JP5842952B2 - Non-aqueous electrolyte and non-aqueous electrolyte battery - Google Patents

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 addition, in order to improve battery characteristics such as load characteristics, cycle characteristics, and storage characteristics of such nonaqueous electrolyte batteries, and to improve battery safety during overcharge, various studies have been made on nonaqueous solvents and electrolytes. ing.
Patent Document 1 proposes to protect the battery by increasing the internal resistance of the battery by mixing an additive that is polymerized at a battery voltage equal to or higher than the maximum operating voltage of the battery in the electrolyte. In 2 the internal electrical disconnection device provided for overcharge protection is ensured by mixing an additive that generates gas and pressure by polymerizing in the electrolyte at a battery voltage higher than the maximum operating voltage of the battery. It has been proposed to work. Moreover, aromatic compounds, such as biphenyl, thiophene, and furan, are disclosed as those additives. Further, Patent Document 3 discloses a non-aqueous system in which phenylcyclohexane is added in a range of 0.1 to 20 parts by weight in a non-aqueous electrolyte solution in order to suppress deterioration of battery characteristics when biphenyl or thiophene is used. A non-aqueous electrolyte secondary battery system including an electrolyte secondary battery and a charge control system that senses an increase in battery temperature and disconnects a charging circuit has been proposed.

  Patent Document 4 proposes adding a phosphoric acid triester to an electrolytic solution in order to improve cycle characteristics.

JP-A-9-106835 JP-A-9-171840 JP 2002-50398 A Japanese Patent Laid-Open No. 7-114940

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.

In the non-aqueous electrolyte secondary battery using the electrolyte solution described in Patent Documents 1 to 3, the high-temperature storage characteristics as described above are deteriorated and are not yet satisfactory.
Further, the non-aqueous electrolyte secondary battery using the electrolyte described in Patent Document 4 is not satisfactory in terms of improving safety during overcharge.

As a result of various studies to achieve the above object, the present inventors have found that the above problems can be solved by including a compound having a specific structure in the electrolytic solution, thereby completing the present invention. I came to let you.
That is, the gist of the present invention is as follows.
(1) A nonaqueous electrolytic solution comprising a electrolyte and a nonaqueous solvent, wherein the nonaqueous electrolytic solution contains a specific phosphate compound.
(2) The nonaqueous electrolyte solution according to (1) above, wherein the total proportion of the specific phosphate compound in the nonaqueous electrolyte solution is 0.001 to 10% by weight.
(3) 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 solution, wherein the non-aqueous electrolyte solution is the non-aqueous electrolyte according to (1) or (2) above A non-aqueous electrolyte battery characterized by being a liquid.

  According to the present invention, it is possible to provide a non-aqueous electrolyte battery having a high capacity and excellent storage characteristics and cycle characteristics while improving safety during overcharge. Performance can be achieved.

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, particularly preferably 0.1% by weight or more, preferably 20% by weight or less, particularly preferably 5% by weight or less. is there. 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.

When the non-aqueous solvent contains 55% by volume or more of γ-butyrolactone, the lithium salt is preferably LiBF ₄ or a combination of LiBF ₄ and another. In this case, LiBF ₄ preferably accounts for 40 mol% or more of the lithium salt. Particularly preferably, the proportion of LiBF _{4 in} the lithium salt is 40 mol% or more and 95 mol% or less, and the rest is Li
The combination is selected from the group consisting of PF ₆ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) ₂ .

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)
The non-aqueous solvent can also be appropriately selected from conventionally known solvents for non-aqueous electrolyte solutions. For example, cyclic carbonates having no carbon-carbon unsaturated bond or fluorine atom, chain carbonates, cyclic ethers, chain ethers, cyclic carboxylic acid esters, chain 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 include alkylene carbonates having an alkylene group having 2 to 4 carbon atoms such as ethylene carbonate, propylene carbonate, butylene carbonate, among these. , Ethylene carbonate and propylene carbonate are preferable from the viewpoint of improving battery characteristics, and ethylene carbonate is particularly preferable.

As the chain carbonates, dialkyl carbonates are preferable, and the number of carbon atoms of the alkyl group constituting each is preferably 1 to 5, particularly preferably 1 to 4. 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, high load discharge characteristics).

Examples of cyclic ethers include tetrahydrofuran and 2-methyltetrahydrofuran.
Examples of chain ethers include dimethoxyethane and dimethoxymethane.
Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone.

Examples of the chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, and ethyl 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.

  These may be used alone or in combination of two or more, but it is preferable to use in combination of two or more. For example, it is preferable to use a high dielectric constant solvent such as alkylene carbonates or cyclic carboxylic acid esters in combination with a low viscosity solvent such as dialkyl carbonates or chain carboxylic acid esters.

  One preferable combination of the non-aqueous solvents is a combination mainly composed of alkylene carbonates and dialkyl carbonates. Among them, the total of alkylene carbonates and dialkyl carbonates in the nonaqueous solvent is 70% by volume or more, preferably 80% by volume or more, more preferably 90% by volume or more, and the alkylene carbonates and dialkyl carbonates. The proportion of the alkylene carbonate with respect to the total of 5% by volume or more, preferably 10% by volume or more, more preferably 15% by volume or more, usually 50% by volume or less, preferably 35% by volume or less, more preferably 30% by volume. Hereinafter, it is more preferably 25% by volume or less. Use of a combination of these non-aqueous solvents is preferable because the balance between the cycle characteristics and high-temperature storage characteristics (particularly, the remaining capacity and high-load discharge capacity after high-temperature storage) of a battery produced using the non-aqueous solvent is improved.

