Self‐Evolving Interfacial Kinetic Highways via Reactive Separator Engineering for Durable Potassium Metal Batteries

Abstract

ABSTRACT The practical deployment of potassium metal batteries (KMBs) is impeded by unstable interfacial chemistry. Currently, most research on KMBs uses the thick, inert glass fiber separator, which compromises energy density and lacks sufficient regulation of dynamic interfaces. Here, we report a reactive separator engineering strategy that transforms the inert separator into an active regulator to construct a robust, self‐evolving anodic interphase. Inspired by mechanistic screening that intercalation compounds are superior to conversion counterparts as separator modulators, intercalative WO 3 is utilized as a prototype to modify polypropylene separator and actively trigger in‐situ formation of the self‐evolving K x WO 3 interphase. Based on density functional theory calculations, this phase features a minimal K + migration barrier of 0.12 eV, acting as a potassiophilic reservoir to build a kinetic highway. The evolving W species construct a chemically stable skeleton that templates the growth of a spatially graded interphase, creating a rigid‐flexible coupling architecture to buffer volume fluctuations. Consequently, the K||Cu half cell achieves a low nucleation overpotential of 17 mV at 0.2 mA cm −2 , while the K||K symmetric cell delivers an ultralong lifespan of 6000 h at 0.05 mA cm −2 . Impressively, exceptional stability exceeding 2500 h with cumulative capacities of 57 095 mAh g −1 at 50 mA g −1 is realized for KMBs.