Characterization of Li2S-SiS2-Li3MO3 (M=B Al, Ga and In) oxysulfide glasses and their application to solid state lithium secondary batteries

The electrical, thermal and electrochemical properties of the LiS-SiS2-Li3MO3 (M=B, Al, Ga and In) oxysulfide glasses were investigated, The addition of small amounts of Li3BO3 or Li3AlO3 to the Li2S-SiS2 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 Li3GaO3 or Li3InO3, the conductivity monotonically decreased with an increase in Li3MO3 content in the glasses. Si-29 MAS-NMR spectra of these glasses revealed that the amounts of SiO2S2 and SiO3S tetrahedral units, which lowered the conductivity of the glasses, were larger in the glasses added with Li3GaO3 and Li3InO3 than in those with Li3BO3 and Li3AlO3. Cyclic voltammetry suggested that the oxysulfide glasses with small amounts of Li3MO3 exhibited wide potential window of 10 V The glasses with Li3BO3 were the most electrochemically stable. The solid-state cells with Li3BO3 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 muA/cm(2) and exhibited excellent cycling performance over 100 times. (C) 2002 Elsevier Science B.V. All rights reserved.