First-principles investigation of the structural changes in Li-rich cathode composites

Lithium ion batteries have high energy densities and are widely used in consumer electronics. However, it is essential to improve their power rate and cycle life for long-term usage. Cathode materials containing Li-excess layered oxide compounds, $x$Li$_2$MnO$_3$(1-$x$)LiMO$_2$, (where M=Mn, Co, Ni and $x$= 0.2-0.7) have two times higher capacities than the conventional cathode material but during cycling a decrease in energy density and a concomitant development of a low voltage plateau are often observed. Furthermore, recent experimental studies have observed the formation and clustering of the anti-site defects near the surface. Thus a detailed understanding of the structural changes at the atomic scale of these Li-rich composites is essential to establish the correlation between the structural and electrochemical property. We present first-principles density functional theory study of the structural and electronic properties in Li-rich cathode composites. These cathode composites are modelled as solid solutions of the LiMnO$_2$ (R$\bar{3}$m) and Li$_2$MnO$_3$ (C$_2$m) phases. We discuss the stability of the proposed model, the diffusion energy barriers of Li$^+$ ions calculated using nudged-elastic band method and the formation energies of the antisite defects.