25 ° C. to 4.2 V, 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. The discharge capacity at the 200th cycle was measured and determined as the 200th cycle discharge capacity retention rate when the initial discharge capacity was 100%.
For the evaluation of the low temperature characteristics, a similar 18650 battery was prepared using an electrolyte solution having the same composition as described above, charged to 4.2 V at a constant current of 25 ° C. and 2.2 A (1 C), and a final voltage of 4 The battery was charged at a constant voltage of 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. At the time of discharge at the 10th cycle, the battery was discharged at a constant current of −20 ° C. and 2.2 A (1 C) to a final voltage of 3.0 V. The discharge capacity at this time was reduced to 2-methoxyethyl methyl carbonate (Comparative Example 2). 1M (LiPF ₆ / LiBF ₄ = 95/5) -EC / VC / DMC / MEC (capacity ratio: 28/2/20/50) added to 1% by weight of non-aqueous electrolyte As compared with the discharge capacity at the 10th cycle (Comparative Example 2) at −20 ° C., the relative capacity was calculated. The results are shown in Table 2.
200 cycle discharge capacity retention rate (%) = (200th cycle discharge capacity) / (first cycle discharge capacity) × 100
Low temperature discharge capacity (relative value) = (10th cycle discharge capacity [−20 ° C.]) / (10th cycle discharge capacity [−20 ° C.] of Comparative Example 2)

Examples 2-14
A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 1.0% by weight of the additives shown in Table 1 was used with respect to the non-aqueous electrolyte as an additive to produce a 18650 size cylindrical battery. A charge / discharge cycle test was conducted. The results are shown in Table 2.
Examples 15-16
A nonaqueous solvent of ethylene carbonate (EC): vinylene carbonate (VC): diethyl carbonate (DEC): methyl ethyl carbonate (MEC) (volume ratio) = 28: 2: 20: 50 was prepared, and LiPF was used as an electrolyte salt thereof. ₆ was dissolved to a concentration of 0.95 M and LiBF ₄ to a concentration of 0.05 M to prepare a non-aqueous electrolyte solution. A 18650 size cylindrical battery was produced in the same manner as in Example 1 except that 0% by weight was used, and a charge / discharge cycle test was performed. The results are shown in Table 2.

Comparative Example 1
Except that the additive of the present invention was not used, a nonaqueous electrolytic solution was prepared in the same manner as in Example 1 to produce a 18650 size cylindrical battery, and a charge / discharge cycle test was performed. The results are shown in Table 2.
Comparative Example 2
As an additive, except that 1% by weight of 2-methoxyethyl methyl carbonate was used with respect to the non-aqueous electrolyte, a non-aqueous electrolyte was prepared in the same manner as in Example 1 to produce a 18650 size cylindrical battery, A charge / discharge cycle test was conducted. The results are shown in Table 2.

Comparative Example 3
As an additive, except that 1% by weight of 2-fluoroethyl methyl carbonate was used with respect to the non-aqueous electrolyte, a non-aqueous electrolyte was prepared in the same manner as in Example 1 to produce a 18650 size cylindrical battery, A charge / discharge cycle test was conducted. The results are shown in Table 2.

  It turns out that the lithium secondary battery of the said Example is excellent in the low temperature battery characteristic and the long-term cycle characteristic compared with the lithium secondary battery of the comparative example.

Claims (6)

In a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, the non-aqueous electrolyte solution contains an ester compound represented by the following general formulas (I) to (IV), bis (2-methoxyethyl ) acetylene dicarboxylate ), At least one selected from 2-methoxyethylmethyl acetylenedicarboxylate and bis (2,2,2-trifluoroethyl) acetylenedicarboxylate , non-aqueous for lithium secondary batteries Electrolytic solution.

(Wherein, R ¹ is an alkenyloxy group having 2 to 8 carbon atoms, alkynyloxy group having 3 to 8 carbon atoms, or shows an alkynyl group having 2 to 8 carbon atoms, an alkynyl group of R ¹ is substituted with an ester group is good .R ² also be represents an alkyl group, or an alkoxyalkyl group having 3 to 12 carbon atoms which may be substituted with a halogen atom having 1 to 8 carbon atoms which may be substituted with a halogen atom, R ¹ and R ^2, which may be branched .X is an alkylene group having 2 to 6 carbon atoms, which may be branched .Y is, -C (= O) -, - S (= O) —, —S (═O) ₂ —, or —C (═O) C (═O) — represents a bonding group, and a represents an integer of 1 to 12.)

