The amount of time it takes to recharge lithium-ion batteries has been a major impediment to consumer acceptance of electric vehicles. But a host of companies and researchers are working intensively to develop a battery that can recharge in 10 minutes and power a car for hundreds of miles.
If stopping for gas took five or six hours, would you rethink that road trip? How about an hour? When it comes to electric vehicles, topping up the “tank” does indeed take a long time, one of the primary barriers to more widespread adoption of EVs. So it is no surprise that there is an aggressive push to improve batteries and charging infrastructure, with a goal of making a stop for a recharge no different than a stop for gas.
But pushing a lot of power into a little battery in a short time presents daunting technical challenges. Standard lithium-ion batteries simply aren’t optimized to receive a charge quickly; the car, the plug, and even the wiring would likely need to be revamped in order to enable substantially faster power flow. And there are serious questions about whether the power grid is sufficiently robust to allow massive hits from thousands — or millions — of rapidly charging EVs.
Still, a wide range of companies — from major EV players like General Motors and Nissan to smaller battery manufacturers like Envia, PolyPlus, and A123 Systems — are all pursuing a durable, rapidly rechargeable battery. This means developing higher energy densities, smaller batteries, and — to reduce charging times — lowering internal resistance to ion flow. All these innovations must be achieved while reducing the chances of catastrophic failure, such as the battery catching fire, and keeping down the costs of manufacturing.
Many think rapid charging is coming within 5 to 10 years.
Paul Braun, who works on battery materials at the University of Illinois, said a car cruising down the road uses about the same power as 100 hundred-watt light bulbs. Charging rapidly would mean moving the power through the battery 20 times faster than it discharges — a major slug of power “many times what is supplied to your house,” Braun said.
Still, progress is being made, and many think rapid charging is coming within 5 to 10 years. Such improvements are sorely needed: Adoption of lower-emissions electric vehicles has been slow, and President Obama’s goal of having 1 million EVs on the road by 2015 may seem overly optimistic at this point.
The longest range EVs on the market now, such as the recently released Tesla Model S, can go up to 300 miles on a single charge, but still cost more than $70,000. The Nissan LEAF, which costs about $30,000, can travel less than 100 miles on a single charge, and the slightly more expensive Ford Focus Electric can travel a similar distance. Tesla’s Model S will yield about 60 miles of range per hour of charging with the best home plug-in systems, and even the LEAF’s smaller battery takes around an hour to charge.
“Part of the drive for the [Chevy] Volt, or even for the [Toyota] Prius, was to minimize changes in consumer behavior,” says Dane Boysen, a program director at the Department of Energy’s Advanced Research Projects Agency-Energy (ARPA-E). “You can buy a Prius and not change your behavior at all.” (The Volt and Prius are hybrid vehicles, sometimes running on electricity and sometimes on gasoline.) But at this point, all-electric vehicles still require significant changes in consumer habits.
So what are the main barriers to reducing charge times?
“One of the key challenges is that the batteries have an internal resistance to flow,” Braun says. Lithium-ion batteries are charged by moving charged particles from a cathode to an anode; pushing those ions into the anode takes time, and forcing them in faster heats up the battery and causes efficiency losses. And if you push too hard, lithium ions may build up in metallic form on the surface of the anode, a phenomenon known as plating, which can drastically shorten a battery’s lifespan. Even without plating, the effects of rapid charging might drop a battery’s life from thousands of cycles down into the hundreds.
“In a conventional battery, the pathways for the ion are very random and not always well connected,” Braun says. “That increases the internal resistance.” His group and others are working on ways to create highly structured internal battery architectures that allow for substantially faster electron and ion transport. Their technology has been licensed by a company called Xerion Advanced Battery Corp.
Scientists are aiming to get between 10 and 50 miles of driving range per minute of charge.
Gleb Yushin, a materials scientist at the Georgia Institute of Technology, says improving the design of the anode part of the battery, which is most commonly made out of graphite, is an active area of research for both increasing speeds and reducing plating issues. Smaller particles of graphite would enable a faster charge by allowing the ions to move in and out more easily, but small particles also mean lower capacity. Yushin says his lab and many others are trying to make anodes out of materials like silicon and tin that ideally would avoid plating when charged rapidly and would also increase energy density of the batteries.
