A team of researchers from Stanford University and the Department of Energy's SLAC National Accelerator Laboratory have made the first battery electrode that heals itself by using a stretchy polymer that coats the electrode, binds it together and spontaneously heals tiny cracks that develop during battery operation.
Chao Wang, a postdoctoral researcher at Stanford, developed the self-healing polymer in the lab of Stanford professor Zhenan Bao, whose group has been working on flexible electronic skin for use in robots, sensors, prosthetic limbs and other applications. For the battery project he added tiny nanoparticles of carbon to the polymer so it would conduct electricity.
"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," Bao said.
"Self-healing is very important for the survival and long lifetimes of animals and plants," said Wang, "We want to incorporate this feature into lithium ion batteries so they will have a long lifetime as well."
To make the self-healing coating, scientists deliberately weakened some of the chemical bonds within polymers—long, chain-like molecules with many identical units. The resulting material breaks easily, but the broken ends are chemically drawn to each other and quickly link up again, mimicking the process that allows biological molecules such as DNA to assemble, rearrange and break down.
"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," Bao said.
"Their capacity for storing energy is in the practical range now, but we would certainly like to push that," said Yi Cui, an associate professor at SLAC and Stanford who led the research with Bao.
The electrodes worked for about 100 charge-discharge cycles without significantly losing their energy storage capacity. "That's still quite a way from the goal of about 500 cycles for cell phones and 3,000 cycles for an electric vehicle," Cui said, "but the promise is there, and from all our data it looks like it's working."
The self-healing electrode, which is made from silicon microparticles seems to offer a practical road forward, Cui said. The researchers said they think this approach could work for other electrode materials as well, and they will continue to refine the technique to improve the silicon electrode's performance and longevity.
The researchers reported the advance in the Nov. 19 issue of Nature Chemistry.
The research was funded by DOE through SLAC's Laboratory Directed Research and Development program and by the Precourt Institute for Energy at Stanford University. DOE's Office of Science is the single largest supporter of basic research in the physical sciences in the United States.
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