Visualization of concentration polarization in thick electrodes

Abstract

The manufacturing of the thick electrodes is vital for lithium-ion batteries (LIBs) to be widely industrialized since it can effectively elevate the energy density of LIBs. However, there is a serious liquid-phase concentration polarization in thick electrodes under high current density, resulting in poor electrochemical reaction kinetics. More importantly, concentration polarization will lead to the gradient distribution of the chemical properties for active materials, which is difficult to characterize. Herein, to reveal the influence of concentration polarization the crystal structure difference of the active materials in thick electrodes during charge-discharge process is explored. Then, the concentration polarization is verified in the configuration of thin-electrode-stacking cells (S-cells) for the first time by determining the Li content of each thin electrode in S-cells. Furthermore, Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS) is applied to visualize the gradient distribution of Li solid-phase content on the section of the thick electrodes under high rates. Additionally, to alleviate the concentration polarization, the holes array is constructed on thick electrodes to enhance rate capability, and the mechanism of that was clarified by electrochemical simulation. This work will provide promising methods for studying the concentration polarization of thick electrodes in the future.