Due to the constant increase in energy density of lithium-ion batteries (LIBs), safety concerns in case of a thermal runaway event become more critical. Thermal runaway propagation (TP) can destroy an entire LIB pack, rapidly releasing energy and material through heat and fire. A solution for TP that minimally affects the LIB pack remains one of the main unsolved safety-related issues in battery systems. This paper presents an eco-friendly thermal barrier made of a high water-content hydrogel derived from natural polymers reinforced by a flame-retardant fiber material. The 2-mm-thick barrier, when placed between 50 Ah LIB cells, was able to prevent thermal propagation in 2-cell modules. Once the barrier temperature reaches around 100 degrees C, it can absorb a large amount of energy due to water vaporization. Afterward, the remaining low thermally conductive fiber material provides thermal insulation between cells. In addition, the mechanical properties of the barrier, such as compressive strength and flexibility, make it a suitable material to be placed between LIB cells. Furthermore, its ease of manufacturing and biodegradability enable the barrier to provide higher safety for LIB packs while maintaining the cost and environmental impact to a minimum.

The battery industry is driven by the need for an increased energy and power density in lithium-ion cells. Therefore, safety aspects are becoming increasingly important. Unfortunately, failure due to quality defects on cell level can neither be reliably predicted nor inhibited by the battery management system (BMS) forcing system manufacturers to implement safety measures in hardware on module level. In this paper, we investigate a novel thermal barrier placed between the individual cells to prevent thermal propagation (TP) in lithium-ion battery packs. A single cell failure may cause different exothermic reactions leading to an uncontrolled release of heat that can trigger subsequent reactions causing a thermal runaway (TR). In this case, the thermal barrier is able to protect neighbouring cells from overheating. Different test setups are used to characterize the functionality of the thermal barrier. Further experiments evaluate the influence of the energy distribution along different heat paths, for example via cell connectors, lateral contact areas and the cooling plate. The results illustrate the successful avoidance of propagation and the influence of the barrier thickness on the temperature behaviour but also show that the size of the setup (multi-cell vs. two-cell) used for propagation testing significantly influences the temperature behaviour.