JP3218982B2 - Non-aqueous electrolyte and lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art In recent years, portable information recording devices such as camcorders, portable information devices such as notebook personal computers, portable telephones, and portable information terminals have been widely used. Since these multimedia devices are desired to have multiple functions, the required power source is a small-sized, light-weight, large-capacity, high-energy-density battery.

To increase the energy density of a battery, one method is to increase the battery voltage. In the case of a lithium battery, a composite oxide of lithium and a transition metal such as lithium cobalt oxide and lithium nickel oxide is used as a positive electrode active material, and a carbon material capable of doping / dedoping lithium ions is used as a negative electrode active material. Voltage3.
A lithium battery reaching up to 6 V can be obtained.

[0004] However, since the active material has extremely high electrochemical activity, it has high reactivity with an electrolytic solution. Since lithium composite oxides such as lithium cobaltate and lithium nickelate have a high oxidation-reduction potential when doped or undoped with lithium, that is, have a strong oxidizing power, the electrolyte must have oxidation resistance. Can be Furthermore, since carbon materials capable of doping and undoping lithium ions have a low oxidation-reduction potential when doping and undoping lithium, that is, have a strong reducing power, the electrolyte must have reduction resistance. Can be

[0005] In particular, since the carbon material has an oxidation-reduction potential for charging and discharging lithium lower than the oxidation-reduction potential of hydrogen, water or a protic solvent cannot be used as a solvent for an electrolytic solution. Is used. In the case of an electrolyte using water, the conductivity reaches about 1 S / cm. However, when an aprotic solvent is used, the conductivity is only tens of mS / cm at most, so the internal resistance of the battery is large. This is a major problem with lithium batteries. Recent electronic devices are often used outdoors, such as notebook computers, camcorders, and mobile phones, and are required to have a large operating temperature range.
In addition, large-current pulse discharge is required with digitization.
Under such usage conditions, the lithium secondary battery did not always have sufficient high-current discharge characteristics and did not always have sufficient low-temperature discharge characteristics as compared with a battery using an aqueous electrolyte solution. .

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a battery having excellent cycle characteristics of repeating charge / discharge and excellent low-temperature discharge characteristics.
In particular, an object of the present invention is to provide a non-aqueous electrolyte and a lithium secondary battery using the same, which are excellent in large-current discharge characteristics, have little deterioration in large-current characteristics due to cycles, and are excellent in safety.

[0007]

[Means for Solving the Problems] In view of such circumstances,
The present inventors have conducted intensive studies and as a result, found that the above problem can be solved by using a specific halogen-substituted ether compound and an acyclic carbonate as an organic solvent of the nonaqueous electrolyte, and completed the present invention. I came to. That is, the present invention provides (1) a non-aqueous electrolyte comprising a non-aqueous solvent and a lithium electrolyte, wherein the non-aqueous solvent contains a halogen-substituted ether compound represented by the general formula [I] and a non-cyclic carbonate; When the content of the halogen-substituted ether compound in the aqueous solvent exceeds 30% by volume and 90% by volume
Hereinafter der is, and the electrolyte concentration of 0.5 mol / l or less
Those of the upper der Ru non-aqueous electrolyte. R ₁ —OR ₂ ... [I] (wherein, R ₁ represents an alkyl group having 2 or less carbon atoms or a halogen-substituted alkyl group, and R ₂ represents a halogen-substituted alkyl group having 2 to 10 carbon atoms) Represents a group.)

Further, the present invention provides (2) a positive electrode capable of doping and undoping lithium ions, a negative electrode made of lithium metal or a lithium alloy or a negative electrode capable of doping and undoping lithium ions, a nonaqueous solvent and lithium. A non-aqueous electrolyte comprising the electrolyte and a non-aqueous electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to (1),
Further, the present invention relates to a lithium secondary battery in which the positive electrode contains a lithium composite oxide containing at least one of manganese, iron, cobalt and nickel.

Further, the present invention provides (3) the lithium secondary battery according to (2), wherein the negative electrode capable of doping / dedoping lithium ions contains a carbon material containing natural graphite, artificial graphite or coke as a single component or as a main component. It relates to a secondary battery.

Further, the present invention relates to (4) the lithium secondary battery according to the above (3), wherein the negative electrode comprises a polymer having a carbonate structure represented by the following general formula [X] and having a number average molecular weight of 300 or more. Things.

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[0011]

Next, the present invention will be described in detail. The non-aqueous electrolytic solution of the present invention comprises a non-aqueous solvent and a lithium electrolyte, and contains a halogen-substituted ether compound represented by the general formula [I] and a non-cyclic carbonate as the non-aqueous solvent. der 90% by volume content exceeds 30 vol% of the halogen-substituted ether compound is, and electrolyte
Quality concentration is characterized in der Rukoto to 0.5 mol / liter. R ₁ in the general formula [I] is an alkyl group having 2 or less carbon atoms or a halogen-substituted alkyl group, and is preferably a methyl group, a fluoromethyl group, a difluoromethyl group or a trifluoromethyl group. Among them, a methyl group, a fluoromethyl group or a difluoromethyl group is preferred. When the number of carbon atoms of R ₁ exceeds 2, the solubility of the electrolyte to be dissolved in the ether compound becomes small, which is not preferable. R ₂ in the general formula [I] is a halogen-substituted alkyl group having 2 to 10 carbon atoms,
Preferably it has 3 to 5 carbon atoms. When the number of carbon atoms of R ₂ exceeds 10, the viscosity of the ether compound is undesirably increased. The ether compound preferably has a low vapor pressure in the operating temperature range of the battery and has a large molecular weight or polarity.
₂ is preferably a halogen-substituted alkyl group having 2 or more carbon atoms, and more preferably a halogen-substituted alkyl group having 3 or more carbon atoms.

