Confining Sulfur in N-Doped Porous Carbon Microspheres Derived from Microalgaes for Advanced Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) battery is one of the most attractive candidates for the next-generation energy storage system. However, the intrinsic insulating nature of sulfur and the notorious polysulfide shuttle are the major obstacles, which hinder the commercial application of Li-S battery. Confining sulfur into conductive porous carbon matrices with designed polarized surfaces is regarded as a promising and effective strategy to overcome above issues. Herein, we propose to use microalgaes (Schizochytrium sp.) as low-cost, renewable carbon/nitrogen precursors and biological templates to synthesize N-doped porous carbon microspheres (NPCMs). These rational designed NPCMs can not only render the sulfur-loaded NPCMs (NPCSMs) composites with high electronic conductivity and sulfur content, but also greatly suppress the diffusion of polysulfides by strongly physical and chemical adsorptions. As a result, NPCSMs cathode demonstrates a superior reversible capacity (1030.7 mA h g^-1) and remarkable capacity retention (91%) at 0.1 A g^-1 after 100 cycles. Even at an extremely high current density of 5 A g^-1, NPCSMs still can deliver a satisfactory discharge capacity of 692.3 mAh g^-1. This work reveals a sustainable and effective biosynthetic strategy to fabricate N-doped porous carbon matrices for high performance sulfur cathode in Li-S battery, as well as offers a fascinating possibility to rationally design and synthesize novel carbon-based composites.