| 摘要 |
PROBLEM TO BE SOLVED: To keep the high initial efficiency and high cycle characteristics of a battery and to realize a capacity exceeding the theoretical discharge capacity of graphite by forming a negative electrode active material with the mixed powder of the carbon material powder containing boron or no boron and the silicon material powder containing a specific ratio of boron. SOLUTION: The silicon material powder containing 0.1-50 wt.% of boron and having a considerably small quantity of SiB4 in an overcooled state is mixed with the graphite carbon powder having high initial efficiency, high cycle characteristics, and low expansion/contraction coefficients at charges/discharges to realize a high capacity. The carbon material powder with a high graphitization factor buffers the high expansion/contraction coefficients of the silicon material powder containing boron at charges/discharges. The mixed powder having the diffraction peak strength in a wide angle X-ray diffraction pattern I (SiB4; 021 plane)/I (Si; 111 plane)<=1 and I (C; 101 plane)/I(C; 100 plane)>=1 is preferably used. Such a constitution is desirable that the contents of carbon, silicon, and boron in the mixed powder of the carbon material powder containing no boron and the silicon material powder containing boron satisfy the prescribed relational expression. |
