Preparation of Li{sub}(4.4)Si alloy by use of mechanical milling methods and its properties as negative electrodes in lithium cells

摘要

Meta-stable phase Li{sub}4.4Si was prepared by mechanical milling process. In order to investigate the electrochemical properties of the meta-stable Li{sub}4.4Si, two types of electrochemical cells were used; one of them was three-electrode cell with usual liquid electrolyte LiPF{sub}6-EC/DMC, and the other was all solid state cell with solid electrolyte a-60Li{sub}2S·40SiS{sub}2, which was also prepared by mechanical milling process and showed high Li{sup}+ ion conductivity of 1.8 × 10{sup}(-4) Scm{sup}(-1) at room temperature. Electrochemical capacity of the meta-stable Li{sub}4.4Si was about 400mAhg{sup}(-1) for Li{sup}+ ion extraction in the liquid electrolyte. The capacity was decreased with an increase in the number of Li{sup}+ extraction-insertion cycles. The Li{sup}+ extraction and insertion from the meta-stable Li{sub}4.4Si brought about the reaction between the Li{sub}4.4Si sample and metallic Cu, which was used as a collector of electronic current. Electrochemical extraction of Li{sup}+ ions from the meta-stable phase showed the capacity exceeding 250 mAhg{sup}(-1) for the all-solid state cell using the solid electrolyte and TiS{sub}2 as counter electrode. In this solid state cell, the meta-stable phase showed almost no structural change during the extraction and insertion of Li{sup}+ ions.