JP4517730B2 - Nonaqueous electrolyte and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a non-aqueous electrolyte that can provide a lithium secondary battery excellent in battery characteristics such as battery cycle characteristics, electric capacity, and storage characteristics, and a lithium secondary battery using the same.

In recent years, lithium secondary batteries have been widely used as driving power sources for small electronic devices and the like. A lithium secondary battery is mainly composed of a positive electrode, a non-aqueous electrolyte, and a negative electrode. In particular, a lithium secondary battery using a lithium composite oxide such as LiCoO ₂ as a positive electrode and a carbon material or lithium metal as a negative electrode is used. It is preferably used. As the non-aqueous electrolyte for the lithium secondary battery, carbonates such as ethylene carbonate (EC) and propylene carbonate (PC) are preferably used.

However, there is a demand for a secondary battery having more excellent battery characteristics such as battery cycle characteristics and electric capacity.
A lithium secondary battery using, for example, LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ or the like as a positive electrode is partially decomposed by oxidation when a solvent in a non-aqueous electrolyte is locally charged. In order to inhibit the desired electrochemical reaction, the battery performance is degraded. This seems 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, a lithium secondary battery using a highly crystallized carbon material such as natural graphite or artificial graphite as the negative electrode is reduced and decomposed on the negative electrode surface when the solvent in the non-aqueous electrolyte is charged. Even in EC that is generally widely used, reductive decomposition occurs partly during repeated charging and discharging, resulting in a decrease in battery performance.

  In order to improve the battery characteristics of this lithium secondary battery, it has been proposed to add a compound having a double bond. For example, Patent Document 1 discloses a cyclic carbonate having a double bond such as vinylene carbonate. In order to improve the electrical characteristics in Patent Document 1, in Patent Document 2, an alkene compound having an ether bond, an ester bond, or a carbonate ester bond is proposed. Proposed. However, the non-aqueous electrolyte secondary battery using 2-butenylenedimethyldicarbonate described in Patent Document 2 is described as having a small decrease in discharge capacity and increase in internal resistance due to charge / discharge, but its cycle The characteristics are not sufficiently satisfactory, and an additive having higher cycle characteristics is required to increase the capacity of the lithium secondary battery.

JP-A-11-260401 JP 2002-100402 A

  The present invention solves the above-described problems related to the non-aqueous electrolyte for a lithium secondary battery, has excellent battery cycle characteristics, and also has excellent battery characteristics such as electric capacity and storage characteristics in a charged state. It aims at providing the nonaqueous electrolyte which can be used for the lithium secondary battery which can comprise a secondary battery, and a lithium secondary battery using the same.

  The present invention relates to a non-aqueous electrolyte solution for a lithium secondary battery in which an electrolyte salt is dissolved in a non-aqueous solvent.

(Wherein R ₁ and R ₂ each independently represents an alkyl group having 1 to 6 carbon atoms which may be branched; R ₃ and R ₄ are unsubstituted or alkyl having 1 to 4 carbon atoms; X represents a vinylene group, a 2-butenylene group, or a 1,3-butadienylene group) . The present invention relates to a nonaqueous electrolytic solution characterized by containing from 01% by weight to 10% by weight .

  The present invention also provides a lithium secondary battery comprising a positive electrode, a negative electrode, and a nonaqueous electrolyte solution in which an electrolyte salt is dissolved in a nonaqueous solvent, wherein the positive electrode is a material containing a lithium composite oxide, and the negative electrode occludes lithium. -A releasable material, and the following general formula (I)

(Wherein R ₁ and R ₂ each independently represents an alkyl group having 1 to 6 carbon atoms which may be branched; R ₃ and R ₄ are unsubstituted or alkyl having 1 to 4 carbon atoms; X represents a vinylene group, a 2-butenylene group, or a 1,3-butadienylene group) . The present invention relates to a lithium secondary battery characterized by containing from 01% by weight to 10% by weight .

  According to the present invention, it is possible to provide a lithium secondary battery excellent in battery characteristics such as battery cycle characteristics, electric capacity, and storage characteristics.

