Conventional lithium-ion batteries cannot be rapidly charged at temperatures below 50 °F. Electric vehicles are popular on the West Coast because the weather is conducive to quick charging. Once the vehicles are moved to the East Coast or Canada, there is a tremendous issue with charging.
A new battery was created that can self-heat, allowing rapid charging regardless of the outside chill. The battery allows 15-minute rapid charging at all temperatures, even as low as -45 °F. When owners can recharge car batteries in 15 minutes at a charging station, electric vehicle refueling becomes nearly equivalent to gasoline refueling in the time it takes. Assuming that charging stations are liberally placed, drivers can drive long distances without worries.
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 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 rapidly charge it.
The self-heating battery could withstand 4,500 cycles of 15-minute charging at 32 °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.
Lithium-ion batteries degrade when rapidly charged under 50 °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 °F. 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 fast-charging method will allow manufacturers to use smaller batteries that are lighter and safer in a vehicle.