Liner Nanostructure of Metal Boride as a Cathode Material for High-Performance and Flexible Solid-State Asymmetric Hybrid Battery Supercapacitors

The development of a high-performance solid-state asymmetric hybrid flexible supercapacitor device with high capacitance, rate capability, high energy density, and flexible stability remains challenging. Herein, cobalt metal-free crystalline NiCuB alloy particles with nanowire-type morphology are developed by a new synthesis process for this sustainable development. The optimized composition Ni0.6Cu0.4B is found to have the maximum synergy effect among the metals and the metalloid. A three-electrode charge storage study shows a specific capacitance of 1621 F g–1 at 5.6 A g–1 for this material along with high rate capability and energy efficiency. A highly flexible all-solid-state asymmetric hybrid supercapacitor (HSC) device is fabricated by using this Ni0.6Cu0.4B as the positive electrode, α-Fe2O3/g-C3N4 as the negative electrode, and KOH-PVA gel as the solid electrolyte. The hybrid flexible device offered a maximum capacitance of 325 F g–1 at 6.2 A g–1 applied current density. The charge storage characteristics remain consistent when the engineered HSC device is bent at 60, 90, 135, and 170°. The device can maintain 93% Coulombic efficiency at 15,000 measured charge–discharge cycles after bending at angle ≤150° over 1000 bending cycles. The HSC device delivers a high energy density of 57.8 Wh kg–1 and a power density of 16,380 W kg–1. A diffusion-controlled charge-storage mechanism is predominant, along with a high diffusion coefficient of electrolytes and a suitable pore size distribution.