Issam Mudawar, a professor of mechanical engineering at Purdue University, has been dealing with heat-related emergencies for 37 years. They often follow a pattern. Anyone who dreams of a supercomputer, or a new avionics system for a fighter jet, will eventually face the same problem: Fancy electronics, packed with thousands billion transistors, generating an enormous amount of heat. So the dreamers came to Mudawar, who studied heat management for a living. “It always seems like cooling is the last thing people think about,” he said.
A few years ago, Mudawar was approached by Ford with a more modest problem: the charging cable. Like other automakers, Ford is in the race to deliver electric vehicles quickly. But there’s a problem with moving electrons faster: It carries heat. If the goal is to fully charge your electric vehicle in five minutes, that extra current response resistance means temperature-related issues inside and outside the battery. In particular, the wire becomes an overheating bottleneck.
Mudawar has been solving a problem that does not really exist. The US Department of Energy has defined so-called “peak” fast charging when the range adds 200 miles in 10 minutes. This is achievable with existing charging stations and cables, a possibility that batteries are still underutilized, in part due to concerns about their temperature. Meanwhile, Mudawar’s work predicts a future when filling cars with electronics can rival the convenience of a gas pump.
Recently, the electric car trend is bigger, better. Automakers now target 400-mile range as an antidote to “range anxiety,” at the same time they are powering American roads — Chevy Silverados, Ford F -150, Hummers. The big cars plus the big range claim means the batteries are absolutely huge. Unsurprisingly, this comes with a trade-off: Charging those big batteries takes extra time. According to the DOE, the fastest option might be to fully charge in 30 or 40 minutes from modern highway chargers, which account for about 5% of electric vehicle fills. Most of these cars, though, are designed for drivers who can plug in at home and let that massive battery pack charge through the night.
Ahmad Pesaran, an energy storage expert at the National Renewable Energy Laboratory, explains both as difficult. A phrase like “five-minute charge” means something very different if you’re charging a 200 kilowatt-hour battery, like the one found in the Hummer, than the 40 kwH battery on the Nissan Leaf. These large batteries require more power, and they have structural barriers that make charging difficult to do quickly. That will likely require new chargers and battery strategies, fancy new cables, perhaps even upgrading the power supply lines for chargers so they can handle the spike in demand. “I question the wisdom of why we need a 500-mile range in an electric car and also want a quick five-minute charge,” he said. “Where do you want to go? How many times do you need to do it?” However, he adds, it can be inevitable.
Currently, most cars It’s impossible to take advantage of the most powerful charging stations we already have, says Chao-Yang Wang, a battery researcher at Penn State University. The causes were found to lie mainly within the battery itself, most notably a phenomenon known as lithium plating. When the battery is fully charged, the lithium ions nestle inside an anode made of graphite. In an attempt to put more power into the battery, the material has been designed to be quite thick, so it can hold more ions. But this becomes a hindrance to the battery charging. As the current becomes more intense, those ions cannot get inside the thick anode material fast enough. So instead, they accumulate on its surface as lithium metal – they form sheets. And once that happens, there’s no going back. The battery gradually loses access to those ions and thus loses its ability to fully charge.
