Temperature-Dependent Electrochemical Impedance Spectroscopy of Li/Li Symmetric Cells and Li/MnO2 Batteries

Abstract

Understanding the electrochemical properties of Lithium metal is a crucial step for developing and optimizing rechargeable batteries with lithium metal anodes. During discharge, the lithium metal is oxidized, generating dissolved lithium cations. Transport of the ions to the electrolyte is a significant part of this process. To investigate this process, temperature-dependent EIS experiments are done to independently measure the resistance due to this transport and, eventually, the activation energy.Electrochemical Impedance Spectroscopy (EIS) is a non-destructive analysis method mainly employed for studying the characteristics of electrochemical energy storage systems. EIS can be invaluable in isolating and studying buried interfaces without physically separating individual components. The anodic process, specifically the charge transfer through the solid-electrolyte interface can be studied without any influence of the rest of the processes.In this study, we built and measured the Potentiostatic EIS of both symmetric (Li/Li) and batteries (Li/MnO2). Button size (CR 2032) cells were constructed with different battery-grade electrolytes. A symmetric cell can isolate the processes related to metallic lithium. In contrast, a battery type (with an anode and a cathode) can differentiate the effect of the cathode on the anode. A broad range of temperatures (15ᵒC to 65ᵒC) was achieved with a Peltier-powered, homemade climate chamber. The limiting factors were selected according to the freezing and boiling temperatures of the electrolyte systems. Cycling of symmetric cells and discharging of batteries were performed, and the cells were measured after cycling/discharging.The evaluation of the spectra as a function of temperature and states-of-charge can give a comprehensive understanding of metallic Li and the oxidation process. The resistance modeling the transport as well as the capacitance values were investigated as functions of temperature. The change in resistance values at different temperatures resulted in not only Arrhenius behavior but also regions where Arrhenius behavior is violated.Interpretation of the temperature dependence provides a detailed understanding of the underlying electrochemical phenomena involving the metallic lithium anode. The effect of electrolytes on Li+ conductance can also be interpreted from the achieved results.