JP5338151B2 - Non-aqueous electrolyte and non-aqueous electrolyte battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide nonaqueous electrolyte capable of providing a battery in which gas is less produced and whose property less deteriorates when stored at high temperatures, and to provide the nonaqueous electrolyte battery manufactured by using the same. <P>SOLUTION: The nonaqueous electrolyte comprises nonaqueous solvent containing ethylene carbonate, chain carbonate, and a carboxylic ester compound having a total carbon number of 6 or more, wherein the content rate of the carboxylic ester compound having the total carbon number of 6 or more to the total nonaqueous solvent is 0.1 capacity% or greater and smaller than 50 capacity%, and also containing a cyclic carbonate compound having carbon-carbon unsaturated bonds, a cyclic carbonate compound having fluorine atoms, and at least one compound selected from a group consisting of monofluorophosphate and difluorophosphate. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte battery using the same.

Non-aqueous electrolyte batteries such as lithium secondary batteries are being put to practical use in a wide range of applications from so-called consumer power sources such as mobile phones and laptop computers to in-vehicle power sources for automobiles and the like. However, the demand for higher performance of non-aqueous electrolyte batteries in recent years is increasing, and there is a demand for improvement in battery characteristics.
The electrolyte used for a non-aqueous electrolyte battery is usually composed mainly of an electrolyte and a non-aqueous solvent. The main components of the non-aqueous solvent include cyclic carbonates such as ethylene carbonate and propylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone. It is used.

In order to improve battery characteristics such as load characteristics, cycle characteristics, and storage characteristics of such non-aqueous electrolyte batteries, various studies have been made on non-aqueous solvents and electrolytes.
Patent Document 1 proposes an electrolytic solution containing a saturated cyclic carbonate, at least one unsaturated cyclic carbonate, and at least one linear ester of a saturated aliphatic monocarboxylic acid. The volume ratio is 20% or more, and 50% or more is preferable.
JP 2000-182670 A

However, the demand for higher performance of batteries in recent years is increasing, and it is required to achieve high capacity, high temperature storage characteristics, and cycle characteristics at a high level.
As a method for increasing the capacity, it has been studied to pack as many active materials as possible in a limited battery volume. For example, a method of increasing the density by pressing an active material layer of an electrode or Designs that minimize the volume occupied by materials other than materials have become common. However, the active material cannot be uniformly used by pressurizing the electrode active material layer to increase the density or reducing the amount of the electrolyte. Thereby, a part of lithium precipitates due to a non-uniform reaction, or deterioration of the active material is promoted, so that a problem that sufficient characteristics cannot be obtained easily occurs. Furthermore, the increase in capacity reduces the gaps inside the battery, and even when a small amount of gas is generated due to the decomposition of the electrolyte, there is a problem that the internal pressure of the battery increases significantly. In particular, in non-aqueous electrolyte two batteries, in most cases used as a backup power source in the event of a power failure or as a power source for portable equipment, a weak current is always supplied to make up for the self-discharge of the battery, and the battery is continuously charged. In such a continuously charged state, the activity of the electrode active material is always high, and at the same time, due to the heat generated by the device, the capacity of the battery is reduced, or the electrolyte is decomposed and gas is easily generated. If a large amount of gas is generated, a safety valve may be activated in a battery that senses this when the internal pressure is abnormally increased due to an abnormality such as overcharge and activates the safety valve. Further, in a battery without a safety valve, the battery may expand due to the pressure of the generated gas, and the battery itself may become unusable.

Therefore, there is a need for a non-aqueous electrolyte battery that generates little gas even when stored at a high temperature and has little characteristic deterioration.
However, the non-aqueous electrolyte secondary battery using the electrolyte described in Patent Document 1 contains a large amount of a saturated aliphatic monocarboxylic acid linear ester that reacts more easily with lithium than a saturated cyclic carbonate. For this reason, it has not yet been satisfactory in terms of the above-described high-temperature storage characteristics in the high-density batteries.

As a result of repeating various studies to achieve the above object, the present inventors have found that the above problems can be solved by using an electrolytic solution having a specific solvent composition using a specific carboxylic acid ester compound, The present invention has been completed.
That is, the gist of the present invention is as follows.
(1) Non-aqueous electrolyte solution containing electrolyte and non- aqueous solvent for dissolving the electrolyte In the non-aqueous electrolyte solution for lithium ion secondary battery, the non-aqueous solvent is ethylene carbonate, chain carbonate and butyl acetate, propyl propionate, butyric acid A non-aqueous solvent for a carboxylic acid ester compound containing at least one carboxylic acid ester compound having a total carbon number of 6 or more selected from the group consisting of ethyl and methyl valerate and having a total carbon number of 6 or more containing ratio in the can be less than 0.1 volume% to 50 volume%, further, the non-aqueous electrolyte, wherein the fluoroethylene carbonate contains 10 wt% or less than 0.01 wt% liquid.
(2) The nonaqueous electrolytic solution according to (1), wherein the content ratio of the carboxylic acid ester compound in all the nonaqueous solvents is 0.1% by volume or more and less than 20% by volume.
(3) The non-aqueous electrolyte solution according to (1) or (2), wherein the chain carbonate is ethyl methyl carbonate.
(4) The chain carbonate is ethyl methyl carbonate, and the content ratio of ethyl methyl carbonate in all nonaqueous solvents is 5% by volume or more and less than 80% by volume (1) or (2) ) Non-aqueous electrolyte .
(5 ) A nonaqueous electrolyte battery including a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a nonaqueous electrolyte solution, wherein the nonaqueous electrolyte solution is any one of (1) to (4) A non-aqueous electrolyte lithium ion secondary battery characterized by being a non-aqueous electrolyte solution.

  According to the present invention, it is possible to provide a non-aqueous electrolyte battery that has a high capacity, generates a small amount of gas, and has excellent storage characteristics, and can achieve downsizing and high performance of the non-aqueous electrolyte battery. it can.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail. However, the description of constituent elements described below is an example (representative example) of an embodiment of the present invention, and is not specified by these contents.
<Non-aqueous electrolyte>
The non-aqueous electrolyte solution of the present invention contains an electrolyte and a non-aqueous solvent that dissolves the electrolyte, as is the case with conventional non-aqueous electrolyte solutions.
(Electrolytes)
As the electrolyte, a lithium salt is usually used. The lithium salt is not particularly limited as long as it is known to be used for this purpose, and any lithium salt can be used. Specific examples include the following.

For example, inorganic lithium salts such as LiPF ₆ and LiBF ₄ ; LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-perfluoroethanedisulfonylimide Lithium cyclic 1,3-perfluoropropane disulfonylimide, LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiPF ₄ (CF ₃ ) ₂ , Li
PF ₄ (C ₂ F ₅ ) ₂ , LiPF ₄ (CF ₃ SO ₂ ) ₂ , LiPF ₄ (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₂ (CF ₃ ) ₂ , LiBF ₂ (C ₂ F ₅ ) ₂ , LiBF ₂ (CF ₃ SO ₂ ) ₂ , LiBF ₂ (C ₂ F ₅ S
Fluorine-containing organic lithium salts such as O ₂ ) ₂ and lithium bis (oxalate) borate, lithium difluoro (oxalate) borate and the like.

