JP5532584B2 - Non-aqueous electrolyte and lithium secondary battery using the same - Google Patents

Description

  The present invention relates to a high-voltage lithium secondary battery and a non-aqueous electrolyte used therefor.

  Lithium secondary batteries have the advantages of high energy density and less self-discharge. Therefore, in recent years, it has been widely used as a power source for consumer mobile devices such as mobile phones, notebook computers, and PDAs.

  Conventional non-aqueous electrolytes for lithium secondary batteries are generally composed of a lithium salt that is a supporting electrolyte and a non-aqueous solvent. The nonaqueous solvent used here is required to have a high dielectric constant in order to dissociate the lithium salt, to exhibit high ionic conductivity in a wide temperature range, and to be stable in the battery. Since it is difficult to achieve these requirements with a single solvent, usually a high boiling point solvent typified by propylene carbonate, ethylene carbonate, etc. and a low boiling point solvent typified by dimethyl carbonate, diethyl carbonate, etc. are used. Used in combination as a non-aqueous solvent.

  In order to improve various characteristics of lithium secondary batteries, various improvements are made to improve initial capacity, rate characteristics, cycle characteristics, high temperature storage characteristics, low temperature characteristics, continuous charge characteristics, self-discharge characteristics, overcharge prevention characteristics, etc. Many methods have been reported so far in which a small amount of the auxiliary is contained in the non-aqueous electrolyte. However, no universal non-aqueous electrolyte has been found for all properties.

  On the other hand, for the purpose of improving energy density, attempts have been made to charge lithium secondary batteries to a high end voltage exceeding 4.2V. That is, when a conventional general lithium secondary battery is charged at 25 ° C., the open circuit voltage between the battery terminals at the end of charging is usually 4.2 V or less. Attempts have been made to develop lithium secondary batteries having an open circuit voltage between battery terminals exceeding 4.2V. In the conventional lithium secondary battery, the higher the voltage, the more unavoidable side reactions are caused by the decomposition of the non-aqueous electrolyte in the positive electrode, and the cycle deterioration tends to become extremely large. When charged up to more than 2V, it was not practical.

  In response to the desire to increase the open circuit voltage between the battery terminals at the end of charging, Patent Document 1 uses a non-aqueous electrolyte solution composed of a non-aqueous solvent and lithium salt containing 50% by volume or more of γ-butyrolactone. Technology has been proposed. In this Patent Document 1, it is described that the capacity of a secondary battery whose open circuit voltage between battery terminals at 25 ° C. at full charge is 4.3 V or more is increased by the above technique, and further, cycle characteristics and the like are improved. Yes.

Patent Document 2 discloses a battery in which the amount of protic impurities and the amount of moisture in the electrolyte are kept low to suppress the elution of transition metals from the lithium composite oxide, and the battery voltage during charging is 4.25 V or more. Describes that the discharge capacity after a 60 ° C. storage deterioration test is improved. Further, there is a description that high battery performance can be obtained by using an electrolytic solution containing less than 50% by volume of cyclic carbonate.
Patent Document 3 discloses a non-aqueous electrolyte secondary battery having a non-aqueous electrolyte containing a carboxylic acid ester having a specific structure and having an upper limit charging voltage exceeding 4.20 V. It is described that the ester content is preferably 0.5% by weight to 30% by weight with respect to the nonaqueous electrolytic solution.

JP 2003-272704 A International Publication No. 03/019713 Pamphlet JP 2008-159419 A

  In recent years, the demand for higher performance of lithium secondary batteries has increased, and it has been required to achieve various characteristics such as high capacity, cycle characteristics, high-temperature storage characteristics, and continuous charge characteristics at a high level. ing. Among them, improvement of cycle characteristics has been particularly demanded recently.

However, as described above, in the conventional nonaqueous electrolyte secondary battery, when the cycle test was performed at the end-of-charge voltage exceeding 4.2 V, the deterioration was extremely large, and satisfactory results were not obtained. Similarly, satisfactory results were not obtained even in the lithium secondary battery proposed in Patent Documents 1, 2, and 3 having a high open circuit voltage between the battery terminals at the end of charging.
The present invention was devised in view of the above problems, and provides a lithium secondary battery that can increase the open circuit voltage between battery terminals at the end of charging and has little capacity deterioration even with respect to charge / discharge cycles. For the purpose.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention have found that a non-aqueous electrolytic solution containing a cyclic carbonate having no carbon-carbon double bond, a cyclic ester, and a chain carbonate in a specific composition. As a result, it was found that the open circuit voltage between the battery terminals at the end of charging can be increased and the cycle capacity retention rate can be improved, and the present invention has been completed.

That is, the gist of the present invention is a non-aqueous electrolysis for a lithium secondary battery that includes a positive electrode, a negative electrode, and a non-aqueous electrolyte, and has an open circuit voltage between battery terminals at 25 ° C. of 4.25 V or more at the end of charging. This cyclic carbonate contains an electrolyte and a solvent, and contains as a solvent a cyclic carbonate having no carbon-carbon double bond, a cyclic ester, and a chain carbonate, and occupies in the component excluding the electrolyte The cyclic ester content is 1% by weight to 24% by weight, the cyclic ester content is 1% by weight to 34 % by weight, and the chain carbonate content is 65% by weight to 95% by weight. It exists in the non-aqueous electrolyte solution characterized by the above-mentioned (Claim 1).

In this case, the cyclic carbonate is preferably at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, monofluoroethylene carbonate, and difluoroethylene carbonate (Claim 2).
Furthermore, the cyclic ester is preferably at least one selected from the group consisting of γ-butyrolactone, α-methyl-γ-butyrolactone, and δ-valerolactone.
The cyclic ester is preferably γ-butyrolactone.
The chain carbonate is preferably at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate (Claim 5 ), and further a cyclic carbonate having a carbon-carbon double bond. It is preferable to contain (Claim 6 ).

Another gist of the present invention is a lithium battery comprising a positive electrode, a negative electrode, and the non-aqueous electrolyte described above, and an open circuit voltage between battery terminals at 25 ° C. at the end of charging is 4.25 V or more. It exists in a secondary battery (Claim 7 ).
At this time, the battery terminals between open circuit voltage is preferably 4.3V or higher (claim 8).
Further, the positive electrode is preferably a positive electrode containing a lithium nickel-containing transition metal oxide as an active material (claim 9 ).

  ADVANTAGE OF THE INVENTION According to this invention, in a lithium secondary battery, while being able to charge to a high open circuit voltage between battery terminals, cycling characteristics can be improved.

  Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments, and can be arbitrarily modified and implemented without departing from the gist of the present invention.

[I. Non-aqueous electrolyte]
The non-aqueous electrolyte solution used in the lithium secondary battery of the present invention (hereinafter also referred to as “non-aqueous electrolyte solution in the present invention” as appropriate) contains an electrolyte and a solvent, and a carbon-carbon double bond as the solvent. A cyclic carbonate, a cyclic ester, and a chain carbonate. In addition, the content of the cyclic carbonate in the component excluding the electrolyte is 1% by weight to 28% by weight, the content of the cyclic ester is 1% by weight to 40% by weight, The carbonate content is 50 wt% or more and 95 wt% or less.

