"EVs are popular on the west coast because the weather is conducive," explains assistant research professor, Xiao-Guang Yang of Penn State. "Once you move them to the east coast or Canada, then there is a tremendous issue. We demonstrated that the batteries can be rapidly charged independently of outside temperature."
When owners can recharge car batteries in 15 minutes at a charging station, EV refueling becomes nearly equivalent to gasoline refueling in the time it takes. Assuming that charging stations are liberally placed, drivers can lose their ‘range anxiety’ and drive long distances without worries.
Previously, the researchers developed a battery that could self-heat to avoid below-freezing power drain. Now, the same principle is being applied to batteries to allow 15-minute rapid charging at all temperatures, even as low as minus 45 degrees F.
The self-heating battery uses a thin nickel foil with one end attached to the negative terminal and the other extending outside the cell to create a third terminal. 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, the researchers say, 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 turns opens and the electric current flows into the battery to quickly charge it.
In the results of their prototype testing, the researchers say that the self-heating battery withstood 4,500 cycles of 15-minute charging at 32 degrees F with only a 20% capacity loss. This provides approximately 280,000 miles of driving and a lifetime of 12.5 years.
A conventional battery tested under the same conditions lost 20% capacity in 50 charging cycles, the researchers add.
Lithium-ion batteries degrade when rapidly charged under 50 degrees F because, rather than the lithium-ions smoothly integrating with the carbon anodes, the lithium deposits in spikes on the anode surface. This lithium plating reduces cell capacity, but also can cause electrical spikes and unsafe battery conditions. Currently, long, slow charging is the only way to avoid lithium plating under 50 degrees F, the team say.
Batteries heated above the lithium plating threshold, whether by ambient temperature or by internal heating, will not exhibit lithium plating and will not lose capacity.
The researchers believe this charging method will also “allow manufacturers to use smaller batteries that are lighter and also safer in a vehicle”.