Regulating Fe–O bond in Ti₃C₂T_x MXene anode for high-capacity Li-ion batteries

Chemical bonding has been regarded as an effective modification strategy to enhance the electrochemical performance of MXenes for Li-ion batteries (LIBs). However, the in-depth mechanism, especially concentrating on the regulation of chemical bond, is rarely explored. Herein, we design an atomically dispersed Fe in Ti₃C₂T_x MXene (Fe-Ti₃C₂T_x) by a doping route and the underlying mechanism of high-capacity LIBs is comprehensively investigated. Density functional theory (DFT) calculations reveal that unsaturated O coordination can be induced by electron transfer on Fe–O bond, which enables improved Li-ion adsorption on the surface of Fe-Ti₃C₂T_x nanosheet during charge/discharge process. The experimental observations from X-ray photoelectron spectroscopy (XPS) confirm the successful introduction of Fe atoms into intrinsic structure of Ti₃C₂T_x MXene, and the X-ray absorption spectroscopy (XAS) data verify the electron transfer of Fe–O bond. Moreover, Fe-Ti₃C₂T_x electrode exhibits greatly enhanced electrochemical performance (564.9 mAh g⁻¹ at 50 mA g⁻¹ under −10 °C), surpassing that of pristine Ti₃C₂T_x (77 mAh g⁻¹). The cycling stability of Fe-Ti₃C₂T_x over 500 cycles (418.8 mAh g⁻¹ at 200 mA g⁻¹ under −10 °C). This work is expected to provide a guideline to develop brand-new MXene-based electrode materials with high-capacity for energy storage.