JP2002008717A - Nonaqueous electrolyte and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte having a long service life and a secondary battery using this nonaqueous electrolyte. SOLUTION: This nonaqueous solvent electrolyte is composed of nonaqueous solvent including diglycol acid derivative and electrolyte, and used for a nonaqueous electrolyte secondary battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte having excellent charge / discharge characteristics and a secondary battery using the same. More specifically, the present invention relates to a non-aqueous electrolyte containing a diglycolic acid derivative and a secondary battery using the same.

[0002]

BACKGROUND OF THE INVENTION A battery using a non-aqueous electrolyte has a high voltage, a high energy density, and a high reliability such as storability, so that it is widely used as a power source for consumer electronic devices. Have been.

As such a battery, there is a non-aqueous electrolyte secondary battery, a typical example of which is a lithium ion secondary battery. Carbonate compounds having a high dielectric constant are known as non-aqueous solvents used for such a purpose, and the use of various carbonate compounds has been proposed. As an electrolytic solution, LiBF ₄ , LiPF ₆ , LiPF ₆ , a mixed solvent of the high dielectric constant carbonate compound solvent such as propylene carbonate and ethylene carbonate, and a low viscosity solvent such as diethyl carbonate.
A solution in which an electrolyte such as LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , or Li ₂ SiF ₆ is mixed is used.

[0004] On the other hand, research on electrodes has been promoted with the aim of increasing the capacity of batteries, and carbon materials capable of occluding and releasing lithium are used as negative electrodes of lithium ion secondary batteries. In particular, highly crystalline carbon such as graphite has characteristics such as a flat discharge potential, and is therefore used as most negative electrodes of currently commercially available lithium ion secondary batteries.

However, when highly crystalline carbon such as graphite is used for the negative electrode, when propylene carbonate or 1,2-butylene carbonate, which is a high dielectric constant solvent having a low freezing point, is used as the nonaqueous solvent for the electrolytic solution, the At the time of charging, a reductive decomposition reaction of the solvent occurs, and the insertion reaction of lithium ion, which is an active material, into graphite becomes difficult to progress. As a result, the initial charge / discharge efficiency decreases and the load characteristics of the battery decrease.

[0006] Therefore, as a non-aqueous solvent having a high dielectric constant, which is used in the electrolytic solution, ethylene carbonate, which is solid at room temperature but hardly undergoes a reductive decomposition reaction, is mixed with propylene carbonate to form a non-aqueous solvent. Attempts have been made to suppress the reductive decomposition reaction of the solvent. Furthermore, in order to improve the viscosity characteristics of the non-aqueous solvent in addition to suppressing the reductive decomposition reaction, devising a combination with a low-viscosity solvent, adding various additives, and reducing the content of propylene carbonate in the electrolytic solution. Restrictions have been proposed.

Although these measures have improved the charge / discharge characteristics of the battery, the load characteristics of the battery caused by minute reductive decomposition reactions, for example, when repeated high-temperature storage and charge / discharge cycles are repeated. There is a need for an electrolyte solution that can improve the reduction in the battery capacity and the battery capacity and further improve the low-temperature characteristics.

[0008]

SUMMARY OF THE INVENTION In order to meet the above demand, the present invention suppresses the decomposition reaction of a solvent on a negative electrode,
An object of the present invention is to provide an electrolytic solution in which deterioration of load characteristics of a battery is suppressed even when stored at a high temperature. It is another object of the present invention to provide a non-aqueous electrolyte that gives a battery excellent load characteristics and low-temperature characteristics. Another object is to provide a secondary battery including the non-aqueous electrolyte.

[0009]

[Means for Solving the Problems]

[0010] The present invention provides a non-aqueous electrolyte comprising a non-aqueous solvent containing a diglycolic acid derivative and an electrolyte.

A nonaqueous electrolyte in which the diglycolic acid derivative is a glycolic anhydride represented by the following general formula (1) is a preferred embodiment of the present invention.

Embedded image (In the formula, R ¹ and R ² may be the same or different and are hydrogen, halogen, or an organic group having 1 to 10 carbon atoms.)

The non-aqueous solvent is at least one selected from the diglycolic acid derivative described above and a cyclic carbonate represented by the following general formula (2a) or (2b) and / or
Alternatively, a non-aqueous electrolyte which is a non-aqueous solvent containing a chain carbonate is a preferred embodiment of the present invention.

Embedded image (In the formula, R ^{4 to} R ⁷ may be the same or different from each other, and are a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.)

Further, the present invention provides a secondary battery including the non-aqueous electrolyte.