  Specific examples of preferable combinations of alkylene carbonates and dialkyl carbonates include ethylene carbonate and dimethyl carbonate, ethylene carbonate and diethyl carbonate, ethylene carbonate and ethyl methyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate, Examples include ethyl methyl carbonate, ethylene carbonate, diethyl carbonate, and ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

A combination in which propylene carbonate is further added to a combination of these ethylene carbonate and dialkyl carbonates is also mentioned as a preferable combination.
In the case of containing propylene carbonate, the volume ratio of ethylene carbonate to propylene carbonate is preferably 99: 1 to 40:60, particularly preferably 95: 5 to 50:50. Furthermore, the lower limit of the proportion of propylene carbonate in the entire non-aqueous solvent is usually 0.1% by volume or more, preferably 1% by volume or more, more preferably 2% by volume or more, and the upper limit is usually 20% by volume or less. Preferably it is 8 volume% or less, More preferably, it is 5 volume% or less. It is preferable to contain propylene carbonate in this concentration range, since the low temperature characteristics are further excellent while maintaining the combination characteristics of ethylene carbonate and dialkyl carbonates.

  Among the combinations of ethylene carbonate and dialkyl carbonates, those containing asymmetrical chain alkyl carbonates as dialkyl carbonates are more preferred, especially ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate, ethylene carbonate, diethyl carbonate and ethyl. Methyl carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, which contain ethylene carbonate, symmetric chain alkyl carbonates, and asymmetric chain alkyl carbonates, have a good balance between cycle characteristics and large current discharge characteristics. preferable. Among them, the asymmetric chain alkyl carbonate is preferably ethyl methyl carbonate, and the alkyl group of the alkyl carbonate preferably has 1 to 2 carbon atoms.

  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 10% 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.

In the case where dimethyl carbonate is contained in the non-aqueous solvent, the lower limit of the proportion of dimethyl carbonate in the total non-aqueous solvent is usually 10% by volume or more, preferably 20% by volume or more, more preferably 25% by volume. Or more, more preferably 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. This is preferable because the load characteristics of the battery are improved.
In addition, in the combination mainly composed of the alkylene carbonates and dialkyl carbonates, other solvents may be mixed.

  Other examples of preferable non-aqueous solvents include one organic solvent selected from the group consisting of ethylene carbonate, propylene carbonate, γ-butyrolactone and γ-valerolactone, or two or more organic solvents selected from the group The mixed solvent becomes 60% by volume or more of the whole. The non-aqueous electrolyte using this mixed solvent is less likely to evaporate or leak when used at high temperatures. Among them, the total of ethylene carbonate and γ-butyrolactone in the nonaqueous solvent is 70% by volume or more, preferably 80% by volume or more, more preferably 90% by volume or more, and ethylene carbonate and γ-butyrolactone. The volume ratio is 5:95 to 45:55, or the total of ethylene carbonate and propylene carbonate in the non-aqueous solvent is 70% by volume or more, preferably 80% by volume or more, more preferably 90% by volume or more. In addition, if a volume ratio of ethylene carbonate to propylene carbonate of 30:70 to 60:40 is used, the balance between cycle characteristics and high temperature storage characteristics is generally improved.

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.
(Phosphoric acid ester compound, carboxylic acid ester compound)
The non-aqueous electrolyte solution according to the present invention contains the above-described electrolyte and a non-aqueous solvent, and further contains a phosphate ester compound and / or a carboxylic acid ester compound having a phenyl group substituted with an alkyl group. The number of carbon atoms of the alkyl group substituted with the phenyl group is 4 or more (such a phosphoric acid ester compound or a carboxylic acid ester compound is referred to in the following description as the phosphoric acid ester of the present invention). A compound or a carboxylic acid ester compound of the present invention).

The phosphate ester compound of the present invention or the carboxylic acid ester compound of the present invention includes a phosphate ester compound in which all phenyl groups are substituted with an alkyl group having 4 or more carbon atoms and / or a chain carboxylic acid ester compound. From the viewpoint of improving safety during overcharge and improving battery characteristics after high temperature storage, a phosphate ester compound is particularly preferred.
As the molecular weight of the phosphate ester compound of the present invention, the lower limit is usually 250 or more, preferably 300 or more, particularly preferably 400 or more, from the viewpoint of improving safety during overcharging, and the upper limit is overcharging. From the viewpoint of improving safety, battery characteristics, and solubility in an electrolytic solution, it is usually 1500 or less, preferably 800 or less, particularly preferably 700 or less.

Further, as the molecular weight of the carboxylic acid ester compound of the present invention, the lower limit is usually 180 or more from the viewpoint of improving the safety during overcharge, and the upper limit is the improvement in safety during overcharge and battery characteristics and From the viewpoint of solubility in the electrolytic solution, it is usually 1000 or less, preferably 500 or less, particularly preferably 400 or less.
Examples of the alkyl group having 4 or more carbon atoms include n-butyl group, i-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, t-amyl group, 1,1-dimethylbutyl group, and cyclobutyl group. , Cyclopentyl group, cyclohexyl group, 1-methylcyclohexyl group, 1-ethylcyclohexyl group, and the like.

The lower limit of the carbon number of the alkyl group is usually 4 or more from the viewpoint of improvement in safety during overcharge, and the upper limit is improvement in safety during overcharge, battery characteristics, and From the viewpoint of solubility, it is usually 12 or less, preferably 8 or less, and more preferably 6 or less. In addition, a secondary alkyl group or a tertiary alkyl group is preferable.
-Butyl group, t-butyl group, t-amyl group, 1,1-dimethylbutyl group, cyclopentyl group, cyclohexyl group, 1-methylcyclohexyl group, 1-ethylcyclohexyl group are more preferable, t-butyl group, t- An amyl group, 1,1-dimethylbutyl group, cyclopentyl group, cyclohexyl group, 1-methylcyclohexyl group, and 1-ethylcyclohexyl group are particularly preferable.
In these alkyl groups, some or all of the hydrogen atoms may be substituted with fluorine atoms.
Further, the number of alkyl groups bonded to the phenyl group may be plural.

