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–O 2 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–O 2 batteries but not in Na–O 2 batteries, which is mainly attributed to the stronger reducibility of potassium and relatively more favorable thermodynamic formation of KO 2 over NaO 2 during the discharge process. It is observed that our K–O 2 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–O 2 cell degradation shows that the O 2 crossover effect and the ether–electrolyte instability are the critical problems for K–O 2 batteries. In a word, this study provides a new route to solve the problems caused by the dendrite growth in alkali metal–oxygen batteries.