[1. solvent]
[1-1. Cyclic carbonate not having a carbon-carbon double bond]
The cyclic carbonate having no carbon-carbon double bond according to the present invention is arbitrary as long as the effects of the present invention are not significantly impaired. For example, carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl ethylene carbonate, diethyl ethylene carbonate, monopropyl ethylene carbonate, dipropyl ethylene carbonate, phenyl ethylene carbonate, diphenyl ethylene carbonate, catechol carbonate; monofluoro ethylene carbonate, difluoro Ethylene carbonate, trifluoroethylene carbonate, tetrafluoroethylene carbonate, monofluoromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, monochloroethylene carbonate, dichloroethylene carbonate, trichloroethylene carbonate, tetrachloroethylene carbonate, monochloromethyl Ethylene carbonate, halogen substituted carbonates such as trichloromethyl carbonate; and the like.

Among these, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, monofluoroethylene carbonate, and difluoroethylene carbonate is preferable.
Furthermore, at least one selected from the group consisting of ethylene carbonate, propylene carbonate, and monofluoroethylene carbonate is particularly preferable in order to improve cycle characteristics.
The cyclic carbonate which does not have a carbon-carbon double bond can be used individually by 1 type or in combination of 2 or more types in arbitrary ratios and combinations.

[1-2. Cyclic ester]
The cyclic ester according to the present invention is arbitrary as long as it is a cyclic compound having an ester group, but a cyclic ester having no carbon-carbon unsaturated bond is preferred. For example, γ-butyrolactone, α-methyl-γ-butyrolactone, α-ethyl-γ-butyrolactone, α-propyl-γ-butyrolactone, α-phenyl-γ-butyrolactone, α-fluoro-γ-butyrolactone, β-methyl- γ-butyrolactone, β-ethyl-γ-butyrolactone, β-propyl-γ-butyrolactone, β-phenyl-γ-butyrolactone, β-fluoro-γ-butyrolactone, γ-methyl-γ-butyrolactone, γ-ethyl-γ- Γ-butyrolactone derivatives such as butyrolactone, γ-propyl-γ-butyrolactone, γ-phenyl-γ-butyrolactone, γ-fluoro-γ-butyrolactone; δ-valerolactone, α-methyl-δ-valerolactone, α-ethyl- δ-valerolactone, α-phenyl-δ-valerolactone, β-methyl-δ-valero Lactone, β-ethyl-δ-valerolactone, β-phenyl-δ-valerolactone, γ-methyl-δ-valerolactone, γ-ethyl-δ-valerolactone, γ-phenyl-δ-valerolactone, δ-methyl Δ-valerolactone derivatives such as δ-valerolactone, δ-ethyl-δ-valerolactone, and δ-phenyl-δ-valerolactone.
Among these, at least one selected from the group consisting of γ-butyrolactone, α-methyl-γ-butyrolactone, and δ-valerolactone is preferable, and γ-butyrolactone improves cycle characteristics. Therefore, it is particularly preferable.
Cyclic ester can be used individually by 1 type or in combination of 2 or more types in arbitrary ratios and combinations.

[1-3. Chain carbonate]
The chain carbonate according to the present invention is arbitrary as long as the effects of the present invention are not significantly impaired. For example, carbonates such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, propyl methyl carbonate, dipropyl carbonate, methyl phenyl carbonate, ethyl phenyl carbonate, diphenyl carbonate; bis (trifluoromethyl) carbonate, methyl trifluoromethyl carbonate, bis And halogen-substituted carbonates such as (monofluoroethyl) carbonate, methyl monofluoroethyl carbonate, bis (trifluoroethyl) carbonate, methyl trifluoroethyl carbonate;
Among these, at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate is preferable.
A chain carbonate can be used individually by 1 type or in combination of 2 or more types in arbitrary ratios and combinations.

[1-4. Composition ratio]
In the non-aqueous electrolyte solution in the present invention, the content of the cyclic carbonate having no carbon-carbon double bond in the components excluding the electrolyte is usually 1% by weight or more, preferably 3% by weight or more, more preferably 5%. % By weight or more, particularly preferably 8% by weight or more, and usually 28% by weight or less, preferably 26% by weight or less, more preferably 24% by weight or less, and particularly preferably 22% by weight or less.

  The content of the cyclic ester in the component excluding the electrolyte in the non-aqueous electrolyte is usually 1% by weight or more, preferably 2% by weight or more, more preferably 3% by weight or more, and particularly preferably 5% by weight or more. It is usually 40% by weight or less, preferably 30% by weight or less, more preferably 25% by weight or less, and particularly preferably 22% by weight or less.

  The content of the chain carbonate in the component excluding the electrolyte in the non-aqueous electrolyte is usually 50% by weight or more, preferably 55% by weight or more, more preferably 60% by weight or more, and particularly preferably 65% by weight. %, Usually 95% or less, preferably 90% or less, more preferably 85% or less, and particularly preferably 80% or less.

[1-5. Cyclic carbonate having a carbon-carbon double bond]
The non-aqueous electrolyte in the present invention preferably contains a cyclic carbonate having a carbon-carbon double bond for the purpose of forming a film on the negative electrode and improving battery characteristics. By containing a cyclic carbonate having a carbon-carbon double bond, cycle characteristics are improved. There is no restriction | limiting in particular as cyclic carbonate which has a carbon-carbon double bond, Arbitrary things can be used.

  Specific examples include vinylene carbonate, methyl vinylene carbonate, 1,2-dimethyl vinylene carbonate, phenyl vinylene carbonate, 1,2-diphenyl vinylene carbonate, fluoro vinylene carbonate, 1,2-difluoro vinylene carbonate, 1-fluoro-2- Vinylene carbonate derivatives such as methyl vinylene carbonate and 1-fluoro-2-phenyl vinylene carbonate; vinyl ethylene carbonate, 1,1-divinyl ethylene carbonate, 1,2-divinyl ethylene carbonate, 1-methyl-2-vinyl ethylene carbonate, And vinylethylene carbonate derivatives such as 1-phenyl-2-vinylethylene carbonate and 1-fluoro-2-vinylethylene carbonate;

Among these, vinylene carbonate derivatives such as vinylene carbonate, methyl vinylene carbonate and 1,2-dimethyl vinylene carbonate; vinyl ethylene carbonate derivatives such as vinyl ethylene carbonate and 1,2-divinyl ethylene carbonate are preferable. In particular, vinylene carbonate and vinyl ethylene carbonate are preferable.
In addition, the cyclic carbonate which has a carbon-carbon double bond may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

The carbon number of the cyclic carbonate having a carbon-carbon double bond is usually 3 or more, and usually 20 or less, preferably 15 or less. When the upper limit of the above range is exceeded, the solubility in the electrolytic solution tends to decrease.
Furthermore, the molecular weight of the cyclic carbonate having a carbon-carbon double bond is usually 80 or more, and usually 250 or less, preferably 150 or less. If the molecular weight is too large, the solubility in the non-aqueous electrolyte solution tends to be lowered, and the effect may not be sufficiently exhibited.

