One of the solutions for reducing greenhouse gas emissions in the transport sector is the electrification of mobility. The technology currently most widely used by car manufacturers is the Li-ion battery (LiB). Unfortunately, Li-ion batteries can suffer dramatic events with catastrophic consequences known as thermal runaway (TR). TR has many possible causes: excessive temperature, mechanical deformation, electrical overcharge, internal short circuit. Typically, TR causes violent combustion that is difficult or impossible to control, with the emission of potentially toxic gases and particles. TR is a major problem for manufacturers and can have serious consequences for users. Understanding TR is a key safety issue.
This paper presents a new methodology to characterize the thermal runaway of Li-ion battery cells, combining gas analysis, thermodynamic measurements and high-speed imaging. The protocol was applied to characterize two commercial battery cell types with different positive electrode chemistries (NCA and NMC). For each battery cell type, the measurements were performed at different states of charge (SOC).
The protocol used allowed the identification of several parameters characterizing the TR event, such as the temperature at which Venting and TR occur or the pressure peak following the TR event. The analysis of the high-speed movies also provided insights into the combustion initiation and its evolution.
As expected, the results showed that the thermal runaway for both chemistries is significantly influenced by the SOC. These parameters provided a coherent and robust description of the event, while also providing valuable data for the validation of numerical models.