Rationalizing Surface Electronic Configuration of Ni-Fe LDO by Introducing Cationic Nickel Vacancies as Highly...

Cationic defect engineering is an effective strategy to optimize the electronic structure of active sites and boost the oxygen electrode reactions in lithium-oxygen batteries (LOBs). Herein, Ni-Fe layered double oxides enriched with cationic nickel vacancies (Ni-Fe LDO-V_Ni ) are first designed and studied as the electrocatalysts for LOBs. Based on the density functional theory calculation, the existence of nickel vacancy in Ni-Fe LDO-V_Ni significantly improves its intrinsic affinity toward intermediates, thereby fundamentally optimizing the formation and decomposition pathway of Li₂ O₂ . In addition, the number of e_g electrons on each nickel site is 1.19 for Ni-Fe LDO-V_Ni , which is much closer to 1 than 1.49 for Ni-Fe LDO. The near-unity occupation of e_g orbital enhances the covalency of transition metal-oxygen bonds and thus improves the electrocatalytic activity of Ni-Fe LDO-V_Ni toward oxygen electrode reactions. The experimental results show that the LOBs with Ni-Fe LDO-V_Ni electrode deliver low overpotentials of 0.11/0.29 V during the oxygen reduction reaction/oxygen evolution reaction, respectively, large specific capacities of 13 933 mA h g^-1 and superior cycling stability of over 826 h. This study provides a novel approach to optimize the electrocatalytic activity of LDO through reasonable defect engineering.