A team at Purdue University have discovered a method of detecting defects in lithium ion battery anodes as they are manufactured, before installing them in actual batteries. Their discovery relies on thermal imaging and could increase the reliability of lithium ion cells used in electric cars.
Anodes and cathodes are the two electrodes of a battery (plus and minus, respectively). Both are made of copper on one side, coated with a black carbon compound on the other side, to store lithium. When the battery is being charged, the lithium ions travel from the anode to the cathode, and when discharged – the other way around.
In theory, so far so good, but in real life the black carbon compound from both of the electrodes expands and contracts itself when charged and discharged, and this leads to cracks in the storing material. The black compound is designed to be viscous, but imperfections such as unevenly-deposited surfaces or air bubbles can lead to a dramatic shortage in the life of the future battery, leading to dissatisfied electric car customers and so on.
The method of sensing these anomalies invented at Purdue uses Xenon bulbs that heat the electrodes while they are still in the manufacturing stage and then uses an infrared camera to detect uneven thickness surfaces or air bubbles. They are calling their method “flash thermography measurement” and it takes a split second to perform it. The technology is also able to detect subtle differences in the ratio of carbon black to the polymer binder, which could be useful in quality control.
The technique has been detailed in a paper written by doctoral students Nathan Sharp, Peter O’Regan, Anand David and Mark Suchomel, Douglas Adams and James Caruthers. The latter two are the leaders of the project.
“We showed that we can sense these differences in thickness by looking at the differences in temperature,” Adams said. “When there is a thickness difference of 4 percent, we saw a 4.8 percent rise in temperature from one part of the electrode to another. For 10 percent, the temperature was 9.2 percent higher, and for 17 percent it was 19.2 percent higher.”
Electric cars like those from Tesla Motors, Nissan, Volt and so on could benefit from the flash thermography measurement big time with basically no or little cost added to the manufacturing process.