  Further, the concentration of the cyclic carbonate having a carbon-carbon double bond is usually 0.01% by weight or more, preferably 0.1% by weight or more, more preferably, based on the whole component excluding the electrolyte from the non-aqueous electrolyte. It is 0.3% by weight or more, and is usually 10% by weight or less, preferably 7% by weight or less, more preferably 5% by weight or less, and further preferably 3% by weight or less. If the concentration of the cyclic carbonate having a carbon-carbon double bond is too high, the high-temperature storage characteristics may be deteriorated, and further, the amount of gas generated increases when the battery is used, and the capacity retention rate may be reduced. On the other hand, if the concentration is too small, the effect may not be sufficiently exhibited. In addition, when using together 2 or more types of cyclic carbonate which has a carbon-carbon double bond, it is made for the sum total of a density | concentration to be in the said range.

[1-6. Other solvents]
The non-aqueous electrolyte in the present invention optionally contains a known solvent other than the above-mentioned cyclic carbonate having no carbon-carbon double bond, cyclic ester, chain carbonate, and cyclic carbonate having a carbon-carbon double bond. You can also Examples thereof include chain esters, chain ethers, cyclic ethers, cyclic amides, chain amides, sulfur-containing organic solvents, and the like. Among these, chain esters, chain ethers, cyclic amides, and sulfur-containing organic solvents are preferable as solvents that exhibit high ionic conductivity and permeability.

Specific examples of the chain esters include methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate and the like.
Specific examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether and the like.
Specific examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 4-methyl-1,3-dioxolane and the like.
Specific examples of cyclic amides include N-methylpyrrolidone, N-ethylpyrrolidone, N-vinylpyrrolidone and the like.
Specific examples of the chain amides include N, N-dimethylformamide, N, N-dimethylacetamide and the like.
Furthermore, specific examples of the sulfur-containing organic solvent include sulfolane and dimethyl sulfoxide.

[2. Electrolytes]
There is no restriction | limiting in particular about the electrolyte used for the non-aqueous electrolyte solution in this invention, A well-known thing can be used arbitrarily if it is used as an electrolyte of a lithium secondary battery. Usually, a lithium salt is used.
As the lithium salt used for the electrolyte, either an inorganic lithium salt or an organic lithium salt may be used.

Examples of inorganic lithium salts include inorganic fluoride salts such as LiPF ₆ , LiAsF ₆ , LiBF ₄ , and LiSbF ₆ ; inorganic chloride salts such as LiAlCl ₄ ; perhalogenates such as LiClO ₄ , LiBrO ₄ , and LiIO _4. And so on.
Examples of organic lithium salts include perfluoroalkane sulfonates such as CF ₃ SO ₃ Li and C ₄ F ₉ SO ₃ Li; perfluoroalkane carboxylates such as CF ₃ COOLi; (CF ₃ CO) Perfluoroalkanecarbonimide salts such as ₂ NLi; perfluoroalkanesulfonimide salts such as (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) ₂ NLi; .

Among these, LiPF ₆ , LiBF ₄ , CF ₃ SO ₃ Li, (CF ₃ SO ₂ ) ₂ NLi, and the like are preferable because they are easily soluble in non-aqueous solvents and exhibit a high degree of dissociation.
In addition, electrolyte may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.
In particular, the combined use of LiPF ₆ and LiBF ₄ or the combined use of LiPF ₆ and (CF ₃ SO ₂ ) ₂ NLi is preferable because it has an effect of improving the continuous charge characteristics.

  Furthermore, the concentration of the electrolyte in the non-aqueous electrolyte is arbitrary as long as the effects of the present invention are not significantly impaired, but usually 0.5 mol / L or more, preferably 0.75 mol / L with respect to the non-aqueous electrolyte. In addition, it is usually 2 mol / L or less, preferably 1.75 mol / L or less. If the concentration of the electrolyte is too low, the electrical conductivity of the non-aqueous electrolyte may be insufficient. On the other hand, if the concentration of the electrolyte is too high, the electrical conductivity may decrease due to an increase in viscosity, or precipitation at a low temperature may occur easily, and the performance of the lithium secondary battery may decrease.

[3. Other auxiliaries]
The non-aqueous electrolyte in the present invention may contain other auxiliary agents for the purpose of improving the wettability, overcharge characteristics, etc. of the non-aqueous electrolyte in a range that does not significantly impair the effects of the present invention.
Examples of auxiliaries include acid anhydrides such as maleic anhydride, succinic anhydride, and glutaric anhydride; carboxylic acid esters such as vinyl acetate, divinyl adipate, and allyl acetate; diphenyl disulfide, 1,3-propane sultone, Sulfur-containing compounds such as 1,4-butane sultone, dimethyl sulfone, divinyl sulfone, dimethyl sulfite, ethylene sulfite, 1,4-butanediol dimethanesulfonate, methyl methanesulfonate, 2-propynyl methanesulfonate; t- Aromatic compounds such as butylbenzene, biphenyl, o-terphenyl, 4-fluorobiphenyl, fluorobenzene, 2,4-difluorobenzene, cyclohexylbenzene, diphenyl ether, 2,4-difluoroanisole, trifluoromethylbenzene; And those obtained by substituting a family compound with a fluorine atom.
Moreover, 1 type may be used independently for an adjuvant, and 2 or more types may be used together by arbitrary combinations and a ratio.

  The concentration of the auxiliary agent in the nonaqueous electrolytic solution is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.01% by weight or more, preferably 0.05% by weight or more, and usually 10% by weight. % Or less, preferably 5% by weight or less. In addition, when using 2 or more types of adjuvants together, it is made for the sum total of these density | concentrations to be settled in the said range.

[4. Non-aqueous electrolyte state]
The nonaqueous electrolytic solution in the present invention is usually present in a liquid state when used in the lithium secondary battery of the present invention. For example, it may be gelled with a polymer to form a semi-solid electrolyte. The polymer used for the gelation is arbitrary, and examples thereof include polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyethylene oxide, polyacrylate, and polymethacrylate. In addition, the polymer | macromolecule used for gelatinization may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  Moreover, when using a non-aqueous electrolyte as a semi-solid electrolyte, the ratio of the non-aqueous electrolyte in the semi-solid electrolyte is arbitrary as long as the effects of the present invention are not significantly impaired. As a suitable range, the ratio of the non-aqueous electrolyte to the total amount of the semisolid electrolyte is usually 30% by weight or more, preferably 50% by weight or more, more preferably 75% by weight or more, and usually 99.95. % By weight or less, preferably 99% by weight or less, more preferably 98% by weight or less. If the ratio of the non-aqueous electrolyte is too large, it may be difficult to hold the non-aqueous electrolyte and liquid leakage may occur, and conversely if too small, the charge / discharge efficiency and capacity may be insufficient. is there.

