Battery Assembly Inspection

Battery Assembly Inspection with Acuros CQD SWIR Cameras

 Battery Assembly Inspection
Figure 1. Schematic showing four typical types of Li metal batteries manufacturing processes. (a) Single sheet stacking; (b) Z-stacking; (c) cylindrical winding and (d) prismatic winding.

Lithium-ion battery technology plays a central role in the race toward mobile electrification. Improved inspection capabilities are needed to help drive down cost, increase energy densities, and improve overall safety and reliability. Short Wave Infrared (SWIR) imaging offers new capabilities for lithium-ion battery inspection.

Lithium-Ion Batteries

Lithium-Ion battery cells come in many shapes and sizes. At their core they consist of anode, cathode, and polymer separator layers that are either rolled or stacked into cells before being filled with an electrolyte solution and encapsulated. During the assembly process, machine vision systems are used to measure and inspect various aspects of the assembly process.

Imaging through the Li:Ion separator with SWIR wavelengths

 Battery Assembly Inspection
Figure 2. Typical battery inspection setup showing a “stacked” type cell with alternating Anode/Cathode (blue & red) layers with polymer separator (green) between each interface. Incident SWIR radiation illuminates the sample and the light reflected back to the SWIR image sensor provides detail regarding the subsurface layers covered by the separator.

One interesting feature of the polymer separator layers common to most lithium-ion batteries is that their optical transparency increases at higher wavelengths; becoming quite transmissive beyond the visible spectrum where SWIR Vision System’s Acuros SWIR and Acuros eSWIR cameras operate.

Our Acuros® CQD® SWIR and eSWIR high resolution cameras deliver full HD imaging capabilities, enabling lithium-ion battery manufacturers to maximize optical ROI while maintaining excellent spatial resolution.

Inspection system configurations

In Figure 2, a SWIR camera integrated into a front-side illuminated battery inspection system captures SWIR photons reflected off the sample and provides an enhanced level of subsurface detail.  The flexibility of this inspection setup, using Acuros CQD high resolution SWIR cameras, frees tool designers to offer a solution with the following properties:

  • Detection Performance: improved visibility through separator material layers
  • Thermal Management: no need to contend with sample heating/cooling impacts on the measurement
  • Inspection Throughput: acquisition speeds dictated by industry standard GigE acquisition standards
  • Total System Cost:  Full-HD 1920 x 1080 CQD SWIR cameras enable fewer cameras to be deployed per system

Battery inspection applications examples

 Battery Assembly Inspection
Figure 3. Visible (left) and SWIR (right) images of lithium-ion anode layer as viewed through a polymer separator. Because the polymer separator material is more transmissive in the SWIR spectrum, the anode edge is clearly visible in the SWIR image on the right versus the faint shadow detected by visible image on the left.

Edge Detection: One area where SWIR battery inspection promises to improve upon legacy solutions, is battery capacity. Battery capacity is proportional to the amount of overlapping electrode area achieved during assembly.   Since visible imaging solutions are limited in their ability to see through the separator layer materials, underlying edges of electrodes can be obscured thus preventing accurate edge identification and alignment.  Even small alignment errors (on the order of 100 um or less) can have a meaningful impact.

The enhanced contrast and superior FOV of SWIR Vision’s Acuros CQD SWIR cameras provide the necessary alignment accuracy of inter-layer electrodes leading directly to more available energy storage capacity and longer battery lifetimes.  

Figure 3 shows a comparison of visible and SWIR images, demonstrating the enhanced contrast achieved using Acuros CQD SWIR cameras. In practice, alignment of electrode layers depends on accurate detection of the previously positioned electrode layers which are hidden beneath the polymer separator once it is laid down. Increasing the contrast of this underlying edge transition enables edge detection algorithms to function with precision.

Particle Inspection

 Battery Assembly Inspection
Figure 4. Visible (top) and SWIR (bottom) images of delaminated particulate generated from the electrode coating during the cutting process as seen without (left) and with (right) a polymer separator overlay. Particle sizes range from 50-100um and are shown on their corresponding Anode/Cathode backgrounds to simulate the most challenging detection scenario.

Particle contamination is another challenge facing lithium ion battery manufacturers. Several high profile incidents of battery fires and explosions have been triggered by minute particles which managed to become lodged between the electrode-separator interfaces. One of the primary sources of particle contamination is the electrode cutting step where the anode and cathode electrode layers must be cut to size before subsequent rolling or stacking processes.  During this cutting process, lithium, carbon, and other electrode coating material fragments have a tendency to delaminate from the edge.  Metal shavings and other airborne particles can also pose a risk to cell reliability.

Figure 4 provides a comparison between visible and eSWIR images acquired with and without an overlaying polymer separator.  In the visible image (top), there are no particles detected as the separator is virtually opaque to the spectral response of the camera.  In the eSWIR image, longer wavelength photons are able to penetrate the separator layer and provide details of the sublayer contamination.  The particle sizes in this demonstration were on the order of 50-100um.  One of the key benefits of SWIR Vision’s 1920×1080 focal plane array technology is that smaller particle sizes can still be detected while still maintaining large imaging FOVs.

Download the Lithium-Ion Battery Assembly Inspection Whitepaper for more details.