Design and characterization of multiscale cellulosic composites for thick electrodes for electrochemical capacitors

To address the high charge density of pseudocapacitive cathodes in aqueous asymmetric capacitors, the development of thick, high-performance carbon anodes is essential. Herein, porous carbons were synthesized via pyrolysis and KOH activation of multiscale cellulosic composites composed of microcrystalline cellulose (MCC) and cellulose nanocrystals (CNC). This approach set out to assess whether the incorporation of nanoscale CNCs within larger MCC particle structures could induce a hierarchical pore network, thereby minimizing ionic resistance and sustaining a consistent gravimetric capacitance with increasing electrode thickness. The effects of activation temperature (800–1000 °C), composite ratio (MCC:CNC = 9:1, 8:2, and 7:3), and electrode thickness (100–500 μm) were systematically investigated. The optimized carbon exhibited a specific surface area exceeding 1800 m 2 g −1 , with predominant pore sizes between 0.5 and 4 nm. In a Swagelok-type cell, the CCM-9:1-1000 sample with 250 μm electrodes delivered a gravimetric capacitance of ∼112 F/g at 1 A g −1 in 6 M KOH. • Composite carbon electrodes from microcrystalline cellulose and cellulose nanocrystals. • Activation temperature was more important for performance than cellulose composition. • A stable gravimetric capacitance was obtained for varying electrode thicknesses for all materials. • It is possible to create thick carbon electrodes with a stable gravimetric capacitance.