The R ₂ of the ether compound represented by the general formula [I] is more preferably represented by the following general formula [II]
Compounds [IX] to [IX] are preferable because of their good high current cycle and low vapor pressure in the operating temperature range of the battery. CF _3- (CF ₂ ) _n -CH ₂ -... [II] (In the formula, n is an integer of 1 to 5.) HCF _2- (CF ₂ ) _n -CH ₂ -... [III (Where n is an integer of 1 to 5) CF ₃ — (CF ₂ ) _m —CHF— (CF ₂ ) _n —CH ₂ — (IV) (where m and n are Each independently represents an integer of 0 to 4,
And the sum of m and n is an integer of 0-4. ) HCF ₂ — (CF ₂ ) _m —CHF— (CF ₂ ) _n —CH ₂ —... [V] (where m and n are each independently an integer from 0 to 4,
And the sum of m and n is an integer of 0-4. _{) (CF 3) 2 -CF- (} CF 2) n -CH 2 -. ··· [VI] ( wherein, n is an integer of _{0~4) (HCF 2) 2 -CF-} (CF 2 _{) n -CH 2 -. ··· [} VII] ( wherein, n is an integer of _{0~4) CF 3 -CF 2 -C (} CF 3) F- (CF 2) n -CH 2 - · [VIII] (where n is an integer of 0 to 2) HCF _2- (CF ₂ ) -C (CF ₃ ) F- (CF ₂ ) _n -CH ₂ -... [IX (In the formula, n is an integer of 0 to 2.)