[5. Method for producing non-aqueous electrolyte]
The non-aqueous electrolyte solution in the present invention dissolves an electrolyte and, if necessary, other auxiliary agents in a solvent containing at least a cyclic carbonate having no carbon-carbon double bond, a cyclic ester, and a chain carbonate. Can be prepared.

  In preparing the non-aqueous electrolyte solution, it is preferable that each raw material of the non-aqueous electrolyte solution, that is, the electrolyte, the solvent, and the other auxiliary agent be dehydrated in advance. As the degree of dehydration, it is desirable to dehydrate until the water content is usually 50 ppm or less, preferably 30 ppm or less. In the present specification, ppm means a ratio based on weight.

If water is present in the non-aqueous electrolyte, electrolysis of water, reaction between water and lithium metal, hydrolysis of lithium salt, and the like may occur.
The dehydration means is not particularly limited. For example, when the object to be dehydrated is a liquid such as a non-aqueous solvent, a molecular sieve or the like can be used. In addition, when the object to be dehydrated is a solid such as an electrolyte, a method of drying at a temperature below which decomposition occurs can be used.

[II. Lithium secondary battery]
The lithium secondary battery of the present invention includes the above-described non-aqueous electrolyte solution according to the present invention, a positive electrode, and a negative electrode. In addition, the lithium secondary battery of the present invention may have other configurations. For example, a lithium secondary battery usually includes a spacer. Moreover, the open circuit voltage between battery terminals in 25 degreeC at the time of completion | finish of charge of the lithium secondary battery of this invention is 4.25V or more.

[1. Positive electrode]
As long as the positive electrode can occlude and release lithium, any positive electrode can be used as long as the effects of the present invention are not significantly impaired.
Usually, a positive electrode having a positive electrode active material layer provided on a current collector is used. Note that the positive electrode may include other layers as appropriate.

[1-1. Positive electrode active material layer]
The positive electrode active material layer includes a positive electrode active material. The positive electrode active material is not limited as long as it can occlude and release lithium ions. Examples thereof include oxides of transition metals such as Fe, Co, Ni, and Mn, composite oxides of transition metals and lithium, and sulfides of transition metals.

Specific examples of transition metal oxides include MnO, V ₂ O ₅ , V ₆ O ₁₃ , and TiO ₂ . Specific examples of the composite oxide of transition metal and lithium include a lithium nickel composite oxide whose basic composition is LiNiO ₂ ; a lithium cobalt composite oxide whose basic composition is LiCoO ₂ ; a basic composition of LiMnO ₂ and LiMnO. _{4 and the} like; and the like. Further, specific examples of the transition metal sulfide include TiS ₂ and FeS.

Among these, a composite oxide of lithium and a transition metal is preferable because it can achieve both high capacity and high cycle characteristics of a lithium secondary battery. In the present invention, lithium nickel-containing transition metal oxides are particularly preferable, and examples thereof include LiNiO ₂ , LiNi _x M _y O ₂ (M is Al, B, Ti, Zr, V, Cr, Mn, Fe, Co, Cu, And at least one selected from Zn, Mg, Ca, and Ga, and x and y represent arbitrary numbers. M is particularly preferably Co, Mn, Fe, Al, Mg, or Ti. In particular, Mn alone or a combination of Co—Mn, Co—Al, and Co—Al—Mg is effective for improving thermal stability. .

Specifically, LiNi _1-ab Mn _a Co _b O ₂ (a, b represents a number of 0 or more and less than 1), LiNi _1-c-d Co _C Al _d Mg _e O ₂ (c, d, e represents less than one digit 0 or more), more _{LiNi 1-a-b Mn a} Co b O 2 (0 ≦ a <0.4,0 ≦ b <0.4), LiNi 1 _{-c-d-e Co c Al} d Mg e O 2 is (0 ≦ c <0.3,0 ≦ d <0.1,0 ≦ e <0.05) preferred, _LiNi 1/3 _{Mn 1 / 3} Co _1/3 O ₂ , LiNi _0.5 Mn _0.3 Co _0.2 O ₂ , LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.1 Al _0.05 O ₂ , LiNi _0.85 Co _0.1 Al _0.03 Mg _0.02 O ₂ is preferred.

Further, the surface of the composite oxide of transition metal and lithium described above is made of a metal such as Al, B, Ti, Zr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Mg, Ca, and Ga. Covering with an oxide is preferable because the oxidation reaction of the solvent at high voltage is suppressed. Among these, Al ₂ O ₃ , TiO ₂ , ZrO ₂ , and MgO are particularly preferable because they have high strength and exhibit a stable coating effect.
In addition, any one of these positive electrode active materials may be used alone, or two or more thereof may be used in any combination and ratio.

The specific surface area of the positive electrode active material is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.1 m ² / g or more, preferably 0.2 m ² / g or more, and usually 10 m ² / g. Hereinafter, it is preferably 5.0 m ² / g or less, more preferably 3.0 m ² / g or less. If the specific surface area is too small, the rate characteristics and capacity may be reduced. If the specific surface area is too large, the positive electrode active material may react with the non-aqueous electrolyte and the like, and the cycle characteristics may be deteriorated.

  Further, the average secondary particle size of the positive electrode active material is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 0.2 μm or more, preferably 0.3 μm or more, and usually 20 μm or less, preferably 10 μm or less. It is. If the average secondary particle size is too small, there is a possibility that the cycle deterioration of the lithium secondary battery becomes large and the handling becomes difficult, and if it is too large, the internal resistance of the battery becomes large and it may be difficult to output.

  The thickness of the positive electrode active material layer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 1 μm or more, preferably 10 μm or more, more preferably 20 μm or more, and particularly preferably 40 μm or more. Usually, it is 200 micrometers or less, Preferably it is 150 micrometers or less, More preferably, it is 100 micrometers or less. If it is too thin, coating may become difficult and uniformity may be difficult to ensure, and the capacity of the lithium secondary battery of the present invention may be reduced. On the other hand, if it is too thick, the rate characteristics may be degraded.

The positive electrode active material layer is formed by, for example, slurrying the above-described positive electrode active material, a binder (binder), and various auxiliary agents as necessary with a solvent to form a coating liquid, and collecting the coating liquid. It can be manufactured by applying to the body and drying. Further, for example, the positive electrode active material described above may be roll-formed to form a sheet electrode, or compression-molded to form a pellet electrode.
Hereinafter, a case where the slurry is applied to the positive electrode current collector and dried will be described.

  The binder is not particularly limited as long as it is a material that is stable with respect to the non-aqueous solvent used in the non-aqueous electrolyte solution or the solvent used during electrode production, but weather resistance, chemical resistance, heat resistance, difficulty It is preferable to select in consideration of flammability and the like. Specific examples include inorganic compounds such as silicate and water glass, alkane polymers such as polyethylene, polypropylene and poly-1,1-dimethylethylene; unsaturated polymers such as polybutadiene and polyisoprene; polystyrene and polymethylstyrene. , Polymers having rings such as polyvinyl pyridine, poly-N-vinyl pyrrolidone; polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polymethyl acrylate, polyethyl acrylate, polyacrylic acid, polymethacrylic acid, Acrylic derivative polymers such as polyacrylamide; Fluorine resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide; Polyvinyl chloride, halogen-containing polymers of polyvinylidene chloride; polyvinyl alcohol polymers such as polyvinyl alcohol conducting polymers such as polyaniline; and the like can be used.

