Electrochemical Performance of M2GeO4 (M = Co, Fe and Ni) as Anode Materials with High Capacity for Lithium-Ion Batteries

$M_2GeO_4$ (M = Co, Fe and Ni) was synthesized as an anode material for lithium-ion batteries and its electrochemical characteristics were investigated. The $Fe_2GeO_4$ electrode exhibited an initial discharge capacity of $1127.8mAh\;g^{-1}$ and better capacity retention than $Co_2GeO_4$ and $Ni_2GeO_4$. A diffusion coefficient of lithium ion in the $Fe_2GeO_4$ electrode was measured to be $12.7{\times}10^{-8}cm^2s^{-1}$, which was higher than those of the other two electrodes. The electrochemical performance of the $Fe_2GeO_4$ electrode was improved by coating carbon onto the surface of $Fe_2GeO_4$ particles. The carbon-coated $Fe_2GeO_4$ electrode delivered a high initial discharge capacity of $1144.9mAh\;g^{-1}$ with good capacity retention. The enhanced cycling performance was mainly attributed to the carbon-coated layer that accommodates the volume change of the active materials and improves the electronic conductivity. Our results demonstrate that the carbon-coated $Fe_2GeO_4$ can be a promising anode material for achieving high energy density lithium-ion batteries.