Crystal structure and multicomponent effects in Tetrahedral Silicate Cathode Materials for Rechargeable Li-ion Batteries

A first principles investigation is performed to study the structural and electrochemical properties of four polymorphs of the Li2FeSiO4 orthosilicate family (Pmn21, Pmnb, P21/n and Pbn21), to predict the effect of the transition metal composition. Our results show that the inclusion of Mn and Ni cations helps to stabilize the layered structures, but the polymorphs with a 3D cation network arrangement (P21/n and Pbn21) still have comparable energetic stability. We also show that the decrease of the cationic repulsion with the extraction of Li (found for these polymorphs during the discharge process) reduces the voltage step between the first and second Li extraction processes. The effect of multiple interactions between Li and the transition metals is examined, and the implications of multicomponent structures to improve the design of battery cathode are also addressed.