Binder-Free\nCore–Shell Zinc Cobalt Layered\nDouble Hydroxide@NiCo<sub>2</sub>O<sub>4</sub> Flexible Composite\nElectrodes for High-Performance Supercapacitors

Synthesis of composite electrode materials intended for\nhigh-performance\nsupercapacitor (SC) applications has attracted the attention of researchers\ndue to their highly porous nature, enhanced electrochemical performance,\nand longer cycle life than their respective pristine components. With\nthis motivation, in this study, a binder-free core–shell zinc\ncobalt layered double hydroxide@NiCo<sub>2</sub>O<sub>4</sub> thin\nfilm composite electrode on a flexible stainless steel mesh (ZnCo-LDH@NiCo<sub>2</sub>O<sub>4</sub>/FSSM) was synthesized by a two-step facile and\nsimple reflux-condensation-mediated method for SC application. The\nZnCo-LDH@NiCo<sub>2</sub>O<sub>4</sub> composite electrode with a\nNiCo<sub>2</sub>O<sub>4</sub> nanosheet core structure and a ZnCo-LDH\nnanoflake as a shell layer exhibited a higher specific surface area\n(122.04 m<sup>2</sup> g<sup>–1</sup>) with enhanced porous\nnature than the pristine ZnCo-LDH (67.4 m<sup>2</sup> g<sup>–1</sup>) and NiCo<sub>2</sub>O<sub>4</sub> (50.76 m<sup>2</sup> g<sup>–1</sup>) components. The ZnCo-LDH@NiCo<sub>2</sub>O<sub>4</sub>/FSSM delivered\na specific capacitance (<i>C</i><sub>sp</sub>) of 2378.0\nF g<sup>–1</sup> at a current density (CD) of 6 mA cm<sup>–2</sup> and maintained <i>C</i><sub>sp</sub> retention of 99%\nafter 2000 cycles at a high CD of 40 mA cm<sup>–2</sup>. Moreover,\nthe device (ZnCo-LDH@NiCo<sub>2</sub>O<sub>4</sub>/FSSM//AC/FSSM)\nassembled by using ZnCo-LDH@NiCo<sub>2</sub>O<sub>4</sub>/FSSM (+ve\nelectrode) and activated carbon (AC/FSSM, −ve electrode) exhibited\nan energy density of 33.3 Wh kg<sup>–1</sup> at a power density\nof 1109.5 W kg<sup>–1</sup> and maintained an appreciable <i>C</i><sub>sp</sub> retention of 91.7% after 4000 cycles at a\nhigher CD (25 mA cm<sup>–2</sup>). These findings signify that\nthe ZnCo-LDH@NiCo<sub>2</sub>O<sub>4</sub>/FSSM composite electrode\nis a promising electrode material and will help open avenues for in\nfurther exploration of electrode material synthesis for SC applications.