Nitrogen and Sulfur Codoped Hierarchical Porous Carbon Derived from Lignin for High-Performance Zinc Ion Capacitors

Aselectrode materials for zinc ion capacitors (ZICs), porous carbonsare an important factor affecting the electrochemical behavior ofZICs. Heteroatom doping is an efficient approach to adjust the porestructure, regulate the electronic structure, increase the surfacewettability, and provide pseudo capacitance. In this work, hierarchicalporous N/S codoped activated carbon (N/S-AC) materials were preparedfrom lignin using urea and thiourea as the dopants. The preparationprocess consisted of first step charring and second step activationwith codoping to yield N/S-AC, which exhibited hierarchical pore structure,suitable for providing abundant active sites. The use of N/S-AC ascathode materials for ZIC delivered an outstanding specific capacitanceof 307 F g(-1) at 1 A g(-1) and aremarkable capacity retention of 99.72% after 20,000 cycles at 10A g(-1). The device also exhibited a high energy densityof 108.8 Wh kg(-1) at 2880 W kg(-1) and 65.8 Wh kg(-1) at 115200 W kg(-1). The excellent electrochemical properties were attributed to thesynergistic effect of nitrogen and sulfur elements, and hierarchicalporous structure. In sum, these findings are promising for developmentof ZIC electrode materials with high energy density.