Furthermore, the present invention provides a negative electrode active material comprising metallic lithium, a lithium-containing alloy, a carbon material capable of doping and undoping lithium ions, tin oxide capable of doping and undoping lithium ions, and lithium ion Titanium oxide, niobium oxide that can be doped and undoped,
Negative electrode containing either vanadium oxide or silicon capable of doping / dedoping lithium ions, and transition metal oxides, transition metal sulfides, composite oxides of lithium and transition metals, and conductive polymer materials as positive electrode active materials And a lithium ion secondary battery including a positive electrode containing any one of a carbon material and a mixture thereof, and the nonaqueous electrolyte.

[0015]

Next, the nonaqueous electrolyte according to the present invention and a nonaqueous electrolyte secondary battery using the nonaqueous electrolyte will be described in detail. Non-aqueous electrolyte according to the present invention,
It comprises a non-aqueous solvent containing a diglycolic acid derivative and an electrolyte, each of which will be described in detail.

Glycolic Acid Derivative The non-aqueous solvent of the present invention contains a diglycolic acid derivative. The diglycolic acid derivative includes diglycolic acid and its derivatives. Specific examples of the diglycolic acid derivative include diglycolic acid, diglycolic acid ester, and diglycolic anhydride.

Each diglycolic acid derivative may have, as a substituent, a halogen or an organic group having 1 to 10 carbon atoms. Examples of the organic group having 1 to 10 carbon atoms include a hydrocarbon group, a halogenated hydrocarbon group, a hydrocarbon group containing a hetero atom, and a halogenated hydrocarbon group containing a hetero atom. Heteroatoms include oxygen, nitrogen, sulfur, phosphorus, boron, and the like.

Specific examples of the substituent include fluorine, chlorine, trifluoromethyl, trifluoroethyl, methoxy, ethoxy, propoxy, isopropoxy, normal butoxy, sec-butoxy, tert- Butoxy, pentoxy, hexyloxy, phenoxy, methyl, ethyl, vinyl, ethynyl, propyl, isopropyl, 1-propenyl, 2-propenyl, 1-propynyl, 2-propynyl , Butyl group,
sec-butyl group, t-butyl group, 1-butenyl group, 2-butenyl group, 3-butenyl group, 2-methyl-2-propenyl group, 1-methylenepropyl group, 1-methyl-2-propenyl group, 1 , 2-dimethylvinyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, pentyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, 1-methyl-2-methylpropyl group, Examples thereof include a 2,2-dimethylpropyl group, a phenyl group, a methylphenyl group, an ethylphenyl group, a carboxyphenyl group, a vinylphenyl group, and an ethenylphenyl group.

From the viewpoint of the solubility of the additive in the electrolytic solution, a substituent having 3 or less carbon atoms is more preferable.

Specific compounds include the compounds shown below. Diglycolic acid, methyldiglycolic acid, dimethyldiglycolic acid, ethyldiglycolic acid, methoxydiglycolic acid, (trifluoromethyl) diglycolic acid, fluorodiglycolic acid, vinyldiglycolic acid, allyldiglycolic acid, ethoxydi Diglycolic acids such as glycolic acid, and acid anhydrides thereof; monomethyl glycolate, dimethyl diglycolate, monoethyl diglycolic acid, diethyl diglycolic acid, monovinyl diglycolic acid, divinyl diglycolic acid, Diglycolic acid esters such as diallylic acid monoallyl ester, diglycolic acid diallyl ester, diglycolic acid monopropargyl ester, diglycolic acid dipropargyl ester and the like can be mentioned. Such a diglycolic acid derivative has an effect of suppressing the reductive decomposition reaction of the non-aqueous solvent during charging. Among these compounds, diglycolic anhydride is particularly desirable.

Preferred examples of the diglycolic anhydride include those represented by the following general formula (1).

Embedded image (In the formula, R ¹ and R ² may be the same or different and are hydrogen, halogen, or an organic group having 1 to 10 carbon atoms.)

The organic group having 1 to 10 carbon atoms has the same meaning as described above. Specific examples of the diglycolic anhydride represented by the general formula (1) include diglycolic anhydride, methyldiglycolic anhydride, dimethyldiglycolic anhydride, ethyldiglycolic anhydride, fluoro Diglycolic anhydride, (trifluoromethyl) diglycolic anhydride, methoxydiglycolic anhydride, ethoxydiglycolic anhydride, vinyldiglycolic anhydride, ethenyldiglycolic acid, ethenyldiglycolic anhydride, Allyl diglycolic anhydride, divinyl diglycolic anhydride and divinyl diglycolic anhydride can be mentioned.

