SnO2 negative electrode for lithium ion cell:: in situ Mossbauer investigation of chemical changes upon discharge

In situ Sn-119 Mossbauer study of an SnO2 electrode was performed during discharge of a lithium ion cell. The first step is lithium intercalation into the SnO2 host structure. This lithium intercalation results in reinforcement of the SnO2 lattice instead of direct decomposition of the oxide upon reduction. This first step is followed by the reduction of tin dioxide into unusual tin species (possibly "exotic" forms of Sn(II) or Sn(0)). The last step of the discharge consists in Li-Sn alloy formation. However, non-reduced SnO2 is present nearly up to the end of the discharge despite a very low discharge regime. It seems highly probable that this fact is related both to slow Li diffusion and disconnection of SnO2 particles due to Li2O formation. The working electrode appears to be rather far from equilibrium during continuous discharge, which means that ideal succession of well-defined stages cannot describe the real phenomena involved in the operating battery. (C) 2004 Elsevier Inc. All rights reserved.