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Cell Environmental Protection
In addition to supporting the cells, a well-designed chassis will protect cells from exposure to corrosive substances
and oxidizing catalysts, such as dust and moisture. The necessary level of protection for cells in a battery pack
varies depending on the intended application. For example, a battery pack designed for use in a vehicle must have
an enclosure that isolates cells from shock and vibration, protects them from dirt and debris, as well as shielding
them from other environmental dangers, such as salt spray. Unless it is hermetically sealed, even a sealed
enclosure is subject to pressure differentials between its insides and the ambient, causing minute amounts of air
exchange. Therefore, over time, some moisture may accumulate and condense on inside surfaces. A battery pack
designed to be sealed from the environment (from dust, moisture, and volatile chemicals) must have a way to
benignly drain off whatever condensate does manage to leak into it and keep it away from circuits and conductors.
In addition, enclosures protecting cells must work with the thermal management system to achieve optimum
durability and safety of the battery pack. For example, a poor choice of materials for the enclosure, combined with
insufficient cooling and controls, may cause the battery pack to overheat.
AMP20 Cell Vents
During abusive conditions (such as Overcharge), the
electrolyte inside the cell will decompose into gaseous
compounds and cause pressure to build within the cell. When
the pressure is high enough, the gases will evacuate or vent
through an intentional weak spot in the top corner of the cell.
Although this process of venting irreversibly damages and
ultimately makes the cell unusable, it prevents the cell from
exploding in an uncontrolled manner.
A properly designed battery pack will allow the vent to
operate in a situation where the cell is significantly abused.
Any mechanical constraints in this corner shall be avoided.
Figure 12 – AMP20 cell corner that will vent under extreme internal pressure
ANR26650 Cell Vents
The ANR26650 cell vents, located on the end cap(s) of the cells (on the
POSITIVE side of the cell), should not be blocked by any mechanical means.
Blocking the cell vent and then sufficiently abusing the cell so as to build up
pressure in the cell prevents the cell from properly venting. A battery pack
designed to install cells end-to-end needs at least 2 mm of space between
the cells to allow the vent to open under fault conditions. Refer to Figure 13
as an example.
Figure 13 – ANR26650 end-to-end cell spacing