Enhancing Lithium-Sulfur Battery Performance through Electronic/Ionic Co-Conductive MWCNTs/LLTO Separator Modification

Abstract

As one of the most promising energy storage devices, Lithium-sulfur batteries (LSBs or Li-S batteries) are still facing obstacles due to the notorious shuttling of soluble polysulfide intermediates, accompanied by low S utilization, corrosion of the lithium anode, and rapid capacity fading leading to a short cycling life. To overcome these issues and achieve high-performance LSBs, we introduce a modified separator composed of multi-walled carbon nanotubes/lithium lanthanum titanium oxide (MWCNTs/LLTO). The proposed MWCNTs/LLTO-modified separator improves the redox reaction kinetics from soluble higher-order lithium polysulfides to the insoluble lower-order ones and ultimately to Li₂S, thereby reducing the polysulfides dissolved in the electrolyte. It also serves as a physical barrier to adsorb polysulfides, efficiently preventing their diffusion from the cathode to the anode. LSBs adopting the MWCNTs/LLTO-modified separator exhibit higher ionic and electronic conductivity than the un-modified counterparts, leading to an initial specific capacity of 1496 mA h g⁻¹ (∼90% of the theoretical capacity) at 0.1C, an excellent rate capability performance, and a remarkable capacity retention of 80% after 200 cycles. Furthermore, the cells with S loading reaching up to 4.18 mg cm^-2 further confirmed the beneficial impact of the MWCNTs/LLTO-modified separator.