Role of Metal-Lithium Oxide Interfaces in the Extra Lithium Capacity of Metal Oxide Lithium-Ion Battery Anode Materials

Abstract

Lithium storage capacities beyond the stoichiometric limit of conversion have been reported for the transition metal oxides MnO, CoO, NiO, CuO, and beyond the alloying limit for the main group metal oxide SnO. This work examines the molecular mechanisms responsible for this extra capacity using first principles plane wave density functional theory with periodic boundary conditions. Energies of the optimized structures were employed to construct first discharge curves. Analysis of lithiated structures of transition metal oxides with moderate lithium content revealed the formation of two different phases within the electrode material, namely bulk metal and lithium oxide, Li2O. At higher lithium content, the interfacial region between the two phases was found to expand, giving rise to "free volume" for additional lithium storage. MnO had the highest free volume in the interfacial region for lithium storage, followed by CoO, NiO, CuO, and SnO. Of particular interest was CuO, which upon lithiation, formed linear and branched chains of Cu atoms that percolated throughout a large portion of the system. This behavior suggests that CuO may better maintain conductivity through the anode material for more cycles than the other transition metal oxides examined.