Battery aging process

During a battery’s lifetime, its performance or "health" tends to deteriorate gradually due to irreversible physical and chemical changes that take place with usage. To ensure accurate State-of-Charge (SoC) calculation while a battery ages, the changes that take place in a battery’s overpotential and Electro-Motive Force (EMF) behaviour need to be fully understood.

This chapter presents a complete description of battery EMF and overpotential behaviour as a function of battery aging in relation to a US18500G3 Li-ion type of battery. The main aspects of battery aging will be presented in section 6.1. EMF measurement by means of GITT as a function of battery aging will be presented in section 6.2. A comparison will be made with a fresh battery’s EMF. The focus in section 6.3 will be on overpotential measurements based on partial charge/discharge cycles as a function of battery aging. New adaptive systems for battery EMF and overpotential based on the phenomena discovered during analysis of the measurement results will be presented in section 6.4. These systems will enable accurate SoC calculation while a battery ages. The voltage prediction model developed in section 4.2 will also be used in the EMF adaptation method. Section 6.5 will present concluding remarks.