Experimental study on thermal runaway propagation of lithium-ion battery modules with different parallel-series hybrid connections

Thermal runaway (TR) propagation significantly affects the safety of lithium-ion battery systems. In this study, the TR propagation behaviours in modules with different electrical connections were investigated. In detail, three different kind of modules were studied: 12 cells having no electrical connections, four cells in parallel and three in series, as well as three cells in parallel and four in series. Considering the maximum temperature and propagation time, the parallel-series connection types of the battery module appeared to have no significant influence on the TR propagation behaviour. An equivalent circuit model was built to calculate the transfer of electricity from the adjacent cells to the runaway cell. According to calculations, the transferred electricity led to a temperature increase of approximately 28.2 °C in the most severe condition. By integrating thermocouples inside the cells, the internal temperatures of the cells in the modules during TR propagation were measured and compared. The internal temperature was 160 °C higher (on average) than that on the cell surface. The significance of the temperature differences requires attention for the further modelling of TR propagation.