Estimation of the representative temperatures of a typical electrochemical battery cell when cooling under natural convection conditions

Abstract

Commercial thermal management systems for electrochemical batteries use information from temperature sensors on the battery surface as the main process characteristic. The main problem of batteries lies in the intense heat energy dissipation in the closed internal volume due to chemical reactions at cyclic charge and discharge. In addition, increasing in the energy intensity of modern batteries, charge and discharge rates, as well as cases of fires and explosions of the battery energy storage systems (ESS) indicate the need to analyze the thermal state of internal electrode battery structures. A multi-layered battery structure and low thermal conductivity of some materials requires ensuring minimum temperature variations between individual battery layers and the battery housing surface, as well as between the battery cells. Currently known instrumental methods for measuring battery cell temperatures do not provide reliable estimates of cell electrolyte, anode and cathode temperatures. The article presents the results of a theoretical analysis of representative temperatures of a typical cell of a fairly common lead-acid battery in typical operating conditions. The results were obtained using the electrothermal model and the solution of the system of non-stationary equations of heat conductivity in the two-dimensional formulation with the finite difference method. Typical operating conditions (ambient temperature of 20 °C, convective heat transfer coefficient 5 of W/(m2K), charge time of 8 h) were considered. The maximum cell temperature was 36 °C, the average temperature was 31 °C, and the case temperature was 26 °C. It has been concluded that it is impossible to predict real thermal condition of the battery without analysis of temperature differences by its cross-sections. Moreover, the temperature of the external surface of the battery housing cannot be used as a key characteristic of battery life analysis.