Nitrogen-enriched hierarchical porous carbon with enhanced performance in supercapacitors and lithium–sulfur batteries

Abstract

It is quite desirable but challenging to prepare highly active materials for various energy storage applications at low cost. Here, an efficient strategy to produce nitrogen-enriched hierarchical porous carbon (N-HPC) is reported by facile pyrolysis of magnesium citrate and subsequent NH₃ treatment. As-prepared N-HPC presents a developed hierarchical micro- and trimodal meso-porosity with a high specific surface area of 1290 m² g⁻¹ and pore volume of 3.04 cm³ g⁻¹. It also shows an abundant nitrogen doping of 3.6%. When used for electrochemical electrodes in supercapacitors and lithium–sulfur (Li–S) batteries, significantly enhanced performances have been obtained compared with commercially available activated carbon. In supercapacitor testing, the N-HPC electrode shows a specific capacitance of 101 F g⁻¹ in a nonaqueous electrolyte. And the capacitance retains 67% even at a 200-fold charge/discharge rate. Moreover, its performance in Li–S batteries is more outstanding. It enables a very high sulfur loading (76.2% by weight) and the resulting N-HPC/S cathode shows high discharge capacities of 1153 mA h g⁻¹_sulfur (or 702 mA h g⁻¹_electrode) at 0.2C and 671 mA h g⁻¹ even at 4C. And it still remains 600 mA h g⁻¹ over 300 charge/discharge cycles at 1C with an average coulombic efficiency of 99.0%.