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

Abstract

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.