Effect of different cooling configurations on thermal gradients inside cylindrical battery cells

摘要

Lithium-ion cells show highly anisotropic thermal properties due to the different layers of the electrodes. This leads to high thermal gradients and a nonuniform temperature distribution inside the cell which affects the local current densities as well as the local charge carrier distribution. These inhomogeneities lead to reduced performance, local aging differences inside the cell and an accelerated global cell aging process. This work investigates the effect of a terminal and a surface cooling configuration on the thermal gradients inside a cylindrical 26650 LiFePO4/graphite cell. Three integrated NTC thermistors measure the core temperature at different locations and enable the determination of the thermal gradients during the operation. Alternating current pulses heat up the cell without varying the average state of charge and therefore enable the operation in the thermal steady state for different investigated cooling capacities. The calculation of the generated heat flow and the cooling capacity allows the comparison of the thermal gradients between both cooling configurations. The terminal cooling configuration reduces the radial temperature gradients inside the cell compared to the surface cooling configuration without strongly increasing the axial temperature gradients. Even for increasing cooling capacities the radial thermal gradients show no increase.