JP2000294273A - Nonaqueous electrolyte and secondary battery using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain reducing/decomposing reaction of a solvent, and to improve the service life of a battery by constituting an electrolytic solution of a nonaqueous solvent composed of a phthalic acid imide derivative of a specific rate, cyclic carbonic ester and chain carbonic ester and an electrolyte. SOLUTION: A nonaqueous electrolyte for a secondary battery is (X=0.01 to 2, Y=5 to 55, Z=43 to 94.99 ad X+Y+Z=100) when a containing rate (wt.%) of a phthalic acid imide derivative of formula I (R1 represents an alkyl group of 1-10C, an aryl group and an organic group having a carbonyl group and/or an oxy group) is denoted by X, a containing rate of at least one kind selected from cyclic carbonic ester of formula II and formula III (R2 to R3 each represent H or a 1-2C alkyl group) is denoted by Y and a containing rate of chain carbonic ester of formula IV (R4 to R5 each represent a 1-3C alkyl group) is denoted by Z. R1 is desirably an alkoxycarbonyloxy group, ethylene carbonate is suitable for the cyclic carbonic ester, and methyl ethyl carbonate is suitable for the chain carbonic ester.

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 suitable for a lithium secondary battery containing a phthalic imide 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 ions have been 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,
It is used as the negative electrode of most lithium ion secondary batteries currently on the market.

However, when highly crystalline carbon such as graphite is used for the negative electrode, propylene carbonate or 1,1, which is a high dielectric constant solvent having a low freezing point, is used as a non-aqueous solvent for the electrolytic solution.
When 2-butylene carbonate is used, a reductive decomposition reaction of the solvent occurs at the time of charging, and the insertion reaction of lithium ions, which is an active material, into graphite hardly progresses, so that the function of the electrolytic solution is not fulfilled. As a result, the first charge / discharge efficiency is extremely reduced.

[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. By these measures, the charge-discharge characteristics and low-temperature characteristics of the battery have been improved, and further, by these measures, the charge-discharge characteristics and low-temperature characteristics of the battery have been improved.
Further, there is a demand for an electrolytic solution that can improve the reduction in battery life caused by minute reductive decomposition reactions when high-temperature storage and charge / discharge cycles are repeated, and can further improve low-temperature characteristics.

[0007]

SUMMARY OF THE INVENTION In order to meet the above demand, the present invention suppresses the reductive decomposition reaction of a solvent even when a highly crystalline carbon such as graphite is used for a negative electrode, thereby shortening the battery life. It is an object of the present invention to provide a non-aqueous electrolyte that improves the charge and discharge efficiency, load characteristics, and low-temperature characteristics of a battery. Another object is to provide a secondary battery including the non-aqueous electrolyte.

[0008]

A non-aqueous electrolyte according to the present invention comprises a phthalic imide derivative represented by the general formula [1]:
A non-aqueous solvent comprising at least one selected from cyclic carbonates represented by the general formula [2a] or [2b], a chain carbonate represented by the general formula [3], and an electrolyte; And the general formula [1] in a non-aqueous solvent
Content of phthalimide derivative represented by the formula (% by weight)
Is X, Y is at least one content ratio (% by weight) selected from the cyclic carbonates represented by the general formula [2a] or [2b], and the content is a chain carbonate represented by the general formula [3]. When the ratio (% by weight) is Z, X, Y, Z
Is in the following range. X = 0.01-2, Y = 5-55, Z = 43-94.9
9, (however, X + Y + Z = 100% by weight)

Embedded image (In the formula [1], R ¹ represents an organic group having an alkyl group having 1 to 10 carbon atoms, an aryl group, a carbonyl group, and / or an oxy group.)

Embedded image (In the formula [2a] or [2b], R ² and R ³ may be the same or different, and represent a hydrogen atom or an alkyl group having 1 to 2 carbon atoms.)

Embedded image (In the formula [3], R ⁴ and R ⁵ may be the same or different from each other and represent an alkyl group having 1 to 3 carbon atoms.) Further, these non-aqueous electrolytes are used as an electrolyte. A non-aqueous electrolyte in which a lithium salt is dissolved can be effectively used as an electrolyte for a primary battery or a secondary battery.