In addition, mixtures such as the above polymers, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, and the like can also be used.
Among these, preferred binders are a fluororesin and a CN group-containing polymer.
In addition, a binder may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and a ratio.

  When a resin is used as the binder, the weight average molecular weight of the resin is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 10,000 or more, preferably 100,000 or more, and usually 300. 10,000 or less, preferably 1,000,000 or less. If the molecular weight is too low, the strength of the electrode tends to decrease. On the other hand, if the molecular weight is too high, the viscosity becomes high and it may be difficult to form an electrode.

  Furthermore, the amount of the binder used is arbitrary as long as the effects of the present invention are not significantly impaired. However, the positive electrode active material (in the case of use in the negative electrode, the negative electrode active material. Hereinafter, the positive electrode active material and the negative electrode active material are distinguished. Without being referred to, simply referred to as “active material”) is usually 0.1 parts by weight or more, preferably 1 part by weight or more, and usually 30 parts by weight or less, preferably 20 parts by weight. It is as follows. If the amount of the binder is too small, the strength of the electrode tends to decrease, and if the amount of the binder is too large, the ionic conductivity tends to decrease.

Moreover, you may make an electrode contain various adjuvants. Examples of the auxiliary agent include a conductive material that increases the conductivity of the electrode, and a reinforcing material that improves the mechanical strength of the electrode.
Specific examples of the conductive material are not particularly limited as long as an appropriate amount can be mixed with the active material to impart conductivity, but usually carbon powders such as acetylene black, carbon black, graphite, and various kinds of metals. Examples thereof include fibers and foils.

As specific examples of the reinforcing material, various inorganic, organic spherical, fibrous fillers and the like can be used.
In addition, these adjuvants etc. may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and ratios.

The solvent for forming the slurry is not particularly limited in type as long as it is a solvent capable of dissolving or dispersing the active material, the binder, and auxiliary agents used as necessary. Either an aqueous solvent or an organic solvent may be used.
Examples of the aqueous solvent include water and alcohol. On the other hand, examples of organic solvents include N-methylpyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyltriamine, NN-dimethylaminopropylamine, ethylene oxide, tetrahydrofuran ( THF), toluene, acetone, dimethyl ether, dimethylacetamide, hexamethylphosphalamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methylnaphthalene, hexane and the like.

In addition, these solvents may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.
The active material layer obtained by coating and drying is preferably consolidated by a roller press or the like in order to increase the packing density of the positive electrode active material.

[1-2. Current collector]
As a material for the current collector, a known material can be arbitrarily used, but usually a metal or an alloy is used. Specifically, examples of the current collector for the positive electrode include aluminum, nickel, and SUS (stainless steel). Among these, aluminum is preferable as the positive electrode current collector. In addition, these may be used individually by 1 type and may use 2 or more types together by arbitrary combinations and ratios.

  Furthermore, in order to improve the binding effect between the current collector and the active material layer formed on the surface, it is preferable that the surfaces of these current collectors are roughened in advance. The surface roughening method includes blasting or rolling with a rough roll, and the surface of the current collector with a wire brush equipped with abrasive cloth paper, grindstone, emery buff, steel wire, etc. to which abrasive particles are fixed. Examples thereof include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method.

  Further, the shape of the current collector is arbitrary. For example, in order to reduce the weight of the battery, that is, to improve the energy density per weight, a perforated type current collector such as an expanded metal or a punching metal can be used. In this case, the weight can be freely changed by changing the aperture ratio. In addition, when a coating layer is formed on both surfaces of such a hole-type current collector, the coating layer tends to be more difficult to peel due to the rivet effect of the coating layer through the hole, but the aperture ratio is too high. In such a case, the contact area between the coating layer and the current collector becomes small, so that the adhesive strength may be lowered.

  When a thin film is used as the positive electrode current collector, its thickness is arbitrary as long as the effects of the present invention are not significantly impaired, but it is usually 1 μm or more, preferably 5 μm or more, and usually 100 μm or less, preferably 50 μm or less. . If it is too thick, the capacity of the whole battery tends to be reduced. Conversely, if it is too thin, handling may be difficult.

[2. Negative electrode]
Any negative electrode can be used as long as it can occlude and release lithium as long as the effects of the present invention are not significantly impaired.
Usually, as in the case of the positive electrode, a negative electrode having a negative electrode active material layer provided on a current collector is used. Note that, similarly to the positive electrode, the negative electrode may include other layers as appropriate.

[2-1. Negative electrode active material layer]
The negative electrode active material is not particularly limited as long as it is a material capable of occluding and releasing lithium ions, and a known negative electrode active material can be arbitrarily used. For example, carbonaceous materials such as coke, acetylene black, mesophase microbeads and graphite; lithium metal; lithium alloys such as lithium-silicon and lithium-tin; etc. are preferably used.

From the viewpoint of high capacity per unit weight and good safety, lithium alloys are particularly preferred, and from the viewpoint of good cycle characteristics and safety, it is particularly preferred to use a carbonaceous material.
In addition, a negative electrode active material may be used individually by 1 type, and may use 2 or more types together by arbitrary combinations and a ratio.

  Further, the particle size of the negative electrode active material is arbitrary as long as the effects of the present invention are not significantly impaired, but is usually 1 μm or more, preferably 15 μm in terms of excellent battery characteristics such as initial efficiency, rate characteristics, and cycle characteristics. These are usually 50 μm or less, preferably 30 μm or less.

  In addition, for example, the above carbonaceous material is coated with an organic substance such as pitch and then baked, or the surface is made of amorphous carbon rather than the above carbonaceous material using a chemical vapor deposition method (CVD method) or the like. What was formed can also be used suitably as a carbonaceous material. Here, organic substances used for coating include coal tar pitch from soft pitch to hard pitch; coal heavy oil such as dry distillation liquefied oil; straight heavy oil such as atmospheric residual oil and vacuum residual oil; crude oil And heavy petroleum oils such as cracked heavy oil (eg, ethylene heavy end) produced as a by-product during thermal decomposition of naphtha and the like. Moreover, what grind | pulverized the solid residue obtained by distilling these heavy oils at 200 to 400 degreeC to 1 micrometer-100 micrometers can also be used. Furthermore, a vinyl chloride resin, a phenol resin, an imide resin, etc. can also be used.

  For example, the negative electrode active material layer can be formed into a sheet electrode by roll molding the negative electrode active material described above, or a pellet electrode by compression molding. Usually, as in the case of the positive electrode active material layer, The negative electrode active material, the binder, and, if necessary, various auxiliary agents and the like can be produced by applying a coating solution obtained by slurrying with a solvent onto a current collector and drying it. it can. As the solvent, binder, auxiliary agent and the like for forming the slurry, the same materials as those described above for the positive electrode active material can be used.

