Fluorinated Covalent Organic Framework-Based Nanofluidic Interface for Robust Lithium-Sulfur Batteries

To realize the practical application of lithium-sulfur (Li-S) batteries, there is a need to inhibit uncontrolled Li deposition by facilitating Li-ion migration, and suppress the irreversible consumption of cathodes by preventing polysulfide shuttling. However, a permse-lective artifical membrane or interlayer which features fast ion transport but low polysulfide crossover is elusive. Here, we report the design and synthesis of a fluorinated covalent organic framework (4F-COF)-based membrane with a high permselectivity and increased battery lifespan. Combining density functional theory calculation, molecular dynamic simulation, and in situ Raman analysis, we demonstrate that fluorinated COF eliminates polysulfides shutting and dendritic lithium formation. Consequently, Li symmetrical cells demonstrate Li plating/stripping behaviors for 2000 h under 1 mA cm???2. More importantly, Li???S batteries based on the 4F-COF/PP separator achieve cycling retention of 82.3% over 1000 cycles at 2 C, rate performance of 568.0 mA h g???1 at 10 C, and an areal capacity of 7.60 mA h cm???2 with a high sulfur loading (???9 mg cm???2). This work demonstrates that functionalizing nanochannels in COFs can impart permselectivity for energy storage applications.

Automated summary

To achieve practical application of lithium-sulfur (Li-S) batteries, the focus is on inhibiting uncontrolled Li deposition and preventing polysulfide shuttling. This study presents the design and synthesis of a fluorinated covalent organic framework (4F-COF)-based membrane that offers high permselectivity and extended battery lifespan. By eliminating polysulfide shuttling and dendritic lithium formation, the 4F-COF/PP separator enables stable Li plating/stripping behaviors and demonstrates excellent cycling retention, rate performance, and areal capacity.