Bendable and flexible supercapacitor based on polypyrrole-coated bacterial cellulose core-shell composite network

We report a bendable and flexible supercapacitor based on polypyrrole-coated core-shell bacterial cellulose composite networks. As an initial step, gel-type bacterial cellulose was transformed into individually ultrathin bacterial cellulose nanofibers (TOBC) with diameters of 3-5 nm, by using 2,2,6,6-tetramethylpylperidine-l-oxyl radical (TEMPO)-mediated oxidation and successive mild disintegration in water. And, PPy-TOBC core-shell nanofiber network electrodes were synthesized in situ by oxidative polymerization of pyrrole with iron (III) chloride on the TOBC nanofibers in aqueous medium. The PPy-TOBC core-shell nanofiber network electrode exhibited a high porosity (101 m²/g) and high conductivity (~6.63 S/cm) due to the homogenous coating of PPy nanoparticles on the TOBC nanofiber network. The as-prepared PPy-TOBC supercapacitor cell, fabricated with PVDF-EMIMBF₄ (1-Ethyl-3-methylimidazolium tetrafluoroborate) polymer electrolyte, showed a specific capacitance of 153 F/g and energy density of 21.22 Wh/kg at the current density of 0.2 A/g. Moreover, the PPy-TOBC supercapacitor exhibited an exceptionally good cyclic stability with ~93% capacitance retention after 100 cycles; it also showed good bending stability due to the mechanical failure tolerance of the nanofiber-networked electrodes. The present approach is a versatile, inexpensive, and promising way to develop the cellulose-based nanofiber network electrodes for practical energy storage applications.