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

Abstract 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.