In the present invention, when a non-aqueous electrolyte obtained by containing a disulfonic acid ester compound in the non-aqueous electrolyte is used for a lithium secondary battery having a high capacity, it is a conventional problem. It was found that the cycle characteristics were excellent. Although its operational effect is not clear, by using the double bond-containing compound having the R ₁ (or R ₂ ) SO ₃ group represented by the general formula (I), a good film can be formed on the negative electrode. It is estimated that it will be formed.
Specific embodiments of the present invention will be described below.

In the double bond-containing compound represented by the general formula (I) contained in the non-aqueous electrolyte in which the electrolyte is dissolved in the non-aqueous solvent, R ₁ and R ₂ are a methyl group, an ethyl group, a propyl group, Alkyl groups having 1 to 6 carbon atoms such as butyl group, pentyl group and hexyl group are preferred. The alkyl group may be a branched alkyl group such as an isopropyl group, an isobutyl group, or an isopentyl group. R ₃ and R ₄ are preferably a methylene group, a methylmethylene group, an ethylmethylene group, a propylmethylene group, or a dimethylmethylene group. X is a vinylene group, 2-butenylene group, or 1,3-butadienylene group.

Of the double bond-containing compounds represented by the general formula (I), compounds in which R ₁ and R ₂ are straight chain alkyl groups include, for example, 2-butene-1,4-diol dimethanesulfonate. (X = vinylene group), 3-hexene-2,5-diol dimethanesulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-diol dimethanesulfonate (X = vinylene group) 3-hexene-1,6-dioldimethanesulfonate (2-butenylene group), 2,4-hexadiene-1,6-dioldimethanesulfonate (1,3-butadienylene group), 2-butene-1,4 -Diol diethane sulfonate (X = vinylene group), 3-hexene-2,5-diol diethane sulfonate (X = vinylene group), 2,5-dimethyl-3-hex -2,5-diol diethane sulfonate (X = vinylene group), 3-hexene-1,6-diol diethane sulfonate (2-butenylene group), 2,4-hexadiene-1,6-diol diethane sulfonate (1,3-butadienylene group), 2-butene-1,4-diol dipropane sulfonate (X = vinylene group), 3-hexene-2,5-diol dipropane sulfonate (X = vinylene group), 2,5 -Dimethyl-3-hexene-2,5-dioldipropanesulfonate (X = vinylene group), 3-hexene-1,6-dioldipropanesulfonate (2-butenylene group), 2,4-hexadiene-1,6 -Diol dipropane sulfonate (1,3-butadienylene group), 2-butene-1,4-diol dibutane sulfonate ( X = vinylene group), 3-hexene-2,5-dioldibutanesulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-dioldibutanesulfonate (X = vinylene group), 3-hexene-1,6-dioldibutanesulfonate (2-butenylene group), 2,4-hexadiene-1,6-dioldibutanesulfonate (1,3-butadienylene group), 2-butene-1,4- Diol dipentane sulfonate (X = vinylene group), 3-hexene-2,5-diol dipentane sulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-diol dipentane sulfonate (X = Vinylene group), 3-hexene-1,6-dioldipentanesulfonate (2-butenylene group), 2,4-hexadiene-1 6-diol dipentane sulfonate (1,3-butadienylene group), 2-butene-1,4-diol dihexane sulfonate (X = vinylene group), 3-hexene-2,5-diol dihexane sulfonate (X = vinylene) Group), 2,5-dimethyl-3-hexene-2,5-dioldihexanesulfonate (X = vinylene group), 3-hexene-1,6-dioldihexanesulfonate (2-butenylene group), 2,4 -Hexadiene-1,6-dioldihexanesulfonate (1,3-butadienylene group), 2-butene-1,4-diolmethaneethanesulfonate (X = vinylene group), 3-hexene-2,5-diolmethaneethane Sulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-diol methane Sulfonate (X = vinylene group), 3-hexene-1,6-diol methaneethane sulfonate (2-butenylene group), 2,4-hexadiene-1,6-diol methaneethane sulfonate (1,3-butadienylene group), 2-butene-1,4-diol methanepropane sulfonate (X = vinylene group), 3-hexene-2,5-diol methanepropane sulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2, 5-diol methanepropane sulfonate (X = vinylene group), 3-hexene-1,6-diol methanepropane sulfonate (2-butenylene group), 2,4-hexadiene-1,6-diol methanepropane sulfonate (1,3 -Butadienylene group), 2-butene-1,4-diol methanebutanesulfonate (X = vinylene group), 3-hexene-2,5-diol methanebutanesulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-diolmethanebutanesulfonate (X = vinylene group) ), 3-hexene-1,6-diol methanebutanesulfonate (2-butenylene group), 2,4-hexadiene-1,6-diolmethanebutanesulfonate (1,3-butadienylene group), 2-butene-1, 4-diol methanepentanesulfonate (X = vinylene group), 3-hexene-2,5-diolmethanepentanesulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-diolmethanepentanesulfonate (X = vinylene group), 3-hexene-1,6-diol methanepentanesulfonate (2-butene Ren group), 2,4-hexadiene-1,6-diol methanepentane sulfonate (1,3-butadienylene group), 2-butene-1,4-diol methane hexane sulfonate (X = vinylene group), 3-hexene- 2,5-diol methane hexanesulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-diol methane hexane sulfonate (X = vinylene group), 3-hexene-1,6-diol methane Hexane sulfonate (2-butylene group), 2,4-hexadiene-1,6-diol methane hexane sulfonate (1,3-butadienylene group), 2-butene-1,4-diol methane (2-propane) sulfonate (X = Vinylene group), 3-hexene-2,5-diol methane (2-propane) sulfonate X = vinylene group), 2,5-dimethyl-3-hexene-2,5-diolmethane (2-propane) sulfonate (X = vinylene group), 3-hexene-1,6-diolmethane (2-propane) Sulfonate (2-butenylene group), 2,4-hexadiene-1,6-diol methane (2-propane) sulfonate (1,3-butadienylene group), 2-butene-1,4-diol methane isobutane sulfonate (X = Vinylene group), 3-hexene-2,5-diol methaneisobutanesulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-diolmethaneisobutanesulfonate (X = vinylene group), 3- Hexene-1,6-diol methaneisobutanesulfonate (2-butenylene group), 2,4-hexadiene-1,6 -Diol methane isobutane sulfonate (1,3-butadienylene group), 2-butene-1,4-diol methane isopentane sulfonate (X = vinylene group), 3-hexene-2,5-diol methane isopentane sulfonate (X = vinylene group) ), 2,5-dimethyl-3-hexene-2,5-diol methaneisopentane sulfonate (X = vinylene group), 3-hexene-1,6-diol methane isopentane sulfonate (2-butenylene group), 2,4- Examples include hexadiene-1,6-diol methaneisopentane sulfonate (1,3-butadienylene group).

