Thermal runaway is one of the biggest safety risks for lithium-ion batteries in electric vehicles. As is often the case, the best strategy is to prevent it from occurring in the first place. But what if it does happen? Flame retardants are supposed to delay the fire. But are they even useful? This question is posed by a recent paper.phonlamaiphoto @ AdobeStock
Do flame retardants in car batteries really protect against fires - or do they cause more harm than they prevent? A publication questions their effectiveness and even sees risks. We asked a manufacturer.
Diagram comparing the potential advantages and disadvantages of flame retardants in battery housings: While they could improve fire safety, they cause environmental damage and hinder the circular economy.https://pubs.acs.org/doi/10.1021/acs.est.4c10630
Why are fire protection measures needed for lithium-ion batteries at all?
Battery fires are particularly dangerous because they occur through a so-called thermal runaway. In this process, a damaged cell heats up uncontrollably and transfers heat to neighbouring cells until a chain reaction is triggered. These fires are difficult to extinguish and can release toxic gases. Electric vehicles are particularly affected, as their batteries contain large amounts of stored energy.
The paper now describes that flame retardants in plastic housings of lithium-ion batteries often do not have the desired protective effect: “Trying to stop thermal runaway fires by adding flame retardants to plastic is like adding a screen door to a submarine.”(Vyto Babrauskas, Ignition Handbook)
The paper argues that flame retardants in battery housings can withstand an open flame for a short time, but have little influence on the actual thermal runaway. Once this process starts, temperatures and reactions occur that the chemical flame retardant can no longer stop. Additionally, the authors raise the question of whether the existing standard tests used to evaluate flame retardants realistically reflect fire scenarios at all.
Lanxess says: “Flame retardants do not help with a thermal runaway of an e-car battery. That is not their task. In the event of an electrode short circuit in the battery cells - triggered, for example, by an accident or a stone impact - a chain reaction starts, causing extremely high temperatures in the battery. A major fire scenario develops within a very short time. Then flame retardants can no longer do anything.
Flame retardants are intended and able to prevent an incipient fire or - if a fire has already started - delay its spread. For example, flame-retardant cable sheaths prevent cables from igniting due to overheating or short circuits for a certain period of time. The same applies to plastic housings. They should not catch fire when in contact with a glowing cable or external heat exposure. Flame retardants can thus help to minimise the risk of thermal runaway by keeping the risk of external fire impact as low as possible."
Health and environmental hazards: How serious are they really?
Furthermore, the authors emphasise that many flame retardants, especially organohalogens and organophosphates, pose significant risks to humans and the environment. They can:
cause neurological, reproductive, and immunological damage,
accumulate in the environment and be difficult to degrade,
deteriorate the mechanical properties of plastics and make recycling more difficult.
The paper states: "The production of chemical flame retardants and their incorporation into electronic devices and other products often results in occupational exposure."
Alternative Solutions
Instead of relying on flame retardants, the authors propose other measures:
Better quality control in production to minimise defects
More stable metal casings instead of plastic
Intelligent battery management systems that detect critical conditions early
Development of safer battery technologies, e.g., solid-state batteries
These alternatives sound sensible, but it remains unclear whether they are economically feasible in practice. For example, metal casings can increase the weight and cost of batteries. Moreover, while solid-state batteries are promising, they are not yet market-ready. What realistic alternatives are available in the short term remains open.
When asked, "What are your future plans in the area of flame protection for batteries for electric cars? For example, regarding substances that release fewer or no harmful gases," Lanxess responds: "We offer an extensive portfolio of flame retardants for use in polymers in electric vehicles, e.g., in battery housings, cables, and high-voltage connectors. In particular, the trend towards lightweight leads to a higher use of polymers compared to other (heavier) materials."
