Design guidelines to prevent thermal propagation and maximize packing density within battery systems with tabless cylindrical lithium-ion cells

Abstract

Large-format tabless cylindrical lithium-ion cells are a promising candidate to not only enhance performance and reduce cost of next generation vehicles but also increase safety compared to other cell formats. In this study, numerical models are developed and validated based on sophisticated mass-produced large-format tabless cylindrical cells that allow analyzing the thermal propagation resilience. Experiments are conducted to prove cylindrical cells may locally drastically exceed common trigger temperatures obtained from accelerating rate calorimetry. A thermal propagation risk map is introduced that establishes an understanding on the influence of the convective and conductive heat paths on different timescales. The influence of varying dimensions and housing materials is revealed and the minimal cell-to-cell spacing is determined that maximizes packing density while still obeying strict no-thermal propagation philosophy. Results show great emphasize must be put on design measures to prevent hot venting gas to introduce heat into the neighboring cells through convection. Afterwards, the cells mass loss and spacing should be optimized to counter the leftover conductive heat path and optimize packing density. The larger the diameter, the further the cells need to be positioned apart. Cells with aluminum housing require less spacing and enable tighter packing density compared to regular deep-drawn steel housings due to the ability to dissipate heat in circumferential and axial direction away from the critical area with highest active material temperatures.