Early warning methods for the detection of thermal runaway in Lithium-ion batteries: An application-oriented look at the state of the art

Lithium-ion batteries are a key energy-storage technology for electromobility due to their high specific and volumetric energy densities. As electric vehicles are required to meet stringent performance and safety standards comparable to those of combustion engine systems, the early detection of safety-critical failure mechanisms in battery cells is becoming increasingly important. When lithium-ion cells are operated outside their designated safe operating window due to electrical, thermal, mechanical or chemical stress, various degradation processes can be triggered, potentially leading to thermal runaway. To mitigate these risks, in-situ monitoring techniques capable of identifying early indicators of abnormal cell behavior are of particular interest. This review paper presents a comprehensive and application-oriented overview of current early warning methods for thermal runaway detection in lithium-ion batteries. The focus is placed on sensor-based approaches at the single-cell level, structured according to electrical, thermal, chemical and mechanical detection principles. The reviewed approaches are systematically evaluated with respect to their applicability in automotive battery systems, considering criteria such as thermal runaway detectability, integration feasibility, robustness, energy efficiency and cost efficiency. The aim of this work is to identify promising sensing strategies that can improve battery safety by enabling the early detection of hazardous operating states.