A bitter cold snap in Chicago forced electric vehicle (EV) drivers to wait in line for hours at charging stations last month; some even found themselves stranded when their battery died while they waited in the queues. The rechargeable lithium-ion batteries that power most EVs perform poorly in the cold, so scientists and carmakers around the world are busy scrambling for solutions. These include fancier computer models to ensure peak performance, as well as hardier batteries that keep cars going—and their drivers safe—whether it’s freezing or scorching on the road.
Such upgrades aim to address significant barriers to the promised EV revolution. The Biden administration is working on increasing EV ownership in an ambitious push to cut greenhouse emissions, and the president hopes for EVs to constitute half of all new vehicles sold in the U.S. by 2030 (up from roughly 8 percent of car sales in 2023’s first half). But recent mishaps, such as the stalling of cars in Chicago, show how current EV technology could flounder as future weather gets even more extreme: climate change continues to drive up average global temperatures, but this disrupts patterns that have long regulated the planet’s weather—so overall warming can usher in worse cold snaps.
“Extreme cold introduces safety risks for charging batteries,” says Paul Gasper, a staff scientist at the National Renewable Energy Laboratory’s Electrochemical Energy Storage group. Scientists generally consider lithium-ion batteries safe to use in a relatively narrow temperature range—between around 32 to 140 degrees Fahrenheit (zero to 60 degrees Celsius), but estimates vary. When it hits 20 degrees F (minus seven degrees C) outside, an EV’s average driving range drops by 12 percent compared to its range at 75 degrees F (24 degrees C), the American Automobile Association found in 2019. To understand why, we have to dip into the chemistry that powers an EV battery.
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Temperature Check
When EV batteries are being juiced up, charge-carrying lithium ions travel through a liquid electrolyte from one end of each battery cell to another (between the positive cathode and the negative anode). Then—as cars sap the battery’s stored energy during drives—the ions shuttle back in the opposite direction. If a battery chills (in a cold snap, for instance), the liquid highway between the anode and cathode thickens, slowing the ions down. This means cooler batteries can take longer to charge, and they can lose that charge sooner than at milder temperatures.
Charging cars when it’s below 32 degrees F can cause lithium ions to pile up on the anode’s surface because the particles can’t move quickly enough. These ion clumps, referred to as plating, can cause the battery to short-circuit and even spark an explosion. (Still, electric cars catch fire relatively rarely compared to gas-powered cars, and researchers are studying designs for batteries that extinguish themselves.)
On top of this, the whole EV works overtime to warm things up. Its thermal management system, which regulates the temperature of the battery, electric motor and other components, also drains the charge. And when a driver flips on the cabin’s heat, the battery must power the HVAC system and other devices such as the defroster and seat warmers. Gas-powered cars with internal combustion engines also do suffer from the cold; their fuel economy shrinks by around 15 percent at 20 degrees F, compared with what they’d get at 77 degrees F (25 degrees C), according to the U.S. Department of Energy. But the equivalent loss for an EV can hit 39 percent at 20 degrees F.
Extremely hot days can harm an EV’s performance, too. Higher temperatures speed up the traveling ions, and at a certain point this sets off a cascade of unintended chemical reactions that can degrade battery components—including the electrolyte—over a car’s lifetime. When outside temps reach 95 degrees F (35 degrees C) and drivers crank up the air conditioning, driving range can decrease by 17 percent, the AAA report said.
AI Tweaks
Tinkering with car software can take better advantage of the batteries that are already on the market. Teslas and other EVs with sophisticated onboard computers use complex artificial intelligence models to ensure batteries are working safely and efficiently; these AI programs analyze data from temperature and voltage sensors to prevent battery overcharging and predict how far a car can drive on its remaining charge. Teslas also have a feature called preconditioning, in which cars heat or cool their battery to the proper charging temperature. But these models need some improvements, Gasper says.
For one thing, they could be better customized to account for a battery’s health as it degrades over time, he explains. He also thinks AI models could push cars to succeed in a wider range of temperatures (by distributing coolant or controlling fans, for instance) without posing risks to the car or driver. As these models improve, we could better trust EVs to safely manage the battery “in its widest possible operating window,” Gasper says.
For now, AI models can only give drivers an approximation of a battery’s current charge levels and health, says electrical engineer I. Safak Bayram, an associate professor at the University of Strathclyde in Scotland. That’s why EV drivers often experience sudden drops in their vehicle’s driving range estimates, he adds. In Chicago this January one Uber driver was left stranded even though his car displayed that there were 30 miles left on his battery.
But smarter AI models can only push cars so far, Gasper says. Taking EVs to the next level in enduring extreme temperatures will also require advances in battery technology itself.
Better Batteries
Scientists are trying multiple strategies to make batteries more weather-resilient. One promising method is to improve the electrolyte. Zheng Chen, a materials scientist and engineer at the University of California, San Diego, and his colleagues created a new electrolyte that worked well in lab tests at temperatures as low as –40 degrees F (–40 degrees C) and high as 122 degrees F (50 degrees C), according to a study the researchers published in 2022.
The team achieved this by mixing a lithium salt with a solvent called dibutyl ether, which easily passes around lithium ions and remains a liquid even at subzero and superhigh temperatures. Although the recipe is promising, it’s difficult to say whether it will work on a large scale with commercially available battery parts. And this kind of formula likely isn’t a sole solution: car makers use a variety of materials in lithium-ion batteries, which they continuously tweak to keep up with technological progress and ensure, for example, more affordable components or longer range. No one solvent or metal salt can mesh with all the battery materials on the market, Chen says.
While it’s hard to find electrolytes and other materials that will excel in varying real-world conditions, Gasper says that artificial intelligence can help speed up the discovery process. Researchers have programmed robots inspired by technology the pharmaceutical industry already uses for drug discovery to test candidate substances.
Some experts think that self-heating batteries could be another way to help EVs beat the cold. In 2018 scientists at Pennsylvania State University announced they had created such a battery by incorporating a nickel foil that intercepts electrons when the battery dips below room temperature. The captured electrons warm the foil, in turn heating up the whole battery. The scientists say this could let batteries quick-charge even at temperatures as low as –58 degrees F (–50 degrees C). Other approaches, such as harnessing pulses of electric current from the car’s motor, can also warm up batteries for faster charging in the cold.
But EV engineers face a dilemma they call the “AND problem”: it’s tough to design a battery that works efficiently in a range of environments and remains affordable and long-lasting. “We’re kind of trying to balance the cost, performance and safety,” Chen says. Car companies may approach these factors differently depending on their priorities. Some, for example, value higher performance more than affordability—and can incorporate more expensive battery materials. That’s why pricier EVs tend to have higher mile ranges.
Ultimately, it may be best to tailor battery designs for specific climates across the country and the world, Gasper suggests. Drivers in climes closer to the poles would use batteries suited for the cold. Heat-resilient batteries, meanwhile, would be especially important for people living in equatorial regions. There, quicker chemical reactions, spurred by the heat, can degrade batteries—potentially leading to higher long-run EV costs in regions where incomes are lower than the global average. “It is an economic justice issue,” Gasper says. The industry isn’t there yet, but it’s a problem that EV experts know they need to solve.