Dendrite-Free Potassium–Oxygen Battery Based on a Liquid Alloy Anode

The safety issue caused by the dendrite growth is not only a key research problem in lithium-ion batteries but also a critical concern in alkali metal (i.e., Li, Na, and K)–oxygen batteries where a solid metal is usually used as the anode. Herein, we demonstrate the first dendrite-free K–O2 battery at ambient temperature based on a liquid Na–K alloy anode. The unique liquid–liquid connection between the liquid alloy and the electrolyte in our alloy anode-based battery provides a homogeneous and robust anode–electrolyte interface. Meanwhile, we manage to show that the Na–K alloy is only compatible in K–O2 batteries but not in Na–O2 batteries, which is mainly attributed to the stronger reducibility of potassium and relatively more favorable thermodynamic formation of KO2 over NaO2 during the discharge process. It is observed that our K–O2 battery based on a liquid alloy anode shows a long cycle life (over 620 h) and a low discharge–charge overpotential (about 0.05 V at initial cycles). Moreover, the mechanism investigation into the K–O2 cell degradation shows that the O2 crossover effect and the ether–electrolyte instability are the critical problems for K–O2 batteries. In a word, this study provides a new route to solve the problems caused by the dendrite growth in alkali metal–oxygen batteries.