Specific examples of the phosphate ester compound of the present invention include the following.
Tris (2-n-butylphenyl) phosphate,
Tris (3-n-butylphenyl) phosphate,
Tris (4-n-butylphenyl) phosphate,
Tris (2,4-di-n-butylphenyl) phosphate,
Tris (3,5-di-n-butylphenyl) phosphate tris (2-i-butylphenyl) phosphate,
Tris (3-i-butylphenyl) phosphate,
Tris (4-i-butylphenyl) phosphate,
Tris (2,4-di-i-butylphenyl) phosphate,
Tris (3,5-di-i-butylphenyl) phosphate,
Tris (2-sec-butylphenyl) phosphate,
Tris (3-sec-butylphenyl) phosphate,
Tris (4-sec-butylphenyl) phosphate,
Tris (2,4-di-sec-butylphenyl) phosphate,
Tris (3,5-di-sec-butylphenyl) phosphate,
Tris (2-t-butylphenyl) phosphate,
Tris (3-t-butylphenyl) phosphate,
Tris (4-t-butylphenyl) phosphate,
Tris (2,4-di-tert-butylphenyl) phosphate,
Tris (3,5-di-tert-butylphenyl) phosphate,
Tris (2-t-amylphenyl) phosphate,
Tris (3-t-amylphenyl) phosphate,
Tris (4-t-amylphenyl) phosphate,
Tris (2,4-di-t-amylphenyl) phosphate,
Tris (3,5-di-t-amylphenyl) phosphate,
Tris (2-cyclopentylphenyl) phosphate,
Tris (3-cyclopentylphenyl) phosphate,
Tris (4-cyclopentylphenyl) phosphate,
Tris (2,4-di-cyclopentylphenyl) phosphate,
Tris (3,5-di-cyclopentylphenyl) phosphate tris (2-cyclohexylphenyl) phosphate,
Tris (3-cyclohexylphenyl) phosphate,
Tris (4-cyclohexylphenyl) phosphate,
Tris (2,4-di-cyclohexylphenyl) phosphate,
Tris (3,5-di-cyclohexylphenyl) phosphate 2-t-butylphenyldiphenylphosphate,
3-t-butylphenyl diphenyl phosphate,
4-t-butylphenyl diphenyl phosphate,
Bis (2-tert-butylphenyl) phenyl phosphate,
Bis (3-t-butylphenyl) phenyl phosphate,
Bis (4-t-butylphenyl) phenyl phosphate,
2-t-butylphenyl dimethyl phosphate,
3-t-butylphenyl dimethyl phosphate,
4-t-butylphenyl dimethyl phosphate,
Bis (2-tert-butylphenyl) methyl phosphate,
Bis (3-t-butylphenyl) methyl phosphate,
Bis (4-tert-butylphenyl) methyl phosphate,
2-t-butylphenyl diethyl phosphate,
3-t-butylphenyl diethyl phosphate,
4-t-butylphenyl diethyl phosphate,
Bis (2-tert-butylphenyl) ethyl phosphate,
Bis (3-tert-butylphenyl) ethyl phosphate,
Bis (4-t-butylphenyl) ethyl phosphate and the like.

Specific examples of the carboxylic acid ester compound of the present invention include the following.
2-n-butylphenyl acetate,
3-n-butylphenyl acetate,
4-n-butylphenyl acetate,
2-i-butylphenyl acetate,
3-i-butylphenyl acetate,
4-i-butylphenyl acetate,
2-sec-butylphenyl acetate,
3-sec-butylphenyl acetate,
4-sec-butylphenyl acetate,
2-t-butylphenyl acetate,
3-t-butylphenyl acetate,
4-t-butylphenyl acetate,
2-t-amylphenyl acetate,
3-t-amylphenyl acetate,
4-t-amylphenyl acetate,
2-cyclopentylphenyl acetate,
3-cyclopentylphenyl acetate,
4-cyclopentylphenyl acetate,
2-cyclohexyl phenyl acetate,
3-cyclohexyl phenyl acetate,
4-cyclohexyl phenyl acetate,
2-n-butylphenyl propionate,
3-n-butylphenyl propionate,
4-n-butylphenyl propionate,
2-i-butylphenylpropionate,
3-i-butylphenylpropionate,
4-i-butylphenylpropionate,
2-sec-butylphenylpropionate,
3-sec-butylphenylpropionate,
4-sec-butylphenylpropionate,
2-t-butylphenylpropionate,
3-t-butylphenylpropionate,
4-t-butylphenylpropionate,
2-t-amylphenylpropionate,
3-t-amylphenylpropionate,
4-t-amylphenylpropionate,
2-cyclopentylphenylpropionate,
3-cyclopentylphenylpropionate,
4-cyclopentylphenylpropionate,
2-cyclohexyl phenyl propionate,
3-cyclohexylphenyl propionate,
4-cyclohexylphenyl propionate,
Methyl-2-n-butylbenzoate,
Methyl-3-n-butylbenzoate,
Methyl-4-n-butylbenzoate,
Methyl-2-i-butylbenzoate,
Methyl-3-i-butylbenzoate,
Methyl-4-i-butylbenzoate,
Methyl-2-sec-butylbenzoate,
Methyl-3-sec-butylbenzoate,
Methyl-4-sec-butylbenzoate,
Methyl-2-t-butylbenzoate,
Methyl-3-t-butylbenzoate,
Methyl-4-tert-butylbenzoate,
Methyl-2-t-amylbenzoate,
Methyl-3-t-amylbenzoate,
Methyl-4-t-amylbenzoate,
Methyl-2-cyclohexylbenzoate,
Methyl-3-cyclohexylbenzoate,
Methyl-4-cyclohexylbenzoate,
Ethyl-2-n-butylbenzoate,
Ethyl-3-n-butylbenzoate,
Ethyl-4-n-butylbenzoate,
Ethyl-2-i-butylbenzoate,
Ethyl-3-i-butylbenzoate,
Ethyl-4-i-butylbenzoate,
Ethyl-2-sec-butylbenzoate,
Ethyl-3-sec-butylbenzoate,
Ethyl-4-sec-butylbenzoate,
Ethyl-2-t-butylbenzoate,
Ethyl-3-t-butylbenzoate,
Ethyl-4-t-butylbenzoate,
Ethyl-2-t-amylbenzoate,
Ethyl-3-t-amylbenzoate,
Ethyl-4-t-amylbenzoate,
Ethyl-2-cyclohexylbenzoate,
Ethyl-3-cyclohexylbenzoate,
Ethyl-4-cyclohexylbenzoate,
Phenyl-2-n-butylbenzoate,
Phenyl-3-n-butylbenzoate,
Phenyl-4-n-butylbenzoate,
Phenyl-2-i-butylbenzoate,
Phenyl-3-i-butylbenzoate,
Phenyl-4-i-butylbenzoate,
Phenyl-2-sec-butylbenzoate,
Phenyl-3-sec-butylbenzoate,
Phenyl-4-sec-butylbenzoate,
Phenyl-2-t-butylbenzoate,
Phenyl-3-t-butylbenzoate,
Phenyl-4-tert-butylbenzoate,
Phenyl-2-t-amylbenzoate,
Phenyl-3-t-amylbenzoate,
Phenyl-4-t-amylbenzoate,
Phenyl-2-cyclohexylbenzoate,
Phenyl-3-cyclohexylbenzoate,
Phenyl-4-cyclohexylbenzoate and the like.