Of these, LiPF ₆ , LiBF ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ are preferable from the viewpoint of improving battery performance, and in particular, LiPF ₆ or LiB.
F ₄ is preferred.
These lithium salts may be used alone or in combination of two or more.
A preferred example in the case of using two or more types in combination is the combined use of LiPF ₆ and LiBF ₄ , which has an effect of improving cycle characteristics. In this case, the proportion of LiBF _{4 in} the total of both is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, particularly preferably 0.2% by weight or more, preferably 20%. % By weight or less, more preferably 5% by weight or less, particularly preferably 3% by weight or less. If the lower limit is not reached, it may be difficult to obtain the desired effect. If the upper limit is exceeded, battery characteristics after high-temperature storage may be deteriorated.

Another example is the combined use of an inorganic lithium salt and a fluorine-containing organic lithium salt. In this case, the proportion of the inorganic lithium salt in the total of both is 70% by weight or more and 99% by weight or less. It is desirable. Examples of the fluorine-containing organic lithium salt include LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropane. It is preferably any of disulfonylimide. The combined use of both has the effect of suppressing deterioration due to high temperature storage.

  The concentration of these electrolytes in the non-aqueous electrolyte solution is not particularly limited in order to exhibit the effects of the present invention, but is usually 0.5 mol / liter or more, preferably 0.6 mol / liter or more, more Preferably it is 0.7 mol / liter or more. The upper limit is usually 3 mol / liter or less, preferably 2 mol / liter or less, more preferably 1.8 mol / liter or less, and still more preferably 1.5 mol / liter or less. If the concentration is too low, the electrical conductivity of the electrolyte solution may be insufficient. On the other hand, if the concentration is too high, the electrical conductivity may decrease due to an increase in viscosity, and the battery performance may decrease. .

(Non-aqueous solvent)
In the present invention, the non-aqueous solvent contains ethylene carbonate, chain carbonate, and a carboxylic acid ester compound having a total carbon number of 6 or more, and the total carbon number in the total non-aqueous solvent is 6 or more. Is a cyclic carbonate compound having a carbon-carbon unsaturated bond, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate. It contains at least one compound selected from the group consisting of ethylene carbonate in the total amount of non-aqueous solvent, the improvement in the electrical conductivity of the electrolyte and the cycle characteristics of the battery. In order to improve, the lower limit is usually 1% by volume or more, preferably 5% by volume or more, more preferably 10% by volume or more, The upper limit is usually 50% by volume or less, preferably 40% by volume or less, more preferably 35% by volume or less, still more preferably 30% by volume or less, and particularly preferably 25% by volume or less.

As the chain carbonate, dialkyl carbonate is preferable, and the number of carbon atoms of the alkyl group is preferably 1 to 5, and particularly preferably 1 to 4, respectively. Specifically, for example, symmetric chain alkyl carbonates such as dimethyl carbonate, diethyl carbonate, and di-n-propyl carbonate; asymmetric chain alkyls such as ethyl methyl carbonate, methyl-n-propyl carbonate, and ethyl-n-propyl carbonate Examples thereof include dialkyl carbonates such as carbonates. Among these, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are preferable from the viewpoint of improving battery characteristics (particularly, cycle characteristics), and ethyl methyl carbonate is particularly preferable from the viewpoint of cycle characteristics and storage characteristics.

These chain carbonates may be used alone or in combination of two or more, but preferably in combination of two or more.
Examples of combinations of chain carbonates include dimethyl carbonate and diethyl carbonate, dimethyl carbonate and ethyl methyl carbonate, diethyl carbonate and ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

  In particular, those containing symmetric chain alkyl carbonates and asymmetric chain alkyl carbonates such as dimethyl carbonate and ethyl methyl carbonate, diethyl carbonate and ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate have cycle characteristics and storage characteristics. It is preferable because the balance of high load discharge characteristics is good.

  The total content of the chain carbonate in the total non-aqueous solvent is to improve the electric conductivity of the electrolytic solution and improve the battery characteristics after storage, so the lower limit is usually 5% by volume or more, and 10% by volume. The above is preferred, more preferably 20% by volume or more, particularly preferably 50% by volume or more, most preferably 60% by volume or more, and the upper limit is usually 90% by volume or less, preferably 85% by volume or less, and preferably 80% by volume or less. More preferred is 75% by volume or less.

  When ethyl methyl carbonate is contained in the non-aqueous solvent, the lower limit of the proportion of ethyl methyl carbonate in the total non-aqueous solvent is 5% by volume or more, preferably 20% by volume or more, more preferably 25% by volume. %, More preferably 30% by volume or more, and the upper limit is 80% by volume or less, preferably 75% by volume or less, more preferably 70% by volume or less, still more preferably 60% by volume or less. This is preferable because the balance between the cycle characteristics and storage characteristics of the battery is improved.

Furthermore, it is preferable to contain dimethyl carbonate and ethyl methyl carbonate in the non-aqueous solvent because the load characteristics of the battery are improved. In particular, it is preferable that the content ratio of dimethyl carbonate is higher than the content ratio of ethyl methyl carbonate.
When diethyl carbonate is contained in the non-aqueous solvent, the lower limit of the proportion of diethyl carbonate in the total non-aqueous solvent is usually 5% by volume or more, preferably 20% by volume or more, more preferably 25% by volume. More preferably, it is 30% by volume or more, and the upper limit is usually 90% by volume or less, preferably 80% by volume or less, more preferably 75% by volume or less, and further preferably 70% by volume or less. When contained, gas generation during high-temperature storage is suppressed, which is preferable.

The carboxylic acid ester compound having a total carbon number of 6 or more is not particularly limited, but preferably has a total carbon number of 8 or less, more preferably a total carbon number of 7 or less, from the viewpoint of viscosity reduction when used as an electrolytic solution. More preferably, it is a compound having 6 total carbon atoms.
Examples of the carboxylic acid ester compound having a total carbon number of 6 or more include a chain compound and a cyclic compound. Among these, a chain compound is preferable from the viewpoint of battery characteristics after high-temperature storage and gas generation suppression.

Specific examples include acetic acid ester, propionic acid ester, butyric acid ester, isobutyric acid ester, 2-methylbutyric acid ester, valeric acid ester, isovaleric acid ester and the like. Among these, from the viewpoint of battery characteristics after high-temperature storage and suppression of gas generation, acetate ester, propionate ester, butyrate ester, and valerate ester are preferable, propionate ester, butyrate ester, and valerate ester are more preferable, butyrate ester. Particularly preferred are valeric acid esters.

