Self-supporting electrode engineering design with composite conductive network for asymmetric MnO2//AC supercapacitor

The development of high areal capacitance effective electrodes is crucial and challenging for practical applications of supercapacitors. In this study, we introduce a self-supporting composite conductive network that can replace metal conductive substrates such as nickel foam with lighter cellulose materials, significantly reducing device weight and enhancing practicality. Firstly, two different morphologies of MnO2 (MnO2@CFCB) were grown on carbon fibers and carbon black via a simple hydrothermal method. Subsequently, a self-supporting conductive-enhanced anode (MnO2@CFCBSC) was constructed using cotton fibers and CB conductive slurry. Furthermore, the addition of redox-active electrolyte (ammonium iron citrate, AFC) in neutral Na2SO4 electrolyte further increases the capacitance. Electrochemical performance tests of asymmetric supercapacitors (ASC) show that when the unit area mass loading of MnO2@CFCBSC electrode is 3.5–4.0 mg and combined with redox-active electrolyte, the resulting ASC (MnO2@CFCBSCA) exhibits excellent specific capacitance (1.3 F/cm2 at a current density of 2.3 mA/cm2), outstanding rate capability (0.9 F/cm2 at a current density of 7.6 mA/cm2), and remarkable cyclic stability (retaining 80.8% of initial capacity after 10,000 cycles at 1.3 A/g). Moreover, at a mass power density of 500 W/kg, operating potential of 2.0 V, mass energy density of 38.6 Wh/kg; at an areal power density of 9.1 W/cm2, areal energy density of 0.7 mWh/cm2. The unit area capacitance of a 7-layer stacked electrode material device reaches 4.9 F/cm2 at a current density of 12.1 mA/cm2. This study proposes a new strategy to advance ASC.