Self-supporting Biomass Li–S Cathodes Decorated with Metal Phosphides–Higher Sulfur Loading, Better Stability, and Longer Cycle Life

Under the premise of high sulfur loading, how to solve the problems of low capacity, short cycle life, and poor rate performance caused by the dynamics of polysulfide and further exert the advantages of the excellent energy density of Li–S batteries is a hot topic nowadays. Herein, the high-S loading self-supporting biomass Li–S cathodes decorated with metal phosphides (MPx, M = Ni, Co, and Fe) were developed. The cattail, an aquatic plant, was employed as a raw material to prepare a three-dimensional self-supporting carbon matrix (SSC) with excellent flexibility. The complex and fluffy structure of the SSC carrier could effectively alleviate volume variation during the cycle of the battery while loading more sulfur, and its carbon nanotube network with favorable conductivity could also achieve rapid electron transfer. In addition, by combining the calculation results of density functional theory with electrochemical properties, we proved that all three phosphides have a strong adsorption and catalytic effect on polysulfides, while further elaborating the specific functions and behaviors of different metal phosphides in promoting polysulfide conversion. Finally, the MPx@SSC-1150 (M = Ni/Co/Fe) not only possesses high initial discharge capacities (1236.96, 1398.45, and 1240.96 mA h g–1, respectively) under a high load (5.5 mg cm–2) but also ensures excellent long-cycle stability. The work opens feasible avenues for the selection and preparation of compounds for the catalytic conversion of polysulfides in Li–S batteries with high-S loading.