Reinvestigation of Li_1-xTi_yV_1-v S_2 Electrodes in Suitable Electrolyte: Highly Improved Electrochemical Properties

摘要

Reversible electrochemical intercalation of Li into the Li_1-xTi_yV_1-yS_2 dichalcogenides, which was frustrated in the 1970s by the use of 1 M LiClO_4 in propylene carbonate as the electrolyte, is reinvestigated with 1 M LiPF_6 in ethylene carbonate:diethyl carbonate (1:1). The choice of the electrolyte allows full electrochemical cycling between MS_2 and LiMS_2 (M = V or Ti_0.3V_0.7). The as-prepared Li_zMS_2 (z≈0.9) samples were fully lithiated after the first discharge, and from a subsequent charge of LiVS_2 to VS_2, the room-temperature solubility limits of the parent 3S phase, the Li-rich hexagonal phase, the intermediate __ and __ phases, and the hexagonal Li-poor hexagonal phase have been determined. Introduction of Ti in LiTi_0.3V_0.7S_2 remarkably improves the capacity at high cycling rates and increases the voltage by about 0.2 V.