Battery internal temperature estimation using electrochemical impedance
The ability to estimate battery temperature is necessary for battery management systems to accurately predict parameters such as state of charge (SOC) and state of health (SOH), and to mitigate problems such as high temperatures triggering thermal runaway and battery fires. While incidents such as battery fires are rare, occurring in anywhere from one in 1 million to one in 10 million batteries according to the best estimates, their consequences include costly recalls of millions of batteries and potential endangerment of human life. For instance, in January of this year, Boeing was forced to ground its entire fleet of 787 Dreamliner’s after multiple incidents of batteries overheating and catching fire. The fleet groundings cost the company an estimated £393m. One of the problems with monitoring battery temperature to prevent problems such as thermal runaway is that, when used in demanding applications (such as automotive and aerospace applications), the inside of a battery can reach over 20°C higher than the surface temperature. This makes it difficult to monitor the true internal temperature of the battery. For instance, conventional temperature sensors can only measure surface temperature, and while efforts are undergoing to develop micro sensors for internal temperature measurement, implementing these in large battery packs containing hundreds or thousands of cells would incur a significant cost penalty. My work has involved developing new approaches to estimate internal temperatures, based on combining cell impedance measurements with surface temperature measurements. Eventually, these sensors may be capable of monitoring the internal state of multiple cells in a pack with high accuracy and minimum additional cost.
Check out the short film below to get an insight into battery thermal management and internal temperature estimation.