Deep eutectic salt-engineered pyridinic-nitrogen dominated mesoporous carbon for boosting Zn-ion storage capability

Carbon-based aqueous zinc ion capacitors (CZICs) have emerged as promising candidate in the energy storage field owing to their long cycle life, low environmental hazard and cost. However, they are restricted by inferior energy density. Thus, it is vital to construct carbon cathodes with rich active sites to enhance the absorption capacity for zinc ions. Here, the porous carbon with rich pyridinic nitrogen (NPC) has been fabricated from coal tar pitch via a deep eutectic salt-assisted pyrolysis strategy. The optimal NPC displays a large specific surface area (1765 m 2  g −1 ), high nitrogen content (4.4 at.%) and rich in pyridinic nitrogen (52 %). Furthermore, the micropores and mesopores of NPC are mainly centered at pore size of 0.93 nm and 2.34 nm, respectively. Due to above structural features, the optimal NPC cathode affords a high specific capacitance (423.4 F g −1 at 0.2 A g −1 ) and robust rate capability (222.8 F g −1 at 40.0 A g −1 ). Impressively, the CZIC assembled by NPC achieves superior energy density of 150.6 Wh kg −1 and power density of 32,000 W kg −1. Furthermore, the quasi-solid-state CZIC based on NPC offers excellent flexibility and high capacitance (292.1 F g −1 ), superb energy density (103.8 Wh kg −1 ) and outstanding cyclic stability (84.4 % retention after 8000 cycles). This strategy supplies a facile method to prepare porous carbon with rich pyridinic‑nitrogen for boosting Zn-ion storage capability.