JP2002008719A - 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 electrolyte is composed of nonaqueous solvent including the compound including an isocyanate group and the electrolyte, and used for a 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 suitable for a lithium secondary battery containing a compound having an isocyanato group, 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. These measures have improved the charge / discharge characteristics of the battery.However, furthermore, for example, when the high-temperature storage and the charge / discharge cycle are repeated, the load characteristics of the battery deteriorate due to a minute reductive decomposition reaction and the battery is deteriorated. To improve capacity loss,
There is a need for an electrolytic solution that further improves low-temperature characteristics.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrolytic solution in which a decomposition reaction of a solvent on a negative electrode is suppressed, and deterioration of a load characteristic of a battery is suppressed even when stored at a high temperature. I do. 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 of the present invention is to provide a secondary battery containing the non-aqueous electrolyte.

[0008]

SUMMARY OF THE INVENTION The present invention provides a non-aqueous electrolyte comprising a non-aqueous solvent containing a compound containing an isocyanato group (isocyanate group) and an electrolyte.

A non-aqueous electrolyte in which the compound containing an isocyanato group is a compound represented by the following general formula (1) is a preferred embodiment of the present invention.

Embedded image (Wherein, m and n are integers, and m + n = 6 and n ≧ 1. When m ≧ 2, Rs may be the same or different from each other, and may be hydrogen, halogen, or C 1-10 It is an organic group.)

The non-aqueous solvent is a compound containing the isocyanato group and at least one and / or chain carbonate selected from the cyclic carbonates represented by formula (2a) or (2b). A non-aqueous electrolyte which is a non-aqueous solvent containing is also a preferred embodiment of the present invention.

Embedded image (In the formula (2a) or (2b), R ^{1 to} R ⁴ 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 containing the above 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, a tin oxide capable of doping and undoping lithium ions, and a lithium ion doping. A negative electrode containing any of undoped titanium oxide, niobium oxide, vanadium oxide or silicon capable of doping / dedoping lithium ions, and a transition metal oxide, a transition metal sulfide, or lithium as a positive electrode active material. There is provided a lithium ion secondary battery including a positive electrode including any of a transition metal composite oxide, a conductive polymer material, a carbon material, or a mixture thereof, and the nonaqueous electrolyte.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A non-aqueous electrolyte according to the present invention and a secondary battery using this non-aqueous electrolyte will be specifically described. The non-aqueous electrolyte according to the present invention comprises a non-aqueous solvent containing a compound containing an isocyanate group, and an electrolyte, each of which will be described in detail.

Compounds Containing Isocyanato Group In the present invention, the compound having an isocyanato group to be contained in a non-aqueous solvent includes a compound in which an isocyanato group is bonded to an aromatic hydrocarbon group such as toluene diisocyanate;
Compounds in which an isocyanate group is bonded to an aliphatic hydrocarbon such as isocyanatobutane, 1,4-diisocyanatobutane and norbornane diisocyanate; unsaturated carbon having a carbon-carbon multiple bond such as isocyanatonorbornene and allyl isocyanate Compound in which isocyanato group is bonded to hydrogen; Isocyanato formate derivative such as methyl isocyanato formate, ethyl isocyanato formate, trifluoroethyl isocyanato formate; Isocyanato acetylate derivative such as methyl isocyanato acetylate; toluene Sulfonyl isocyanate derivatives such as sulfonyl isocyanate, methanesulfonyl isocyanate and trifluoromethanesulfonyl isocyanate; such as dimethoxyphosphinyl isocyanate Foss Fini Lil isocyanate derivatives; isocyanuric acid tri (isocyanatomethyl norbornyl), di (isocyanatomethyl norbornyl) Urechijin -
2,4-dione, di (isocyanatonorbornyl)-
1,3,5-oxadiazine-2,4,6-trione and the like.

