A Poly(ethylene oxide)/Lithium bis(trifluoromethanesulfonyl)imide-Coated Polypropylene Membrane for a High-Loading...

In lithium-sulfur cells, the dissolution and relocation of the liquid-state active material (polysulfides) lead to fast capacity fading and low Coulombic efficiency, resulting in poor long-term electrochemical stability. To solve this problem, we synthesize a composite using a gel polymer electrolyte and a separator as a functional membrane, coated with a layer of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). The PEO/LiTFSI-coated polypropylene membrane slows the diffusion of polysulfides and stabilizes the liquid-state active material within the cathode region of the cell, while allowing smooth lithium-ion transfer. The lithium-sulfur cells with the developed membrane demonstrate a high charge-storage capacity of 1212 mA∙h g^-1, 981 mA∙h g^-1, and 637 mA∙h g^-1 at high sulfur loadings of 2 mg cm^-2, 4 mg cm^-2, and 6 mg cm^-2, respectively, and maintains a high reversible capacity of 534 mA∙h g^-1 after 200 cycles, proving its ability to block the irreversible diffusion of polysulfides and to maintain the stabilized polysulfides as the catholyte for improved electrochemical utilization and stability. As a comparison, reference and control cells fabricated using a PEO-coated polypropylene membrane and a regular separator, respectively, show a poor capacity of 662 mA∙h g^-1 and a short cycle life of 50 cycles.