Researchers Develop Tool to Detect Flaws in Li-ion Batteries During Production Process

A newly developed tool by Purdue University researchers to detect flaws in lithium-ion batteries as they are being manufactured is being hailed as a step toward reducing defects and inconsistencies in the thickness of electrodes that affect battery life and reliability.

The electrodes, called anodes and cathodes, are copper on one side and coated with a black compound to store lithium on the other. Li-ions travel from the anode to the cathode when the battery is being charged and in the reverse direction when discharging energy.

The material expands as Li-ions travel into it, and this expansion and contraction causes mechanical stresses that eventually can damage a battery and reduce its lifetime.

The coating is a complex mixture of carbon, particulates that store lithium, chemical binders and carbon black. The quality of the electrodes depends on this battery paint being applied with uniform composition and thickness.

The Purdue team has developed a system that uses a flashbulb-like heat source and a thermal camera to read how heat travels through the electrodes. It uses a flashing xenon bulb to heat the copper side of the electrode, while an infrared camera reads the heat signature on the black side, producing a thermal image.

The “flash thermography measurement” takes less than a second and reveals differences in thickness and composition.

“This technique represents a practical quality-control method for lithium-ion batteries," says Douglas Adams, professor of mechanical engineering and director of the Center for Systems Integrity. “The ultimate aim is to improve the reliability of these batteries.”

Purdue has applied for a patent on the new sensing technology, which was developed by Adams and James Caruthers, professor of chemical engineering. Their findings show the technology also is able to detect subtle differences in the ratio of carbon black to the polymer binder, which could be useful in quality control.

Additionally, the technique reveals various flaws, such as scratches and air bubbles, as well as contaminants and differences in thickness, factors that could affect battery performance and reliability.

“We showed that we can sense these differences in thickness by looking at the differences in temperature,” Adams says in a statement. “When there was a thickness difference of 4%, we saw a 4.8% rise in temperature from one part of the electrode to another. For 10%, the temperature was 9.2%, and for 17% it was 19.2%.”

The researchers say the thermal-imaging process is ideal for a manufacturing line because it is fast and accurate and can detect flaws prior to the assembly of the anode and cathodes into a working battery.

“For example, if I see a difference in temperature of more than one degree, I can flag that electrode right on the manufacturing floor,” Adams says. “The real benefit, we think, is not just finding flaws but also being able to fix them on the spot.”