[2-2. Current collector]
As a material for the current collector of the negative electrode, a known material can be arbitrarily used. For example, a metal material such as copper, nickel, or SUS is used. Among these, copper is particularly preferable from the viewpoint of ease of processing and cost.

The negative electrode current collector is also preferably subjected to a roughening treatment in advance, as with the positive electrode current collector.
Further, like the positive electrode, the shape of the current collector is also arbitrary, and a perforated current collector such as expanded metal or punching metal can also be used. Moreover, the preferable thickness when using a thin film as a current collector is the same as that of the positive electrode.

[3. Spacer]
In order to prevent a short circuit, a spacer is usually interposed between the positive electrode and the negative electrode. The material and shape of the spacer are not particularly limited, but those that are stable with respect to the non-aqueous electrolyte described above, have excellent liquid retention properties, and can reliably prevent short-circuiting between electrodes are preferable.

As a material for the spacer, for example, polyolefin such as polyethylene and polypropylene, polytetrafluoroethylene, polyethersulfone and the like can be used, and polyolefin is preferable.
The spacer is preferably porous. In this case, the non-aqueous electrolyte is used by impregnating a porous spacer.

  The thickness of the spacer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 1 μm or more, preferably 5 μm or more, more preferably 10 μm or more, and usually 50 μm or less, preferably 40 μm or less, more preferably. Is 30 μm or less. If the spacer is too thin, the insulation and mechanical strength may decrease. If the spacer is too thick, not only the battery performance such as rate characteristics may be decreased, but also the energy density of the entire battery may be decreased. There is.

  Further, when a porous film is used as the spacer, the porosity of the spacer is arbitrary as long as the effect of the present invention is not significantly impaired, but is usually 20% or more, preferably 35% or more, more preferably 45% or more. It is usually 90% or less, preferably 85% or less, and more preferably 75% or less. If the porosity is too small, the membrane resistance increases and the rate characteristics tend to deteriorate. On the other hand, if it is too large, the mechanical strength of the film tends to decrease and the insulating property tends to decrease.

  Further, when a porous film is used as the spacer, the average pore diameter of the spacer is arbitrary as long as the effect of the present invention is not significantly impaired, but it is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.8. It is 05 μm or more. If it is too large, a short circuit is likely to occur, and if it is too small, the film resistance may increase and the rate characteristics may deteriorate.

[4. Assembly of secondary battery]
The lithium secondary battery of the present invention is manufactured by assembling the above-described non-aqueous electrolyte solution according to the present invention, a positive electrode, a negative electrode, and a spacer used as necessary into an appropriate shape. Furthermore, other components such as an outer case can be used as necessary. Furthermore, the shape of the lithium secondary battery of the present invention is not particularly limited, and can be appropriately selected from various shapes generally employed according to the application. For example, a coin-type battery, a cylindrical battery, a square battery, etc. are mentioned. The method for assembling the battery is not particularly limited, and can be appropriately selected from various commonly used methods according to the shape of the target battery.

[5. Action]
By using the non-aqueous electrolyte in the present invention for the lithium secondary battery of the present invention, the open circuit voltage between the battery terminals at 25 ° C. at the end of charging is usually 4.25 V or higher, preferably 4.30 V or higher, more preferably. Even when charged to 4.40 V or higher, the reaction of the electrolyte can be suppressed, the generation of gas can be greatly suppressed, and the cycle characteristics can be greatly improved.

[6. Others]
[6-1. Regarding the open circuit voltage between battery terminals at the end of charging]
In this specification, the open circuit voltage between battery terminals is a battery voltage in a state where no current flows in the circuit. Although the measuring method is arbitrary, it can measure with a normal charging / discharging apparatus, for example.

[6-2. About charging]
When charging a lithium secondary battery, the battery is generally charged in a state where a voltage drop of resistance is added. That is, the charging voltage is obtained by adding the product of the charging current and the resistance to the open circuit voltage between the battery terminals. Therefore, the difference between the charging voltage and the open circuit voltage between the battery terminals increases as the charging current increases and as the internal resistance of the lithium secondary battery or the resistance of the protection open circuit increases.

In the lithium secondary battery of the present invention, the charging method is not particularly limited and can be charged by any charging method. For example, constant current charging (CC charging), constant current-constant voltage charging (CCCV charging), pulse charging, reverse taper charging, or the like is used.
As for the end of charging, the charging may be performed for a predetermined time (for example, longer than the time required for calculation for completion of charging), or it may be detected that the charging current value has become a specified value or less. The voltage value may reach the specified value.

  In current lithium secondary batteries, the open circuit voltage between battery terminals at the end of charging is usually in the range of 4.08V to 4.20V. The higher the open circuit voltage between the battery terminals at the end of charging, the higher the capacity (mAh) of the lithium secondary battery. In addition, the higher the open circuit voltage between the battery terminals at the end of charging, the higher the voltage of the lithium secondary battery itself, so the weight energy density (mWh / kg) also increases, and the lithium secondary battery is light and long in duration. Can be obtained.

[6-3. mechanism]
The mechanism by which the effect of the present invention can be obtained is not clear, but is considered as follows.
As described above, the development of a lithium secondary battery capable of increasing the open circuit voltage between battery terminals at the end of charging has been conventionally desired. However, in the conventional technique, under a high voltage condition of 4.25 V or more, In particular, since the oxidation reaction of the electrolyte solution on the positive electrode occurs remarkably, the cycle characteristics may be poor, and a practical secondary battery cannot be obtained.

  On the other hand, the cyclic ester according to the present invention forms a protective film on the positive electrode at a high potential and suppresses the reaction between the positive electrode and the electrolyte. This film formation reaction did not proceed under the conventional voltage condition of less than 4.25 V, but it is presumed that the reaction has proceeded by setting it to 4.25 V or more. The formation of the positive electrode film may be caused by a direct reaction at the positive electrode or may be caused by the reduction product at the negative electrode moving to the positive electrode and undergoing an oxidation reaction. The reduction product at the negative electrode here may be generated during initial charging, or may be generated during a charge / discharge cycle. Regarding the content of the cyclic ester, if the cyclic ester is excessively present, the protective film becomes thick and the resistance becomes high, so that an optimum value exists. In addition, since the cyclic carbonate having no carbon-carbon double bond is reduced in concert with the cyclic ester during initial charging, a hybrid protective film derived from both is formed on the negative electrode, thereby contributing to improvement of cycle characteristics. . In order to improve the stability of this hybrid film, the content of the cyclic carbonate having no carbon-carbon double bond is essential to a certain amount or more. However, if the content is too large, the viscosity increases and Li ions move. Since it becomes difficult, the cycle characteristics tend to deteriorate. Further, the chain carbonate is necessary for lowering the viscosity, but if the content is too large, the dissociation of Li ions hardly occurs and the cycle characteristics tend to deteriorate. Accordingly, there is an optimum content for cyclic carbonates and chain carbonates having no carbon-carbon double bond. For these reasons, the solvent contains a cyclic carbonate having no carbon-carbon double bond, a cyclic ester, and a chain carbonate, and the content of the cyclic carbonate in the component excluding the electrolyte is 1% by weight or more. Cycle characteristics are particularly improved when the cyclic ester content is 1% by weight or more and 40% by weight or less and the chain carbonate content is 50% by weight or more and 95% by weight or less. Inferred.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. However, the present invention is not limited to these examples and comparative examples, and may be arbitrarily set without departing from the gist of the present invention. It can be implemented with deformation.

