actively manage their reaction pathway, not simply block them
For decades, lithium-sulfur batteries have carried an unfulfilled promise: extraordinary energy density undermined by a slow chemical dissolution of their own potential. Researchers from Lanzhou, Tohoku, and SRM universities have now answered that long-standing failure with a molecularly engineered interlayer — TUS-44@G — that transforms a passive plastic separator into an active chemical interface, anchoring and converting the very compounds that once caused these batteries to fade. In doing so, they have moved lithium-sulfur technology measurably closer to the devices and vehicles that the world is still waiting to power.
- Polysulfide shuttling — the slow migration of dissolved sulfur compounds across the battery — has quietly killed every practical attempt to bring lithium-sulfur batteries to market, draining capacity cycle by cycle.
- The new TUS-44 framework doesn't merely block this chemical wandering; it intercepts polysulfides through a precisely engineered hierarchy of imine nitrogen anchors, crown-ether ion pathways, and electron-conducting TTF units working in concert.
- Fused with graphene into a hybrid coating on the battery separator, TUS-44@G converts what was once a passive membrane into a reactive interface that manages sulfur chemistry rather than simply containing it.
- The results are striking: 1455.7 mAh/g reversible capacity, stability across 1000 cycles, and a capacity fade of just 0.034% per cycle — numbers that cross the threshold from laboratory curiosity into engineering credibility.
- A pouch cell prototype reaching 674 Wh/kg signals that the design survives the translation from coin cell to practical format, opening a scalable path toward high-energy, long-life batteries for real-world applications.
A research collaboration spanning Lanzhou, Tohoku, and SRM universities has produced a material that may finally give lithium-sulfur batteries a viable path to the real world. The obstacle they targeted is well known: sulfur's theoretical energy density is exceptional, but dissolved sulfur compounds — polysulfides — migrate freely through the battery during cycling, steadily eroding capacity until the cell fails. That single flaw has kept lithium-sulfur technology out of phones and electric vehicles despite decades of interest.
Their solution is TUS-44, a covalent organic framework built from two interlocking chemical components — a tetrathiafulvalene unit rich in sulfur and a benzocrown structure derived from crown ethers — joined through Schiff-base condensation into a two-dimensional lattice. The resulting material is not simply porous; it is chemically purposeful. Imine nitrogen atoms anchor lithium ions, crown-ether oxygens guide ion movement, and the TTF units manage electron transfer. Pore sizes of 0.9 and 1.2 nanometers and a surface area of roughly 516 square meters per gram give the framework both the geometry and the chemistry to intercept polysulfides at multiple stages of their reaction pathway.
Paired with graphene, TUS-44 becomes TUS-44@G — a thin hybrid coating applied directly to the polypropylene separator between the battery's two electrodes. Graphene supplies the electronic conductivity; the COF supplies the chemical selectivity. Together they turn the separator from a passive physical barrier into an active interface that anchors intermediate sulfur species and catalyzes their conversion back into useful forms.
The performance data reflects the design's ambition. Cells equipped with the interlayer delivered 1455.7 mAh/g at standard discharge rates and retained 773 mAh/g even under ten-times higher demand. Over 1000 cycles at 5 A/g, capacity faded by only 0.034% per cycle — a stability figure that moves the technology into practical territory. Tohoku's Saikat Das described the guiding philosophy as active management of reaction pathways rather than passive blockade, while Professor Yuichi Negishi framed the broader implication: reticular chemistry can now be used to program battery interfaces at the molecular level.
The team also built a pouch cell — 5.0 by 6.5 centimeters, loaded with 44.558 mg of sulfur — that achieved an initial energy density of approximately 674 Wh/kg, demonstrating that the approach survives the step from laboratory coin cell to a more practical format. What the work ultimately shows is that a separator, long treated as inert infrastructure, can be redesigned as a chemical reactor — one engineered to solve, from within the battery itself, the problem that has long kept lithium-sulfur technology waiting.
A team of researchers working across three universities—Lanzhou, Tohoku, and SRM—has engineered a new material that could reshape how lithium-sulfur batteries work. The problem they set out to solve is old and stubborn: sulfur batteries promise enormous energy density, but they fail because of a chemical ghost called polysulfide shuttling. Dissolved sulfur compounds migrate through the battery, stealing capacity with each cycle until the cell dies. It's the reason these batteries, despite their theoretical promise, haven't made it into phones or cars yet.
