A Self-Heating Solution to Fast-Charging Cold Batteries

Penn State researchers have found a way to dramatically improve cold-charging cycle life of lithium ion batteries in EVs.

Low temperatures and lithium ion batteries are not a good match—at least in electric vehicles (EVs). When the thermometer drops below 50 degrees F, the ability of lithium ions to be easily inserted between the graphite layers of the battery anode during charging is lessened. Instead, the lithium ions attach to one another and form spiky dendrite crystals that can grow large enough to eventually reach the cathode and short out the battery. This cool weather behavior has limited the ability of EVs to be rapidly charged during parts of the year in the colder regions of the US and Canada. Long, slow charging has been the only option when it’s below 50 degrees F.

Penn State self-heating battery

Penn State’s self-heating battery allows fast charging for all outside temperatures. (Image source: Chao-Yang Wang / Penn State)

Pre-Heat

Now, Penn State University has developed a modification to lithium ion batteries that pre-heats them before applying high charging currents. According to a Penn State press release, a thin nickel foil is incorporated into each battery cell. One end of the foil is attached to the negative battery terminal, while the other end extends outside the cell to form a third terminal.

The third terminal comes into play when the battery cells need to be heated. According to the release, “A temperature sensor attached to a switch causes electrons to flow through the nickel foil to complete the circuit when the temperature is below room temperature. This rapidly heats up the nickel foil through resistance heating and warms the inside of the battery. Once the battery's internal temperature is above room temperature, the switch opens and the electric current flows into the battery to rapidly charge it.”

"One unique feature of our cell is that it will do the heating and then switch to charging automatically," Chao-Yang Wang, professor of chemical engineering and professor of materials science and engineering at Penn State, said in the release. "Also, the stations already out there do not have to be changed. Control off heating and charging is within the battery, not the chargers," he added.

Positive Results

Results from tests with a prototype were reported in a recent edition of the Proceedings of the National Academy of Sciences. The researchers found that the self-heating battery could withstand 4,500 cycles of 15-minute charging at 32 degrees F with only a 20-percent capacity loss. A conventional lithium ion battery, without self-heating and tested under the same conditions, lost 20-percent capacity in 50 charging cycles, according to the Penn State press release. The 4,500 charging cycles represents “…approximately 280,000 miles of driving and a lifetime of 12.5 years,” according to Penn State.

Game Changer

The ability to fast-charge an EV in 15-30 minutes is often described as one of the critical steps to widespread acceptance of electrification of the transportation system. Range anxiety remains one of the biggest concerns of potential EV buyers. With reasonable numbers of strategically placed fast charging stations and an ability to rapidly charge—even in cold weather—an EV becomes viable, even for long-distance travel.

Fast charging stations are rolling out across the US. Tesla currently has 1,308 Supercharger Stations with 10,622 Superchargers available. Meanwhile, Electrify America is building a network of 650 community-based and 300 highway-based charging sites with fast-charging capability. The Penn State self-heating battery concept will go a long way to making those fast-charging sites more viable all year round, regardless of the outside temperature.

Senior Editor Kevin Clemens has been writing about energy, automotive, and transportation topics for more than 30 years. He has masters degrees in Materials Engineering and Environmental Education and a doctorate degree in Mechanical Engineering, specializing in aerodynamics. He has set several world land speed records on electric motorcycles that he built in his workshop.

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