Nitrogen-doped CoSe₂as a bifunctional catalyst for high areal capacity and lean electrolyte of Li-S battery

The sluggish redox kinetics of polysulfides and difficult oxidation process of Li2S severely hinder practical application of Li-S batteries under high sulfur loading and a low electrolyte dosage. To address these issues, we develop a bifunctional catalyst by manipulation of anion N doping in CoSe2 (N-CoSe2). Theoretical simulation results uncover that an introduced N element into CoSe2 could form a shorter Co-N bond, create a higher charge number of the Co central atom, bring new defect levels, and induce the Co 3d band closer to Fermi level. Further atomic level analysis revealed that N-CoSe2 could form shorter Co-S bonds with sulfur species and simultaneously weaken the S-S bridged bond of Li2S4 and Li-S bond of Li2S, which eventually facilitate the polysulfide conversion reaction in the discharge process and the Li2S oxidation in the charge process. With N-CoSe2 as a bifunctional catalyst, the battery exhibited a high areal capacity of 9.26 mAh g-1 under the low E/S (electrolyte/sulfur) ratio of 4.4 μL mg-1. Understanding the design concept of a bifunctional catalyst with anion doping would provide a new vision for realizing a high-performance Li-S battery.