# Thermal Failure Propagation in Lithium-Ion Battery Modules with Various Shapes
## 1 Introduction  
As one of the most promising power sources, lithium-ion batteries (LIBs) have been widely used, ranging from consumer electronic devices to electric vehicles due to their excellent properties, such as good stability, high voltage, low self-discharge rate, high energy density, long life cycle, etc. [1; 2]. Nevertheless, hazards also arise from fire or explosion accidents of LIBs, which frequently result from the sensitivities of LIBs to abusive conditions, including high temperature, crushing, overcharge, over-discharge, short-circuit, etc. [3; 4; 5]. Especially in battery modules where quantities of batteries are connected together to provide power, the hazards will be greatly aggravated. Once out of control, the failure of some batteries will propagate to the surrounding ones and lead to rigorous consequences. The battery modules in the several accidents of electrical vehicles (EVs) reported recently all caught fire fire and resulted in serious outcomes. Thence, the safety issues of LIBs, and especially the thermal failure propagation in battery modules and the management of battery modules, cannot be overemphasized. So far, considerable research efforts have been directed toward the thermal behaviors of LIBs under high-temperature conditions [6; 7; 8; 9; 10; 11; 12]. [PERSON] et al. investigated the fire-induced hazards of LIBsby fire calorimetry and analyzed the toxicity of gases generated, including CO, CO\({}_{2}\), SO\({}_{2}\), and HF. It was observed that the production of these gases mainly depended on the battery state of charge (SOC). [PERSON] et al. took six fire abuse tests to evaluate the heat release rate and HF emissions of commercial LIBs. They found that LIBs exposed to a fire were significantly more reactive at 100% SOC than that at lower SOCs, and energetic outbursts were observed during tests. [PERSON] et al. employed a technique, Copper Slug Battery Calorimetry (CSBC), to investigate a widely used LIB at various SOCs. It was shown that the total energy generated inside the battery increased with increasing SOC. Additionally, more work concerned the management of battery modules which can be summarized as several types, such as air, liquid, and phase change material (PCM) based systems [13; 14; 15; 16; 17; 18; 19]. [PERSON] et al. conducted a numerical simulation to analyze the air cooling of a battery module and the results demonstrated that an increase of cooling air flow rate could result in the increase of heat transfer coefficient and pressure drop. [PERSON] et al. designed a minichannel, cold-plate-based battery thermal management system to investigate the effects of number of channels, flow direction, inlet mass flow rate, and ambient temperature on temperature rise and distribution of the battery. They found that the maximum temperature of the battery decreased with increasing number of channels and inlet mass flow rate. Besides that, [PERSON] et al. investigated the thermal performance of PCM-based battery thermal management systems in dynamic cycling, and identified several factors influencing the PCM system. Results showed that the cooling performance of the PCM system was superior to that of the natural convection system, especially at a high current rate, and they recommended the PCM with a phase change temperature of 45 \({}^{\circ}\)C to be used in the real battery pack system. Moreover, many scholars performed experiments or simulations to probe the thermal runaway propagation in LIB modules [20; 21; 22; 23; 24; 25; 26; 27]. [PERSON] et al. established a 3D thermal runaway propagation model for a large-format LIB module based on energy balance equation. They proposed that the thermal runaway propagation could be postponed or prevented by increasing the thermal runaway triggering temperature, reducing the total electric energy released during thermal runaway, enhancing the heat dissipation level by increasing the convection coefficient, and adding an extra thermal regulation layer between adjacent batteries. [PERSON] et al.