Semi-solid electrolyte improves lithium-sulphur batteries

Researchers in Singapore have designed a semi-solid electrolyte for lithium-sulphur batteries that is claimed to improve their safety without compromising battery performance.

L-R: Dr. Ayman AbdelHamid, Prof. Jackie Y. Ying and Mr. Jian Liang Cheong

The advance from A*STAR’s NanoBio Lab (NBL) is said to pave the way for lithium-sulphur batteries to be used as power solutions in electronic and energy storage applications.

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According to A*STAR, solid-state electrolytes have shown potential for improving the safety profile of lithium batteries, but their poor electrode/electrolyte contact and limited ionic conductivity have resulted in major conductivity bottlenecks and low performance. Their findings are published in Nano Energy.

Prof. Jackie Y. Ying, head of the NBL research team said: “Hybrid quasi-solid electrolytes comprising both liquid and solid components have emerged as a practical compromise to obtain safer batteries while maintaining good performance.

“However, the high resistance of the solid component has thus far limited the performance of such batteries. To overcome this, we have re-engineered the microstructure of the solid component. Our solution eliminates electrolyte leakage and is thermally and mechanically stable.”

The NBL research team is said to have designed a hybrid quasi-solid electrolyte comprised of a liquid-infused porous membrane made of Li7La3Zr2O12 (LLZO) sheets. The team also developed a novel one-step process of fabricating the LLZO sheets used to construct the framework for the electrolyte.

LLZO was chosen for its high ionic conductivity, and good chemical and electrochemical stability. The electrolyte’s non-rigid structure allows it to maintain very good contact with electrodes and prevents it from cracking during handling and battery assembly. This results in safer batteries with better performance. NBL’s semi-solid electrolyte is also claimed to be stable over a wide voltage range, allowing it to be used with different lithium battery electrode materials including high-voltage cathodes.

A lithium-sulphur battery made using NBL’s novel electrolyte showed high capacity, fast charge/discharge capability, and ‘interesting polysulfide shuttling control’ that stabilised the battery’s performance. In tests, the electrolyte achieved rate capability (~515 and ~340mAh/g at 1 and 2C, respectively) at 1.5 mg/cm2 loading density. A*STAR said in a statement that this is among the highest known performance achieved by lithium-sulphur hybrid quasi-solid batteries.

“Our 3D sheet-based framework was found to be crucial for optimal battery performance,” said Prof. Ying. “Moreover, our system demonstrated outstanding stability under extreme temperatures. These results illustrate the excellent potential of our sheet-based structure as a framework for other semi-solid lithium batteries.”

The NBL team is developing novel lithium-ion, lithium-sulphur and lithium solid-state batteries towards commercialisation.