Of these, a compound in which an isocyanate group is bonded to an aromatic hydrocarbon and a compound in which an isocyanate group is bonded to an unsaturated hydrocarbon having a carbon-carbon multiple bond are preferable. Among them, a compound in which an isocyanato group is bonded to an aromatic hydrocarbon group is particularly preferably used. As a compound in which an isocyanate group is bonded to an aromatic hydrocarbon, a compound in which an isocyanate group is bonded to an aromatic ring as in the following general formula (1) can be mentioned as a preferable example.

Embedded image

In the formula, m and n are integers, and m + n =
6, n ≧ 1. R may be the same or different from each other when m ≧ 2, and may be hydrogen, halogen, or a group having 1 to 1 carbon atoms.
10 organic groups.

The halogen is preferably chlorine or fluorine. Examples of the organic group include a hydrocarbon group, a halogenated hydrocarbon group, a hydrocarbon group containing a hetero atom, and a hydrocarbon group containing a hetero atom and a halogen. Heteroatoms include oxygen, nitrogen, sulfur, phosphorus,
Boron and the like. As the organic group having 1 to 10 carbon atoms, specifically, as a hydrocarbon group, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, a sec-butyl group, a t-butyl group, a 1-methylenepropyl group, Alkyl groups such as pentyl, 1-methylbutyl, 2-methylbutyl, 3-methylbutyl, 1-methyl-2-methylpropyl, and 2,2-dimethylpropyl; vinyl, 1-propenyl, 2- Propenyl group, 1-butenyl group, 2-butenyl group, 3-
Alkenyl groups such as butenyl group, 2-methyl-2-propenyl group, 1-methyl-2-propenyl group and 1,2-dimethylvinyl group; ethynyl group, 1-propynyl group, 2-propynyl group, 1-
Alkynyl groups such as butynyl group, 2-butynyl group and 3-butynyl group; and aryl groups such as phenyl group, methylphenyl group, ethylphenyl group, vinylphenyl group and ethynylphenyl group.

Examples of the halogenated hydrocarbon group include halogenated alkyl groups such as trifluoromethyl group, trifluoroethyl group and pentafluoroethyl group; fluorovinylphenyl group, fluoroethynylphenyl group, fluorophenyl group and difluorophenyl group. And a halogenated aryl group such as a trifluoromethylphenyl group and a chlorophenyl group.

The hydrocarbon group containing a hetero atom includes methoxy, ethoxy, propyloxy, butoxy, allyloxy, propargyloxy, phenoxy, methoxycarbonyl, ethoxycarbonyl,
Acetyl group, propionyl group, isocyanatophenyl group, etc., and trifluoromethoxy group, trifluoroethoxy group, trifluoroacetyl group, trifluoroacetyl group, pentafluoroethoxy group, fluoromethoxyphenyl group , A difluoromethoxyphenyl group, a trifluoroethoxycarbonyl group, and the like.

Among the substituents exemplified above, it is preferable that R has 3 or less carbon atoms from the viewpoint of solubility in an electrolytic solution.

N is an integer of 1 to 6,
Preferably 1 to 3, and more preferably 1, 2.

Specific examples of the isocyanate-containing compound represented by the above formula (1) include the following compounds. Isocyanatobenzene, diisocyanatobenzene, fluoroisocyanatobenzene, difluoroisocyanatobenzene, (fluoro) (trifluoromethyl) isocyanatobenzene, chlorofluoroisocyanatobenzene, methyl isocyanatobenzene, ethyl isocyanatobenzene, methyl Diisocyanatobenzene, ethyldiisocyanatobenzene, trimethyldiisocyanatobenzene, methoxycarboxyisocyanatobenzene, di (methoxycarboxy) isocyanatobenzene, di (trifluoromethyl) isocyanatobenzene,
Pentafluoroisocyanatobenzene, diisocyanatonaphthalene, diisocyanatobiphenyl, isocyanatonaphthalene, trifluoromethoxyisocyanatobenzene, methoxyisocyanatobenzene, fluoromethoxyisocyanatobenzene, chloromethoxyisocyanatobenzene, 2,2-bis ( (Isocyanatophenyl) hexafluoropropene, (methanesulfonyl) (isocyanato) benzene, 2,2,4,4-tetrafluoro-6
Isocyanato-1,3-benzodioxene and the like.

