ZnNi₂O₄/WS₂ Nanoflake-Based Electrodes for Quasi-Solid-State Asymmetric Supercapacitors

The spinel compounds are a class of intriguing electrode materials for redox-based supercapacitors owing to their high specific capacity and variable redox sites, but they are constrained by cyclic instability and an inadequate rate capability. The integration of suitable two-dimensional (2D) electrode nanomaterials with spinel compounds not only facilitates an effective charge transfer but also introduces more redox active sites, presenting significant electrochemical performance. Herein, a 0D/2D ZnNi2O4/WS2 (WZNO) hybrid nanostructure has been developed where WS2 nanoflakes (WNFS) act as a supportive matrix, allowing effective dispersion of ZnNi2O4 nanoparticles (ZNO) over its surface and thereby exposing numerous electrochemically active sites. The developed flexible electrode shows remarkable faradaic redox phenomena, exhibiting significant specific capacitance (184.8 F/g), impressive cyclic stability (38.5 ± 0.03%), and coulombic efficiency (94.7 ± 0.004%) up to 10,000 cycles. The ab initio calculations have demonstrated synergistic coupling between the constituents of the metallic ZnNi2O4/WS2 hybrid nanostructure, via interfacial charge transport, elucidating its significant electrochemical properties. The asymmetric supercapacitor exhibits superior specific capacitance (171.3 F/g), showcasing remarkable energy (61.6 W h/kg) and power density (1236.5 W/kg). Conversely, the quasi-solid-state supercapacitor demonstrates significant power (20.4 W h/kg) and energy density (921.2 W/kg) with impressive capacitance retention (97.2 ± 0.03%). The fabricated devices can illuminate different-colored LEDs, along with a fully operational clock and calculator, highlighting their significant potential as electrode materials in storage applications.