Design Principles of Mediation Layer for Current Collectors Toward High‐Performance Anode‐Free Potassium‐Metal Batteries: A Case Study of Cu₆Sn₅ on Copper

Abstract Anode‐free potassium (K) metal batteries are promising candidates in high‐energy‐density batteries. Nevertheless, the notorious potassium dendrite growth and poor K plating/stripping efficiency originating from the potassiophobicity of conventional Cu current collectors impede their practical applications. Herein, by means of systematically multi‐scale theoretical simulations, the correlations among K deposition morphology, nucleation sites, and potassiophilicity of mediation layers are well illuminated from thermodynamics and dynamics perspectives. As a proof of concept, a potassiophilic alloy Cu₆Sn₅ layer is constructed on commercial Cu foils via a facile electroless plating approach. The designed Cu₆Sn₅@Cu can guide the homogeneous distribution of K⁺ flux and regulate the electronic field, promoting uniform K⁺ plating and stripping. Meanwhile, a KF‐rich solid electrolyte interphase (SEI) layer with high mechanical strength is electrochemically induced and formed, facilitating the transport of K⁺ through SEI and enhancing the stability of SEI. Consequently, Cu₆Sn₅@Cu delivers great performance with durable stability of up to 600 h (1 mA cm⁻² and 1 mAh cm⁻²) in no‐reservoir half‐cells. Benefiting from the unique mediation layer design, a novel anode‐free K‐metal full‐cell prototype demonstrates ameliorative cyclic stability. This work advances a fundamental understanding and establishes the bridge between the potassium deposition morphology and mediation layer properties for anode‐free potassium‐metal batteries.