Advanced Li-S Batteries Enabled by a Biomimetic Polysulfide-Engulfing Net.

Lithium-sulfur batteries are attractive because of their high specific capacity and energy density, but issues with the polysulfide dissolution and shuttling intrinsically hinder their wide application. Here, hydroxylate multiwalled carbon nanotubes (MWCNT-OH) were grafted with a supramolecular polymer (heptakis(6-amino-6-deoxy)-β-cyclodextrin) to form a polysulfide-engulfing net, which was coated on a separator. Such a molecular microarray structure of a polymer can block the polysulfides and have biomimetic cellular behavior for engulfing polysulfides. The cavity (∼6 A) and functional groups of the supramolecular polymer can provide a dynamic structure for reversible adsorption of polysulfides while the conductive MWCNT-OH ensure fast electron transfer. The batteries with the modified separator exhibited excellent rate capacities (945.5 and 625.4 mA h g-1 at 2 C and 4 C rates, respectively). Especially, the high areal capacities of 5.86 and 7.2 mA h cm-2 achieved at S loadings of 4.5 and 6.0 mg cm-2 and good cycling stability after 200 cycles at 0.1 C can be obtained. This demonstrates a strategy of supramolecular polymer-grafted carbon for dynamic polysulfide adsorption toward advanced Li-S batteries.