The effect of niobium doping on lithium manganese oxide surfaces, LiMn2-xNbxO4: DFT study

Abstract

Lithium manganese oxide (LiMn₂O₄) is one of the promising cathode material for lithium-ion batteries (LIBs), however, it suffers from capacity fading mainly due to surface manganese (Mn²⁺) ion dissolution during Charge/discharge processes. Although many studies focused on reducing Mn-dissolution, surface modification has proven to be an ideal method of reducing Mn^₂₊ ion dissolution in secondary Li-ion batteries. In this study, the density functional theory calculations were carried out to study the bulk properties and investigate the effect of Nb surface doping on major LiMn₂O₄ spinel surfaces. Upon surface Nb doping, we observed a decrease in surface free energy as compared to the surface energies of pure surfaces, indicating that the surface stabilizes upon doping. However, the (001) surface remained the most stable facet, with a similar trend of increasing energies and decreasing stability, i.e. (001) < (011) < (111). Due to the stronger binding energy of Nb-O as compared to Mn-O, doping with Nb can suppress the Mn dissolution during intercalation and hence improve the electrochemical performance.