Cation-Selective Dual-Functional Separator as an Effective Polysulfide Barrier and a Li Dendrite Inhibitor for Lithium–Sulfur Batteries

Lithium–sulfur (Li-S) batteries are deemed to be one of the most promising energy storage devices due to their abundant material sources and high energy density. However, the uncontrollable growth of Li dendrites and the shuttle effect severely deteriorate the cycling performances, and consequently, hamper their practical application. In this research, a cation-selective dual-functional separator was designed by coating a thin layer containing sulfonated polyether ether ketone (SPEEK) polymer and Super P (SP) particles on a commercial polyethylene (PE) separator. Here, SPEEK can offer lithium-ion transport channels and inhibit polysulfide anions through a Coulomb action. SP with excellent electronic conductivity and a relatively large specific surface area can achieve physical adsorption to polysulfide anions and can act as an additional collector to promote electron transport, so as to achieve better electrochemical exploitation of sulfur and ensure the reactivation of captured active substances. The composite separators can adjust the deposition of Li to a certain extent, therefore achieving uniform lithium-ion flux and lithium-ion deposition. As expected, the SP/SPEEK-coated separator batteries show an outstanding Coulomb efficiency of 99% and a superior capacity of 950.7 mA h g–1, and the capacity retention rate was 77.5% after 500 cycles at 0.5 C. This work provides an effective strategy to suppress the shuttle effect in Li–S batteries.