Epoxy-driven carbon host engineering enables ultrafast wetting and dendrite-free K metal anode

K metal anodes are plagued by uncontrolled dendrite growth and interfacial instability, severely limiting their practical viability. To address this, we engineer a carbon paper host with surface epoxy groups (OCP) to regulate K metal deposition. This design enables ultrafast wetting of molten K (<0.1 s) and dendrite-free plating. In situ microscopy confirms uniform K deposition on OCP, in stark contrast to the rampant dendrite formation observed on bare K. Symmetric cells achieve excellent stability, operating over 2000 h at 2 mA cm−2/0.5 mAh cm−2 and sustaining dendrite suppression up to 5 mA cm−2. Mechanistic insights demonstrate that the epoxy groups in OCP promote the formation of an inorganic-rich solid–electrolyte interphase by enhancing electron shielding and facilitating desolvation. As a result, the OCP host achieves a high average Coulombic efficiency of 99.6% over 800 cycles at 1 mA cm−2/1 mAh cm−2. When integrated with a Prussian blue analog, the full cells further exhibit almost no capacity decline after 600 cycles at 500 mA g−1. We believe that our work provides a promising strategy for suppressing dendrite growth and extending the cycle life of K metal batteries.