Luckily, major explosions caused by Li-ion batteries are an uncommon occurrence. If they are exposed to the wrong conditions, however, there is a slight chance of them catching fire or exploding. Mathias Henriksen’s (USN) PhD project focuses on the combustible gases released from a malfunctioning Li-ion battery and the flame speed and pressure build-up of these gas mixtures. The study provides insight into what types of explosion hazards and scenarios one can expect upon a Li-ion battery failure, and may help integrate the technology more safely in their various applications.
A quick search on YouTube or Google will provide several hundred videos and images of lithium ion (Li-ion) batteries causing fires and explosions. Lithium ion batteries are used in all types of products today, perhaps most commonly in electronic devices such as laptops, cell phones, and cameras, but they are also an attractive option for large scale energy storage such as in power grid systems and electric vehicles. Unfortunately, if Li-ion batteries are exposed to the wrong conditions, there is a slight chance that a violent failure can occur. Such a failure can have severe implications for large battery systems, and research shedding light on these consequences are essential to implement better safety measures.
Li-ion batteries have all the elements needed to self-sustain a fire
To understand how a Li-ion battery can catch fire or explode, it is necessary to investigate how the battery is built. A Li-ion battery store and release its electrical energy through electrochemical reactions. When electrical energy is drawn/discharged from the battery, lithium ions move from one electrode to the other. The electrodes are submerged in a liquid called an electrolyte, which allows for the movement of ions and consists of lithium salt and organic solvents. It is these organic solvents which are the leading fire hazard in Li-ion batteries. Furthermore, the positively charged electrode (cathode) in the battery contains oxygen, which may be released if the battery is subjected to specific stresses, e.g., internal short, excessive heat, and more. This means that the Li-ion batteries have all the elements needed to self-sustain a fire.
In a powerful thermal incident, the Li-ion battery may release some of the flammable electrolyte along with various flammable/toxic gases such as hydrogen (H2), methane (CH4), carbon monoxide (CO) and hydrofluoric acid (HF). The amount and rate of the gas released depend on different parameters that are related to battery chemistry and the amount of electrical energy stored. A release of these flammable gases is what can cause fires and explosions.
The study of fast-moving flames and shock waves
The focus of my Ph.D. study is on the combustible gases released from a malfunctioning Li-ion battery, and the understanding of the types of explosion hazards and scenarios one can expect upon a violent failure. To assess the danger related to an explosion, I focus on the pressure build-up and on the flame speed of the combustible gas mixture. In our laboratory, we have an explosion sphere where we can study all of these explosion mechanisms for different types of flammable mixtures. By using high-speed cameras to capture movies of the moving flame inside the explosion sphere, we can study the flame in detail. We have high-tech cameras available which can film with frame rates ranging from 50 to 5 000 000 frames per second. This allows us to study even extremely fast-moving flames and shock waves. The results from these experiments will be used as inputs and for verification for a simulation tool, so predictions of potential consequences can be made. These predications may help integrate Li-ion technology more safely in their various applications.
Luckily, major explosions caused by Li-ion batteries are an uncommon occurrence. However, it is still essential to understand the potential consequences of Li-ion vapor cloud explosions. By understanding the consequences, better safety measures can be implemented. The importance of this work is that it lays the framework for an advance in safety-features that can reduce or avoid damage to materials, human life, and the environment.
For more information about the work done in this Ph.D. study, see the following publications:
- Henriksen M, Vaagsaether K, Lundberg J, Forseth S, Bjerketvedt D. Explosion characteristics for Li-ion battery electrolytes at elevated temperatures. Journal of Hazardous Materials 2019;371:1–7. https://doi.org/10.1016/j.jhazmat.2019.02.108.
- Henriksen M, Vaagsaether K, A.V: Gaataug, Lundberg J, Forseth S, Bjerketvedt D.Laminar burning velocity of the dimethyl carbonate-air mixture formed by the Li-ion electrolyte solvent. Combustion, Explosion, and Shock Waves (Accepted for publication, 2020).