Specific compounds include the following compounds. That is, 3, 3, 3, 2, 2-pentafluoropropyl methyl ether, 3, 3, 3, 2, 2-pentafluoropropyl fluoromethyl ether, 3, 3,
3,2,2-pentafluoropropyldifluoromethyl ether, 3,3,3,2,2-pentafluoropropyltrifluoromethyl ether, 3,3,3,2,2-
Pentafluoropropyl ethyl ether, 3, 3, 3,
2,2-pentafluoropropyl-2,2,2-trifluoroethyl ether, 4,4,4,3,3,2,2-
Heptafluorobutyl methyl ether, 4, 4, 4,
3,3,2,2-heptafluorobutyl fluoromethyl ether, 4,4,4,3,3,2,2-heptafluorobutyl difluoromethyl ether, 4,4,4,3,
3,2,2-heptafluorobutyl trifluoromethyl ether, 4,4,4,3,3,2,2-heptafluorobutyl ethyl ether, 4,4,4,3,3,2,2
-Heptafluorobutyl-2,2,2-trifluoroethyl ether, 5,5,5,4,4,3,3,2,2-
Nonafluoropentyl methyl ether, 5, 5, 5,
4,4,3,3,2,2-nonafluoropentylfluoromethyl ether, 5,5,5,4,4,3,3,2,
2-nonafluoropentyl difluoromethyl ether,
5, 5, 5, 4, 4, 3, 3, 2, 2-nonafluoropentyl trifluoromethyl ether, 5, 5, 5, 4,
4,3,3,2,2-nonafluoropentyl ethyl ether, 5,5,5,4,4,3,2,2-nonafluoropentyl-2,2,2-trifluoroethyl ether, 3 3,2,2-tetrafluoropropyl methyl ether, 3,3,2,2-tetrafluoropropyl fluoromethyl ether, 3,3,2,2-tetrafluoropropyl difluoromethyl ether, 3,3,2,2 −
Tetrafluoropropyl trifluoromethyl ether,
3,3,2,2-tetrafluoropropylethyl ether, 3,3,2,2-tetrafluoropropyl-2,
2,2-trifluoroethyl ether, 4,4,3,
3,2,2-hexafluorobutyl methyl ether,
4,4,3,3,2,2-hexafluorobutylfluoromethyl ether, 4,4,3,3,2,2-hexafluorobutyl difluoromethyl ether, 4,4,3,
3,2,2-hexafluorobutyl trifluoromethyl ether, 4,4,3,3,2,2-hexafluorobutyl ethyl ether, 4,4,3,3,2,2-hexafluorobutyl-2, 2,2-trifluoroethyl ether, 5,5,4,4,3,3,2,2-octafluoropentyl methyl ether, 5,5,4,4,3,3,
2,2-octafluoropentylfluoromethyl ether, 5,5,4,4,3,3,2,2-octafluoropentyldifluoromethyl ether, 5,5,4,4,
3,3,2,2-octafluoropentyl trifluoromethyl ether, 5,5,4,4,3,3,2,2-octafluoropentyl ethyl ether, 5,5,4,
4,3,3,2,2-octafluoropentyl-2,
2,2-trifluoroethyl ether, 3,3,3,2
-Tetrafluoro-2-trifluoromethylpropylmethyl ether, 3,3,3,2-tetrafluoro-2-
Trifluoromethylpropyl fluoromethyl ether,
3,3,3,2-tetrafluoro-2-trifluoromethylpropyldifluoromethyl ether, 3,3,3,
2-tetrafluoro-2-trifluoromethylpropyltrifluoromethyl ether, 3,3,3,2-tetrafluoro-2-trifluoromethylpropylethyl ether, 3,3,3,2-tetrafluoro-2-triethyl Fluoromethylpropyl-2,2,2-trifluoroethyl ether, 4,4,4,3,2,2-hexafluoro-
3-trifluoromethylbutyl methyl ether, 4,
4,4,3,2,2-hexafluoro-3-trifluoromethylbutylfluoromethyl ether, 4,4,4,
3,2,2-hexafluoro-3-trifluoromethylbutyl difluoromethyl ether, 4,4,4,3,
2,2-hexafluoro-3-trifluoromethylbutyltrifluoromethyl ether, 4,4,4,3,2,
2-hexafluoro-3-trifluoromethylbutyl ethyl ether, 4,4,4,3,2,2-hexafluoro-3-trifluoromethylbutyl-2,2,2-trifluoroethyl ether, 3,3 3,2-tetrafluoropropylmethyl ether, 3,3,3,2-tetrafluoropropylfluoromethyl ether, 3,3,
3,2-tetrafluoropropyldifluoromethyl ether, 3,3,3,2-tetrafluoropropyltrifluoromethyl ether, 3,3,3,2-tetrafluoropropylethyl ether, 3,3,3,2-tetra Fluoropropyl-2,2,2-trifluoroethyl ether, 4,4,4,3,2,2-hexafluorobutyl methyl ether, 4,4,4,3,2,2-hexafluorobutyl fluoromethyl ether 4, 4, 4, 3,
2,2-hexafluorobutyl difluoromethyl ether, 4,4,4,3,2,2-hexafluorobutyl trifluoromethyl ether, 4,4,4,3,2,2-
Hexafluorobutyl ethyl ether, 4, 4, 4,
3,2,2-hexafluorobutyl-2,2,2-trifluoroethyl ether, 5,5,5,4,3,3,
2,2-octafluoropentyl methyl ether, 5,
5, 5, 4, 3, 3, 2, 2-octafluoropentyl fluoromethyl ether, 5, 5, 5, 4, 3, 3,
2,2-octafluoropentyl difluoromethyl ether, 5,5,5,4,3,3,2,2-octafluoropentyltrifluoromethyl ether, 5,5,5,
4,3,3,2,2-octafluoropentyl ethyl ether, 5,5,5,4,3,3,2,2-octafluoropentyl-2,2,2-trifluoroethyl ether, 3,3 , 2-trifluoropropyl methyl ether, 3,3,2-trifluoropropyl fluoromethyl ether, 3,3,2-trifluoropropyl difluoromethyl ether, 3,3,2-trifluoropropyl trifluoromethyl ether, 3 3,2-trifluoropropyl ethyl ether, 3,3,2-trifluoropropyl-2,2,2-trifluoroethyl ether,
4,4,3,2,2-pentafluorobutyl methyl ether, 4,4,3,2,2-pentafluorobutyl fluoromethyl ether, 4,4,3,2,2-pentafluorobutyl difluoromethyl ether, 4, 4, 3,
2,2-pentafluorobutyl trifluoromethyl ether, 4,4,3,2,2-pentafluorobutyl ethyl ether, 4,4,3,2,2-pentafluorobutyl-2,2,2-trifluoro Ethyl ether, 5,
5,4,3,3,2,2-heptafluoropentyl methyl ether 5,5,4,3,3,2,2-heptafluoropentyl fluoromethyl ether 5,5,4,
3,3,2,2-heptafluoropentyl difluoromethyl ether, 5,5,4,3,3,2,2-heptafluoropentyl trifluoromethyl ether, 5,5,
4,3,3,2,2-heptafluoropentyl ethyl ether, 5,5,4,3,3,2,2-heptafluoropentyl-2,2,2-trifluoroethyl ether and the like.

