Abstract:

First\|principle  calculation  based on density functional theory was employed to investigate the effects of Co\|doping in monoclinic LiMnO₂. It was found that Co\|doping shortened the distances between the anions and the cations effectively, suppressed the Jahn\|Teller distortion markedly and decreased the insulating band gap greatly, which respectively  enhanced the structural stability of monoclinic LiMnO₂, increased the intercalation voltage, improved the stability during electrochemical cycles, and increased the electrical conductivity. The calculated results also revealed that the Co ion in the doped system was in non\|spin state with an electron configuration of t⁶_2ge⁰_g and a valence of +3, and the Mn ion was in high\|spin state with an electron configuration of t³_2ge¹_g and also a valence of +3, nevertheless there were strong covalent interactions between the transition\|metal ions and the oxygen ions. The doped material is not an ideal ionic crystal.

Key words: lithium-lion batteries, first-principles calculation, monoclinic LiMnO₂, Co-doping