Structural coupling design of MXene for high-energy-density solid-state flexible supercapacitors

The electrochemical performance of MXene is restricted by the easy oxidation and nanosheet re-stacking, and it remains challenging to simultaneously realize oxidation resistance improvement, re-stacking suppression and heteroatom coupling under mild conditions. Herein, a simple, mild and effective strategy is developed to enable structural coupling design of MXene by hydrothermal tannic acid and thiourea. Ti 3 C 2 T x MXene dispersion mixed with tannic acid (TA) and thiourea (T) is conducted with simple hydrothermal treatment to prepare the h-MXene@TA:T composite. The structural coupling of h-MXene@TA:T involves the favorable interactions between MXene and hydrothermal tannic acid and thiourea, including surface adsorption and surface substitution (chemical bonding), which simultaneously enables oxidation resistance improvement, re-stacking suppression and N, S heteroatoms coupling. As a result, the h-MXene@TA:T film electrode shows remarkably high capacitances of 903 F g −1 at 2 mV s −1 and 1095 F g −1 at 1 A g −1 , with ∼100% retention after 50,000 cycles, outperforming most of MXene-based film electrodes reported so far. Moreover, solid-state flexible symmetric supercapacitor also exhibits outstanding energy storage performance of 37 Wh kg −1 at 300 W kg −1 . The impressive results indicate the structural coupling design of MXene is very promising for high-performance flexible supercapacitors.