In situ X-ray absorption and diffraction study of the Li reaction with a tin composite oxide glass

We have measured the X-ray absorption fine structure spectra of a sample of tin-based composite oxide (TCO) material with a nominal composition of Sn1 .0B0.56P0.40Al0.42O3.47 during the discharge and charge cycles in an in sit u configuration. Our results confirm the amorphous nature of TCO material a nd show that Sn in the pristine state of TCO is coordinated with three oxyg en atoms at a distance of 2.12 a. Upon discharging, initially LE interacts with the electrochemically active Sn-O center, forming metallic Sn in a hig hly dispersed form (i.e., clusters containing just a few atoms). Upon furth er discharge, Li alloys with Sn, forming highly dispersed forms of Li,Sn al loys with x being dependent on the degree of Li intercalation. The structur al nature of the highly dispersed alloys differs from those of the correspo nding crystalline phases such as Li2Sn5, LiSn, Li7Sn3, Li5Sn2, Li13Sn5, and Li7Sn2. Upon charging, Li dealloys from Li,Sn, forming metallic Sn in a hi ghly dispersed form with a Sn-Sn distance intermediate to those of gray and white Sn. (C) 2000 The Electrochemical Society. S0013-4651(99)04-108-5. Al l rights reserved.