(In the formula, X and a are the same as defined above, and R ³ represents an alkyl group having 1 to 8 carbon atoms which may be substituted with a halogen atom , or a formyl group only when a is 2 or more, It may be branched.)

(Wherein, Y is as defined above, R ⁴ is alkenyloxy group having 2 to 8 carbon atoms, or .R ⁵ showing the alkynyloxy group having 3 to 8 carbon atoms is at least one or more halogen atoms in a substituted alkyl group having 1 to 6 carbon atoms, R ⁴ and R ^5, may be branched.)

(Wherein, R ⁶ represents at least one or more alkyl groups of 1 to 6 carbons substituted with a halogen atom, it may be branched.) The ester compounds represented by the general formulas (I) to (IV), bis (2-methoxyethyl) acetylene dicarboxylate, 2-methoxyethyl methyl acetylenedicarboxylate, and bis (2,2,2-trimethyl acetylene dicarboxylate) The nonaqueous electrolytic solution for a lithium secondary battery according to claim 1, wherein at least one selected from fluoroethyl) is contained in an amount of 0.01 to 10 wt% in the nonaqueous electrolytic solution. The ester compound represented by the general formula (I) is 2-propynyl 2-methoxyethyl carbonate, 2-propynyl 2- (2-fluoroethoxy) ethyl carbonate, 2-propynyl 2- (2-chloroethoxy) ethyl carbonate, 2-propynyl 2- (2-methoxyethoxy) ethyl carbonate; 2-methoxyethyl propiolate, 2-ethoxyethyl propiolate, 2- (2-fluoroethoxy) ethyl propiolate; 2-propynyl 2-methoxyethyl Sulfite, 2-propynyl 2- (2-fluoroethoxy) ethyl sulfite, allyl 2-methoxyethyl sulfite; 2-propynyl 2-methoxyethyl sulfate, 2-propynyl 2-ethoxyethyl sulfate, 2-propynyl 2- ( 2-Fluoroethoxy) Ethyl sulfate; at least one selected from 2-propynyl 2-methoxyethyl oxalate, 2-propynyl 2-ethoxyethyl oxalate, and 2-propynyl 2- (2-fluoroethoxy) ethyl oxalate;
The ester compound represented by the general formula (II) is at least one selected from 2-methoxyethyl formate, 2-ethoxyethyl formate, and diethylene glycol diformate,
The ester compound represented by the general formula (III) is 2-propynyl 2-fluoroethyl carbonate, 2-propynyl 2,2,2-trifluoroethyl carbonate, 2-propynyl pentafluorophenyl carbonate, methoxyethyl propiolate, Acetylenedicarboxylic acid bis (2,2,2-trifluoroethyl), 1,2-ethanediol dipropiolate, 1,3-propanediol dipropiolate, 2-propynyl 2-fluoroethyl sulfite, 2-propynyl 2 2,2-trifluoroethyl sulfite, 2-propynyl pentafluorophenyl sulfite, 2-fluoroethyl propiolate, 2,2,2-trifluoroethyl propiolate, 2-propynyl 2-fluoroethyl oxa Rate, and 2-propynylpe At least one selected from n-fluorophenyl oxalate,
The lithium according to claim 1 or 2, wherein the ester compound represented by the general formula (IV) is at least one selected from 2-fluoroethyl formate and 2,2,2-trifluoroethyl formate. Nonaqueous electrolyte for secondary batteries . In a nonaqueous electrolytic solution in which an electrolyte salt is dissolved in a nonaqueous solvent, the nonaqueous electrolytic solution contains 0.01 to 10% by weight of the ester compound represented by the general formula (II) or (IV). And at least one selected from vinylene carbonate, 1,3-propane sultone, glycol sulfite, 1,4-butanediol dimethanesulfonate and divinylsulfone, and a non-aqueous electrolysis for a lithium secondary battery liquid. The nonaqueous electrolytic solution for a lithium secondary battery according to any one of claims 1 to 4 , wherein the nonaqueous solvent contains a cyclic carbonate and a chain carbonate. Positive electrode, a negative electrode, and a lithium secondary battery, comprising the nonaqueous electrolytic solution according to any one of claims 1-5.