Of the double bond-containing compounds represented by the general formula (I), compounds in which R ₁ and R ₂ are branched alkyl groups include, for example, 2-butene-1,4-dioldi (2- Propane) sulfonate (X = vinylene group), 3-hexene-2,5-dioldi (2-propane) sulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-dioldi (2- Propane) sulfonate (X = vinylene group), 3-hexene-1,6-dioldi (2-propane) sulfonate (2-butenylene group), 2,4-hexadiene-1,6-dioldi (2-propane) sulfonate ( 1,3-butadienylene group), 2-butene-1,4-diol di (2-propane) sulfonate (X = vinylene group), 3-hexene-2,5-diol di (2 Propane) sulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-dioldi (2-propane) sulfonate (X = vinylene group), 3-hexene-1,6-dioldi (2- Propane) sulfonate (2-butenylene group), 2,4-hexadiene-1,6-dioldi (2-propane) sulfonate (1,3-butadienylene group), 2-butene-1,4-dioldiisobutanesulfonate (X = Vinylene group), 3-hexene-2,5-diol diisobutane sulfonate (X = vinylene group), 2,5-dimethyl-3-hexene-2,5-diol diisobutane sulfonate (X = vinylene group), 3 -Hexene-1,6-diol diisobutanesulfonate (2-butenylene group), 2,4-hexadiene-1,6-di All diisobutane sulfonate (1,3-butadienylene group), 2-butene-1,4-diol diisopentane sulfonate (X = vinylene group), 3-hexene-2,5-diol diisopentane sulfonate (X = vinylene group) 2,5-dimethyl-3-hexene-2,5-diol diisopentane sulfonate (X = vinylene group), 3-hexene-1,6-diol diisopentane sulfonate (2-butenylene group), 2,4-hexadiene Examples include compounds such as -1,6-diol diisopentanesulfonate (1,3-butadienylene group). However, the present invention is not limited to these compounds.