Among these, in terms of improving safety during overcharge and battery characteristics,
Tris (2-sec-butylphenyl) phosphate,
Tris (3-sec-butylphenyl) phosphate,
Tris (4-sec-butylphenyl) phosphate,
Tris (2,4-di-sec-butylphenyl) phosphate,
Tris (3,5-di-sec-butylphenyl) phosphate,
Tris (2-t-butylphenyl) phosphate,
Tris (3-t-butylphenyl) phosphate,
Tris (4-t-butylphenyl) phosphate,
Tris (2,4-di-tert-butylphenyl) phosphate,
Tris (3,5-di-tert-butylphenyl) phosphate,
Tris (2-t-amylphenyl) phosphate,
Tris (3-t-amylphenyl) phosphate,
Tris (4-t-amylphenyl) phosphate,
Tris (2,4-di-t-amylphenyl) phosphate,
Tris (3,5-di-t-amylphenyl) phosphate,
Tris (2-cyclopentylphenyl) phosphate,
Tris (3-cyclopentylphenyl) phosphate,
Tris (4-cyclopentylphenyl) phosphate,
Tris (2,4-di-cyclopentylphenyl) phosphate,
Tris (3,5-di-cyclopentylphenyl) phosphate tris (2-cyclohexylphenyl) phosphate,
Tris (3-cyclohexylphenyl) phosphate,
Tris (4-cyclohexylphenyl) phosphate,
Tris (2,4-di-cyclohexylphenyl) phosphate,
Tris (3,5-di-cyclohexylphenyl) phosphate 2-t-butylphenyldiphenylphosphate,
3-t-butylphenyl diphenyl phosphate,
4-t-butylphenyl diphenyl phosphate,
Bis (2-tert-butylphenyl) phenyl phosphate,
Bis (3-t-butylphenyl) phenyl phosphate,
Bis (4-t-butylphenyl) phenyl phosphate,
2-t-butylphenyl dimethyl phosphate,
3-t-butylphenyl dimethyl phosphate,
4-t-butylphenyl dimethyl phosphate,
Bis (2-tert-butylphenyl) methyl phosphate,
Bis (3-t-butylphenyl) methyl phosphate,
Bis (4-tert-butylphenyl) methyl phosphate,
2-t-butylphenyl diethyl phosphate,
3-t-butylphenyl diethyl phosphate,
4-t-butylphenyl diethyl phosphate,
Bis (2-tert-butylphenyl) ethyl phosphate,
Bis (3-tert-butylphenyl) ethyl phosphate,
Bis (4-tert-butylphenyl) ethyl phosphate,
2-sec-butylphenyl acetate,
3-sec-butylphenyl acetate,
4-sec-butylphenyl acetate,
2-t-butylphenyl acetate,
3-t-butylphenyl acetate,
4-t-butylphenyl acetate,
2-t-amylphenyl acetate,
3-t-amylphenyl acetate,
4-t-amylphenyl acetate,
2-cyclopentylphenyl acetate,
3-cyclopentylphenyl acetate,
4-cyclopentylphenyl acetate,
2-cyclohexyl phenyl acetate,
3-cyclohexyl phenyl acetate,
4-cyclohexyl phenyl acetate,
2-sec-butylphenylpropionate,
3-sec-butylphenylpropionate,
4-sec-butylphenylpropionate,
2-t-butylphenylpropionate,
3-t-butylphenylpropionate,
4-t-butylphenylpropionate,
2-t-amylphenylpropionate,
3-t-amylphenylpropionate,
4-t-amylphenylpropionate,
2-cyclopentylphenylpropionate,
3-cyclopentylphenylpropionate,
4-cyclopentylphenylpropionate,
2-cyclohexyl phenyl propionate,
3-cyclohexylphenyl propionate,
4-cyclohexylphenyl propionate,
Methyl-2-sec-butylbenzoate,
Methyl-3-sec-butylbenzoate,
Methyl-4-sec-butylbenzoate,
Methyl-2-t-butylbenzoate,
Methyl-3-t-butylbenzoate,
Methyl-4-tert-butylbenzoate,
Methyl-2-t-amylbenzoate,
Methyl-3-t-amylbenzoate,
Methyl-4-t-amylbenzoate,
Methyl-2-cyclohexylbenzoate,
Methyl-3-cyclohexylbenzoate,
Methyl-4-cyclohexylbenzoate,
Ethyl-2-sec-butylbenzoate,
Ethyl-3-sec-butylbenzoate,
Ethyl-4-sec-butylbenzoate,
Ethyl-2-t-butylbenzoate,
Ethyl-3-t-butylbenzoate,
Ethyl-4-t-butylbenzoate,
Ethyl-2-t-amylbenzoate,
Ethyl-3-t-amylbenzoate,
Ethyl-4-t-amylbenzoate,
Ethyl-2-cyclohexylbenzoate,
Ethyl-3-cyclohexylbenzoate,
Ethyl-4-cyclohexylbenzoate,
Phenyl-2-sec-butylbenzoate,
Phenyl-3-sec-butylbenzoate,
Phenyl-4-sec-butylbenzoate,
Phenyl-2-t-butylbenzoate,
Phenyl-3-t-butylbenzoate,
Phenyl-4-tert-butylbenzoate,
Phenyl-2-t-amylbenzoate,
Phenyl-3-t-amylbenzoate,
Phenyl-4-t-amylbenzoate,
Phenyl-2-cyclohexylbenzoate,
Phenyl-3-cyclohexylbenzoate,
Compounds having a phenyl group substituted with a secondary alkyl group or a tertiary alkyl group such as phenyl-4-cyclohexylbenzoate are preferred,

