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

Abstract

The effect of lithium insertion for two Sn-based composite oxide glasses, Sn 2BPO 6 and Sn 2P 2O 7, was examined during the first electrochemical discharge/charge cycle. Electrodes based on these glasses were analysed with micro-Raman spectroscopy at different steps during the cycle. In-situ X-ray diffraction has been used to confirm the amorphous state during the lithium insertion 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 place resulting in Li 3PO 4, Li 2O and SnO 2 formation. The charge compensation mechanism is thought to be the reduction of Sn 2+ to Sn. The formation of Li 3PO 4 is found to be irreversible and is as such partly responsible for the large observed capacity loss during the first cycle.