How worried should we really be?

Electric vehicles (EVs) bring not only environmental promises, but also raise critical safety questions – chief among them, the fire risks presented by their lithium-ion batteries. Although indispensable for powering electric vehicles, these batteries present unique challenges, particularly in confined spaces such as parking lots, where the potential for fire has significant consequences.

At the heart of this risk is the lithium-ion (LiB) battery, a powerful energy storage device with considerable vulnerabilities. Some of the components of these batteries feature a risk of firebut the part known as the cathode is critical in this regard. These are usually made from either nickel manganese cobalt oxide (NMC) or lithium iron phosphate (LFP). NMC is more cost-effective, but also more prone to thermal runawaya dangerous reaction that causes sudden fires in LiB batteries.

Thermal runaway is a self-accelerating reaction that leads to a rapid rise in temperature. It is often caused by overloading, overheating, damage or defects and, once initiated, can cause uncontrollable fires that are difficult to extinguish.

The risk of thermal runaway is mitigated by built-in battery management systems (BMS) that include real time monitoring, automatic shutdown functions and compartmentalized fire isolation modules. However, as the range and performance of electric vehicles improve, their batteries become larger, making fire safety a serious challenge, especially in indoor environments.

Types of EV batteries

To better understand the global electric vehicle market, we analyzed 100 electric vehicles from Europe, Asia and the Americas, covering various makes and models. The data provided information on vehicle dimensions, battery types, sizes and positions.

The findings showed that about 90% of these vehicles use NMC batteries. Although preferred by manufacturers for lower production costs, these batteries are more prone to thermal runaway, making them a major safety concern.

The ratio of battery weight to a battery’s efficiency is an important consideration for EV manufacturers, often dictating what type of battery is used. However, our comparison of NMC and LFP batteries revealed unexpected results. NMC batteries, at 6.74 kg per kWh, are only slightly heavier than LFP batteries at 6.51 kg per kWh.

This minor difference calls into question the supposed weight/energy advantage of NMC batteries, especially given their increased fire risk.

Fire behavior of NMC and LFP batteries

Our research also looked at the fire behavior of NMC and LFP batteries, the two most common types of EV batteries.

We analyzed data from 24 studies, examining experiments that fired lithium-ion cells to measure the Heat Release Rate (HRR) over time—essentially a measurement of how fast they burn. Although insightful, these assays reflect single-cell behavior. Fires in full EV batteries, which contain thousands of cells, are much more complex, involving chain reactions and additional energy release from the vehicle itself.

Our analysis, however, revealed notable differences in fire behavior between NMC and LFP batteries as capacity increases. At lower capacities, NMC batteries show relatively low maximum HRR, but this increases dramatically at higher capacities, exceeding 100 kW, as the graph below demonstrates.

In contrast, LFP batteries show more stable HRR, increasing gradually without reaching the extreme levels of NMC. This suggests that NMC batteries present higher fire risks at higher capacities, emphasizing the need to consider battery type and capacity when evaluating EV safety, especially for larger packs.

Battery charging and fire hazard

Beyond battery type and capacity, the study also explored whether the level of charge in a battery – known as the state of charge (SoC) – influences the power released during a fire. The data was divided into five segments – load levels of 0%, 25%, 50%, 75% and 100% – and a new measurement, kW per Ah, was introduced to account for the rate of heat release ( HRR) as a function of battery capacity.

The results were clear: from 0% to 75% charge, the fire intensity remained stable, but at full charge, the fire power increased to 31 kW/Ah for the LFP batteries and 38 kW/Ah for the NMC batteries. This increase aligns with real-world incidents, as many fires occur during vehicle loading.

This underlines the importance of effective fire prevention systems at charging stations in car parks, especially underground ones, to mitigate the risks associated with charging electric vehicles, especially those with high-capacity NMC batteries.

So is it safe to own an electric vehicle?

The answer is yes, but only if it is safe safety measures are followed. Systemic measures such as advanced fire suppression systems in public spaces are critical, but individual EV owners also play a vital role in reducing the risks. Owning an electric vehicle with a home charging setup offers great convenience, but it’s critical to address the potential dangers.

Following the manufacturer’s instructions, performing regular battery health checks and equipping the garage with fire protection tools such as electric extinguishers and fire blankets can significantly improve safety. By taking these proactive steps, we can embrace the future of cleaner transportation with confidence and peace of mind.

This article is republished from conversation under a Creative Commons license. Read on original article.