Characterization of Li 2S–SiS 2–Li 3MO 3 (M=B, Al, Ga and In) oxysulfide glasses and their application to solid state lithium secondary batteries

Abstract

The electrical, thermal and electrochemical properties of the Li 2S–SiS 2–Li 3MO 3 (M=B, Al, Ga and In) oxysulfide glasses were investigated. The addition of small amounts of Li 3BO 3 or Li 3AlO 3 to the Li 2S–SiS 2 sulfide system kept high conductivity over 10 −3 S cm −1 at room temperature and improved thermal stability against crystallization. In the case of the addition of Li 3GaO 3 or Li 3InO 3, the conductivity monotonically decreased with an increase in Li 3MO 3 content in the glasses. 29Si MAS-NMR spectra of these glasses revealed that the amounts of SiO 2S 2 and SiO 3S tetrahedral units, which lowered the conductivity of the glasses, were larger in the glasses added with Li 3GaO 3 and Li 3InO 3 than in those with Li 3BO 3 and Li 3AlO 3. Cyclic voltammetry suggested that the oxysulfide glasses with small amounts of Li 3MO 3 exhibited wide potential window of 10 V. The glasses with Li 3BO 3 were the most electrochemically stable. The solid-state cells with Li 3BO 3 glasses as solid electrolytes were fabricated and their charge–discharge performance was investigated. These cells worked as lithium secondary batteries under various current densities from 64 to 2038 μA/cm 2 and exhibited excellent cycling performance over 100 times.