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A Self Heating Fast Charging Lithium Ion Battery
July 4, 2018 | Leave a Comment
A Penn State team of engineers has created a battery that can self-heat, allowing rapid charging regardless of the outside chill. People in California do not purchase electric vehicles because they are cool, they can buy and use buy EVs because they live in a warm climate. Conventional lithium-ion batteries cannot be rapidly charged at temperatures below 50º F. That may explain your cell phones early battery demise.
Xiao-Guang Yang, assistant research professor in mechanical engineering at Penn State said, “Electric vehicles are popular on the west coast because the weather is conducive. 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.”
A fast charging battery for all outside temperatures that rapidly heats up internally prior to charging battery materials. Image Credit: Chao-Yang Wang. Penn State University. Click image for the largest view.
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 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 45º F. That’s 45º below zero. About -45º C, too.
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.
Chao-Yang Wang, William E. Diefenderfer Chair of mechanical engineering, professor of chemical engineering and professor of materials science and engineering, and director of the Electrochemical Engine Center said, “One unique feature of our cell is that it will do the heating and then switch to charging automatically. Also, the stations already out there do not have to be changed. Control off heating and charging is within the battery, not the chargers.”
The researchers reported the results of their prototype testing in the Proceedings of the National Academy of Sciences. They found that their self-heating battery could withstand 4,500 cycles of 15-minute charging at 32º F with only a 20-percent capacity loss. This provides approximately 280,000 miles of driving and a lifetime of 12.5 years, longer than most warranties.
A conventional battery tested under the same conditions lost 20-percent capacity in 50 charging cycles.
Lithium-ion batteries degrade when rapidly charged under 50º 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 50º 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.
“This ubiquitous fast-charging method will also allow manufacturers to use smaller batteries that are lighter and also safer in a vehicle,” said Wang.
With these results and those of yesterday one might think the lithium ion battery issues are about solved. One hopes so, but more research, testing and development are going to be needed well before any scale up or commercial production. Perhaps all will go well. Or the problems that arise are easily and cheaply solved. Hopes are high and fingers crossed here.
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