Tris (2-t-butylphenyl) phosphate,
Tris (3-t-butylphenyl) phosphate,
Tris (4-t-butylphenyl) phosphate,
Tris (2,4-di-tert-butylphenyl) phosphate,
Tris (3,5-di-tert-butylphenyl) phosphate,
Tris (2-t-amylphenyl) phosphate,
Tris (3-t-amylphenyl) phosphate,
Tris (4-t-amylphenyl) phosphate,
Tris (2,4-di-t-amylphenyl) phosphate,
Tris (3,5-di-t-amylphenyl) phosphate,
Tris (2-cyclopentylphenyl) phosphate,
Tris (3-cyclopentylphenyl) phosphate,
Tris (4-cyclopentylphenyl) phosphate,
Tris (2,4-di-cyclopentylphenyl) phosphate,
Tris (3,5-di-cyclopentylphenyl) phosphate tris (2-cyclohexylphenyl) phosphate,
Tris (3-cyclohexylphenyl) phosphate,
Tris (4-cyclohexylphenyl) phosphate,
Tris (2,4-di-cyclohexylphenyl) phosphate,
Tris (3,5-di-cyclohexylphenyl) phosphate 2-t-butylphenyldiphenylphosphate,
3-t-butylphenyl diphenyl phosphate,
4-t-butylphenyl diphenyl phosphate,
Bis (2-tert-butylphenyl) phenyl phosphate,
Bis (3-t-butylphenyl) phenyl phosphate,
Bis (4-t-butylphenyl) phenyl phosphate,
2-t-butylphenyl dimethyl phosphate,
3-t-butylphenyl dimethyl phosphate,
4-t-butylphenyl dimethyl phosphate,
Bis (2-tert-butylphenyl) methyl phosphate,
Bis (3-t-butylphenyl) methyl phosphate,
Bis (4-tert-butylphenyl) methyl phosphate,
2-t-butylphenyl diethyl phosphate,
3-t-butylphenyl diethyl phosphate,
4-t-butylphenyl diethyl phosphate,
Bis (2-tert-butylphenyl) ethyl phosphate,
Bis (3-tert-butylphenyl) ethyl phosphate,
Bis (4-tert-butylphenyl) ethyl phosphate,
2-t-butylphenyl acetate,
3-t-butylphenyl acetate,
4-t-butylphenyl acetate,
2-t-amylphenyl acetate,
3-t-amylphenyl acetate,
4-t-amylphenyl acetate,
2-cyclopentylphenyl acetate,
3-cyclopentylphenyl acetate,
4-cyclopentylphenyl acetate,
2-cyclohexyl phenyl acetate,
3-cyclohexyl phenyl acetate,
4-cyclohexyl phenyl acetate,
2-t-butylphenylpropionate,
3-t-butylphenylpropionate,
4-t-butylphenylpropionate,
2-t-amylphenylpropionate,
3-t-amylphenylpropionate,
4-t-amylphenylpropionate,
2-cyclopentylphenylpropionate,
3-cyclopentylphenylpropionate,
4-cyclopentylphenylpropionate,
2-cyclohexyl phenyl propionate,
3-cyclohexylphenyl propionate,
4-cyclohexylphenyl propionate,
Methyl-2-t-butylbenzoate,
Methyl-3-t-butylbenzoate,
Methyl-4-tert-butylbenzoate,
Methyl-2-t-amylbenzoate,
Methyl-3-t-amylbenzoate,
Methyl-4-t-amylbenzoate,
Methyl-2-cyclohexylbenzoate,
Methyl-3-cyclohexylbenzoate,
Methyl-4-cyclohexylbenzoate,
Ethyl-2-t-butylbenzoate,
Ethyl-3-t-butylbenzoate,
Ethyl-4-t-butylbenzoate,
Ethyl-2-t-amylbenzoate,
Ethyl-3-t-amylbenzoate,
Ethyl-4-t-amylbenzoate,
Ethyl-2-cyclohexylbenzoate,
Ethyl-3-cyclohexylbenzoate,
Ethyl-4-cyclohexylbenzoate,
Phenyl-2-t-butylbenzoate,
Phenyl-3-t-butylbenzoate,
Phenyl-4-tert-butylbenzoate,
Phenyl-2-t-amylbenzoate,
Phenyl-3-t-amylbenzoate,
Phenyl-4-t-amylbenzoate,
Phenyl-2-cyclohexylbenzoate,
Phenyl-3-cyclohexylbenzoate,
More preferred are compounds having a phenyl group substituted with a t-alkyl group or a cycloalkyl group, such as phenyl-4-cyclohexylbenzoate,

