Structural investigation of the Li+ ion insertion/extraction mechanism in Sn-based composite oxide glasses

The effect of lithium insertion for two Sn-based composite oxide glasses, S n2BPO6 and Sn2P2O7, was examined during the first electrochemical discharge /charge cycle. Electrodes based on these glasses were analysed with micro-R aman spectroscopy at different steps during the cycle. In-situ X-ray diffra ction has been used to confirm the amorphous state during the lithium inser tion and extraction process. No alloy formation between Li and Sn could be discerned throughout the first cycle. It was found that when lithium enters the electrode, a reaction at the surface of the glass particles takes plac e resulting in Li3PO4, Li2O and SnO2 formation. The charge compensation mec hanism is thought to be the reduction of Sn2+ to Sn. The formation of Li3PO 4 is found to be irreversible and is as such partly responsible for the lar ge observed capacity loss during the first cycle. (C) 2001 Elsevier Science Ltd. All rights reserved.