High-Performance 2.2 V Asymmetric Supercapacitors Achieved by Appropriate Charge Matching between Ultrahigh Mass-Loading Mn₃O₄ and Sodium-Jarosite Derived FeOOH

For the advancement of high-energy asymmetric supercapacitors, the breakthrough point is matching charge storage capacity and balanced electrode kinetics between the positive and negative electrodes. Herein, Mn₃O₄ nanosheets composed of nanoparticles are anchored on activated carbon cloth (ACC) as the positive electrode by electrodeposition. FeOOH nanoparticles derived from NaFe₃(SO₄)₂(OH)₆ truncated cubes serve as the negative electrode. Due to the unique sheet-like network structure, ultrahigh mass-loading (73.3 mg cm⁻²), and enhanced kinetics, the Mn₃O₄@ACC electrode exhibits an ultrahigh specific capacitance of 12.77 F cm⁻². Besides, the FeOOH@ACC electrode with a low-crystalline structure also exhibits a maximum specific capacitance of 17.84 F cm⁻². The Na⁺ diffusion process, the charge storage mechanism, and the electrochemical reaction kinetics of the Mn₃O₄@ACC are investigated by ex situ characterization. Theoretical calculations show that Mn₃O₄ has metallic electronic conductivity and reveal the adsorption and diffusion mechanism of Na ions during the electrode process. The assembled aqueous Mn₃O₄//FeOOH asymmetric supercapacitor device successfully extends the operating voltage to 2.2 V and exhibits a high energy density of 3.75 mWh cm⁻² and ultra-long cycle life (81.6% capacity retention after 26,000 cycles). Therefore, this study provides a feasible pathway for the further development of asymmetric supercapacitors with high energy density. © 2024 Wiley-VCH GmbH.