Rationalizing Surface Electronic Configuration of Ni-Fe LDO by Introducing Cationic Nickel Vacancies as Highly Efficient Electrocatalysts for Lithium-Oxygen Batteries.

Abstract

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-VNi ) 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-VNi significantly improves its intrinsic affinity toward intermediates, thereby fundamentally optimizing the formation and decomposition pathway of Li2 O2 . In addition, the number of eg electrons on each nickel site is 1.19 for Ni-Fe LDO-VNi , which is much closer to 1 than 1.49 for Ni-Fe LDO. The near-unity occupation of eg orbital enhances the covalency of transition metal-oxygen bonds and thus improves the electrocatalytic activity of Ni-Fe LDO-VNi toward oxygen electrode reactions. The experimental results show that the LOBs with Ni-Fe LDO-VNi electrode deliver low overpotentials of 0.11/0.29V during the oxygen reduction reaction/oxygen evolution reaction, respectively, large specific capacities of 13 933mA 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.