Measuring temperatures of exploding batteries
As electric vehicles become widespread, the demand for lithium-ion batteries is forecast to expand exponentially over the next three years. To prevent accidents, batteries are equipped with safety mechanism. However, fire and explosions have been known to be caused by batteries.
Researchers in Malaysia are studying the conditions in which batteries fail and cause thermal runaway - an uncontrollable increase in temperature.
They subjected batteries to a variety of electrical, themal and mechanical conditions and compared the characteristics of thermal runaway.
For measuring temperatures, the engineers used type-K Inconel sheathed thermocouples to measure temperatures inside an oven. The data was recorded at a frequency of 1 Hz with a resolution of 0.001 0C by using Microlink 751 data logging interface and Windmill data acquisition software.
They placed a battery inside two ceramic pots. They then enclosed the pots in a stainless steel holder. This was to prevent damage to the oven.
Inside the pots they connected three thermocouples which would measure the temperatures around the battery. Two further thermocouples measured the temperature of the oven air and of the base of the steel holder.
The Windmill system continually logged temperatures as the oven heated to 190 oC, a sufficiently high temperature to start thermal runaway. The oven then switched off but data logging continued until thermal runaway reactions ceased and temperatures stabilised.
The oven air reached the preset temperature of 190 oC after 53 minutes and subsequently increased to, and remained a,t 195 oC thereafter. The rise of battery temperature inside the ceramic pot reached 182 oC after 127 min. This situation was subsequently followed by a violent thermal runaway, causing battery temperature inside the ceramic pots to spike to 738 0C.
When the researchers later investigated the batteries, they found evidence of a violent explosion of battery contents.
Thermal runaway hazard of lithium-ion batteries stems from a combination of highly reactive electrodes and flammable organic electrolytes. It doesn't necessarily need high temperatures to occur but can also be triggered by, for example, charging and discharging beyond the specified limit or physical impact inducing an internal short-circuit.
Further Reading
Microlink 751: Multi-Function USB Unit: Voltage, Temperature, Strain, pH, Current, Counting, Control, etc
https://www.microlink.co.uk/751.html
Mohamad Syazarudin Md Said, Mohd Zahirasri Mohd Tohir, Characterisation of thermal runaway behaviour of cylindrical lithium-ion battery using Accelerating Rate Calorimeter and oven heating, Case Studies in Thermal Engineering, Volume 28, 2021, 101474, https://doi.org/10.1016/j.csite.2021.101474
