what's mean battery pack -The Pouch Cell

?Cell design made a profound advance in 1995 when the pouch cell concept was developed.

Rather than using an expensive metallic cylinder and glass-to-metal electrical feed-through

to insulate the opposite polarity, the positive and negative plates are enclosed in

flexible, heat-sealable foils. The electrical contacts consist of conductive foil tabs that

are welded to the electrode and sealed to the pouch material. Figure 3-4 illustrates the

pouch cell.

The pouch cell concept allows tailoring to exact cell dimensions. It makes the most

efficient use of available space and achieves a packaging efficiency of 90 to 95 percent,

the highest among battery packs. Because of the absence of a metal can, the pouch pack has

a lower weight. The main applications are mobile

phones and military devices. No standardized pouch cells exist, but rather, each

manufacturer builds to a special application.

The pouch cell is exclusively used for Li-ion

and Li-ion polymer chemistries. At the present time, it costs more to produce this cell

architecture and its reliability has not been fully proven. In addition, the energy density

and load current are slightly lower than that of conventional cell designs. The cycle life

in everyday applications is not well documented but is, at present, less than that of the

Li-ion system with conventional cell design.

A critical issue with the pouch cell is the swelling that occurs when gas is generated

during charging or discharging. Battery

manufacturers insist that Li-ion or Polymer cells do not generate gas if properly

formatted, are charged at the correct current and are kept within allotted voltage levels.

When designing the protective housing for a pouch cell, some provision for swelling must be

made. To alleviate the swelling issue when using multiple cells, it is best not to stack

pouch cells, but lay them side by side.

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