Ultrathin nanosheets of FeOOH with oxygen vacancies as efficient polysulfide electrocatalyst for advanced lithium–sulfur batteries

Developing high effectively affinitive to lithium polysulfides (LiPSs) conversion, permanent electrochemical stability, and cost-effective electrocatalyst for sulfur reduction reaction (SRR) in a high‐sulfur‐loading and lean-electrolyte condition is highly desired for the application of lithium–sulfur batteries (LSBs). Here, an amorphous FeOOH (A-FeOOH) with nanosheet architecture is obtained by a mild oxidation transformation process at room temperature, which is constructed as a practical catalyst to facilitate the conversion of LiPSs. A systematic structure analysises and calculation simulations reveal that the enhanced surface electron transfer dynamics of the as-formed A-FeOOH is modulated by a loss of oxygen coordination, and retention ligand oxygens are also found to be activated as co-catalysts to boost SRR process. Unsaturated Fe-O bondings tuning of catalysts via shifting of d band centers, leading to an elevated interaction between Fe 3d orbitals and S 2p orbitals, which much more effectively accelerate the breaking of S-S bonds in LiPSs. Meanwhile, enhanced electrical conductivity originated from oxygen vacancies accelerates electron repopulation, thereby promoting the smooth conversion reaction of sulfur. Additionally, A-FeOOH acts as non-carbon-based catalysts, which alleviates short circuits while reducing non-catalytic domains. The amorphous nanosheets are also uniformly and spontaneously coating on the surface of cathodes, inhibiting the shuttle effect and buffering volumetric expansion. A-FeOOH based Li-S cathode (A-FeOOH@SCM) exhibits a reversible capacity of 723 mAh . g −1 over 250 cycles at 1C and delivers a high energy density of 363 wh . kg −1 at 0.2C on multilayer-pouch cell level under lean electrolyte of 3.2 g . g −1 Sulfur and high loading of 9.36 mg . cm −2 .