How to Test the Capacity of Pouch Cells Safely?

Recently another application for a pouch cell was developed for use in electric vehicles (EVs), energy storage systems (ESS), consumer electronics, and larger vehicle batteries. These batteries come in various shapes and sizes depending on their purpose and can be flat as a pancake or even large enough to fill a room.
Why test the capacity?
The different kinds of pouch cells mentioned above are used in total electric cars or automobiles of the future utilizing digital delivery systems. To be effective, it is important that these cells do not produce more heat than they absorb. The cells are needed to replace today’s batteries if it is ever possible to do away with combustion altogether. I am not sure if the cell is ready for all that yet!
Simply put the capacity of a battery is the amount of charge it will hold and may be expressed in milliampere-hours (mAh) or ampere-hours (Ah). Testing of the cell enables one to check for the following:
1. Quality of testing in the cell, ie, to test whether the same discharge capacity occurs with a test load as when not loaded.
2. Confirmed degeneration, over time, the test reveals less and less capacity until finally the cell fails.
3. Adequate size, whether small enough, for the intended application. No sense in going overboard unless required.
Testing the cell
Before doing any testing one should assemble all necessary tools and testing equipment. Battery testing equipment first, of course, should be of the safest kind where particular reference to a pouch cell is given.
A battery analyzer within the foregoing specifications should be used.
Care should be taken to ascertain ambient temperature present during testing, and should be done preferably within a dry room of 75 F. or better if possible. Keep direct warmth from sunlight, etc., from the cell prior to starting the test.
Avoid direct touching of cell with bare skin and wear rubber gloves whenever possible.So as you’ll see below, things like this will be covered under connections, but please be sure that you have properly measured, reliable test leads, connectors, and any terminal connections. Make sure you’re not going to short yourself out or create a higher risk of short circuit from internal power paths leading to a proper link. Properly attract the battery lead on and off the post to avoid those worrying short circuit “pops” on or off the battery. Now onto charging.
Charging a pouch cell is pretty simple. You’ll need a respectable constant power source.
Charging the pouch cell.
For testing the capacity you’ll want to charge the pack as quickly and completely as possible. You’d want something like a CC/CV charger that would full charge the pouch cell as these Type ofLithium-ion of cells (pouch cells that is) exhibit a fully charged battery voltage of around 4.2V. You might not have that sort of luxury. You should take care that your cell does not charge faster than allows. There must be appropriate cut-off after charging. You might have a battery charger that has automatic cut-off when your test cell is fully charged. Keep an eye on it, and try to observe when the battery is fully charged. Tests may vary from simply extending way past or not even beyond threshold voltage power deliveries discharging the cell pack further for the test purpose.
Discharging the cell.
Your cell will be fully charged. Now during discharging will you take care if too short a cell being discharged too quick. Your test should perhaps adjust its parameters to suit a critical low rate of current drawn designed for such tests. You want to be discharging at lower than specified (so check the recommend discharge rate) . Try a discharge at a half cell current draw or less to start. Discharge of cell amp rate to estimated capacity specifications would be a half “ C” rate (1/2). Keep an eye on the temperature of the cell l (while also being a good distance from the test at the same time if able). Shy away from getting over 60°C.Use an appropriate load: Connect the pouch cell to a discharging load that can reliably draw a constant current. Some testers have a built-in load function for this purpose.
5. Measuring the Capacity
How much capacity can it deliver? The answer lies in measuring a simple variable:
Those are the guts of it. How much capacity does this thing have? Capacity is a simple multiplication of total current times the time it takes to reduce the voltage to the cut-off voltage of choice (usually 3.0V for cheap lithium-ion pouch cells).
Compare that with the rated capacity. If it is way out, the cell is rotten through heat shock or made badly.
6. Safety Considerations
Pouch cells can be made rather sensitive to all sorts of conditions. Stay safe when doing this test.
Don’t overcharge: Never exceed the voltage when charging (usually 4.2V) that you are supposed to charge the pouch cell, or you may start an unwanted and unkind thermal runaway situation burning it down or venting acrid gas.
Don’t overdischarge: Irreparably damage once you go below its’ cut-off voltage (2.5V) recklessly. Temperature makes it much worse.
Watch for reaction: When discharging, doing clandestine work if you see bumps, leaks, or it heating; stop!
Use a fire-resistant bag: Bag like in the thermal runaway so there is no other explosion or burn damage.
7. Post-Test Considerations
What now? Flush it down the toilet? Probably not, Gerald. Store the pouch cell at least.
Talk about storage: If in the good bag, it has room at ambient temperature and all, leave it out of hot spots and sun. Hint: get a second fridge dedicated to the project at least.
And, if the latter does not help, croak and flunk the cell, and crush the silly twisted lithium-yonbattery into crumbs: in accordance with local ordnance, or ordinance if you insist, poisonous waste in especial since it’s a movin’ battery.
Conclusion
Tested the capacity of that pouch cell. Excellent; did the whole bag do?
Test that charger well since that bag of cells came cheap enough. We do special pricing job right.