Nitrate Salt Assisted Fabrication of Highly N-Doped Carbons for High-Performance Sodium Ion Capacitors

Hybrid sodium ion capacitors have been considered promising energy storage devices with superior energy and power performances by combining the advantages of batteries and supercapacitors. However, it is desirable to design anode materials with large specific capacity and excellent rate performance. Herein, we provide a large-scalable process to create the highly N-doped carbons by employing k-carrageenan as precursor and alkali metal nitrate as activating agent and dopant. Remarkably, the nitrate salt assisted synthesis process leads to a high nitrogen content of 8.6–12.6 at. % in the carbon framework. When applied as an anode for a sodium ion battery, the carbon delivers a high reversible capacity of 419 mA h g–1 at 50 mA g–1. The kinetics analysis manifests that the capacity contribution is mainly from capacitive storage, resulting in an excellent rate performance, e.g., 131 mA h g–1 at 10 A g–1. Benefiting from the rational design of the carbon anode, the optimized sodium ion capacitor exhibits a large energy density of 110.8 W h kg–1 and retains 85% of its initial capacity after 10 000 cycles. This work provides an effective way to fabricate highly N-doped carbons for advanced energy storage devices.