<Explanation of test operation>
[Production of positive electrode]
94 parts by weight of lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) which is a positive electrode active material, ₃ parts by weight of polyvinylidene fluoride (hereinafter referred to as “PVdF” as appropriate) and acetylene black 3 parts by weight was mixed, and N-methylpyrrolidone added to form a slurry was applied to both sides of a current collector made of aluminum and dried to obtain a positive electrode.

[Manufacture of negative electrode]
A negative electrode was obtained by mixing 92 parts by weight of graphite powder as a negative electrode active material and 8 parts by weight of PVdF, adding N-methylpyrrolidone into a slurry, and applying and drying on one side of a current collector made of copper. .

[Manufacture of lithium secondary batteries]
The positive electrode, the negative electrode, and the polyethylene separator were laminated in the order of the negative electrode, the separator, the positive electrode, the separator, and the negative electrode. The battery element thus obtained was wrapped in a cylindrical aluminum laminate film, and a non-aqueous electrolyte solution described later was injected, followed by vacuum sealing to produce a sheet-like non-aqueous electrolyte secondary battery. Furthermore, in order to improve the adhesion between the electrodes, the sheet-like battery was sandwiched between glass plates and pressurized.

[Cycle evaluation test]
In a constant temperature bath at 25 ° C., the sheet-like non-aqueous electrolyte secondary battery was charged at a constant current-constant voltage (hereinafter, referred to as “CCCV charging” as appropriate) at a predetermined voltage at 0.2 C, and then 3. The charge / discharge cycle for discharging to 0 V was repeated 100 times. The cut-off current during charging was 0.01C. The capacity retention rate after 100 cycles was determined by the following calculation formula, and the cycle characteristics were evaluated using the calculated value. The larger this value is, the less the cycle deterioration of the battery is. Moreover, the open circuit voltage between battery terminals was measured at the end of the first charge.
In addition, 1C is a current value when discharging the entire capacity of the battery in one hour.

<Example 1>
A combination of ethylene carbonate (EC) and monofluoroethylene carbonate (MFEC), which are cyclic carbonates having no carbon-carbon double bond, γ-butyrolactone (GBL), which is a cyclic ester, and dimethyl carbonate (DMC), which is a chain carbonate. LiPF ₆ as an electrolyte was dissolved in a mixed solvent (mixing weight ratio 11.7: 10.6: 10.0: 66.5) at a rate of 1 mol / L to obtain a nonaqueous electrolytic solution.

  Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Example 2>
A mixed solvent of ethylene carbonate (EC), which is a cyclic carbonate having no carbon-carbon double bond, γ-butyrolactone (GBL), which is a cyclic ester, and dimethyl carbonate (DMC), which is a chain carbonate (a mixture weight ratio of 17. 6: 5.0: 76.2), LiPF ₆ as an electrolyte was dissolved at a rate of 1.5 mol / L to obtain a nonaqueous electrolytic solution.
Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Example 3>
Ethylene carbonate (EC) which is a cyclic carbonate having no carbon-carbon double bond, γ-butyrolactone (GBL) which is a cyclic ester, dimethyl carbonate (DMC) which is a chain carbonate, and a carbonate having a carbon-carbon double bond As an electrolyte, LiPF ₆ as an electrolyte is dissolved at a rate of 1.0 mol / L in a mixed solvent (mixing weight ratio 17.6: 5.0: 76.2: 1.2) with vinylene carbonate (VC) as a non-aqueous system. An electrolyte was used. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Example 4>
Cyclic carbonate with no carbon-carbon double bond, ethylene carbonate (EC), cyclic ester with γ-butyrolactone (GBL), chain carbonate with dimethyl carbonate (DMC), and cyclic with carbon-carbon double bond LiPF ₆ as an electrolyte was dissolved in a mixed solvent (mixing weight ratio 11.8: 10.1: 76.9: 1.2) with vinylene carbonate (VC) as a carbonate at a rate of 1.0 mol / L. An aqueous electrolyte was used. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Example 5>
Cyclic carbonate with no carbon-carbon double bond, ethylene carbonate (EC), cyclic ester with γ-butyrolactone (GBL), chain carbonate with dimethyl carbonate (DMC), and cyclic with carbon-carbon double bond LiPF ₆ as an electrolyte was dissolved in a mixed solvent (mixing weight ratio 23.1: 9.9: 65.8: 1.2) with vinylene carbonate (VC) as a carbonate at a rate of 1.0 mol / L. An aqueous electrolyte was used. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Example 6>
Cyclic carbonate with no carbon-carbon double bond, ethylene carbonate (EC), cyclic ester with γ-butyrolactone (GBL), chain carbonate with dimethyl carbonate (DMC), and cyclic with carbon-carbon double bond LiPF ₆ as an electrolyte was dissolved at a rate of 1.0 mol / L in a mixed solvent (mixing weight ratio 11.7: 20.1: 67.0: 1.2) with vinylene carbonate (VC) as carbonate. An aqueous electrolyte was used. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

< Reference Example A7 >
Cyclic carbonate with no carbon-carbon double bond, ethylene carbonate (EC), cyclic ester with γ-butyrolactone (GBL), chain carbonate with dimethyl carbonate (DMC), and cyclic with carbon-carbon double bond LiPF ₆ as an electrolyte was dissolved at a rate of 1.0 mol / L in a mixed solvent (mixing weight ratio 11.7: 30.0: 57.1: 1.2) with vinylene carbonate (VC) as carbonate. An aqueous electrolyte was used. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

