Purdue University researchers have created a new tool to detect flaws in lithium-ion batteries as they are being manufactured, 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 the building blocks of powerful battery arrays like those used in electric and hybrid vehicles. They are copper on one side and coated with a black compound to store lithium on the other. Lithium ions travel from the anode to the cathode while the battery is being charged and in the reverse direction when discharging energy. The material expands as lithium ions travel into it, and this expansion and contraction causes mechanical stresses that can eventually 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 researchers have developed a system that uses a flashbulb-like heat source and a thermal camera to read how heat travels through the electrodes. The "flash thermography measurement" takes less than a second and reveals differences in thickness and composition.

The researchers found that the viscous compound is sometimes spread unevenly, producing a wavelike pattern of streaks that could impact performance. 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.

The technique also has revealed various flaws, such as scratches and air bubbles, as well as contaminants and differences in thickness, factors that could affect battery performance and reliability.