- UNIST and KAIST develop high-performance electrolyte by mixing two solvents previously deemed incompatible

- Battery retains 80 percent capacity after 150 charge-discharge cycles, extending lifespan for electric vehicles and ESS

UNIST Professor Song Hyun-kon (left) and researcher Hong Jin-ki, who conducted the study. [UNIST]
UNIST Professor Song Hyun-kon (left) and researcher Hong Jin-ki, who conducted the study. [UNIST]

Korean researchers have developed a technology that can triple the lifespan of next-generation electric vehicle batteries by combining two solvents long considered unsuitable for the purpose — and finding that the mixture actually boosts performance.

The Ulsan National Institute of Science and Technology (UNIST) announced Monday that a joint research team led by Professor Song Hyun-kon of its Department of Energy and Chemical Engineering and Professor Seo Dong-hwa of KAIST's Department of Materials Science and Engineering had developed a high-performance electrolyte that dramatically extends the lifespan of lithium-metal batteries.

Lithium-metal batteries are a next-generation technology that uses lithium metal as the anode instead of the graphite found in conventional lithium-ion batteries. They can theoretically nearly double battery capacity, making them a key technology for extending the driving range of electric vehicles.

A persistent problem, however, has been that lithium metal reacts unnecessarily with the electrolyte during charging and discharging, causing battery capacity to drop sharply. The effect worsens the higher the voltage used to store more electricity.

To address this, the research team turned its attention to two solvents: ethylene carbonate (EC) and sulfolane (SL).

Both solvents had been considered unsuitable for lithium-metal batteries because of their tendency to bind strongly to lithium ions.

The team flipped the conventional approach. Rather than avoiding the two solvents, it mixed them together.

EC and SL were blended in a 3-to-7 ratio, then combined with a lithium salt and a small amount of an additive to stabilize the protective film on the electrodes.

Mixing the two solvents actually weakened each one's grip on lithium ions. The molecules of the two solvents attracted each other, reducing their individual binding strength with lithium ions. The team named this phenomenon "co-solvation."

When the team applied the new electrolyte to a high-nickel cathode lithium-metal battery and charged it to 4.5 volts at 25 degrees Celsius, the battery retained about 80 percent of its initial capacity after 150 charge-discharge cycles.

The "co-solvation" effect that occurs when the two solvents are mixed. [UNIST]
The "co-solvation" effect that occurs when the two solvents are mixed. [UNIST]

By contrast, batteries using conventional carbonate-based electrolytes fell below 80 percent of initial capacity after roughly 50 cycles — meaning the new electrolyte delivers about three times the charge-discharge lifespan under the same capacity threshold.

Coulombic efficiency, which measures how effectively lithium is reused during cycling, reached 98.24 percent initially and averaged 99.35 percent.

Gas generation from electrolyte decomposition and the dissolution of nickel from the cathode were also reduced.

The team expects the technology to be applicable not only to lithium-metal batteries but also to high-voltage lithium-ion batteries and next-generation sodium- and potassium-ion batteries.

"We improved electrolyte performance using commercially available solvents without relying on expensive fluorinated solvents or high-concentration salts," Song said. "We expect this to help extend the service life of high-capacity lithium-metal batteries for use in ESS and electric vehicles."

The findings were published in the Aug. 11 issue of ACS Nano, an international journal in the field of nanoscience.


nbgkoo@heraldcorp.com