Researchers at Gyeongsang National University in South Korea, working with battery materials company Energy 11 Co., the Korea Basic Science Institute, Jeonbuk National University, and Xi'an University of Technology in China, have developed a dual-site-doped perovskite oxide separator coating that addresses the polysulfide "shuttle effect" limiting lithium-sulfur (Li-S) battery performance. Cells built with the modified separator held stable cycling over 500 cycles at a 2C rate, with a capacity decay rate of just 0.04% per cycle, and the team also validated the approach in pouch-cell format rather than coin cells alone.
Li-S batteries are attractive for their high theoretical energy density (2,600 Wh/kg) and specific capacity (1,675 mAh/g), along with low cost and environmental friendliness, but commercialization has been held back by sluggish reaction kinetics, the poor electronic conductivity of sulfur and Li2S, and above all the shuttle effect: soluble polysulfide intermediates that dissolve into the electrolyte during cycling and migrate between electrodes, degrading capacity and cycling stability. Researchers have tried a range of inorganic catalysts, including metal oxides, nitrides, and carbides, to accelerate polysulfide conversion, but single-component catalysts tend to offer a limited number of active sites and little independent control over adsorption versus catalytic activity.
The team turned instead to ABO3-type perovskite oxides, whose A-site and B-site can be doped independently to tune those two properties separately. Starting from electrospun, one-dimensional hollow LaCoO3 (LCO) nanofibers, they introduced strontium at the A-site to produce La0.6Sr0.4CoO3 (LSCO), then added iron at the B-site to arrive at the dual-doped La0.6Sr0.4Co0.2Fe0.8O3 (LSCF). A-site strontium substitution introduces oxygen vacancies that enhance polysulfide adsorption, but adsorption alone can be counterproductive if it is too strong, trapping polysulfides rather than helping convert them. B-site iron substitution instead tunes the local electronic environment around the catalytic centers to accelerate redox kinetics. Combining the two, the researchers found, strikes a better balance between adsorption and conversion than single-site doping alone.
Using X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption near-edge structure (XANES) analysis, and density functional theory calculations, the team traced the electrochemical differences across the LCO, LSCO, and LSCF series to the distinct roles played by cobalt and iron in the catalytic centers. The optimized LSCF composition showed moderate rather than excessive polysulfide adsorption, along with accelerated lithium-ion diffusion and greater active-material utilization, which the researchers say promotes more complete Li2S nucleation and dissolution during cycling and supports operation at higher sulfur loadings.
The LSCF nanofibers were made by electrospinning a lanthanum, strontium, cobalt, and iron nitrate precursor solution blended with polyacrylonitrile at 20 kV, then calcining the resulting fibrous mat, a route the researchers used to coat the separator rather than modify the sulfur cathode directly. The team frames the results as evidence that deliberately splitting a separator's two competing jobs, adsorbing polysulfides and catalyzing their conversion, across two different lattice sites of the same perovskite is a viable design principle for advanced Li-S battery materials.