Further, specific compounds include the following compounds. As a specific compound represented by the general formula [I], a compound in which at least one hydrogen of the ethyl group of ethyl methyl ether is substituted with halogen, that is, 2-fluoroethyl methyl ether, 1-fluoroethyl methyl ether, 2, 2 -Difluoroethyl methyl ether,
1,2-difluoroethyl methyl ether, 1,1-difluoroethyl methyl ether, 2,2,2-trifluoroethyl methyl ether, 1,2,2-trifluoroethyl methyl ether, 1,2,2,2- Tetrafluoroethyl methyl ether, 1,1,2,2-tetrafluoroethyl methyl ether, pentafluoroethyl methyl ether; a compound in which at least one hydrogen of the propyl group of propyl methyl ether is substituted with halogen, that is, 2,2,3 3,3-pentafluoropropyl methyl ether, 1,2,3,3,3-pentafluoropropyl methyl ether, 1,1,3,3,3-pentafluoropropyl methyl ether, 1,2,2,3 , 3-pentafluoropropyl methyl ether, 1, 1, 2,
3,3-pentafluoropropyl methyl ether, 1,
2,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl ether, 1,1,2,3,3,3-hexafluoropropyl methyl Ether, 1,1,2,2,
3,3-hexafluoropropyl methyl ether, heptafluoropropyl methyl ether; a compound in which at least one hydrogen of the 1-methylethyl group of 1-methylethyl methyl ether is substituted with halogen, that is, 1-methyl-2fluoroethyl methyl ether, 1-methyl-1
Fluoroethyl methyl ether, 1-methyl-2, 2 difluoroethyl methyl ether, 1-methyl-1, 2 difluoroethyl methyl ether, 1-fluoromethyl-
2 fluoroethyl methyl ether, 1-methyl-2,
2,2-trifluoroethyl methyl ether, 1-methyl-1,2,2 trifluoroethyl methyl ether, 1-
Fluoromethyl-2,2 difluoroethyl methyl ether, 1-fluoromethyl-1,2 difluoroethyl methyl ether, 1-methyl-1,2,2,2 tetrafluoroethyl methyl ether, 1-fluoromethyl-2,
2,2 trifluoroethyl methyl ether, 1-fluoromethyl-1,2,2 trifluoroethyl methyl ether, 1-difluoromethyl-2,2 difluoroethyl methyl ether, 1-fluoromethyl-1,2,2,2 Tetrafluoroethyl methyl ether, 1-difluoromethyl-2,2,2 trifluoroethyl methyl ether,
1-difluoromethyl-1,2,2 trifluoroethyl methyl ether, 1-trifluoromethyl-2,2,2
Trifluoroethyl methyl ether, 1-difluoromethyl-1,2,2 trifluoroethyl methyl ether,
Examples thereof include 1-trifluoromethyl-1,2,2,2-tetrafluoroethyl methyl ether.

The non-aqueous electrolyte solution of the present invention contains a non-cyclic carbonate in addition to the halogen-substituted ether compound represented by the general formula [I], and the content of the halogen-substituted ether compound in the non-aqueous solvent is 30. It is characterized by being more than 90% by volume and more than 90% by volume. As the acyclic carbonate, dimethyl carbonate, diethyl carbonate,
Examples include ethyl methyl carbonate, methyl propyl carbonate, isopropyl methyl carbonate, ethyl propyl carbonate, isobutyl methyl carbonate and the like. One of these acyclic carbonate compounds may be used alone, or two or more of them may be used in combination, if necessary. Particularly, a mixed solvent containing one or more of dimethyl carbonate and ethyl methyl carbonate is preferable.

The content of the halogen-substituted ether compound in the mixed solvent, that is, the non-aqueous solvent is more than 30% by volume and 90%.
% By volume, preferably from 30% by volume to 70% by volume, more preferably from 40% by volume to 70% by volume.
% By volume or less. If the content of the halogen-substituted ether compound is not more than 30% by volume or more than 90% by volume, it is not preferable because the large current discharge characteristics are deteriorated. Further, since the non-aqueous electrolyte of the present invention contains a relatively large amount of the halogen-substituted ether compound as described above, the flash point is high and the safety is improved. Even more surprisingly, conventionally, when a carbon material capable of doping / dedoping lithium ions is used as a negative electrode active material, it is considered that the presence of a cyclic carbonate such as propylene carbonate and ethylene carbonate is essential for maintaining cycle characteristics. However, it has been found that when the non-aqueous electrolyte of the present invention is used, high cycle characteristics can be maintained even without containing these cyclic carbonates.

When a cyclic carbonate such as ethylene carbonate or vinylene carbonate is added to the above mixed solvent, the initial discharge capacity is improved. In particular, when a graphite-based material is used as the negative electrode carbon material, ethylene carbonate is preferable. However, as the content of these cyclic carbonates increases, large current characteristics and low-temperature discharge characteristics deteriorate, so that the content of the cyclic carbonates is preferably 50% by volume or less, more preferably 30% by volume or less.
The following is preferred. Examples of the carbonate compound include cyclic carbonates such as ethylene carbonate (1,3 dioxolan-2-one), vinylene carbonate, propylene carbonate (4-methyl-1,3 dioxolan-2-one), and 1,2-butylene carbonate. (4-ethyl-1,3 dioxolan-2-one),
2,3-butylene carbonate (4,5-dimethyl-
1,3 dioxolan-2-one), isobutylene carbonate (4,4-dimethyl-1,3 dioxolan-2-one)
ON) and the like. One of these carbonate compounds may be used alone, or two or more of them may be used in combination as needed.

As the lithium salt in the non-aqueous electrolyte of the present invention, any of conventionally known lithium salts can be used.
AsF ₆ , LiPF ₆ , LiBF ₄ , LiClO ₄ , L
iCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ or Li
C (SO ₂ CF ₃ ) ₃ . These lithium salts may be used alone or in combination of two or more as needed.

In the non-aqueous electrolyte of the present invention, the electrolyte concentration is preferably 0.5 mol / l to 2 mol / l, and more preferably, 0.7 mol / l to 1 mol / l because of high ionic conductivity. More preferably, it is 0.5 mol / liter.

