Pouch Cell - Small but not Trouble Free

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In 1995, Li-polymer surprised the battery world with a radical new design, the pouch cell. Rather than using a metallic cylinder and glass-to-metal electrical feed-through for insulation, conductive foil tabs welded to the electrode and sealed to the pouch carry the positive and negative terminals to the outside. Figure 1 illustrates such a pouch cell.

Figure 1: The pouch cell
The pouch cell offers a simple, flexible and lightweight solution to battery design. Exposure to high humidity and hot temperature can shorten service life.

Courtesy of Cadex
The pouch cell makes the most efficient use of space and achieves a 90 to 95 percent packaging efficiency, the highest among battery packs. Eliminating the metal enclosure reduces weight but the cell needs some alternative support in the battery compartment. The pouch pack finds applications in consumer, military, as well as automotive applications. No standardized pouch cells exist; each manufacturer builds the cells for a specific application.
Pouch packs are normally Li-polymer. The energy density can be lower and be less durable than Li-ion in the cylindrical package. Swelling as a result of gas generation during charge and discharge is a concern. Battery manufacturers insist that Li-ion batteries do not generate excess gases that can lead to swelling when properly used. Nevertheless, some swelling can occur and most is due to faulty manufacturing. The pressure from swelling can crack a battery cover open and in some cases break the display or electronic circuit. Manufacturers say that an inflated cell is safe. While this may be true, do not puncture a swollen cell in close proximity of fire or heat; the escaping gases can ignite. Figure 2 illustrates a pouch cell that has swelled.

Figure 2: Swelling pouch cell
Swelling can occur as part of gas generation. Battery manufacturers are at odds why this occasionally happens.

Courtesy of Cadex

To prevent swelling, the manufacturer adds excess film to create a “gas bag” outside the cell. During the first charge, gases escape into the gasbag, which is then cut off and the pack is resealed as part of the finishing process. Gas buildup on subsequent charges is minimal; nevertheless, when designing the battery compartment for pouch cells, provision must be made to allow for some expansion. It is best not to stack pouch cells but to lay them flat side by side. The battery compartment must be made to protect the cell from mechanical stress and be free of sharp edges.
 

Summary of Packaging Advantages and Disadvantages

  • A cell in a cylindrical metallic case has good cycling ability, offers a long calendar life, is economical to manufacture, but is heavy and has low packaging density.
     
  • The prismatic metallic case has improved packaging density but can be more expensive to manufacture, is less efficient in thermal management and may have a shorter cycle life.
     
  • The prismatic pouch pack is light and cost-effective to manufacture. Exposure to high humidity and hot temperature can shorten service life.

Comments

On January 11, 2011 at 5:10pm
navaratnam thangaratnavel wrote:

What is the EMF of a unit Pouch cell?
How economical it will be, when commercially available?
I think it may be good if made for one time use,
provided environmentally friendly.

On January 16, 2011 at 8:37pm
BWMichael wrote:

The Pouch cell is available now. Some mobile phone batteries are Li-Po pouch cells. I blew one up the other day, very cool.

On February 2, 2011 at 2:21am
ROSHAN wrote:

SMALL USEFULBUT TRUBBLE FULL BATTERY

On March 13, 2011 at 11:23pm
James Kim wrote:

Now, I am a fresh student studying on the Li-ion pouch battery, especially lower swelling. I am much wondering the reasons of cell swelling. where is its reason from? Pz. help me~, somebody~~~~^^

On March 31, 2011 at 6:11pm
Mickey wrote:

Any harm in using a small pin to puncture a cell that is slightly beginning to expand?  I noticed the article said not to puncture near flame or heat (duh, hydrogen gas in there), but what about in open air?  This battery still holds a 4.5 out of 5 hour charge and I’d really hate to get rid of it if it has 100 or so more cycles left.

The enclosure around the cells has started to exceed the tight constraints in which the laptop battery is meant to fit.

