A new hybrid material could bring lithium-sulfur batteries closer to practical use by improving their stability and energy storage performance.
A new covalent organic framework (COF)-graphene-based composite material has been created by scientists from Tohoku University and collaborating institutions have created a new material that may help overcome one of the key challenges preventing lithium-sulfur (Li-S) batteries from becoming commercially viable. The new material targets the so-called polysulfide shuttle effect responsible for active materials loss, self-discharge, and rapid decline in capacity.
Li-S batteries are regarded as a potential replacement of traditional lithium-ion (Li-ion) batteries due to their ability to deliver higher energy density and the use of sulphur, a cheap and plentiful substance. However, the formation of lithium polysulfides in charge or discharge cycles results in their migration from the sulfur cathode to the lithium anode.
In order to solve this problem, the research group designed a tetrathiafulvalene crown ether COF structure, named TUS-44, and combined it with graphene, which serves as an excellent electron transfer material, to prepare the TUS-44@G functional layer. This COF framework consists of imine nitrogen atoms, crown-ether oxygen atoms and sulphur-containing tetrathiafulvalene centers that can interact with lithium polysulfides.
Tested in batteries, this material proved to have high energy-storage performance, excellent performance even at higher charging rates, and low capacity fade over 1,000 cycles of charging and discharging. A Li-S pouch cell incorporating the material achieved an initial energy density of approximately 674 Wh kg⁻¹.
“Our goal was to design an interlayer that does not simply block polysulfides, but actively manages their reaction pathway,” explains Saikat Das, Junior Associate Professor at the Institute of Multidisciplinary Research for Advanced Materials, Tohoku University.
“This study shows that reticular chemistry can be used to program battery interfaces at the molecular level,” remarks 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.”
