Safer, Longer-Lasting Batteries for Cars
An Orlando startup has developed new manufacturing techniques that could improve the stability and lifetime of batteries used in electric vehicles. Planar Energy, a spin-off of the National Renewable Energy Laboratories (NREL), is working on scaling up solid-state lithium-ion batteries.
Conventional batteries, which typically use a liquid electrolyte, can suffer from undesirable chemical reactions that damage the battery’s cathode. Replacing the liquid electrolyte with a solid ion conductor can improve battery stability and lifetime, and also allow a battery to be smaller because additional components aren’t needed to maintain stability. Solid electrolytes are also compatible with a wider range of battery chemistries that could potentially offer higher power or storage density.
But solid-state batteries are expensive to make and have been difficult to scale up to the size needed for laptops or vehicles. Like other solid-state devices, solid-state batteries are normally made using complex, costly, vacuum-based deposition methods. The vacuum deposition limits the thickness of solid-state batteries, which, in turn, limits their energy storage capacity. So these thin-film batteries have been limited to use in small devices.
Efforts to use printing processes to make thicker solid-state batteries have been stymied by the lack of a printable solid electrolyte material (printed electrodes must usually be combined with a liquid electrolyte to carry the ions back and forth during charging and recharging).
Planar Energy has developed a roll-to-roll process for making larger solid lithium-ion batteries. The company, which received $4 million in funding from the Advanced Research Projects Agency Energy program this spring, says it can print solid batteries that offer three times more storage than liquid lithium-ion batteries of the same size. This boost in energy storage is possible primarily because the company’s all-solid batteries don’t require many of the support structures and materials that take up space in conventional batteries, making more space for energy storage.
Planar Energy expects to reduce capital costs by half compared with solid-state battery manufacturing using high-vacuum machinery. And the company says its processes can be used to make cells big enough to power electric vehicles.
“They’re able to make a solid electrolyte using a roll-to-roll process–that’s their strength,” says Sudipta Seal, director of the Advanced Materials Processing and Analysis Center at the University of Central Florida. The Florida center has independently verified the conductivity of Planar Energy’s electrolyte, which is as high as that of the liquid electrolytes used in today’s lithium-ion batteries. “The data show that the materials performance is very good,” says Seal.
The key to Planar’s technology is its printing process, says CEO Scott Faris. The advantage of vacuum deposition is that it’s possible to make very high-quality films, which result in materials with higher conductivity. Normally, this film quality is difficult to match using roll-to-roll processes.
Faris says Planar’s process is driven by chemical self-assembly. As chemical precursors stream onto the surface of a rolling metal or plastic substrate, they react with one another to form a network of nanoparticles. The company has adapted this self-assembling chemistry to make both the electrodes and the electrolyte.
“These batteries have many of the same attributes as thin-film batteries, but can be packaged in large formats,” says Roland Pitts, a senior scientist at NREL who has agreed to join the company. Planar Energy is developing three different battery chemistries. One of them combines lithium manganese oxide with other ions, and operates at about three to five volts with a charge capacity of 200 milliamp hours per gram. Pitts says this compares favorably with lithium cobalt oxide–a high-energy, high-power battery chemistry currently on the market.
Faris says the company plans to build its pilot line next year, and will start by making batteries for portable electronics to prove the viability of the printed solid-state batteries. In the long-term, he says, solid batteries have the potential to scale to automotive batteries. “We want to leapfrog current technologies and push onto something better,” says Pitts of Planar’s goals.
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