Dense coating of Li4Ti5O12 and graphene mixture on the separator to produce long cycle life of lithium-sulfur battery

The high solubility of polysulfides in the electrolyte, together with the resulting poor cycling performance, is one of the main obstacles to the industrial production and use of lithium-sulfur (Li-S) batteries. We have developed a novel hybrid and dense separator coating that greatly improves the cycling and rate performance of the battery. The coating is fabricated by mono-dispersed Li4Ti5O12 (LTO) nanospheres uniformly embedded in graphene layers. In this hybrid dense coating, the LTO nanospheres have a high chemical affinity for polysulfides and an excellent ionic conductivity to produce highly efficient ionic conductive channels, while the graphene layers play twin roles as a physical barrier for polysulfides and an upper current collector. The unique hybridization guarantees a very dense coating that does not significantly add the volume of the battery and meanwhile achieves an ideal combination of an effective barrier for polysulfide diffusion with a fast ion transport. For a normal coating, a loose and very thick structure is needed to meet these requirements. Cells using a pure sulfur electrode with the dense coating separator show an ultra-high rate performance (709 mA hg(-1) at 2 C and 1408 mA h g(-1) at 0.1 C) and an excellent cycling performance (697 mA h g(-1) after 500 cycles at 1 C with 85.7% capacity retention). The easy achieving of such excellent performance indicates the possibility of producing an industrially practical Li-S battery.