[0009] The present invention also provides a method for doping lithium metal, a lithium-containing alloy, and lithium ion as a negative electrode active material.
Dedoping of tin oxide and lithium ion
A negative electrode including any of titanium oxide capable of undoping, silicon capable of doping / dedoping lithium ions, and a carbon material capable of doping / dedoping lithium ions;
A positive electrode including a transition metal oxide, a transition metal sulfide, a composite oxide of lithium and a transition metal, a conductive polymer material, a carbon material, or a mixture thereof as a positive electrode active material,
The present invention relates to a secondary battery including the non-aqueous electrolyte.

[0010]

Next, the non-aqueous electrolyte according to the present invention and a non-aqueous electrolyte secondary battery using this non-aqueous electrolyte will be described in detail. Nonaqueous Electrolyte The nonaqueous electrolyte according to the present invention comprises a phthalic imide derivative represented by the general formula [1] and a general formula [2a] or [2b].
And a non-aqueous solvent comprising a chain carbonate represented by the general formula [3], and an electrolyte. Each of these will be described in detail.

Phthalimide Derivative The compound represented by the general formula [1] is used as the phthalimide derivative to be contained in the non-aqueous solvent in the present invention.

Embedded image In the formula [1], R ¹ represents an organic group having an alkyl group having 1 to 10 carbon atoms, an aryl group, a carbonyl group and / or an oxy group. Here, the oxy group indicates a -O- group.

Examples of the organic group having an alkyl group, aryl group, carbonyl group or oxy group having 1 to 10 carbon atoms include methyl, ethyl, vinyl, propyl, isopropyl, methoxy, Ethoxy, phenoxy, carboxyl, methoxycarbonyl, ethoxycarbonyl, methoxycarbonyloxy, ethoxycarbonyloxy, carboxyethyl, methoxycarbonylethyl, ethoxycarbonylethyl, methoxycarbonyloxyethyl, ethoxycarbonyloxy Ethyl group, butyl group, isobutyl group, sec-
Butyl group, t-butyl group, pentyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, 1-methyl-2
-Methylpropyl group, 2,2-dimethylpropyl group, phenyl group, phenyl group substituted at the o-, p-, m-position with a methyl group,
o-, p-, m-position substituted phenyl group with ethyl group, o-, p
phenyl group substituted at the-, m- position with a propyl group, o-, p-, m
Examples thereof include a phenyl group substituted at the -position with a methoxy group, a phenyl group substituted at the o-, p-, and m-positions with an ethoxy group, and other hexyl groups, octyl groups, nonyl groups, and decyl groups.

Specific examples of the phthalimide derivative represented by the general formula [1] include ethoxycarbonyloxyphthalimide, methylphthalimide, ethylphthalimide and phenylphthalimide.

In the present invention, the number of carbon atoms of R ^{1 in} the phthalic imide derivative represented by the above general formula [1] is desirably 3 or less, particularly from the viewpoint of solubility of the additive in the electrolytic solution.

The phthalic imide derivative represented by the general formula [1] has the effect of suppressing the reductive decomposition reaction of the non-aqueous solvent during charging and improving the charge / discharge efficiency.

Non-aqueous solvent In the non-aqueous electrolyte according to the present invention, in addition to the phthalic imide derivative represented by the general formula [1], a non-aqueous electrolyte is selected from the cyclic carbonates represented by the general formula [2a] or [2b]. And a chain carbonate represented by the general formula [3].

The cyclic carbonate used in the present invention is
At least one carbonate selected from the cyclic carbonates represented by the following general formula [2a] or [2b] is exemplified.

Embedded image (In the formula [2a] or [2b], R ² and R ³ may be the same or different, and represent a hydrogen atom or an alkyl group having 1 to 2 carbon atoms.)

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 and 1 , 2-
Pentylene carbonate, 2,3-pentylene carbonate, vinylene carbonate and the like. Among these, ethylene carbonate and propylene carbonate having high dielectric constants are particularly preferably used. In order to improve the battery life, ethylene carbonate is particularly preferable. These cyclic carbonates may be used as a mixture of two or more.

The chain carbonate used in the present invention is:
A chain carbonate represented by the following general formula [3] is exemplified.

Embedded image (In formula [3], R ⁴ and R ⁵ may be the same or different, and represent an alkyl group having 1 to 3 carbon atoms.)
Specific examples of the chain carbonate represented by the general formula [3] include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, and ethyl propyl carbonate. Among them, methyl ethyl carbonate having a low viscosity and a low freezing point is particularly preferably used. These chain carbonates may be used as a mixture of two or more.

