Flexible quasi-solid-state supercapacitors for anti-freezing power sources based on polypyrrole@cation-grafted bacterial cellulose

Polypyrrole (PPy)/cellulose nanofiber (CNF) composites have been widely used in flexible energy storage devices because of their lightweight, inherent mechanical flexibility and large specific surface area. However, it is still a challenge to obtain PPy/CNF composite electrodes with high cycling stability. Herein, an electrostatic self-assembly strategy was adopted to deposit anion-doped PPy onto cationic poly(methacryloxyethyltrimethyl ammonium chloride)-grafted bacterial cellulose (BCD) nanofibers. The optimized PPy@BCD electrode demonstrated a high areal capacitance of 6208 mF cm^-2 at a current density of 0.5 mA cm^-2 and superior cycling stability (a capacitance retention of 100 % after 10,000 charge-discharge cycles at 10 mA cm^-2). A quasi-solid-state anti-freezing flexible supercapacitor (AF-FSC) was designed by employing polyacrylamide organohydrogel electrolyte, yielding an areal capacitance of 2930.6 mF cm^-2 at 1 mA cm^-2 and a capacitance retention of 92.2 % after 1000 cycles at -20 °C. The present AF-FSC is expected to serve as a power source in real-life low-temperature applications.