In the double bond-containing compound, if the content of the double bond-containing compound represented by the general formula (I) is excessively large, the conductivity of the electrolytic solution may change and the battery performance may be deteriorated. The amount is 10% by weight or less and more preferably 5% by weight or less based on the weight of the non-aqueous electrolyte. On the other hand, if the amount is too small, a sufficient film is not formed, and the expected battery characteristics cannot be obtained. Therefore, the amount is 0.01% by weight or more, particularly 0.05% by weight or more , based on the weight of the non-aqueous electrolyte. And more preferably 0.1% by weight or more.

  Examples of the non-aqueous solvent used in the present invention include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate, vinylene carbonate (VC), dimethyl vinylene carbonate, vinyl ethylene carbonate, γ- Lactones such as butyrolactone, γ-valerolactone, α-angelicalactone, dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), diethyl carbonate (DEC), methyl propyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, etc. Chain carbonates, tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1 Ethers such as 2-dibutoxyethane, nitriles such as acetonitrile and adiponitrile, phosphate esters such as trimethyl phosphate and trioctyl phosphate, methyl propionate, methyl pivalate, butyl pivalate, octyl pivalate, oxalic acid Chain esters such as dimethyl, ethylmethyl oxalate and diethyl oxalate, amides such as dimethylformamide, 1,3-propane sultone, 1,4-propane sultone, 1,3-butane sultone, divinyl sulfone, 1,4 -Sulfuric acid ester compounds such as butanediol dimethanesulfonate, glycol sulfite, propylene sulfite, glycol sulfate, and propylene sulfate.

  These non-aqueous solvents are usually used as a mixture in order to achieve appropriate physical properties. The combination includes, for example, a combination of a cyclic carbonate and a chain carbonate, a combination of a cyclic carbonate and a lactone, a combination of a lactone and a chain ester, a combination of a cyclic carbonate, a lactone and a chain ester, a cyclic carbonate Combinations of chain, chain carbonates and lactones, combinations of cyclic carbonates and ethers, combinations of cyclic carbonates, chain carbonates and ethers, cyclic carbonates, chain carbonates and chain esters Various combinations such as a combination thereof are mentioned, and the mixing ratio is not particularly limited.

  Among these, the ratio of the cyclic carbonate and the chain carbonate is preferably 20:80 to 40:60, and particularly preferably 25:75 to 35:65 in terms of the volume ratio. Of the chain carbonates, asymmetric carbonates such as methyl ethyl carbonate, methyl propyl carbonate, and methyl butyl carbonate are preferably used. Among them, it is preferable to use methyl ethyl carbonate, which is an asymmetric chain carbonate that is liquid at low temperatures and has a relatively high boiling point and therefore has little evaporation. Furthermore, among the chain carbonates, the volume ratio of methyl ethyl carbonate, which is an asymmetric chain carbonate, to dimethyl carbonate and / or diethyl carbonate, which is a symmetric chain carbonate, is 100/0 to 51/49. Is preferable, and 100/0 to 70/30 is more preferable.

  Further, among the above combinations, in the combination using lactones, a ratio that maximizes the volume ratio of lactones is preferable.

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 , 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 F ₇ ), etc. And lithium salts containing cyclic alkylene chains such as (CF ₂ ) ₂ (SO ₂ ) ₂ NLi, (CF ₂ ) ₃ (SO ₂ ) ₂ NLi, and the like. . These electrolyte salts may be used alone or in combination of two or more. The concentration used by dissolving these electrolyte salts is usually preferably 0.3 M or more, more preferably 0.5 M or more, and most preferably 0.7 M or more with respect to the non-aqueous solvent. The concentration of these electrolyte salts 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, for example, mixed with a nonaqueous solvent such as ethylene carbonate, propylene carbonate, or methyl ethyl carbonate, dissolved in the electrolyte salt, and represented by the general formula (I). It can be obtained by dissolving the disulfonic acid ester compound.

  In addition, by including, for example, air or carbon dioxide in the nonaqueous electrolytic solution of the present invention, it is possible to suppress gas generation due to decomposition of the electrolytic solution, and to improve battery performance such as cycle characteristics and storage characteristics.

