In situ XAS of the reaction mechanism of lithium with tin-based composite oxide glass

We have measured the XAFS spectra of tin-based composite oxide (TCO) glass with nominal composition of Sn1.0B0.56P0.40Al0.42O3.47 during the discharge and charge cycles in an in a non-aqueous cell. Our results confirm the amo rphous nature of TCO material and show that Sn in TCO is coordinated with 3 oxygen atoms at a distance of 2.12 Angstrom. Upon discharge (i.e., Li inse rtion), initially, Li interacts with the electrochemically active Sn-O cent er forming metallic Sn, most likely in the form of highly dispersed cluster s, and Li2O. Upon further discharge, our results are consistent with a mode l in which additional Li alloys with Sn forming various alloys with composi tion dependent on the amount of Li inserted. The formed alloys appear to be in the form of highly dispersed clusters and/or amorphous in nature. Their local structure differs somewhat from the crystalline structure of the kno wn Li-Sn alloys such as LiSn, Li7Sn3, or Li7Sn2. Upon charging (i.e., Li re moval), metallic Sn is reversibly produced with a Sn-Sn distance intermedia te to those of gray and white Sn.