Designed construction of yolk–shell structured trimanganese tetraoxide nanospheres via polar solvent-assisted etching and biomass-derived activated porous carbon materials for high-performance asymmetric supercapacitors

Abstract

Recently, yolk–shell structured electrode materials have attracted increasing interest in supercapacitors (SCs) due to their high surface area, good electrochemical activity and excellent mechanical stability towards superior energy storage performance. However, the synthesis strategies to prepare such yolk–shell structured materials without using chemical surfactants/solid templates are still inferior. Herein, a facile and cost-effective strategy to design yolk–shell structured trimanganese tetraoxide nanospheres (Mn₃O₄ NSs) with a distinctive core–void–shell configuration to use as an efficient positive electrode material in asymmetric SCs is demonstrated. Specifically, the yolk–shell structured Mn₃O₄ NSs were prepared by the inclusion of water droplets to the manganese precursor–isopropyl alcohol system, which facilitates the inside-out Ostwald ripening process to construct a yolk–shell-like configuration with porous properties. In aqueous electrolyte solution, the corresponding material exhibited a high specific capacitance (211.36 F g⁻¹ at a current density of 0.5 A g⁻¹), a good rate capability (79.4% at 10 A g⁻¹) and an excellent cycling stability (92% after 2000 cycles) compared to its solid counterparts. Meanwhile, a low-cost material based on biomass-derived activated carbon with a honeycomb-like structure is also prepared using waste corrugated boxes, which exhibits a reliable electrochemical performance for use as a negative electrode material. Moreover, the fabricated asymmetric SC using both electrode materials offers a maximum potential window of 2 V with higher energy density (19.47 W h kg⁻¹) and power density (2263.89 W kg⁻¹) values, which can effectively power up commercial light-emitting diodes for practical applications.