A molecularly engineered interface finally overcome a major barrier preventing high energy lithium sulphur batteries from reaching practical applications. How?
Researchers from Tohoku University and collaborating institutions have developed a covalent organic framework and graphene hybrid interlayer that significantly improves the performance of lithium sulfur batteries by suppressing polysulfide shuttling. Reported in the journal Small, the molecularly engineered interface combines chemical trapping, charge transport, and catalytic activity to address one of the biggest obstacles limiting the commercial adoption of lithium sulfur battery technology.
Lithium sulfur batteries are considered a promising alternative to conventional lithium ion cells because sulfur is abundant, inexpensive, and capable of storing much higher amounts of energy. However, during charging and discharging, soluble lithium polysulfides can migrate between the battery electrodes, causing active material loss, unwanted side reactions, self discharge, and gradual capacity degradation. The newly developed interlayer is designed to regulate these intermediate species rather than simply blocking their movement.
The research team created a tetrathiafulvalene crown ether covalent organic framework called TUS 44 and integrated it with conductive graphene to form a functional separator coating. The framework contains imine nitrogen, crown ether oxygen, and sulfur rich tetrathiafulvalene sites that selectively interact with lithium polysulfides, while graphene provides a conductive pathway for rapid electron transport. The material also promotes sulfur conversion reactions, improving electrochemical efficiency throughout repeated charge and discharge cycles.
Battery testing demonstrated a reversible capacity of 1455.7mAh g⁻¹ at 0.2A g⁻¹, retained 773mAh g⁻¹ at 10A g⁻¹, and exhibited a capacity fade of only 0.034 percent per cycle over 1000 cycles at 5A g⁻¹. A lithium sulfur pouch cell using the same interlayer also achieved an initial energy density of approximately 674Wh kg⁻¹.
“Our goal was to design an interlayer that does not simply block polysulfides, but actively manages their reaction pathway. By integrating crown ether and tetrathiafulvalene chemistry into an ordered COF and coupling it with graphene, we created a cooperative interface that can anchor, redistribute, and convert sulfur species more efficiently,” says Saikat Das, Junior Associate Professor at the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University.