[0020] The ratio of the non-aqueous solvent used for the electrolytic solution of the proportion present invention the non-aqueous solvent is described. The phthalic imide derivative represented by the general formula [1] is composed of the entire non-aqueous solvent (the phthalic imide derivative represented by the general formula [1] and the general formula [2a] or [2b]
0.01 to 2% by weight, and preferably 0.05 to 2% by weight, based on at least one selected from the cyclic carbonates represented by the general formula [3] and the chain carbonate represented by the general formula [3]. To 2% by weight, more preferably 0.1 to 1%
It is included in amounts by weight. By making such a ratio,
It is possible to suppress the reductive decomposition reaction of the non-aqueous solvent at the time of charging without inhibiting the electrode reaction related to the charge and discharge of the battery.

At least one selected from the cyclic carbonates represented by the general formula [2a] or [2b] is 5 to 55% by weight, preferably 10 to 55% by weight, based on the whole nonaqueous solvent. More preferably, the content is 15 to 35% by weight. The chain carbonate represented by the general formula [3] is 43 to 99.99% by weight, preferably 43 to 89.95% by weight, more preferably 64 to 84.99% by weight, based on the whole non-aqueous solvent. %included. With such a ratio, the dissociation of the electrolyte can be promoted while the viscosity of the electrolyte is kept low, and the conductivity of the electrolyte relating to the discharge characteristics of the battery can be increased.

By setting the combination and the mixing ratio of the non-aqueous solvents as described above, the reductive decomposition reaction of the non-aqueous solvent during charging can be suppressed, so that the battery life in high-temperature storage and cycle tests is improved, and The solidification of the non-aqueous electrolyte is unlikely to occur at room temperature, and the viscosity of the non-aqueous electrolyte at room temperature is low, so that an electrolyte having excellent discharge characteristics from room temperature to low temperature can be obtained. Therefore, the charge and discharge efficiency of the battery, and
Battery life such as high-temperature storage characteristics and cycle characteristics can be improved, and low-temperature characteristics such as load characteristics at low temperatures can be improved.

Therefore, the non-aqueous solvent of the present invention is selected from the phthalic imide derivative represented by the general formula [1] and the cyclic carbonate represented by the general formula [2a] or [2b]. It contains at least one kind and the chain carbonate represented by the general formula [3].

