Nonaqueous electrolyte and nonaqueous-electrolyte battery

Abstract

A nonaqueous electrolyte includes an organic solvent and a lithium salt dissolved in the organic solvent, and a quaternary ammonium salt in an amount of 0.06 mol / L or greater and 0.5 mol / L or less, the quaternary ammonium salt having a structure represented by (chemical formula 3):wherein R is an organic linking group or an organic linking group forming an aromatic ring, the organic linking groups each having a main chain which has 4-5 atoms and is constituted of at least one member selected from carbon, oxygen, nitrogen, sulfur, and phosphorus and having one single-bond end and one double-bond end; R1 is an alkyl group having 1-6 carbon atoms or an alkyl group in which at least one of the hydrogen atoms has been replaced by a fluorine atom; and X− is a fluorine-containing anion.

Description

RELATED APPLICATIONS[0001]The present Application is a divisional Application of U.S. patent application Ser. No. 10 / 536,829 which was filed on May 27, 2005.TECHNICAL FIELD[0002]The present invention relates to a nonaqueous electrolyte and a nonaqueous-electrolyte battery. More particularly, the invention relates to an improvement in nonaqueous electrolytes.BACKGROUND ART[0003]Nonaqueous-electrolyte batteries, in particular, lithium secondary batteries, are recently attracting attention as power sources for portable appliances such as portable telephones, PHSs (simplified portable telephones), small computers, etc., power sources for power storage, and power sources for electric motorcars. In general, a lithium secondary battery is constituted of a positive electrode comprising a positive active material as a main component, a negative electrode comprising a negative-electrode material as a main component, and a nonaqueous electrolyte, and is produced by covering a power-generating ...

AI Technical Summary

Benefits of technology

[0024]The nonaqueous-electrolyte battery of the invention comprises a positive electrode, a negative electrode, and a nonaqueous electrolyte, and is characterized by having been fabricated using the nonaqueous electrolyte described above. Due to this constitution, a nonaqueous-electrolyte battery can be provided in which the effects of the invention described above are produced.

[0025]Furthermore, the nonaqueous-electrolyte battery of the invention may be characterized in that the negative electrode employs a graphite. Due to this constitution, although a graphite is used as a negative-electrode material, first charge can be conducted while effectively inhibiting the decomposition of the organic solvent constituting the nonaqueous electrolyte. This constitution further brings about an improvement in high-rate discharge characteristics. Consequently, by using a graphite in the negative electrode, a nonaqueous-electrolyte battery can be provided which sufficiently takes advantage of that property of a graphite negative electrode material which is the property of showing a flat potential change to enable a high energy density.

[0026]Moreover, the nonaqueous-electrolyte battery of the invention may be characterized by having a sheath comprising a metal / resin composite material. In this constitution, even though the sheath is made of a flexible material, there is no possibility that the battery might swell during charge because the nonaqueous electrolyte in the battery system of the invention can be effectively inhibited from decomposing during charge due to the functions described above and, hence, almost no gas generation occurs during charge. Consequently, a sheath comprising a lightweight metal / resin composite material can be employed and a nonaqueous-electrolyte battery having a further improved energy density can hence be provided.

[0027]It is thought that in the nonaqueous-electrolyte battery according to the invention, part of the quaternary ammonium salt is consumed by the reaction for forming a protective coating film in a first charge step. There are hence cases where the concentration of the quaternary ammonium salt in the nonaqueous electrolyte present in the nonaqueous-electrolyte battery according to the invention after the first charge step is lower than the concentration of the quaternary ammonium salt in the nonaqueous electrolyte of the invention used in the battery.

[0028]Embodiments of the invention will be shown below, but the invention should not be construed as being limited by the following statements.

[0029]The quaternary ammonium salt to be used in the invention more preferably has a structure represented by any of (chemical formula 1), (chemical formula 2), and (chemical formula 3). Examples of the quaternary ammonium salt represented by (chemical formula 1) include quaternary ammonium salts such as (CH3)4NBF4, (CH3)4NBr , (CH3)4N(CF3SO2)2N, (CH3)4N(C2F5SO2)2N, (C2H5)4NBF4, (C2H5)4NClO4, (C2H5)4NI, (C2H5)4N(CF3SO2)2N, (C2H5)4N(C2F5SO2)2N, (C3H7)4NBr, (n-4H9)4NBF4, (n4H9)4N(CF3SO2)2N, (n-C4H9)4N(C2F5SO2)2N, (n-C4H9)4NClO4, (n-C4H9)4NI, (C2H5)4N-maleate, (C2H5)4N-benzoate, and (C2H5)4N-phtalate. However, the quaternary ammonium salt represented by (chemical formula 1) should not be construed as being limited to these.

Problems solved by technology

However, especially in the case of using a graphite in the negative electrode, there has been a problem that the organic solvent such as propylene carbonate decomposes on the graphite negative electrode and, hence, charge / discharge cannot be conducted at a high efficiency.

However, this technique was insufficient in the effect of inhibiting the decomposition of the organic solvent during first charge.

Furthermore, there has been a problem that vinylene carbonate has poor oxidation resistance and decomposes on the positive-electrode side and, hence, the addition of vinylene carbonate in a large amount reduces battery performances.

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