Fluorine/sulfur-comodulated covalent organic frameworks cathode for high-performance lithium ion batteries

Sulfur-based LIBs (S-LIBs) are expected to stand out to replace conventional lithium ion batteries as candidate for sustainable high-density energy storage. However, the main obstacles to the practical application of S-LIBs are the easy dissolution of lithium polysulfides (Li2Sx) intermediates, as well as the poor electrical conductivity of sulfur species and transport of charge carriers. To achieve high-capacity and long-lifespan S-LIBs, rational design and construction of cathode materials as hosts for Li2Sx species with simultaneously strong bonding and high electric/ionic conductivity are essential but very challenging. Herein, according to the density functional theory (DFT) prediction, a series of sulfurized covalent organic frameworks (COFs) are synthesized by the nucleophilic aromatic substitution reaction (SNAr). Benefiting from the chemical confinement to Li2Sx by synergistic carbonyl groups and strong C-S chains, the S-LIBs based on the optimized TpF-1S delivers a high specific capacity of 1377 mAh/g and remains 1150 mAh/g after 1000 cycles at 2C with-100% Coulombic efficiency. The S-LIBs also achieves an energy density up to 2000 Wh/kg, which is approaching 78% of the theoretical value and four times over the commercial lithium-ion batteries. This work paves the way for exploiting a new generation of ultrastable sulfur hosts for high-density S-LIBs.