[0024] In addition to these, a non-aqueous solvent for batteries is usually used.
Solvent that is widely used as
It is also possible to use it in an amount added. Solvents that can be used
Specific examples of methyl formate, ethyl formate, formic acid
Propyl, methyl acetate, ethyl acetate, propyl acetate,
Methyl lopionate, ethyl propionate, methyl butyrate,
Chain esters such as methyl valerate and trimethyl phosphate
Which phosphate ester, 1,2-dimethoxyethane, 1,2-die
Toxicethane, diethyl ether, dimethyl ether,
Chain form such as methyl ethyl ether and dipropyl ether
Ether, 1,4-dioxane, 1,3-dioxolan, tetra
Hydrofuran, 2-methyltetrahydrofuran, 3-methyl
-1,3-dioxolane, 2-methyl-1,3-dioxolane, etc.
Amides such as cyclic ethers and dimethylformamide,
Chain carbamates such as chill-N, N-dimethyl carbamate
, Γ-butyrolactone, γ-valerolactone, 3-methyl
Le-γ-butyrolactone, 2-methyl-γ-butyrolactone
Any cyclic ester, cyclic sulfone such as sulfolane, N
Cyclic carbamates such as -methyloxazolidinone, N
Cyclic amides such as -methylpyrrolidone, N, N-dimethyl
Cyclic urea such as imidazolidinone, 4,4-dimethyl-5-
Methylene ethylene carbonate, 4-methyl-4-ethyl-5-
Methylene ethylene carbonate, 4-methyl-4-propyl-
 5-methylene ethylene carbonate, 4-methyl-4-butyl
-5-methyleneethylene carbonate, 4,4-diethyl-5-meth
Tylene ethylene carbonate, 4-ethyl-4-propyl-5-
Methylene ethylene carbonate, 4-ethyl-4-butyl-5-
Methylene ethylene carbonate, 4,4-dipropyl-5-methyl
Tylene ethylene carbonate, 4-propyl-4-butyl-5-
Methylene ethylene carbonate, 4,4-dibutyl-5-methyl
Renethylene carbonate, 4,4-dimethyl-5-ethylide
Ethylene carbonate, 4-methyl-4-ethyl-5-ethyl
Denethylene 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-butane
Cyl-5-ethylidene ethylene carbonate, 4,4-dipro
Pill-5-ethylidene ethylene carbonate, 4-propyl-
4-butyl-5-ethylidene ethylene carbonate, 4,4-di
Butyl-5-ethylidene ethylene carbonate, 4-methyl-
4-vinyl-5-methyleneethylene carbonate, 4-methyl-
4-allyl-5-methyleneethylene carbonate, 4-methyl-
4-methoxymethyl-5-methyleneethylene carbonate, 4
-Methyl-4-acryloxymethyl-5-methyleneethylene
Carbonate, 4-methyl-4-allyloxymethyl-5-methyl
Cyclic carbonates such as ethylene carbonate,
4-vinylethylene carbonate, 4,4-divinylethylene
Carbonate, 4,5-divinylethylene carbonate, etc.
Vinyl ethylene carbonate derivative, 4-vinyl-4-meth
Tylethylene carbonate, 4-vinyl-5-methylethyl
Carbonate, 4-vinyl-4,5-dimethylethylene carbonate
Bonate, 4-vinyl-5,5-dimethylethylene carbonate
G, 4-vinyl-4,5,5-trimethylethylene carbonate
Derived alkyl-substituted vinyl ethylene carbonate
Isomer, 4-allyloxymethylethylene carbonate, 4,5-
Ants such as diallyloxymethyl ethylene carbonate
Leoxymethyl ethylene carbonate derivative, 4-methyl
-4-allyloxymethylethylene carbonate, 4-methyl
-5-allyloxymethyl ethylene carbonate
Alkyl-substituted allyloxymethyl ethylene carbonate
Derivative, 4-acryloxymethylethylene carbonate
G, 4,5-acryloxymethyl ethylene carbonate
Which acryloxymethyl ethylene carbonate derived
Body, 4-methyl-4-acryloxymethylethylene carb
Nate, 4-methyl-5-acryloxymethylethylene
Alkyl-substituted acryloxymethyl ester such as carbonate
Tylene carbonate derivative, sulfolane, dimethyl sulfate
Sulfur-containing compounds such as trimethylphosphoric acid, tri
Phosphorus-containing compounds such as ethylphosphoric acid, and the following general formula
And the like. HO (CH_TwoCH_TwoO)_aH, HO ｛CH_TwoCH (CH_Three)
O｝_bH, CH_ThreeO (CH _TwoCH_TwoO)_cH, CH_ThreeO ｛C
H_TwoCH (CH_Three) O｝_dH, CH_ThreeO (CH_TwoCH_TwoO)
_eCH_Three, CH_ThreeO ｛CH_TwoCH (CH_Three) O｝_fCH_Three,
C₉H₁₉PhO (CH _TwoCH_TwoO)_g｛CH (CH_Three) O｝
_hCH_Three(Ph is a phenyl group), CH_ThreeO ｛CH_TwoCH
(CH_Three) O｝_iCO ｛O (CH_Three) CHCH_Two｝_jOCH_Three (In the above formula, a to f are integers of 5 to 250, and g to j are 2
An integer of 249, 5 ≦ g + h ≦ 250, 5 ≦ i + j ≦ 2
50. ) These solvents may be used alone or in combination of two or more.
It can be mixed and used.

Non-aqueous Electrolyte The non-aqueous electrolyte of the present invention comprises a phthalic imide derivative represented by the above general formula [1] and the above-mentioned general formula [2a] or [2
b) a non-aqueous solvent containing at least one selected from the cyclic carbonates represented by the general formula [3] and the chain carbonate represented by the general formula [3], and an electrolyte. 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_TwoR⁶, LiN (SO_TwoR⁷) (SO_TwoR⁸), L
iC (SO_TwoR⁹) (SO_TwoR^Ten) (SO_TwoR¹¹), LiN
(SO_TwoOR¹²) (SO_TwoOR¹³(Where R⁶~ R¹³Are the same but different
May have less fluorine atoms having 1 to 6 carbon atoms
And an alkyl group containing at least one).
Alkali gold in which lithium in the salt is replaced by an alkali metal
Genus salts and the like. These lithium salts and alkalis
The metal salt may be used alone, or two or more kinds may be mixed.
May be used.

