How to Measure Swelling in Pouch Cells Before Sorting?

When handling pouch cells in battery sorting and testing applications, it is important to accurately determine the extent of any swelling that may have occurred to the cells prior to sorting. Swelling may be indicative of anything from internal damage to underperforming batteries and is highly relevant to the sorting process. In this article we explore how swelling in pouch cells is measured prior to sorting, and why this process is relevant to battery sorting systems.
What is swelling in pouch cells?
Pouch cells are commonly used for powering electric vehicles (EVs), portable electronics and renewable energy storage systems. These soft and safe to handle battery cells are constructed essentially from a pouch containing the various components strung together. As the battery matures or is subjected to stress, gas gradually accumulates inside the cell, causing the pouch to expand. Thus, ‘swelling’ occurs in pouch cells over the course of their life cycle. A pouch cell degree of swelling may be expected, so that rapid excessive swelling correlates to poor performance or unsuitable batch characteristics that call for further characterisation.
Why measure swelling before sorting?
Sorting presents some hazards if the risk of swelling cells gains a prioritised sweep, and for a good reason. Pouch cells represent a potential fire hazard if they fail in service. Further measures that must be taken into account include:Swelling Measurements to Determine if a Battery should be Sorted Out
“Is the battery we need to sort out, can it deliver accurately with respect to performance?”
Correct swelling measurements will enable sorting machines to sort cells by their condition. Swollen cells can be identified easily, ensuring that they no longer form part of the battery.
Methods for Measuring Swelling in Pouch Cells
There are many ways to measure the swelling in pouch cells, from visualisation to more sophisticated. Following are some of the most effective ways that swelling can be assessed before sorting.
Visual inspection
The most simple means of measuring swelling. While this may not be as accurate as one would wish, it can gauge at a quick glance obviously swollen cells. This is suited to larger batches which need checking quickly, though it will miss cells that are slightly swollen and may lead to a poor performing battery.
Caliper measurementThis is particularly useful when needing to sort machines that have to assess cells that are presumed to be under certain conditions for further processing.
3. Volume Measurement
A sophisticated measurement technique is to measure the volume of the pouch cell (displacement method, specialized tool that assesses the overall internal volume of the cell). This gives a better picture of whether the cell has swollen up compared to its original size derived statistics. Particularly handy in discovering minor albeit very relevant swelling.
4. Pressure Testing
A pressure test would induce a certain amount of pressure on the pouch cell and be able to measure deformation accordingly. Balls out that if a cell is swollen, that swelling cell would provide a certain resistance that a non-swollen cell would not, enabling researchers to practice the real world foibles that come season two with a battery, and trying to determine whether the swelling arose from foibles elsewhere (gas, electrolyte breakdown etc).
5. EIS (Electrochemical Impedance Spectroscopy testing)
This is a diagnostic measure for discovering resistance internally. Required a specialist piece of kit, EIS would help identify if the pouch cell internal structure has foible distortion this may ascertain or create swelling or neglect and other forms of degradation. Generally born for higher end machines where higher standards of accuracy are required, particularly if the objective of the game is to weed out the less habile cells.
Sorting Swollen Pouch Cells
Once swelling has been ascertained, depending on the degree of swelling and the measurement used there are broadstrokes usually ways to sort cells:
– Non-swallon- these are good and should be kept in that standard sorting category for further use.
– Mildly Swollen Cells- these may still of useable capacity , but may not hit the spot in everything. Should thus generally be sorted/utilized in a different category.
– Severly Swollen Cells- these should be isolated balls out for safe disposal or recycling as it likely would not take long for them to go pop with these foibles already engendered.
Conclusion measuring out swelling in pouch cells prior to sorting machines is an important part of the equation showing it before packing battery packs with so-called functional cells. In doing this properly whether it be visual inspection 10 millimeters calipers, volumetric, EIS or other measures form part of a concerted effort to significantly improve the sort rate, and lead only an operationally safe, functional cell into crucial category’s across the board. Are you a business looking to stake a claim in the battery industry, then why not give our operation a churn with a few swellings in your (battery pack) pack the shuffle…
By concentrating on these measuring metrics sorters of the machines separating the damaged or degraded cell can provide extra guile and service to existence balling a day.