More specific examples include butyl acetate, sec-butyl acetate, isobutyl acetate, t-acetate
-Butyl, propyl propionate, isopropyl propionate, ethyl butyrate, ethyl isobutyrate, methyl valerate, methyl isovalerate, ethyl 2-methylbutyrate, pentyl acetate, butyl propionate, propyl butyrate, ethyl valerate, etc. Butyl acetate, sec-butyl acetate, isobutyl acetate, t-butyl acetate, propyl propionate, isopropyl propionate, ethyl butyrate, ethyl isobutyrate, methyl valerate, methyl isovalerate, ethyl 2-methylbutyrate, acetic acid Butyl, propyl propionate, ethyl butyrate, and methyl valerate are more preferable, propyl propionate, ethyl butyrate, and methyl valerate are more preferable, and ethyl butyrate and methyl valerate are particularly preferable.

  The content ratio of the carboxylic acid ester compound having a total carbon number of 6 or more in the total non-aqueous solvent improves the electric conductivity of the electrolytic solution and improves the cycle characteristics of the battery. % By volume or more, preferably 1% by volume or more, more preferably 2% by volume or more, more preferably 5% by volume or more, and the upper limit is less than 50% by volume, preferably less than 35% by volume, and less than 20% by volume. More preferred is 18% by volume or less, and most preferred is 15% by volume or less.

The total amount of ethylene carbonate, chain carbonate, and carboxylic acid ester compound having a total carbon number of 6 or more in the total non-aqueous solvent is to improve the electrical conductivity of the electrolyte and improve the cycle characteristics of the battery. The lower limit is usually preferably 60% by volume or more, more preferably 70% by volume or more, still more preferably 80% by volume or more, and particularly preferably 90% by volume or more.
Further, in the combination mainly composed of the above solvents, other solvents may be mixed.

Other nonaqueous solvent components can be appropriately selected from those conventionally proposed as solvents for nonaqueous electrolyte solutions. For example, the following are mentioned.
Cyclic carbonates having no carbon-carbon unsaturated bonds or fluorine atoms other than ethylene carbonate, cyclic ethers, chain ethers, cyclic carboxylic acid esters having a total carbon number of 5 or less, and chains having a total carbon number of 5 or less Examples thereof include carboxylic acid esters, sulfur-containing organic solvents, and phosphorus-containing organic solvents.

Examples of the cyclic carbonates having no carbon-carbon unsaturated bond or fluorine atom other than ethylene carbonate include alkylene carbonates such as propylene carbonate and butylene carbonate. Among these, propylene carbonate is preferable.
Examples of chain ethers include dimethoxyethane and dimethoxymethane.
Examples of cyclic carboxylic acid esters having a total carbon number of 5 or less include γ-butyrolactone and γ-valerolactone.

Examples of chain carboxylic acid esters having a total carbon number of 5 or less include methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, and methyl butyrate.
Examples of the sulfur-containing organic solvent include sulfolane, 2-methylsulfolane, 3-methylsulfolane, and diethylsulfone.
Examples of the phosphorus-containing organic solvent include trimethyl phosphate, triethyl phosphate, dimethyl ethyl phosphate, methyl diethyl phosphate, ethylene methyl phosphate, ethylene ethyl phosphate, and the like.
Of these, propylene carbonate is particularly preferred.

Two or more of these may be used in combination.
When propylene carbonate is contained in the non-aqueous solvent, the lower limit of the propylene carbonate content in the entire non-aqueous solvent is usually 0.01% by volume or more, preferably 1% by volume or more, more preferably 2%. The upper limit is usually 50% by volume or less, preferably 40% by volume or less, more preferably 20% by volume or less, and still more preferably 10% by volume or less.
In the present specification, the capacity of the non-aqueous solvent is a measured value at 25 ° C., but a measured value at the melting point is used for a solid at 25 ° C. such as ethylene carbonate.
In the present invention, in addition to the above compound, at least one selected from the group consisting of a cyclic carbonate compound having a carbon-carbon unsaturated bond, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate. Contains compounds.

(Cyclic carbonate compound having a carbon-carbon unsaturated bond)
Examples of the cyclic carbonate compound having a carbon-carbon unsaturated bond include vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, 4,5-diethyl vinylene carbonate, fluoro vinylene carbonate, trifluoromethyl. Vinylene carbonate compounds such as vinylene carbonate; vinyl ethylene carbonate, 4-methyl-4-vinylethylene carbonate, 4-ethyl-4-vinylethylene carbonate, 4-n-propyl-4-vinylethylene carbonate, 5-methyl-4- Vinyl ethylene carbonate compounds such as vinyl ethylene carbonate, 4,4-divinyl ethylene carbonate, 4,5-divinyl ethylene carbonate; 4,4-dimethyl-5- Chi Ren ethylene carbonate, methylene ethylene carbonate compounds such as 4,4-diethyl-5-methylene ethylene carbonate. Among these, vinylene carbonate, vinyl ethylene carbonate, 4-methyl-4-vinyl ethylene carbonate or 4,5-divinyl ethylene carbonate is preferable from the viewpoint of improving cycle characteristics, and among them, vinylene carbonate or vinyl ethylene carbonate is more preferable. Vinylene carbonate is preferred. These may be used alone or in combination of two or more.
When using 2 or more types together, it is preferable to use together vinylene carbonate and vinyl ethylene carbonate.

  When the non-aqueous electrolyte contains a cyclic carbonate compound having a carbon-carbon unsaturated bond, the proportion in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably. Is 0.3% by weight or more, most preferably 0.5% by weight or more. When there are too few cyclic carbonate compounds which have a carbon-carbon unsaturated bond, the effect of improving the cycling characteristics of a battery may not fully be exhibited. However, if the content of the cyclic carbonate compound having a carbon-carbon unsaturated bond is too large, the amount of gas generated may increase during storage at high temperatures or the discharge characteristics at low temperatures may decrease. It is 8% by weight or less, preferably 4% by weight or less, particularly preferably 3% by weight or less.

(Cyclic carbonate compound having a fluorine atom)
Examples of the cyclic carbonate compound having a fluorine atom include fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate, 4,4,5,5. -Tetrafluoroethylene carbonate, 4-fluoro-5-methylethylene carbonate, 4-fluoro-4-methylethylene carbonate, 4,5-difluoro-4-methylethylene carbonate, 4,4,5-trifluoro-5-methyl Examples include ethylene carbonate and trifluoromethyl ethylene carbonate. Of these, fluoroethylene carbonate, 4,5-difluoroethylene carbonate, and 4-fluoro-5-methylethylene carbonate are preferable from the viewpoint of improving cycle characteristics.
These may be used alone or in combination of two or more.

