Three-Dimensional Model of a cylindrical Lithium-Ion Cell – Influence of Cell Design on State Imbalances and Fast-Charging Capability

To find the best trade-off among fast-charging capability, lifespan and energy density, three-dimensional electrical and thermal models of lithium-ion cells are essential tools. The cell design, like the porosity and thickness of the electrodes, tab number, alignment and design as well as the cell geometry and format are important parameters to achieve said optimum. In this article a three-dimensional electrical and thermal model based on a half-cell Equivalent Circuit Model (ECM) of a cylindrical lithium-ion cell is presented. The model parametrization is based on a high-energy 18650 cell (NMC-811/SiC). For validation, measurements of a lithium-ion cell with an integrated temperature sensor are conducted. This allows to measure the core and surface temperature of the cell. The model shows a sufficient agreement to experimental data. Based on the model the influence of tab design and the cell format on state imbalances within the cell and the fast-charging capability are investigated. Increasing the number of tabs especially using the so called tabless design lead to a reduction of state imbalances and charging time while not increasing the potential of Li-plating or thermal hot-spots. These positive effects of tab design became more significant with increasing cell format.