The operation of machines causes the generation of internal heat, which can put the health of functioning components at risk. Notably, it is the same story with the cells that make up batteries.
Chemical reactions inside cells generate energy for electronic gadgets. This chemical reaction also produces heat while charging, discharging, and short-circuiting. And, at a certain temperature, the battery cell will go into thermal runaway.
This article will discuss everything about thermal runaway in battery packs and how to prevent it.
What is Thermal Runaway & What Causes it to Happen?
Batteries are key in unlocking the potential of renewable energy through storage technologies but are at risk of thermal runaway. This occurs in battery packs when the heat buildup exceeds the amount being released. Thermal runaway is a chain reaction that, once started, can be extremely difficult to halt.
When a battery's internal temperature rises enough, a chemical reaction occurs. Thus, the internal battery cell temperature increases quickly, and all energy releases at once. Then, this chain reaction produces temperatures of approximately 752 degrees Fahrenheit, or 400 degrees Celsius. Extreme heat can cause the battery to start gassing and ignite a fire.
The Repercussions of Thermal Runaway
Without intervention, the battery will overheat, and the outside shell will swell, melt, or explode due to the heat buildup inside.
Hydrogen sulfide gas, with a pungent odor, is released when the battery case gets broken. If this occurs, you must disconnect the battery immediately. If thermal runaway goes unnoticed, it can cause fires, thermal explosions, sudden system failures, expensive damage to equipment, and even personal injuries.
How can Thermal Runaway be Prevented through Product Design & Development?
There are several potential ways to mitigate thermal runaway in battery packs. Here are some best practices for preventing thermal runaway during the design and development stages.
Cell Arrangement
The prevention of thermal runaway is highly dependent on the number of cells required for the battery pack and the configuration of the cells. The accumulation of heat along the cells is the primary concern; thus, a battery pack should always work to alleviate it.
When possible, lining up the cells helps the temperature spread more uniformly among them. Thus, the heat radiates away from each cell, without generating heat sinks. The heat sinks can handle higher temperatures when the cells are put together in even rows and columns.
Battery Management System
Battery cell monitoring for overcharging and over-discharging is another design consideration. The battery management system (BMS) regulates and monitors many cell operations, such as voltage, current, charge control, charge balance, and cell temperature. The BMS will act as a safety switch whenever there is a problem with an internal short circuit and protects against ESD & EOS.
The BMS can activate cooling mechanisms in the event of an increase in temperature. Additionally, it can help keep the microenvironment of cells in check. If thermal runaway occurs and the cooling methods are ineffective, the BMS can prevent more cells from overheating by shutting them down.
However, it is important to remember that there are situations in which thermal runaway can occur even with a BMS installed. While the system cannot eliminate the possibility of a chain reaction, it can significantly reduce the frequency of such reactions and include safety features that reduce the likelihood of thermal runaway in the other cell.
Ventilation
Given that the battery cell is enclosed, vents are useful for facilitating heat transfer. These openings allow hot air to escape while cooler air gets drawn in from the surroundings. Besides removing excess heat from the battery cell and application, the vents can also help cool the electronics.
Battery venting is common across battery types. When being charged, lead-acid batteries give off hydrogen gas; hence, ventilation is essential. On the other hand, cells powered by lithium do not off-gas any harmful byproducts.
Even though consumers typically do not think the cells need to be vented, doing so can help reduce the dangers of thermal runaway by allowing heat to exit the enclosure and reduce temperatures along the cells.
Conclusion
To a greater or lesser extent, all battery cell chemistries are vulnerable to the dangerous phenomenon known as thermal runaway. But if you manage your system well, you can reduce that danger and take advantage of battery power whenever it is practical.
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