Sulfur-doped LaNiO3 perovskite oxides with enriched anionic vacancies and manipulated orbital occupancy facilitating oxygen electrode reactions in lithium-oxygen batteries

Abstract

The rational design of effective bifunctional catalysts with enhanced activity toward oxygen reduction reaction and oxygen evolution reaction is of significance to develop high-performance lithium-oxygen (Li–O2) batteries. Herein, sulfur-doped LaNiO3 nanoparticles are elaborately synthesized, and their catalytic activity toward oxygen redox reactions in Li–O2 batteries is comprehensively studied. As confirmed by the density functional theory calculations and experimental results, the substitution of oxygen atoms by sulfur atoms with lower Pauling electronegativity can enhance the covalent feature of bonds, thus increasing electrical conductivity of catalyst. In addition, abundant oxygen vacancies created after sulfur doping are capable of providing concentrated active sites. Simultaneously, sulfur dopants boost the hybridization between Ni 3d orbital and O 2p orbital and increase the covalency of Ni–O bonds due to the increase of Ni3+ with the near-unity occupancy of the eg orbital, thereby increasing the adsorption strength of oxygen-containing intermediates on the surface. Eventually, lowered reaction energy barriers and accelerated reaction kinetics of oxygen electrode reactions are realized, contributing to the optimized electrochemical performance of Li–O2 battery. The Li–O2 battery based on sulfur-doped LaNiO3 with the optimized S-doping level of 2.89 wt% (marked as S2.89 wt%-LNO) delivers a high specific discharge capacity of 24067 mAh/g, an ultralow overpotential of 0.37 V and extended life of 347 cycles.