Tris (2-t-butylphenyl) phosphate,
Tris (3-t-butylphenyl) phosphate,
Tris (4-t-butylphenyl) phosphate,
Tris (2,4-di-tert-butylphenyl) phosphate,
Tris (3,5-di-tert-butylphenyl) phosphate,
Tris (2-t-amylphenyl) phosphate,
Tris (3-t-amylphenyl) phosphate,
Tris (4-t-amylphenyl) phosphate,
Tris (2,4-di-t-amylphenyl) phosphate,
Tris (3,5-di-t-amylphenyl) phosphate,
Tris (2-cyclopentylphenyl) phosphate,
Tris (3-cyclopentylphenyl) phosphate,
Tris (4-cyclopentylphenyl) phosphate,
Tris (2,4-di-cyclopentylphenyl) phosphate,
Tris (3,5-di-cyclopentylphenyl) phosphate,
Tris (2-cyclohexylphenyl) phosphate,
Tris (3-cyclohexylphenyl) phosphate,
Tris (4-cyclohexylphenyl) phosphate,
Tris (2,4-di-cyclohexylphenyl) phosphate,
Tris (3,5-di-cyclohexylphenyl) phosphate,
2-t-butylphenyl diphenyl phosphate,
3-t-butylphenyl diphenyl phosphate,
4-t-butylphenyl diphenyl phosphate,
Bis (2-tert-butylphenyl) phenyl phosphate,
Bis (3-t-butylphenyl) phenyl phosphate,
Bis (4-t-butylphenyl) phenyl phosphate,
2-t-butylphenyl dimethyl phosphate,
3-t-butylphenyl dimethyl phosphate,
4-t-butylphenyl dimethyl phosphate,
Bis (2-tert-butylphenyl) methyl phosphate,
Bis (3-t-butylphenyl) methyl phosphate,
Bis (4-tert-butylphenyl) methyl phosphate,
2-t-butylphenyl diethyl phosphate,
3-t-butylphenyl diethyl phosphate,
4-t-butylphenyl diethyl phosphate,
Bis (2-tert-butylphenyl) ethyl phosphate,
Bis (3-tert-butylphenyl) ethyl phosphate,
Bis (4-tert-butylphenyl) ethyl phosphate,
2-t-butylphenyl acetate,
3-t-butylphenyl acetate,
4-t-butylphenyl acetate,
2-t-amylphenyl acetate,
3-t-amylphenyl acetate,
4-t-amylphenyl acetate,
2-cyclopentylphenyl acetate,
3-cyclopentylphenyl acetate,
4-cyclopentylphenyl acetate,
2-cyclohexyl phenyl acetate,
3-cyclohexyl phenyl acetate,
4-cyclohexyl phenyl acetate,
2-t-butylphenylpropionate,
3-t-butylphenylpropionate,
4-t-butylphenylpropionate,
2-t-amylphenylpropionate,
3-t-amylphenylpropionate,
4-t-amylphenylpropionate,
2-cyclopentylphenylpropionate,
3-cyclopentylphenylpropionate,
4-cyclopentylphenylpropionate,
2-cyclohexyl phenyl propionate,
3-cyclohexylphenyl propionate,
More preferred are phosphate compounds such as 4-cyclohexylphenylpropionate and chain carboxylic acid ester compounds,

Tris (2-t-butylphenyl) phosphate,
Tris (3-t-butylphenyl) phosphate,
Tris (4-t-butylphenyl) phosphate,
Tris (2,4-di-tert-butylphenyl) phosphate,
Tris (3,5-di-tert-butylphenyl) phosphate,
Tris (2-t-amylphenyl) phosphate,
Tris (3-t-amylphenyl) phosphate,
Tris (4-t-amylphenyl) phosphate,
Tris (2,4-di-t-amylphenyl) phosphate,
Tris (3,5-di-t-amylphenyl) phosphate,
Tris (2-cyclopentylphenyl) phosphate,
Tris (3-cyclopentylphenyl) phosphate,
Tris (4-cyclopentylphenyl) phosphate,
Tris (2,4-di-cyclopentylphenyl) phosphate,
Tris (3,5-di-cyclopentylphenyl) phosphate,
Tris (2-cyclohexylphenyl) phosphate,
Tris (3-cyclohexylphenyl) phosphate,
Tris (4-cyclohexylphenyl) phosphate,
Tris (2,4-di-cyclohexylphenyl) phosphate,
Phosphate ester compounds such as tris (3,5-di-cyclohexylphenyl) phosphate are particularly preferred,

Tris (2-t-butylphenyl) phosphate,
Tris (3-t-butylphenyl) phosphate,
Tris (4-t-butylphenyl) phosphate,
Tris (2,4-di-tert-butylphenyl) phosphate,
Tris (3,5-di-tert-butylphenyl) phosphate,
Tris (2-t-amylphenyl) phosphate,
Tris (3-t-amylphenyl) phosphate,
Tris (4-t-amylphenyl) phosphate,
Tris (2,4-di-t-amylphenyl) phosphate,
Most preferred is tris (3,5-di-t-amylphenyl) phosphate.

  The phosphate ester compound of the present invention and the carboxylic acid ester compound of the present invention may be used alone or in combination of two or more. The proportion of the phosphoric acid ester compound of the present invention and the carboxylic acid ester compound of the present invention in the non-aqueous electrolyte (the proportion of the total when two or more are used) is usually 0.001% by weight or more, preferably 0.01. % By weight or more, more preferably 0.05% by weight or more, particularly preferably 0.1% by weight or more. If the concentration is lower than this, the effects of the present invention may not be easily exhibited. On the other hand, if the concentration is too high, the capacity of the battery may decrease. Therefore, the upper limit is usually 10% by weight or less, preferably 5% by weight or less, more preferably 3% by weight, particularly preferably 2% by weight or less, Most preferably, it is 1.5 wt% or less.

The reason why the non-aqueous electrolyte according to the present invention is excellent in safety during overcharge and excellent in high-temperature storage characteristics is not clear, and the present invention is not limited to the following operation principle, It is guessed as follows.
In general, the electron donating property of an alkyl group increases as the carbon number of the alkyl group increases. Further, the secondary alkyl group and the tertiary alkyl group have higher electron donating properties than the primary alkyl group. Therefore, compared to phosphate ester compounds and carboxylate compounds having phenyl groups not substituted with alkyl groups, phosphate ester compounds and carboxylate compounds having phenyl groups substituted with alkyl groups having 4 or more carbon atoms are oxidized. The potential becomes lower, and it reacts at an earlier stage during overcharge, thereby improving safety during overcharge. Usually, a compound having a low oxidation potential reacts at a site where the activity of the electrode is high even at high temperature storage, and deteriorates battery characteristics after high temperature storage, but has an alkyl group having 4 or more carbon atoms, When the carbon number of the alkyl group substituted with the phenyl group is 4 or more, the steric hindrance of the alkyl group suppresses side reactivity during high temperature storage and suppresses a significant decrease in discharge characteristics after high temperature storage. It is done.
Moreover, the compound of this application should just be contained in the inside of a battery, for example, you may make it contain in a positive electrode, a negative electrode, and / or a separator, without containing beforehand in electrolyte solution. When it is contained in the positive electrode or the separator, the side reaction on the negative electrode side during initial charging is suppressed, which may be preferable.

