Enhanced low-temperature Li-ion storage in MXene titanium carbide by surface oxygen termination

Current lithium-ion batteries (LIBs) suffer from poor cycling and rate performance at low temperature (LT), which prohibit their applications in cold climate area and winter. As temperature decreases, the Li⁺ desolvation energy and electrode polarization increase, which lead to Li dendrite formation and battery performance fading. Herein, we report a new material surface engineering strategy to enhance Li-storage performance at LT in MXene-(Ti₃C₂T_x) by substituting O selectively for F termination. The pristine MXene was processed calculation at 300 °C in different atmospheres to control the partial O substitutions. The x-ray photoelectron spectroscopy (XPS), Raman spectroscopy and high-resolution transmission electron microscope (HRTEM) have been used to disclose the surface element state and fine structure. Investigated as anode of LIBs, the Ti₃C₂T_x(O) sample displays an improved capacity and cycle life both at -20 °C and room temperature. A discharge capacity of 226 mAh g^-1 (the 10th cycle) is observed and still keep 193.9 mAh g^-1 even after 1000 cycles. This is far better than that of graphite anode. Furthermore, the discharge capacity is 405 mAh g^-1 (the 10th cycle) at room temperature (100 mA g^-1). Even after 500 cycles, it remains 403 mAh g^-1, which is much better than Ti₃C₂T_x(F/OH). Density functional theory (DFT) calculations show that the Li ion migration barrier could be greatly decreased with O terminal group, rationalizing the improved electrochemical performance. The O-rich surface enhance the electrolyte wettability, facilitate the Li ion desolvation and speed up the Li insertion into layered Ti₃C₂T_x(O). The present result demonstrates that the surface engineering strategy could promote the Li storage performance in MXene especially at LT.