Bumps ahead for EV drivers: ‘Plating’ and demand spikes

Source: By John Fialka, E&E News reporter • Posted: Wednesday, August 5, 2020

Researchers see two challenges that could disrupt the nation’s transition to electric transportation: degraded batteries stemming from rushed charging and spikes in power demand as plug-in cars flood U.S. roadways.

A pair of studies from the National Renewable Energy Laboratory (NREL) assert that there’s no quick fix to these problems without more research into lithium-ion batteries and further innovations in the nation’s charging systems.

The first study points to “critical barriers” to how fast EVs can be recharged. To be competitive with gasoline vehicles, electric cars should be capable of a full charge in 15 minutes or less, the researchers say.

According to Donal Finegan, a scientist at NREL’s Center for Integrated Mobility Systems, the current life of big, expensive car batteries can be degraded by what is called “lithium plating.” The condition occurs on car battery terminals when attempting superfast charging.

Lithium, a soft, silvery-white and soluble metal, tends to be unstable. Plating, Finegan pointed out, “makes it more so when you’re trying to charge as fast as you can.” Instead of being absorbed into the graphite battery terminal, lithium can solidify during fast charging, forming plates on the terminals.

Finegan and a team of other scientists were able to watch the plating process by probing recharging batteries with powerful X-rays from a device called a synchrotron. “Once lithium plating occurs, the cell becomes increasingly unstable, potentially leading to thermal runaway and battery failure,” they concluded.

Steps can be taken to minimize plating damage. One suggested by an auto manufacturer is to use the EV’s motors to heat the battery before recharging.

Another is already done by many EV drivers: Charge the car overnight. The slower rate of charge prevents plating. But Finegan noted in an interview that some drivers may not have the patience or the schedule for that method.

He thinks a better fix will require additional research into the use of more tolerant battery materials. The plating problem is currently controlled with software that prevents a battery from being fully recharged at high speeds.

Finegan calls this a “trilemma” for auto manufacturers. They think the ideal EV should be reasonably priced, be able to travel 300 miles on a single charge and allow fast charging.

“You can have two of those but not all three,” he said, noting that most car manufacturers value range and moderate prices more than fast charging.

With current technology, faster charging would shorten battery life. That is expensive because lithium-ion batteries can account for as much as 65% of the price of an EV.

The problem posed in a second NREL study is about helping the nation’s electric grids deal with “gigawatt-growth in electricity demand” from EVs.

That leads to another paradox.

If every EV owner was able to drive home and begin charging their vehicle overnight, it would help extend battery life. But it could also overload power grids by creating spikes in energy demand in the evening when homeowners turn on their appliances, televisions and air conditioning.

Andrew Meintz, an NREL researcher leading two teams of scientists exploring EV charging and its impact on power grids, described two approaches to the problem. There’s the “supersimple” one in which it’s left up to automakers and consumers to work out.

Then there’s the “whiz-bang” approach. That’s when local governments might ration charging times to avoid big, regional power spikes.

Meintz’s researchers found problems with both of them.

Under the first one, electric car owners might eventually find ways to stagger their evening charging habits to avoid blackouts. But that could be negated by the arrival of heavy-duty electric trucks, which might create large power demands at all hours of the day.

“Picture every employee at your workplace driving home at 5 p.m. and charging their vehicle. That is the grid’s equivalent of going 0 to 100 mph, and if it does not wreck the system, it is at least very expensive,” Meintz noted in a paper.

Instead, his study suggests encouraging hydrogen-powered electric trucks, which use fuel cells to make their electricity.

One simulated solution the researchers are pondering would be for charging station owners to use electrolyzers to separate hydrogen from water during periods of low electricity use. The hydrogen could then be stored and used to refuel fuel cell trucks during periods of high electric demand.

As one researcher put it, perhaps somewhat hopefully: “If done smoothly, the utility doesn’t even know it’s happening.”

The study noted that “several well-known transportation and fuel companies have recently initiated a multimillion-dollar partnership with NREL to advance heavy-duty hydrogen vehicle technologies.”