Self-heating battery promises to make electric vehicles climate-immune

The battery will automatically switch from heating to fast charging when it reaches a safe temperature. Image: Chao-Yang Wang, Penn State

Lithium ion batteries do not like the cold. Below 10°C, conventional LI-ion batteries cannot be charged rapidly, which is a major problem for electric vehicles in many regions. In Scandinavia, electric vehicles have a small heater installed in the battery compartment which can be plugged in at the charging point; the take-up of EVs in California is notably larger than that in Minnesota and Canada.

The Penn State team, led by director of the electrochemical engine centre Chao-Yang Wang, had briefly developed a battery that could self heat to avoid below-freezing power drain. It is now using the same principle to allow batteries to recharge 15 minutes at a rapid charging station, even when the ambient temperature dips to -43°C.

The battery uses a thin nickel foil with one end attached to the negative terminal and the other extending outside the battery to create a third terminal. A temperature sensor attached to a switch causes current to flow through the nickel when it detects ambient temperatures below around 25° C. Electrical resistance heats up the foil and warm the inside of the battery. Once the temperature rises above room temperature, the switch automatically diverts the current to charge the battery. This means that charging stations do not have to be replaced, Wang said. “Control of heating and charging is within the battery, not the chargers."

In the Proceedings of the National Academy of Sciences, the researchers report that their prototype could withstand 4500 cycles of 15 minute charging at 0°C with a 20 per cent capacity loss. This would give the battery a lifetime of 12 ½ years. A conventional battery  lost 20per cent capacity in only 50 charging cycles.

The innovation could also make batteries safer, Wang added. Below 10°C, charging lithium ion batteries cause lithium to deposit in spikes on the anode surface which can cause short circuits, runaway heating and fires. "This ubiquitous fast-charging method will also allow manufacturers to use smaller batteries that are lighter and also safer in a vehicle," said Wang.