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

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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, NH 2 –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 NH 2 –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 NH 2 –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 NH 2 –CuBDC significantly enhance the chemisorption of polysulfides, which is in accordance with the experimental results and simulation. Consequently, batteries with an NH 2 –CuBDC/PP composite separator demonstrate a significantly extended cycle life. Specifically, the Li–Li batteries with NH 2 –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.

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