We have all seen the attention-grabbing headlines when on the exceedingly rare occasion the Li-ion battery in an electric vehicle (EV) has caught fire. Next to range anxiety and long recharge times, the fear of a battery fire is among the key reasons for consumers being reluctant to switch over to an EV. So ever more advanced battery condition monitoring is needed to reduce if not eliminate this fear, regardless of whether it is from a damaged battery or the increased stress on battery cells as fast-charging technology improves.

The growth in electric cars sales continues to increase as more and more drivers make the switch to green mobility. And despite meeting all the strict automotive regulations,  Li-ion batteries do pose a potential fire risk, especially if damaged or under high stress when being quickly recharged. That is why battery conditioning monitoring plays such a crucial role in terms of vehicle safety and giving advance warning to drivers and passengers.

In fact, the United Nations in their Global Technical Regulation on the Electric Vehicle Safety (EVS) state the following. A “vehicle shall provide an advance warning indication to allow egress or 5 minutes prior to the presence of a hazardous situation inside the passenger compartment caused by thermal propagation which is triggered by an internal short circuit leading to a single cell thermal runaway such as fire, explosion or smoke.”

Thermal runaway, propagation and fire
Thermal runaway occurs when there is a rapid and uncontrolled increase in temperature within a battery cell. This can result in a self-accelerating reaction that generates more heat until the cell fails or even undergoes a violent failure, such as an explosion or fire. It can also result in the transfer of heat to neighboring cells, resulting in chain reaction with multiple cells within the battery pack undergoing thermal runaway and release heat, gases, or even flames.

That is why preventing and mitigating both thermal runaway and thermal propagation in Li-ion batteries is crucial for battery safety. Systems with effective thermal management and safety mechanisms are vital to reducing the risk, containing any temperature increases to avoid thermal runaway and giving adequate warning if the battery is going to explosively fail. At the heart of these systems are an array of sensor technologies including those for temperature and voltage monitoring.

Gas sensors spot the warning signs
While temperature and voltage sensing are great for monitoring the condition of the battery cells, unfortunately they tend to only indicate a measurable increase once the battery cell has entered thermal runaway. To achieve the UN’s 5-minute warning, battery condition monitoring systems need to be able to better anticipate potential thermal runaway.

Fortunately, due to the chemistries involved, thermal runaway often involves the release of flammable gases including hydrogen, carbon monoxide and organic solvents. All of which are easily measured by accurate automotive-proven broadband metal oxide (MOX) sensor technology. In fact, during testing by independent institutes, ScioSense’s dedicated Battery Condition Monitor for Li-ion batteries (BCM1) was able to react to outgassing from the cell up to 40 seconds before the temperature and voltage sensors indicated thermal runaway.