Electrochemical Impedance Spectroscopy Study of 3D-Structured Thick Electrodes induced by Laser Structuring Process

Abstract

The most useful and practical way of increasing energy density of battery is the application of thick electrodes for cell. Thickening the electrode can easily reduce the number of electrodes inserted into the cell stack. Besides, inactive materials (current collector and separator) constituting the stack can also be replaced with the active materials. However, in order to use thick electrode in battery industry, there remains challenges to be improved: a long lithium-ion transport pathway and high internal electrical resistance. The long lithium-ion transport pathway of the thick electrode makes it difficult to diffuse lithium ions, which in turn increases the ionic resistance (diffusion resistance) of the electrode. In addition, the long electron conduction pathway of the thick electrode multiplies the electronic resistance of the electrode. In our previous researches, the above problems have been solved by laser structuring. We used femtosecond laser ablation to form line-shaped grooves on the thick LiNi0.5Mn0.3Co0.2O2 cathode surfaces. The newly formed grooves create an effective environment where lithium-ions and electrons can move easily. In this work, using galvanostatic method, we obtained the improved electrochemical properties and performances of the laser structured electrodes compared to the unstructured electrodes. In particular, electrochemical impedance spectroscopy is used to verify the effectiveness of the 3D-structed electrode. Especially, we characterized the changes in ionic and electronic resistance according to various laser structured electrode designs.