Abstract: Abstract: With the continuous development of new energy vehicles in my country, lithium-ion batteries are the most important energy storage devices for new energy electric vehicles. Due to their high energy density, there is rapid combustion, explosion, and thermal runaway transfer of adjacent batteries. The safety hazard restricts the application and promotion on a larger scale and seriously threatens the safety of people's lives and property. The thermal runaway of a battery is mainly related to its shape, state of charge, and connection method. The research on the thermal runaway of batteries under the coupling conditions of different states of charge and different diameters is the focus of research to improve the safety performance of lithium batteries.In order to investigate the main influencing mechanism of the thermal runaway propagation process of lithium-ion batteries, this paper uses ternary lithium-ion batteries with different diameters (10440, 14500, 18650, 21700, 26650, 32650) and different charge states (50%, 70%, 100%) as the research object. The characteristics of thermal runaway propagation time and thermal runaway spatial propagation rate under the one-dimensional linear arrangement are investigated, and then the influence mechanisms of cell diameter and state of charge on thermal runaway propagation time and thermal runaway spatial propagation rate are analyzed in depth. A computational model for blocking the thermal runaway propagation chain of batteries was developed using a combination of experimental data, heat transfer theory, and dimensionless analysis, and then predicted the thermal runaway propagation time between batteries. The characteristic relationship between thermal runaway propagation time and cell diameter (10,14,18,21,26,32 mm) for different charge states (50%,70%,100%) was obtained by combining dimensionless analysis, and a prediction model for thermal runaway propagation time of lithium-ion batteries in the one-dimensional arrangement was proposed. The experimental results show that when the battery state of charge is certain, the larger the battery diameter, the higher the total thermal resistance, which in turn leads to an increase in thermal runaway propagation time and a decrease in the spatial thermal runaway propagation rate. Under the condition of the same total electric power, the higher the charge of the Li-ion battery, the higher the heat production. The influence of cell diameter on the thermal runaway propagation process of the battery mainly depends on the change of thermal resistance in the heat transfer process of the battery, and the thermal resistance formula of the whole lithium-ion battery module is established by using the aggregate model theory, Fourier theory and the interface continuity condition, and the relationship between the charge state of the lithium-ion battery and the heat production of the battery is deduced by the formula. The research results show that when the cell diameter is certain, the total heat production of the thermal runaway process of the cells in the module increases with the increase of the battery state of charge; the thermal runaway propagation rate between the cells will also increase significantly under the high-temperature environment.In this paper, we design a computational model to block the propagation chain during the thermal runaway propagation time of lithium-ion batteries, and then predict the thermal runaway propagation time between batteries. The relationship between the average dimensionless thermal runaway propagation time between single cells and the cell aspect ratio and cell state of charge at 50%, 70%, 100% is fitted with the dimensionless analysis coefficients, and the prediction model of thermal runaway propagation time between adjacent single cells in the module is proposed.

Key words: Key words: lithium-ion battery, thermal runaway propagation time, thermal runaway space propagation rate, battery diameter