We frequently publish studies that show new materials for batteries that can increase their energy density or lifespan. But they have more issues to overcome, such as lithium plating and SEI – or solid electrolyte interphase – growth.
Researchers from the Penn State University, such as Chao-Yang Wang, found an apparently simple way to deal with that: changing charging and discharging temperatures. Their method is called ATM – Asymmetric Temperature Modulation. It may help put 200 mi on a battery pack in only ten minutes.
Gallery: Penn State University Researchers Develop Assymetric Temperature Modulation
These requirements come from the US Department of Energy (DOE). It has given researchers the goal of developing extreme fast charging tech – also known as XFC – based precisely on adding 200 mi of driving range in ten minutes. The DOE is funding promising researches towards that goal, including this one.
You will probably ask how changing temperatures can help in that. Here’s the situation: if you charge the batteries at a higher temperature, you lower the odds of lithium plating – the deposition of this metal in the anode. That is one of the leading causes of Li-Ion battery malfunction.
The scientists elevate the battery temperature to 60ºC (140ºF) for ten minutes. That is enough for a battery to get 200 mi more, according to the researchers. It is not longer than that because high temperatures increase SEI, one of the main reasons for lithium loss in the battery.
The biggest problem in doing that is that an external heating method would take too long to get the batteries to the ideal temperature. That is why Wang’s team developed a nickel foil that goes inside each cell and makes it reach the 60ºC faster.
Another critical part of the ATM is keeping the batteries fresh while discharging. A regular BMS – battery management system – already takes care of that, even if not all EVs have it, and some manufacturers claim it is not necessary. A future BMS would also manage self-heating batteries. The energy for heating would come from the fast charger.
Curiously, the researchers found out that the heating device for charging made the need to cool down the battery lower by more than 12 times. According to the researchers, “owing to a smaller internal heat generation and an enlarged temperature difference driving heat dissipation.”
To have an idea of what that represents, the Penn State University researchers made a 9.5-Ah 170-Wh/kg pouch cell endure 1,700 XFC cycles, or a 6 C charge to 8 percent SOC – state of charge. The capacity loss was 20 percent. A control cell did not stand 60 XFC cycles.
When the researchers tried a high-energy (209 Wh/kg) Li-ion cell, the results were even better. It lost just 8.3 percent of capacity after 2,500 XFC cycles. That amounts to 500,000 mi of use. The DOE wanted only a battery that could deal with 500 cycles to a maximum loss of 20 percent.
You could think these guys are happy by doing that much with the Li-Ion batteries we already know, but check what Wang told the Green Car Congress:
"We are working to charge an energy-dense electric vehicle battery in five minutes without damaging it. This will require highly stable electrolytes and active materials in addition to the self-heating structure we have invented."
We have no doubts these guys will get there. We just hope that they do so as fast as possible and that production does not take too long as well.