Composite protective coating on lithium metal anodes for polysulfide shielding in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries face significant challenges due to the environmental sensitivity, dendrite growth and polysulfide-induced side reactions of lithium metal anodes (LMAs), which compromise their safety and cycle life. To address these issues, we develop a composite protective layer comprising layer-by-layer assembled graphene oxide (GO) films coated with 1H,1H,2H,2H-perfluorodecyl trichlorosilane (FDTS). The lithium-reduced GO framework establishes uniform ion-conducting channels that homogenize Li-ion flux, enabling uniform deposition and suppressing dendrite formation. At the same time, the hydrophobic organic coating serves as a robust barrier against water, air and lithium polysulfides (LiPSs), enabling the environmental and electrochemical stability of LMAs. As a result, the protected LMAs maintain exceptional stability upon direct contact with water and exposure in humid air (relative humidity 35%). When integrated into Li-S batteries with high sulfur loadings (4.5 mg cm⁻²), the protected LMAs enable a capacity retention of 61.1% over 300 cycles, showing improved cycling performance. This work provides a scalable approach to stabilizing LMAs for practical Li-S batteries.