Numerical Analysis of Multiphysics Behaviors of Lithium-Ion Batteries for Internal and External Short

Lithium-ion batteries are believed promising technology for electrical energy storage system enabling advanced electrified powertrain vehicles. However, safety issue originated from thermal instabilities of the components of lithium-ion batteries at exposure to high temperatures is one of the most daunting problems that should be overcome. Thermal runaway of lithium-ion batteries due to internal short-circuit is considered as a major safety concern. Initial latent defects leading to later internal shorts would not be easily controlled, and evolve into a hard short through various mechanisms such as separator wear-out, metal dissolution and deposition on electrode surface, or extraneous metal debris penetration. The objectives of the presented study are to develop integrated multi-physics models predicting short evolution and thermal runaway propagation in lithium-ion battery systems, and to provide better insight about the behavior of cells and multi-cell battery systems under internal and external short circuit conditions. This talk will describe the methodologies of NREL's lithium-ion battery short modeling, and then present analysis results for cell response study and multi-cell pack response study. Figure 1 shows concept of multiphysic model integration for the short circuit study. In our multiphysics model approach, competing mechanisms between heat release from component decomposition reactions at high temperatures and heat dissipation through spatial variation of material distributions are captured. Electrochemical responses of shorted cell are resolved by solving lithium diffusion dynamics and charge transfer. Three dimensional pathways of electrical current flow in a system are solved to evaluate joule heating from short current. Figure 2 shows time evolution of thermal behavior of a 20 Ah stacked prismatic cell for a short between metal current collectors. The model predict this type of low impedance short results in highly localized heating in a large format cells leading to a thermal runaway relatively in short time. For the extended pack level study, we developed an integrated network model resolving highly coupled thermal-electrical (electrochemical ) responses from individual cells and inter-cell interactions. Multi-node thermal model for the selected cell was developed to capture critical temperature distribution in a cell. Cell temperature distribution at 6000 seconds after the external short of middle bank in 80 cell (16-in-parallel and 5-in- series) pack where each cell is equipped with positive temperature coefficient (PTC) device is presented at Figure 3. The simulation results imply that evolution of a internal short circuit and the thermal, electrical, chemical response of a lithium-ion cell for the short strongly depend on the nature of short itself, the characteristics of