Nonaqueous Solvent In the nonaqueous electrolyte according to the present invention, a nonaqueous solvent containing a diglycolic acid derivative is used. The diglycolic acid derivative in this molecule can be used as an additive to a commonly used non-aqueous solvent.

The non-aqueous solvent of the present invention is a non-aqueous solvent containing a diglycolic acid derivative. Examples of such a non-aqueous solvent include at least one selected from cyclic carbonates represented by the following general formula (2a) or (2b).

Embedded image (In the formula (2a) or (2b), R ^{4 to} R ⁷ may be the same or different and are a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.)

In the above, the alkyl group has 1 to 1 carbon atoms.
3 alkyl groups are preferred, and specific examples include a methyl group, an ethyl group, and an n-propyl group.

Specific examples of the cyclic carbonate represented by the general formula (2a) or (2b) include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate,
Examples thereof include 2-pentylene carbonate, 2,3-pentylene carbonate, and vinylene carbonate.

In particular, ethylene carbonate and propylene carbonate having a high dielectric constant are preferably used. When the improvement of the battery life is particularly intended, ethylene carbonate is particularly preferable. These cyclic carbonates may be used as a mixture of two or more kinds.

Other non-aqueous solvents that may contain a diglycolic acid derivative include chain carbonates. Specific examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, and ethyl propyl carbonate. In particular, dimethyl carbonate, methyl ethyl carbonate, and diethyl carbonate having low viscosity are preferably used. These chain carbonates may be used as a mixture of two or more.

When such a chain carbonate is contained in the non-aqueous solvent, the viscosity of the non-aqueous electrolyte can be reduced, the solubility of the electrolyte can be further increased, and the electric conductivity at normal temperature or low temperature can be improved. It is possible to obtain an electrolytic solution having excellent properties.
Therefore, low-temperature characteristics such as load characteristics at low temperatures of the battery can be improved.

In the present invention, the non-aqueous solvent may be a combination of the cyclic carbonate represented by formula (2a) or (2b) and the chain carbonate.

Specific examples of the combination of a cyclic carbonate and a chain carbonate of a nonaqueous solvent include ethylene carbonate and dimethyl carbonate, ethylene carbonate and methyl ethyl carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, and propylene carbonate. And methyl ethyl carbonate, propylene carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate, ethylene carbonate and propylene carbonate and methyl ethyl carbonate,
Ethylene carbonate and propylene carbonate and diethyl carbonate, ethylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and dimethyl carbonate and diethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate and propylene carbonate and dimethyl carbonate Diethyl carbonate and the like.

In the present invention, in particular, a non-aqueous solvent containing a diglycolic acid derivative and at least one and / or a chain carbonate selected from the cyclic carbonates represented by the above formula (2a) or (2b) It is desirable to use

The amount of the diglycolic acid derivative to be added may be, for example, the total amount of the diglycolic acid derivative and the nonaqueous solvent containing the diglycolic acid derivative and
In the case of a non-aqueous solvent comprising at least one selected from the cyclic carbonates represented by the general formula (2a) or (2b) and / or a chain carbonate, a diglycolic acid derivative and a cyclic carbonate 0.001% by weight or more, preferably 0.01 to 10% by weight, more preferably 0.05 to 5% by weight, particularly preferably 0.1 to 5% by weight, based on the total amount with the chain carbonate. Desirably, it is included in an amount of 2% by weight.

When the diglycolic acid derivative is contained in the entire non-aqueous solvent containing the diglycolic acid derivative in such a mixing ratio, the reductive decomposition reaction of the solvent that occurs during charging can be suppressed to a low level, and the battery life such as high-temperature storage characteristics can be reduced. Can be improved.

In a non-aqueous solvent, the compound represented by the general formula (2a)
Alternatively, the mixing ratio of the cyclic carbonate and the chain carbonate represented by (2b) is represented by a weight ratio, and at least one of the cyclic carbonates represented by the general formula (2a) or (2b) is used. : Chain carbonate is 0: 100
To 100: 0, preferably 5:95 to 80:20, more preferably 10:90 to 70:30, and particularly preferably 15:85 to 55:45. With such a ratio, the increase in the viscosity of the electrolyte can be suppressed, and the degree of dissociation of the electrolyte can be increased. Therefore, the conductivity of the electrolyte relating to the charge / discharge characteristics of the battery can be increased.

Accordingly, a preferred non-aqueous solvent according to the present invention is a diglycolic acid derivative and the above-mentioned general formula (2a)
Or at least one selected from the cyclic carbonates represented by (2b) and / or the chain carbonate.