(Other compounds)
The non-aqueous electrolyte solution according to the present invention is a cyclic carbonate compound having a carbon-carbon unsaturated bond, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate within a range not impairing the effects of the present invention. And various other compounds such as conventionally known overcharge inhibitors may be contained as auxiliary agents.

Among these, when containing 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, a negative electrode In order to form a highly stable film, cycle characteristics and battery characteristics after high-temperature storage are improved, which is preferable.
(Cyclic carbonate compound having a carbon-carbon unsaturated bond)
Since the cyclic carbonate compound having a carbon-carbon unsaturated bond forms a stable protective film on the surface of the negative electrode, battery cycle characteristics and battery characteristics after high-temperature storage can be improved.

  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, 4,4-divinyl ethylene carbonate, vinyl ethylene carbonate such as 4,5-divinyl ethylene carbonate; 4,4-dimethyl-5-methyle Ethylene carbonate, 4,4-such as methylene ethylene carbonate compounds such as 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 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. It is 0.3% by weight or more, most preferably 0.5% by weight or more. If there are too few cyclic carbonates having a carbon-carbon unsaturated bond, the effect of improving battery cycle characteristics and battery characteristics after high-temperature storage may not be sufficiently exhibited. However, if the content of the cyclic carbonate 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 deteriorate. % By weight or less, preferably 4% by weight or less, particularly preferably 3% by weight or less.

(Cyclic carbonate compound having a fluorine atom)
Since the cyclic carbonate compound having a fluorine atom also forms a stable protective film on the surface of the negative electrode, it is possible to improve battery cycle characteristics and battery characteristics after high-temperature storage.
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 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 the battery characteristic after cycling characteristics improvement or high temperature storage.
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. If there are too few cyclic carbonates having fluorine atoms, the effect of improving battery cycle characteristics and battery characteristics after high-temperature storage may not be sufficiently exhibited. However, if the content of the cyclic carbonate having fluorine atoms 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 it is 5 weight% or less, Most preferably, it is 3 weight% or less.

(Monofluorophosphate, difluorophosphate)
Since monofluorophosphate and difluorophosphate also form a stable protective film on the surface of the negative electrode, battery cycle characteristics and battery characteristics after high-temperature storage can be improved.
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.
Further, it may be used in combination with a cyclic carbonate having a carbon-carbon unsaturated bond or a cyclic carbonate compound having a fluorine atom. From the viewpoint of improving cycle characteristics, vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, difluoroethylene. It is preferable to use in combination with carbonate or the like.

  When the non-aqueous electrolyte contains a monofluorophosphate or difluorophosphate, the proportion in the non-aqueous electrolyte is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably It is 0.3% by weight or more, most preferably 0.5% by weight or more. If there are too few monofluorophosphates and difluorophosphates, the effect of improving battery cycle characteristics and battery characteristics after high-temperature storage may not be sufficiently exhibited. However, if the content of monofluorophosphate and difluorophosphate is too large, the discharge characteristics at low temperature may deteriorate, so the upper limit is usually 5% by weight or less, preferably 3% by weight or less, More preferably, it is 2 weight% or less, Most preferably, it is 1 weight% or less.

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, 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 proportion 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 0.5% by weight. The upper limit is usually 5% by weight or less, preferably 3% by weight or less, 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, and adiponitrile.

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, and adiponitrile are more 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 exhibit the effects of the present invention, but is usually 0.01% by weight or more, preferably 0.1% by weight or more, particularly preferably. Is 0.2% by weight or more, and 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.

In addition, the above-mentioned cyclic carbonate compound having a carbon-carbon unsaturated bond, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, a difluorophosphate, a conventionally known overcharge inhibitor and other auxiliaries are arbitrarily combined. May be used in combination.
(Preparation of electrolyte)
The nonaqueous electrolytic solution according to the present invention can be prepared by dissolving the electrolyte, the phosphoric acid ester compound of the present invention or the carboxylic acid ester compound of the present invention, and other compounds as required in a nonaqueous 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 occlusion / release of lithium ions is stable (M is composed of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb). Represents at least one element selected from the group).

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, Ni, Cu, Zn, Mg, Ga, Zr, and those substituted with other metals such as 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 or the like.

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 electrolyte used in manufacturing the electrode. 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 above-described non-aqueous electrolyte secondary battery of the present invention is usually in the range of 2V to 4.9V.

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 of. 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 for example, 0.2C represents a current value of 1/5 thereof.

[Overcharge characteristics evaluation]
After the capacity evaluation test was completed, the volume was measured by immersing the battery in an ethanol bath. Then, at 25 ° C., the battery was charged at a constant current of 0.2 C to 5 V, and the current was cut when 5 V was reached. Then, the open circuit voltage (OCV) of the battery after the overcharge test was measured.
Next, the volume was measured by immersion in an ethanol bath, and the amount of gas generated from the volume change before and after overcharging was determined.
The lower the OCV of the battery after the overcharge test, the lower the overcharge depth and the higher the safety during overcharge.

Further, the larger the amount of gas generated after overcharging, the more preferable the battery that senses this when the internal pressure rises abnormally due to an abnormality such as overcharging and operates the safety valve because the safety valve can be activated earlier. .
In addition, the greater the difference between the amount of gas generated after overcharging and the amount of gas generated during high-temperature storage, etc., prevents the safety valve from malfunctioning during high-temperature storage, etc., while reliably operating the safety valve during overcharging. Is preferable.

