Bifunctional Separator with a Light‐Weight Carbon‐Coating for Dynamically and Statically Stable Lithium‐Sulfur Batteries

Sulfur is appealing as a high‐capacity cathode for rechargeable lithium batteries as it offers a high theoretical capacity of 1672 mA h g −1 and is abundant. However, the commercialization of Li‐S batteries is hampered by fast capacity fade during both dynamic cell cycling and static cell resting. The poor electrochemical stability is due to polysulfide diffusion, leading to a short cycle life and severe self‐discharge. Here, we present the design of a bifunctional separator with a light‐weight carbon‐coating that integrates the two necessary components already inside the cell: the conductive carbon and the separator. With no extra additives, this bifunctional carbon‐coated separator allows the use of pure sulfur cathodes involving no complex composite synthesis process, provides a high initial discharge capacity of 1389 mA h g −1 with excellent dynamic stability, and facilitates a high reversible capacity of 828 mA h g −1 after 200 cycles. In addition, the static stability is evidenced by low self‐discharge and excellent capacity retention after a 3 month rest period.