Thermal analysis of a LTO cylindrical battery cell in natural convection: Numerical approach and experimental validation

Lithium-ion (Li-ion) batteries dominate the EVs field due to unique features like high power and energy density, excellent storage capabilities and memory-free recharge characteristics. Despite that, assorted phenomena affect the reliability of battery packs at high temperatures, causing efficiency loss, danger of explosions and rapid degradation. Consequently, it is necessary to understand the thermal behaviour of Li-ion batteries under specific discharge and charge conditions for operating in critical hot spots, dissipating the generated heat and decreasing the average temperature and internal temperature spans. This paper contributes to developing a thermal model for Li-ion batteries subjected to any discharge and charge current profile, estimating the generated heat, the dissipated heat in natural convection, the average temperature and the maximum internal temperature span. These results have been obtained by coupling the widely known Equivalent Circuit Model (ECM) with the Bernardi et al. equation, which permits estimating the heat generated by any battery cell, knowing the voltage drops caused by ohmic and polarisation losses. The results were validated through two tests conducted on a 1500 mAh LTO cell, whose ECM was obtained through an experimental characterisation by following the HPPC procedures. As a result, the model reached percentage errors below ± 7%. This approach defines a necessary initial step to characterise the maximum average temperature reachable by the Li-ion cell, verifying if this value overcomes the acceptable working limit.