Such a compound containing an isocyanane group has an effect of suppressing a reductive decomposition reaction of a nonaqueous solvent during charging.

Non-Aqueous Solvent In the non-aqueous electrolytic solution according to the present invention, a non-aqueous solvent containing a compound having an isocyanate group is used.

Examples of the non-aqueous solvent that can be used 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 ^{1 to} R ⁴ may be the same or different from each other 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.

Specific examples of the chain carbonate include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, ethyl propyl carbonate and the like. 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, as the non-aqueous solvent, a non-aqueous solvent containing at least one and / or a chain carbonate selected from the cyclic carbonates represented by the general formula (2a) or (2b) is used. It is desirable to use.

When the non-aqueous solvent is used in combination with the cyclic carbonate and the chain carbonate, the combination of the cyclic carbonate and the chain carbonate is specifically ethylene carbonate and dimethyl carbonate, and ethylene carbonate and methyl ethyl. Carbonate, ethylene carbonate and diethyl carbonate, propylene carbonate and dimethyl carbonate, 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 Doo and methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate and diethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and methyl ethyl carbonate, ethylene carbonate, propylene carbonate, dimethyl carbonate and diethyl carbonate.

The amount of the compound having an isocyanate group is, for example, the total amount of the compound having an isocyanate group and the total amount of the non-aqueous solvent containing the compound and the compound having an isocyanate group, In the case of a non-aqueous solvent comprising at least one kind selected from the cyclic carbonates represented by (2a) or (2b) and / or a chain carbonate, a compound having an isocyanate group;
0.001% by weight or more, preferably 0.01 to 10% by weight, more preferably 0.02 to 5% by weight based on the total amount of the cyclic carbonate and / or chain carbonate.
%, Particularly preferably 0.05 to 2% by weight.

When the compound having an isocyanato group in the molecule is contained in the entire non-aqueous solvent containing the compound at such a mixing ratio, the reduction reaction of the electrolytic solution is suppressed, and the load characteristics after storage at high temperature are reduced. Can be suppressed.

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 the cyclic carbonate represented by the general formula (2a) or (2b):
The chain carbonate is 0: 100 to 100: 0, preferably 5:95 to 80:20, and more preferably 10: 9.
0 to 70:30, particularly preferably 15:85 to 55: 4
5 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.

Therefore, a preferred non-aqueous solvent according to the present invention is a compound containing an isocyanato group and at least one kind selected from the cyclic carbonates represented by the general formula (2a) or (2b) and / or It contains the chain carbonate.

