Characterization and Modelling of Second-Life 18650 Lithium-Ion Batteries

Abstract

The potential to shift from heavily reliant on fossil fuels for traditional energy systems to more sustainable ones depends on energy storage technology developments. One of the main contributors to this transformation nowadays is Lithium-ion (Li-ion) batteries, which offer the best energy density, longevity, and dependability. These batteries are commonly served in electric vehicles (EVs) as their primary purpose but can be served in stationary Energy Storage Systems (ESS) because of their vast capacity.

This master’s thesis explores the complex area of second life for lithium-ion batteries, primarily focusing on the 18650-cell format. By combining the theoretical framework, experimental studies, and optimization approaches, this work enriches the advancements in the fast-growing area of battery science. The first part of the study focuses on reviewing the literature on lithium-ion batteries to demonstrate their background, chronology, chemistry, and degradation mechanism. Based on that, the research further involves modeling and characterizing essential parameters of 18650 Li-ion cells utilized in Tesla EVs. Therefore, the study performs a real-world valid model using experimental data and equivalent circuit modeling and optimization tools for these cells and their performance under different operating conditions.

Each critical performance factor, like internal resistance, open circuit voltage, and polarization resistance, is highly elucidated. Optimization of capacity involves compromise decisions concerning capacity factors, load of internal stimulants, deterioration, thermal factors, and costs at a particular phase of time. Some practical solutions prove the efficiency of the introduced optimization methods and illustrate how second-life batteries can be incorporated into grid storage systems and portable devices. The thesis also considers the cost-benefit analysis of second-life batteries, thus offering recommendations in terms of applicability for people in industries and scholars globally. Some of the subjects addressed are the next cell sorting infrastructure issues, thermal control systems, batteries’ control systems, and integration issues. Moreover, it also investigates the trends for the future, such as the need for a more integrative approach and advancements in technologies on battery research.