Electrochemical Impedance Spectroscopy Characterization of Silicon-Based Electrodes for Li-Ion Batteries

Lithium-ion cells are currently the most promising electrochemical power sources. New high-capacity electrodes made of silicon are presently under intensive study. Besides its high capacity, silicon undergoes a significant volume increase (up to 300%) during lithiation. The main research on the silicon-based electrodes is focused on the nanostructure development and capacity/life cycle measurements. Variations in other electrochemical parameters, SEI layer resistance and charge transfer resistance, are also important and give the information about structural changes and mechanisms of side processes that occur during an electrode lithiation/delithiation. This work presents electrochemical impedance spectroscopy measurements of three silicon-graphite composite electrodes, containing various silicon contents. A clear correlation between the SEI and charge transfer resistances and the active material lithiation level is presented. The effect of the cycle number on the measured parameters is also visible. We present possible mechanisms that lead to observed changes and highlight the requirement of the proper Si-based electrode formation and the correct estimation of operational parameters.