A tailored electrolyte for safe and durable potassium ion batteries

Electrolytes are critical for the safety and long-term cyclability of potassium ion batteries (PIBs). However, conventional low-concentration electrolytes cannot simultaneously achieve safe and durable PIBs due to their highly flammable solvents or ineffective solid-electrolyte interphase (SEI). Herein, we demonstrate a low-concentration, non-flammable, and weakly solvating electrolyte that simultaneously enhances the safety and cyclability of PIBs. The solvent exhibits non-flammable and weak solvation features, which bolsters the battery safety and the formation of anion-derived SEI even in the low-concentration electrolyte. Specifically, the proposed electrolyte enables a running time of over 200 days and 2 years for K||Cu and K||graphite cells, respectively. In addition, the K0.5MnO2||graphite full cell combined with this proposed electrolyte can operate for 100 cycles with high Coulombic efficiency of 99.7%. This study provides a guiding principle in tailoring electrolytes for achieving safe and long-lasting potassium ion batteries.