In the nonaqueous electrolytic solution of the present invention, it is required that the water content in the solvent before dissolving the electrolyte is 1000 ppm or less, because when used in a lithium battery, the capacity and cycle characteristics of the battery are good. preferable.

Since the halogen- substituted ether compound represented by the general formula [I] has a low solubility of a lithium salt, it is essential to use a mixed solvent to which a compound having a high solubility of a lithium salt is added. Practically, it is preferable that the electrolyte concentration is 0.5 mol / l or more. Therefore, a compound capable of dissolving the lithium electrolyte in the mixed solvent of 0.5 mol / l or more by adding to the halogen-substituted ether can be used. Is added. As the compound to be added, an acyclic carbonate compound is used because it has low reactivity with the active material of the battery and has excellent large current characteristics . Examples of the non-cyclic carbonate compound include those described in the section of the non-aqueous electrolyte of the present invention.

Further, the lithium secondary battery of the present invention comprises a positive electrode capable of doping and undoping lithium ions, a negative electrode made of lithium metal or a lithium alloy or a negative electrode capable of doping and undoping lithium ions, and a non-aqueous solvent. And a non-aqueous electrolyte comprising a lithium electrolyte, wherein the non-aqueous electrolyte is the non-aqueous electrolyte according to the above (1), and the positive electrode comprises manganese, iron, cobalt or nickel. It is characterized by containing a lithium composite oxide containing at least one kind. In the lithium secondary battery of the present invention, by using a lithium composite oxide containing at least one transition metal as the active material of the positive electrode, the charging voltage is high and the energy density of the battery can be increased. Among them, a layered lithium composite oxide mainly composed of a lithium-nickel composite oxide is preferable in terms of excellent cycle characteristics.

The positive electrode in the nonaqueous electrolyte lithium secondary battery of the present invention uses a lithium composite oxide containing at least one of manganese, iron, cobalt and nickel as an active material. Specifically, as the positive electrode, an active material powder of the lithium composite oxide, an auxiliary conductive agent powder, a binder for binding these powders and the like are uniformly mixed and then molded under pressure, or a solvent or the like. , Which is applied to a current collector, dried and pressed, and then fixed to a current collector sheet.

The auxiliary conductive agent powder used for the positive electrode includes:
Has a conductive effect, resistance to the non-aqueous electrolyte used,
Any material having resistance to the electrochemical reaction at the positive electrode may be used, and examples thereof include graphite powder, carbon black, coke powder, and a conductive polymer. The amount of the auxiliary conductive agent is 1 to 100 parts by weight of the active material powder to be used.
It is preferred to be about 20 parts by weight.

In the lithium secondary battery of the present invention, natural graphite, artificial graphite, or a coke material is preferably used as a single component or as a main component because of good charge / discharge cycle characteristics as an active material of the negative electrode. It is also possible to use lithium metal or a lithium metal alloy as the negative electrode active material. When using natural graphite or artificial graphite or coke material as the active material of the negative electrode, the negative electrode may contain a polymer having a number average molecular weight of 300 or more having a carbonate group represented by the general formula [X], if necessary. Can be.

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The binder used for the positive electrode and the negative electrode may be any binder that has a binding effect and has resistance to the nonaqueous electrolyte used and resistance to the electrochemical reaction at the positive electrode and the negative electrode. Examples thereof include fluororesins such as tetrafluoroethylene (hereinafter, sometimes referred to as PTFE) and polyvinylidene fluoride (hereinafter, sometimes referred to as PVdF), polyethylene polypropylene, and the like. The amount of the binder is preferably 1 to 20 parts by weight based on 100 parts by weight of the active material powder to be used.

The current collector used for the positive electrode and the negative electrode may be any one having resistance to the non-aqueous electrolyte used and resistance to the electrochemical reaction at the positive electrode and the negative electrode. Examples include stainless steel and aluminum. The thickness of the current collector is preferably as thin as possible while maintaining strength, from the viewpoint of increasing the volume energy density of the battery, and is preferably about 5 to 100 μm. As a current collector for the positive electrode, it can be easily processed into a thin film,
Aluminum foil is preferred in that it is inexpensive. As the current collector of the negative electrode, a copper foil is preferable because it is difficult to form an alloy with lithium and easily processed into a thin film.

In the non-aqueous electrolyte lithium secondary battery of the present invention, the separator has a function of preventing contact between the two electrodes, having an insulating property, holding the non-aqueous electrolyte, and allowing lithium ions to pass therethrough. Any material that has resistance to the non-aqueous electrolyte used or resistance to electrochemical reactions at the positive electrode and the negative electrode may be used. Examples thereof include non-woven fabrics and woven fabrics such as olefin resins such as fluororesins, polyethylene and polypropylene, and nylons. it can. The thickness of the separator is preferably as thin as possible, as long as the mechanical strength is maintained, from the viewpoint that the volume energy density of the battery increases and the internal resistance decreases, and preferably about 10 to 200 μm.

