Ultra‐Efficient Synthesis of Nb4C3Tx MXene via H2O‐Assisted Supercritical Etching for Li‐Ion Battery

Abstract Nb 4 C 3 T x MXene has shown extraordinary promise for various applications owing to its unique physicochemical properties. However, it can only be synthesized by the traditional HF‐based etching method, which uses large amounts of hazardous HF and requires a long etching time (> 96 h), thus limiting its practical application. Here, an ultra‐efficient and environmental‐friendly H 2 O‐assisted supercritical etching method is proposed for the preparation of Nb 4 C 3 T x MXene. Benefiting from the synergetic effect between supercritical CO 2 (SPC‐CO 2 ) and subcritical H 2 O （SBC‐H 2 O）, the etching time for Nb 4 C 3 T x MXene can be dramatically shortened to 1 h. The as‐synthesized Nb 4 C 3 T x MXene possesses uniform accordion‐like morphology and large interlayer spacing. When used as anode for Li‐ion battery, the Nb 4 C 3 T x MXene delivers a high reversible specific capacity of 430 mAh g −1 at 0.1 A g −1 , which is among the highest values achieved in pure‐MXene‐based anodes. The superior lithium storage performance of the Nb 4 C 3 T x MXene can be ascribed to its high conductivity, fast Li + diffusion kinetics and good structural stability.