Pouch Cell - Small but not Trouble Free

Untitled Document
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.
Previous Lesson Next Lesson

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!