Researchers have found a promising alternative to conventional lithium-ion batteries: rubber. EV batteries consisting of rubber are expected to be cost-effective, stronger, and safer. Li-ion batteries have a high energy density. They are fragile, however. They contain flammable electrolytes and if damaged or incorrectly charged can lead to explosions and fires. If a lithium-ion battery is damaged, crushed, or is subjected to a higher electrical load without having overcharge protection, then problems may arise. External short circuits can trigger the battery explosion. Solid-state electrolytes can help reduce that risk, but they bring their own problems. Often made of ceramic materials, they can be somewhat fragile, and the interface between them and the electrodes can be patchy, reducing the conductivity of ions through the battery. All this can be evaluated in a failure analysis lab.
The Georgia Tech researchers say their new elastomer electrolyte takes steps towards solving both these problems. The rubbery material can bounce back from bumps to the battery, and maintains a smooth connection with the electrodes. That keeps its conductivity high but also prevents the growth of lithium dendrites, which are often the first step towards failure of a battery and can be determined in a suitable failure analysis lab.
Rubbers have superior mechanical properties. Therefore, they are widely used in consumer products and advanced technologies such as wearable electronics. The researchers 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.
Slow lithium-ion transport and poor mechanical properties are the major problems of batteries today. Georgia Tech engineers have solved these problems using the rubber electrolytes. The crucial insight was allowing the material to form a three-dimensional (3D) interconnected plastic crystal phase within the robust rubber matrix. When researchers tested the material in a metrology lab, they found that this unique structure has resulted in high ionic conductivity, superior mechanical properties and electrochemical stability.
“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, who is part of a team of researchers who have uncovered a rubber-based organic polymer superior to other materials. 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
This rubber electrolyte can be made using a simple polymerization process at low temperature conditions, generating robust and smooth interfaces on the surface of electrodes. These unique characteristics of 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 the 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, their efforts have seen a two-time improvement in the battery’s performance / cycle time.
“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.
“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.”Kyounghwan Choi, Director, SK Innovation
“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,” added Choi.
The research, conducted in collaboration with the Korea Advanced Institute of Science and Technology, was published in the journal Nature.
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Lee, M. J., et al. (2022) Elastomeric electrolytes for high-energy solid-state lithium batteries. Nature. doi.org/10.1038/s41586-021-04209-4.
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