A dual-coated multifunctional separator for the high-performance lithium-sulfur batteries

The lithium-sulfur (Li-S) battery has received widespread attention because of the high theoretical energy density and inexpensive raw material. However, some issues still restrict its commercialization, including the shuttle effect, the lithium dendrite growth and low safety, etc. In this work, a PMMA-LLZO/PP/AB multifunctional separator was designed and facilely prepared to overcome these problems. A composite dense layer of the PMMA and LLZO sheets with excellent interface stability was coated on one side of the PP separator to face lithium metal anode, which can inhibit the lithium dendrites growth and increase the safety. Meanwhile, this composite coating possesses high affinity with the liquid electrolyte and the soluble polysulfides, which can improve the ionic conductivity, effectively adsorb the polysulfides. An acetylene black (AB) layer was further coated on the other side of the PP separator to not only act as an electron conductor but also adsorb and hinder the migration of lithium polysulfides. The co-modified PMMA-LLZO/PP/AB separator displays remarkable electrochemical performances and an excellent thermal stability. The cell with the co-modified separator exhibits high specific capacities of 1456 mAh g−1 at 0.1 C and 969 mAh g−1 at 1.0 C, and retains a capacity of 413 mAh g−1 after 500 cycles, corresponding to a retention of 42.6% as well as a low decay of 0.114%/cycle. Especially, the cell with the multifunctional separator also displays a high capacity and a low decay even for a high sulfur mass loading cathode of 2.5–3.0 mg cm−2 or at a high temperature of 60 °C. The co-modified multifunctional separator has great application potential in the high-performance Li-S battery.