Researchers develop rubber electrolyte for EV batteries

ATLANTA—Researchers at the Georgia Institute of Technology have developed rubber electrolytes for electric vehicle batteries, which they say will make them more cost-efficient, safer and longer-lasting.

The research, conducted in collaboration with the Korea Advance Institute of Science and Technology, replaced liquid electrolytes in EV batteries with rubber-based polymers, according to Jan. 12 statement by Georgia Tech.

The team found that the material, when formulated into a 3D structure, acted as a "superhighway" for fast lithium-ion transport "with superior mechanical toughness resulting in longer charging batteries that can go farther."

In conventional lithium-ion batteries, ions are moved by a liquid electrolyte. However, the battery is inherently unstable, meaning that the slightest damage can leak into the electrolyte, leading to explosion or fire.

Due to such safety issues, the automotive industry is now looking into solid-state batteries, which can be made using inorganic ceramic material or organic polymers.

Currently, the main focus is on building inorganic solid-state electrolytes, said Seung Woo Lee, associate professor at the George W. Woodruff School of Mechanical Engineering.

But, he added, these materials are "hard to make, expensive and are not environmentally friendly."

According to the research team, rubber-based organic polymers are potentially superior to other materials due to their low manufacturing cost, non-toxicity and soft nature.

However, conventional polymer electrolytes do not have sufficient ionic conductivity and mechanical stability for reliable operation of solid-state batteries.

To address that issue, the team allowed the material to form a 3D interconnected plastic crystal phase within the robust rubber matrix.

"This unique structure resulted in high ionic conductivity, superior mechanical properties and electrochemical stability," said the Georgia Tech statement.

The rubber electrolyte, it noted, can be made using a simple polymerization process at low temperature conditions, generating "robust and smooth interfaces" on the surface of electrodes.

The rubber electrolytes prevent lithium dendrite growth and allow for faster moving ions, enabling reliable operation of solid-state batteries even at room temperature.

"Rubber has been used everywhere because of its high mechanical properties, and it will allow us to make cheap, more reliable and safer batteries," said Lee.

"Higher ionic conductivity means you can move more ions at the same time," said Michael Lee, a mechanical engineering graduate researcher.

"By increasing specific energy and energy density of these batteries, you can increase the mileage of the EV."

The researchers are now looking at ways to improve the battery performance by increasing its cycle time and decreasing the charging time through even better ionic conductivity.

So far, according to Georgia Tech, their efforts have seen "a two-time improvement" in the battery's performance/cycle time.

The project is part of an ongoing collaboration with SK Innovation, an intermediate holding company of Seoul-based chemicals giant SK Group.

SK Innovation, Georgia Tech said, is funding additional research of the electrolyte material to build "next-generation solid-state batteries."

The company announced in April last year that it was building a new EV battery plant in Georgia to produce an annual volume of lithium-ion batteries equal to 21.5 gigawatt-hours by 2023.

"All-solid-state batteries can dramatically increase the mileage and safety of electric vehicles," said Kyounghwan Choi, director of SK Innovation's battery research centre.

"Fast-growing battery companies, including SK Innovation, believe that commercialising all-solid-state batteries will become a game changer in the electric vehicle market," he added.