New graphene layer helps lithium-sulfur batteries last 1,000 cycles
Researchers have developed a molecularly engineered interlayer that tackles one of the biggest barriers to commercial lithium-sulfur batteries, allowing the cells to retain capacity over 1,000. . .
Researchers have developed a molecularly engineered interlayer that tackles one of the biggest barriers to commercial lithium-sulfur batteries, allowing the cells to retain capacity over 1,000 charge-discharge cycles while delivering high energy density. The team, led by researchers at Tohoku University and collaborating institutions, created a covalent organic framework (COF)-graphene interface that prevents the movement of lithium polysulfides inside the battery. The unwanted migration, known as the polysulfide shuttle effect, has long reduced the lifespan and efficiency of lithium-sulfur batteries. Lithium-sulfur batteries are considered a promising alternative to today’s lithium-ion technology because sulfur is abundant, inexpensive, and capable of storing much more energy. However, dissolved lithium polysulfides formed during charging and discharging can migrate between the battery’s electrodes, triggering side reactions and causing rapid capacity loss. Instead of relying on a physical barrier, the researchers designed an interlayer that chemically captures polysulfides while also helping them continue participating in the battery’s electrochemical reactions. Solving shuttle challengeThe new material, called TUS-44, is a tetrathiafulvalene-crown ether covalent organic framework combined with conductive graphene. Together, they form a lightweight functional layer that both traps lithium polysulfides and speeds electron transport. The COF contains imine nitrogen, crown-ether oxygen, and sulfur-rich tetrathiafulvalene sites that interact with lithium polysulfides. Graphene provides a conductive pathway that improves charge transfer and supports sulfur conversion during battery operation. In laboratory tests, lithium-sulfur cells equipped with the TUS-44@G interlayer delivered a reversible capacity of 1,455. 7 mAh g⁻¹ at 0. 2 A g⁻¹ and maintained 773 mAh g⁻¹ even at a high current density of 10 A g⁻¹. The batteries also recorded capacity fading of just 0. 034% per cycle over 1,000 cycles at 5 A g⁻¹. The researchers also built a lithium-sulfur pouch cell using the same interlayer. It achieved an initial energy density of about 674 Wh kg⁻¹, highlighting the material’s potential for practical high-energy battery applications. “Our goal was to design an interlayer that does not simply block polysulfides, but actively manages their reaction pathway,” explained Saikat Das, junior associate professor at the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University. “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. ”Molecular design mattersUnlike conventional porous carbon materials that interact weakly with polysulfides, covalent organic frameworks can be engineered with precise pore structures and chemical functionalities. This allows them to capturelithiumpolysulfides while promoting electron transport and sulfur conversion at the same time. The researchers synthesized TUS-44 using Schiff-base chemistry to create a two-dimensional porous framework with uniform micropores and a high surface area. When coated onto a polypropylene separator withgraphene, the material formed a thin interfacial layer that readily absorbed electrolyte while suppressing polysulfide migration. “This study shows that reticular chemistry can be used to program battery interfaces at the molecular level,” said Professor Yuichi Negishi of Tohoku University. “The TUS-44@G design offers a route toward lightweight, durable and high-rate Li-S batteries by unifying polysulfide immobilization with catalytic sulfur conversion. ”The study was published in the journalSmall. Get the latest in engineering, tech, space & science - delivered daily to your inbox. With over a decade-long career in journalism, Neetika Walter has worked with The Economic Times, ANI, and Hindustan Times, covering politics, business, technology, and the clean energy sector. Passionate about contemporary culture, books, poetry, and storytelling, she brings depth and insight to her writing. When she isn’t chasing stories, she’s likely lost in a book or enjoying the company of her dogs.