A novel three-dimensional ordered mesoporous microspheres comprising N-doped graphitic carbon-coated FexP nanoparticles as multifunctional interlayers to suppress polysulfide crossover in Li–S batteries

Abstract

Highly porous and conductive microspheres comprising three-dimensionally ordered arrays of mesopores and biphasic iron phosphide (FexP) nanoparticles embedded into nitrogen-doped graphitic carbon (NGC) framework (P-FexP@NGC) were synthesized by spray pyrolysis method followed by phosphidation. The ordered arrays of mesopores (ϕ = 40 nm) were generated via the thermal breakdown of the polystyrene nanobeads (ϕ = 100 nm). The porous structure not only reduces the effective diffusion length for the charged species but also guarantees efficient electrode wetting along with the accommodation of undesired volume perturbations. The highly conductive NGC framework provides numerous conductive paths for rapid electron transfer, which facilitates kinetically favored redox reactions. Additionally, the polar biphasic FexP nanoparticles allow chemical confinement and catalytic conversion of trapped polysulfides, thus enhancing active material utilization. Correspondingly, the assembled Li–S cells featuring the P-FexP@NGC-coated separator exhibit good rate performance (350 mA h g−1 at 2.0C) and extended cycling stability at 0.1, 0.5, and 1.0C mainly due to high diffusion of charged species (diffusion coefficient (DLi+) = 10−7 cm2 s−1) and low charge transfer resistance. Even at high sulfur loading (3.46 mg cm−2) and a low electrolyte/sulfur ratio of 5.6 µL mg−1, the Li−S cells exhibit stable cycling performance.