Enabling Structural and Electrochemical Stability of 2D Antimonene for Potassium-Ion Storage with Nonflammable Electrolyte

Alloy-type anodes with high theoretical capacities and low working potentials are promising candidates for use in rechargeable batteries. However, their development faces significant challenges due to active material pulverization associated with large volume expansion and an unstable solid electrolyte interphase (SEI) formed with conventional electrolytes. In this study, we report a two-dimensional (2D) metallene, 2D antimonene, as anode material combined with nonflammable 1 M triethyl phosphate (TEP) and tris(2,2,2-trifluoroethyl) phosphate (TFP)-based electrolytes, achieving structural and electrochemical stability for potassium-ion storage. We disclose that the 2D antimonene develops a wrinkled morphology while retaining its structural integrity without cracking after cycling, highlighting its effectiveness in accommodating stress from large volume change. Meanwhile, TEP-based electrolyte accelerates the formation of stable anion-derived SEI, and TFP-based electrolyte produces a KF-rich SEI, effectively passivating the electrochemical interface and preventing electrolyte depletion. In potassium-ion batteries (PIBs), 2D antimonene delivers stable capacities of 486.8/492.6 mAh g^-1 with retention of 94.6/91.4% over 200 cycles in nonflammable TEP and TFP-based electrolytes, respectively. Impressively, it obtains superior rate performance and long-term stability, maintaining a capacity of 312.3 mAh g^-1 over 400 cycles at 0.5 A g^-1 in the TEP system. Furthermore, the full cell was successfully demonstrated at temperatures of 50 and -20 °C. This work advances the development of 2D metallenes with nonflammable electrolytes, enabling the application of high-performance alloy-type anodes for safe PIBs.