Hierarchical and Nanocrystallite-Assembled Ultraporous NiO/MnCo₂O₄ for All Solid-State Hybrid Supercapacitors with Robust Energy Efficiency and Extended Operational Durability

Abstract

To address the growing demand of highly Ragone efficient electrochemical energy storage devices, we have innovated a synthetic design strategy and employed a tartrate-mediated kinetic precipitation process to fabricate an ultraporous ribbon-like hierarchical microstructure of Ni-, Mn-, and Co-based ternary oxide, i.e., NiO/MnCo 2 O 4 , and employed it as a battery-type positive electrode material to assemble an ASSHSC (all-solid-state hybrid supercapacitor) device with nitrogen-doped reduced graphene oxide (N-rGO) as the positive electrode material. NiO/MnCo 2 O 4 exhibits distinct crystallographic phase, nearperfect elemental stoichiometry, evident bulk porosity, and rich nanocrystallite assembly in the randomly arranged microstructure of near-uniform size and shape. Thorough electrochemical studies corroborate that the battery-type NiO/MnCo 2 O 4 exhibits remarkable electrochemical reversibility during charge transfer, high efficiency in supercapacitive charge storage, low charge transfer, series and diffusion resistance. The NiO/MnCo 2 O 4 ||N-rGO ASSHSC device assembled with the PVA-KOH film as the separator electrolyte offers rich charge storage physiognomies, which accentuates excellent electromicrostructural compatibility between the electrode materials in the device. The NiO/MnCo 2 O 4 ||N-rGO ASSHSC device shows low charge transfer and diffusion resistance, and it also delivers high mass and areal specific capacitance/ capacity, energy and power density, Ragone efficiency (∼131 Wh kg −1 at ∼2134 W kg −1 and ∼31 Wh kg −1 at ∼5005 W kg −1 ), and extended operational durability (98.2% specific capacitance retention after 12,000 successive GCD cycles) under high-rate working conditions. The present optimized approach to design highly efficient multiple transition-metal-based oxides as battery-type electrode materials and fabricate rich Ragone-efficient ASSHSC devices can be widely adopted in the future development of highperformance hybrid supercapacitors, which may be largely integrated in various pioneering technologies.