Interface Engineering on Cellulose‐Based Flexible Electrode Enables High Mass Loading Wearable Supercapacitor with Ultrahigh Capacitance and Energy Density

For practical energy storage devices, a bottleneck is to retain decent integrated performances while increasing the mass loading of active materials to the commercial level, which highlights an urgent need for novel electrode structure design strategies. Here, an active nitrogen-doped carbon interface with "high conductivity, high porosity, and high electrolyte affinity" on a flexible cellulose electrode surface is engineered to accommodate 1D active materials. The high conductivity of interface favors fast electron transport, while its high porosity and high electrolyte affinity properties benefit ion migration. As a result, the flexible anode accommodated by carbon nanotubes achieves an ultrahigh capacitance of 9501 mF cm^-2 (315.6 F g^-1 ) at a high mass loading of 30.1 mg cm^-2 , and the flexible cathode accommodated by polypyrrole nanotubes realizes a remarkably high capacitance of 6212 mF cm^-2 (248 F g^-1 , 25 mg cm^-2 ). The assembled flexible quasi-solid-state asymmetric supercapacitor delivers a maximum energy density of 1.42 mWh cm^-2 (2.2 V, 2105 mF cm^-2 ), representing the highest value among all reported flexible supercapacitors. This versatile design concept provides a new way to prepare high performance flexible energy storage devices.