[0029]

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. (I) Specifications of Lithium Secondary Battery Used for Test The positive electrode was prepared as follows. Lithium nitrate, nickel carbonate, and gallium nitrate were mixed, and calcined in an oxygen stream at 660 ° C. for 15 hours. 87% by weight of gallium-added lithium nickel oxide powder obtained had a number average primary particle size of 40%.
1 part by weight of acetylene black [manufactured by Denki Kagaku Kogyo Co., Ltd., trade name: Denka Black 50% pressed product] and a weight average particle diameter of 7.2 μm flaky artificial graphite (manufactured by Lonza Co., Ltd .;
Product name: KS15) 9% by weight of the mixture
Polyvinylidene fluoride using N-methylpyrrolidone as a solvent as a binder [manufactured by Kureha Chemical Industry Co., Ltd., trade name:
KF # 1300] was added in an amount equivalent to 3% by weight and kneaded sufficiently to obtain a paste. The lithium nickelate powder,
It was confirmed by powder X-ray diffraction that it had an α-NaFeO ₂ type structure.

The paste was applied to a 20 μm-thick aluminum foil as a current collector, dried, pressed to form a sheet, and then cut into small pieces of 1.3 × 1.8 cm to obtain a positive electrode. The active material weight of this positive electrode is 40 mg to 45 mg. The negative electrode was manufactured as follows. A negative electrode carbon powder was produced as follows. Heat-treated at 3000 ° C., the specific surface area by nitrogen adsorption method is 9 m ² / g, the number average particle diameter is 10 μm, the true specific gravity is 2.26, the lattice spacing d ₀₀₂ in X-ray diffraction is 3.36 °, and the ash content is 0. For 95% by weight of natural graphite (from Madagascar) powder of 05% by weight,
Pseudo-graphitic carbon black powder having a specific surface area of 30 m ² / g, a true specific gravity of 2.04, and a number average primary particle diameter of 66 nm by a nitrogen adsorption method graphitized at 2800 ° C. [trade name, manufactured by Tokai Carbon Co., Ltd. : TB3800] 5% by weight of a carbon material mixed, and a silane coupling [manufactured by Nippon Unicar Co., Ltd., trade name A186] previously dispersed in pure water was added in an amount of 1 part by weight. After vacuum drying, a carbon powder treated with a silane coupling agent was obtained.

Next, with respect to 90% by weight of the silane coupling agent-treated material, 10% by weight of polyvinylidene fluoride using N-methylpyrrolidone as a solvent as a binder.
A considerable amount was added and kneaded sufficiently to obtain a paste. The paste was applied to a 10 μm thick copper foil as a current collector, dried and pressed to form a sheet, and then cut into small pieces of 1.5 × 2 cm to obtain a negative electrode. As the separator, a polypropylene porous film (manufactured by Daicel Chemical Industries, trade name: Celgard # 2400) was used.

(II) Cycling Test Conditions The cyclability of the discharge capacity of the battery was determined by alternately repeating the following conditions (1) and (2) four times, and finally repeating the condition (1) once and the conditions (2) ), Only the first cycle was tested, and a total of 91 charge / discharge cycles were repeated, and the cycle characteristics and large current discharge characteristics were examined. (1) A charging current of 7.7 mA, a maximum charging voltage of 4.24 V,
The battery was charged at a constant current and a constant voltage for a charging time of 3 hours, and discharged at a charging current of 1.54 mA and a voltage of 2.75 V throughout. This is performed twice consecutively. (Referred to as low current discharge conditions) (2) Charge current 7.7 mA, maximum charge voltage 4.24 V,
The battery was charged at a constant current and a constant voltage for a charging time of 1 hour, and discharged at a charging current of 7.7 mA and a voltage of 2.75 V throughout. This is 2
Perform 0 times in succession. The cycle characteristics are evaluated based on the capacity retention ratio of the discharge capacity in the 90th charge / discharge to the discharge capacity in the second charge / discharge. The large-current discharge characteristics are evaluated based on the capacity retention ratio of the second-time discharge capacity under the low-current discharge condition to the subsequent first-time discharge capacity under the high-current discharge condition. The initial large current discharge characteristic is the ratio of the discharge capacity at the third cycle to the discharge capacity at the second cycle, and the large current discharge characteristic after the cycle is the ratio of the discharge capacity at the 91st cycle to the discharge capacity at the 90th cycle. It is.

Example 1 Pentafluoropropyl methyl ether (hereinafter sometimes referred to as PFPME) and dimethyl carbonate (hereinafter sometimes referred to as DMC) as a non-aqueous electrolyte solvent.
In a solvent in which 1: 1 is mixed by volume ratio, and Li is used as an electrolyte.
Using a non-aqueous electrolyte in which PF ₆ was dissolved to 1 mol / liter, the positive electrode and the negative electrode obtained as described above were opposed to each other with a separator interposed therebetween, and stored in a stainless steel container to produce a battery A1. . Table 1 shows the test results of the cycle characteristics and the large current discharge characteristics.

Example 2 EC, DMC and PFPME were used as non-aqueous electrolyte solvents.
Batteries A2 and A3 in the same manner as in Example 1 except that a solvent mixed at a volume ratio of 0:45:45 and 30:35:35 was used.
And charge and discharge conditions were the same as in Example 1. Table 1 shows the test results of the cycle characteristics and the large current discharge characteristics.

