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 situ configuration. Our results confirm the amorphous nature of TCO material and show that Sn in the pristine state of TCO is coordinated with three oxygen 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 highly dispersed form (i.e., clusters containing just a few atoms). Upon further discharge, Li alloys with Sn, forming highly dispersed forms of Li,Sn alloys with x being dependent on the degree of Li intercalation. The structural nature of the highly dispersed alloys differs from those of the corresponding crystalline phases such as Li2Sn5, LiSn, Li7Sn3, Li5Sn2, Li13Sn5, and Li7Sn2. Upon charging, Li dealloys from Li,Sn, forming metallic Sn in a highly 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. All rights reserved.