In order to prevent such events from happening again, it is vital to understand the various stages of battery failure. They can be divided into prevention and control areas and are divided into four phases.
1. Prevention area
Stage 1: Battery abuse.
In the first stage, heat, electrical or mechanical failure can lead to battery damage, resulting in increased battery temperature and pressure.
Stage 2: Generation of flammable exhaust gases.
As the battery temperature and pressure increase, flammable gases are exhausted from the battery. This is the critical point at which steps must be taken to avoid thermal runaway and fire.
Stage 3: Thermal Runaway
Thermal runaway marks the end of the protective zone and the beginning of the containment zone. Temperatures rise rapidly by several hundred degrees and smoke is produced. It is at this point that catastrophic failure is imminent.
2. Area of containment
Stage 4: Fire
The battery begins to catch fire after thermal runaway. The structure of the lithium-ion battery rack maximizes the deployment density of the battery, but it also allows the fire to spread rapidly. After a fire has started, it can easily transfer to adjacent cells and building materials and will become uncontrollable.
A closer look at these four stages reveals that early intervention is the ideal moment to prevent thermal runaway. Ideally, the response should occur within the prevention zone, but this needs to be detected in the first or second stage. If exhaust gases can be detected before thermal runaway begins to occur and the faulty battery can be disconnected in time, the fire hazard can be avoided.
Early intervention can prevent thermal runaway
As an analysis of the four stages of lithium-ion battery failure shows, one of the best warning signs detected is the release of exhaust gas. By definition, exhaust gas is a byproduct of the battery's chemical reaction process. This chemical process produces electrolyte vapor from the battery cell when the lithium-ion battery begins to fail. This exhaust gas is generated shortly after cell damage occurs and a few minutes before thermal runaway begins.
A lithium-ion battery failure will also eventually produce detectable fumes, but only after thermal runaway has begun. By detecting the presence of exhaust fumes, affected cells can be treated in time to prevent thermal runaway.
Integrated solutions enable early intervention
Effective lithium-ion battery risk prevention solutions use monitoring and reference sensors that continuously check for the presence of lithium-ion battery-generated exhaust fumes in the battery rack. Reference sensors provide ambient air data to the controller, while sensors within the battery rack are monitored to obtain data related to the air near the lithium-ion battery. These sensors can detect exhaust gases from lithium-ion batteries at concentrations as low as parts per million (ppm).
This risk prevention system is designed to disconnect the battery and prevent thermal runaway in less than five seconds. However, even after disconnecting the battery, flammable gases may still be present. Unless the area is large enough or can be ventilated, these exhaust gases can still cause a fire.
This is where fire detection and extinguishing comes into play. If an inert gas is used, a gaseous fire suppression system can be used to inert the exhaust gas space after it has been released. This can help reduce the likelihood of exhaust gas combustion. The release point of an inert system needs to be carefully considered to be effective and may need to be integrated with other systems.
At specified design concentrations, fire protection systems can be used to help protect the battery from sources of ignition (e.g., Class A materials) and other electronic component failures that could be sources of heat to ignite the battery.
Combining exhaust gas detection with fire detection and suppression provides the early intervention needed to help prevent the risk of thermal runaway and fire from occurring in the battery. The system does not require electrical or mechanical contact with the battery cells and is essentially an upgrade to existing fire protection systems to allow them to operate in a charged operating environment.
The number of energy storage systems using lithium-ion batteries is expected to increase significantly over the next five years. Because lithium-ion batteries can fail and fire, often with little warning, it is more important than ever to detect and prevent thermal runaway before the worst happens. Combining early exhaust gas detection with fire detection, suppression or inerting systems can provide a total solution that provides the early warning needed to enhance battery storage system safety.
