Electrochemical performance and structural change during charge–discharge reaction of SnO–P2O5 glassy electrodes in rechargeable lithium batteries

Using melt quenching, SnO–P2O5 glasses were synthesized, and then characterized as negative electrode materials for lithium secondary batteries. The electrochemical cell Li/the 67SnO·33P2O5 (mol%) glass maintained reversible capacity of about 400 mAh g−1 for 20 cycles. The cell’s cycle performance was better than those of cells using Sn-based crystals such as Sn, SnO, and SnO2 as working electrodes. The local structure of the 67SnO·33P2O5 glass after lithium insertion and extraction was analyzed. 7Li MAS-NMR measurements revealed that the Li–Sn alloy was formed during the first lithium insertion to the glass and that alloying–dealloying of the Li–Sn domain occurred during charge–discharge cycling. The glassy matrix surrounding the alloy was investigated using 31P MAS-NMR. The P2O74- group might be changed to PO43- and P2O64- groups by the first lithium insertion to the glass. The formed phosphate groups remained after the consecutive lithium extraction process. An all-solid-state cell with the 67SnO·33P2O5 glass exhibited the discharge capacity of 750 mAh g−1 at the first cycle, which is greater than that of a cell with the 50SnO·50B2O3 glass.