A couple of months ago, we told you about a so-called Terminator polymer that could heal itself. Now, researchers at Stanford University are using a similar material to improve the durability of lithium-ion batteries so they don’t crack under the pressure of use.
Researchers in Stanford’s and the Department of Energy’s SLAC National Accelerator Laboratory have developed a conductive self-healing polymer and used it to coat the electrode of a battery, which binds the electrode together and spontaneously heals tiny cracks that develop during battery operation.
This makes the battery more durable and able to withstand more charge and discharge cycles, lasting 10 times longer in tests in the lab than typical lithium-ion batteries, Chao Wang, a post-doctoral researcher working on the project, told Design News, in an email.
Stanford postdoctoral researcher Chao Wang holds a solid piece of the stretchy, self-healing polymer used to coat and protect silicon battery electrodes. Wang and colleagues at Stanford developed the polymer to help increase the lifetime of the batteries so if they crack under the pressure of use they can repair themselves.
(Source: Brad Plummer/SLAC National Accelerator Laboratory)
The benefit of using self-heal polymer is that the mechanical failures inside the battery can self-heal at the same time, maintaining the electrical and mechanical contact of the materials. In this way, the decay of the capacity can be much slower. We don't need to change the chemistry of the battery. The self-healing polymer composite serves as a coating on the active materials.
Wang -- who developed the polymer and coating method with Professor Zhenan Bao -- said the inspiration for the work comes from nature, pointing out the ability humans have to heal once we’ve been injured. However, existing self-healing polymers to date have not been conductive, which required Bao, Wang, and their team to modify a self-healing material that already existed by adding tiny nanoparticles of carbon to the polymer, Wang said.
We want to make the self-healing materials with electrical property, so we modified a previously known self-healing polymer, tuned the mechanical properties according to our need, and made it conductive. It can self-heal because it has a lot of hydrogen bonds, which are weak and reversible. So when there are mechanical damages, these hydrogen bonds will break first instead of covalent bonds. The hydrogen bonds will reversibly form and self-heal when the damaged interfaces get in touch again.
Wang and Hui Wu, a former Stanford postdoc who is now a faculty member at Tsinghua University in Beijing, co-authored a paper about their research in a recent article in Nature Chemistry.
Indeed, researchers have been trying a number of ways to create longer-lasting batteries for myriad devices and in particular electric vehicles (EVs), which still lack a viable battery that lasts long enough to go long distances without being recharged. Battery lifetime is also an issue for electronic devices like smartphones, as researchers seek ways to make batteries not only last longer before needing a recharge but also have a longer life span in general.
Many research efforts under way are experimenting with battery chemistries, trading ion for air in lithium-based batteries or trying a new spin on old chemistries, such as lead-acid batteries. The Stanford effort appears to be one of the first to find a new way to improve lithium-ion batteries not by altering the chemistry itself but by adding this self-healing property.
Wang said the next step for the research is to increase the battery’s lifetime even further and to apply the self-healing concept to other batteries besides lithium-ion. However, while the concept is promising to the future of batteries, it will likely be some time -- at least five to 10 years -- before this technology might be commercially available.