Others are taking more radical looks at lithium-ion design. Prieto Battery, spun out of research at Colorado State University, uses copper nanowires as the anode and separates them from a cathode array with a polymer rather than the standard liquid electrolyte separator. The three-dimensional structure created by the tiny wires makes the distance a lithium ion must travel much shorter.
These approaches could yield a dramatic cut in charge time. Instead of one mile per minute, Braun says there is a reasonable goal of getting between 10 and 50 miles of driving range per minute of charge. At that pace, even a large battery could top up a 300-mile range in less than 10 minutes.
Braun says that in the lab, at least, very rapid charging is already here. In a paper published in the journal Nature Nanotechnology in 2011, Braun’s group reported achieving a charging rate that would yield a 90 percent full battery in only two minutes, using a three-dimensional nanoarchitecture. Prieto’s designs, meanwhile, could theoretically yield a 400-mile-range battery that could charge in only 10 to 20 minutes. The company thinks it can commercialize its battery within the next year; Braun says that 30 miles per minute of charge is coming within the next two to five years.
“The real question is, can the cost basis of the batteries be low enough to be competitive?” asks Braun. “A 50-percent increase in cost is not going to be tolerated.”
Some companies are pursuing other avenues for rapid charging, like battery swapping.
The big car companies are clearly focused on bringing those costs down and improving range. The next Nissan LEAF will reportedly have a longer, 155-mile range, and a low-end version could cost only around $27,000. GM has invested $7 million into a company called Envia Systems that has achieved an energy density in its battery of two to three times those currently in use, meaning 300-mile or greater range is possible at far lower costs than the Tesla Model S. Envia’s batteries could be used in future versions of the Chevy Volt or other EVs.
It isn’t just the battery that needs to improve. Boysen of ARPA-E says that as rapid charging technology is improved, it’s vital to develop a charging infrastructure. For example, there is almost no chance in the near future that real rapid charging — on the order of 30 miles per minute of charge or more — will take place when an EV is plugged in at home. The power capabilities of electrical outlets in a home simply aren’t built for the massive current needed to deliver such charges. Instead, the focus is on charging stations, just like gas stations.
Some “rapid charging” stations have already started to spring up around the U.S., with many more of them elsewhere around the world, most notably in Japan. Norway has installed 3,200 stations that offer slower charging of charge EVs, but plans to add 70 rapid charging stations by the end of the year. California-based AeroVironment is installing rapid-charge stations in the U.S. Frank Wong, the company’s director of strategic accounts, says their rapid chargers can take a Nissan LEAF from 20 percent to 80 percent charged in under 30 minutes. The company has more than 20 of these stations installed in Washington and Oregon, with more on the way in Texas and elsewhere. Tesla also recently announced plans for “Supercharger” stations to be installed on high-traffic corridors within a year that will be capable of charging the 300-mile-range batteries within an hour.
If rapid charging stations become ubiquitous, though, they may overload the grid. Braun imagines a rest stop on the New Jersey Turnpike at rush hour, 100 cars all plugging in and trying to charge up in a matter of minutes. “If they were all trying to put in 300 miles of electricity in five minutes, you’re going to need a major power plant sitting next door,” he says.
Some companies are pursuing other avenues for rapid EV charging, including ideas like battery swapping and wireless charging from current-emitting devices embedded in highways. One company, Better Place, has installed swapping stations in Israel and elsewhere, car wash-like structures where robots replace an EV’s depleted battery with a fresh one. Ideas like this would require substantial infrastructure, however, and aren’t likely to make a dent in the near term. For this concept to take off, some standardization of EV batteries would also be necessary.
All of the attempts to improve charge time basically boil down to the desire to keep using cars as we always have. People don’t complain that it takes a few minutes to put gas into the tank. If EVs are ever going to take over the market, refilling the battery will most likely have to be just as painless.
Article by Dave Levitan, appearing courtesy Yale Environment 360.
