The Role of Oxygen During Thermal Runaway of Lithium-Ion Batteries

Energy storage has become an important technology due to the increasing utilization of renewable resources and the increasing demand of battery electric vehicles. Although LIB usage continues to rise, latent defects and abuse conditions pose safety risks to people and infrastructure. To better understand the nature of LIB failures, modeling and simulation tools are applied to simulate failure conditions such as thermal runaway. Computational fluid dynamics (CFD) tools may be used simulate thermal runaway with consideration of important physics including: gas generation, venting, and combustion of evolved gases. Previous CFD-based studies have investigated various aspects of thermal runaway and venting, but none have considered the instantaneous composition of gases which may lead to ignition within the cell body. The work explores the progression of thermal runaway in a single Li-ion battery cell by modeling the time-dependent generation of individual gaseous species. To determine the conditions leading to ignition in the cell, the time-dependent gas sources are applied to a CFD model which implements a detailed kinetic mechanism for gas phase reactions. Simulation results show the gas composition, temperature and residence time do not support autoignition within the cell. For ignition to occur, a local hot spot from a short circuit or a spark is necessary. Ignition was also likely to occur in the air surrounding the cell rather than within the cell. The findings have important implications on the progression of thermal runaway modeling of Li-ion battery cells.