Enabling Efficient Anchoring-Conversion Interface by Fabricating Double-Layer Functionalized Separator for Suppressing Shuttle Effect.

Lithium-sulfur batteries (LiSBs) with high energy density still face challenges on sluggish conversion kinetics, severe shuttle effects of lithium polysulfides (LiPSs), and low blocking feature of ordinary separators to LiPSs. To tackle these, a novel double-layer strategy to functionalize separators is proposed, which consists of Co with atomically dispersed CoN decorated on Ketjen black (Co/CoN@KB) layer and an ultrathin 2D TiCT MXene layer. The theoretical calculations and experimental results jointly demonstrate metallic Co sites provide efficient adsorption and catalytic capability for long-chain LiPSs, while CoN active sites facilitate the absorption of short-chain LiPSs and promote the conversion to LiS. The stacking MXene layer serves as a microscopic barrier to further physically block and chemically anchor the leaked LiPSs from the pores and gaps of the Co/CoN@KB layer, thus preserving LiPSs within efficient anchoring-conversion reaction interfaces to balance the accumulation of "dead S" and LiS. Consequently, with an ultralight loading of Co/CoN@KB-MXene, the LiSBs exhibit amazing electrochemical performance even under high sulfur loading and lean electrolyte, and the outperforming performance for lithium-selenium batteries (LiSeBs) can also be achieved. This work exploits a universal and effective strategy of a double-layer functionalized separator to regulate the equilibrium adsorption-catalytic interface, enabling high-energy and long-cycle LiSBs/LiSeBs.