One action, two benefits: improving the performance of lithium-sulfur batteries with a poly(ionic liquid)

Lithium-sulfur (Li-S) batteries have been considered as one of the most promising candidates for high energy-density batteries due to their high theoretical capacity (1675 mA h g-1). However, the cycling performance is not satisfactory due to the "shuttle effect" of polysulfide and the growth of Li dendrites. In this study, imidazole-based poly(ionic liquid) (PIL) is synthesized. Using PIL in Li-S batteries, we realize the goal of achieving two benefits with one action. The cross-linked PIL (c-PIL) is used to modify the S cathode, and the shuttling of polysulfides is effectively inhibited due to the strong adsorption capability. Density functional theory (DFT) calculations indicate that the strong van der Waals and electrostatic interaction promote the adsorption of polysulfides. PIL, as an artificial solid electrolyte interface layer, is coated on the Li anode to prevent the corrosion of liquid electrolyte and homogenize Li+ flux. The results of DFT and X-ray photoelectron spectroscopy indicate that the N containing imidazole in PIL can be reduced by active Li to form a Li3N rich layer on the interface. The Li3N containing interfacial layer can promote dendrite-free Li deposition beneath the PIL coating layer. By functionalizing the S cathode and Li anode, the PIL@Li||c-PIL@S batteries show much improved cycling stability and C-rate performance. The results manifest that our strategy of modification of the cathode and anode electrodes is effective, which is sure to promote the development of advanced Li-S batteries. Poly(ionic liquid) is synthesized to modify the S cathode and Li anode to inhibit the shuttling of polysulfides and suppress dendritic Li deposition. The cycling performance of Li-S batteries is greatly improved with modification on both electrodes.