On the Mechanism of Magnesium Storage in Micro- and Nano-Particulate Tin Battery Electrodes

This study reports on the electrochemical alloying-dealloying properties of Mg2Sn intermetallic compounds. Sn-119 Mossbauer spectra of beta-Sn powder, thermally alloyed cubic-Mg2Sn, and an intermediate MgSn nominal composition are used as references. The discharge of a Mg/micro-Sn half-cell led to significant changes in the spectra line shape, which is explained by a multiphase mechanism involving the coexistence of c-Mg2Sn, distorted Mg2-delta Sn, and Mg-doped beta-Sn. Capacities and capacity retention were improved by using nanoparticulate tin electrodes. This material reduces significantly the diffusion lengths for magnesium and contains surface SnO and SnO2, which are partially electroactive. The half-cell potentials were suitable to be combined versus the MgMn2O4 cathodes. Energy density and cycling properties of the resulting full Mg-ion cells are also scrutinized.