Seung Woo Lee (left) and Michael Lee (right) demonstrate their novel solid polymer electrolyte (rubber material) for all-solid-state batteries. Image: Georgia Tech.
Seung Woo Lee (left) and Michael Lee (right) demonstrate their novel solid polymer electrolyte (rubber material) for all-solid-state batteries. Image: Georgia Tech.

For electric vehicles (EVs) to become mainstream, they need cost-effective, safer, longer-lasting batteries that won’t explode during use or harm the environment. Researchers at the Georgia Institute of Technology (Georgia Tech) and the Korea Advanced Institute of Science and Technology have now discovered that such batteries could potentially be produced by utilizing rubber as the electrolyte.

Elastomers, or synthetic rubbers, are widely used in consumer products and advanced technologies such as wearable electronics and soft robotics because of their superior mechanical properties. The researchers found that the material, when formulated into a 3D structure, could act as a superhighway for fast lithium-ion transport with superior mechanical toughness, resulting in longer charging batteries that can go farther. They report their findings in a paper in Nature.

In conventional lithium-ion batteries, ions move through a liquid electrolyte. But this makes the battery inherently unstable: even the slightest damage can leak into the electrolyte, leading to explosion or fire. These safety issues have forced the industry to look at solid-state batteries, which can be made using inorganic ceramic materials or organic polymers.

“Most of the industry is focusing on building inorganic solid-state electrolytes. But they are hard to make, expensive and are not environmentally friendly,” said Seung Woo Lee, associate professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. Solid polymer electrolytes continue to attract great interest because of 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.

Georgia Tech engineers have now solved common problems with rubber electrolytes, such as slow lithium-ion transport and poor mechanical properties. The key breakthrough was allowing the material to form a three-dimensional (3D) interconnected plastic crystal phase within the robust rubber matrix. This unique structure results in high ionic conductivity, superior mechanical properties and electrochemical stability.

The rubber electrolyte can be made using a simple polymerization process at low temperatures, generating robust and smooth interfaces on the surface of electrodes. These unique characteristics of the rubber electrolytes prevent the growth of lithium dendrites and allow for faster moving ions, allowing 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,” explained Michael Lee, a mechanical engineering graduate researcher at Georgia Tech. “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 the cycle time and decreasing the charging time through even better ionic conductivity. So far, their efforts have seen a two-time improvement in the battery's cycle time.

This work could enhance Georgia’s reputation as a center for EV innovation. SK Innovation, a global energy and petrochemical company, is funding additional research of the electrolyte material as part of its ongoing collaboration with Georgia Tech to build next-generation solid-state batteries that are safer and more energy dense than conventional lithium-ion batteries. SK Innovation recently announced construction of a new EV battery plant in Commerce, Georgia, which is expected 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. Fast-growing battery companies, including SK Innovation, believe that commercializing all-solid-state batteries will become a game changer in the electric vehicle market,” said Kyounghwan Choi, director of SK Innovation’s next-generation battery research center. “Through the ongoing project in collaboration with SK Innovation and Professor Seung Woo Lee of Georgia Tech, there are high expectations for rapid application and commercialization of all-solid-state batteries."

This story is adapted from material from Georgia Institute of Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.