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

A study is reported on the electrochemical alloying-dealloying properties of Mg₂Sn intermetallic compounds. ¹¹⁹Sn Mössbauer spectra of β-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 spectra line shape that are explained by a multiphase mechanism involving the coexistence of c-Mg₂Sn, distorted Mg_2-δSn and Mg-doped β-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 MgMn₂O₄ cathodes. Energy density and cycling properties of the resulting full Mg-ion cells are also scrutinized.