Moreover, you may use together with the cyclic carbonate compound which has a carbon-carbon unsaturated bond, and it is preferable to use together with vinylene carbonate or vinyl ethylene carbonate from the point of cycling characteristics improvement.
When the non-aqueous electrolyte contains a cyclic carbonate compound having a fluorine atom, the proportion in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably 0.3%. % By weight or more, most preferably 0.5% by weight or more. When there are too few cyclic carbonate compounds which have a fluorine atom, the effect of improving the cycling characteristics of a battery may not fully be exhibited. However, if the content of the cyclic carbonate compound having a fluorine atom is too large, the amount of gas generated during high-temperature storage may increase or the discharge characteristics at low temperatures may decrease, so the upper limit is usually 20% by weight or less. , Preferably 10% by weight or less, more preferably 5% by weight or less, particularly preferably 3% by weight or less.

(Monofluorophosphate and difluorophosphate)
The counter cation of monofluorophosphate and difluorophosphate is not particularly limited, and examples thereof include lithium, sodium, potassium, magnesium, calcium, and lithium is preferable.

  Specific examples of monofluorophosphate and difluorophosphate include lithium monofluorophosphate, sodium monofluorophosphate, potassium monofluorophosphate, lithium difluorophosphate, sodium difluorophosphate, and potassium difluorophosphate. And lithium monofluorophosphate and lithium difluorophosphate are preferable, and lithium difluorophosphate is more preferable.

These may be used alone or in combination of two or more.
In addition, it may be used in combination with a cyclic carbonate compound having a carbon-carbon unsaturated bond or a cyclic carbonate compound having a fluorine atom. From the viewpoint of improving cycle characteristics, it is used in combination with vinylene carbonate, vinyl ethylene carbonate, or fluoroethylene carbonate. It is preferable to do this.

  When the non-aqueous electrolyte contains a monofluorophosphate and / or difluorophosphate, the proportion in the non-aqueous electrolyte is usually 0.001% by weight or more, preferably 0.01% by weight or more, particularly Preferably it is 0.1 weight% or more, Most preferably, it is 0.2 weight% or more. If the content is too small, the effect of improving the cycle characteristics of the battery may not be sufficiently exhibited. The upper limit is usually 5% by weight or less, preferably 3% by weight or less, particularly preferably 2% by weight or less.

When the non-aqueous electrolyte solution according to the present invention is used, the reason why the non-aqueous electrolyte secondary battery has low gas generation and excellent high-temperature storage characteristics is not clear, and the present invention is limited to the following principle of operation. Although it is not a thing, it is guessed as follows.
When comparing the chain carbonate and the chain carboxylate, the chain carboxylate easily reacts with the positive electrode and the negative electrode in a charged state, which causes deterioration of battery characteristics particularly during high temperature storage.

  At least one compound selected from the group consisting of a cyclic carbonate compound having a carbon-carbon unsaturated bond, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate is a stable protection on the surface of the negative electrode. In order to form a film, by containing these compounds, a side reaction between the chain carboxylic acid ester and the negative electrode can be suppressed. Moreover, when it contains a monofluorophosphate and a difluorophosphate, it is thought that a protective film is formed also on the positive electrode side and a side reaction on the positive electrode side during high temperature storage can be suppressed.

  In addition, a carboxylic acid ester compound having a total carbon number of 6 or more is estimated to have a larger molecular size and a slower diffusion rate in the electrolytic solution than a carboxylic acid ester compound having a total carbon number of 5 or less. It is thought that the opportunity to react on the material surface will decrease. Furthermore, when the carboxylic acid ester compound having a total carbon number of 6 or more undergoes side reaction, it is considered that the decomposed product is difficult to gasify and forms a protective film on the surface of the positive electrode.

Therefore, ethylene carbonate, chain carbonate, and a carboxylic acid ester compound having a total carbon number of 6 or more are contained, and the content ratio of the carboxylic acid ester compound having a total carbon number of 6 or more in the total nonaqueous solvent is set to 0. At least selected from the group consisting of a cyclic carbonate compound having a carbon-carbon unsaturated bond, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate. By containing one or more compounds, it is considered that by suppressing side reactions occurring inside the battery during high temperature storage, gas generation can be suppressed and storage characteristics can be improved.
(Other compounds)
The non-aqueous electrolyte solution according to the present invention may contain various other compounds such as a conventionally known overcharge inhibitor as an auxiliary agent as long as the effects of the present invention are not impaired.

Conventionally known overcharge inhibitors include alkylbiphenyls such as biphenyl and 2-methylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane, trans Aromatic compounds such as -1-propyl-4-phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane, trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran Partial hydrocarbons of the aromatic compounds such as 2-fluorobiphenyl, 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene; Motobakemono; 2,4-difluoro anisole, 2,5-difluoro anisole, 2,6-difluoro anisole, 3,5-difluoro anisole, etc. fluorinated anisole compound of the like.

Among these, biphenyl, alkylbiphenyl such as 2-methylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclopentylbenzene, cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane, trans-1-propyl-4 -Aromatic compounds such as phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane, trans-1-butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran; 2-fluorobiphenyl, A partially fluorinated product of the aromatic compound such as 3-fluorobiphenyl, 4-fluorobiphenyl, 4,4′-difluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene is preferable, -Partially hydrogenated phenyl, cyclopentylbenzene, cyclohexylbenzene, cis-1-propyl-4-phenylcyclohexane, trans-1-propyl-4-phenylcyclohexane, cis-1-butyl-4-phenylcyclohexane, trans-1- Butyl-4-phenylcyclohexane, t-butylbenzene, t-amylbenzene, o-cyclohexylfluorobenzene, and p-cyclohexylfluorobenzene are more preferable, and a partially hydrogenated terphenyl and cyclohexylbenzene are particularly preferable.

Two or more of these may be used in combination. When two or more types are used in combination, in particular, a partially hydrogenated terphenyl, a combination of cyclohexylbenzene and t-butylbenzene or t-amylbenzene, or a partially hydrogenated biphenyl, alkylbiphenyl, terphenyl or terphenyl. It is overcharged to use together those selected from oxygen-free aromatic compounds such as cyclohexylbenzene, t-butylbenzene and t-amylbenzene and those selected from oxygen-containing aromatic compounds such as diphenyl ether and dibenzofuran. This is preferable from the viewpoint of the balance between prevention characteristics and high-temperature storage characteristics.

  The lower limit of the ratio of these overcharge inhibitors in the non-aqueous electrolyte is usually 0.1% by weight or more, preferably 0.2% by weight or more, particularly preferably 0.3% by weight or more, most preferably 0. The upper limit is usually 5% by weight or less, preferably 3% by weight or less, and particularly preferably 2% by weight or less. If the concentration is lower than this lower limit, the desired effect of the overcharge inhibitor may hardly be exhibited. Conversely, if the concentration is too high, battery characteristics such as high-temperature storage characteristics tend to deteriorate.

