A bismuth oxide-modified copper host achieving bubble-free and stable potassium metal batteries.

Due to the minimal electrochemical oxidation-reduction potential, the potassium (K) metal anode has emerged as a focal in K-ion batteries. However, the reactivity of the K metal anode leads to significant side reactions, particularly gas evolution. Mitigating gas generation from K metal anodes has been a persistent challenge in the field. In this study, we propose a dual protective layer design through pre-treatment of the K metal anode, employing a BiO modification layer alongside a stable solid electrolyte interface (SEI) formed during the initial charge-discharge cycle, which significantly suppresses gas evolution. Furthermore, we observe that the BiO modification layer enhances K nucleation due to its strong potassiophilicity when incorporated into the substrate material. The resultant SEI, consisting of dual inorganic layers of Bi-F and K-F formed through the BiO modification, effectively mitigates side reactions and gas generation while inhibiting dendrite growth. Utilizing a Cu@BO@K host, we achieve a nucleation overpotential as low as 40 mV, with a stability of 1900 h in a Cu@BO@K‖Cu@BO@K cell and a high average Coulombic efficiency of 99.2% in a Cu@BO@K‖Cu cell at 0.5 mA cm/0.5 mA h cm. Additionally, Cu@BO@K‖PTCDA also presents a high reversible capacity of 114 mA g at 100 mA g after 200 cycles. We believe that this work presents a viable pathway for mitigating side reactions in K metal anodes.