Enhanced Lithium Polysulfide Conversion via the Second Current Collector Based on Multitransition-Metal-Phosphides for Li-S Batteries

The shuttle effect of electrolyte-soluble lithium polysulfides hinders the practical application of high theoretical energy density Li-S batteries. Usually, introducing an interlayer between the S-based cathode and separator can act as a functional secondary current collector, which not only provides a physical barrier but also captures and reuses the escaped active S species from the cathode, thus achieving high S utilization. Herein, multitransition metal phosphides [(Mn/Co/Fe)Fe-P or (Mn/Co/Ni)Fe-P] with strong chemical interaction and catalytic effect to lithium polysulfides are employed to decorate commercial polypropylene (PP). Especially in the case of (Mn/Co/Fe)Fe-P, the corresponding particles with a small size of similar to 50 nm guarantee strong lithium polysulfide adsorption and fast Li+ diffusion, thus effectively confining the active S species in the cathode region during Li-S battery operation. As a result, the Li-S battery with (Mn/Co/Fe)Fe-P/PP delivers a specific capacity of 870.41 mA h g-1 at 3 C, which retains 345.32 mA h g-1 after 1000 cycles, corresponding to a capacity decay of 0.06% per cycle. In addition, the symmetrical Li||Li cell with (Mn/Co/Fe)Fe-P/PP exhibits stable performance for almost 1000 cycles, which further demonstrates the possibility of (Mn/Co/Fe)Fe-P/PP to tune Li+ plating/stripping behaviors and hinder Li dendrites.