Designing energy storage devices from thick carbon electrodes with high areal/volumetric energy density via a simple and green way is very attractive but still challenging. Cellulose, as an excellent precursor for thick carbon electrodes with abundant sources and low cost, is usually activated by a chemical activator and pyrolysis route to achieve high electrochemical performance. However, there are still some problems to be addressed, such as the harsh activation conditions, easy collapse of porous structures, and the high cost. Herein, a 3D self‐supporting thick carbon electrode derived from wood‐based cellulose is proposed for high areal and volumetric energy density of supercapacitor from a mild, simple, and green enzymolysis treatment. Benefiting from the high specific surface area (1418 m2 g−1) and abundant active sites on the surface of wood‐derived hierarchically porous structures and enzymolysis‐induced micropores and mesopores, the assembled symmetry supercapacitor from the thick carbon electrode can realize the high areal/volumetric energy density of 0.21 mWh cm−2/0.99 mWh cm−3 with excellent stability of 86.58% after 15 000 long‐term cycles at 20 mA cm−2. Significantly, the simple and universal strategy to design material with high specific surface area, provides a new research idea for realizing multi‐functional application.

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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.

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