Non-invasive measurement of internal temperature of a cylindrical Li-ion cell during high-rate discharge

Li-ion cells are a technologically important class of devices for electrochemical energy storage and conversion. Overheating of a Li-ion cell during operation is undesirable as it directly affects performance and safety. Although a number of methods have been used for temperature measurement in Li-ion cells, there is a lack of non-invasive techniques to determine the peak temperature at the core of the cell. Measuring only the outside surface temperature, while straightforward, is not sufficient since the core temperature may be much higher. This paper presents non-invasive measurement of the core temperature of a Li-ion cell using a recently developed technique that utilizes space and time integrals of the measured temperature field at the outside surface. The surface temperature field of an operating Li-ion cell is measured using infrared thermography at multiple discharge rates up to 10C, using which, the core temperature is predicted as a function of time. In each case, there is excellent agreement throughout the discharge period between the predicted core temperature and measurements from a thermocouple embedded at the core of the cell. These measurements quantify the temperature gradient within the cell, which is particularly high at large discharge rates. The non-invasive core measurement methods described here may contribute towards performance optimization and improved safety of Li-ion cells.