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Section 3: Application and Design Considerations
Excessive exposure to air can have an adverse affect on Zinc Air battery operation, primarily due to carbon dioxide reacting with the electrolyte in the air electrode. The battery can also absorb water or dry out depending on ambient conditions. Balancing the air requirement of the battery during discharge versus the need to minimize exposure during rest is called air management. Air management might be as simple as removing the tab from the battery and inserting it into a device, or it might include a system to open and control air access to the battery as needed. Air management is application specific, and most devices will require some degree of air management to optimize battery performance.
3.1 ‐‐ Air Management
There are several types of air management. The simplest method of air management is removing the tab and putting the battery in the device. This is how miniature zinc air cells are used in hearing aids since the total battery life is typically expected to be 6‐8 weeks. As the device usage becomes more intermittent, other methods of air management are needed to deliver optimal battery performance.
Throttling is a technique to permanently restrict air access to only what is needed by the battery in a specific application. Throttling is most appropriate in devices that require a small portion of the maximum current that a battery can sustain. For example, a device might require 10 mA of current compared to the maximum of 100 mA that a PP355 can sustain. This technique works best for devices that have a low average drain rate with little increased power needs. By restricting the air access to the battery, the performance life can be extended.
As device use becomes more intermittent and as device power demands increase, valved (open and shut) air management becomes more appropriate. Valved systems are either mechanical or electronic. Each system requires a sealed battery or battery compartment, into which air is introduced by the valve when the device needs power. A seal can be accomplished with common materials such as o‐rings, gaskets, over‐molded or two‐part injection molded materials, or other methods. A mechanical solution might be an ON / OFF slide switch which acts as a simple air valve. Other device specific mechanical actions could also be used to open and close the air access. Examples include changing device settings, moving a piece or a part of the device during use, pressing a button, turning a dial, or manipulating a threaded component. An electronic valve would act in a similar fashion, except that the device electronics would open the air access automatically. A valve could be opened as a function of device state (on = open, off = closed), or it might be a function of the instantaneous power needs of the device. In a valved air management solution, a low level of air access might still be needed to be able to provide the quiescent, or background, power required to activate the ON/OFF valve. Figure 11 shows generally where each of these air management techniques is appropriate.
ENERGIZER BATTERY MANUFACTURING
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