Of these, LiPF ₆ , LiBF ₄ , LiO
SO ₂ R ⁶ , LiN (SO ₂ R ⁷ ) (SO ₂ R ⁸ ), LiC
(SO ₂ R ⁹ ) (SO ₂ R ¹⁰ ) (SO ₂ R ¹¹ ), LiN (S
O ₂ OR ¹² ) (SO ₂ OR ¹³ ) is preferred. In particular, LiP
F ₆ is desirable in terms of conductivity.

It is desirable that such an electrolyte is usually 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 phthalic imide derivative represented by the above general formula [1] and an electrolyte as essential components, and may further contain other additives as necessary. May be added.

The non-aqueous electrolyte according to the present invention as described above comprises:
Not only is it suitable as a non-aqueous electrolyte for a lithium ion secondary battery, but it can also be used as a non-aqueous electrolyte for a primary battery and a non-aqueous electrolyte for an electric double layer capacitor.

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.

As the negative electrode active material constituting the negative electrode, metallic lithium, a lithium-containing alloy, tin oxide capable of doping and dedoping lithium ions, titanium oxide capable of doping and dedoping lithium ions, Either silicon capable of doping and dedoping lithium ions or carbon material capable of doping and dedoping 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, 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 oxides such as O ₄ , LiNiO ₂ , LiNi _x Co _(1-x) O _2, composite oxides composed of lithium and transition metal, polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole / polyaniline composite Polymer materials and the like can be mentioned. 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 porous membrane, and usually a microporous polymer film is suitably used. 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.

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 disk-shaped negative electrode, a separator, a disk-shaped positive electrode, and a stainless steel plate are housed in a coin-type battery can in a state of being stacked in this order.

[0038]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

[0039]

Example 1 <Preparation of non-aqueous electrolyte> Propylene carbonate (PC) and diethyl carbonate (DEC) were
After mixing at a ratio of PC: DEC = 55: 45 (weight ratio), 1 part by weight of N-ethoxycarbonyloxyphthalimide was added to 99 parts by weight of the mixed solvent to reduce the content of N-ethoxycarbonyloxyphthalimide. A non-aqueous solvent was prepared so as to be 1% by weight with respect to the entire non-aqueous solvent (total amount of PC, DEC and N-ethoxycarbonyloxyphthalimide). 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> Mesocarbon microbeads (trade name: MCMB6-28, d, manufactured by Osaka Gas Co., Ltd.)
002 = 0.337 nm, 90 parts by weight of carbon powder having a density of 2.17 g / cm ³ ) and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder were mixed, and N-
It was dispersed in methylpyrrolidone (NMP) to prepare a paste-like negative electrode mixture slurry. Next, this negative electrode mixture slurry was applied to a negative electrode current collector made of a 20-μm-thick strip-shaped copper foil, and dried to obtain a strip-shaped carbon negative electrode. The thickness of the negative electrode mixture after drying was 25 μm. Further, after punching out this strip-shaped electrode into a disk shape having a diameter of 15 mm, compression molding was performed to obtain a negative electrode.

<Preparation of Positive Electrode> L manufactured by Honjo Chemical Co., Ltd.
iCoO ₂ (product name: HLC-21, average particle size 8 μm)
91 parts by weight of fine particles, 6 parts by weight of graphite as a conductive material, and polyvinylidene fluoride (PVD) as a binder
F) was mixed with 3 parts by weight to prepare a positive electrode mixture, and dispersed in N-methylpyrrolidone (NMP) to obtain a positive electrode mixture slurry. This slurry was applied to a 20-μm-thick aluminum foil positive electrode current collector, dried, and compression-molded to obtain a belt-shaped positive electrode. The thickness of the positive electrode mixture after drying is 40 μm
Met. Thereafter, the strip-shaped electrode was punched into a disk having a diameter of 15 mm to obtain a positive electrode.

<Preparation of Battery> A disk-shaped negative electrode and a disk-shaped positive electrode thus obtained, and a separator made of a microporous polypropylene film having a thickness of 25 μm and a diameter of 19 mm were prepared. After each of the negative electrode, the separator, and the positive electrode were laminated in the order of a 2032-sized stainless steel battery can, the nonaqueous electrolyte was injected into the separator.
Then, a stainless steel plate (2.4 m thick) was placed in the battery can.
m, diameter 15.4 mm), and the battery can (lid) was caulked via a gasket made of polypropylene.
As a result, the airtightness in the battery can be maintained, the diameter is 20 mm,
A button-type nonaqueous electrolyte secondary battery having a height of 3.2 mm was obtained.

