Magnetic resonance shows health of battery cells in production

Technology News |
By Nick Flaherty

The chemists at New York University used a technique similar to magnetic resonance imaging to look at the state of charge and the development of internal defects in teh cells. This could be a signficant tool for quality analysis on battery manufacturing lines.

“The use of alternative energy and electrically powered vehicles will further increase the demand for better and safer batteries,” said Alexej Jerschow, a professor in New York University’s Department of Chemistry, who led the research team. “However, there are currently only a very limited set of tools available to diagnose a battery’s health without destroying the battery–our non-invasive technique offers a faster and more expansive method for making these assessments.”

“Ensuring cell quality and safety is paramount to the manufacturing process that can save companies significant cost and prevent catastrophic cell failures from occurring,” says Matthew Ganter, co-director of the RIT Battery Prototyping Center who prepared the cells for the project.

X-ray CT and electron microscope scans have been used for non-invasive examination of cells, but this is relatively slow and so not applicable for high throughput manufacturng lines. This also looks at the denser components of a cell and does not offer insights into subtle chemical or physical changes of the materials inside. In contrast, magnetic resonance (MR) methods provide the ability to measure tiny changes in magnetic fields. 

MRI uses large magnetic fields which are a problem for examining the lithium ion cells that contain metal. Often the cell casing is made of conductive material, such as polymer-lined aluminum in pouch or laminate cells, but also the electrodes preclude the use of conventional MR for realistic or commercial-type cell geometries. Instead the team used the induced or permanent magnetic field produced by the cell, and mapped this to the processes occurring inside the cell.

This can be highly informative as the magnetic susceptibility is material dependent, and the resulting magnetic field is dependent on the distribution of the materials inside the cell, which can change during cell operation.

The magnetic susceptibility also depends on the electronic configuration of the material, and hence during redox reactions, such as battery charging or discharging, there can be large changes in magnetic susceptibility. Measuring the magnetic susceptibility outside the cell therefore gives detailed information about the oxidation state of the materials inside an electrochemical device to give insights into the state of charge (SOC) of the battery and its failure mechanisms. This also works on the wide range of lithium salts and anode and cathode materials used in lithium ion cells. 

However this needs comlex modelling and verification, so the team examined Li-ion batteries in different states, with various levels of charge and in different levels of damage, all prepared by collaborators at RIT’s Battery Prototyping Center.

With these cells, the NYU team was able to match magnetic field changes surrounding the batteries to different internal conditions, revealing state of charge and certain defects. These included bent and missing electrodes as well as small foreign objects in the cell, which are flaws that can occur during the normal manufacturing process.

“With future enhancements to this method, it could provide a powerful means of predicting battery failures and battery lifetimes as well as facilitate the development of next-generation high-performance, high-capacity, and long-lasting or fast-charging batteries,” said Jerschow.

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