Multifunctional Ion-Sieve Constructed by 2D Materials as an Interlayer for Li-S Batteries

For Li-S batteries, the interlayer between the separator and sulfur cathode preventing lithium polysulfide (LiPS) travel across the membrane is a research hotspot. The good blocking ability for LiPSs indicates that these interlayers can promote the electrochemistry performance with high S loading. However, most of these interlayers are just used as a simple blocking wall. Such a blocking wall, for example, the lower Li⁺ ion conductivity, would often reduce the electrochemical performance, especially under large current density. Here, we report a multifunctional ion-sieve made by three two-dimensional (2D) sheets, graphitic carbon nitride (g-C₃N₄), boron nitride (BN), and graphene. A g-C₃N₄ sheet which possesses orderly channels with a size of 3 Å in the crystalline structure can effectively prevent polysulfides from passing through but allow lithium ions to pass freely, whereas a BN sheet acts as an excellent catalyst for sulfur redox, and graphene acts as an extended collector, which can promote the conductivity of the sulfur electrode region. Benefiting from the synergistic effect among these 2D materials, the ion-sieve interlayer makes the Li-S battery show excellent performance at a large rate with both high sulfur loadings and high sulfur content. In addition, the host materials are not necessary in these cells. The ion-sieve liberated a discharge capacity of about 600 mA h g^-1 after 500 cycles at 1 C, and the capacity attenuation was less than 0.01% per cycle with a 6 mg cm^-2 areal S-loading (pure S as the active material). The reversible capacity could be maintained at more than 400 mA h g^-1 at 2 C, which amounts to an area current density of 26.88 mA cm^-2.