Other auxiliaries include carbonate compounds such as erythritan carbonate, spiro-bis-dimethylene carbonate, methoxyethyl-methyl carbonate; succinic anhydride, glutaric anhydride, maleic anhydride, itaconic anhydride, citraconic anhydride, anhydrous Carboxylic anhydrides such as glutaconic acid, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride and phenylsuccinic anhydride; dimethyl succinate, diethyl succinate, diallyl succinate, dimethyl maleate , Diethyl maleate, diallyl maleate, dipropyl maleate, dibutyl maleate, bis (trifluoromethyl) maleate, bis (pentafluoroethyl) maleate, bis (2,2,2-trifluoroethyl) maleate, etc. Dicarboxylic Diester compounds; spiro compounds such as 2,4,8,10-tetraoxaspiro [5.5] undecane and 3,9-divinyl-2,4,8,10-tetraoxaspiro [5.5] undecane; ethylene Sulfite, propylene sulfite, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, methyl methane sulfonate, ethyl methane sulfonate, methyl-methoxy methane sulfonate, methyl-2 -Methoxyethanesulfonate, busulfan, diethylene glycol dimethanesulfonate, 1,2-ethanediol bis (2,2,2-trifluoroethanesulfonate), 1,4-butanediol bis (2,2,2-trifluoroethanesulfonate) ), Sulfolane, sulfo , Sulfur compounds such as dimethylsulfone, diphenylsulfone, N, N-dimethylmethanesulfonamide, N, N-diethylmethanesulfonamide; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl Nitrogen-containing compounds such as 2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone and N-methylsuccinimide; heptane, octane, nonane, decane, cycloheptane, methylcyclohexane, ethylcyclohexane, propylcyclohexane, n Hydrocarbon compounds such as butylcyclohexane, t-butylcyclohexane and dicyclohexyl; fluorinated benzene and toluene fluoride such as fluorobenzene, difluorobenzene, hexafluorobenzene and benzotrifluoride; acetonitrile, propioni Examples include nitrile compounds such as tolyl, butyronitrile, malononitrile, succinonitrile, glutaronitrile, adiponitrile, and pimelonitrile.

  Among these, ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, 1,3-propene sultone, 1,4-butene sultone, busulfan, 1,4 in terms of improving battery characteristics after high-temperature storage -Sulfur-containing compounds such as butanediol bis (2,2,2-trifluoroethanesulfonate); nitrile compounds such as acetonitrile, propionitrile, butyronitrile, malononitrile, succinonitrile, glutaronitrile, adiponitrile, and pimelonitrile are preferable.

Two or more of these may be used in combination.
The ratio of these auxiliaries in the non-aqueous electrolyte solution is not particularly limited in order to express the effect of the present invention, but the lower limit is usually 0.01% by weight or more, preferably 0.1% by weight or more. The upper limit is usually 10% by weight or less, preferably 5% by weight or less, more preferably 3% by weight or less, and particularly preferably 1% by weight or less. By adding these auxiliaries, capacity maintenance characteristics and cycle characteristics after high temperature storage can be improved. If the concentration is lower than this lower limit, the effect of the auxiliary agent may be hardly exhibited. On the other hand, if the concentration is too high, battery characteristics such as high load discharge characteristics may deteriorate.
Moreover, you may use together said conventionally well-known overcharge prevention agent and other adjuvant in arbitrary combinations.

(Preparation of electrolyte)
The non-aqueous electrolyte solution according to the present invention can be prepared by dissolving an electrolyte and, if necessary, other compounds in a non-aqueous solvent. In preparing the non-aqueous electrolyte solution, each raw material is preferably dehydrated in advance in order to reduce the water content when the electrolyte solution is used. Usually, it is good to dehydrate to 50 ppm or less, preferably 30 ppm or less, particularly preferably 10 ppm or less. Moreover, you may implement dehydration, a deoxidation process, etc. after electrolyte solution preparation.

The non-aqueous electrolyte of the present invention is suitable for use as a secondary battery among non-aqueous electrolyte batteries, that is, as an electrolyte for a non-aqueous electrolyte secondary battery, for example, a lithium secondary battery. Hereinafter, a non-aqueous electrolyte secondary battery using the electrolyte of the present invention will be described.
<Non-aqueous electrolyte secondary battery>
The non-aqueous electrolyte secondary battery of the present invention is a non-aqueous electrolyte battery including a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte, and the non-aqueous electrolyte is the above-described electrolyte. It is characterized by being.

(Battery configuration)
The non-aqueous electrolyte secondary battery according to the present invention is the same as the conventionally known non-aqueous electrolyte secondary battery except that it is produced using the electrolyte of the present invention, and a negative electrode capable of inserting and extracting lithium ions and A non-aqueous electrolyte battery including a positive electrode and a non-aqueous electrolyte solution, usually obtained by housing the positive electrode and the negative electrode in a case through a porous membrane impregnated with the non-aqueous electrolyte solution according to the present invention. . Therefore, the shape of the secondary battery according to the present invention is not particularly limited, and may be any of a cylindrical shape, a square shape, a laminate shape, a coin shape, a large size, and the like.

(Negative electrode)
The negative electrode active material is not particularly limited as long as it can occlude and release lithium ions. Specific examples thereof include carbonaceous materials, alloy-based materials, lithium-containing metal composite oxide materials, and the like.
These negative electrode active materials may be used alone or in combination of two or more. Of these, preferred are carbonaceous materials and alloy materials.
Among the carbonaceous materials, graphite and graphite whose surface is coated with amorphous carbon as compared with graphite are particularly preferable.

  Graphite preferably has a lattice plane (002 plane) d value (interlayer distance) of 0.335 to 0.338 nm, particularly 0.335 to 0.337 nm, as determined by X-ray diffraction using the Gakushin method. The crystallite size (Lc) determined by X-ray diffraction by the Gakushin method is usually 10 nm or more, preferably 50 nm or more, and particularly preferably 100 nm or more. The ash content is usually 1% by weight or less, preferably 0.5% by weight or less, particularly preferably 0.1% by weight or less.

The graphite surface coated with amorphous carbon is preferably graphite having a d-value of 0.335 to 0.338 nm on the lattice plane (002 plane) in X-ray diffraction as a core material. A carbonaceous material having a larger d-value on the lattice plane (002 plane) in X-ray diffraction than the core material is attached, and the d-value on the lattice plane (002 plane) in X-ray diffraction is greater than that of the core material and the core material. The ratio with respect to the carbonaceous material having a large is 99/1 to 80/20 by weight. When this is used, a negative electrode having a high capacity and hardly reacting with the electrolytic solution can be produced.

The particle size of the carbonaceous material is a median diameter measured by a laser diffraction / scattering method, and is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, most preferably 7 μm or more, and usually 100 μm or less, preferably 50 μm or less. More preferably, it is 40 micrometers or less, Most preferably, it is 30 micrometers or less.
The specific surface area of the carbonaceous material by the BET method is usually 0.3 m ² / g or more, preferably 0.5
m ² / g or more, more preferably 0.7 m ² / g or more, and most preferably 0.8 m ² / g or more and usually 25.0 m ² / g or less, preferably 20.0 m ² / g, more Preferably it is 15.0 m < ² > / g or less, Most preferably, it is 10.0 m < ² > / g or less.

