Estimation of the Internal Temperature of High-Capacity Li-Ion Cells Using Embedded Impedancemetry

The internal temperature of electrochemical accumulators is a crucial parameter that significantly impacts their aging and safety. In particular, the phenomenon of thermal runaway must be detected early due to its rapid progression and potentially catastrophic consequences. However, measuring the temperature of each cell within a battery pack is costly and typically only provides access to the external temperature of the elements. Moreover, as cell size increases, their thermal capacity also rises, leading to a significant time lag between the internal temperature and the surface temperature. Electrochemical Impedance Spectroscopy is a precise method for assessing electrochemical parameters and phenomena, which are closely correlated with the internal temperature of batteries; therefore, temperature estimation can be achieved using impedance measurements. This article presents an innovative, low-cost approach using an embedded version of the impedance spectroscopy technique to estimate the internal temperature of high-capacity 175 Ah Li-ion cells, which exhibit very low impedances (less than 1 m$\Omega$ on average). Experimental results demonstrate that embedded impedancemetry enables internal temperature estimation of individual cells in a battery pack with an RMSE of 1.5 $^{\circ }$ C.