[Evaluation of high-temperature storage characteristics (continuous charging characteristics)]
After the capacity evaluation test was completed, the volume was measured by immersing the battery in an ethanol bath. Then, constant current charging was performed at a constant current of 0.5 C at 60 ° C., and after reaching 4.25 V, constant voltage charging was performed. Switching was performed continuously for one week.
After the battery was cooled, it was immersed in an ethanol bath to measure the volume, and the amount of gas generated from the volume change before and after continuous charging was determined.
After measuring the amount of gas generated, discharge to 3 V at a constant current of 0.2 C at 25 ° C., measure the remaining capacity after the continuous charge test, and determine the ratio of the discharge capacity after the continuous charge test to the initial discharge capacity. Was the remaining capacity (%) after continuous charging.

(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, 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, a mixture of ethylene carbonate, ethylmethyl carbonate and dimethyl carbonate (volume ratio 2: 3: 3), 2% by weight of vinylene carbonate and tris (4-t-butylphenyl) as the content in the non-aqueous electrolyte solution ) 1% by weight of phosphate was mixed, and then sufficiently dried LiPF ₆ was dissolved at a rate of 1.0 mol / liter to obtain an electrolyte.

[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-like battery was manufactured, and overcharge characteristics and continuous charge 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 tris (4-cyclohexylphenyl) phosphate was used in place of tris (4-t-butylphenyl) phosphate in the electrolytic solution of Example 1. Then, overcharge characteristics and continuous charge characteristics were evaluated. The evaluation results are shown in Table 1.
( Reference Example 3)
A sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that 4-t-butylphenyl acetate was used in place of tris (4-t-butylphenyl) phosphate in the electrolytic solution of Example 1. The overcharge characteristics and the continuous charge characteristics were evaluated. The evaluation results are shown in Table 1.

(Reference Example 4)
A sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that methyl-4-t-butylbenzoate was used instead of tris (4-t-butylphenyl) phosphate in the electrolytic solution of Example 1. Then, overcharge characteristics and continuous charge characteristics were evaluated. The evaluation results are shown in Table 1.
(Example 5)
In a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 2: 3: 3), the content in the non-aqueous electrolyte is 2% by weight of vinylene carbonate, 0.5% by weight of lithium difluorophosphate and tris (4 1% by weight of t-butylphenyl) phosphate was mixed. Next, a sheet-like lithium secondary battery was prepared 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. Charging characteristics and continuous charging characteristics were evaluated. The evaluation results are shown in Table 1.

(Comparative Example 1)
As a content in the non-aqueous electrolyte, 2% by weight of vinylene carbonate was mixed with a mixture of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate (volume ratio 2: 3: 3). Next, a sheet-like lithium secondary battery was prepared 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. Charging characteristics and continuous charging characteristics were evaluated. The evaluation results are shown in Table 1.

(Comparative Example 2)
A sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that phenylcyclohexane was used in place of tris (4-t-butylphenyl) phosphate in the electrolytic solution of Example 1, and the battery was overcharged. Characteristics and continuous charge characteristics were evaluated. The evaluation results are shown in Table 1.
(Comparative Example 3)
A sheet-like lithium secondary battery was produced in the same manner as in Example 1 except that triphenyl phosphate was used instead of tris (4-t-butylphenyl) phosphate in the electrolytic solution of Example 1, and overcharge characteristics were obtained. And the continuous charge 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 tris (4-methylphenyl) phosphate was used in place of tris (4-t-butylphenyl) phosphate in the electrolytic solution of Example 1. Then, overcharge characteristics and continuous charge characteristics were evaluated. The evaluation results are shown in Table 1.

  As is apparent from Table 1, the batteries of Comparative Examples 1, 3, and 4 are excellent in battery characteristics after high-temperature storage, but have low safety during overcharge. The battery of Comparative Example 2 is highly safe when overcharged, but the battery characteristics are greatly deteriorated after high-temperature storage. Therefore, it can be seen that the battery using the non-aqueous electrolyte according to the present invention has high safety during overcharge and is excellent in high temperature retention characteristics.

Claims (7)

In a non-aqueous electrolyte solution containing an electrolyte and a non-aqueous solvent, the non-aqueous electrolyte solution is an n-butyl group, i-butyl group, sec-butyl group, tert-butyl group, n-pentyl group, t-amyl group, 1 , Phosphoric acid having a phenyl group substituted only with at least one group selected from the group consisting of 1-dimethylbutyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, 1-methylcyclohexyl group, and 1-ethylcyclohexyl group Contains ester compounds,
The non-aqueous electrolyte solution, wherein the phenyl group is bonded to a phosphorus atom through an oxygen atom .   2. The non-aqueous electrolyte solution according to claim 1, wherein the phosphate ester compound in the non-aqueous electrolyte solution is 0.001 to 10 wt%.   It contains at least one compound selected from a cyclic carbonate compound having a carbon-carbon unsaturated bond, a cyclic carbonate compound having a fluorine atom, a monofluorophosphate, and a difluorophosphate. The non-aqueous electrolyte solution described in 1.   The non-aqueous electrolyte solution according to claim 3, wherein the non-aqueous electrolyte solution contains a cyclic carbonate compound having a carbon-carbon unsaturated bond in an amount of 0.01 to 8% by weight.   The non-aqueous electrolyte solution according to claim 3, wherein the non-aqueous electrolyte solution contains a cyclic carbonate compound having a fluorine atom in an amount of 0.01 to 20% by weight.   The non-aqueous electrolyte solution according to claim 3, wherein the non-aqueous electrolyte solution contains at least any one compound of monofluorophosphate or difluorophosphate in an amount of 0.01 to 5% by weight. It is a non-aqueous electrolyte battery containing the negative electrode and positive electrode which can occlude / release lithium ion, and a non-aqueous electrolyte solution, Comprising: This non-aqueous electrolyte solution is a non-aqueous electrolyte solution as described in any one of Claims 1-6. A non-aqueous electrolyte battery characterized by the above.