  In the present invention, as a method for containing (dissolving) carbon dioxide or air in the non-aqueous electrolyte, (1) contacting the air or carbon dioxide-containing gas before injecting the non-aqueous electrolyte into the battery in advance. (2) After pouring, before or after sealing the battery, either a method of containing air or a carbon dioxide-containing gas in the battery may be used, or a combination of these may be used. 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.

  The nonaqueous electrolytic solution of the present invention is used as a constituent member of a secondary battery, particularly a lithium secondary battery. The constituent members other than the non-aqueous electrolyte constituting the secondary battery are not particularly limited, and various conventionally used 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. Only one type of these positive electrode active materials may be selected and used, or two or more types may be used in combination. Examples of such composite metal oxides include LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and LiCo _1-x Ni _x O ₂ (0.01 <x <1). Further, LiCoO ₂ and LiMn ₂ O ₄ , LiCoO ₂ and LiNiO ₂ , LiMn ₂ O ₄ and LiNiO ₂ may be appropriately mixed and used. As described above, the positive electrode active material is a lithium composite metal oxide such as LiCoO ₂ , LiMn ₂ O ₄ , LiNiO ₂ , and the like that has an open circuit voltage after charging of 4.3 V or more based on Li Most preferably, a lithium composite metal oxide containing Co or Ni is used as the positive electrode material, and a part of the lithium composite metal 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, or the like.

  Any conductive material that does not cause a chemical change as the conductive agent for the positive electrode may be used. Examples thereof include graphite such as natural graphite (such as flake 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.

  The positive electrode is composed of a conductive agent such as acetylene black or carbon black, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), a copolymer of acrylonitrile and butadiene. After kneading with a binder such as a polymer (NBR) or carboxymethyl cellulose (CMC) to form a positive electrode mixture, this positive electrode material is rolled into an aluminum foil or stainless steel lath plate as a current collector, and 50 It is produced by heat-treating under a vacuum at a temperature of about 0 to 250 ° C. for about 2 hours.

The negative electrode is made of a material capable of inserting and extracting lithium. For example, lithium metal, lithium alloys, and carbon materials (pyrolytic carbons, cokes, graphites (artificial graphite, natural graphite, etc.), organic polymer compounds Combustion body, carbon fiber], tin, tin compound, silicon, silicon compound are used. Battery capacity can be increased by replacing part or all of the carbon material with tin, a tin compound, silicon, or a silicon compound.
As the negative electrode (negative electrode active material), in the carbon material, it is particularly preferable that the plane spacing (d ₀₀₂ ) of the lattice plane ( ₀₀₂ ) is 0.340 nm or less, and the graphite type is 0.335 to 0.340 nm. It is more preferable to use graphites having a crystal structure. Only one kind of these negative electrode active materials may be selected and used, or two or more kinds may be used in combination. Powder materials such as carbon materials are ethylene propylene diene terpolymer (EPDM), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), a copolymer of styrene and butadiene (SBR), and a copolymer of acrylonitrile and butadiene. Kneaded with a binder such as a polymer (NBR) or carboxymethylcellulose (CMC) and used as a negative electrode mixture. The manufacturing method of a negative electrode is not specifically limited, It can manufacture with the method similar to the manufacturing method of said positive electrode.

  The structure of the lithium secondary battery is not particularly limited, and a coin-type battery having a positive electrode, a negative electrode, and a single-layer or multi-layer separator, and a cylindrical battery or a square type having a positive electrode, a negative electrode, and a roll separator. An example is a battery. As the separator, a known microporous film of polyolefin such as polypropylene or polyethylene, woven fabric, non-woven fabric or the like is used. Further, the battery separator may have any configuration of a single layer porous film and a laminated porous film. Although the battery separator used in the present invention varies depending on production conditions, the air permeability is preferably 50 to 1000 seconds / 100 cc, more preferably 100 to 800 seconds / 100 cc, and most preferably 300 to 500 seconds / 100 cc. . If the air permeability is too high, the lithium ion conductivity is lowered, so that the function as a battery separator is not sufficient, and if it is too low, the mechanical strength is lowered. The porosity is preferably 30 to 60%, more preferably 35 to 55%, and most preferably 40 to 50%. In particular, it is preferable to set the porosity within this range because the capacity characteristics of the battery are improved. Furthermore, the thickness of the battery separator is preferably as thin as possible because the energy density can be increased, but it is preferably 5 to 50 μm, more preferably 10 to 40 μm, and most preferably 15 to 25 μm from both sides of mechanical strength and performance.

