Thermocouple selection and its influence on temperature monitoring of lithium-ion cells

Accurate battery modelling requires precise measurements of key battery characteristics, including their surface temperature during fast charging and discharging states. Battery surface temperature measurements are also used to mitigate thermal events such as thermal runaway, which can cause fires. Established literature has shown that there are significant variations in temperature measurements of the surface of lithium-ion cells between various thermocouple sensors, including common K and T-Type thermocouples. In this paper, these variations in temperature measurements are investigated for the first time in the context of battery characterisation. The surface temperatures of two lithium-ion cells, a 21700-model Lithium Nickel Cobalt Aluminium Oxide (NCA) cylindrical cell and a Lithium Titanate Oxide (LTO) pouch cell, are measured during high current cycling using a variety of different thermocouples and an infrared camera to study the variations and response times in the temperature measurements recorded. The impact of electromagnetic fields emitted by the lithium-ion cells on the temperature measurements is also investigated. Results reported indicate a trend in the size of the temperature sensor with the response time of the cell surface temperature measurements. The recommendations of temperature sensors based on these findings allow for improved response time and accuracy of cell surface temperature measurements.