On June 30, 2011 at 4:52am
David wrote:

I also have removed a battery cell from an MP4 player that wasn’t holding charge. The thing is far too big to fit back into the slim case and looks like it’s going to pop.

How to dispose of these things? Is it safe to pop them?

On November 1, 2011 at 8:56am
Hussam wrote:

Hello:
I have some questions:
For the pouch cells, how much will it swell and what maximum pressure should be applied to the battery pack?
Also, does the inflate occurs during charging or gradually with time?
Thanks

On November 1, 2011 at 9:53am
David wrote:

My pouch cell swelled to similar size as the one in the picture figure 2.

After swelling there is no way you can put it back.

With mine it happened quickly. One day it was working fine and the next it stopped. When I opened it up the battery just got bigger and bigger. Humidity could be the cause as I often used my MP4 player to watch movies in the bath!

On August 21, 2012 at 4:37am
Stijn wrote:

How much can these cells swell in function of their original size?

On October 31, 2012 at 11:49am
Richard Jesch wrote:

Having observed this phenomenon on several occasions I am convinced that swelling of the pouch (as being inflated) is the result of the cell being at voltages outside of it’s safe operating area. some scenerio comes to mind:
1.)Cell was charging while the terminals exceeded ~ 4.35 vpc (volts per cell)
2.)Cell was discharged such that the open cell voltage (OCV) dropped below ~2.5 vpc
3.)Cell was charged at an excessive current, exceeding ~1.5C (varies by formulation)
4.)Cell was discharged at an excessive current, exceeding it’s rating, (varies)
5.)Cell was exposed to excessive temperature.
I am leaning to number 2 as more likely, more data needed. Here is the scenario. The cell is discharged to a 100% discharged state of charge (SOC). Perhaps exacerbated by continued discharge current at near rated current. Then possibly left in the discharged state for extended period of time. When charging is finally applied the charging current may be at the rated max charge current. Under these conditions , Thesis is that the cell impedance is high, current is also high, and the electrode to media voltage increases and heat it generated in the wet part of the cell near the electrode. This thermal process runs away leading to structural problems in the cell and the evolved gas does not go back into solution because it has different character than the electrolyte it evolved from.
This is just my own personal opinion. I wish some expert would come along and shed some light on this matter. We are losing too many cells to this problem.

On October 31, 2012 at 11:06pm
Bernardo David wrote:

Richard,

The same is happening to our batteries, We do not know why this occurs because each LiPo battery has it own PCM to protect and prevent Overcharge and discharges, Our PCM control the charge at 4.28V max and discharge at 3.05V . But suddenly this week two of our Lipo are Inflated. Would be great if an expert can explain more about it

On March 14, 2014 at 10:36am
Rick wrote:

Any battery with lithium in its chemistry will swell if over charged or over discharged.  Keeping HVC set at 4.2 volts per cell will prevent over charging and maximum life. (For Lifepo4 chemistry max charge is 3.65volts per cell)  Not discharging total capacity below 20%SOC will also maximise cycle life. Problem with most lithium powered appliances I see is lacking a battery analyst ot montior consumption.  So the user depends on the internal LVC to prevent over discharging.

On June 20, 2014 at 8:00am
KS wrote:

Any suggestions on where to purchase a pouch pack? Any how to make the feedthrough connections?

On October 14, 2014 at 1:42pm
Paul Reeve wrote:

I have a macbook pro 1281 battery which started to inflate bulge with time. It holds charge accordingly with a 9% wear. but works great. Only problem is that I had to remove my laptop battery cover as it was pushing it. So I had to keep the battery with some tape.
  Question is, I’ve seen lot’s of videos of people puncturing the cells to remove this gas. With a toothpick something which is not metal. Is this actually doable and safe? obviously doing this outside in open air.  After you remove the gas what’s the best method to seal the punturing hole? as it will need some kind of material resistant to stress and expansion. Thanks