Non-flammable phosphate-ester-based electrolyte with high concentration for high safety potassium-based anode-free dual ion battery

Dual ion batteries, which have emerged as a novel energy storage device in recent years, are highly valued for their high operating voltage, safety, and environmental friendliness, attracting significant attention. However, the safety characteristics of these batteries are greatly reduced due to the high flammability of conventional carbonate-based electrolytes. The development of a non-flammable electrolyte with high safety and excellent reversible plating/stripping characteristics is crucial for the advancement of potassium (K) −based dual ion batteries. Compared to high concentration electrolytes, the use of low electrolyte concentration limits the capacity derived from anion intercalation into the graphite layers. In this work, a 3.75 M KFSI/TEP:DMC (2:1 v/v) electrolyte was configured using non-flammable triethyl phosphate (TEP) as the main solvent, dimethyl carbonate (DMC) as the co-solvent, and potassium bis(fluorosulfonyl)imide (KFSI) as the salt. This electrolyte not only exhibits highly non-flammable properties but also demonstrates excellent plating/stripping reversibility in K||Al half batteries, achieving an average coulombic efficiency of ∼ 98.9 % over 1200 cycles. Furthermore, long-term reversibility tests conducted with K||K symmetric batteries indicate a cycle life exceeding 6000 h, which corresponds to more than 250 days of continuous operation. In conclusion, we assembled a K-based anode-free dual ion battery, with aluminum serving as the anode and graphite as the cathode, which exhibited an exceptional cyclic lifespan. At 0.2 A g⁻¹, the battery demostrated stable cycling for over 200 cycles, maintaining a capacity retention rate of 100 %. This research paves the way for the development of high-safety K-based anode-free dual ion batteries.