Overheat-to-thermal-runaway characteristics and fuzzy risk assessment of automotive lithium-ion cells with different cathode materials, capacities, packaging, and states of charge

Abstract

As a primary cause of vehicle fires, battery overheating-induced thermal runaway (TR) warrants adequate attention. Most existing studies use heating pads for thermal induction and focus on small-capacity cells, which limits their practical relevance. This study first uses simulation to identify a more application-oriented heating approach for triggering TR, and then conducts thermal chamber heating experiments on commercial cells with two cathode chemistries (LiFePO₄ (LFP) and Li[Ni_0.8Co_0.1Mn_0.1]O₂ (NCM)), three capacities (135 Ah, 51 Ah, and 5.2 Ah), two packaging types (prismatic and pouch), and two states of charge (SoC, 100 % and 80 %). Based on the experimental data, the overheating process of the cells can be divided into five stages. In terms of safety, larger-capacity cells show shorter TR initiation times, higher temperature rise rates, and higher peak temperatures. NCM cells exhibit significantly higher maximum temperature rise rates and peak temperatures compared to LFP cells, indicating that large-capacity NCM batteries require greater safety precautions in practical use. Additionally, cells at higher SoC levels demonstrate greater TR risk. By covering a wide range of cell types, this study comprehensively describes and analyzes the TR characteristics of commercial lithium-ion batteries from multiple aspects, offering valuable insights for the new energy industry.