Site-exchange of Li and M ions in silicate cathode materials Li2MSiO4 (M = Mn, Fe, Co and Ni): DFT calculations

Abstract

First principles calculations have been used to investigate the occurrence of site-exchange of Li and M ions and the effect of the site-exchange on Li extraction of silicate cathode materials Li₂MSiO₄ (M = Mn, Fe, Co and Ni). Total energy calculations suggest that Li (in the 4b site) and M (in the 2a site) ions become site-exchanged upon delithiation. This structural arrangement leads to significant cell expansion as two Li ions are extracted. Elastic property calculations indicate that the ductility of the fully delithiated MSiO₄ is impaired, which is likely to induce structural collapse and rapid capacity attenuation during the charge–discharge cycles. Restraining the site-exchange or improving the ductility may be an effective way of developing high performance Li₂MSiO₄ for Li-ion batteries.