Synergistic multi-functional active MoS2/PI separator for high energy density potassium metal batteries

The practical application of high-energy-density potassium metal batteries (KMBs) is currently hindered by severe safety hazards derived from dendritic growth and the energy-diluting nature of electrochemically inactive components. Here we report a synergistic multi-functional strategy to construct an active separator (MoS 2 /PI), comprising a robust polyimide (PI) nanofiber skeleton and a kinetic-regulating MoS 2 coating. Corroborated by theoretical simulations and experimental characterizations, the potassiophilic MoS 2 layer effectively modulates the local electric field and minimizes the nucleation barrier, thereby orchestrating a uniform K + flux for dendrite-free deposition. Distinguishing this work from conventional inert barriers, the proposed design activates the separator into an energy-boosting component. Both the accessible carbonyl sites in the PI backbone and the MoS 2 coating participate in reversible potassiation. They contribute individual specific capacities of ∼7.0% and ∼21.2% relative to the KPB cathode, respectively, achieving a total capacity enhancement of ∼28.2%. Benefiting from this dual-active mechanism, the K||K symmetric cells exhibit ultra-stable cycling for over 4000 h. Potassium Prussian Blue (KPB)||K full cells equipped with the MoS 2 /PI separator deliver a superior capacity of 93.1 mAh g -1 , significantly outperforming those using commercial PP (69.3 mAh g -1 ) and GF (72.6 mAh g -1 ) separators. The device also demonstrates exceptional durability by maintaining 80.7% capacity after 1000 cycles, corresponding to a stable lifespan of 3270 h. This study validates the active separator strategy as a critical pathway for developing next-generation high-energy-density alkali metal batteries.