Browsing by Subject "Non-linear harmonic analysis"

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Open Access
Non-linear harmonics in EIS of batteries with lithium anodes: Proper controls and analysis
(Elsevier, 2022-10-10) Zabara, Mohammed Ahmed; Katırcı, Gökberk; Ülgüt, Burak
Non-linear Harmonic Analysis is used to investigate the distortions accompanying the Electrochemical Impedance Spectroscopy (EIS) measurements. The distortions emerge from non-linearity and non-stationarity due to the underlying redox reactions as well as the capacitance. Identifying each response and its source is crucial to correlate the obtained harmonics to their corresponding electrochemical processes. In this study, we identify the distortions of Galvanostatic-EIS measurements of Lithium Primary Batteries by means of comparing mathematical simulations and experimental measurements. The simulations were performed on RC-based equivalent circuit models, which showed the presence of certain distortions. The experimental measurements displayed distortions in the form of both non-linearity and non-stationarity in the case of batteries. The level of the harmonics in the measurements is either similar or higher than the harmonics simulated in the RC equivalent circuits at different frequencies. The obtained harmonics compared to simulations highlights the importance of control measurements before the analysis of non-linear harmonics of EIS measurements galvanostatically excited.
Open Access
Temperature-dependent electrochemical impedance spectroscopy (EIS) of lithium thionyl chloride and Li-ion batteries
(2024-05) Katırcı, Gökberk
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.