Linking Key Features of Commercial Lithium Ion Cells to Thermal Runaway Effects

Abstract

Abuse of lithium-ion battery (LIB) cells can lead to heat buildup, triggering thermal runaway (TR). The TR of one cell can propagate to adjacent cells, potentially causing the TR of the whole battery. Predicting TR-characteristics based on easily accessible key cell features — such as i) cell format, ii) cathode type, iii) cell capacity and/or energy, and iv) state of charge (SOC) — would be highly beneficial.Herein, 10 different commercial LIB-cell types with four cathode variations were tested at various SOCs in both single cell and propagation scenarios, totaling 170+ abuse tests. The TR-effects, including TR-onset temperature, maximum cell temperature, amount of gas emitted (Vgas), and maximum overpressure (pmax), are analyzed based on the key cell features. Additionally, the impact of the testing atmosphere is discussed, showing that oxygen presence increases pmax by up to 4.6 times Based on the various TR-effects, two main groups emerge by cathode material: A) Li(Ni1-x-yMnxCo­y)O2 (NMC), LiCoO2 (LCO) and Li(Ni1-x-yCoxAly)O2 (NCA), and B) LiFePO4 (LFP). Intriguingly, Vgas from group (A) scales linearly with the SOC-dependent cell energy regardless of the test atmosphere, yielding 0.46 L Wh-1. TR-propagation tests showed no propagation for LFP-cells at any SOC, while NMC/LCO/NCA-cells typically propagated at 70% and 100% SOC, but not at 30% SOC. TR-propagation speeds fell into three categories: non-, slow-, and fast-propagating.Overall, the insights gained suggest that it may be possibly to predict the TR-effects of a specific LIB-cell, and improve the understanding of the TR-mechanism, driving the development of advanced cell-level safety measures.

Keywords: lithium-ion-batteries, thermal runaway, battery safety, safety prediction, thermal runaway propagation, propagation speed