Lithium secondary battery

Abstract

A lithium secondary battery including: an electrode group, a non-aqueous electrolyte and a battery case housing the electrode group and the non-aqueous electrolyte, the electrode group including a positive electrode, a negative electrode and a separator layer interposed between the positive electrode and the negative electrode, wherein an end-of-charge voltage and an end-of-discharge voltage are set in such a manner that the electrode group has an energy density of not less than 700 Wh / L, the separator layer includes a porous heat-resistant layer, and a short circuit area A produced when an internal short circuit has occurred between the positive electrode and the negative electrode, and a reduced area B of the porous heat-resistant layer that is produced by heat generation satisfy 1≦(A+B) / A≧10.

Description

CROSS-REFERENCE TO RELATED APPLICATION [0001] This application is a continuation-in-part of U.S. patent application Ser. No. 11 / 339,617 filed Jan. 26, 2006 which in turn claims the benefit of Japanese Application No. 2005-174585 filed Jun. 15, 2005, the disclosures of which Applications are incorporated by reference herein in their entirety.FIELD OF THE INVENTION [0002] The present invention relates to a lithium secondary battery including an electrode group with a high energy density, and more particularly to a lithium secondary battery having excellent short circuit resistance. BACKGROUND OF THE INVENTION [0003] Lithium secondary batteries are attracting attention as high-capacity power sources, and are considered to be promising particularly as power sources for portable devices. A commonly used lithium secondary battery includes an electrode group, a non-aqueous electrolyte and a battery case housing the electrode group and the non-aqueous electrolyte. The electrode group includ...

AI Technical Summary

Benefits of technology

[0007] The present invention was made in view of the foregoing problems, and it is an object of the invention to improve the safety during an internal short circuit and the storage characteristics of a lithium secondary battery having a high energy density.

[0034] In the case where a short circuit has occurred between the positive electrode and the negative electrode, conventional separator layers will be melted by heat generated, since they only include a porous resin membrane. Consequently, the area of the short circuit portion increases to the total of the short circuit area A and the reduced area of the separator layer, further increasing the amount of heat generated. The amount of heat generated at the time of occurrence of a short circuit significantly increases when the energy density of the electrode group exceeds 700 Wh / L. Particularly, when an internal short circuit has occurred during storage in a high temperature environment and the short circuit portion expands, then the heat generation is greatly accelerated. On the other hand, the separator layer according to the present invention includes the porous heat-resistant layer, and the reduced area B of the porous heat-resistant layer that has resulted from the heat generated during a short circuit is limited to a small amount. Accordingly, it is possible to reduce the duration of a short circuit, thereby suppressing the increase of the amount of heat generated, or the acceleration of the heat generation. Thus, according to the present invention, it is possible to provide a lithium secondary battery that offers a high level of safety in case of an internal short circuit and excellent storage characteristics, while having a high energy density.

Problems solved by technology

These theoretical capacities cannot be considered very high.

Thus, it is difficult to stably supply lithium secondary batteries including an electrode group with an energy density of not less than 700 Wh / L.

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