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) cm(2) 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.