Temperature-dependent electrochemical impedance spectroscopy (EIS) of lithium thionyl chloride and Li-ion batteries

Abstract

Batteries are one of the most researched and developed energy storage systems in recent years due to their utilization in portable and mobile devices. Therefore, operando and in-situ characterization of batteries should be properly performed to understand the electrochemical processes. For this purpose, Electrochemical impedance spectroscopy (EIS) and its complementary techniques have been utilized in this thesis to investigate various electrochemical systems. This thesis starts with a detailed electrochemistry review, which is necessary for understanding the discussions. Then, experimental and technical details regarding the measurement practices are presented. The initial transient occurrence with a simplified Randles cell and using both experimental and simulation data eventually shows that the initial transients are observed in every measurement and simulation scenario. Even with the real-life dummy cells made of resistors and capacitors, the initial transients are present and cannot be eliminated completely. Thereafter, the temperature-dependent EIS studies are presented, including the temperature-dependent EIS of symmetric and complete cells as well as the spiral/bobbin architectures of Lithium Thionyl Chloride (Li/SOCl2) batteries. The evaluation and comparison of the impedance response of different cell geometries and architectures with the consideration of Arrhenius relations. The Arrhenius relations are utilized for the determination of the activation energies of electro-chemical processes detected by EIS. Thus, the result concludes that the activation energies are dependent on the SoC of the battery, temperature, and chemistry, and these parameters are investigated in detail. Following, another study with similar chemistry, Li/SOCl2/SO2Cl2 batteries, is investigated in terms of EIS and Non-linear Harmonic Analysis (NHA), which shows the relation between the Kramers Kronig (KK) compatibility and NHA based on this cell chemistry. The proper way of measuring this chemistry is also presented with experimental de-tails, which necessitates changing the impedance parameters to acquire linear and reproducible results. Lastly, in the appendix, my personal interest in electric guitar pickups is investigated, and the single-coil and humbucker structures are compared in terms of their impedance responses.