Researchers at Tohoku University have developed a molecularly engineered battery interface that enables lithium-sulfur (Li-S) batteries to maintain stable performance over 1,000 charge-discharge cycles, addressing one of the technology’s biggest obstacles to commercial deployment.
Developed with collaborating institutions, the new graphene-enhanced covalent organic framework (COF) interlayer suppresses the polysulfide shuttle effect—a major cause of rapid capacity degradation in lithium-sulfur batteries. The research was published in the journal Small.
Battery Maintains Performance for 1,000 Cycles
Lithium-sulfur batteries offer significantly higher theoretical energy density than today’s lithium-ion batteries while using sulfur, an abundant and low-cost material. Their widespread adoption, however, has been limited by the migration of dissolved lithium polysulfides during charging and discharging.
These sulfur compounds move between the battery’s electrodes, triggering unwanted chemical reactions that gradually consume active material and reduce battery capacity over time.
Instead of relying on a physical barrier, the research team designed a multifunctional molecular interface that chemically captures polysulfides while allowing them to continue participating in the battery’s electrochemical reactions.
The new material, known as TUS-44@G, combines a tetrathiafulvalene-crown ether covalent organic framework with conductive graphene. The COF provides multiple chemical binding sites for lithium polysulfides, while graphene creates an efficient pathway for electron transport, allowing sulfur conversion reactions to proceed more effectively.
High Capacity With Minimal Degradation
Laboratory testing demonstrated that 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 retained 773 mAh g⁻¹ at a current density of 10 A g⁻¹.
Most notably, the batteries exhibited capacity fading of only 0.034% per cycle across 1,000 charge-discharge cycles, highlighting the effectiveness of the molecular interface in preserving long-term battery performance.
The researchers also demonstrated the technology in a lithium-sulfur pouch cell, achieving an initial energy density of approximately 674 Wh kg⁻¹, indicating its potential for practical high-energy storage applications.
“Our goal was to design an interlayer that does not simply block polysulfides, but actively manages their reaction pathway,” said 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.”
Toward Longer-Lasting High-Energy Batteries
The researchers say the study demonstrates how molecular engineering can significantly improve the lifetime of lithium-sulfur batteries.
Unlike conventional porous carbon materials, covalent organic frameworks can be designed with precisely controlled pore structures and chemical functionalities that simultaneously capture polysulfides, promote electron transport and accelerate sulfur conversion.
Professor Yuichi Negishi of Tohoku University said the approach offers a new strategy for engineering battery interfaces at the molecular scale.
“This study shows that reticular chemistry can be used to program battery interfaces at the molecular level.”
He added:
“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.”
By demonstrating stable operation over 1,000 cycles with exceptionally low degradation, the research represents an important step toward commercially viable lithium-sulfur batteries for electric vehicles, portable electronics and large-scale renewable energy storage.
