Joule Heating-Assisted Synthesis of CoP-Loaded Carbons with Developed Porosity and Surface Phosphorous Functionality as Cathode Materials for Lithium–Sulfur Batteries

Given the confining effect of porous carbon and strong surface polarity of transition metal phosphides, their composite would be a promising cathode candidate to solve the problems of lithium–sulfur batteries including volume expansion and the shuttling effect of polysulfides. Herein, cobalt phosphide (CoP)-loaded phosphorous (P)-containing carbonized bamboo (CoP/PCBs) composites were fabricated via the co-pyrolysis of phytic acid, waste bamboo and Co(NO3)2·6H2O via Joule heating at 600–1200 °C. Hydrogen radicals released from phytic acid enabled CoP/PCBs with developed porosity (438.1–812.4 m2/g). CoP nanoparticles coated with graphitic carbon were distributed uniformly on a porous matrix of PCBs. CoP/PCBs presented obviously enhanced adsorption capabilities for Li2S6, and 57.8–80.4 wt.% of sulfur was confined in CoP/PCBs/S cathodes. CoP/PCB heated at 1200 °C exhibited a high reversible capacity of 477.5 mAh/g after 500 cycles at a current density of 1 C with an average capacity decay rate of 0.045%. The specific capacity remained at 453.3 mAh/g after 300 cycles even under a high sulfur load of 4.0 mg/cm2. Conversion of sulfur/polysulfides during the electrochemical process could be promoted via the physical confinement of sulfur and chemical confinement of Li2S6. This work provided a valuable reference for the facile fabrication of lithium–sulfur cathodes and utilization of metal phosphides in advanced lithium–sulfur battery systems.