Atomically distributed asymmetrical five-coordinated Co–N5 moieties on N-rich doped C enabling enhanced redox kinetics for advanced Li–S batteries

Abstract

Lithium–sulfur (Li–S) batteries show great promise to serve as high-energy-density energy storage devices. Nevertheless, the practical applications of Li–S batteries are significantly limited by the shuttle effect and sluggish sulfur redox reaction (SROR) kinetics. Herein, an ingenious urea-mediated pyrolysis strategy is for the first time reported to obtain well-defined atomically distributed asymmetrical five-coordinated Co–N₅ moieties anchored on nitrogen-rich (30.0 at%) doped carbon (CoN5 SA/NC) as a highly efficient SROR electrocatalyst. CoN5 SA/NC with a high atomically distributed Co loading (2.12 wt%) effectively catalyzes the liquid–liquid and liquid–solid conversions of lithium polysulfides greatly accelerating the SROR kinetics. When CoN5 SA/NC is served as a coating layer for the separator, the Li–S battery exhibits outstanding capacity properties (1060 mA h g⁻¹ at 1C and 922 mA h g⁻¹ at 2C) and superior cycling stability (ultralow decay of 0.033% per cycle at 3C for 1600 cycles). An ultrahigh areal capacity of 7.25 mA h cm⁻² can be acquired for the CoN5 SA/NC based Li–S battery even with a high sulfur loading of 6.5 mg cm⁻². Obviously, the asymmetrical single-atom site engineering strategy demonstrates great potential for practical applications of advanced metal–S batteries.