Enhanced cycle performance of lithium-sulfur batteries using a separator modified with a PVDF-C layer

High energy density Li-S batteries are highly attractive. However, their use in practical applications has been greatly affected by their poor cycle life and low rate performance, which can be partly attributed to the dissolution of polysulfides from the S cathode and their migration to the Li anode through the separator. While much effort has been devoted to designing the structure of the S cathodes for suppressing the dissolution of polysulfides, relatively little emphasis has been placed on modifying the separator. Herein, we demonstrate a new approach for modifying the separator with a polyvinylidene fluoride-carbon (PVDF-C) layer, where the polysulfides generated in the Li-S cells can be localized on the cathode side. Li-S batteries based on the novel separator and a cathode prepared by the simple mixing of a S powder and super P have delivered discharge capacities of 918.6 mAh g(-1), 827.2 mAh g(-1), and 669.1 mAh g(-1) after 100, 200, and 500 cycles, respectively, at a discharge rate of 0.5 C. Even under current densities of up to 5 C, the cells were able to retain a discharge capacity of 393 mAh g(-1), thereby demonstrating an excellent high rate performance and stability. The exceptional electrochemical performance could be attributed to the intense adsorption capability of the micropores, presence of C-C double bonds, and conductivity of the C network in the PVDF-C layer. This economical and simple strategy to overcome the polysulfide dissolution issues provides a commercially feasible method for the construction of Li-S batteries.