Thermal Runaway of Li-Ion Batteries Caused by Mechanical Abuse Under Different Temperatures: Battery Deformation and Fracture

Abstract

Thermal runaway (TR) of Li-ion batteries (LIBs) presents a disastrous safety hazard and a significant barrier to the wider adoption of electric vehicles (EVs). Inner short circuit (ISC) induced by mechanical abuse is one of the causes of battery TR, but the triggering processes of ISC and TR are not yet clear. This paper uses a hemispherical indenter to trigger an ISC in the battery at different temperatures and studies the battery deformation and fracture process. Results show as the initial temperature increases, the hardness and the maximum load that the battery can take decreases, and the fracture mode of the laminar structure changes from multilayer cracks to localized rupture. In the multilayer cracks failure mode, the ISC homogeneously heats the battery, and it does not directly trigger TR. In the localized rupture mode, the ISC is only induced at the layers close to the indenter and generates a hot spot exceeding 200°C, leading to the initiation of TR. Therefore, the mechanical properties of batteries under different conditions need to be studied in more detail to develop batteries that are safer under mechanical abuse.

Keywords: Lithium-ion battery, Mechanical abuse, Structure failure, Inner short circuit, Thermal runaway