In the non-aqueous electrolyte of the present invention, the above-mentioned non-aqueous solvent
Besides, it is widely used as a non-aqueous solvent for batteries
It is also possible to use a mixture of solvents. this
Other solvents that may be included, specifically,
Methyl formate, ethyl formate, propyl formate, methyl acetate,
Ethyl acetate, propyl acetate, methyl propionate, pro
Chain forms such as ethyl pionate, methyl butyrate, and methyl valerate
Esters; phosphate esters such as trimethyl phosphate; 1,
2-dimethoxyethane, 1,2-diethoxyethane, diethyl
Ether, dimethyl ether, methyl ethyl ether,
Chain ethers such as dipropyl ether; 1,4-dioxa
1,3-dioxolane, tetrahydrofuran, 2-methyl
Tetrahydrofuran, 3-methyl-1,3-dioxolan, 2-
Cyclic ethers such as methyl-1,3-dioxolane;
Amides such as formamide; methyl-N, N-dimethyl
Chain carbamates such as carbamates; γ-butyrolact
Ton, γ-valerolactone, 3-methyl-γ-butyrolactone
, Cyclic esters such as 2-methyl-γ-butyrolactone;
Cyclic sulfones such as sulfolane; N-methyloxazoly
Cyclic carbamates such as dinone; N-methylpyrrolidone
Cyclic amides such as N, N-dimethylimidazolidinone
Which cyclic urea; 4,4-dimethyl-5-methyleneethylene
-Carbonate, 4-methyl-4-ethyl-5-methyleneethylene
-Carbonate, 4-methyl-4-propyl-5-methyleneethylene
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-methylene ethylene carbonate
-Carbonate, 4-propyl-4-butyl-5-methyleneethylene
Carbonate, 4,4-dibutyl-5-methylene ethylene carbonate
Bonate, 4,4-dimethyl-5-ethylidene ethylene carbonate
Nate, 4-methyl-4-ethyl-5-ethylidene ethylene car
Bonate, 4-methyl-4-propyl-5-ethylideneethylene
Carbonate, 4-methyl-4-butyl-5-ethylideneethyl
Lencarbonate, 4,4-diethyl-5-ethylideneethylene
Carbonate, 4-ethyl-4-propyl-5-ethylidene
Tylene carbonate, 4-ethyl-4-butyl-5-ethylidene
Ethylene carbonate, 4,4-dipropyl-5-ethylidene
Ethylene carbonate, 4-propyl-4-butyl-5-ethyl
Denethylene carbonate, 4,4-dibutyl-5-ethylide
Ethylene carbonate, 4-methyl-4-vinyl-5-methyl
Ethylene carbonate, 4-methyl-4-allyl-5-methyl
Ethylene carbonate, 4-methyl-4-methoxymethyl-
5-methylene ethylene carbonate, 4-methyl-4-acrylic
Luoxymethyl-5-methyleneethylene carbonate, 4-
Methyl-4-allyloxymethyl-5-methyleneethylene car
Cyclic carbonates such as carbonates; 4-vinylethylene
-Carbonate, 4,4-divinylethylene carbonate, 4,5-
Vinyl ethylene carbonate such as divinyl ethylene carbonate
-Carbonate derivative; 4-vinyl-4-methylethylene carb
, 4-vinyl-5-methylethylene carbonate, 4-
Vinyl-4,5-dimethylethylene carbonate, 4-vinyl-
5,5-dimethylethylene carbonate, 4-vinyl-4,5,5-
Alkyl-substituted vinyl such as trimethyl ethylene carbonate
Nylethylene carbonate derivative; 4-allyloxymethyl
Ethylene carbonate, 4,5-diallyloxymethyl ether
Allyloxymethyl ethylene such as ethylene carbonate
Carbonate derivative; 4-methyl-4-allyloxymethyl
Ethylene carbonate, 4-methyl-5-allyloxymethyl
Alkyl-substituted allyl oxides such as ethylene carbonate
Cimethylethylene carbonate derivative; 4-acryloxy
Cimethylethylene carbonate, 4,5-acryloxime
Acryloxymethyl such as tyl ethylene carbonate
Ethylene carbonate derivative; 4-methyl-4-acrylo
Xymethylethylene carbonate, 4-methyl-5-acryl
Alkyl units such as ruoxymethyl ethylene carbonate
A substituted acryloxymethyl ethylene carbonate derivative;
Sulfur-containing compounds such as sulfolane and dimethyl sulfate
Substance; phosphorus-containing such as trimethylphosphoric acid and triethylphosphoric acid
Compound: trimethyl borate, triethyl borate, boric acid
Tributyl, trioctyl borate, tritrimethyl borate
A boron-containing compound such as lusilyl; and represented by the following general formula:
And the like. HO (CH_Two
CH_TwoO)_aH, HO ｛CH_TwoCH (CH_Three) O｝_bH, C
H_ThreeO (CH_TwoCH _TwoO)_cH, CH_ThreeO ｛CH_TwoCH (CH
_Three) O｝_dH, CH_ThreeO (CH_TwoCH_TwoO)_eCH_Three, CH_ThreeO
｛CH_TwoCH (CH_Three) O｝_fCH_Three, C₉H₁₉PhO (C
H_TwoCH_TwoO)_g｛CH (CH_Three) O｝_hCH_Three(Ph is Fe
Nyl group), CH_ThreeO ｛CH_TwoCH (CH_Three) O｝_iCO ｛O
(CH_Three) CHCH_Two｝_jOCH_Three(In the above formula, a to f are
An integer of 5 to 250; g to j are integers of 2 to 249;
+ H ≦ 250 and 5 ≦ i + j ≦ 250. )

