As electric vehicles (EVs) are rapidly adopted worldwide, large numbers are now transported by sea on dedicated car carriers. With this trend, concerns are increasing about fires and explosions caused by battery thermal runaway during marine transport, while existing SOC limits before loading remain largely empirical. This study experimentally investigates gas generation and explosion characteristics of EV lithium-ion cells under thermal runaway conditions representative of enclosed vehicle decks. We identify and quantify the main off-gas components and clarify the flammability behavior and explosion limits of key combustible species. The results provide basic data for assessing EV battery accidents at sea and support the development of safer ventilation and gas-management strategies for ships.

Lithium-ion batteries (LIBs) have become a main energy storage device in various applications, such as portable appliances, renewable energy facilities, and electric vehicles. However, the poor thermal stability of LIBs may cause explosion or fire. The thermal runaway is the result of a failure of the separator inside LIB. Damages like tearing, piercing, and collapsing of the separator were simulated in a mechanical, an electrical, and a thermal way, and small discharge pulses of a few mV were detected at the time of separator damages. From the experimental results, this paper provided a method that can identify the separator failure before thermal runaway in the aspect of a potential explosion and fire prevention measures.

Thermal batteries use inorganic salt as electrolyte, which is inactive at room temperature. As soon as heat pellets are fired by an igniter, all the solid electrolytes are instantly melted into excellent ionic conductors. However, the abnormal heat generation by the igniter flame or heat pellets causes the thermal decomposition of the electrode and the melting of the anode, eventually leading to a thermal runaway, which results in overheating or explosion. The thermal runaway can be significantly reduced by the adoption of Zr/BaCrO4 heat papers. In this study, the heat papers with various ratios of fuel (Zr) and oxidizer (BaCrO4) were prepared by the paper-making process. We have investigated the calorimetric value, burning rate, and ignition sensitivity. The ignition test of heat pellets and the discharge test of thermal batteries were also carried out. At the composition of 40 wt.% of Zr, the heat papers showed the highest specific calorimetric value and burning rate. As a result, Zr/BaCrO4 heat paper made by the paper-making process has shown the applicability for thermal batteries.

Thermal batteries are primary power sources for military applications requiring high reliability, robustness and long storage life. Conventional electrodes for thermal batteries are prepared by compacting powder mixtures into pellets. Separator is composed of halide mixture, such as LiCl-KC1 eutectic salt, blended with MgO to immobilize the molten salt. In order to increase the power density and energy density, the resistance of electrolyte should be reduced because the resistance of electrolyte is predominant in thermal batteries. In this study, wetting behaviors and impregnation weight of molten salts as well as the micro structures of ceramic felt were investigated to be applicable to thin electrolyte. Discharge performances of single cell with the ceramic separator impregnated by molten salt were evaluated also. Zirconia felt with high porosity and large pore outperformed alumina felt in wetting characteristics and molten salt impregnation as well as discharge performances. Based on the results of this study, ceramic felt separator impregnated with molten salt have revealed as an alternative of conventional thick MgO based separator with no conspicuous sign of thermal runaway by short circuit.

Citations

• RETRACTED: Optimization of thermal battery electrolytes: Ionic diffusion, conductivity enhancement, and structural effects in lithium salt systems for military-grade thermal batteries
  Lifeng Zheng, Xing Li
  Case Studies in Thermal Engineering.2026; 83: 108191.     CrossRef

Thermal batteries are primary reserve batteries that use inorganic salt as electrolytes which areinactive at room temperature. The two principal heat sources that have been used in thermal batteries areheat paper and heat pellets. As soon as the heat paper, which is ignited by the initiator, in turn ignites theheat pellets, all the solid electrolytes are melted into excellent ionic conductors. However, the highcombustion temperature by heat papers in thermal batteries causes thermal decomposition at the cathode,eventually leading to a thermal runaway. In this paper, we have attempted to prepare Zr/BaCrO4 heatpapers coated with KCl molten salt. We have also investigated the effect of a molten salt coating on theheat papers through the thermal characteristics such as calorimetric value, combustion temperature andburning rate. The calorimetric value and combustion temperature of heat papers were reduced with anincrease in the molten salt coating. As a result, the molten salt coating on heat papers greatly reducedrisk of a thermal runaway and improved the stability of thermal batteries.