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

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.