High Performance, Flexible, Solid-State Supercapacitors Based on a Renewable and Biodegradable Mesoporous Cellulose Membrane

A flexible, transparent, and renewable mesoporous cellulose membrane (mCel-membrane) featuring uniform mesopores of ≈24.7 nm and high porosity of 71.78% is prepared via a facile and scalable solution-phase inversion process. KOH-saturated mCel-membrane as a polymer electrolyte demonstrates a high electrolyte retention of 451.2 wt%, a high ionic conductivity of 0.325 S cm−1, and excellent mechanical flexibility and robustness. A solid-state electric double layer capacitor (EDLC) using activated carbon as electrodes, the KOH-saturated mCel-membrane as a polymer electrolyte exhibits a high capacitance of 110 F g−1 at 1.0 A g−1, and long cycling life of 10 000 cycles with 84.7% capacitance retention. Moreover, a highly integrated planar-type micro-supercapacitor (MSC) can be facilely fabricated by directly depositing the electrode materials on the mCel-membrane-based polymer electrolyte without using complicated devices. The resulting MSC exhibits a high areal capacitance of 153.34 mF cm−2 and volumetric capacitance of 191.66 F cm−3 at 10 mV s−1, representing one of the highest values among all carbon-based MSC devices. These findings suggest that the developed renewable, flexible, mesoporous cellulose membrane holds great promise in the practical applications of flexible, solid-state, portable energy storage devices that are not limited to supercapacitors.