First-principles study on lithium metal borate cathodes for lithium rechargeable batteries

Abstract

A computational study of the electrochemical properties of three isotopic LiMBO${}_{3}$ compounds (M $=$ Mn, Fe, and Co) as cathode materials is conducted using state-of-the-art first-principles calculations. The calculation of the Li intercalation potentials of LiMBO${}_{3}$ predicts that the theoretical energy density (660--860 Wh kg${}^{\ensuremath{-}1}$) can be comparable to or even higher than the corresponding olivine phosphates (595 Wh kg${}^{\ensuremath{-}1}$ for LiFePO${}_{4}$). In addition, the volume changes during cycling are notably low (less than 2% for M $=$ Mn, Fe, and Co), which may be advantageous for the long-term cyclability of Li rechargeable batteries. An investigation of the electronic structure suggests that the small polaron is likely to be a main conductor of Li${}_{x}$MBO${}_{3}$. A study of Li mobility in Li${}_{x}$MBO${}_{3}$ crystal structures indicates that zigzag one-dimensional (1D) Li diffusion tunnels are present with reasonably low activation barriers for Li motion. However, relatively low antisite energy for Li-M site exchange is observed, indicating that the metal ions in the Li site can block the 1D Li diffusion path. This implies that the synthesis condition and nanosizing of the material can be critical for this class of electrode material to achieve high-power capability.