Modified separator engineering with 2D ultrathin Ni3B@rGO: Extraordinary electrochemical performance of the lithium-sulfur battery with enormous-sulfur-content cathode in low electrolyte/sulfur ratio

Compared to other batteries, a next-generation lithium-sulfur (Li-S) battery's specific capacity and energy density are relatively high. However, the actual electrochemical performance (particularly for the cell with a high cathode sulfur content and a lean electrolyte/sulfur ratio) falls well short of practical usage requirements. The ultrathin Ni3B@rGO-PP is designed in this study as a unique modified separator for Li-S cells. Because of its distinct electronic structure, the modified separator shows outstanding adsorption ability toward polysulfide through the boron element's active sites. Additionally, it has excellent electrocatalytic activity, significantly enhancing the performance of Li-S batteries. After the 100th cycle, the cell with 80 wt% sulfur content can retain 819 mA h g−1 under 0.2 C. Also, when the electrolyte/sulfur ratio is reduced to 15 µL mg−1 and 5 µL mg−1, respectively, considerable capacity retention of 736.3 mA h g−1 and 615 mA h g−1 is achieved after the 100th cycle at 0.2 C. What's more, for the high sulfur loading (single-side up to 4.5 mg cm−2) cathode, the cell obtains a retention capacity of 578 mA h g−1 after the 200th cycle under 0.2 C. The surface engineering strategy with the Ni3B@rGO modified coating adopted in this work would open an efficient route to acquire the Li-S battery's outstanding electrochemical capability in the practical application situation.