Improving the electrocatalytic activity of Fe, N co-doped biochar for polysulfides conversion by regulation of N-C and Fe-N configurations

Conversion of agricultural residual biomass into biochar as sulfur host materials for Li-S batteries is a promising approach to alleviate green house effect and realize waste resource re-utilization. However, the low electrical conductivity and less electocatalytic sites of pristine biochar hinder its large-scale application. Herein, these challenges are addressed by constructing Fe-N co-doped biochar (Fe-NOPC) through co-pyrolysis of sesame shells and NaFeEDTA. During synthesis process, NaFeEDTA can be used as an extra carbon resource to regulate the chemical environment of N-doped, producing high content of graphitic, pyridinic, pyrrolic N, and Fe-N_x bonds. When the resulted Fe-NOPC is used as a sulfur host, the pyridinic and pyrrolic N can greatly adjust the surface electron structure of biochar for accelerating the electron/ion transport, while electropositive graphitic N can combine with sulfur-related species by electrostatic attraction. Moreover, the Fe-N_x is capable of promoting the redox reaction of LiPSs owing to the strong Li-N and S-Fe binding. Benefiting from these advantages, the resultant Fe-NOPC/S cathode with a sulfur loading of 3.8 mg cm^-2 delivers an areal capacity of 4.45 mAh cm^-2 under 0.1 C, and retains 3.45 mAh cm^-2 at 1 C, holding enormous potential for achieving energy-dense Li-S batteries.