In the present invention, the density of the electrode material layer is important in order to obtain an effective additive effect. In particular, the density of the positive electrode mixture layer formed on the aluminum foil is preferably 3.2~4.0g / cm ^3, more preferably 3.3~3.9g / cm ^3, and most preferably 3.4 to 3.8 g / cm ³ . If the density of the positive electrode mixture exceeds 4.0 g / cm ³ , the production becomes substantially difficult. On the other hand, the density of the negative electrode mixture layer formed on the copper foil 1.3~2.0g / cm ^3, more preferably 1.4~1.9g / cm ^3, and most preferably 1.5 to 1. Between 8 g / cm ³ . If the density of the negative electrode mixture layer exceeds 2.0 g / cm ³ , the production becomes substantially difficult.

  In addition, the thickness of the positive electrode layer (per collector side) suitable in the present invention is 30 to 120 μm, preferably 50 to 100 μm, and the thickness of the negative electrode layer (per collector side). ) Is from 1 to 100 μm, preferably from 3 to 70 μm. If the thickness of the electrode material layer is less than the preferred range, the amount of active material in the electrode material layer is reduced, and the battery capacity is reduced. On the other hand, if the thickness is larger than the above range, the cycle characteristics and rate characteristics deteriorate, which is not preferable.

  Further, the configuration of the lithium secondary battery is not particularly limited, and examples thereof include a coin battery, a cylindrical battery, a square battery, and a stacked battery having a positive electrode, a negative electrode, a porous membrane separator, and an electrolytic solution.

  The lithium secondary battery according to the present invention has excellent cycle characteristics over a long period of time even when the end-of-charge voltage is greater than 4.2V, and particularly when the end-of-charge voltage is 4.3V or more. Excellent cycle characteristics. The end-of-discharge voltage can be 2.5 V or higher, and can be 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. In addition, the lithium secondary battery in the present invention can be charged / discharged at −40 ° C. or higher, preferably 0 ° C. or higher. Moreover, although it can charge / discharge at 100 degrees C or less, Preferably it is 80 degrees C or less.

  As a countermeasure against the increase in internal pressure of the lithium secondary battery in the present invention, a safety valve can be used for the sealing plate. In addition, a method of cutting a member such as a battery can or a gasket can be used. In addition, it is preferable to provide various conventionally known safety elements (at least one of fuses, bimetals, and PTC elements as overcurrent prevention elements).

  A plurality of lithium secondary batteries according to the present invention are assembled in series and / or in parallel as needed. In addition to safety elements such as PTC elements, thermal fuses, fuses and / or current interrupting elements, the battery pack also monitors the safety circuit (voltage, temperature, current, etc. of each battery and / or the entire battery pack and interrupts the current) A circuit having a function to do this may be provided.

  EXAMPLES Hereinafter, although an Example and a comparative example are given and this invention is demonstrated more concretely, this invention is not limited to these Examples.

Example 1
(Preparation of non-aqueous electrolyte)
After preparing a non-aqueous solvent of EC: VC: MEC (volume ratio) = 30: 2: 68, and dissolving LiPF ₆ as an electrolyte salt so as to have a concentration of 1M, a non-aqueous electrolyte was prepared. Further, 2-butene-1,4-dioldimethanesulfonate was added to the nonaqueous electrolytic solution so as to be 0.1% by weight.