According to the present invention, a non-aqueous solvent containing a compound containing an isocyanato group, preferably a compound containing an isocyanato group, and the compound represented by the general formula (2a) or (2b)
By the non-aqueous solvent containing a cyclic carbonate and / or the chain carbonate represented by the formula, the low-temperature characteristics of the battery are improved. However, when the aim is to improve the flash point of the solvent, in addition to the non-aqueous solvent, Among the solvents exemplified above, in particular,
It is desirable to mix sulfolane, γ-butyrolactone, methyl oxazolinone, and phosphoric acid triester.

Specific combinations of solvents include ethylene carbonate and sulfolane, ethylene carbonate and γ-butyrolactone, ethylene carbonate and trimethyl phosphate, ethylene carbonate and propylene carbonate and γ-butyrolactone, ethylene carbonate, propylene carbonate and trimethyl phosphate, and the like. Is exemplified.

In this case, a compound having an isocyanato group and a chain carbonate in a non-aqueous solvent containing the cyclic carbonate represented by the general formula (2a) or (2b) and / or the chain carbonate are used. The amount of the carbonate ester used is desirably not more than 20% by weight based on the total amount of the isocyanato group-containing compound, the cyclic carbonate and the chain carbonate.

Nonaqueous Electrolyte The nonaqueous electrolyte of the present invention comprises a nonaqueous solvent containing a compound having an isocyanato group and an electrolyte. It is obtained by dissolving 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_TwoR^Five, Lin (SO_TwoR⁶) (S
O_TwoR⁷), LiC (SO_TwoR⁸) (SO_TwoR⁹) (SO
_TwoR^{1 0}), LiN (SO_TwoOR¹¹) (SO_TwoOR¹²)(here
And R^Five~ R¹²Are 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 , LiB
F ₄ , LiOSO ₂ R ⁵ , LiN (SO ₂ R ⁶ ) (SO
₂ R ⁷ ), LiC (SO ₂ R ⁸ ) (SO ₂ R ⁹ ) (SO
^{_{2 R 1 0), LiN (}} SO 2 OR 11) (SO 2 OR 12) is preferable.

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 compound containing an isocyanate group and an electrolyte as essential constituents, but may further contain other additives as 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 for adding hydrogen fluoride to the electrolyte, a method of directly blowing a predetermined amount of hydrogen fluoride gas into the electrolyte may be used. Further, 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. Alternatively, 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 to indirectly generate HF in the electrolytic solution, two molecules of HF are generated almost quantitatively from one molecule of water. 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 amount of hydrogen added as the hydrogen is 0.001 to 0.7 wt%, preferably 0.01 to 0.3 wt%, more preferably 0.0 to 0.3 wt%.
2 to 0.2 wt%.

The non-aqueous electrolyte according to the present invention as described above comprises:
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.

As the negative electrode active material constituting the negative electrode, metallic lithium, lithium alloy, carbon material capable of doping and undoping lithium ions, tin oxide capable of doping and undoping lithium ions, oxide 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 allows lithium ions to pass therethrough, 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.

[0057]

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.

[0058] (Examples 1-9) 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), and then added to this non-aqueous solvent as a compound containing an isocyanato group as 1,3-
Diisocyanato-4-methylbenzene (Examples 1-3),
Di (isocyanatonorbornyl) uretidine-2,4-dione (Examples 4-6) or di (isocyanatonorbornyl) 1,3,5-oxadiazine-2,4,6-trione (Example 7)
To 9) were added so that the concentration of the isocyanato group-containing compound became the concentration (% by weight) shown in Table 1 with respect to the total amount of EC, MEC, and the compound containing the isocyanato group. Next, LiPF ₆ as an electrolyte is dissolved in a non-aqueous solvent,
A non-aqueous electrolyte was prepared so that the electrolyte concentration was 1.0 mol / liter.

