Battery pack designs take into consideration the type of environment for the application. Harsh conditions such as extreme temperatures, vibrations, shocks, moisture, dust, and humidity may degrade battery cells.
This degradation can cause short circuits, swelling, capacity loss, damage, and charging or discharging issues. Selecting the appropriate battery pack design can address environmental issues to reduce risks.
Environmental and Use Case Considerations
Industries such as military, aerospace, oil and gas, construction, marine, and many others require the use of portable devices in outdoor conditions. The devices may have to be exposed to salt water, high humidity, cold temperatures, mining dust, excessive heat, and vibrations.
Ruggedized battery enclosed and potted for industrial use.
Extremely Cold Temperatures
Battery cells exposed to extremely cold temperatures, such as lithium-ion chemistries, can experience a drop in capacity. This capacity loss may cause power disruption where the device can periodically stop working. When it comes to machinery that must continue to operate, it can cause safety concerns and slow down productivity. Conversely, if the device is used in environments with high temperatures, the battery pack's internal operating temperatures may exceed safety limits. The pack may experience swelling. For lithium-based chemistries, high temperatures can cause cells to overheat as this factor leads to thermal runaway.
Humidity and Moisture
Some devices may be used in places with humidity and moisture content. High humidity may contribute to excessive degradation and corrosion of the battery enclosure and cells. It can also cause electrical shorts due to internal resistance. Low humidity can also cause safety issues by creating static discharge, which could negatively interact with mechanical systems. When moisture is present, water can cause cell chemistry instability that could lead to fires or explosions.
Charging and Discharging Issues
Even when not experiencing catastrophic damage, battery cells may deal with charging and discharging issues. Dust, vibration, and shocks may cause wire assemblies to loosen to create power disruptions. Issues may also shorten the lifespan of the battery cells, make it difficult for batteries to charge fully, or create faster discharging phases.
Understanding the type of environment helps manufacturers design a battery pack and enclosure suitable for those conditions. Customers may require a battery pack that offers higher capacity, enhanced safety features, or additional enclosure requirements.
Chemistry and Architecture Requirements
Battery chemistry has specific parameters for charging and discharging stages. For example, lithium-ion batteries have a temperature range of 32°F to 113°F for charging and -4°F to -140°F for discharging. Lead-acid batteries have a range of -4°F to 122°F for charging and discharging. Nickel-based chemistries (NiCd and NiMH) have ranges of 32°F to 113°F for charging and -4°F to 149°F for discharging. Knowing the typical temperatures in the harsh environment allows you to select a chemistry most suitable for the device.
If the battery pack will experience temperatures that go beyond these ranges, additional safety features may be added to the architecture of the enclosure. Heaters, cooling functions, and vents can keep temperatures stable and vent built-up gases. A battery management system (BMS) can monitor the pack's temperature and control heating, cooling, and venting functions when the battery becomes too hot or cold.
For shocks and vibrations, redesigning the battery enclosure can offer additional protection for the battery cells. To prevent dislodgement, punctures, and cracks, material selection options may include plastic, steel, or aluminum. The cells may also have channels with coolants for heat dissipation, or flame-retardant materials to increase safety from thermal runaway risks.
Electrical and Power Determination for Battery Cells
Determining the electrical and power needs of the device requires evaluating factors such as the internal resistance that will be experienced during exposure to the harsh environment, the state of health (SoH) of the pack during short-term and long-term use, and the power capabilities.
Creating simulated environmental conditions allows manufacturers to test how the battery responds when in use and charging. Manufacturers may develop machine learning models that use gathered historical data to analyze the operation of batteries and make electrical and power adjustments based on voltage and current measurements.
To see what type of internal resistance is present due to extreme temperatures, tests using AC and DC signals will check the impedance and voltage drop. Additional current tests can also check internal resistance to further understand the cell's available power when charging and discharging at certain temperatures.
Summary
Customers and manufacturers need to understand what occurs to battery packs used in harsh environments. Specific industries may have requirements for battery packs to undergo special design and testing parameters, such as MIL-STD-810 for military equipment, to ensure safe operation. Selecting the right cell chemistry, architecture, capacity, and safety controls will allow the battery pack to operate efficiently even when experiencing hazardous conditions.
Key Takeaways
- Determine environmental conditions: Knowing the common environmental problems allows consideration when selecting temperature control, vibration, and moisture penetration features for battery packs.
- Select battery chemistry based on temperature range: Staying within the specific environmental range allows the battery pack's chemistry to operate as desired.
- Vents, fans, and heating components improve battery operation: These components allow for venting of heat buildup or to warm cells when temperatures are expected to drop below safety parameters.
- Internal resistance testing and simulation measurements are vital: Manufacturers perform testing in simulated conditions to observe how the battery functions in harsh environments.
