(52h) Investigating the Thermal Characteristics of Lithium-Ion Battery from Safety Perspective Using the Electrochemical Thermal Model

Transportation and electric energy generation are two major contributors to greenhouse gas emissions, amounting to more than 50% of annual emissions. To curb these emissions, researchers have been focusing on employing compact energy storage technologies. One of the potential storage technologies is the rechargeable lithium-ion batteries, having higher energy density and power against its competitors (e.g. Nickel Cadmium, Nickel Metal Hydride, Vanadium Redox flow rechargeable batteries).

One of the operational constraints for the broader commercialization of lithium-ion batteries is its unsafe thermal behavior during abnormal operation. Lithium-ion batteries have higher temperature sensitivity and a relatively narrower operating range because of electrochemical reactions. It is observed through experiments that at low temperatures, the reaction rate is limited, inducing lithium metal deposition at the electrodes, leading to dendrite formation, which has the potential to cause undesired events (e.g. internal short circuit). Similarly, at a higher temperature, Solid Electrolyte Interphase (SEI) at the electrode surface starts to decompose which again can lead to events such as melting of separator, the evolution of combustible gas from the electrodes. Thus, to prevent these events from happening, it is imperative to understand the fundamental mechanisms of temperature dependency of electrochemical parameters and their influence on heat generation.

In this study battery chemistry is used to characterize the thermal behavior of the battery using coupled electrochemical-thermal model (more robust than equivalent circuit model). In the thermal model, the heat generation rate (includes reversible entropy change and more prominent, irreversible ohmic heating, active polarization, and mixing) in each cell is calculated by electrochemical parameters. The electrochemical parameters are then calculated based on the temperature at that time. In addition, operating conditions such as State of Charge (SOC) and current-rate also influence the internal battery heat generation (generally heat generation rate increases with decreasing SOC, and rising current rate). These factors are also studied in the model for newer applications in automotive vehicles.

The results from this study help us to develop better understanding of the cell behavior at microscopic and macroscopic level. This behavior is influenced by physio-chemical parameters, the dominance of type of heat generation, and wider operating conditions. A better understanding will assist to identify unsafe conditions and develop strategies to enhance the safer operating regions of the battery.