Comparative Example 1 Only DMC was used as the non-aqueous electrolyte solvent, and
DMC and ethyl methyl carbonate (hereinafter referred to as EMC)
There are times. ) Using a mixed solvent of 50:50 in volume ratio
And the volume ratio of DMC, EC and EMC was 3
Example 1 except that a mixed solvent of 0:35:35 was used.
Battery R₁, R_Two, R _ThreeAnd make
The charge / discharge test was performed in the same manner as in Example 1. Cycle characteristics
Table 1 shows the test results of the high current discharge characteristics.

[0036]

[Table 1]

The battery A1 of the present invention is superior in cycle characteristics, especially in large current discharge characteristics, as compared with the batteries R ₁ , R ₂ and R ₃ containing no PFPME. It should be further noted that the batteries R ₁ and R ₂ containing no PFPME greatly deteriorate their large-current discharge characteristics after repeated charge / discharge cycles, whereas the batteries of the present invention have large current even after repeated charge / discharge cycles. No deterioration is observed in the discharge characteristics, and the cycle characteristics of the large current discharge characteristics are remarkably excellent. Even more surprisingly, the batteries A2 and A according to the invention containing EC
No. ₃ is much more excellent in cycle characteristics than the conventionally proposed battery R3 using a mixed nonaqueous electrolyte of a cyclic carbonate and a non-cyclic carbonate. An improvement in the initial discharge capacity was observed as compared with the batteries containing EC and not containing A2 and A3 according to the present invention. However, in the battery A3 having an EC content of 30 vol%, a large decrease in the large current discharge characteristics was observed, and the EC content was at most 30 vol.
% Is preferable.

Example 3 The battery A2 obtained in Example 2 was charged at 20 ° C. with a charging current of 7.7 mA, a maximum charging voltage of 4.24 V, and a constant current and constant voltage of 3 hours, and then discharged at −20 ° C. Current 1.5
Discharge was performed at 4 mA and a final voltage of 2.75 V. The low-temperature discharge characteristics are evaluated based on the ratio of the discharge capacity during low-temperature discharge to the discharge capacity during room-temperature discharge. Table 2 shows the obtained low-temperature discharge characteristics.

Comparative Example 2 For the batteries R ₁ and R ₂ produced in Comparative Example 1, Example 3 was used.
The low-temperature discharge characteristics were measured in the same manner as described above. Table 2 shows the obtained low-temperature discharge characteristics.

[Table 2] Table 2 shows that the battery A2 according to the present invention exhibits excellent low-temperature discharge characteristics as compared with the battery not containing PFPME.

Example 4 The batteries A2 and A3 obtained in Example 2 were subjected to constant current and constant voltage charging at 20 ° C. at a charging current of 7.7 mA, a maximum charging voltage of 4.24 V, and a charging time of 3 hours. The battery was discharged at a discharge current of 1.54 mA and a final voltage of 2.75 V, and was subjected to a charge / discharge test again at room temperature. As a result, charge / discharge was possible.

Example 5 The flash point of the electrolyte solution for a battery obtained in Examples 1 and 2 was measured by a closed tag measurement method. Table 3 shows the obtained flash points.

Comparative Example 3 The flash point of the battery electrolyte obtained in Comparative Example 1 was measured by a tag-closed measuring method. Table 3 shows the obtained flash points.

[Table 3]

From Table 3, it can be seen that the electrolyte used in the battery according to the present invention has a significantly higher flash point and a drastically improved safety. It is possible to reduce the risk of ignition when the electrolyte leaks for some reason, and to improve the handling at the time of manufacturing.

Example 6 A fluorinated ether shown in Table 4 as a non-aqueous electrolyte solvent,
Using a non-aqueous electrolyte obtained by dissolving LiPF ₆ at a concentration of 1 mol / liter in a solvent obtained by mixing dimethyl carbonate (hereinafter sometimes referred to as DMC) at a volume ratio of 1: 1 as an electrolyte, The positive electrode and the negative electrode obtained as described above were opposed to each other with a separator interposed therebetween, and stored in a stainless steel container to produce batteries B1 to B9. A charge / discharge test was performed in the same manner as in Example 1. Table 4 shows the test results of the cycle characteristics and the large current discharge characteristics.

[Table 4]

Example 7 A number average molecular weight of 5 using N-methylpyrrolidone as a solvent was 97% by weight of the silane coupling agent-treated material.
0.6% by weight of polyethylene carbonate (hereinafter sometimes referred to as PEC) of 0000 and 2.4% by weight of polyvinylidene fluoride using N-methylpyrrolidone as a solvent as a binder, and sufficiently kneaded. And used as a paste. After applying the paste to a 10 μm thick copper foil as a current collector, the paste is dried and pressed to form a sheet.
It was cut into small pieces of 5 × 2 cm to obtain a negative electrode containing PEC. Using the negative electrode obtained as described above, using a mixed solvent of PFPME and DMC at a volume ratio of 1: 1 as the non-aqueous electrolyte, and using 2,2,3,3-tetrafluoropropyldifluoro Methyl ether (hereinafter TFPDE)
May be called. ) And DMC were used in the same manner as in Example 1 except that a mixed solvent having a volume ratio of 1: 1 was used, and batteries P1 and P2 were produced. The charge / discharge test was performed in the same manner as in Example 1. The initial discharge capacities were 6.5 mAh and 6.6, respectively.
mAh. From the above results, by using a negative electrode containing polyethylene carbonate for the negative electrode, EC
It can be seen that the initial capacity is improved without using.

