Improving the electrical conductivity and structural stability of the Li2MnO3 cathode via P doping

Li2MnO3 and Li-rich mLi(2)MnO(3)center dot nLiMO(2) (M - Mn, Ni, Co) solid solution materials are important high capacity cathodes for Li ion batteries. There are two factors that hinder the wide application of the Li2MnO3 cathodes, i.e., the intrinsic low electrical conductivity and the poor structural stability upon cycling. It is reported that F-doping and replacing O can create polaron states in Li2MnO3, but these polaron states are trapped by the doped F atoms and contribute little to the electrical conductivity. In this work, from first principles calculations, we demonstrate that more polaron states can be created through P-doping, and the trapping effect of the polaron states by the doped P atom is much weak than that of occurred in the case of F-doping. Polaron migration pathways in the P-doped Li2MnO3 are optimized and the migration energy barriers range from 0.17 to 0.48 eV for different pathways. It is also found that P-doping suppresses the O charge deficiency, and thus prevents the formation and release of O-2 upon charging to high potentials. Furthermore, P-doping is also beneficial to the structural stability of the Li2MnO3 as it decreases the driving force of the phase transition from layered structure to spinel structure. (C) 2015 Elsevier B.V. All rights reserved.