The team's answer is a molecularly designed framework called TUS-44, built from two chemical components that fit together like puzzle pieces. One piece is based on tetrathiafulvalene, a sulfur-rich molecule; the other is a benzocrown structure derived from crown ethers. When these components condense together through a chemical reaction called Schiff-base condensation, they form a two-dimensional lattice with precisely engineered pores—some 0.9 nanometers across, others 1.2 nanometers—and a surface area of about 516 square meters per gram. What makes TUS-44 different from conventional porous carbons is that it doesn't just create empty space. It creates a hierarchy of chemical sites, each one designed to do something specific. Imine nitrogen atoms act as anchors for lithium ions. Crown-ether oxygen atoms provide secondary coordination and ion pathways. The sulfur-rich TTF units handle electron movement and chemical mediation. Together, these sites form what the researchers call a hierarchical interaction network, a single material that can simultaneously coordinate ions, bind polysulfides, and move electrons.
But a good material alone isn't enough. The team paired TUS-44 with graphene, creating a hybrid coating they call TUS-44@G. This thin layer sits on the polypropylene separator—the membrane between the battery's two halves—and transforms it from a passive barrier into an active interface. The graphene provides the electronic highway; the COF provides the chemical intelligence. Together, they don't just block polysulfides from wandering. They actively manage the chemical reactions that govern sulfur electrochemistry, anchoring the intermediate compounds and converting them back into useful forms.
The numbers tell the story of what this design achieves. In electrochemical testing, cells with the TUS-44@G layer delivered a reversible capacity of 1455.7 milliamp-hours per gram at a modest discharge rate. Push the battery harder—discharge it at ten times that rate—and it still held 773 milliamp-hours per gram. Over a thousand cycles at a high discharge rate of 5 amperes per gram, the battery lost only 0.034 percent of its capacity per cycle. That's the kind of stability that makes a battery practical. Saikat Das, a junior associate professor at Tohoku University, described the philosophy behind the design: the goal wasn't to simply block polysulfides, but to actively manage their reaction pathway. By integrating crown ether and tetrathiafulvalene chemistry into an ordered framework and coupling it with graphene, the team created a cooperative interface that could anchor, redistribute, and convert sulfur species more efficiently than anything before it.
The work extends beyond laboratory coin cells. The researchers built a pouch cell—a larger, more practical format measuring 5.0 by 6.5 centimeters—with 44.558 milligrams of sulfur loading. This device achieved an initial energy density of approximately 674 watt-hours per kilogram, a figure that suggests the approach scales. Professor Yuichi Negishi of Tohoku University framed the broader significance: reticular chemistry—the art of designing ordered frameworks with specific chemical functions—can now be used to program battery interfaces at the molecular level. The TUS-44@G design offers a route toward lightweight, durable, and high-rate lithium-sulfur batteries by unifying polysulfide immobilization with catalytic sulfur conversion. What the team has shown is that you can take a separator—a piece of plastic that was once just a physical barrier—and turn it into a chemical reactor, one that actively solves the problems that have kept lithium-sulfur batteries from the real world.
Citas Notables
Our goal was to design an interlayer that does not simply block polysulfides, but actively manages their reaction pathway.— Saikat Das, Tohoku University
Reticular chemistry can be used to program battery interfaces at the molecular level, offering a route toward lightweight, durable and high-rate Li-S batteries.— Professor Yuichi Negishi, Tohoku University
La Conversación del Hearth Otra perspectiva de la historia
Why does polysulfide shuttling matter so much? Why not just use a different battery chemistry?
Because lithium-sulfur batteries have something no other chemistry offers at this scale: sulfur is abundant, cheap, and theoretically holds about five times more energy per gram than lithium-ion cathodes. The problem is that the intermediate compounds—the polysulfides—dissolve in the electrolyte and drift back and forth, stealing capacity. It's like having a perfect engine that leaks fuel. You can't just walk away from it.
So this TUS-44 material—it's not just a sponge that soaks up polysulfides?
No. That's the old thinking. A passive sponge would fill up and stop working. TUS-44 is more like a chemical assembly line. The nitrogen atoms grab the polysulfides, the crown ethers help move ions through, and the sulfur-rich units actually participate in the redox reaction. It's orchestrated.
What does the graphene add if the COF is already doing all that chemical work?
Speed. The COF is smart but it's not conductive. Graphene is a highway for electrons. Together they create what the researchers call cooperative chemical-electronic coupling—the COF tells the polysulfides what to do, and the graphene makes sure the electrons can get there fast enough to actually do it.
The numbers—1455 milliamp-hours per gram—how does that compare to what exists now?
Current lithium-sulfur batteries in the lab typically achieve 1000 to 1200 milliamp-hours per gram before they start degrading. This holds 1455 and keeps doing it for a thousand cycles. The real test is that 0.034 percent fade per cycle. That's the difference between a battery that works for a year and one that works for five.
Is this ready for a phone?
Not yet. The pouch cell they built is a proof of concept—it shows the chemistry scales beyond coin cells. But there's still work on manufacturing, cost, and integration. What this paper shows is that the fundamental problem—polysulfide shuttling—can be solved at the interface level. That's the hard part. The engineering comes next.