Upcycling of electroplating sludge into Fe3C-decorated N,P dual-doped porous carbon via microalgae as efficient sulfur host for lithium–sulfur batteries

Abstract

Some crystal planes of metal compound nanocrystals play an important role in the anchoring and transformation of lithium polysulfide (LiPSs), which effectively improves the shuttle effect and electrochemical reaction kinetics of LiPSs. While, as a new generation of secondary batteries with great potential, the commercial applications of Li-S batteries are limited by rapid capacity decay due to the shuttle effect of LiPSs and large volume change of sulfur. Herein, nano-Fe3C@N,P dual-doped porous carbon microspheres (Fe3C@NPC) were designed as cathode hosts of Li-S batteries. Fe3C@NPC composite materials were prepared by upcycling mental from electroplating sludge via microalgae. The adsorption transformation of microalgae enables Fe3C nanocrystals of 10–30 nm to be evenly embedded in the N and P dual-doped carbon materials, which makes the crystal planes (220) of Fe3C nanocrystals more involved in the reaction, thus improving the coulomb efficiency and long cycle stability of Li-S battery. Besides, the hierarchically porous spherical structure with high specific surface area not only effectively adapts to the change of sulfur volume during the charging/discharging process, but also significantly increases the electrolyte contact area and shortens the Li ion transport distance. Therefore, Fe3C@NPC, as the multifunctional hosts of sulfur for Li-S batteries, realizes high catalytic activity and strong chemical binding with LiPSs, providing a high reversible coulomb efficiency (> 99%) and a high reversible capacity of 575 mAh g−1 at 1 C after 500 cycles, with low-capacity decay rates of 0.056% per cycle.