Multi-channel cellular carbon fiber as electrode for Zn-ion hybrid capacitor with enhanced capacity and energy density

Zn-ion hybrid capacitors (ZICs) recently receive an extensive attention owning to their theoretical energy density as well as high safety. Hollow porous carbon fibers (HPCF) are used as a promising cathode for ZICs due to abundant active sites. However, it is hard to deal with the “trade-off” between defect design and graphitic degree in HPCF electrode. In this work, hollow porous carbon fiber (HPCF) cathodes are prepared via a spinning-co-foaming technique, followed by zinc oxide nanoparticles as template and activation process. The aligned channels and hierarchical cavities in HPCF wall provide a high-speed diffusion path for electrolyte penetration via capillary force. Meanwhile, due to higher exposed surface area and metal-catalytic effect of reduce zinc during pyrolysis, self-standing ZHPCF-5 exhibits a good graphitic degree (ID/IG = 0.84). Its high electrical conductivity (158.3 S m−1) provides fast electron transport. The optimized ZHPCF-5 cathode displays a capacity of 220 mAh g−1 at 0.2 A g−1 and an energy density of 224 Wh kg−1 at a 14400 W kg−1 of power density. The assembled quasi-solid-state self-standing ZIC exhibits a high capacity (153.5 mAh g−1 at 0.5 A g−1). This work finds a way to simultaneously maintain abundant defects and high electric conductivity in self-standing carbon electrode for boosting Zn2+ storage.