The Li3PO4-Li2S-SiS2 glass electrolyte exhibited instability against a Li metal electrode in the charge-discharge cycle using a LiCoO2 positive electrode. The interface products between the Li electrode and the glass electrolyte were investigated by Si and S-K edge near-edge X-ray absorption fine structure analyses. It was suggested that Li2S and Si coordinated to three sulfur atoms formed after charge-discharge cycles. This side reaction could be suppressed by modifying the surface of Li metal by N-2 gas, leading to improvement of the charge-discharge property compared to unmodified Li electrode. The operating voltage attained to about 4 V in the modified Li/Li3PO4-Li2S-SiS2 glass electrolyte/LiCoO2 cell, which was comparable to Li- ion battery using a liquid electrolyte. (C) 2004 The Electrochemical Society.