Theoretical investigation of Li2MnSiO4 as a cathode material for Li-ion batteries: a DFT study

Transition metal lithium orthosilicates are of interest as cathode materials for lithium batteries. Density functional theory (DFT) calculations were performed to evaluate the structural and electrochemical properties of the different polymorphs of Li2MnSiO4. Our computational studies predict superior properties for the Pmn21 polymorph even after extraction of two Li per formula unit. We state that the shortcomings observed for Li2MnSiO4 as a cathode are caused by two mechanisms. Switching of the magnetic state occurs during the first cycles. The subsequent transition, under delithiated conditions, from the Pmn21 or Pmnb polymorphs to the electrochemically weakest P21/n polymorph is the second mechanism that may gradually lead to electrochemical and structural collapse. A comparison with companion data obtained on Li2FeSiO4 is also made.