Free-standing N-self-doped carbon nanofiber aerogels for high-performance all-solid-state supercapacitors

N-self-doped carbon nanofiber (NCNF) aerogels with highly porous, three dimensional (3D) interconnected network and silk cocoon-like node morphology have been fabricated via in situ growth of zeolitic imidazolate frameworks (ZIF8) nanocrystals on bacterial cellulose (BC) in an aqueous system, followed by a dry-freezing process and a subsequent thermal treatment. Benefiting from the unique shape and structural characteristics, the optimized aerogel electrode (NCNF2-900) exhibits remarkable capacitances of ~224 F/g at 0.5 A/g and ~612 mF/cm2 at 1.37 mA/cm2, superior energy density of 31.04 Wh/kg (13.19 Wh/L) at a power density of 250 W/kg, and excellent long-term durability (capacity retention of ~97% after 10 000 cycles at 5 A/g). Further, an all-solid-state symmetric supercapacitor (SSC) constructed from two identical NCNF2-900 aerogel electrodes delivers significantly improved electrochemical performances, ~41.1 F/g at 0.25 A/g (based on total mass of electrodes), ~2.5 F/cm3 at 1.37 mA/cm2, ~5.7 Wh/kg (~0.34 Wh/L) at power density of 125 W/kg, and ~2.5 Wh/kg (0.15 Wh/L) at 1250 W/kg, while maintaining excellent stability (capacitance retention of 91% over 5000 cycles at 2.5 A/g). Moreover, the simple, low-cost, green, and scalable approach for construction of free-standing porous carbon aerogels is applicable to other advanced functional materials for a wide range of applications.