Heat generation effect and failure mechanism of pouch-type lithium-ion battery under over-discharge for electric vehicle

Heat generation is a crucial factor for lithium-ion batteries during the charge and discharge process, which can trigger serious safety issue such as fire hazard and explosion. Over-discharge is a common inducement which can result in not only heat generation effect, but electrode and electrolyte failure. However, it is not definite that the accurate mechanism of heat generation and battery failure triggered by over-discharge. Here, we propose an over-discharge strategy to understand the mechanism of heat generation and battery failure. 36 Ah pouch-type battery is charged at 1C (36 A) current density, and is discharged for 1.5 h at 1C (36 A) with 0.5 h over-discharge degree. The battery was disassembled and analyzed by X-ray diffraction (XRD), Raman test, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Our results revealed the hidden the heat generation of over-discharge, which is associated with the copper dissolution on anode and deposition on cathode, the degradation of electrolyte under over-discharge process. The proposed method offers a beneficial guidance for researchers to study the over-discharge behaviors of other decomposition reactions.