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.