Balancing the gravimetric and volumetric capacitance of nitrogen-enriched lignin porous carbon for high performance supercapacitors

Carbon-based supercapacitors are prospective candidates for next-generation energy storage systems. However, there remains challenges in the development of high volumetric capacitance carbon electrodes. Herein, nitrogen -enriched lignin-derived porous carbons (NLSCs) were fabricated by co-pyrolysis of sodium lignosulfonate with zinc oxalate and melamine via an efficient nitrogen doping strategy. The in-situ generation of zinc cyanamide (ZnNCN) achieves a high nitrogen conversion rate of 13.5 %, much higher than that of ZnCl2 activation (1.9 %), and endows the optimized NLSC-800 an extremely high nitrogen doping (14.47 at.%), abundant edged nitrogen species, and a high bulk density (1.26 g cm-3), contributing to substantially improved surface property and boosting pseudocapacitance. Consequently, the NLSC-800 supercapacitor electrode delivered a high gravimetric capacitance of 300 F g-1 and superior volumetric capacitance of 378 F cm-3. More remarkably, the symmetric supercapacitor assembled by NLSC-800 performs an exceptional volumetric energy density of 5.1 Wh L-1 at 173.0 W L-1. The capacitance retention rate is 97.6 % over 20,000 charge/discharge cycles at 2.0 A g-1, exhibiting outstanding cycling stability. This strategy suggests a novel route for fabricating nitrogen-doped biomass-derived carbon for supercapacitors with balanced the gravimetric and volumetric capacitance.