Layer-by-Layer Assembly of CeO 2- x @C-rGO Nanocomposites and CNTs as a Multifunctional Separator Coating for Highly Stable Lithium-Sulfur Batteries.

Commercialization of high-energy Li-S batteries is greatly restricted by their unsatisfactory cycle retention and poor cycling life originated from the notorious "shuttling effect" of lithium polysulfides. Modification of a commercial separator with a functional coating layer is a facile and efficient strategy beyond nanostructured composite cathodes for suppressing polysulfide shuttling. Herein, a multilayered functional CeO 2- x @C-rGO/CNT separator was successfully achieved by alternately depositing conductive carbon nanotubes (CNTs) and synthetic CeO 2- x @C-rGO onto the surface of the commercial separator. The cooperation of multiple components including Ce-MOF-derived CeO 2- x @C, rGO, and CNTs enables the as-built CeO 2- x @C-rGO/CNT separator to perform multifunctions from the separator surface: (i) to hinder the diffusion of polysulfide species through physical blocking or chemical adsorption, (ii) to accelerate the sluggish redox reactions of sulfur species, and (iii) to enhance the conductivity for sulfur re-activation and efficient utilization. Serving as a multilayer and powerful barrier, the CeO 2- x @C-rGO/CNT separator greatly constrains and reutilizes the polysulfide species. Thus, the Li-S battery assembled with the CeO 2- x @C-rGO/CNT separator demonstrates an excellent combination of capacity, rate capability, and cycling performances (an initial capacity of 1107 mA h g -1 with a low decay rate of 0.060% per cycle over 500 cycles at 1 C, 651 mA h g -1 at 5 C) together with remarkably mitigated self-discharge and anode corrosion. This work provides guidelines for functional separator design as well as rare-earth material applications for Li-S batteries and other energy storage systems.