A bifunctional separator consisting of a layer of multiwall carbon nanotubes (MWCNTs) on the cathode-side of a Celgard polypropylene sheet has been investigated to overcome the challenges of Li-S cells. The conductive/porous MWCNT-coating functions (i) as an upper current collector to facilitate electron transport and high active-material utilization and (ii) as a filter to intercept/absorb the migrating polysulfides and thereby suppress the polysulfide diffusion. Also, the access to the electrolyte through the porous network of MWCNT along with its fast electronic transport facilitates the reutilization of the trapped active material and superior long-term cyclability. The MWCNT-coating is lightweight (0.17 mg cm-2), yet allows the successful use of regular sulfur cathodes (high sulfur content of 70 wt %) with high discharge capacity, excellent rate performance, and long cycle life, demonstrating that the MWCNT-coated separator is a viable solution to practical Li-S batteries.
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