<Preparation of Negative Electrode> Natural graphite (LF made of Chuetsu graphite)
-18A) 87 parts by weight 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. The thickness of this natural graphite electrode mixture is 1
10 microns, weight was 20 mg / Φ14 mm.

<Preparation of LiCoO ₂ Electrode>
₂ (HLC-2 manufactured by Honjo FMC Energy Systems Co., Ltd.)
1) 90 parts by weight, 6 parts by weight of graphite as a conductive agent, 1 part by weight of acetylene black, and polyvinylidene fluoride 3 as a binder
Parts by weight were mixed and dispersed in N-methylpyrrolidone as a solvent to prepare a LiCoO ₂ mixture slurry. This LiC
The oO ₂ mixture slurry was applied to a 20-μm-thick aluminum foil, dried, compression-molded, and 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.

<Preparation 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.

[0062] 2. Measurement of Battery Characteristics <Load Characteristic Index> A coin battery prepared as described above was used, and the current value was 0 at a constant voltage of 4.2 V and a constant current of 4.2 V at a constant current of 4.2 mA. The battery was charged until the current became 0.05 mA, and then discharged under the condition of a constant current of 1 mA and a constant voltage of 3.0 V until the current value at a constant voltage of 3.0 V became 0.05 mA. Next, the battery was operated at a constant current of 1 mA.
The battery was charged under the condition of a constant voltage of 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 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 discharge.

<Remaining 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, "load characteristic index after high-temperature storage" was measured by the same method as that used during aging.

[0067] 3. Measurement results Table 1 shows the measurement results of the above electrical characteristics. (Comparative Example 1) A battery was fabricated in exactly the same manner as in <Preparation of non-aqueous electrolyte> in Example 1 except that the addition of a compound containing an isocyanato group was omitted, and battery characteristics were measured. Table 1 shows the measurement results.

[Table 1]

As is apparent from the above examples, the use of a non-aqueous solvent electrolyte containing a compound containing an isocyanate group increases the residual ratio, suppresses the decrease in the load characteristic index after storage, and improves the battery performance. The resistance could be reduced. In particular, 1,3-diisocyanato-4-methylbenzene having an isocyanate group bonded to an aromatic ring showed an excellent effect of improving the residual ratio, suppressing load characteristics after storage, and suppressing deterioration of resistance.

[0069]

By using the non-aqueous electrolyte of the present invention, it is possible to obtain a non-aqueous electrolyte secondary battery in which a decrease in load characteristics and an increase in battery resistance are suppressed. 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) CB05 CB07 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 compound containing an isocyanato group and an electrolyte. 2. The non-aqueous electrolyte according to claim 1, wherein the compound having an isocyanato group is represented by the following general formula (1). Embedded image (Wherein, m and n are integers, and m + n = 6 and n ≧ 1. When m ≧ 2, Rs may be the same or different from each other, and may be hydrogen, halogen, or C 1-10 It is an organic group.) 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 (2a) or (2b), R ^{1 to} R ⁴ 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 method according to claim 3, wherein the cyclic carbonate represented by the general formula (2a) or (2b) is any one of ethylene carbonate, propylene carbonate, butylene carbonate, and vinylene carbonate. The non-aqueous electrolyte according to the above. 5. The method according to claim 3, wherein the chain carbonate is any one of dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.
3. The non-aqueous electrolyte according to 1. 6. The non-aqueous electrolysis according to claim 1, wherein the compound containing an isocyanato group is contained in an amount of 0.02 to 5% by weight based on the whole non-aqueous solvent. liquid. 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, 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 a mixture of lithium and a transition metal as a positive electrode active material. A lithium ion battery comprising: a positive electrode containing any of a composite oxide, a conductive polymer material, a carbon material, or a mixture thereof; and the non-aqueous electrolyte according to claim 1. Next battery. 11. The carbon material capable of doping / dedoping lithium ions has an interplanar 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.