Gas detector flags early battery failure

A gas sensor that can provide an early warning of battery failure could improve the safety of lithium-ion batteries, used in everything from electric vehicles to grid-scale storage systems.

Lithium-ion batteries are transforming the global energy landscape, but they also come with risks. If a battery is damaged or overheated, it can trigger an unstoppable “thermal runaway” reaction that releases flammable and toxic gases and leads to catastrophic battery failure.

KAUST researchers have developed a sensor designed to detect those gases at a very early stage before conditions escalate^[1]. “Our ultimate goal is to demonstrate a closed-loop early warning and response system that could serve as the basis for a practical safety architecture in battery packs,” says Aamir Farooq, who led the team.

When a battery gets too hot, the chemicals inside start to break down and release gases. As pressure builds, a safety valve ruptures to vent them.

This breakdown also generates heat, potentially causing a chain reaction that accelerates gas formation and can ultimately cause the battery to catch fire or explode.

Among the most hazardous gases released during battery failure is hydrogen fluoride (HF), a highly toxic and corrosive compound. Previous studies have shown that HF can be detected during safety venting, before the thermal runaway process takes hold. However, conventional methods for measuring HF rely on bulky equipment and tend to underestimate emissions.

The KAUST team developed a more compact gas-sensing technique called tunable diode laser absorption spectroscopy (TDLAS). Positioned directly above the safety vent, the system provides a much more accurate HF reading.

The researchers tested the TDLAS sensor on two types of lithium-ion batteries, commonly found in laptops and electric vehicles. One type uses a cathode containing nickel, manganese and cobalt (NMC), while the other has a lithium iron phosphate (LFP) cathode. These batteries, charged to either 50 percent or 100 percent of their capacity, were heated to trigger thermal runaway.

The NMC batteries reached thermal runaway at 174–215 °C, while LFP cells were more stable, doing so at 242–249 degrees Celsius. Both types released a small burst of HF during initial safety venting, followed by a much larger burst once thermal runaway had started. “These concentrations of HF are orders of magnitude above the level that is immediately dangerous to life and health,” says Ahmad Alsewailem, a Ph.D. student in the team who led the experimental work.

Crucially, the time between the early and later bursts was about one minute for NMC cells and five minutes for LFP cells. That would be long enough for a miniaturized TDLAS sensor to act as an early warning system in electric vehicle battery packs or grid-scale energy storage systems.

“A single sensor positioned within a battery pack enclosure could monitor the gas environment continuously and trigger an alarm or automatic shutdown the moment HF is detected above a threshold level,” says Janardhanraj Subburaj, a research scientist in the team. “This is faster than other thermal runaway sensors, giving a warning window before the more violent thermal runaway phase.”

The researchers now plan to study how overcharging and mechanical damage can cause similar gas releases, and hope to couple their HF sensor with an automated battery safety system.