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

• Published in: Journal of alloys and compounds Vol. 658; pp. 818 - 823
• Main Authors: Wang, Z.Q., Wu, M.S., Xu, B., Ouyang, C.Y.
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.02.2016
• Subjects: Doping; Li2MnO3; Lithium ion batteries; Polaron conduction; Lithium ion batteries; Li2MnO3; Polaron conduction; Doping
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2015.11.013

Li2MnO3 and Li-rich mLi2MnO3·nLiMO2 (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 O2 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. •Li site P-doping to the Li2MnO3 is thermodynamically favorable.•P-doping is beneficial to the structural stability of Li2MnO3 cathode at high potential.•P-doping improves the electrical conduction of the Li2MnO3 cathode.•Jahn–Teller type small polaron serves as an effective charge carrier in Li2MnO3.