Bulk Ti3C2Tx anodes for superior sodium storage performance: the unique role of O-termination†
Abstract
The regulation of surface O-termination of Ti3C2Tx MXenes is a fascinating problem in the development of anodes for sodium ion batteries. However, the preparation of bulk Ti3C2Tx anodes with O-rich termination (O-Ti3C2Tx) is still a great challenge, due to their poor antioxidant properties in air. Moreover, the electrochemical behaviors of bulk O-Ti3C2Tx are less clear. In this study, bulk O-Ti3C2Tx anodes were prepared by a simple “hot melting-decomposition” strategy. The melt organic matter during heat treatment isolates bulk Ti3C2Tx from air, resulting in bulk Ti3C2Tx remaining stable up to 300 °C in air. Furthermore, we revealed the Na+ storage mechanism of bulk O-Ti3C2Tx electrodes by studying the structural evolution of both O-Ti3C2Tx and bulk Ti3C2Tx electrodes during the charge and discharge process. Surprisingly, it was found that bulk O-Ti3C2Tx easily evolved into active Ti3C2Tx nanoparticles, while bulk Ti3C2Tx formed an amorphous matrix. The unique role of O-termination in stabilizing nanocrystals and the anti-aggregation effect of the as-formed Na16Ti10O28 nanocrystals produced at the edge of Ti3C2Tx nanoparticles resulted in enhanced sodium storage performance in bulk O-Ti3C2Tx electrodes. The bulk O-Ti3C2Tx electrode can still deliver a reversible capacity of 153 mA h g−1 after 2500 cycles even at a current density as high as 1 A g−1, showing superior sodium storage performance. The proposed method could be a general approach to improve the antioxidant properties of MXenes in air. Moreover, our work lays the foundation for O-termination regulation of MXenes and their electrochemical mechanism.