Two-dimensional transition metal carbide (Ti0.5V0.5)3C2Tx MXene as high performance electrode for flexible supercapacitor

MXenes have gained widespread interest in flexible supercapacitor due to their rich electrochemical activity and free-standing electrode structure. However, it has been a challenge to obtain an electrode with high (mass and volumetric) specific capacitance, high rate and long cycle life simultaneously. Herein, we have prepared a novel few-layer double transition metal carbide (Ti0.5V0.5)3C2Tx MXene. Multivalent V atoms with high electrochemical activity were constructed in stable M3C2-type MXene to obtain the (Ti0.5V0.5)3C2Tx electrode with excellent performance in flexible supercapacitors. The (Ti0.5V0.5)3C2Tx film has an excellent specific capacitance of 387F g-1 (1625 mF cm-3) at 1.0 A g-1, and 267 F g-1 (1121 mF cm-3) even at a high current density of 20.0 A g-1, demonstrating superior rate performance (69%). Moreover, the capacitance of the (Ti0.5V0.5)3C2Tx film remains stable during 100,000 cycles. The symmetric supercapacitor assembled using (Ti0.5V0.5)3C2Tx film has high energy and power densities, up to 5.6 Wh kg-1 and 5210.3 W kg-1. And the all-solid-state (Ti0.5V0.5)3C2Tx flexible SC maintains stable electrochemical performance after 200 bending cycles. This work shows the huge potential of (Ti0.5V0.5)3C2Tx in flexible supercapacitor, and provides a new idea for the design of high performance flexible electrodes.