Preparation of Li_4.4Si Alloy by Use of Mechanical Milling Methods and Its Properties as Negative Electrodes in Lithium Cells

Abstract

Meta-stable phase Li_4.4Si was prepared by mechanical milling process. In order to investigate the electrochemical properties of the meta-stable Li_4.4si, two types of electrochemical cells were used; one of them was three-electrode cell with usual liquid electrolyte LiPF₆-EC/DMC, and the other was all solid state cell with solid electrolyte a-60Li₂S⋅40SiS₂, which was also prepared by mechanical milling process and showed high Li+ ion conductivity of 1.8×10^-4 Scm^-1 at room temperature. Electrochemical capacity of the meta-stable Li_4.4Si was about 400 mAhg-1 for Li⁺ ion extraction in the liquid electrolyte. The capacity was decreased with an increase in the number of Li⁺ extraction-insertion cycles. The Li+ extraction and insertion from the meta-stable Li_4.4Si brought about the reaction between the Li_4.4Si sample and metallic Cu, which was used as a collector of electronic current. Electrochemical extraction of Li+ ions from the meta-stable phase showed the capacity exceeding 250mAhg-1 for the all-solid state cell using the solid electrolyte and TiS₂ as counter electrode. In this solid state cell, the meta-stable phase showed almost no structural change during the extraction and insertion of Li⁺ ions.