In the non-aqueous electrolyte of the present invention, as the non-aqueous solvent, in addition to the above-mentioned non-aqueous solvent, a solvent which is widely used as a non-aqueous solvent for batteries can be further mixed and used. . Specific examples of the other solvents that may be contained include methyl formate, ethyl formate, propyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, methyl butyrate, and methyl valerate. A chain ester such as trimethyl phosphate; a chain ether such as 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, dimethyl ether, methyl ethyl ether, dipropyl ether; -Dioxane, 1,3-dioxolan, tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyl-1,3-
Cyclic ethers such as dioxolan and 2-methyl-1,3-dioxolan; amides such as dimethylformamide; linear carbamates such as methyl-N, N-dimethylcarbamate; γ-butyrolactone, γ-valerolactone, and 3-methyl
cyclic esters such as -γ-butyrolactone and 2-methyl-γ-butyrolactone; cyclic sulfones such as sulfolane; N-
Cyclic carbamates such as methyl oxazolidinone; N-
Cyclic amides such as methylpyrrolidone; cyclic ureas such as N, N-dimethylimidazolidinone; 4,4-dimethyl-5-methyleneethylene carbonate, 4-methyl-4-ethyl-5-methyleneethylene carbonate, 4-methyl- 4-propyl-5
-Methylene ethylene carbonate, 4-methyl-4-butyl-5
-Methyleneethylene carbonate, 4,4-diethyl-5-methyleneethylene carbonate, 4-ethyl-4-propyl-5-methyleneethylene carbonate, 4-ethyl-4-butyl-5-methyleneethylene carbonate, 4,4-dipropyl -5-methyleneethylene carbonate, 4-propyl-4-butyl-5-methyleneethylene carbonate, 4,4-dibutyl-5-methyleneethylene carbonate, 4,4-dimethyl-5-ethylideneethylene carbonate, 4-methyl-4 -Ethyl-5-ethylidene ethylene carbonate, 4-methyl-4-propyl-5-ethylidene ethylene carbonate, 4-methyl-4-butyl-5-
Ethylidene ethylene carbonate, 4,4-diethyl-5-ethylidene ethylene carbonate, 4-ethyl-4-propyl-
5-ethylidene ethylene carbonate, 4-ethyl-4-butyl-5-ethylidene ethylene carbonate, 4,4-dipropyl-5-ethylidene ethylene carbonate, 4-propyl-4-
Butyl-5-ethylidene ethylene carbonate, 4,4-dibutyl-5-ethylidene ethylene carbonate, 4-methyl-4-
Vinyl-5-methylene ethylene carbonate, 4-methyl-4-
Allyl-5-methyleneethylene carbonate, 4-methyl-4-
Methoxymethyl-5-methyleneethylene carbonate, 4-
Cyclic carbonates such as methyl-4-acryloxymethyl-5-methyleneethylene carbonate and 4-methyl-4-allyloxymethyl-5-methyleneethylene carbonate; 4-vinylethylene carbonate, 4,4-divinylethylene carbonate, 4 Vinylethylene carbonate derivatives such as 1,5-divinylethylene carbonate; 4-vinyl-4-methylethylene carbonate, 4-vinyl-5-methylethylene carbonate, 4-vinyl-4,5-dimethylethylene carbonate, 4-vinyl-5 , 5-dimethylethylene carbonate, 4
Alkyl-substituted vinyl ethylene carbonate derivatives such as -vinyl-4,5,5-trimethyl ethylene carbonate; allyloxymethyl ethylene carbonate derivatives such as 4-allyloxymethyl ethylene carbonate and 4,5-diallyloxymethyl ethylene carbonate; 4-methyl Alkyl-substituted allyloxymethylethylene carbonate derivatives such as -4-allyloxymethylethylene carbonate and 4-methyl-5-allyloxymethylethylene carbonate;
Acryloxymethyl ethylene carbonate derivatives such as 4-acryloxymethyl ethylene carbonate and 4,5-acryloxymethyl ethylene carbonate; 4-methyl
Alkyl-substituted acryloxymethylethylene carbonate derivatives such as -4-acryloxymethylethylene carbonate and 4-methyl-5-acryloxymethylethylene carbonate; sulfur-containing compounds such as sulfolane and dimethyl sulfate; trimethylphosphoric acid, triethylphosphoric acid And a compound represented by the following general formula. HO (CH ₂ CH ₂ O)
_a H, HO {CH ₂ CH (CH ₃ ) O} _b H, CH ₃ O (C
H ₂ CH ₂ O) _c H, CH ₃ O ｛CH ₂ CH (CH ₃ ) O｝ _d
H, CH ₃ O (CH ₂ CH ₂ O) _e CH ₃ , CH ₃ O ｛CH ₂
CH (CH ₃ ) O｝ _f CH ₃ , C ₉ H ₁₉ PhO (CH ₂ CH ₂
O) _g ｛CH (CH ₃ ) O｝ _h CH ₃ (Ph is a phenyl group), CH ₃ O ｛CH ₂ CH (CH ₃ ) O｝ _i CO ｛O (C
H ₃ ) CHCH ₂ ｝ _j OCH ₃ (where a to f are 5-250
And g to j are integers of 2 to 249, and 5 ≦ g + h ≦ 25.
0, 5 ≦ i + j ≦ 250. )

