A high-performance potassium metal battery using safe ionic liquid electrolyte

Significance Rechargeable potassium batteries are promising alternatives of Li batteries owing to the earth abundance and low cost of potassium. The safety of K metal battery involving highly reactive potassium metal and flammable organic electrolyte remains poor, risking fire hazards during use. This work presents the development of an ionic liquid electrolyte that allows safe and high-performance potassium metal batteries. An impressive capacity retention of 89% after 820 cycles is achieved with a high average Coulombic efficiency of 99.9%. Moreover, the K metal battery can safely and stably work at 60 °C. This work provides insights to future design and innovation of other metal batteries toward safe and long-life energy storage.