A-site cationic defects induced electronic structure regulation of LaMnO3 perovskite boosts oxygen electrode reactions in aprotic lithium–oxygen batteries

Lanthanide-based perovskite oxides have been theoretical predicted as the most prospective cathode catalysts for lithium-oxygen (Li-O2) batteries owing to their superior chemical stability and composition adjustability. However, their inherent activity still needs further improvement and the intrinsic catalytic mechanisms are poorly understood during oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) process. Herein, a facile nonstoichiometric strategy is implemented to fabricate perovskite LaMnO3-δ with abundant A-site cationic defects for the first time. The Li-O2 cell with the as-prepared La0.7MnO3-δ (L0.7MO) dual-function electrocatalyst delivers ultrahigh discharge capacity (29,286 mAh g−1), extremely low overpotential (0.38 V) and superior long-term cycling durability (375 cycles at 300 mA g−1). The well-defined La defects make crucial contribution in modulating the local unsaturated coordination state of active Mn atoms and thus regulating the electronic structure of L0.7MO, which prominently enhances the oxygen redox kinetics in Li-O2 battery. Specifically, experimental results and density function theory (DFT) calculations demonstrate that La vacancies conspicuously increase the covalency of Mn-O bonds, thus optimizing the eg electron filling states of the active Mn cation and enhancing the overlapping state of Mn 3d-O 2p hybridization, which promotes lattice oxygen participated redox reaction and accelerates the electron transport between the Mn cations and oxygen adsorbates (e.g., O22−, O2−). In addition, the abundant crystal defects endow the surface with strong adsorption capability for LiO2 intermediate and hence fundamentally regulate the formation and decomposition mechanism of Li2O2.