Ni-MH Rechargeable Batteries
Battery
Construction
(cont.)
4.3 Prismatic Cell Construction
The basic differences between the prismatic cell and the cylindrical cell are the construction of the electrodes and the shape of the can. Prismatic cells are designed to meet the needs of compact equipment where space for the battery is limited. The rectangular shape of the prismatic cell permits more efficient battery assembly by eliminating the voids that occur in a battery constructed with cylindrical cells. Thus, the volumetric energy density of a battery can be increased by constructing it with prismatic instead of cylindrical cells.
Figure 4.3.1 shows the structure of the pris- matic nickel-metal hydride cell. The electrodes are manufactured in a manner similar to those of the cylindrical cell, except that the finished electrodes are flat and rectangular in shape. The positive and negative electrodes are interspaced by separator sheets. The assembly is then placed in a nickel-plated steel can and the electrolyte is added. The positive electrodes are connected to the metal lid with a tab. The cell is then sealed by crimping the top assembly to the can. The top assembly incorporates a resealable safety vent, a metal lid and a plastic gasket that is similar to the one used in the cylindrical cell. A heat- shrink tube is placed over the metal can. The bottom of the metal can serves as the negative terminal and the top metal lid as the positive terminal. The insula- tor and gasket insulate the terminals from each other. The vent provides additional safety by re- leasing any excess pressure that may build up if the battery is subjected to abusive conditions.
FIGURE 4.3.1
(+) Positive Terminal
Safety Vent
Cosmetic | Metal Lid | Heat Shrink Tube |
Disk |
|
|
Gasket
Insulator
Positive Tab
Positive Electrode
Separator
Negative Electrode
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