<Measurement of Charge / Discharge Efficiency> The charge / discharge efficiency of the secondary battery thus obtained was measured at room temperature by the following method. In this example, the current direction in which the negative electrode was doped with Li ions was defined as charging, and the current direction in which undoping was performed was defined as discharging. Charging was performed by a 4.1 V, 1 mA constant current, constant voltage charging method, and was terminated when the charging current became 50 μA or less. Discharge was performed at a constant current of 1 mA, and the voltage was 2.7 V.
It ended when it reached. From the charge capacity and the discharge capacity of this charge / discharge cycle, the charge / discharge efficiency is calculated by the following equation,
The results are shown in Table 1. Charge / discharge efficiency (%) = {discharge capacity (mAh / g)} / {charge capacity (mAh / g)} × 100

[0044]

Comparative Example 1 A non-aqueous electrolyte solution and a battery were prepared in the same manner as in Example 1 except that the phthalic imide derivative was not added. The charge / discharge efficiency of the battery was evaluated. The results are shown in Table 1.

[0045]

[Table 1]

[0046]

The non-aqueous electrolyte of the present invention can suppress the reductive decomposition reaction of the solvent which occurs when highly crystalline carbon such as graphite is used for the negative electrode. As a result, a secondary battery using this non-aqueous electrolyte is excellent in battery life such as high-temperature storage characteristics and cycle characteristics, charge / discharge characteristics, load characteristics, and battery characteristics at low temperatures. Therefore, this non-aqueous electrolyte is particularly suitable as a non-aqueous electrolyte for a lithium ion secondary battery.

Claims (10)

[Claims] 1. A phthalic imide derivative represented by the general formula [1], at least one selected from cyclic carbonates represented by the general formula [2a] or [2b], and a compound represented by the general formula [3]: The content ratio (% by weight) of the phthalic imide derivative represented by the general formula [1] in the non-aqueous solvent is defined as X, Y represents the content (% by weight) of at least one type selected from the cyclic carbonates represented by the formula [2a] or [2b], and the content (% by weight) of the chain carbonate represented by the general formula [3]. ) Wherein Z, X, Y, and Z are in the following ranges. X = 0.01-2, Y = 5-55, Z = 43-94.9
9. (However, X + Y + Z = 100% by weight) (In the formula [1], R ¹ represents an organic group having an alkyl group, an aryl group, a carbonyl group, and / or an oxy group having 1 to 10 carbon atoms.) (In the formula [2a] or [2b], R ² and R ³ may be the same or different and represent a hydrogen atom or an alkyl group having 1 to 2 carbon atoms.) (In formula [3], R ⁴ and R ⁵ may be the same or different and represent an alkyl group having 1 to 3 carbon atoms.) 2. The non-aqueous electrolyte according to claim ¹ , wherein in the compound represented by the general formula [1], R ¹ has 1 to 3 carbon atoms. 3. The non-aqueous electrolyte according to claim 1, wherein in the compound represented by the general formula [1], R ¹ is an alkoxycarbonyloxy group. 4. The method according to claim 1, wherein at least one selected from the cyclic carbonates represented by the general formula [2a] or [2b] is any one of ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate. The non-aqueous electrolytic solution according to claim 1. 5. The non-aqueous electrolyte according to claim 1, wherein the chain carbonate represented by the general formula [3] is one of dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate. . 6. The cyclic carbonate represented by the general formula [2a] or [2b] is ethylene carbonate, and the chain carbonate represented by the general formula [3] is methyl ethyl carbonate. The non-aqueous electrolyte according to claim 1, wherein 7. The non-aqueous electrolyte according to claim 1, wherein the electrolyte is LiPF ₆ . 8. A secondary battery comprising the non-aqueous electrolyte according to claim 1. 9. A negative electrode active material comprising metal 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 doping and undoping of lithium ions. Negative electrode containing either silicon or titanium oxide capable of doping or undoping lithium ions, and transition metal oxides, transition metal sulfides, composite oxides of lithium and transition metals as positive electrode active materials, and conductivity A positive electrode containing any of a polymer material, a carbon material, and a mixture thereof, and a cathode.
And a non-aqueous electrolyte according to any one of the above. 10. The carbon material capable of doping / dedoping lithium ions was measured by X-ray analysis (002).
The plane distance (d002) on the plane is 0.340 nm
The lithium ion secondary battery according to claim 9, wherein: