Enhanced Ion Diffusion in Flexible Ti3C2TX MXene Film for High-Performance Supercapacitors

Ti3C2Tx MXene is a good candidate of electrode materials for supercapacitors due to its high conductivity and outstanding pseudocapacitance. However, restacking among MXene sheets is inevitable when they are assembled into a freestanding film electrodes, which hinders electrolyte ion diffusion to active sites and results in sluggish energy-storage kinetics. Herein, the volumetrically expanded ester reaction between ethanol and phosphoric acid is exploited to improve interlayer path within the Ti3C2Tx film. These two kinds of molecules jointly intercalate into the interlayer space of the Ti3C2Tx film and then react to produce phosphate under heating, leading to an expanded molecular scale but uniform interlayer gallery. The optimized film shows enhancement in both gravimetric and volumetric capacitances along with better rate capability. It exhibits a capacitance of 297 F g(-1)/965 F cm(-3) at 2 mV s(-1) and retains 108 F g(-1)/300 F cm(-3) at 200 mV s(-1), which are greatly superior to those of the pristine film without the treatments. The assembled symmetric and asymmetric supercapacitors with optimized film structure can deliver an energy density of 6.33 and 7 Wh Kg(-1), respectively. Herein, a novel yet simple method to ameliorate restacking of MXene sheets for its better supercapacitor application is demonstrated.