Boosting energy density for Zn-ion hybrid capacitors by engineering chitin-derived carbon in molten salt

Zn-ion hybrid capacitors (ZIHCs) have been deemed a promising candidate for energy storage equipment to overcome the primary drawback of supercapacitors—low energy density. Herein, inspired by the laminated structure of chitin fibrils, molten salt strategy is proposed to engineer functional carbon as cathode material for ZIHCs, for the first time. Orthogonal design was adopted to ascertain the optimum synthetic conditions for the chitin-derived NaCl-templated and NaNO 3 -activated carbons (CNNs). The resultant C2NN1-800-1-5 possesses high surface area of 1256 m 2  g −1 and rich surface heteroatom content of 11.3 at%, as well as numerous thin intertwined nanofibre bundles. Associated with the synergy of surface capacitive reaction and diffusion battery behavior, the Zn//ZnSO 4 ( aq , 2 M)//C2NN1-800-1-5 ZIHC can be conducted in a relatively broad potential window ranging from 0 to 1.8 V and manifests remarkable energy density of 133.4 Wh kg −1 at 180 W kg −1 . Moreover, charge/discharge cycling further revealed that this device can retain 100% of its initial capacity, together with almost 100% coulombic efficiency after 10,000 cycles at 6 A g −1 . The study emphasizes the green synthesis of heteroatom-doped hierarchical porous carbon cathode material, notably facilitating the rapidly increasing popularity of Zn-ion hybrid energy storage devices.