There are a number of obstacles limiting public acceptance of battery-electric vehicles, everything from price and range to the lack of a nationwide public charging network. And then there’s the hassle of waiting once a battery-electric vehicle is plugged in.
At best it takes 20 minutes or more to get an 80% recharge using the latest “quick” chargers. And with most BEVs, that can push to an hour or more. But a new technology being developed by researchers at Ford and Purdue University could bring those times down to the point where an EV can charge up as quickly as a motorist can fill a gas tank.
The Ford system uses a novel technology capable of “pumping” out more current than today’s chargers. Meanwhile, researchers at General Motors and elsewhere are focusing on new battery designs that can store energy more quickly.
“Today, chargers are limited in how quickly they can charge an EV’s battery due to the danger of overheating,” said Michael Degner, senior technical leader, Ford Research and Advanced Engineering.
More power, more heat
There are a variety of different types of chargers. Level 2 systems, the one most commonly in use today, deliver 240 volts of AC power. For a vehicle capable of delivering 300 miles of range they typically require eight hours or more if the battery pack is drained. Quick chargers switch to 400-volt DC current and can provide anywhere from 50 to 350 kilowatts of energy.
“Charging faster requires more current to travel through the charging cable,” said Degner. “The higher the current, the greater the amount of heat that has to be removed to keep the cable operational.”
Today’s 350 kW chargers use a liquid cooling system for the cable that plugs into an EV. But the Ford/Purdue liquid-to-gas system appears to dissipate substantially more heat, Degner claims, and that would allow it to deliver even more power.
“The cable uses liquid as an active cooling agent, which can help extract more heat from the cable by changing phase from liquid to vapor,” Ford explained in a statement, “the key difference between this and current liquid-cooled technology on the market.”
The system will now go through a two-year test program that could lead to it being put into production, said Issam Mudawar, a professor of mechanical engineering at Purdue.
The better battery
Heat doesn’t just build up in the charging cable. It’s also a problem within the battery itself. And that also limits the speed at which a pack can charge. Excess heat also presents a risk of fire, especially if there are manufacturing defects within a battery — as is the case with the Chevrolet Bolt EV now being recalled.
Onboard climate control systems dissipate heat — but only so quickly. Other researchers are focusing on ways to improve the battery itself in order to speed up the charging process. As with a charger, the challenge is overcoming resistance that creates heat and limits the speed at which energy can flow.
Researchers are looking at solutions that include new materials for a battery’s cathode and anode, as well as new chemistries for the slurry of liquid inside today’s lithium-ion batteries. GM President Mark Reuss told TheDetroitBureau.com this approach could reduce charging times for the automaker’s new Ultium batteries to as little as 10 minutes — though he doesn’t expect to reach that target until late this decade.
Even more dramatic approaches are under development. Solid-state batteries replace the goo inside a battery with a solid “substrate,” such as a ceramic. That promises less resistance and heat, among other benefits. And there could be entirely new batteries in the industry’s future, such as aluminum ion and metal air.
A better experience for EV owners
Whatever the approach, finding a way to speed up battery charging will prove just as important as expanding the public charging network, said Stephanie Brinley, principal auto analyst with IHS Markit.
“It comes down to a better holistic experience for the driver” that makes it easier to switch from internal combustion to battery-electric power, said Brinley.