As an abundant biomaterial, lignin is often used as a low-end material, because it has an inferior formability at normal temperature and a poor solubility in most solvents. In this study, an innovative lignin/cellulose carbon aerogel with a 3D hierarchical network structure composed of nanochains connecting nanospheres is successfully synthesized by dissolving cellulose and lignin in 1-butyl-3-methylimidazolium chloride, regenerating in deionized water, freeze-drying, and carbonizing. Cellulose, as the adhesive connects lignin by hydrogen bonds, increases the specific surface area and improves the graphitization degree. Consequently, the sample with 10 wt % cellulose (C-10) has a high specific capacitance (166 F g À 1 at 0.1 A g À 1 ), low impedance (τ = 5.56 ms), and excellent capacitance retention (98.6 % after 1000 cycles). The C-10-based flexible supercapacitor exhibits a stable output capability (� 99 %) at different bending angles, long cycle life (� 1000 cycles), and high energy density (102 Wh kg À 1 at 175 W kg À 1 ).[a] T.