Nitrogen-Doped CoSe₂ as 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.