Porphyrin Based Covalent Organic Framework Modified Separators: Boosting Long Cycle Lifespan and Rate Capability of Li–S Batteries

Covalent organic framework (COF) based modified separators have been extensively employed in lithium–sulfur (Li–S) batteries to enhance electrochemical performance by mitigating the shuttle effect. In this study, a novel porphyrin based COF (TaTp-COF) was rationally designed and successfully synthesized for use as a functional coating on commercial polypropylene separators (TaTp-COF@PP), aiming to improve the overall electrochemical performance of Li–S batteries. The TaTp-COF, featuring an ordered mesoporous architecture and abundant nitrogen and oxygen containing active sites, effectively immobilizes soluble lithium polysulfides (LiPSs) through strong chemical adsorption and facilitates their catalytic conversion, thereby significantly suppressing the shuttle effect. Therefore, the shuttle effect can be effectively suppressed, thereby significantly enhancing the reaction kinetics. In addition, this material exhibits excellent electrolyte wettability, high ionic conductivity (2.22 mS cm–1), and a relatively high tLi+ of 0.83. It demonstrates favorable Li+ conductivity, which facilitates uniform Li+ transport and contributes to the suppression of lithium dendrite formation. The Li–S battery incorporating TaTp-COF@PP exhibited an exceptionally high initial reversible capacity of 1321.2 mAh g–1 at a current density of 0.1C, significantly outperforming the counterpart with a conventional PP separator. Furthermore, it demonstrated outstanding cycling stability, maintaining capacity over 500 cycles at 1C with an average capacity decay rate of merely 0.1%. Theoretical calculations further elucidate the role of TaTp-COF in lowering the energy barrier associated with the polysulfide conversion reaction. This work presents a novel strategy for developing high performance Li–S batteries through the rational design and application of multifunctional COF based separators.