Modulating eg orbitals through ligand engineering to boost the electrocatalytic activity of NiSe for advanced lithium-sulfur batteries

Abstract

Accelerating the sluggish redox kinetics of lithium polysulfides (LiPSs) by electrocatalysis is essential to achieve high performance lithium-sulfur (Li-S) batteries. However, the issue of insufficient catalytic activity remains to be addressed. Herein, a strategy of modulating eg orbitals through ligand engineering has been proposed to boost the catalytic activity of NiSe for rapid LiPSs redox conversion. The X-ray spectroscopic measurements and theoretical calculations reveal that partial substitution of Se with N disrupts the octahedral coordination of Ni atoms in NiSe, leading to the reduced degeneracy and upward shift of eg orbitals of Ni 3d states. As a consequence, the bonding strength of N-substituted NiSe (N-NiSe) with LiPSs is enhanced, which facilitates the interfacial charge transfer kinetics and accelerates the LiPSs redox kinetics. Therefore, the Li-S batteries assembled with N-NiSe present a high capacity of 682.6 mAh g−1 at a high rate of 5 C and a high areal capacity of 6.5 mAh cm−2 at a high sulfur loading of 6 mg cm−2. This work provides a promising strategy to develop efficient transition-metal based electrocatalysts for Li-S batteries through eg orbital modulation.