Optimizing d-orbital occupation on interfacial transition metal sites via heterogeneous interface engineering to accelerate oxygen electrode reaction kinetics in lithium-oxygen batteries

Abstract

Aprotic lithium-oxygen batteries (LOBs) possess extremely high theoretical energy density of about 3500 Wh kg-1, which is superior to state-of-the-art lithium-ion batteries. However, the poor energy efficiency and cyclability originated from sluggish kinetics of oxygen electrode reactions in LOBs severely restrict their development and practical application. The solution to these challenges is closely related to the construction of electrocatalysts with both high catalytic activity and stability for oxygen redox reactions in LOBs. In this work, Co3O4 @NiFe2O4 composite with modified heterogeneous interface is fabricated and studied as oxygen electrode catalyst for LOBs. It is theoretically predicted that the electron transfer at the heterogeneous interface in Co3O4 @NiFe2O4 is capable of reducing the occupation of eg electrons in the interfacial Ni sites, leading to the rearrangement of electrons with enhanced spin polarization in the d orbital and the upshift of the d-band center toward Fermi level, eventually enabling the smooth electron transfer between Co3O4 @NiFe2O4 and oxygenated species due to the facile formation of Ni-O bond. This endows Co3O4 @NiFe2O4 based LOBs with high specific capacity of 12697 mAh g-1 and extremely low overpotential of 0.68 V at 100 mA g-1, as well as long cycle life of 274 times at a high current density of 500 mA g-1. This work provides a new strategy for adjusting the surface electronic structure of oxygen electrode catalysts to accelerate oxygen redox kinetics in LOBs.