Potassium-ion batteries (PIBs) are attractive for low-cost and large-scale energy storage applications, in which graphite is one of the most promising anodes. However, the large size and the high activity of K+ ions and the highly catalytic surface of graphite largely prevent the development of safe and compatible electrolytes. Here, a nonflammable, moderate-concentration electrolyte is reported that is highly compatible with graphite anodes and that consists of fire-retardant trimethyl phosphate (TMP) and potassium bis(fluorosulfonyl)imide (KFSI) in a salt/solvent molar ratio of 3:8. It shows unprecedented stability, as evidenced by its 74% capacity retention over 24 months of cycling (over 2000 cycles) at the 0.2 C current rate. Electrolyte structure and surface analyses show that this excellent cycling stability is due to the nearly 100% solvation of TMP molecules with K+ cations and the formation of FSI- -derived F-rich solid electrolyte interphase (SEI), which effectively suppresses the decomposition of the solvent molecules toward the graphite anode. Furthermore, excellent performance on high-mass loaded graphite electrodes and in a full cell with perylenetetracarboxylic dianhydride cathode is demonstrated. This study highlights the importance of the compatibility of both electrolyte and the interface, and offers new opportunities to design the electrolyte-SEI nexus for safe and practical PIBs.
Keywords: F-rich solid electrolyte interphase; graphite; nonflammable materials; potassium-ion batteries; trimethyl phosphate.
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