Scientists working at the Oak Ridge National Laboratory (ORNL) have developed a new kind of solid-state battery technology that could double the energy density in electric cars.
The distance electric vehicles (EVs) can travel between charges — known as their range — has been on a steady upward curve for the past decade, tripling from 80 miles (129 kilometers) in 2010 to 220 miles (354 km) in 2021.
But limits apply on how efficient they can become due to both the chemistry of liquid electrolyte lithium-ion (Li-ion) batteries that currently power EVs and their weight. As explained in Heatmap in 2023: “The lithium-ion packs in EVs are the state of the art in modern battery technology … But their energy density still pales in comparison to gasoline. So, giving a car hundreds of miles of driving range means slinging a huge, heavy battery along the bottom of the vehicle.”
A new advancement in solid-state batteries, outlined in a study published May 10 in the journal ASC Energy Letters, could change all that, though.
It relies on storing power in flexible and durable sheets of solid-state electrodes that are 30 micrometers thick — roughly the width of a human hair. The technology, if developed, could double energy storage from the current maximum energy density in EV batteries to 500 watt-hours per kilogram, the scientists said in a statement.
The problem with solid-state
Solid-state batteries are not a new idea, and researchers at ORNL previously laid the foundations for their creation and use in the 1990s. They have been used in small formats to power pacemakers, RFID tags — such as loss prevention tags used in stores —, and wearables for many years.
But when it comes to powering EVs, they haven't been durable or scalable enough. Furthermore, the plastic polymers used in most solid-state batteries currently have a lower conductivity than liquid electrolytes, which makes them less performant.
The scientists overcame these problems by using a polymer to create a "strong yet springy thin film" that could give solid-state batteries a much higher energy density. This exceeds not only what's currently available in the best solid-state batteries but liquid Li-ion technology too, the scientists said in the statement.
The sheets allow for the separation of negative and positive electrodes, preventing short circuits while still providing high-conduction paths for ion movement. It also uses sulfide solid-state electrolytes, which have a similar level of conductivity to the liquid electrolytes used in Li-ion batteries and thus offer a similar level of performance.
"We want to minimize the polymer binder because it does not conduct ions," lead author of the study Guang Yang, R&D associate at ORNL, said in the statement. "The binder's only function is to lock the electrolyte particles into the film. Using more binder improves the film's quality but reduces ion conduction. Conversely, using less binder enhances ion conduction but compromises film quality."
A high-performing, safer EV battery
The next step for the scientists will be to build a device that allows them to test their findings under practical battery conditions in a lab. They will also partner with researchers in academia and industry to develop wider testing.
Should the research lead to the production of a new generation of EV batteries, it could not only give electric cars a much greater range but also make them safer, the scientists added in the statement.
Li-ion batteries are volatile and, while fires are rare, they're highly toxic and difficult to extinguish. According to the U.K's Institution of Fire Engineers (IFE), over 100 organic chemicals are generated during an EV fire, including fatal carbon monoxide and hydrogen cyanide.
Nevertheless, rather than attempting to put out the fire, car manufacturers recommend that firefighters let the fire burn out. This is in part because of how much water would be used — approximately 1,125 liters per minute — which would create dangerous runoff that could enter public drainage systems, according to the IFE.
Additionally, even when Li-ion battery fires have been seemingly extinguished they can reignite "hours, days or even weeks" later not just once but many times over. The new ORNL-developed technology, on the other hand, is non-volatile meaning there would be no such risk in EVs using it in a solid-state battery.
