Lithium-metal battery charges in 15 minutes, retains 94% capacity after 100 cycles

South Korean scientists have just unveiled a new liquid-crystal polymer separator, which, when tested in a lithium-metal battery, retained 94 percent of its capacity after 100 charge-discharge cycles at a 4C charging rate.

The separator was built by the a research team at the Korea Advanced Institute of Science and Technology (KAIST). It could reportedly improve battery stability and charging speed, meaning drivers could charge their EVs in just 15 minutes.

The study was led by Dong Ki Yoon, PhD, and Hye Ryung Byon, PhD, professors at KAIST’s Department of Chemistry. “Lithium metal batteries can store more energy than conventional batteries,” they stated. “However, during charging, lithium can accumulate in sharp, branch-like structures known as ‘dendrites.'”

For the separator, the researchers used liquid-crystalline polymers to control how the lithium ions move inside lithium-metal batteries. Both Yoon and Byon believe that their find could address slow ion transport and dendrite formation.

A highway for lithium ions

Lithium-metal batteries can store more energy than conventional ones. However, during charging, lithium can accumulate on the electrode surface and, as a result, form dendrites. These tiny needle-like metallic crystals grow on the anodes, and they can damage the separator between the electrodes, which could cause short circuits and increase the risk of fires.

To address this problem, the team created a porous separator made from liquid-crystalline polymers, which have an ordered structure like solids. They also share some properties with liquids. For the project, the team incorporated polyethylene glycol (PEG) chains into the material to facilitate lithium-ion transport.

The scientists then monitored the alignment of the liquid-crystal molecules and arranged them either vertically or horizontally to examine how their orientation affected ion movement. The vertically aligned separator created direct pathways for lithium ions to travel toward the electrodes.

In contrast to the horizontally aligned separator, it reduced the tortuosity (winding nature), of the ion transport pathways by about 2.5 times. This allowed the lithium ions to move faster and more uniformly. What’s more, it suppressed the dendrite formation and improved the battery stability.

Longer battery life

Ultimately, the researchers tested the separator in a working lithium-metal battery to evaluate its performance. To their massive surprise, the cell retained 94 percent of its initial capacity after 100 charge-discharge cycles at 4C. In simple terms, a 4C charging rate means a battery can fully recharge in 15 minutes.

According to the team, controlling how molecules are arranged could potentially make batteries charge faster and last longer without compromising safety. Yoon emphasized the significance of this finding for future battery development.

He said that molecular alignment plays a key role in battery performance. “We expect this approach to contribute to the development of high-energy-density next-generation battery technologies, for which long driving ranges and rapid charging are essential,” he concluded in a press release.

The scientists believe the approach could contribute to the development of high-energy-density batteries for future EVs, where rapid charging and longer driving ranges are essential. Further tests will, however, show whether it works in larger batteries as well.

The study has been published in the journal ACS Nano.