Team develops fast-charging tech for EVs

A team of researchers at Pennsylvania State University has developed a technology that enables electric vehicle batteries to obtain a full charge in just 10 minutes.

The breakthrough in EV battery design, reported in the Oct. 12 edition of the journal Nature, produced a record-breaking combination of a shorter charge time and more energy acquired for a longer travel range.

"The need for smaller, faster-charging batteries is greater than ever," said Chao-Yang Wang, the William E. Diefenderfer Professor of Mechanical Engineering at Penn State and lead author on the study. "There are simply not enough batteries and critical raw materials, especially those produced domestically, to meet anticipated demand."

"Lithium-ion batteries with nickel-rich layered oxide cathodes and graphite anodes have reached specific energies of 250–300 Wh kg (watt-hours per kilogram), and it is now possible to build a 90-kWh (kilowatt-hour) electric vehicle pack with a 300-mile cruise range," Wang wrote in the paper reporting the breakthrough.

"Unfortunately, using such massive batteries to alleviate range anxiety is ineffective for mainstream EV adoption, owing to the limited raw resource supply and prohibitively high cost.

"Ten-minute fast charging enables downsizing of EV batteries for both affordability and sustainability, without causing range anxiety. However, fast charging of energy-dense batteries ... remains a great challenge."

The Penn State team has overcome this challenge with a self-heating battery that can be charged to 75% in 12 minutes for more than 900 cycles – "equivalent to a 'half-million' mile range in which every charge is a fast charge," the researchers wrote.

"Further, we build a digital twin of such a battery pack to assess its cooling and safety and demonstrate that thermally modulated 4C charging only requires air convection. This offers a compact and intrinsically safe route to cell-to-pack development. The rapid thermal modulation method to yield highly active electrochemical interfaces only during fast charging has important potential to realize both stability and fast charging of next-generation materials, including anodes like silicon and lithium metal," they added.

Challenges in EV conversion

One sign of the imminent challenges facing the EV battery manufacturing sector is a recent decision by California's Air Resources Board to adopt an extensive plan to restrict and ultimately ban the sale of gasoline-powered cars within the state. By 2035, the largest auto market in the United States will effectively retire the internal combustion engine.

If new car sales are going to shift to battery-powered electric vehicles, Wang said they will need to overcome two major drawbacks – long charging times and large size, which renders them inefficient and expensive. Instead of taking a few minutes at the gas pump, drivers of electric vehicles would need all day to recharge their batteries.

All that changes with the innovative design developed by Wang's lab in partnership with EC Power, a Penn State-based startup that intends to manufacture the fast-charging batteries.

"Our fast-charging technology works for most energy-dense batteries and will open a new possibility to downsize electric vehicle batteries from 150 kWh to 50 kWh without causing drivers to feel range anxiety," Wang said. "The smaller, faster-charging batteries will dramatically cut down battery cost and usage of critical raw materials such as cobalt, graphite and lithium, enabling mass adoption of affordable electric cars."

Temperature is key

The lithium-ion cells now used in electric vehicles suffer significant performance loss when they are cold – a major barrier to widespread EV adoption. EC Power says its thermally modulated cell technology (TMCT) overcomes this drawback, even down to bone-chilling temperatures of minus 50 degrees Celsius (minus 48 degrees Fahrenheit).

The Penn State researchers chose to regulate the temperature from inside the battery by building a new structure that adds an ultrathin nickel foil as a fourth component beside the anode, electrolyte, and cathode. Acting as a stimulus, the nickel foil self-regulates a battery's temperature and reactivity, which enables 10-minute fast charging on just about any EV battery, Wang said.

"By heating inside out, not outside in, we achieve thermal modulation rates greater than 60 times faster than what (service-oriented architecture) electric vehicle thermal management can achieve," says EC Power, describing the advantages of the new technology on its website.

The design relies on the active method of temperature control to demand the best performance possible from the battery, said Wang.

Batteries operate most efficiently when they are hot, but not too hot. Keeping batteries consistently at just the right temperature has been a major challenge for battery engineers. Historically, they have relied on external, bulky heating and cooling systems to regulate battery temperature, which responds slowly and wastes substantial energy, according to Wang.

EC Power said the automotive industry more recently has implemented clever outside-in heating systems to enable faster charging. However, pre-heating EV battery packs can take 20-45 minutes.

Using its inside-out method, EV battery cells can reach safe, fast-charging temperatures within 30 seconds, the company touts on its website.

"Our cells were recently third-party evaluated for their ability to meet (the U. S. Department of Energy's) extreme fast-charging goal. They found that our cells with TMCT are the only product to exceed the DOE's standard, still having about 90% of their capacity after 1,200 extreme fast-charging cycles," the company said.

In a real-world test, three electric vehicles equipped with lithium-ion cells containing the innovative technology were cold-soaked for three days at -40 °C. Within three minutes of 'ignition,' all three vehicles had achieved nominal performance, EC Power said.

Fast-charging capability is recognized as a crucial feature needed for broad electric vehicle adoption. Additionally, fast charging enables the use of smaller battery packs, saving resources and lowering off-the-lot cost, according to the startup.

Indeed, DOE has specifically called for 'extreme fast-charging' technology where 200 miles of range can be added within 10 minutes for at least 500 cycles.

The speed at which a lithium-ion cell can be safely charged directly depends on how warm the cell is. Inside cold cells, the lithium ions simply move more slowly, increasing the risk of the lithium becoming stuck – and stuck lithium ions mean the risk of fire.

Potential major impact

Solid-state and lithium-metal batteries promise greater energy density, cheaper manufacturing, and enhanced safety. EC Power said these future chemistries, however, require higher operating temperatures to achieve adequate performance and safe, fast charging.

As no other technology can heat lithium cells as efficiently, evenly, and quickly as thermal modulation, the company said it is poised to enable this exciting battery future by manufacturing and commercializing its fast-charging battery.

"True fast-charging batteries would have immediate impact," the researchers said. "Since there are not enough raw minerals for every internal combustion engine car to be replaced by a 150 kWh-equipped EV, fast-charging is imperative for EVs to go mainstream."

The study's coauthors are: Teng Liu, Xiao-Guang Yang, Shanhai Ge and Yongjun Leng of Penn State and Nathaniel Stanley, Eric Rountree and Brian McCarthy of EC Power.

The work was supported by the U.S. Department of Energy, the U.S. Department of Defense, the U.S. Air Force, and the William E. Diefenderfer Endowment.