Most prismatic cells are flat. but sometimes you may meet "swollen"cells.
You may get worried at the glance of the "swelling"
This "swollen" is not the real "swollen" which is caused by over charge/ over discharge/ short circuit.
We are just talking about the "unflat" cells. Now be calm. After you read this article, you will say: it's nothing! ;-D
WHY THEY ARE NOT FLAT?
The unflat cells use different technology during manufacturing.
This one use the similar technology like the round cells (Please see the picture below, solution A on the left)
Here is the the process of rolling/piled technology during cell manufacturing. (prismatic cell is similar to this)
One is rolling like a ball,other is like piled paper.
You can see the cell manufacturing process as below. For the step of coating and rolling in,
they are rolled in the way as the cylindrical cells. The thickness of the cell is a bit thicker in the middle than other sides.
So they look like “swollen”.Actually they are not.
1,when you receive the batteries,please charge and recharge them soon and don’t storage them for weeks.
They need to be activated. Long time storage is harmful for any li ion batteries.
2, please make a good insulation protection for the pack.
You need to use Epoxy plate between each cell. Please see the picture below.
You can see the plate in yellow among the cells.
Or use holder to fix each cell. Or they are risky to be short circuit if any cell ‘s blue PVC is damaged.
3, Do some compression (such as using high temp resistant adhesive tape)
4, Add EV foam to make it flat among the cells
5,Use high quality and proper BMS.Prevent over charge/discharge/short circuit.
6,Charge and discharge the cells within 1C constantly.
7,Keep the batteries balanced. Adding active battery balancer to double the cycle life.
Hope these tips are helpful to you.
Please don’t get nervous about “unflat”. This is normal for this cell.It is different with “swollen”
If they are directly from factory and brand new, no worries but they just need some professional treatments.
No matter you get flat cells or non-flat cells, please keep the tips above in your mind.
This is our idea about this issue.
If you have any thoughts about it, welcome to discuss with us.
Anyhow if the batteries swelling seriously by over charging or over discharging or short curcuit,
You must replace the swollen cells soonest. This situation is different with the topic we are talking about.
------ Mandy from Deligreen