Non-flammable phosphate electrolyte with high salt-to-solvent ratios for safe potassium-ion battery

Potassium-ion batteries are now regarded as powerful competitors to lithium-ion batteries due to their merits of low-cost and abundant resource contrasted with state-of-art lithium ion batteries. However, the extremely flammable electrolytes may cause severe safety issues. Herein, we report an intrinsic non-flammable trimethyl phosphate-based potassium ion battery electrolyte. The problem of its poor electrochemical compatibility with graphite electrode is successful settled by using concentrated salt electrolyte. Graphite anode with high concentrated potassium bis(fluorosulfonyl)imide (KFSI)/trimethyl phosphate (TMP) electrolyte demonstrates high Coulombic efficiency and stable cyclability after 80 cycles. The performance enhancement mechanism is further probed via X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM). The flame-retarding character of the concentrated electrolyte with stable electrochemical performance paves the way toward low cost and highly safe potassium ion batteries.