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Quality Check Technique Devised for Lithium-Ion Batteries

Chevrolet Volt and battery replica (Photo by John F. Martin for General Motors)

A Chevrolet Volt and replica of the t-shaped battery pack ((Photo by John F. Martin for General Motors))

Engineers at Purdue University in Indiana developed a method that can detect flaws in lithium-ion battery electrodes during their manufacture. The team led by mechanical engineering professor Douglas Adams and chemical engineering faculty James Caruthers will discuss its technique next month at the annual meeting of the Society for Experimental Mechanics near Chicago.

Arrays of lithium-ion batteries are used increasingly for powering systems from smartphones to electric cars, but battery makers so have no simple way to quickly and accurately check on the consistent quality of their manufactured products. The technology, for which Purdue has filed a patent application, aims to reduce the defects and fluctuations in the thickness of electrodes — cathodes and anodes — in lithium-ion batteries, which generate the battery’s electric current. In these batteries, lithium ions move from the anode to the cathode while being charged, and from cathode to anode while being discharged.

The material in the electrodes expands and contracts, which over time, can cause mechanical stresses and eventually damage the battery. To protect the electrodes, they are coated with a viscous compound of carbon particulates, carbon black, and and polymer binders that store the lithium. Thus the quality of the batteries depends on the uniform thickness and consistency of this coating.

The technique devised by the Purdue team adapts a flashing xenon bulb that heats one side of the electrode, usually made of copper. The system also has an infrared camera to read the heat signature on the other side of the electrode, which produces a thermal image. The thermal images then provide visual evidence of discrepancies in the coating.

Tests of the system returned thermal images showing that the viscous coating on the electrodes was sometimes applied unevenly, as well as detecting differences in proportions of carbon black and polymer binders in the coating material. Tests also uncovered streaks, bubbles, and contaminants on electrodes.

The Purdue team believes the speed and accuracy of the technique will fit in with battery makers’ manufacturing processes, and detect flaws while the battery is being made, thus making it possible to fix the battery before leaving the factory.

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