An everyday material that we all know well may lead to safer, longer-lasting batteries for the electric vehicle.
Mechanical engineering graduate researcher Michael Lee, part of a team at Georgia Institute of Technology, is rethinking an essential battery component by reshaping rubber.
The polymer acts as a new structure for the battery transport solution known as the electrolyte.
The Georgia Tech-developed electrolytes, synthesized from a liquid precursor solution, consist of plastic and salt monomers that bond to form a rubber polymer. Through heat, the rubber transforms into what the researchers refer to as a "3D interconnected plastic crystal phase."
When the monomers turn to polymers, the plastic crystals "coarsen," said Lee, within a rubber matrix, enabling the three-dimensional shape.
Lee worked alongside Georgia Tech Professor Seung Woo Lee in the development effort.
The rubber-based battery has the following components: a lithium metal anode, rubber electrolyte, and a lithium nickel manganese cobalt oxide cathode. The rubber electrolyte is mainly composed of lithium salt, an elastomer known as poly (butyl acrylate), and a plastic crystal called succinonitrile.
The unique structure has resulted in high ionic conductivity, improved mechanical properties, and electrochemical stability — three traits that support the advancement of the electric vehicle.
Electric vehicles call for lithium-ion batteries, but the ions are usually moved by a liquid electrolyte. When a battery is damaged, the flammable electrolyte presents a fire hazard.
The safety issues presented by lithium-ion batteries have led to alternative ideas, like solid-state batteries that use rubber materials.
Lee and the team's rubber electrolyte can be made at low-temperature conditions, generating robust and smooth interfaces on the surface of electrodes. The structure of the rubber electrolytes prevent damaging lithium dendrite growth and allow for faster moving ions, enabling reliable operation of solid-state batteries even at room temperature.
“Higher ionic conductivity means you can move more ions at the same time,” said Michael Lee in a recent news release . “By increasing specific energy and energy density of these batteries, you can increase the mileage of the [electric vehicle] EV.”
In a Q&A with Tech Briefs below, Lee explains more about the possibility of rubber-based battery hitting the road.
Tech Briefs: What inspired you to try rubber?
Michael Lee: The conventional solid-polymer electrolytes have been limited to employ, due to their low ionic conductivity at room temperature and insufficient mechanical stability. Rubber is a very common material that is used exceptionally in different industries. Rubber, however, has not been considered as electrolyte for lithium batteries due to its low ionic conductivity: a measure related to the movement of ions, and an important parameter for the electrolyte to operate batteries.
Here, we hypothesized that the 3D-structured rubber electrolyte simultaneously enabled the use of rubber as electrolyte material and overcome the aforementioned challenges of conventional solid polymer electrolytes.
Tech Briefs: Is this considered an “unconventional” material choice?
Lee: I would say, we have selected conventional materials, but it is an “unconventional” material choice for battery applications.
Tech Briefs: Are there any manufacturing challenges?
Lee: We think that the rubber is highly possible to be employed in the current manufacturing process.
Tech Briefs: Why is rubber a special material to use as an electrolyte?
Lee: The solid electrolytes are not able to stretch and bend due to their brittleness; rubber, however, has a superior mechanical stability. Based on our experimental data, our rubber electrolyte can be extended up to almost 300% from the original state. Such a mechanical property is a key factor to operate the next-generation lithium batteries, including lithium metal batteries, which calls for replacing the graphite anode from lithium-ion batteries with a lithium metal anode to increase energy density of batteries.
Tech Briefs: What makes the use of rubber safer?
Lee: The conventional organic liquid electrolytes are employed in lithium-ion batteries. These electrolytes easily catch on fire, leading to battery explosion. On the other hand, the rubber electrolytes are safer due to their flame retardancy.
Tech Briefs: How much power is possible from a battery using this rubber component?
Lee: The rubber electrolyte-based lithium metal batteries can exhibit high energy density exceeding 410 Watt-hours per kilogram (Wh/kgelectrode+electrolyte) and maintained a high energy density of 235 Wh/kgelectrode+electrolyte at a power density of 184 Wh/kgelectrode+electrolyte. If it can be commercialized, the EVs with the rubber electrolytes-based Li batteries can travel over 490 miles on a single charge compared to EVs with the conventional Li-ion batteries (310 miles)
Tech Briefs: What needs to happen for a rubber component to be a mainstream part of battery technology?
Lee: Large-scale productions of rubber electrolytes need to be investigated at a manufacturing level to be a mainstream part of battery technology.
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