An ultrathin and highly efficient interlayer for lithium-sulfur batteries with high sulfur loading and lean electrolyte

Lithium-sulfur (Li-S) batteries are considered to have great potential due to their high theoretical specific energy and natural abundance of sulfur. However, the practical specific energy and cycle life of Li-S pouch cells are significantly hindered by thin sulfur cathodes, flooded electrolytes and excess Li metal anodes. Here, an ultrathin and highly efficient boron nitride/single-wall carbon nanotube (BN/SWCNT) interlayer (UHEI) achieves excellent Li-S pouch cell performance with high sulfur loading and a lean electrolyte. Compared with the reported interlayer materials, the UHEI can not only hinder the diffusion of polysulfides, but also promote further redox reactions and allow Li+ to pass through easily. Meanwhile, this UHEI can significantly improve lean electrolyte performance (E/S ratio of 8 mu L mg(-1)) and both high and low plateau capacities of Li-S batteries with a high sulfur loading (10 mg cm(-2)). Moreover, a normalized "ratio of the areal loading interlayer to sulfur (I/S)" was proposed and two "interlayer efficiency index (IEI)" were obtained by using I/S to quantify the efficiency of interlayers at a certain current density and guide the design of high-efficiency interlayers. The IEI of our UHEI@PP is dozens of times higher than previously reported results. Li-S cells with UHEI@PP delivered a remarkable discharge capacity of 6.6 mA h cm(-2) after 100 cycles at 0.2C for pouch cells (4.1 mg cm(-2) per side, E/S ratio of 10 mu L mg(-1)). The work provides new insights into separator modification for the practical application of lithium-sulfur batteries in the future.