< Reference Example A8 >
Cyclic carbonate with no carbon-carbon double bond, ethylene carbonate (EC), cyclic ester with γ-butyrolactone (GBL), chain carbonate with dimethyl carbonate (DMC), and cyclic with carbon-carbon double bond LiPF ₆ as an electrolyte was dissolved in a mixed solvent (mixing weight ratio 11.6: 35.1: 52.1: 1.2) with vinylene carbonate (VC) as a carbonate at a rate of 1.0 mol / L. An aqueous electrolyte was used. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Example 9>
A carbon-carbon double bond-free cyclic carbonate, ethylene carbonate (EC), a cyclic ester, γ-butyrolactone (GBL), a chain carbonate, dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), and carbon- LiPF ₆ as an electrolyte was added to a mixed solvent (mixing weight ratio 23.3: 10.0: 47.5: 18.0: 1.2) with vinylene carbonate (VC) as a cyclic carbonate having a carbon double bond. It was dissolved at a rate of 1.0 mol / L to obtain a non-aqueous electrolyte solution. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Example 10>
A carbon-carbon double bond-free cyclic carbonate, ethylene carbonate (EC), a cyclic ester, γ-butyrolactone (GBL), a chain carbonate, ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and carbon- LiPF ₆ as an electrolyte was added to a mixed solvent (mixing weight ratio 20.0: 7.2: 60.6: 11.0: 1.2) with vinylene carbonate (VC) as a cyclic carbonate having a carbon double bond. It was dissolved at a rate of 1.0 mol / L to obtain a non-aqueous electrolyte solution. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Example 11>
Cyclic carbonates having no carbon-carbon double bond, ethylene carbonate (EC) and propylene carbonate (PC), cyclic ester γ-butyrolactone (GBL), chain carbonate dimethyl carbonate (DMC), and carbon-carbon As a cyclic carbonate having a double bond, LiPF ₆ as an electrolyte is 1 in a mixed solvent (mixing weight ratio 11.7: 10.6: 10.0: 66.5: 1.2) with vinylene carbonate (VC). It was dissolved at a rate of 0.0 mol / L to obtain a non-aqueous electrolyte. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Example 12>
Cyclic carbonate with no carbon-carbon double bond, ethylene carbonate (EC), cyclic ester with γ-butyrolactone (GBL), chain carbonate with dimethyl carbonate (DMC), and cyclic with carbon-carbon double bond LiPF ₆ as an electrolyte was added to a mixed solvent (mixing weight ratio 11.8: 10.1: 76.9: 0.6: 0.6) of vinylene carbonate (VC) and vinyl ethylene carbonate (VEC) as carbonate. It was dissolved at a rate of 1.0 mol / L to obtain a non-aqueous electrolyte solution. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Comparative Example 1>
Cyclic carbonate with no carbon-carbon double bond, ethylene carbonate (EC), cyclic ester with γ-butyrolactone (GBL), chain carbonate with dimethyl carbonate (DMC), and cyclic with carbon-carbon double bond LiPF ₆ as an electrolyte was dissolved in a mixed solvent (mixing weight ratio 31.1: 8.9: 59.0: 1.2) with vinylene carbonate (VC) as a carbonate at a rate of 1.0 mol / L. An aqueous electrolyte was used. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Comparative example 2>
Cyclic carbonate with no carbon-carbon double bond, ethylene carbonate (EC), cyclic ester with γ-butyrolactone (GBL), chain carbonate with dimethyl carbonate (DMC), and cyclic with carbon-carbon double bond LiPF ₆ as an electrolyte was dissolved at a rate of 1.0 mol / L in a mixed solvent (mixing weight ratio 11.6: 49.5: 37.7: 1.2) with vinylene carbonate (VC) as carbonate. An aqueous electrolyte was used. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Comparative Example 3>
Ethylene carbonate (EC) which is a cyclic carbonate having no carbon-carbon double bond, methyl butyrate which is a chain ester, dimethyl carbonate (DMC) which is a chain carbonate, and vinylene as a cyclic carbonate having a carbon-carbon double bond LiPF ₆ as an electrolyte is dissolved in a mixed solvent with carbonate (VC) (mixing weight ratio 11.7: 30.0: 57.1: 1.2) at a rate of 1.0 mol / L, and a nonaqueous electrolytic solution It was. Using the obtained nonaqueous electrolytic solution, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.35V. The results are shown in Table 1.

<Reference Example 1>
Using the non-aqueous electrolyte solution used in Example 4, a lithium secondary battery was produced according to the method described above, and the cycle characteristics were evaluated at a predetermined voltage of 4.20V. The results are shown in Table 1.
<Reference Example 2>
Using the non-aqueous electrolyte solution used in Comparative Example 1, a lithium secondary battery was produced according to the method described above, and cycle characteristics were evaluated at a predetermined voltage of 4.20V. The results are shown in Table 1.

From Table 1, when the non-aqueous electrolytes of Examples 1 to 6 , 9 to 12 and Reference Examples A7 and A8 according to the present invention are used, a cyclic carbonate having no carbon-carbon double bond is contained in an amount of more than 28% by weight. Compared to the case (Comparative Example 1), the case where the cyclic ester exceeds 40% by weight (Comparative Example 2), and the case where the chain ester is included instead of the cyclic ester (Comparative Example 3), It can be seen that the capacity recovery rate is large and that excellent cycle characteristics can be achieved.
It can also be seen that when the circuit voltage between the battery terminals is less than 4.25 V, the use of an electrolytic solution having the same composition as the electrolytic solution of the present application has little effect (Reference Examples 1 and 2).

  The use of the lithium secondary battery of the present invention is not particularly limited, and can be used for various known uses. Specific examples include notebook computers, pen input computers, mobile computers, electronic book players, mobile phones, mobile faxes, mobile copy, mobile printers, headphone stereos, video movies, LCD TVs, handy cleaners, portable CD players, and mini disc players. , Walkie-talkies, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power supplies, motors, lighting equipment, toys, game machines, watches, strobes, cameras, etc.

Claims (9)

A non-aqueous electrolyte solution for a lithium secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte solution, and an open circuit voltage between battery terminals at 25 ° C. at the end of charging is 4.25 V or more,
Containing an electrolyte and a solvent, and as the solvent, a cyclic carbonate having no carbon-carbon double bond, a cyclic ester, and a chain carbonate,
The content of the cyclic carbonate in the component excluding the electrolyte is 1 wt% or more and 24 wt% or less,
The content of the cyclic ester is 1% by weight or more and 34 % by weight or less,
A non-aqueous electrolytic solution, wherein the content of the chain carbonate is 65% by weight or more and 95% by weight or less. The non-aqueous electrolyte solution according to claim 1, wherein the cyclic carbonate is at least one selected from the group consisting of ethylene carbonate, propylene carbonate, butylene carbonate, monofluoroethylene carbonate, and difluoroethylene carbonate. The non-aqueous electrolysis according to claim 1 or 2, wherein the cyclic ester is at least one selected from the group consisting of γ-butyrolactone, α-methyl-γ-butyrolactone, and δ-valerolactone. liquid. The non-aqueous electrolyte solution according to claim 1, wherein the cyclic ester is γ-butyrolactone. The non-aqueous electrolyte solution according to any one of claims 1 to 4, wherein the chain carbonate is at least one selected from the group consisting of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. . Furthermore, the cyclic carbonate which has a carbon-carbon double bond is contained, The non-aqueous electrolyte solution as described in any one of Claims 1-5 characterized by the above-mentioned. A positive electrode, a negative electrode, and the non-aqueous electrolyte solution according to any one of claims 1 to 6,
A lithium secondary battery, wherein an open circuit voltage between battery terminals at 25 ° C. at the end of charging is 4.25 V or more. The lithium secondary battery according to claim 7, wherein the open circuit voltage between the battery terminals is 4.3 V or more. The lithium secondary battery according to claim 7 or 8, wherein the positive electrode is a positive electrode containing a lithium nickel-containing transition metal oxide as an active material.