Binder-Free Core–Shell Zinc Cobalt Layered Double Hydroxide@NiCo2O4 Flexible Composite Electrodes for High-Performance Supercapacitors

Abstract

Synthesis of composite electrode materials intended for high-performance supercapacitor (SC) applications has attracted the attention of researchers due to their highly porous nature, enhanced electrochemical performance, and longer cycle life than their respective pristine components. With this motivation, in this study, a binder-free core–shell zinc cobalt layered double hydroxide@NiCo₂O₄ thin film composite electrode on a flexible stainless steel mesh (ZnCo-LDH@NiCo₂O₄/FSSM) was synthesized by a two-step facile and simple reflux-condensation-mediated method for SC application. The ZnCo-LDH@NiCo₂O₄ composite electrode with a NiCo₂O₄ nanosheet core structure and a ZnCo-LDH nanoflake as a shell layer exhibited a higher specific surface area (122.04 m² g^–1) with enhanced porous nature than the pristine ZnCo-LDH (67.4 m² g^–1) and NiCo₂O₄ (50.76 m² g^–1) components. The ZnCo-LDH@NiCo₂O₄/FSSM delivered a specific capacitance (C_sp) of 2378.0 F g^–1 at a current density (CD) of 6 mA cm^–2 and maintained C_sp retention of 99% after 2000 cycles at a high CD of 40 mA cm^–2. Moreover, the device (ZnCo-LDH@NiCo₂O₄/FSSM//AC/FSSM) assembled by using ZnCo-LDH@NiCo₂O₄/FSSM (+ve electrode) and activated carbon (AC/FSSM, −ve electrode) exhibited an energy density of 33.3 Wh kg^–1 at a power density of 1109.5 W kg^–1 and maintained an appreciable C_sp retention of 91.7% after 4000 cycles at a higher CD (25 mA cm^–2). These findings signify that the ZnCo-LDH@NiCo₂O₄/FSSM composite electrode is a promising electrode material and will help open avenues for in further exploration of electrode material synthesis for SC applications.