In Situ Scattering Study of Structural Dynamics and Capacity Fading Mechanism in NCM Cathode Materials

Description

LiNixCoyMnzO2 (NCM, 0 ≤ x, y, z ≤ 1) has been considered to dominate the cathode technology of future automotive industry due to its high capacity and low cost. Despite the excellent prospects, however, severe capacity degradation of NCM cathodes during operation has prevented this promising material from further success. The mechanism of capacity fading in NCMs remains controversial, and might be attributed to the structural changes as follows: intermixing of Li/Ni ions, re-arrangements of transition metal (TM: Ni, Co and Mn) ions, anisotropic volumetric changes and complex phase transformations at high voltage. Therefore, an in-depth understanding of the coupling between structural changes and capacity fading mechanism is of critical importance to the improvement of NCM cathodes. However, precisely determining the structural dynamics of NCMs over cycling is still a challenging task to date. This is due to the difficulty in distinguishing light (Li) and nearby (Mn, Co and Ni) elements for the conventional X- rays method. Here, we propose to investigate a series of important NCM cathode materials with advanced time-resolved synchrotron and neutron scattering techniques such as in situ diffraction, in situ pair distribution function (PDF) of total scattering, etc. The characterization limitations of X-ray could be complementarily overcome by neutron, and the combination of diffraction and PDF analysis will provide both longrange and short-range structural information simultaneously. Specifically, we will precisely determine the fine structural dynamics in NCM compounds, including Li/Ni migration kinetics, transition metal arranging kinetics, anisotropic lattice evolutions and phase transition behaviors via in situ scattering techniques. It is expected that a comprehensive insight into the severe capacity degradation of NCM cathode materials will be provided from structural point of view, which could offer important guidance to the improvement of NCM cathodes and be in turn cooperated into the battery design especially for electrical vehicle (EV) industry.