Further, the carbonaceous material is analyzed by Raman spectrum using argon ion laser light, the peak is the peak intensity of the peak P _A in the range of 1570~1620cm ^-1 I _A, in the range of 1300~1400cm ^-1 P If the peak intensity of the _B was I _B, R value represented by the ratio of I _B and _{I a (= I B / I} a) is what is preferably in the range of 0.01 to 0.7. Further, the half width of the peak in the range of 1570～1620Cm ^-1 is, 26cm ^-1 or less, are preferred in particular 25 cm ^-1 or less.

  The alloy material is not particularly limited as long as it can occlude and release lithium, and single metals and alloys that form lithium alloys, or oxides, carbides, nitrides, silicides, sulfides, and phosphides thereof. Any of these compounds may be used. Preferably, it is a material including a single metal and an alloy forming a lithium alloy, more preferably a material including a group 13 and group 14 metal / metalloid element (that is, excluding carbon), and further, aluminum, silicon, and It is preferably a simple metal of tin (hereinafter sometimes referred to as “specific metal element”) and an alloy / compound containing these elements.

  Examples of the negative electrode active material having at least one element selected from specific metal elements include a single metal element of any one specific metal element, an alloy composed of two or more specific metal elements, one type, or two or more types Alloys composed of specific metal elements and other one or more metal elements, compounds containing one or more specific metal elements, and oxides, carbides, nitrides, and the like of the compounds Examples include composite compounds such as silicides, sulfides, and phosphides. By using these simple metals, alloys or metal compounds as the negative electrode active material, the capacity of the battery can be increased.

  Moreover, the compound which these complex compounds combined with several elements, such as a metal simple substance, an alloy, or a nonmetallic element, can also be mentioned as an example. More specifically, for example, for silicon and tin, an alloy of these elements and a metal that does not operate as a negative electrode can be used. In addition, for example, in the case of tin, a complex compound containing 5 to 6 kinds of elements in combination with a metal that acts as a negative electrode other than tin and silicon, a metal that does not operate as a negative electrode, and a nonmetallic element can also be used. .

Among these negative electrode active materials, since the capacity per unit weight is large when a battery is made, any single element of a specific metal element, an alloy of two or more specific metal elements, an oxide of a specific metal element In particular, silicon and / or tin metal alone, alloys, oxides, carbides, nitrides and the like are preferable because of their large capacity per unit weight.
In addition, although the capacity per unit weight is inferior to that of a single metal or an alloy, the following compounds containing silicon and / or tin are also preferred because of excellent cycle characteristics.

The element ratio of silicon and / or tin to oxygen is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and usually 1.5 or less, preferably 1. Silicon and / or tin oxide of 3 or less, more preferably 1.1 or less.
-Element ratio of silicon and / or tin and nitrogen is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and usually 1.5 or less, preferably 1. Silicon and / or tin nitride of 3 or less, more preferably 1.1 or less.

The elemental ratio of silicon and / or tin to carbon is usually 0.5 or more, preferably 0.7 or more, more preferably 0.9 or more, and usually 1.5 or less, preferably 1. Silicon and / or tin carbide of 3 or less, more preferably 1.1 or less.
These alloy materials may be in the form of powder or thin film, and may be crystalline or amorphous.

  The average grain size of the alloy-based material is not particularly limited in order to exhibit the effect of the present invention, but is usually 50 μm or less, preferably 20 μm or less, particularly preferably 10 μm or less, usually 0.1 μm or more, preferably 1 μm. As described above, it is particularly preferably 2 μm or more. When this upper limit is exceeded, the expansion of the electrode increases, and the cycle characteristics may deteriorate. Moreover, when less than this minimum, it becomes difficult to collect current and there is a possibility that the capacity is not sufficiently developed.

The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it can occlude and release lithium, but a lithium-containing composite metal oxide material containing titanium is preferable. An oxide (hereinafter abbreviated as “lithium titanium composite oxide”) is more preferable.
In addition, lithium or titanium of the lithium titanium composite oxide is at least selected from the group consisting of other metal elements such as Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb. Those substituted with one element are also preferred.

Furthermore, it is a lithium titanium composite oxide represented by Li _x Ti _y M _z O ₄ , and 0.7 ≦ x ≦ 1.5, 1.5 ≦ y ≦ 2.3, and 0 ≦ z ≦ 1.6. It is preferable that the structure at the time of doping / undoping lithium ions is stable (M is Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb). Represents at least one element selected from the group consisting of:

Above all,
(A) 1.2 ≦ x ≦ 1.4, 1.5 ≦ y ≦ 1.7, z = 0
(B) 0.9 ≦ x ≦ 1.1, 1.9 ≦ y ≦ 2.1, z = 0
(C) 0.7 ≦ x ≦ 0.9, 2.1 ≦ y ≦ 2.3, z = 0
This structure is particularly preferable because of a good balance of battery performance, and a particularly preferable representative composition is Li _4/3 Ti _5/3 O ₄ in (a), Li ₁ Ti ₂ O ₄ in (b), ( In c), it is Li _4/5 Ti _11/5 O ₄ .

As for the structure of Z ≠ 0, for example, Li _4/3 Ti _4/3 Al _1/3 O ₄ is preferable.
(Positive electrode)
The positive electrode active material is not particularly limited as long as it can occlude and release lithium ions. A substance containing lithium and at least one transition metal is preferable, and examples thereof include a lithium transition metal composite oxide and a lithium-containing transition metal phosphate compound.

The transition metal of the lithium transition metal composite oxide is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu or the like, and specific examples include lithium / cobalt composite oxide such as LiCoO ₂ or LiNiO ₂ . Lithium / nickel composite oxide, LiMnO ₂ , LiMn ₂ O ₄ , Li ₂ MnO _{3 and} other lithium / manganese composite oxides, Al, Ti , V, Cr, Mn, Fe, Co, Li, N
Examples include those substituted with other metals such as i, Cu, Zn, Mg, Ga, Zr, and Si. Specific examples of the substituted ones include, for example, LiNi _0.5 Mn _0.5 O ₂ , LiNi _0.85 Co _0.10 Al _0.05 O ₂ , LiNi _0.33 Co _0.33 Mn _0.33 O ₂ , LiMn _1.8 Al _0.2 O ₄ , LiMn _1.5 Ni _0.5 O _4, etc. Is mentioned.

As the transition metal of the lithium-containing transition metal phosphate compound, V, Ti, Cr, Mn, Fe, Co, Ni, Cu and the like are preferable. Specific examples include, for example, LiFePO ₄ , Li ₃ F
e ₂ (PO ₄ ) ₃ , iron phosphates such as LiFeP ₂ O ₇ , cobalt phosphates such as LiCoPO ₄ , and some of the transition metal atoms that are the main components of these lithium transition metal phosphate compounds are Al, Ti , V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si and the like substituted with other metals.

