A comprehensive understanding of electrode thickness effects on the electrochemical performances of Li-ion battery cathodes

LiNi1/3Co1/3Mn1/3O2 (NCM) and LiFePO4 (LFP) electrodes of different active material loadings are prepared. The impact of electrode thickness on the rate capability, energy and power density and long-term cycling behavior is comparatively investigated. Peukert coefficient slightly increases with increasing electrode thickness, showing a severe capacity loss at higher rate for thicker electrode. A power-law relation between the maximum working C rate and electrode loading is obtained. Increase of the specific resistance with increasing electrode thickness is not an important factor responsible for the poor rate performance for thicker electrode. The power–law relationship is typical for a diffusion-related system, indicating that Li ion diffusion within the electrode is the rate-determining step for the discharge process. As the result of the deterioration of rate capability, enhancing energy density through increasing electrode thickness is accompanied by a significant loss of power density. Long-term cycling performance is also deteriorated, which is attributed to the high internal resistance and poor mechanical integrity of thicker electrode.

► Electrochemical performances for LiNi1/3Co1/3Mn1/3O2 (NCM) and LiFePO4 (LFP), as a function of the electrode thickness were comparatively investigated.
► A power-law relation between maximum working C rate and electrode loading is obtained.
► Li ion diffusion within the electrode is specified to be the rate-determining step for the discharge process of the two cathodes.
► Higher capacity fading-rate of Li-ion cells containing thicker electrode is attributed to large polarization and severe mechanical issue of the electrode at high thickness.