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Predicting How Much Range EV Batteries Lose over Time

Predicting How Much Range EV Batteries Lose over Time

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Only recently has it become possible to study EV battery range degradation effectively, with large enough numbers of electric vehicles beginning to hit the 100,000-mile mark and beyond.Previously published papers pointed to batteries losing 10% range after 200,000 miles, while some individuals have reported a 2% to 3% drop per year. One study by Canadian Light Source put lithium-ion battery cells through up to 1500 cycles, then produced detailed x-ray scans of the wear. The cells showed cracking and mechanical degradation.Electric cars have only been on the road in any numbers for a little more than a decade, so we’re only now gathering data on how they perform after the odometer clicks into six figures. With some Teslas and Chevy Bolts well over 100,000 miles (or even 200,000 to 300,000 miles), early indications are that EVs in general lose range by about 2% to 3% a year. Or, some experts say, the loss could be more dramatic if drivers fast-charge their cars often. But some drivers say their high-mileage cars are still pretty close to full capacity. Rob Neary is an IT security consultant in Westford, Massachusetts, and an early Tesla adopter, still driving his bought-new 2013 Model S Performance with the 85-kilowatt-hour battery. Although he has other cars, it’s his daily driver, and he’s put 204,000 miles on the odometer, including two California trips and three to Florida. But at least until he replaces the battery pack (a new 90-kWh unit is $20,000), the Model S’ long-range driving career may be over.When the car was new, Neary would see a rated range of 252 miles after a full charge. “But now I don’t trust the car beyond 100 miles of range,” he said. The range degradation combines a number of factors. Now, when fully charged the gauge shows 174 miles. “And for the last two years, I can’t drive to an indicated zero miles anymore,” Neary said. “With a rated 30 miles left the car will tell me to pull over and shut down.” In cold weather, the Model S has gotten “crankier,” Neary said. The vaunted full performance capability of his car isn’t available until he’s in the middle of its 100-mile range. “The computer looks at the state of the battery and decides how much power I can have,” he said. Fast charging could be a factor, because Neary made those cross-country trips in his Model S, but he discounts it, pointing to a now-defunct California company called Tesloop that used a Model S as a 17,000-mile-per-month shuttle car. The company’s “eHawk” Model S lost only 6% capacity after traveling 300,000 miles, TechCrunch said. These results could indicate that EVs (like gas cars) do well when used a lot, rather than being statically stored.Neary’s car may be an anomaly. A chart Tesla published as part of its 2019 Impact Report showed an approximate 10% loss in S and X batteries after 200,000 miles. A period analysis by Dutch professor Maarten Steinbuch said Tesla’s figures show “a fast decay the first 25,000 miles of about 5%, and then a slow decay of approximately 7% in 175,000 miles.” According to EV writer John Voelcker, a test of a Chevrolet Volt plug-in hybrid showed little or no range loss after 300,000 miles. Back in 2019, Tesla was promising it would soon be installing million-mile batteries in its cars. Obviously, despite many technical advances, we’re not there yet, though research is ongoing. EV batteries can and do start to lose range over time. New Jersey-based Tom Moloughney, senior editor at InsideEVs.com, said he’s observed an average 2% to 3% annual range drop in the EVs he’s owned, which are driven 15,000 to 20,000 miles per year. He’s currently driving a 2021 Tesla Model 3 with 21,000 miles, but before that had a 2019 Model 3 and three BMW electrics. One issue is that consumers buy EVs that come with, say, three years of unlimited charging at Electrify America (EA) stations. That encourages owners, Moloughney said, to routinely fast charge at EA down the street instead of running up a bill by plugging in at home. “I despise these offers,” he said. “Fast charging should be reserved for special occasions.” “Fast charging a lot adds to battery degradation,” Moloughney said. “I would discourage owners from using Tesla Superchargers or other 480-volt fast chargers unnecessarily. If you’re going on a long trip, then fine.”Joel Levin, executive director of advocacy group Plug In America, says he’s heard of EVs losing 10% of their range at 100,000 miles. “Not many people have EVs with that many miles yet,” Levin said. “And recent EV batteries, as on the Tesla Model Y, last longer. I think we’re going to be pleasantly surprised by EV range longevity.”Levin has 55,000 miles on his 2015 Nissan Leaf, and says he still has “11 bars,” or 90% to 95% capacity. That means 80 miles of range instead of 85. “It’s fine for me driving around Los Angeles,” he said. “I use my Bolt for trips of any distance.”About that million-mile battery, Levin said he thinks most consumers wouldn’t want to pay for one if it cost twice as much as the standard issue. Indeed, the average car owner keeps his or her vehicle 8.4 years, but owners still enthusiastic after 20 or more are probably rare—factors other than the battery (outdated infotainment, for one) are likely to prod earlier trade-ins. Neary said replacing his 85-kilowatt-hour battery pack with a new 90-kWh version from Tesla would be approximately $20,000, versus a used “recertified” battery at $15,000 to $16,000. He said he’s likely to buy a new battery, after first “driving the car as-is for as long as possible, probably another year or two.” Toby Bond recently peered into the innards of some EV-type cells. He’s a researcher at Canadian Light Source in Saskatoon, Saskatchewan. Bond put some commercially manufactured lithium-ion prototype pouch battery cells through up to 1500 cycles (the equivalent of 120,000 to, in some cases, 450,000 miles), then produced detailed x-ray scans of the wear inside them using a particle accelerator. It took two years. “We were surprised by the level of wear,” he said. “There was cracking and mechanical degradation. Excess electrolyte was getting sucked up into the electrode assembly cracks. That can result in loss of capacity and range because there won’t be enough active electrolyte to go around.” Although the work didn’t involve fast charging, Bond said, “Generally speaking, higher-voltage fast charging generates more heat, and I would expect it to cause more degradation, particularly if it’s done often. But there’s more at play with battery wear than just mechanical stress—high outside temperatures, as in California and Florida—might also cause degradation to speed up.” Bond’s results showed faster degradation in cells drained to a 0% charge, indicating that consumers might want to avoid that scenario if possible. He said forthcoming cathodes made with single-crystal materials will likely be tougher and more resistant to degradation, with hope yielding those million-mile batteries everyone wants to see. Tesla has a patent on this technology, filed by Jeff Dahn of Canada’s Dalhousie University, head of the Tesla battery research team at the school. Dahn and his team said in a 2019 paper published in the Journal of The Electrochemical Society, “We conclude that cells of this type should be able to power an electric vehicle for over 1.6 million kilometers [one million miles] and last at least two decades in grid energy storage.”

Source : autoweek.com
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