Electrochemical Impedance Spectroscopy (EIS) Fundamentals
📌 EIS is a non-destructive method used to analyze the electrochemical processes occurring within a battery cell.
🔬 Battery reactions occur at different speeds: lithium ion diffusion (slowest), charge transfer reactions, and lithium ion migration within the electrolyte (fastest).
📡 Applying an AC test signal at different frequencies excites these specific processes; lower frequencies observe slower reactions, while higher frequencies observe faster ones.

Analyzing Impedance Data
📈 Measuring impedance over a range of frequencies (high to low) and plotting negative reactance versus resistance creates a Nyquist plot (or Cole-Cole plot).
⚫ The Nyquist plot displays three distinct regions corresponding to the different processes: the first region is lithium ion migration, the circular area shows charge transfer reactions, and the $45^\circ$ angle represents lithium ion diffusion.
🛠️ Data from EIS allows engineers to create an equivalent circuit model that describes the battery's electrochemical system, enabling targeted improvements.

EIS Implementation with Hioki Equipment
💻 Hioki offers the BT 4560 battery impedance meter to facilitate EIS analysis, connecting to devices like a typical pouch cell.
🖱️ A Nyquist plot can be generated easily with just a few clicks using the associated PC application.

Key Points & Insights
➡️ EIS allows researchers to effectively "dissect the battery" by observing internal behavior without physically opening the cell.
➡️ The method provides a safe and non-destructive analysis for observing the behavior of electrochemical systems.
➡️ Understanding the different frequency responses allows for tweaking specific processes to achieve battery performance improvements.

📸 Video summarized with SummaryTube.com on Nov 19, 2025, 07:35 UTC