NH ₂ –CuBDC Nanosheet Composite Membranes with Fast Li ⁺ Flux and Inhibiting Polysulfide Migration for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries with high energy density are considered to be one of the most promising next-generation secondary batteries. However, the shuttle effect and lithium dendrites significantly shorten battery life, seriously hindering commercial application. Herein, NH2–CuBDC/PP composite membranes with homogenic ion transport and high polysulfide retention are designed and fabricated by a simple-preparation and low-cost method. Systematic investigations reveal how ion transport channels of NH2–CuBDC/PP composite membranes correlated with selective Li+ conduction and battery performance. Notably, the high length–thickness ratio structure and inherent pore structure of two-dimensional NH2–CuBDC nanosheets provide sufficient and homogenic transport channels for Li+ flux while simultaneously creating tortuous paths for polysulfides. Meanwhile, the immobilized amino and metal sites in NH2–CuBDC significantly enhance the chemisorption of polysulfides, which is in accordance with the experimental results and simulation. Consequently, batteries with an NH2–CuBDC/PP composite separator demonstrate a significantly extended cycle life. Specifically, the Li–Li batteries with NH2–CuBDC/PP exhibit stable operation for over 700 h (approximately 4 times longer than PP) with a small and stable polarization, effectively suppressing lithium dendrites. The assembled Li–S battery delivers a high specific capacity of 736.5 mAh g–1 at 2 C and maintains a stable cycle over 400 cycles (doubling the cycle life compared with that of PP). Even with a high sulfur loading of 4.5 mg cm–2, a high specific discharge capacity of 1007.3 mAh g–1 can be achieved at 0.1 C. This work provides a strategy for designing ion-selective functional separators to achieve dendrite-free and high-performance Li–S batteries.