Understanding electronic and Li-ion transport of LiNi0.5Co0.2Mn0.3O2 electrodes affected by porosity and electrolytes using electrochemical impedance spectroscopy

The design of the electrode structure affects the energy/power density of batteries. To understand the effect on electrochemical performance, tools to analyze the microstructure of electrodes in a situation similar to that of an actual lithium-ion battery systems are still needed. Herein, electrochemical impedance spectroscopy (EIS) is applied to a blocking symmetric cell to analyze the effect of the electrode structure in detail. In addition, the diffusion and accumulation of Li ions in the low-frequency region are investigated by applying complex capacitance analysis. Through the capacitive peak of the imaginary capacitance plot, the Li-ion diffusion rate can be compared by analyzing the time constant (τ1), and the electrode uniformity can be confirmed by distribution. Herein, when comparing porosity at the same electrode loading, the 20% and 30% porous electrodes have the smallest Rcontact and Rion, respectively. However, the 20% porosity electrode shows the best rate capability because it has the smallest time constant (τ1) for both resistances. Comparing the electrolyte effect on identical electrodes implies that Li-ion diffusion is affected by the interaction between the electrode and electrolyte. Ultimately, this work proves that Li-ion diffusion is the result of electron-mass transport and electrode-electrolyte interactions.