A Continuous Model on the Electrochemical Impedance Spectroscopy of Solid-State Electrolyte

Abstract

Solid state batteries have emerged as a potential next-generation energy storage device due to safety and energy density advantages. Development of electrolyte is one of the most important topics in solid state batteries. The ionic conductivity is a crucial factor to characterize the electrolyte for research and applications. Electrochemical Impedance Spectroscopy (EIS) is a popular measurement technique to obtain the conductivity; a typical experiment setup is to connect the electrolyte with two conductive electrodes, and apply an alternating current. As for post-processing, the intersection of the EIS curve with the real axis is treated as the bulk resistance. This simple interpretation, however, discards other information revealed by EIS such as the slope of the curve at low frequency. What is worse, some features on the curve are not fully interpreted. For instance, the semicircle in the Nyquist plot, often interpreted as charge transfer, also occurs when the electrolyte is connected to two non-reacting electrodes such as stainless steel and gold. To better understand the transport mechanism and interpret EIS curves, we introduce a continuous model to quantify the ion transport and current flow in the electrolyte. Experiments are conducted to verify our model. The produced EIS curves from the model are compared with experiment data to show good agreement.