In the present invention, as a preferable combination for improving low-temperature characteristics of a battery, a diglycolic acid derivative, a cyclic carbonate represented by the above general formula (2a) or (2b) and / or the above chain are preferable. Although it is recommended to include a carbonic acid ester, especially when aiming to improve the flash point of the solvent, among the solvents exemplified above,
It is desirable to mix sulfolane, γ-butyrolactone, methyl oxazolinone, and phosphoric acid triester.

Specific examples of solvent combinations include ethylene carbonate and sulfolane, ethylene carbonate and gamma-butrolactone, ethylene carbonate and trimethyl phosphate, ethylene carbonate, propylene carbonate and gamma-butrolactone.

In this case, a diglycolic acid derivative and a chain carbonate in a non-aqueous solvent containing the cyclic carbonate represented by formula (2a) or (2b) and / or the chain carbonate are used. Is preferably 20% or less by weight based on the total amount of the diglycolic acid derivative, the cyclic carbonate and the chain carbonate.

Nonaqueous Electrolyte The nonaqueous electrolyte of the present invention comprises a nonaqueous solvent containing a diglycolic acid derivative and an electrolyte. For example, the electrolyte is dissolved in the above nonaqueous solvent containing a diglycolic acid derivative. It is. As the electrolyte to be used, any electrolyte which is usually used as an electrolyte for a non-aqueous electrolyte can be used.

As a specific example of the electrolyte, LiPF₆, Li
BF_Four, LiClO_Four, LiAsF₆, Li _TwoSiF₆, LiC_FourF
₉SO_Three, LiC₈F₁₇SO_ThreeLithium salts such as
You. In addition, a lithium salt represented by the following general formula is also used.
be able to. LiOSO_TwoR⁸, Lin (SO_TwoR⁹) (S
O_TwoR^Ten), LiC (SO_TwoR¹¹) (SO_TwoR¹²) (SO_Two
R¹³), LiN (SO_TwoOR¹⁴) (SO_TwoOR^Fifteen)(here
And R⁸~ R^FifteenAre the same but different
And a perfluoroalkyl group having 1 to 6 carbon atoms.
). These lithium salts may be used alone or
Or two or more of them may be used in combination.

Among these, in particular, LiPF ₆ and LiB
F ₄ , LiOSO ₂ R ⁸ , LiN (SO ₂ R ⁹ ) (SO
^{_{2 R 10), LiC (SO}} 2 R 11) (SO 2 R 12) (SO 2 R
¹³ ), and LiN (SO ₂ OR ¹⁴ ) (SO ₂ OR ¹⁵ ) are preferred.

It is desirable that such an electrolyte is contained in the non-aqueous electrolyte at a concentration of 0.1 to 3 mol / l, preferably 0.5 to 2 mol / l.

The non-aqueous electrolyte in the present invention contains a non-aqueous solvent containing a diglycolic acid derivative and an electrolyte as essential components, but may further contain other additives if necessary. Examples of the additive include hydrogen fluoride and the like in addition to the solvents which may be mixed as exemplified above.

When hydrogen fluoride is used as an additive, as a method of adding hydrogen fluoride to the electrolyte, a method of directly blowing a predetermined amount of hydrogen fluoride gas into the electrolyte may be used. When the lithium salt used in the present invention is a lithium salt containing fluorine such as LiPF ₆ or LiBF ₄ , water is added to the electrolyte by utilizing the reaction between water and the electrolyte shown in the following formula. Then, a method of generating hydrogen fluoride and making it substantially present in the electrolytic solution can be adopted. LiMF _n + H ₂ O → LiMF _n−2 O + 2HF (where M represents P, B, etc., and when M = P, n
= 6 and M = B, n = 4. )

When water is added to the electrolytic solution and HF is indirectly generated in the electrolytic solution, two molecules of HF are generated almost quantitatively from one molecule of water. It is preferable to calculate and add according to the concentration. Specifically, it is preferable to add 0.45 times (weight ratio) water of a desired HF amount.

