Electrolyte Conditions in Li-Ion Batteries in Presence of a Thermal Gradient

Abstract

Safety is one of the big concerns to tackle for large-scale application of Li-ion batteries. With higher amounts of energy stored per unit volume and higher current densities flowing through the device, energy dissipation in the form of heat is becoming one of the main issues for proper battery operation. If temperature increases, secondary chemical reactions may be initiated. These reactions release more heat and undesired products, triggering an auto-catalytic feedback process to occur, which is commonly classified into thermal-runaway mechanisms. This can potentially lead to a complete degradation of the battery, and possible explosion or combustion of the battery components.Several researchers have worked on developing models to predict thermal behavior under abuse conditions with potential thermal runaway outcomes on Li-ion batteries. Hatchard et al. (2001) proposed a model that emulates the SEI decomposition and regeneration reactions on a standard 18650 cylindrical cell. Lopez et al. (2015) extended the previous work and also included the reactions of cathode decomposition and electrolyte decomposition with potential combustion. Although macroscopic level energy balance helps to predict potential thermal behavior in a battery of multiple layers, the study of all the different transport mechanisms that happen inside a single layer battery is essential for a better understanding of the process taking place when temperature begins to rise. With the aim of improving heat dissipation inside a battery, the electrolyte is a key component to consider as it can potentially handle heat flux easier through convention within the solution. This work investigates spatially dependent electrolyte conditions in the presence of a thermal gradient in order to produce a thermal runaway model. The objective of the study is to model transport mechanisms that might lead to thermal degradation of the battery. Li- ions, electrons, momentum, and thermal flux are the main components of the analysis. Numerical simulation techniques are used for this purpose. A thorough comprehension of the transport processes taking place inside the battery contributes to avoiding damage induced due to thermal abuse conditions.