The Car of the Future Will Heal Itself

One clear advantage of electric vehicles over conventional cars is the simplicity and longevity of the electric drive system. That's a big plus for fleet managers in terms of maintenance, repair and replacement costs, and now a research team from Stanford University and the Department of Energy's SLAC National Accelerator Laboratory has extended the savings by engineering a self-healing element into the EV battery itself.

Inspired by biomimicry, the team has come up with a new polymer (a form of plastic) that can be coated onto the electrode in a lithium ion battery. As with natural systems like the human body, which rely on self healing to survive, the flexible coating is designed to act autonomously and heal the cracks that develop on electrodes during the battery lifecycle.

A biomimicry tweak for EV batteries

In one of those happy accidents of science, the immediate motivator for the team's self-healing battery project was the need to develop a long-lasting, flexible "electronic skin" for robots and prosthetic devices.

As it turned out, the polymer coating also tackles a huge problem in lithium ion (Li-ion) energy storage, which is the loss of capacity over time as the battery runs through charging and discharging cycles.

The problem is the use of silicon in Li-ion EV batteries. As a non-exotic, relatively low-cost material, silicon is of great interest in EV battery technology. However, while silicon has a tremendous capacity for absorbing and releasing ions, it also swells and shrinks as the battery charges and discharges. Over time, this causes cracks to form and the silicon becomes brittle, putting a big crimp in battery performance.

To solve this problem, the biomimicry angle goes to work on a molecular level. Polymers are long molecules formed in chains. Rather than strengthening the bonds that hold the chain together to form a tougher material, the research team weakened some of them.

The result was a new polymer that breaks apart easily like human skin, but the ends can quickly find each other and form a new bond.

A good beginning for self-healing electrodes

As described by Stanford writer Andy Freeberg, when carbon nanoparticles are added to the polymer it conducts electricity, so its application to a battery electrode is an obvious one.

In lab tests, the cracks in a polymer-coated electrode healed themselves within a matter of hours, and the battery experienced no significant loss of energy storage capacity after 100 charging cycles.

For those of you familiar with EV battery technology, 100 charging cycles is peanuts, but at least it's a promising start. The results indicate that silicon electrodes last ten times longer when coated with the self healing polymer, and the research team has already set a goal of 3,000 cycles for EV batteries.

We built this!

If the research team is successful, the result will be EV batteries that promote important lifecycle benefits for vehicle fleets by avoiding the use of expensive and/or toxic materials while reducing replacement costs.

Since this is a benefit for individual consumers, fleet owners and EV manufacturers alike, it's worth noting that all of us taxpayers have chipped in to get the job done.

The research team was funded by the Department of Energy through SLAC, a federal laboratory managed by Stanford University for the Energy Office of Science. It conducts foundational cutting edge research that might not involve bottom line benefits in the here and now, but could eventually lead to commercial applications that translate into profitability and economic growth.

[Image: Bandages by Keith Ramsey]

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