As the compound that generates HF by utilizing the reaction with the electrolyte, a protic compound having a strong acidity other than water can be used. Specific examples of such compounds include methanol, ethanol, ethylene glycol, propylene glycol and the like. The preferable addition amount as the hydrogen of the hooker is 0.001 to 0.7 wt.
%, Preferably 0.01 to 0.3 wt%, more preferably 0.02 to 0.2 wt%.

The non-aqueous electrolyte according to the present invention as described above
Not only is it suitable as a non-aqueous electrolyte for lithium ion secondary batteries, but it can also be used as a non-aqueous electrolyte for primary batteries.

Secondary Battery The non-aqueous electrolyte secondary battery according to the present invention comprises a negative electrode, a positive electrode,
The non-aqueous electrolyte is basically configured to include,
Usually, a separator is provided between the negative electrode and the positive electrode.

The negative electrode active material constituting the negative electrode includes metallic lithium, a lithium alloy, a carbon material capable of doping and undoping lithium ions, a tin oxide capable of doping and undoping lithium ions, and a tin oxide capable of doping and undoping lithium ions. Any of niobium, vanadium oxide, titanium oxide capable of doping and undoping lithium ions, and silicon capable of doping and undoping lithium ions can be used. Among these, a carbon material capable of doving / de-doping lithium ions is preferable. Such a carbon material may be graphite or amorphous carbon, and activated carbon, carbon fiber, carbon black, mesocarbon microbeads, natural graphite and the like are used.

As the negative electrode active material, the (002) plane spacing (d002) measured by X-ray analysis was 0.340 nm.
The following carbon materials are preferable, and the density is 1.70 g / cm ³
The graphite described above or a highly crystalline carbon material having properties similar thereto is desirable. When such a carbon material is used, the energy density of the battery can be increased.

As the positive electrode active material constituting the positive electrode, Mo is used.
Transition metal oxides or sulfides such as S ₂ , TiS ₂ , MnO ₂ , V ₂ O ₅ , LiCoO ₂ , LiMnO ₂ , LiMn ₂
Conductive polymers such as composite oxides composed of lithium and a transition metal such as O ₄ , LiNiO ₂ , and LiNi _x Co ₁ -x O ₂ , polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, and dimercaptothiadiazole / polyaniline composite Materials and the like. Among these, a composite oxide composed of lithium and a transition metal is particularly preferable. When the negative electrode is a lithium metal or lithium alloy, a carbon material can be used as the positive electrode. Further, as the positive electrode, a mixture of a composite oxide of lithium and a transition metal and a carbon material can be used.

The separator is a film that electrically insulates the positive electrode and the negative electrode and transmits lithium ions, and examples thereof include a porous film and a polymer electrolyte. A microporous polymer film is suitably used as the porous film, and examples of the material include polyolefin, polyimide, and polyvinylidene fluoride. In particular, a porous polyolefin film is preferable, and specific examples thereof include a porous polyethylene film, a porous polypropylene film, and a multilayer film of a porous polyethylene film and polypropylene. Examples of the polymer electrolyte include a polymer in which a lithium salt is dissolved, a polymer swelled with an electrolytic solution, and the like. The electrolyte of the present invention may be used for the purpose of obtaining a polymer electrolyte by swelling a polymer.

Such a non-aqueous electrolyte secondary battery can be formed in a cylindrical shape, a coin shape, a square shape, or any other shape. However, the basic structure of the battery is the same regardless of the shape, and the design can be changed according to the purpose. Next, the structures of the cylindrical and coin type batteries will be described. The negative electrode active material, the positive electrode active material, and the separator constituting each battery are commonly used.

For example, in the case of a cylindrical non-aqueous electrolyte secondary battery, a negative electrode obtained by applying a negative electrode active material to a negative electrode current collector;
A positive electrode formed by applying a positive electrode active material to a positive electrode current collector is wound through a separator into which a non-aqueous electrolyte is injected, and is housed in a battery can with an insulating plate placed above and below the wound body. ing.

The non-aqueous electrolyte secondary battery according to the present invention can be applied to a coin-type non-aqueous electrolyte secondary battery. In a coin-type battery, a disc-shaped negative electrode, a separator, a disc-shaped positive electrode, and a stainless steel or aluminum plate are housed in a coin-shaped battery can in a state of being stacked in this order.

[0058]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, which should not be construed as limiting the present invention.

