Thermal runaway occurs when a battery cell gets too hot, leading to a self-reinforcing cycle of heat generation. This can happen in various lithium-ion chemistries due to internal short circuits, overcharging, mechanical damage, or exposure to high temperatures. If not controlled, this process can lead to a fire or explosion as the battery releases its stored energy rapidly.
Although thermal runaway is a significant concern for many lithium-ion chemistries, LiFePO₄ batteries are much more resistant to this dangerous phenomenon. But while they are safer, it’s still important to know how to mitigate the risks and recognize the limits.
Why LiFePO₄ is Less Prone to Thermal Runaway
There are several reasons why LiFePO₄ batteries are considered safer:
Thermal Stability: The chemistry of LiFePO₄ is much more stable at high temperatures than other types of lithium-ion batteries. The strong bond between iron and phosphate in the cathode gives it a higher thermal threshold before breaking down.
Lower Risk of Fire: Even if a LiFePO₄ battery reaches high temperatures, it doesn’t release oxygen like some other chemistries (such as lithium cobalt oxide). This means that it’s less likely to fuel a fire.
Lower Energy Density: LiFePO₄ cells have a slightly lower energy density than some alternatives, such as lithium nickel manganese cobalt (NMC) batteries. This reduces the likelihood of overheating and allows for more efficient heat dissipation during charging and discharging.
These factors make LiFePO₄ a safer option, but it’s still crucial to understand potential risks and how to prevent thermal runaway in even the safest batteries.
Can Thermal Runaway Happen in LiFePO₄ Batteries?
While LiFePO₄ batteries are highly resistant to thermal runaway, it can still occur under extreme circumstances. For example:
Overcharging: Pushing too much current into the battery for too long can lead to overheating and damage. Although LiFePO₄ batteries have a relatively flat voltage curve, overcharging can still cause internal heating and potential thermal runaway.
Physical Damage: Puncturing or crushing a battery can cause an internal short circuit, leading to a rapid rise in temperature. Mechanical abuse can initiate the chain reaction that leads to thermal runaway.
Severe Heat Exposure: If a LiFePO₄ battery is exposed to extreme external heat, such as a fire, it can still overheat and enter thermal runaway. While it won’t catch fire as easily as other lithium-ion batteries, it can still fail.
What is the Runaway Temperature of LiFePO₄?
One of the reasons LiFePO₄ is safer than other lithium-ion chemistries is that its thermal runaway temperature is significantly higher. For most LiFePO₄ cells, thermal runaway typically begins at around 270°C (518°F). This is substantially higher than the runaway temperatures for other types of lithium-ion batteries, such as lithium cobalt oxide (LiCoO₂), which can begin runaway at just 150-200°C (302-392°F).
The higher temperature threshold provides a larger safety margin in normal operating conditions, but it’s still important to keep the battery within its recommended temperature range to avoid any issues.
How to Prevent Thermal Runaway in LiFePO₄ Batteries
Even though LiFePO₄ is inherently safer, best practices can further reduce the risk of thermal runaway:
Use a Battery Management System (BMS): The BMS monitors the battery’s voltage, temperature, and current flow to ensure the battery stays within safe limits. It can prevent overcharging, over-discharging, and overheating by automatically cutting off power when thresholds are exceeded.
Avoid Overcharging: Overcharging a battery can lead to excessive heat buildup, which increases the risk of thermal runaway. Always charge within the specified voltage range for the battery and never bypass safety features like the BMS.
Protect the Battery from Physical Damage: Avoid puncturing, crushing, or subjecting the battery to extreme mechanical stress. Any damage to the internal structure of the battery can cause a short circuit and lead to dangerous heat generation.
Store in a Controlled Environment: Batteries should be stored in a cool, dry place away from direct sunlight or extreme heat. Prolonged exposure to high temperatures can accelerate degradation and potentially lead to thermal runaway.
Regular Inspections: Check your battery regularly for signs of swelling, corrosion, or any unusual behavior during charging or discharging. These can be early indicators of a problem that could lead to thermal runaway.
Can Thermal Runaway Be Stopped?
Once thermal runaway starts, it can be extremely difficult to stop. The process is self-sustaining because the heat generated by the reaction triggers further reactions, leading to more heat. However, with LiFePO₄ batteries, the chances of runaway spiraling out of control are much lower.
If thermal runaway does begin in a LiFePO₄ battery, it is unlikely to result in a catastrophic fire or explosion. LiFePO₄ batteries tend to vent non-flammable gases rather than igniting. Still, once runaway begins, it usually requires external intervention—such as cooling or cutting off the power supply—to prevent further escalation.
In large battery systems, advanced cooling mechanisms or fire suppression systems are often used to control runaway. Some systems use thermal fuses that cut the circuit when excessive heat is detected, which can help slow or stop the reaction.
Further reading : Can LiFePO4 batteries catch fire?