Carbon microspheres with embedded FeP nanoparticles as a cathode electrocatalyst in Li-S batteries

Abstract This study reports a composite of FeP nanoparticles embedded in gradient-porous carbon microspheres (PCM) as a high-efficiency cathode electrocatalyst with simultaneous sulfur immobilization and redox promotion for improved high-rate capability and cycling stability in Li-S batteries. The PCM possesses micro-, meso- and macropores that provide effective adsorption of polysulfides and accommodation of volume-expanded Li2S as indicated by post-discharge SEM examinations. The embedment of FeP nanoparticles within the PCM ensures maximized exposure of catalytic sites and their improved interactions with sulfur redox species under the confinement effect of carbon nanopores. Compared with Fe3O4, which shows a stronger polysulfide binding strength, FeP offers a balance between effective polysulfide trapping and elevated conversion kinetics for the subsequent liquid-solid transitions. Significantly improved sulfur utilizations and confinement are obtained for Li2S deposition and decomposition, which are regarded as the rate- and capacity-limiting steps during charge/discharge. Detailed working mechanisms are revealed by electrochemical measurements and density functional theory calculations. PCM/FeP enables outstanding high-rate capability up to 4 C and Li-S pouch cells with high areal (8.6 mAh cm-2) and total (414 mAh) capacities are also demonstrated. This study provides new opportunities for the design of high-performance Li-S electrocatalysts.