[0059] (Examples 1 to 3) 1. Preparation of Battery < Preparation of Non-Aqueous Electrolyte> Ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed with EC: MEC
= 4: 6 (weight ratio), then diglycolic anhydride was added to the non-aqueous solvent, and diglycolic acid was added to the total amount of EC, MEC and diglycolic anhydride. 1% by weight of each anhydride (Example 1), 2% by weight
(Example 2) and 4% by weight (Example 3). Next, LiPF ₆ as an electrolyte was dissolved in a non-aqueous solvent to prepare a non-aqueous electrolyte so that the electrolyte concentration was 1.0 mol / L.

<Preparation of negative electrode> Natural graphite (L made by Chuetsu Graphite Co., Ltd.)
87 parts by weight of F-18A) and 13 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed and dispersed in N-methylpyrrolidinone as a solvent to prepare a natural graphite mixture slurry. Next, this negative electrode mixture slurry was applied to a 18 μm-thick negative electrode current collector made of strip-shaped copper foil, dried, compression-molded, and punched into a 14 mm disk shape to form a coin-shaped natural graphite. An electrode was obtained. This natural graphite electrode mixture had a thickness of 110 microns and a weight of 20 mg / Φ14 mm.

<Preparation of LiCoO ₂ electrode>
₂ (HLC-21 manufactured by Honjo FMC Energy Systems)
90 parts by weight, 6 parts by weight of graphite as a conductive agent and 1 part by weight of acetylene black and 3 parts by weight of polyvinylidene fluoride as a binder were mixed and dispersed in N-methylpyrrolidone as a solvent.
A LiCoO ₂ mixture slurry was prepared.

This LiCoO ₂ mixture slurry was applied to a thickness of 20
It was applied to a micron aluminum foil, dried, and compression molded. This was cut into a diameter of 13 mm to produce a LiCoO ₂ electrode. This LiCoO ₂ mixture had a thickness of 90 microns and a weight of 35 mg / Φ13 mm.

<Production of Battery> A natural graphite electrode having a diameter of 14 mm, a LiCoO ₂ electrode having a diameter of 13 mm, a thickness of 25 μm,
A separator made of a microporous polypropylene film having a diameter of 16 mm was laminated in a stainless steel battery can of 2032 size in the order of a natural graphite electrode separator and a LiCoO ₂ electrode. Thereafter, 0.03 ml of the non-aqueous electrolyte was poured into the separator, and an aluminum plate (thickness: 1.2 mm, diameter: 16 mm, and a spring was housed. Finally, a battery can lid was inserted via a polypropylene gasket. By caulking, a coin-type battery having a diameter of 20 mm and a height of 3.2 mm was produced while maintaining the airtightness in the battery.

2. Evaluation of Battery Characteristics <Measurement of Load Characteristic Index> A coin battery prepared as described above was used, and the current value at a constant voltage of 4.2 V under a condition of a constant current of 0.5 mA and a constant voltage of 4.2 V was used. Is 0.05m
A, and then, under the condition of 1 mA constant current and 3.0 V constant voltage, the current value at the time of 3.0 V constant voltage becomes 0.05
The battery was discharged until the current reached mA. Next, this battery was charged under the condition of a constant current of 3.85 V and a constant current of 3.85 V until the current value at a constant voltage of 3.85 V became 0.05 mA. Thereafter, the battery was maintained at a high temperature (called aging) for 24 hours in a thermostat at 60 ° C.

After holding at a high temperature, under the conditions of a constant current and a constant voltage of 1 mA, the termination condition is a current value of 0.05 mA at the time of a constant voltage, and
The charge / discharge of 4.2 V to 3.0 V was performed once, and the discharge capacity was measured (referred to as low load discharge capacity). Next, after the battery was charged to 4.2 V under the same conditions, the battery was discharged under the condition of a constant current of 10 mA and the discharge was terminated when the battery voltage became 3.0 V, and the discharge capacity was measured (high load discharge capacity). And). Then, the ratio of the high-load discharge capacity to the low-load discharge capacity at this time was determined and defined as a “load characteristic index”.

<Battery Resistance> After the high temperature was maintained, the “battery resistance” was determined from the change in battery voltage two minutes after the start of discharging.

<Residual rate> Further, this battery was re-used in 4.2.
After the battery was charged to V and the charge capacity was measured, it was stored at 60 ° C. for 7 days at high temperature (referred to as “high temperature storage”).
The battery was discharged to 0 V and the remaining capacity was measured. At this time, the ratio of the remaining capacity to the charged capacity was determined as an index indicating the self-discharge property of the battery, and this was named "residual rate".

<Load characteristic index after high-temperature storage> Further, after this, the "load characteristic index after high-temperature storage" was measured by the same method as that during high-temperature storage (aging).

[0069] 3. Measurement results Table 1 shows the measurement results of the above electrical characteristics.

