Preparation and Evaluation of a New Water-Based Binder for Sulfur Cathode in Lithium-Sulfur Batteries

Sulfur cathode has attracted great interest in recent years due to its high energy density. However, dramatic reduction in cathode energy density and sulfur shuttle effects during charge and discharge processes result in poor battery performance. A new water-based sulfur cathode binder, poly(styrene-b-n-butyl acrylate-b-styrene) (SnBAS) was designed and synthesized via RAFT emulsion polymerization in this study. Polymer membranes of the prepared binder were employed to study swelling ratio of the material in an ether electrolyte. The properties of the binder were compared with those of PS, PnBA and a commercial SBR binder, and the results show that SnBAS binders with proper St/nBA weight ratios can significantly improve battery performance. Cathodes with SnBAS have satisfactory mechanical strength and appropriate swelling ratios in the electrolyte. The sulfur cathode prepared with the binder shows capacity of 781 mAh·g^-1 at 0.2C after charge and discharge cycles at 0.1, 0.2, 0.5, 1, 2, 0.1C, which has a capacity retention rate of 73.6%. The specific capacity is 740 mAh·g^-1 after additional 100 cycles at 0.2C, which corresponds to capacity decay of 0.05% per cycle and a capacity retention rate of 94.7%. This work demonstrates that SnBAS is a promising water-based binder for sulfur cathode of lithium-sulfur batteries.