Analysis of Internal Short Circuit and Thermal Runaway of Li-Ion Battery Due to Mechanical Abuse

Abstract

Due to the growing electric vehicle market and new trends to reduce fuel consumption for a healthy environment, safe and reliable vehicles are desirable for reasons beyond EV and new technology. Although certain safety standards and legislation are in place and continuously improving but several concerns including battery safety, battery performance, vehicle structure, and battery design to be considered as these affect the overall reliability of Electric vehicles (EVs). Lithium-ion battery technology is considered a good solution to power electric vehicles but potential overheating due to stressful conditions such as mechanical abuse, overcharge, over-discharge, short circuit, and excessive heat from external environment gives rise to safety issues and the occurrence of one or more than one of these can lead to thermal runaway. In most cases, an electric short circuit is a necessary but not sufficient condition for the occurrence of thermal runaway after mechanical abuse. Chemistry of the cell, the resistance of separator to heat, size of the fractured part, and rate of heat transfer all play a role in processes leading to a thermal runaway, if the cell has not gone to thermal runaway right away it can still go into a slow process of electrochemical reaction, releasing gases that eventually could lead to a catastrophic event. This abstract investigates the mechanical behaviour of the separator in the LiCoO2/Graphite cylindrical 18650 cells. Internal short circuit (ISC) behaviour, strain rate dependency, and electrochemical status of the cells (i.e. SOC dependency) are studied to understand failure patterns. Furthermore, a simple and effective constitutive model for the separator layer is formed, facilitating further mechanical analysis and numerical simulation of lithium-ion battery study. The occurrence of ISC is investigated by jellyroll deformation where the casing is removed, and quasi-static load is applied. The numerical simulation model is developed to further investigate sequential structural failures and temperature changes. Simulation results showed good accuracy with experimental results and are useful to predict structural failure of cells. The number of failures including electrolyte leakage, change in shape, sudden voltage drop/temperature rise, and gas venting are observed.