Phase stability of cation-doped LiMnO$_{2}$]{Phase stability of cation-doped LiMnO$_{2}$ within the GGA+U approximation

Details Phase stability of cation-doped LiMnO$_{2}$]{Phase stability of cation-doped LiMnO$_{2}$ within the GGA+U approximation Phase stability of cation-doped LiMnO$_{2}$]{Phase stability of cation-doped LiMnO$_{2}$ within the GGA+U approximation

2008-06-30

arxiv.org/abs/0806.4849v1

Modelling Simul. Mater. Sci. Eng. 16 (2008) 055008

Physics

Condensed Matter

Materials Science

9 pages, 3 figures

Scientific paper

First principles density functional theory calculations within the GGA+U approximation were performed for LiMn$_{1-x}$M$_x$O$_{2}$, a candidate cathode material for lithium-ion batteries, with ($x=0.25$, M=Ni, Fe, Co, Mg), to investigate the effect of doping on the destabilization of the monoclinic structure relative to the layered rhombohedral structure. A primary motivation of this work was to determine to what extent the predictions of the electronically more realistic GGA+U treatment would differ from those obtained within the GGA. Several significant qualitative changes are found. For the pristine system in the rhombohedral structure, Mn ions show a high-spin state within GGA+U, rather than the low spin (metallic) state found in GGA. The doped rhombohedral structure is unstable within GGA+U, rather than metastable, as in GGA. In the monoclinic structure, the dopant oxidation states are the same (trivalent Fe, divalent Co, Ni) in GGA+U and GGA. Co and Ni ions show a higher spin state in GGA+U than in GGA. The divalent dopants destabilized the monoclinic structure to a greater extent than trivalent dopants within the GGA+U, as expected from previous GGA calculations. Overall, our results suggest that the relatively close agreement sometimes found between properties calculated within the GGA and GGA+U may be misleading, because the underlying electronic behaviors may be profoundly different.

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