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<\/a>This prototype lithium ion battery contains a silicon electrode protected with a coating of self-healing polymer. The cables and clips in the background are part of an apparatus for testing the battery’s performance. Photo: Brad Plummer \/ SLAC<\/p><\/div>\n
Since that internal flexing eventually leads to cracking of electrodes, Dr. Cui\u2019s latest announcement brings some hope that such things can not only be overcome, but literally healed.\u00a0 Just as our bodies have internal resources to fight diseases and repair muscle and bone, batteries can be made to be self-healing.<\/p>\n
Dr. Cui has been a proponent of using silicon as a major component in electrodes, since its ability to soak up lithium during battery charging and release it readily on discharge is one of the best of any electrode materials.\u00a0 This has issues, though, in that as it flexes, the silicon tends to pulverize, rendering the battery useless.<\/p>\n
By coating electrodes with a stretchy polymer, Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory\u00a0 researchers have found a way to bind elements of the electrodes together <\/a>and \u201cspontaneously heal\u201d tiny cracks that otherwise develop and spread during the battery\u2019s operation.\u00a0 The team\u2019s report will appear in the November 19 issue of Nature Chemistry<\/i><\/a>.<\/p>\n Chao Wang, one of the post-doctoral researchers and co-author of the paper, explains, “Self-healing is very important for the survival and long lifetimes of animals and plants. We want to incorporate this feature into lithium ion batteries so they will have a long lifetime as well.”\u00a0 Wang developed the self-healing polymer alongside electronic skin created by Zhenan Bao, a professor of chemical engineering.\u00a0 This skin can be used on robots, sensors, and prosthetic limbs, mimicking human skin.\u00a0 Chao incorporated carbon nanoparticles to the polymer to make it electrically conductive.\u00a0 We seem to end up with a chemical circulatory system and electronic nerve replicants in this brave new battery world.<\/p>\n The comparison seems more apt when one realizes the scientists \u201cdeliberately weakened some of the chemical bonds within polymers \u2013 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.\u201d<\/p>\n This biomicry apparently paid off, with Bao reporting, “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.”<\/p>\n Dr. Cui and Bao reported that the coated electrodes worked for \u201cabout 100 charge-discharge cycles without significantly losing their energy storage capacity.\u201d\u00a0 Their goal for practical applications would be 500 cycles for cell phones and 3,000 cycles for an electric vehicle.<\/p>\n Stanford\u2019s report concludes, \u201cThe 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.\u201d<\/p>\n The research team also included Zheng Chen and Matthew T. McDowell of Stanford. Cui and Bao are members of the Stanford Institute for Materials and Energy Sciences, a joint SLAC\/Stanford institute. Hui Wu, a former Stanford postdoc who is now a faculty member at Tsinghua University in Beijing, is the other principal author of the paper.<\/p>\n The research was funded by the Department of Energy through SLAC’s Laboratory Directed Research and Development program and by the Precourt Institute for Energy at Stanford.<\/p>\n