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

Abstract

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-(Ti3C2Tx) 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 Ti3C2Tx(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 Ti3C2Tx(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 Ti3C2Tx(O). The present result demonstrates that the surface engineering strategy could promote the Li storage performance in MXene especially at LT.