In situ x-ray absorption spectro-electrochemical study of amorphous tin-Based composite oxide material

摘要

We have measured the XAFS spectra of a sample of tin-based composite oxide (TCO) material with a nominal composition of Sn_1.0B_0.56P_0.40Al_0.42O_3.47 during the discharge and charge cycles in an "in situ" configuration. Our results confirm the amorphous nature of TCO material and show that Sn-O bond length in TCO is 2.12 A. Upon discharging, initially Li interacts with the electrochemically active Sn-O center forming metallic Sn in amorphous form and/or highly dispersed clusters containing just a few atoms. Upon further discharge, Li alloys with Sn forming initially amorphous and/or highly dispersed forms of Li_2Sn_5 and/or LiSn and then Li_7Sn_3, Li_5Sn_2, Li_13Sn_5, or Li_7Sn_2. The true nature of the highly dispersed alloys differs from that of the corresponding crystalline phases. Upon charging, metallic Sn is produced with a Sn-Sn distance intermediate to those of gray and white Sn.