NONAQUEOUS ELECTROLYTE SECONDARY BATTERY AND METHOD FOR MANUFACTURING NEGATIVE ELECTRODE OF THE SAME

摘要

A nonaqueous electrolyte secondary battery and a graphite powder for negative electrodes for overcoming conventional problems in a well-balanced manner, and for attaining improvement in a high-rate discharging capability with a high energy density and in reliability when left at high temperature. The conventionally used graphite powder for negative electrodes in which lithium ions can reversibly repeat intercalation and deintercalation by electric charge and discharge has not reached the approximate level of the theoretical capacitance value of 372 mAh/g. In addition, when the high-rate charging and discharging characteristics of the powder are improved, the shelf life of the powder at high temperature is adversely effected. These problems can be solved by using a graphite powder which has disk- or tablet-like shapes, an average particle size of 10-30 mu m, an average thickness of 3-9 mu m at the thinnest parts, and a (110) to (004) X-ray diffraction peak intensity ratio of at least 0.015 as measured by wide-angle X-ray diffractometry and which is obtained by chamfering and screening scaly graphite particles having a (002)-plane spacing (d002) of 3.350-3.360 ANGSTROM and a crystal size (Lc) of at least 1000 ANGSTROM in the C-axis direction in the course of further pulverizing the scaly graphite particles.