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New Inspection Process For Detecting Particles in Li-ion Batteries

VITRONIC has developed a process for the quality inspection of lithium-ion batteries for electric vehicles, to detect particle contamination in battery cells. In rare cases, particles can cause short circuits, as a result of which the battery can ignite during operation. As the production volume of Li-ion batteries will multiply in the coming years, this could result in a relevant safety problem. The new process offers a solution: it enables inexpensive, continuous inline inspection in mass production.

Particle Contamination As a Cause of Battery Fires

When electric vehicles catch fire as out of nothing, they could be responsible: production residues just micrometers in size in the cells of lithium-ion batteries. They stem from the electrodes and separator foils being cut to size or from the abrasion of mechanical parts in the production line. Despite cleaning systems, individual particles remain stuck on the foils of the battery cell.

When particles are 10 micrometers and larger, they can penetrate the 10-40 micrometer thick separators between the anode and cathode. This usually happens only after the batteries have been in use for a while – perhaps during a car trip. The battery shorts, can ignite and set the entire vehicle on fire.

The Problem Has Been Accepted So Far

With the usual quality controls in battery production, such particle contamination cannot be detected; at the time of delivery, the battery is still functioning normally. Available inspection systems – industrial microscopes – must be operated manually. They are only suitable for spot checks, but not for mass production.

Due to the relatively small number of units produced to date, the safety risk could be accepted up to now. However, the current figure of around 20 million e-vehicles worldwide is expected to grow into hundreds of millions in the coming years. The current individual cases could then become a relevant number of incidents.

Inspection System For Mass Production

Seamless particle inspection will therefore soon become standard in battery production. The new process from VITRONIC, a specialists for industrial image processing, is now offering a solution for this. A high-resolution 16k camera sensor simultaneously takes several images of the electrode foils from different angles, with different illumination. This makes it possible to detect tiny particles that have hardly any contrast with the background and are practically invisible. The detected particles are measured and automatically classified. Other flaws can also be detected, such as position deviations, edge and cutting defects, or surface defects of the electrodes caused by transport.

The inspection is performed directly in the production line, after laser cutting and before stacking the electrode and separator foils. The transport of the foils does not have to be interrupted for this. The inline inspection system is therefore suitable for use in mass production. It supports battery cell manufacturers in further increasing product quality and implementing a zero-defect strategy.

VITRONIC will present their inspection solution at the upcoming Battery Show in Stuttgart, Germany.

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