[Production of lithium secondary battery and measurement of battery characteristics]
LiCoO ₂ (positive electrode active material) 89% by weight, acetylene black (conductive agent) 5.3% by weight, and polyvinylidene fluoride (binder) 5.7% by weight are mixed with 1-methyl. A mixture prepared by adding a -2-pyrrolidone solvent was applied onto an aluminum foil, dried, pressure-molded, and heat-treated to prepare a positive electrode. 90% by weight of artificial graphite (negative electrode active material) and 10% by weight of polyvinylidene fluoride (binder) were mixed, and 1-methyl-2-pyrrolidone solvent was added to this, and the resulting mixture was added to the copper foil. The negative electrode was prepared by drying, pressure molding, and heat treatment. And using the separator of a polypropylene microporous film, said nonaqueous electrolyte solution was inject | poured and the coin battery (diameter 20mm, thickness 3.2mm) was produced.
Using this coin battery, it was charged at a constant current and a constant voltage of 1.1 mA at room temperature (25 ° C.) for 5 hours to a final voltage of 4.2 V, and then at a constant current of 1.1 mA and a final voltage of 2. The battery was discharged to 7 V, and this charge / discharge was repeated. The battery characteristics after 50 cycles were measured. The production conditions and battery characteristics of the coin battery are shown in Table 1.

Examples 2-4
As an additive, non-water was used in the same manner as in Example 1 except that 2-butene-1,4-dioldimethanesulfonate was used in an amount of 1% by weight, 2% by weight and 5% by weight, respectively, with respect to the non-aqueous electrolyte. An electrolyte solution was prepared to prepare a coin battery, and a charge / discharge cycle was performed. The production conditions and battery characteristics of the coin battery are shown in Table 1.

Examples 5-10
As additives, 3-hexene-2,5-diol dimethanesulfonate, 2,5-dimethyl-3-hexene-2,5-diol dimethanesulfonate, 2-butene-1,4-diol di (2-propane) Sulfonate, 2-butene-1,4-diol dibutane sulfonate, 2,4-hexadiene-1,6-diol dimethane sulfonate, 2-butene-1,4-diol methane isopropane sulfonate with respect to the non-aqueous electrolyte A non-aqueous electrolyte was prepared in the same manner as in Example 1 except that 2% by weight of each was used, and a coin battery was prepared, and a charge / discharge cycle was performed. The production conditions and battery characteristics of the coin battery are shown in Table 1.

Example 11
A non-aqueous electrolyte was prepared in the same manner as in Example 3 except that LiMn ₂ O ₄ was used as the positive electrode (positive electrode active material) instead of LiCoO ₂ , and a charge / discharge cycle was performed. The production conditions and battery characteristics of the coin battery are shown in Table 1.

Comparative Example 1
Except that the additive was not used, a non-aqueous electrolyte was prepared in the same manner as in Example 1 to produce a coin battery, and a charge / discharge cycle was performed. The production conditions and battery characteristics of the coin battery are shown in Table 1.

Comparative Example 2
A non-aqueous electrolyte solution was prepared in the same manner as in Example 1 except that 2-butenylenedimethyl dicarbonate was used as an additive in an amount of 2% by weight based on the non-aqueous electrolyte solution. A cycle was performed. The production conditions and battery characteristics of the coin battery are shown in Table 1.

In addition, this invention is not limited to the Example described, The various combination which can be easily guessed from the meaning of invention is possible. In particular, the combination of solvents in the above examples is not limited. Furthermore, although the said Example is related with a coin battery, this invention is applied also to a square-shaped battery, a cylindrical battery, or a laminate type battery.

Claims (2)

In a non-aqueous electrolyte for a lithium secondary battery in which an electrolyte salt is dissolved in a non-aqueous solvent, the following general formula (I) is contained in the non-aqueous electrolyte.

(Wherein R ₁ and R ₂ each independently represents an alkyl group having 1 to 6 carbon atoms which may be branched; R ₃ and R ₄ are unsubstituted or alkyl having 1 to 4 carbon atoms; X represents a vinylene group, a 2-butenylene group, or a 1,3-butadienylene group) . A non-aqueous electrolyte characterized by containing from 01% by weight to 10% by weight . In a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution in which an electrolyte salt is dissolved in a non-aqueous solvent, the positive electrode is a material containing a lithium composite oxide, and the negative electrode is a material capable of inserting and extracting lithium. In the non-aqueous electrolyte, the following general formula (I)

(Wherein R ₁ and R ₂ each independently represents an alkyl group having 1 to 6 carbon atoms which may be branched; R ₃ and R ₄ are unsubstituted or alkyl having 1 to 4 carbon atoms; X represents a vinylene group, a 2-butenylene group, or a 1,3-butadienylene group) . A lithium secondary battery comprising 01 wt% or more and 10 wt% or less .