Experimental Investigation of Nail Penetration-Induced Thermal Runaway and Particulate Emissions in NMC Lithium-Ion Batteries

Abstract

Lithium-ion batteries (LIBs) have become a prominent energy storage technology for electric vehicles (EVs), consumer electronics, and stationary energy storage systems due to their high energy density and long cycle life. The growing demand for clean transportation and energy storage has accelerated their widespread adoption. However, this rapid growth has also heightened concerns regarding thermal runaway (TR), a hazardous failure phenomenon in LIBs capable of producing fires, explosions, and the release of toxic gaseous and particulate emissions. Among the abuse tests used to investigate LIB safety, nail penetration (NP) testing is widely employed to simulate mechanically induced internal short circuits (ISCs) within the cell. Despite extensive research, the influence of operating conditions on NP-induced TR behaviour and the characteristics of particulate emissions generated during failure remain insufficiently understood.

This thesis experimentally investigates the influence of state-of-charge (SOC) and low-temperature preconditioning on NP-induced TR behaviour of commercially available LG-HG2 (INR18650HG2) LIB cells. Temperature measurements and visual observations were used to evaluate ignition behaviour, thermal response, combustion characteristics, and test repeatability. The TR behaviour of commercially available LIBs with different chemistries and form factors was also compared. Finally, particulate matter (PM) generated during NP-induced TR was characterized using particle size distribution (PSD) analysis, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD).

The experimental results demonstrated a strong dependence of TR severity on SOC. Cells tested at 100%, 95%, and 77% SOC underwent immediate TR following NP, whereas the 68% SOC cell did not ignite and exhibited only sustained venting and smoke generation. Low-temperature preconditioning reduced the severity of TR, producing lower peak temperatures and, at −40 °C, delayed ignition in multiple experiments. Comparative testing further demonstrated distinct differences in ignition behaviour, venting characteristics, and combustion response among cells with different chemistries and form factors, emphasizing the influence of battery design on failure behaviour.

Post-mortem characterization of TR ejecta revealed that the emitted PM consisted predominantly of submicron particles with spherical, irregular, agglomerated, and flake-like morphologies. SEM-EDX analysis identified carbon-rich particles together with metallic species originating from battery components, while XRD analysis confirmed the presence of crystalline decomposition products associated with cathode materials. These findings contribute to a more comprehensive understanding of NP-induced TR and particulate emissions from LIBs, providing valuable information for battery safety assessment, failure modelling, and the development of safer battery technologies.