Battery Electric vehicle (BEV), plug-in hybrid electric vehicle (PHEV) and hybrid electric vehicle (HEV) batteries are at the forefront of modern automotive technology, driving the shift towards sustainable transportation — but do you know how they work?
Let’s explore the chemistry, including the risks of fire associated with these portable power plants and help demystify electric battery chemistry and safety.
All electric vehicle batteries (generally 200–900-volt DC) rely on advanced chemistry to provide efficient and reliable power sources. The two most used battery chemistries available are lithium-ion (Li-ion) and nickel-metal hydride (NiMH).
Li-ion batteries are becoming more prevalent and are the preferred choice for most electric vehicles and other electronic equipment due to their high energy density, relative lightweight and long cycle life. They consist of a positive electrode (cathode), a negative electrode (anode) and an electrolyte. The cathode typically comprises lithium metal oxides, such as lithium cobalt oxide (LiCoO2) or lithium iron phosphate (LiFePO4), while the anode is often made of graphite. The electrolyte, usually a lithium salt in an organic solvent, facilitates the movement of lithium ions between the electrodes during charge and discharge cycles.
On the other hand, NiMH batteries which are commonly used in hybrid vehicles are still available and for some manufacturers such as Toyota, were the mainstay for many years. They feature a nickel-based positive electrode, a hydrogen-absorbing negative electrode (usually composed of a metal hydride) and an alkaline electrolyte, such as potassium hydroxide (KOH). NiMH batteries offer good power output, cost-effectiveness and safety, although they have a lower energy density compared to Li-ion batteries.
The chemistry behind these batteries revolves around electrochemical reactions. During charging, Li-ion batteries undergo a process called intercalation, where lithium ions move from the cathode to the anode, embedding themselves within the graphite structure. Discharging reverses this process, allowing the lithium ions to migrate back to the cathode, producing an electric current in the process.
Similarly, NiMH batteries operate based on electrochemical redox reactions. Charging involves the oxidation of the nickel-based positive electrode and the reduction of the hydrogen-absorbing negative electrode, which absorbs and releases hydrogen ions. During discharge, the reverse reactions occur, releasing the stored energy.
Both battery chemistries require sophisticated control systems to ensure safe and efficient operation. Factors such as temperature, voltage limits and charging rates must be carefully regulated to maximize battery performance, longevity and safety.
All electric vehicle batteries store a significant amount of energy. Li-ion batteries can experience thermal runaway — a rapid, uncontrolled increase in temperature that can cause fires with extreme temperatures. Electric vehicle battery fires can reach over 2,000 degrees Celsius — most common metals, including steel, begin to melt at just over 1,200 degrees Celsius, to give some perspective.
While modern battery management systems have improved safety measures, incidents can still occur, especially in high-impact collisions or when the battery is damaged. In addition, the chemicals used in electric vehicle batteries can pose hazards if mishandled or exposed. Li-ion batteries contain flammable electrolytes that can release toxic gases such as fluoride gas.
To mitigate these dangers, manufacturers implement safety features, such as thermal management systems, robust battery enclosures and sophisticated battery management systems. These electronic systems play a crucial role in managing power distribution — “controlling the chemistry” if you will — while also monitoring vehicle performance and controlling drivetrain components.
Manufacturers and regulators provide detailed safe-down instructions. But remember: The damaged vehicle may no longer look like it does in the manual.
But what happens when the vehicle does catch fire?
When encountering an electric vehicle fire, the first step is to prioritize safety. Contact local emergency services immediately, isolate the vehicle, if possible, and provide accurate details about the location and the type of vehicle involved. If possible, evacuate the area to ensure the safety of nearby bystanders.
Training and knowledge are key here. Manufacturers and regulators provide detailed safe-down instructions. But remember: The damaged vehicle may no longer look like it does in the manual. First and secondary responders or anyone handling, maintaining or transporting electric vehicles should undergo specialized training on handling electric vehicles and the potential for fires.
This training should cover the unique properties of electric vehicle batteries and the proper methods for extinguishing such fires.
Several factors are at play. Most electric vehicle fires have thermal runaway potential as well as a flammable liquid electrolyte. Although foam and dry chemical methods are sometimes recommended, the National Fire Protection Agency in the U.S., which guides both American and Canadian approaches, recommends water — and lots of it.
Water can be used to cool the battery and suppress thermal runaway, which, again, is the uncontrolled increase in temperature that leads to advancement of the fire or even explosions. It can take over 30,000 litres of water to cool and extinguish an electric vehicle fire.
Applying water mist or fine water spray is more effective than a direct stream to avoid spreading hazardous chemicals. However, it’s not recommended to use a high-pressure water stream as it might damage the battery casing and escalate the situation.
Li-ion batteries are prone to flare ups especially if moved and can burn for days so how the vehicle is transported or stored afterwards needs to be considered.
Chemical and foam fire suppressants are being developed as well as the use of fireboxes, cement or metal enclosures that would be effective in suppressing, isolating and controlling electric vehicle fires. Infrastructure both on our highways and where charging areas are being installed needs to consider these issues at the planning stages. The use of bunker areas or dedicated charging areas that are isolated and open are important. Our recommendation to fleet operators or sites storing these vehicles or their batteries is to isolate them.
Addressing electric vehicle fires in North America and Europe requires a comprehensive approach that will include well-trained first responders, awareness campaigns, specialized personal protective equipment and the right fire isolation or suppression techniques.
Today, these occurrences are isolated. But as we see more vehicles, especially those in fleet or urban environments where the potential of larger fire catastrophes could occur, more collaborative fire safety protocols for electric vehicle fires should be developed between automotive manufacturers, government regulators and emergency service agencies, including the design of highway and parking areas.
By following these guidelines and fostering collaborative efforts, we can effectively mitigate the risks associated with electric vehicle fires and ensure the safety of communities embracing electric mobility.
Originally trained as a chemist, David Mayers is chief executive officer at Environmental Motorworks, an innovative services company centred on providing hands-on EV and hybrid training to technicians and fleet operators in the automotive and heavy equipment sectors.