Wood‐Derived High‐Mass‐Loading MnO2 Composite Carbon Electrode Enabling High Energy Density and High‐Rate Supercapacitor

The simple design of a high-energy-density device with high-mass-loading electrode has attracted much attention but is challenging. Manganese oxide (MnO₂ ) with its low cost and excellent electrochemical performance shows high potential for practical application in this regard. Hence, the high-mass-loading of the MnO₂ electrode with wood-derived carbon (WC) as the current collector is reported through a convenient hydrothermal reaction for high-energy-density devices. Benefiting from the high-mass-loading of the MnO₂ electrode (WC@MnO₂ -20, ≈14.1 mg cm^-2 ) and abundant active sites on the surface of the WC hierarchically porous structure, the WC@MnO₂ -20 electrode shows remarkable high-rate performance of areal/specific capacitance ≈1.56 F cm^-2 /45 F g^-1 , compared to the WC electrode even at the high density of 20 mA cm^-2 . Furthermore, the obtained symmetric supercapacitor exhibits high areal/specific capacitances of 3.62 F cm^-2 and 87 F g^-1 at 1.0 mA cm^-2 and high energy densities of 0.502 mWh cm^-2 /12.2 Wh kg^-1 with capacitance retention of 75.2% after 10 000 long-term cycles at 20 mA cm^-2 . This result sheds light on a feasible design strategy for high-energy-density supercapacitors with the appropriate mass loading of active materials and low-tortuosity structural design while also encouraging further investigation into electrochemical storage.