Systematic Exploration of the Role of a Modified Layer on the Separator in the Electrochemistry of Lithium-Sulfur Batteries.

As a significant constituent of lithium-sulfur batteries, the separator also exerts a considerable effect on the performance of the sulfur cathode. In our work, the mixture of acetylene black and multiwalled carbon nanotubes is uniformly applied onto the commercial polypropylene membranes to attain the modified separators. While investigating different samples, the underlying influence of the coating layer is systematically scrutinized on the electrochemical behaviors of sulfur cathodes, relying on the extensive electrochemical and structural measurements. During the charge/discharge process, the coating layer can function as the second current collector and drastically contribute to the improved lithium ions diffusion, determining the electrochemical kinetics of sulfur-involved reactions. Moreover, it is found that the thicker the layer, the faster the lithium ions diffuse. It should be noted that the coating layer also plays a role of the second sulfur reservoir to endow the ample active sites for sulfur and polysulfides, which is directly witnessed for the first time. Because of the positiveness and effectiveness of the modified layer on separators, the sulfur cathode can offer the superior cycling and rate performance to that with the original separator.