Study of state-of-charge and degradation in lithium ion battery pack

Abstract

Rechargeable batteries in portable electronics, powertrains and energy storage systems need to handle more energy and power that are beyond a single cell's capability. Therefore, in today's battery applications, connecting cells in series/parallel configurations to meet energy and power requirements is a common practice. As the number of cells in the battery configuration increases, the complexity in the control and managing the cells becomes sophisticate as well. There is an urgent need to understand the behavior of multi-cell strings through proper assessments to derive adequate knowledge for the control and management of the battery packs. Here two very important aspects in the string assessments and evaluations in term of state-of-charge estimation and pack degradation using Li-ion commercial cells are studied. The ability to characterize cell variability using non-destructive electrochemical techniques such as incremental capacity analysis and accurate state-of-charge tracking, enables us to understand the inherent variations among the cells and their impact on the string performance characteristics as well as their degradation mechanisms in different cycle aging processes.