Comparative Example 1 A battery was prepared in the same manner as in Example 1 except that the addition of diglycolic anhydride in <Preparation of Nonaqueous Electrolyte> was omitted, and the battery characteristics were measured. Table 1 shows the measurement results.

(Examples 4 to 6) <Preparation of non-aqueous electrolyte> Ethylene carbonate (EC) and methyl ethyl carbonate (MEC) were mixed at a ratio of EC: MEC = 4: 6 (weight ratio). In this non-aqueous solvent, sulfobenzoic anhydride was added, and in each case 0.5% by weight of sulfobenzoic anhydride (Example 4) based on the total amount of EC, MEC and diglycolic anhydride, It was added so as to be 1% by weight (Example 5) and 2% by weight (Example 6). Next, LiPF ₆ as an electrolyte was dissolved in a non-aqueous solvent to prepare a non-aqueous electrolyte so that the electrolyte concentration was 1.0 mol / L.

In the obtained non-aqueous electrolyte, hydrogen fluoride was added in an amount of 0.1%.
Water was added so as to produce 1% by weight, and hydrogen fluoride was produced in the electrolytic solution. The determination of hydrogen fluoride was performed by titration with alkali three days after the addition of water.

A battery was fabricated and the battery characteristics were measured in exactly the same manner as in Example 1 except that the non-aqueous electrolyte thus obtained was used. Table 1 shows the measurement results.

[Table 1]

As is clear from the above Examples and Comparative Examples, the use of the electrolyte solution of the present invention containing diglycolic anhydride suppresses a decrease in the load characteristic index after storage and lowers the battery resistance. I was able to do things. In addition, the effect was further enhanced by the presence of hydrogen fluoride.

[0075]

By using the non-aqueous electrolyte of the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery in which the load characteristics and the battery resistance are suppressed even after high-temperature storage. This non-aqueous electrolyte is particularly suitable as an electrolyte for a lithium ion secondary battery.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) CB08 CB09 CB12 DA03 DA13 EA22 EA25 HA01 HA02 HA13

Claims (11)

[Claims] 1. A non-aqueous electrolytic solution comprising a non-aqueous solvent containing a diglycolic acid derivative and an electrolyte. 2. The non-aqueous electrolyte according to claim 1, wherein the diglycolic acid derivative is glycolic anhydride represented by the following general formula (1). Embedded image (In the formula, R ¹ and R ² may be the same or different and are hydrogen, halogen, or an organic group having 1 to 10 carbon atoms.) 3. The non-aqueous solvent comprises at least one compound selected from the group consisting of the compound represented by the general formula (1) and the cyclic carbonate represented by the general formula (2a) or (2b) and / or 3. The non-aqueous electrolyte according to claim 1, further comprising a chain carbonate. Embedded image (In the formula, R ^{4 to} R ⁷ may be the same or different from each other, and are a hydrogen atom or an alkyl group having 1 to 6 carbon atoms.) 4. The cyclic carbonate represented by the general formula (2a) or (2b) is at least one compound selected from ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate. The non-aqueous electrolyte according to claim 3. 5. The non-aqueous electrolyte according to claim 3, wherein the chain carbonate is at least one compound selected from dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. 6. The non-aqueous electrolyte according to claim 1, wherein the diglycolic acid derivative is contained in an amount of 0.001 to 5% by weight based on the whole non-aqueous solvent. 7. A weight ratio of the cyclic carbonate and the chain carbonate represented by the general formula (2a) or (2b) in the non-aqueous solvent is 15:85 to 55:45. The non-aqueous electrolyte according to claim 4. 8. The non-aqueous electrolyte according to claim 1, wherein the electrolyte is a lithium salt. 9. A secondary battery comprising the non-aqueous electrolyte according to claim 1. 10. A negative electrode active material comprising metallic lithium, a lithium-containing alloy, or a carbon material capable of doping and undoping lithium ions, tin oxide capable of doping and undoping lithium ions, and doping and undoping lithium ions. A negative electrode containing any of titanium oxide, niobium oxide, vanadium oxide, or silicon capable of doping and undoping lithium ions, and a transition metal oxide, a transition metal sulfide, and lithium and transition metals as positive electrode active materials. A lithium ion secondary comprising: a positive electrode containing any one of a composite oxide, a conductive polymer material, a carbon material, and a mixture thereof; and the nonaqueous electrolyte according to any one of claims 1 to 8. battery. 11. The carbon material capable of doping / dedoping lithium ions has a plane distance (d002) on the (002) plane measured by X-ray analysis of 0.340 nm or less. The lithium ion secondary battery according to claim 10.