Impedance-based state estimation of lithium-ion batteries

Kieran McCarthy
This thesis can be divided into two interconnecting sections. The first section is centered on the development of an internal temperature (IT) and state of health (SoH) estimator for lithium-ion batteries (LIB) through the use of online electrochemical impedance spectroscopy (EIS) measurements. Correlation analysis on the relationship between sensitive impedance variables and battery state parameters was also performed and the strength of this relationship quantified. The second section focuses
more » ... on the electrochemical performance of the nanostructured Li-alloying materials silicon (Si) and germanium (Ge) nanowires (NW) for next-generation LIBs. EIS is used throughout in order to gain insights into the electrochemical properties of the novel materials. Chapters are arranged as research articles, each with an introductory summary. Chapter 3 describes the development of a novel LIB IT estimator using EIS. The proposed model used a single frequency impedance point, which displayed high sensitivity to changes in temperature while simultaneously showing low dependence to the change in state of charge (SoC) and SoH. The model was able to accurately estimate the internal temperature of commercial LIBs, over the temperature range 10 °C to 55 °C, achieving an average RMSE of 1.41 °C across 9 data sets. Chapter 4 describes the development of a SoH estimation model for LIBs. Similar to the previous chapter, the impedance at a single frequency is used to relate the fade in capacity to the increase in impedance as the battery aged. The model successfully estimated the capacity of 6 commercial batteries over 300 cycles, with an RMSE of 0.0064 Ah achieved between actual and estimated capacities. In chapter 5, sensitivity correlation analysis is performed to identify and quantify the dependence of various equivalent circuit elements and frequencies to the vital battery parameters of SoC, SoH and IT. Each parameter demonstrated high sensitivity to particular frequency ranges and parts of impedance, thus validating the intrinsic rel [...]
doi:10.34961/researchrepository-ul.21533925 fatcat:ywo25in2ivefrhq3dynii47uia