A "stretchy" polymer developed by scientists at Stanford University and the U.S. Department of Energy's SLAC National Accelerator Laboratory in Menlo Park, CA, could open a path to self-healing electrodes in the lithium-ion batteries of future electric vehicles. The polymer coats a silicon electrode, binds it together, and spontaneously heals small cracks that develop during battery operation, the researchers said. Carbon nanoparticles are added to the polymer to conduct electricity. Silicon electrodes swell to three times their normal size when ions flow into them during charging, then return to normal size upon release of the ions in discharge. Tests found that the electrodes lasted 10 times longer when coated with the polymer, "which repaired any cracks within just a few hours," said Stanford Professor Zhenan Bao. A major challenge to overcome is the polymer's durability. Significant energy-storage capacity loss occurred after about 100 charge-discharge cycles—far fewer than 3000 typical of an electric vehicle, the researchers acknowledge. "But the promise is there," said Yi Cui, an Associate Professor at SLAC and Stanford who led the research with Bao.