Electric vehicles are quieter, easier to repair and maintain, and far better for the environment than traditional internal combustion cars. Still, numbers of EVs on the road are trailing behind the cars they’re supposed to replace, in part due to charging times.
While refueling a gas tank only takes a few minutes, charging an EV takes a lot longer. Right now, the fastest chargers available to consumers, sometimes called Level 3 chargers, can charge a vehicle battery to 80 percent in as quickly as 20 minutes. But the most available (and affordable) chargers are far slower. Level 2 chargers take several hours to charge a vehicle, and Level 1 chargers—which plug into a typical home outlet—can take more than two days.
These slow charging speeds have only exacerbated “range anxiety”—the concern that batteries could run out of charge on the road. More than 50 percent of 500 EV owners who participated in a 2022 OnePoll survey commissioned by Forbes Wheels said they frequently or always have this concern. While Secretary of Transportation Pete Buttigieg has pushed back on the idea that drivers should be so worried about range, it remains a major hurdle for prospective EV buyers. That, and the fact that demand for EVs outpaces the ability of car manufacturers to make them, threatens to slow down the road to electrification.
Scientists, including those at universities, at major electric vehicle manufacturers and at the Department of Energy, think that EVs could power up more quickly if we push the science of charging to its limits. They argue that tweaking the internal chemistry of EV batteries and the design of charging cables can help eliminate this major barrier to adoption. The challenge is speeding up charging without compromising on safety or the long-term life of the battery. The goal is to get as close as possible to the time it takes to refuel an internal combustion vehicle.
“There are a lot of innovations on the electrochemistry side that are still in the laboratory,” says Christopher Rahn, who co-directs the Battery and Energy Storage Technology Center at Penn State University. “They may be more expensive [and] maybe require different manufacturing processes. They’re not necessarily ready to be rolled out on a massive scale, but certainly lots of researchers have some exciting results.”
The fundamental challenge of charging lies in batteries’ electrochemistry. Batteries are designed with two electrodes: an anode and a cathode. Lithium ions flow between these two components. When a battery is discharging and powering a car, lithium ions travel from the anode to the cathode, which produces free electrons and electric charge. When the vehicle is charging, the reverse happens, and the lithium ions are pushed back toward the anode.
The problem is that inside the battery, lithium ions face a critical speed bump. If they travel too quickly, they’ll get stuck and won’t be able to enter the anode. When lithium ions get caught, there are fewer lithium ions to provide charge, which makes the battery less effective. Worse still, if too many lithium ions build up, the battery can short-circuit and, potentially, start a battery fire.
“It turns out that moving lithium is a bit like getting 100 people into a narrow room,” says Venkat Srinivasan, director of the Argonne Collaborative Center for Energy Storage Science and deputy director of the Joint Center for Energy Storage Research in Illinois. “There’s a small door. I’d have 100 people start piling into the doorway. They’re all going to get stuck in that doorway.”
Now, some think that using new battery chemistries could make it easier for lithium ions to move within a battery cell. At Argonne, researchers are studying whether it’s possible to use multiple pathways for lithium ions to travel within a battery—and essentially reduce crowding. The challenge is designing these doorways on a microscopic level, explains Srinivasan.
Another idea is to investigate whether using different electrolytes—the liquid component used to shuttle lithium ions in the batteries—as well as new solvents and additives could speed up the charging process.
Of course, changing battery chemistries is an extremely arduous process and requires extensive testing and validation. An easier approach to implement involves updating the software used to manage the batteries as they charge. Right now, batteries charge at a constant current, which causes charging speeds to decline as the battery refuels. Researchers at the Idaho National Laboratory believe better battery algorithms could make charging faster, by adjusting the current flowing into the battery as it’s being charged.
“Maybe you keep the current low and then when the battery reaches around 30 percent state of charge, you can increase the current, because at that time the battery’s internal resistance is low,” explains Tanvir Tanim, a senior staff scientist at the Idaho National Laboratory. “When it goes closer to fully charged, then you, again, reduce rate.”
Some futuristic charging concepts go beyond the battery. At Purdue University, mechanical engineering professor Issam Mudawar is investigating how new cooling technology could improve EV charging cables. Right now, researchers think that faster-charging EVs would need charging cables that can handle far more amperes—the unit for electric current—than what vehicles can handle today. Most chargers today can provide about 500 amperes. Right now, any additional current would produce too much heat.
But Mudawar, who has previously collaborated with Ford Motor Co., is developing a system that would use special cooling technology to get more than 2,400 amperes—1,400 amperes of current would put five-minute EV charging within reach. Mudawar’s system uses a modified form of liquid coolant that has its roots in technology used by NASA. Rather than using a pure liquid coolant, the system uses a form of subcooling boiling that takes advantage of forming bubbles.
“The higher the electrical current, the more heat is dissipated,” explains Mudawar. “When you're talking about very high currents in order to achieve the five-minute charging, the amount of heat that has to be removed internally is very large.”
Super-fast EV charging would require more than successful laboratory demonstrations. In order to work, these futuristic charging concepts would eventually need to be manufactured at scale, so drivers can access them easily along their journeys. The Biden administration is hoping to install 500,000 EV chargers across the country by the end of the decade, but the supply chain for critical battery components, including cobalt and nickel, is already fraught.
And if super-fast charging did go mainstream, the electric grid would also need some major upgrades, as Buttigieg has already acknowledged. The grid can only deliver so much charge at any one time, and adding a fleet of fast chargers would require equipment that can handle that capacity. Right now, that’s a difficult process, and even simple equipment like transformers can take a while to obtain.
But while super-fast EV chargers will, ideally, mimic the experience of the gas pump, most chargers wouldn’t need to operate that quickly. The fastest EV chargers are only needed for people on the road and outside their normal routines. The hope is that slower chargers will do much of the heavy lifting of keeping the country’s cars charged up, refueling the vehicles as they sit in people’s homes and office parking lots.
“All of us societally need to remember that we drive cars to get from A to B, not because we like going into the gas station,” says Tim Pennington, a senior research engineer in the Energy Storage & Advanced Transportation department at the Idaho National Laboratory. “We don’t need a ten-minute charge every day.”