COF-graphene hybrid opens new horizons for lithium-sulfur batteries
Researchers at Tohoku University have developed a covalent organic framework (COF)-graphene interlayer that significantly reduces polysulfide shuttling in lithium-sulfur batteries, achieving a high reversible capacity of 1455.7 mA h g⁻¹ at 0.2 A g⁻¹. This advancement is crucial for the practical deployment of lithium-sulfur batteries, as it addresses the long-standing challenge of polysulfide migration, potentially leading to more efficient and durable energy storage solutions.
Researchers from Tohoku University and collaborating institutions have developed a novel covalent organic framework (COF)-graphene interlayer to address the challenge of polysulfide shuttling in lithium-sulfur (Li-S) batteries. This innovative interface combines chemical trapping, rapid charge transport, and sulfur-conversion promotion to mitigate the migration of dissolved sulfur intermediates. The study was published in the journal Small on June 16, 2026.
Li-S batteries offer significant energy-storage potential due to their ability to undergo multielectron reactions, converting solid sulfur into lithium polysulfides and lithium sulfides during discharge, and reversing the process during charging. However, the formation of intermediate lithium polysulfides can lead to active-material loss and performance decay as they migrate within the battery. The COF-graphene interlayer functions as an intelligent checkpoint, selectively capturing polysulfides and facilitating their conversion, rather than simply blocking them.
The research team synthesized a new tetrathiafulvalene-crown ether COF, named TUS-44, and integrated it with graphene to form the TUS-44@G layer. This structure provides various interaction sites for lithium polysulfides and an efficient electron-transport pathway. Battery tests demonstrated that cells with the TUS-44@G layer achieved a high reversible capacity of 1455.7 mA h g⁻¹ at 0.2 A g⁻¹ and maintained excellent rate capability and long-term durability.
Saikat Das, Junior Associate Professor at Tohoku University, explained that the goal was to design an interlayer that actively manages the reaction pathway of polysulfides. By incorporating crown ether and tetrathiafulvalene chemistry into a COF and coupling it with graphene, the team created a cooperative interface that anchors, redistributes, and converts sulfur species efficiently. COFs offer a molecularly engineered platform that captures, conducts, and catalyzes, transforming the polysulfide shuttle problem into a controllable aspect of sulfur electrochemistry.
The TUS-44 COF was synthesized through Schiff-base condensation, resulting in a two-dimensional framework with uniform micropores and a significant surface area. The COF's functional sites perform complementary tasks, such as docking lithium ions and promoting charge delocalization. Integrating TUS-44 with graphene onto a separator produced a thin interfacial coating that absorbs electrolyte and blocks polysulfide migration effectively.
Professor Yuichi Negishi of Tohoku University remarked that the TUS-44@G design unifies polysulfide immobilization with catalytic sulfur conversion, offering a route toward lightweight, durable, and high-rate Li-S batteries. This study highlights the potential of reticular chemistry to program battery interfaces at the molecular level.
Source: Graphene Feed