Electric cars have not seen widespread use in part because the batteries don’t last long enough. But new research may clear the way for a new generation of batteries that can store more energy and have a longer life.
Researchers at Stanford University and the Department of Energy have made the first battery electrode that heals itself. The discovery opens the way for a new generation of longer-lasting lithium ion batteries that can be used in electric cars, cell phones and other devices.
The research, reported in the Nov. 19 issue of Nature Chemistry, involves the discovery of a stretchy polymer that coats the electrode, binds it together and spontaneously mends any tiny fissures that may occur during the battery’s lifetime. By mending the cracks, the battery lasted longer, says the team from Stanford University and the DOE’s SLAC National Accelerator Laboratory.
“We found that silicon electrodes lasted 10 times longer when coated with the self-healing polymer, which repaired any cracks within just a few hours,” says Stanford Professor Zhenan Bao.
Stanford researcher Chao Wang, one of the authors on the paper, said having a self-healing mechanism is vital to plants and animals and is what enables them to survive and live long lives. Researchers wanted to see if they could create such a mechanism for lithium ion batteries, so that they, too, could live long lives.
Researchers came up with the self-healing coating by making the chemical bonds in the polymer weaker. The result was a material that breaks easily but the cracked ends have a chemical attraction to each other, forcing them to link up again like magnets. Scientists liken it to DNA, which can assemble, rearrange and then break down.
Chao came up with the self-healing polymer in the same laboratory being used by researchers trying to create a more flexible electronic skin for prosthetic limbs, robots and other applications. Chao inserted carbon nanoparticles into the polymer he was creating for batteries, so they would conduct electricity, Stanford University reports.
A lithium battery can now store enough energy to make them practical, but researchers at Stanford wanted to see if they could extend that, said Yi Cui, a professor at both Stanford and SLAC. The polymer-coated electrodes performed well after 100 charge-discharge cycles, losing very little of their capacity to store energy. Their goal was to make it through 500 charge-discharge cycles for cell phones and 3,000 such cycles for electric cars, Cui said. While they’re tests fell short of that goal, the data was promising enough to make them believe they are on the right path, he said.
The holy grail for scientists doing research on lithium ion batteries is to create one that can store more energy in the battery’s negative electrodes without adding too much weight. Many have been making electrodes with silicon because they can soak up a great amount of lithium ions from the battery fluid as it charges, and those ions are then released as the battery is used. But electrodes made of silicon swell and shrink every time the battery charges and discharges, creating cracks in the brittle material that can hurt the performance of the battery.
It’s a problem for all electrodes in high-capacity batteries, says Hui Wu, who is on the faculty of Tsinghua University in Beijing and an author of the new research paper.
The researchers who worked on this project say they believe the approach, of making electrodes from silicon microparticles, could be applied to other electrode materials and may have applications in other industries.
To read the Stanford university aricle mentioned in this story, click here
To read the Nature Chemisty article mentioned in this story, click here