Suppressing Surface Oxidation of Pyrite FeS₂ by Cobalt Doping in Lithium Sulfur Batteries

Lithium-sulfur batteries have emerged as a promising energy storage device due to ultra-high theoretical capacity, but the slow kinetics of sulfur and polysulfide shuttle hinder the batteries' further development. Here, the 10% cobalt-doped pyrite iron disulfide electrocatalyst deposited on acetylene black as a separator coating in lithium-sulfur batteries is reported. The adsorption rate to the intermediate Li₂S₆ is significantly improved while surface oxidation of FeS₂ is inhibited: iron oxide and sulfate, thus avoiding FeS₂ electrocatalyst deactivation. The electrocatalytic activity has been evaluated in terms of electronic resistivity, lithium-ion diffusion, liquid-liquid, and liquid-solid conversion kinetics. The coin batteries exhibit ultra-long cycle life at 1 C with an initial capacity of 854.7 mAh g^-1 and maintained at 440.8 mAh g^-1 after 920 cycles. Furthermore, the separator is applied to a laminated pouch battery with a sulfur mass of 326 mg (3.7 mg cm^-2) and retained the capacity of 590 mAh g^-1 at 0.1 C after 50 cycles. This work demonstrates that FeS₂ electrocatalytic activity can be improved when Co-doped FeS₂ suppresses surface oxidation and provides a reference for low-cost separator coating design in pouch batteries.