MgFeSiO₄ as a potential cathode material for magnesium batteries: Ion diffusion rates and voltage trends

Developing rechargeable magnesium batteries has become an area of growing interest as an alternative to lithium-ion batteries largely due to their potential to offer increased energy density from the divalent charge of the Mg ion. Unlike the lithium silicates for Li-ion batteries, MgFeSiO₄ can adopt the olivine structure as observed for LiFePO₄. Here we combine advanced modelling techniques based on energy minimization, molecular dynamics (MD) and density functional theory to explore the Mg-ion conduction, doping and voltage behaviour of MgFeSiO₄. The Mg-ion migration activation energy is relatively low for a Mg-based cathode, and MD simulations predict a diffusion coefficient (D_Mg) of 10^-9 cm² s^-1, which suggest favourable electrode kinetics. Partial substitution of Fe by Co or Mn could increase the cell voltage from 2.3 V vs. Mg/Mg²⁺ to 2.8-3.0 V. The new fundamental insights presented here should stimulate further work on low-cost silicate cathodes for Mg batteries.