[0046]

By using the electrolytic solution of the present invention,-
Lithium secondary that operates in a wide temperature range of 20 ° C to 60 ° C and has little deterioration in discharge capacity even when repeatedly charged and discharged, and is particularly excellent in large current discharge characteristics, and has little deterioration in large current characteristics due to cycles and is safe. You can get a battery. The lithium secondary battery has an extremely large industrial value for use in portable equipment, transportation vehicles, and machine tools requiring a large current and a large capacity.

Continuation of the front page (56) References JP-A-8-37024 (JP, A) JP-A-8-190912 (JP, A) JP-A-8-124562 (JP, A) JP-A-5-198316 (JP) JP-A-6-176768 (JP, A) JP-A-3-1555061 (JP, A) JP-A-1-17838 (JP, A) JP-A-7-249432 (JP, A) (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 6/16 H01M 4/02-4/04 H01M 4/38-4/62

Claims (9)

(57) [Claims] 1. A non-aqueous electrolytic solution comprising a non-aqueous solvent and a lithium electrolyte, wherein the non-aqueous solvent contains a halogen-substituted ether compound represented by the general formula [I] and a non-cyclic carbonate. Ri der content less than 90 vol% greater than 30 volume percent of the halogen-substituted ether compound,
And nonaqueous electrolytic solution of an electrolyte concentration is characterized in der Rukoto to 0.5 mol / liter. R ₁ —OR ₂ ... [I] (wherein, R ₁ represents an alkyl group having 2 or less carbon atoms or a halogen-substituted alkyl group, and R ₂ represents a halogen-substituted alkyl group having 2 to 10 carbon atoms) Represents a group.) 2. A halogen-substituted ether compound represented by the general formula [I], In the formula, R ₁ is either a methyl group, fluoromethyl group, difluoromethyl group or a trifluoromethyl group, and R ₂ Has the following general formula [II]
The non-aqueous electrolyte according to claim 1, which is a fluorine-substituted alkyl group represented by any one of [IX] to [IX]. CF _3- (CF ₂ ) _n -CH ₂ -... [II] (In the formula, n is an integer of 1 to 5.) HCF _2- (CF ₂ ) _n -CH ₂ -... [III (Where n is an integer of 1 to 5) CF ₃ — (CF ₂ ) _m —CHF— (CF ₂ ) _n —CH ₂ — (IV) (where m and n are Each independently represents an integer of 0 to 4,
And the sum of m and n is an integer of 0-4. ) HCF ₂ — (CF ₂ ) _m —CHF— (CF ₂ ) _n —CH ₂ —... [V] (where m and n are each independently an integer from 0 to 4,
And the sum of m and n is an integer of 0-4. _{) (CF 3) 2 -CF- (} CF 2) n -CH 2 -. ··· [VI] ( wherein, n is an integer of _{0~4) (HCF 2) 2 -CF-} (CF 2 _{) n -CH 2 -. ··· [} VII] ( wherein, n is an integer of _{0~4) CF 3 -CF 2 -C (} CF 3) F- (CF 2) n -CH 2 - · .. [VIII] (where n is an integer of 0 to 2) HCF ₂ —CF ₂ —C (CF ₃ ) F— (CF ₂ ) _n —CH ₂ —. Wherein n is an integer of 0 to 2.) 3. The non-cyclic carbonate is one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, isopropyl methyl carbonate, ethyl propyl carbonate and isobutyl methyl carbonate. The non-aqueous electrolyte according to claim 1 or 2, wherein 4. The non-aqueous electrolytic solution according to claim 1, wherein the non-aqueous electrolytic solution further comprises a cyclic carbonate. 5. The method according to claim 4, wherein the cyclic carbonate is contained.
Non-aqueous electrolysis characterized in that the amount is 30% by volume or less
liquid. 6. The cyclic carbonic acid according to claim 1, 2 or 3,
A non-aqueous electrolyte solution containing no ester. 7. A non-aqueous electrolyte comprising a positive electrode capable of doping and undoping lithium ions, a negative electrode comprising lithium metal or a lithium alloy or a negative electrode capable of doping and undoping lithium ions, a non-aqueous solvent and a lithium electrolyte. Liquid, the non-aqueous electrolyte is the non-aqueous electrolyte according to claim 1, 2 , 3 , 4, 5 or 6 , and the positive electrode comprises manganese, iron, cobalt or nickel. A lithium secondary battery comprising a lithium composite oxide containing at least one kind. 8. The lithium secondary battery according to claim 7 , wherein the negative electrode capable of doping / dedoping lithium ions contains a carbon material containing natural graphite, artificial graphite or coke as a single component or a main component. . 9. The lithium secondary battery according to claim 8, wherein the negative electrode contains a polymer having a carbonate structure represented by the following general formula [X] and having a number average molecular weight of 300 or more. Embedded image