Unravelling the Polymorph Dependant Electrochemical Behavior of VO₂ for Advanced Supercapacitor Applications

The development of sustainable, high-performance electrode materials is essential for scalable energy storage devices. A key challenge lies in developing cost-effective systems that combine high energy and power densities. Vanadium dioxide (VO₂) with its remarkable pseudo-capacitive behavior emerges as a promising candidate owing to its polymorphic forms and unique phase transition property. Herein, VO₂ polymorphs (A, B, D, and M) are hydrothermally synthesized and systematically investigated. Among them, VO₂(M) micro-rods exhibited a superior electrochemical performance, delivering a specific capacitance of 150 F g^-1 at 1 A g^-1 current density and demonstrating 99% of capacitive contribution at 40 mV s^-1, as confirmed by kinetic studies. Furthermore, an asymmetric hybrid supercapacitor employing VO₂(M) micro-rods as the positive electrode and Ti₃C₂T_x MXene as the negative electrode achieved remarkable energy storage performance, delivering a specific capacitance of 92.8 F g^-1 at 2 A g^-1. The device delivered a maximum energy density of 68.18 Wh kg^-1 and power density of 2298.2 W kg^-1, while maintaining 100% capacitive retention and coulombic efficiency over 5000 cycles. The high capacitive contribution observed in both pristine VO₂(M) and the asymmetric VO₂(M)//Ti₃C₂ system highlights their potential as a promising electrode material for the next generation energy storage technologies.