Researchers at Penn State University have created a self-heating battery. Why? Because cold temperatures (often experienced by drivers outside of California) slow down the charging rate of conventional lithium ion batteries. That means they have to remain plugged in longer to allow drivers enough charge for their daily driving needs. Charging at temperatures below 50º F can also lead to faster battery degradation, the researchers say.
“Electric vehicles are popular on the west coast because the weather is conducive,” says Xiao-Guang Yang, an assistant research professor in mechanical engineering. “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.” Previously, the researchers developed a self-heating battery that would prevent power drain in sub-zero temperatures. Now they have built upon the foundation of that research to create a battery that can be recharged in 15 minutes using a fast charger in all temperatures down to -45º 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, according to Penn State. 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,” says engineering professor Chao-Yang Wang. He is also the director Penn State’s Electrochemical Engine Center. “Also, the stations already out there do not have to be changed. Control off heating and charging is within the battery, not the chargers.”
In laboratory testing, the researchers found their self-heating battery could withstand 4,500 cycles of 15-minute charging at 32º F with only a 20-percent capacity loss — equivalent to about 280,000 miles of driving and a lifetime of 12.5 years. A conventional battery tested under the same conditions suffered a 20% loss of capacity after only 50 charging cycles.
The scientists say that fast charging at low temperatures promotes the formation of dendrites on the surface of anodes which degrades battery performance. They did not reveal the manufacturer of the conventional batteries they tested in the lab. They also did not discuss how much of the available power in the batteries is consumed by the heating process.
“This ubiquitous fast-charging method will also allow manufacturers to use smaller batteries that are lighter and also safer in a vehicle,” said Wang. Smaller, lighter batteries are also likely to be significantly less expensive than conventional batteries, bringing the point where electric cars costs the same as traditional vehicles with internal combustion engines closer than ever. That could be an important turning point for the electric car revolution.
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