Structural modulation of tin nickelate nanostructures embedded in reduced graphene oxide for high-performance asymmetric supercapacitors

Development of a new, cost-effective, advanced energy storage material <i>via</i> a simple method is a great challenge among researchers. In this study, we have synthesized efficient spinel tin nickelate nano-popcorns, SnNi₂O₄ (SNNPs), <i>via</i> a solvothermal process. Furthermore, to enhance their charge transfer characteristics, SNNPs were impregnated on reduced graphene oxide (rGO) nanosheets through ultrasonication to obtain SnNi₂O₄@rGO (SNNPR). By varying the percentage load ratio of SNNPs and rGO, six different nanocomposites, namely, SNNPR-1, SNNPR-2, SNNPR-3, SNNPR-4, SNNPR-5 and SNNPR-6, were produced. They were thoroughly characterized using spectroscopic and microscopic techniques. The electrochemical analysis of all the SNNP-based electrode materials was performed using cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS). Among these six electrode materials, SNNPR-3 produces a maximum specific capacitance (<i>C</i>_sp) of 225 mA h g^-1 (1624 F g^-1) in a three-electrode assembly at 1 A g^-1 and retains a cycle stability of 94% up to 1000 cycles. Based on the superiority of SNNPR-3, an asymmetric supercapacitor (ASC) was fabricated with SNNPR-3 as the cathode and activated carbon (AC) as the anode (SNNPR-3//AC). Exhibiting a thorough electrochemical performance, the present ASC yielded a specific capacitance, <i>C</i>_sp of 264 F g^-1, high energy density of 62.3 W h kg^-1 and power density of 2600 W kg^-1. The device exhibited 80.02% of retention capacitance even after 5000 cycles. Also, SNNPR-3//AC was able to illuminate a green light emitting diode. Therefore, this asymmetric energy storage device has enormous potential for practical applications in the future.