Simulated thermal response of a battery pack used by electric two-wheelers

This article presents a theoretical investigation into the thermal behavior of a pack of 18650 lithium-ion commercial batteries used for the propulsion of two-wheeled electric vehicles. In the first part, we highlight the theoretical aspects that describe the energy balance of a cylindrical lithium-ion battery based on the law of conservation of energy. The research aims to emphasize the effect of temperature on the technical performance of batteries. Next, using the COMSOL Multiphysics 6.2 software package, "Heat transfer in Solids and Fluids", the thermal behavior was modeled for a single cylindrical battery cell, type 18650 lithium-ion, 3.7V, 2200mAh, respectively a battery pack with the same type of cells, 18650 lithium-ion. The battery pack was made in the structure of 3 cells in series and 7 cells in parallel - 3S7P. The distribution of the temperature generated inside the battery cell, respectively in the structure of the 3S7P battery pack, was taken into account, at a charge/discharge rate considered extreme of 5.5C. In order to ensure a quality mesh in the process of simulating the geometry of the 3S7P battery pack, a mesh convergence study was also considered through progressively finer runs until the temperature of the battery pack did not change significantly with the subsequent refinement of the mesh. Simulations of thermal behavior were conducted while accounting for thermal conductivity, density, heat capacity, and heat source in the batteries. The battery pack was thermally loaded to measure temperatures inside the protective case, starting from an initial ambient temperature. The results obtained demonstrate several characteristics that can enhance the technical performance of battery packs used in electric two-wheeled vehicles.