These positive electrode active materials may be used alone or in combination.
In addition, a material in which a substance having a composition different from that of the substance constituting the main cathode active material is attached to the surface of the cathode active material can be used. Surface adhering substances include aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, bismuth oxide, lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate And sulfates such as aluminum sulfate and carbonates such as lithium carbonate, calcium carbonate and magnesium carbonate.

  The amount of the surface adhering substance is not particularly limited in order to exhibit the effects of the present invention, but is preferably 0.1 ppm or more, more preferably 1 ppm or more as a lower limit in terms of mass with respect to the positive electrode active material. The upper limit is preferably 10 ppm or more, preferably 20% or less, more preferably 10% or less, and still more preferably 5% or less. The surface adhering substance can suppress the oxidation reaction of the non-aqueous electrolyte solution on the surface of the positive electrode active material, and can improve the battery life. However, when the amount of the adhering quantity is too small, the effect is not sufficiently exhibited. If the amount is too large, the resistance may increase in order to inhibit the entry and exit of lithium ions.

(electrode)
As the binder for binding the active material, any material can be used as long as it is a material that is stable with respect to the solvent and the electrolytic solution used during electrode production. For example, fluororesins such as polyvinylidene fluoride and polytetrafluoroethylene, polyolefins such as polyethylene and polypropylene, polymers having unsaturated bonds such as styrene / butadiene rubber, isoprene rubber and butadiene rubber, and copolymers thereof, ethylene-acrylic Examples thereof include acrylic acid polymers such as acid copolymers and ethylene-methacrylic acid copolymers, and copolymers thereof.

The electrode may contain a thickener, a conductive material, a filler and the like in order to increase mechanical strength and electrical conductivity.
Examples of the thickener include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, and casein.

Examples of the conductive material include a metal material such as copper or nickel, and a carbon material such as graphite or carbon black.
The electrode may be manufactured by a conventional method. For example, it can be formed by adding a binder, a thickener, a conductive material, a solvent or the like to a negative electrode or a positive electrode active material to form a slurry, applying the slurry to a current collector, drying it, and then pressing it.

In addition, a material obtained by adding a binder or a conductive material to an active material is roll-formed as it is to form a sheet electrode, a pellet electrode is formed by compression molding, and an electrode is formed on the current collector by a technique such as vapor deposition, sputtering, or plating. A thin film of material can also be formed.
When graphite is used as the negative electrode active material, the density of the negative electrode active material layer after drying and pressing is usually 1.45 g / cm ³ or more, preferably 1.55 g / cm ³ or more, more preferably 1.60 g. / Cm ³ or more, particularly preferably 1.65 g / cm ³ or more.

The density of the positive electrode active material layer after drying and pressing is usually 2.0 g / cm ³ or more, preferably 2.5 g / cm ³ or more, more preferably 3.0 g / cm ³ or more.
Various types of current collectors can be used, but metals and alloys are usually used. Examples of the current collector for the negative electrode include copper, nickel, and stainless steel, and copper is preferred. Examples of the positive electrode current collector include metals such as aluminum, titanium, and tantalum, and alloys thereof, and aluminum or an alloy thereof is preferable.
(Separator, exterior body)
A porous film (separator) is interposed between the positive electrode and the negative electrode to prevent a short circuit. In this case, the electrolytic solution is used by impregnating the porous membrane. The material and shape of the porous film are not particularly limited as long as it is stable to the electrolytic solution and excellent in liquid retention, and a porous sheet or nonwoven fabric made of a polyolefin such as polyethylene or polypropylene is preferable.

The material of the battery casing used in the battery according to the present invention is also arbitrary, and nickel-plated iron, stainless steel, aluminum or an alloy thereof, nickel, titanium, a laminate film, or the like is used.
The operating voltage of the non-aqueous electrolyte secondary battery of the present invention described above is usually in the range of 2V to 6V.

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 as long as the gist thereof is not exceeded.
In addition, each evaluation method of the battery obtained by the following Example and the comparative example is shown below.
[Capacity evaluation]
The non-aqueous electrolyte secondary battery is charged to 4.2 V at a constant current corresponding to 0.2 C at 25 ° C. in a state of being sandwiched between glass plates in order to improve the adhesion between the electrodes, and then 0.2 C The battery was discharged to 3 V at a constant current. This is done for 3 cycles to stabilize the battery. In the 4th cycle, after charging to 4.2V with a constant current of 0.5C, charging is performed until the current value reaches 0.05C with a constant voltage of 4.2V. The initial discharge capacity was determined by discharging to 3 V at a constant current of 0.2C.
Here, 1C represents a current value for discharging the reference capacity of the battery in one hour, and 0.2C represents a current value of 1/5 thereof.

[Evaluation of high-temperature storage characteristics]
After the capacity evaluation test was completed, the battery was immersed in an ethanol bath and the volume was measured. Then, the battery was charged to 4.2 V at a constant current of 0.5 C at 25 ° C., and the current value was set to 0.2 at a constant voltage of 4.2 V. The battery was charged until it reached 05C. Thereafter, the battery stored at 85 ° C. for 1 day was sufficiently cooled and then immersed in an ethanol bath to measure the volume, and the amount of gas generated from the volume change before and after storage was determined.

Next, it was discharged to 3 V at a constant current of 0.2 C at 25 ° C., the remaining capacity after the high-temperature storage test was measured, and the ratio of the discharge capacity after the storage test to the initial discharge capacity was obtained. The remaining capacity (%) was used.
Next, after charging to 4.2 V at a constant current of 0.5 C at 25 ° C., charging is performed until the current value becomes 0.05 C at a constant voltage of 4.2 V, and discharged to 3 V at a constant current of 1 C. The 1C discharge capacity after the high temperature storage test was measured, the ratio of the 1C discharge capacity after the storage test to the initial discharge capacity was determined, and this was defined as the 1C discharge capacity (%) after the high temperature storage.

Example 1
[Manufacture of negative electrode]
The d value of the lattice plane (002 plane) in X-ray diffraction is 0.336 nm, the crystallite size (Lc) is 652 nm, the ash content is 0.07 parts by weight, the median diameter by laser diffraction / scattering method is 12 μm, and the ratio by BET method The half-value width of a peak whose surface area is 7.5 m ² / g and R value (= I _B / I _A ) determined from Raman spectrum analysis using argon ion laser light is 0.12, 1570 to 1620 cm ^−1. Was mixed with 94 parts by weight of natural graphite powder having a weight of 19.9 cm ⁻¹ and 6 parts by weight of polyvinylidene fluoride, and N-methyl-2-pyrrolidone was added to form a slurry. This slurry was uniformly applied to one side of a 12 μm thick copper foil, dried, and then pressed so that the density of the negative electrode active material layer was 1.67 g / cm ³ to form a negative electrode.

[Production of positive electrode]
90 parts by weight of LiCoO ₂ , 4 parts by weight of carbon black and 6 parts by weight of polyvinylidene fluoride (manufactured by Kureha Chemical Co., Ltd., trade name “KF-1000”) are mixed, and N-methyl-2-pyrrolidone is added to form a slurry. After uniformly applying and drying on both surfaces of an aluminum foil having a thickness of 15 μm, the positive electrode active material layer was pressed to a density of 3.2 g / cm ³ to obtain a positive electrode.

