Infrared and in situ119Sn Mössbauer study of lithiated tin borate glasses

Abstract

The effect of lithium ion insertion/extraction in a SnB₂O₄ glass electrode, particularly how it affects the glass network structure and the tin environment, has been investigated using in situ Mössbauer and diffuse reflectance infrared (DR-IR) spectroscopy. Two different potential ranges for the electrochemical cycle were investigated; (0.01–0.8) V and (0.01–1.0) V. During the first cycle of both potential ranges the lithium ions first inserted in to the electrode are observed to cause substantial disruption to the glass network. This disruption to the glass network appears to cause a large (50%) irreversible capacity loss in the first cycle. We also demonstrated differences in the cycling stability for different voltage ranges. The (0.01–0.8) V range showed superior cycling stability with a capacity of around 530 mA h g⁻¹ for at least 25 cycles. The in situ Mössbauer and DR-IR results show that during the subsequent 25 cycles the glass structure undergoes mainly reversible changes for both the potential ranges. However, the Mössbauer spectra of electrodes cycled in the (0.01–1.0) V range indicate a continuous change in the tin environment towards a more symmetric and lithium rich one for the fully charged state after 25 cycles, which is not observed for cycling in the (0.01–0.8) V range. This may explain the lower capacity experienced for cells cycled in the (0.01–1.0) V range.