[Manufacture of electrolyte]
Under a dry argon atmosphere, 2% by weight of vinylene carbonate as a content in the non-aqueous electrolyte solution was mixed with a mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, and ethyl butyrate (volume ratio 15: 30: 40: 15), Subsequently, fully dried LiPF ₆ was dissolved at a rate of 1.0 mol / liter to obtain an electrolytic solution.

[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 to produce a battery element. The battery element was inserted into a bag made of a laminate film in which both surfaces of aluminum (thickness: 40 μm) were coated with a resin layer while projecting positive and negative terminals, and then the electrolyte was poured into the bag and vacuum sealed. The sheet-shaped battery was manufactured and the high-temperature storage characteristics were evaluated. The evaluation results are shown in Table 1.

(Example 2)
A sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that propyl propionate was used in place of ethyl butyrate in the electrolytic solution of Example 1, and the high-temperature storage characteristics were evaluated. The evaluation results are shown in Table 1.
(Example 3)
A sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that butyl acetate was used instead of ethyl butyrate in the electrolytic solution of Example 1, and the high-temperature storage characteristics were evaluated. The evaluation results are shown in Table 1.

Example 4
Mixing ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl butyrate (volume ratio 15: 30: 40: 15) with 2% vinylene carbonate and 1% fluoroethylene carbonate as content in non-aqueous electrolyte did. Subsequently, a sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ sufficiently dried at a ratio of 1.0 mol / liter was used. Storage characteristics were evaluated. The evaluation results are shown in Table 1.

(Example 5)
A mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl butyrate (capacity ratio 15: 30: 40: 15), 2% by weight of vinylene carbonate and 0.5% by weight of lithium difluorophosphate as content in the non-aqueous electrolyte % Mixed. Subsequently, a sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ sufficiently dried at a ratio of 1.0 mol / liter was used. Storage characteristics were evaluated. The evaluation results are shown in Table 1.

(Example 6)
2% by weight of vinylene carbonate as a content in the non-aqueous electrolyte was mixed with a mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl butyrate (volume ratio 15: 30: 25: 30). Subsequently, a sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ sufficiently dried at a ratio of 1.0 mol / liter was used. Storage characteristics were evaluated. The evaluation results are shown in Table 1.

(Comparative Example 1)
Ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate mixture volume ratio 15:30:55) was mixed with 2% by weight of vinylene carbonate as the content in the non-aqueous electrolyte. Subsequently, a sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ sufficiently dried at a ratio of 1.0 mol / liter was used. Storage characteristics were evaluated. The evaluation results are shown in Table 1.

(Comparative Example 2)
Prepared by dissolving well-dried LiPF ₆ in a mixture of ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate and ethyl butyrate (volume ratio 15: 30: 40: 15) to a ratio of 1.0 mol / liter. A sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that the electrolyte solution was used, and the high-temperature storage characteristics were evaluated. The evaluation results are shown in Table 1.

(Comparative Example 3)
2% by weight of vinylene carbonate was mixed with the mixture of ethylene carbonate, dimethyl carbonate and ethyl butyrate (volume ratio 15:25:60) as the content in the non-aqueous electrolyte. Subsequently, a sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that an electrolyte prepared by dissolving LiPF ₆ sufficiently dried at a ratio of 1.0 mol / liter was used. Storage characteristics were evaluated. The evaluation results are shown in Table 1.

(Comparative Example 4)
A sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that ethyl acetate was used instead of ethyl butyrate in the electrolytic solution of Example 1, and the high-temperature storage characteristics were evaluated. The evaluation results are shown in Table 1.

As is clear from Table 1, it can be seen that the battery according to the present invention has a small amount of gas generation after high-temperature storage and is excellent in storage characteristics.
That is, when comparing the example of the present application and the comparative example 1, the example of the present application containing a carboxylic acid ester compound having a total carbon number of 6 or more has less gas generation, and carbon is formed by forming a film on the positive electrode. -It suppresses that the cyclic carbonate compound etc. which have a carbon unsaturated bond raise | generate a side reaction on a positive electrode.

  In addition, when Examples of the present application and Comparative Example 2 are compared, they are selected from the group consisting of a cyclic carbonate compound having a carbon-carbon unsaturated bond, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate. The embodiment of the present application containing at least one compound suppresses the side reaction between the chain carboxylic acid ester and the negative electrode by forming a stable protective film on the negative electrode, and reduces battery characteristics after high-temperature storage. Suppressed.

Further, when comparing the example of the present application and the comparative example 3, the example of the present application suppresses the reaction on the surface of the positive electrode and the negative electrode active material because the carboxylic acid ester compound having a total carbon number of 6 or more is an appropriate amount. In addition, deterioration of battery characteristics after high temperature storage is suppressed.
Further, when comparing the Example of the present application and Comparative Example 4, the carboxylic acid ester compound having a total carbon number of 6 or more has a larger molecular size than the carboxylic acid ester compound having a total carbon number of 5 or less, and the electrolytic solution. The diffusion rate inside is estimated to be slow, and it is considered that the chance of reaction on the surface of the positive electrode active material is reduced. Furthermore, when the carboxylic acid ester compound having a total carbon number of 6 or more undergoes a side reaction, the decomposition product is difficult to gasify and forms a protective film on the surface of the positive electrode. Occurrence is suppressed.

Claims (5)

In the electrolyte and non-aqueous electrolyte nonaqueous electrolyte for a lithium ion secondary battery including a nonaqueous solvent for dissolving the non-aqueous solvent, ethylene carbonate, chain carbonate, and either butyl acetate and propionate propyl Le Ranaru Containing at least one carboxylic acid ester compound having a total carbon number of 6 or more selected from the group, and the content ratio of the carboxylic acid ester compound having a total carbon number of 6 or more in the total non-aqueous solvent, A nonaqueous electrolytic solution characterized by containing 0.1% by volume or more and less than 50% by volume and further containing 0.01% by mass or more and 10% by mass or less of fluoroethylene carbonate.   2. The non-aqueous electrolyte solution according to claim 1, wherein a content ratio of the carboxylic acid ester compound in all the non-aqueous solvents is 0.1 volume% or more and less than 20 volume%.   The non-aqueous electrolyte solution according to claim 1 or 2, wherein the chain carbonate is ethyl methyl carbonate.   The chain carbonate is ethyl methyl carbonate, and the content ratio of ethyl methyl carbonate in the total non-aqueous solvent is 5% by volume or more and less than 80% by volume. Aqueous electrolyte. 5. A non-aqueous electrolyte battery comprising a negative electrode and a positive electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte solution, wherein the non-aqueous electrolyte solution is a non-aqueous electrolyte solution according to claim 1. A non-aqueous electrolyte lithium ion secondary battery.