Nanoscale Lithium Distribution within a Secondary Cathode Particle for Li-Ion Battery Using Identical Location (S)TEM-EELS

Abstract

Energy density of LIBs are primarily limited by cathodes and further development of cathode materials requires in-depth understanding of the structural and compositional changes spanning across various length scales involved during electrochemical delithiation/lithiaton. Cathode materials are usually synthesized as secondary particles (∼10 µm) that are sintered agglomerates of smaller primary particles (∼100s µm). Lithium distribution may not necessarily be uniform across the entirety of these particles in typical state-of-the-art layered cathodes during electrochemical cycling. A detailed knowledge of lithium distribution within secondary particles is crucially important for obtaining a comprehensive understanding of the energy storage system. To truly understand the structural changes taking place at the nano and atomic scales, high spatial resolution techniques are of paramount importance for understanding the lithium distribution and optimizing/developing future LIB cathodes. STEM-EELS is ideally suited for obtaining such information at the desired (atomic) spatial resolution. In the present work, nanoscale lithium-ion distribution was investigated among various primary particles within a secondary particle of state-of-the-art Ni-rich layered LIB cathode using identical location scanning transmission electron microscopy with electron energy loss spectroscopy (IL-STEM-EELS) by making use of a specially designed electrochemical cell employing TEM grids. Identical location allows for the imaging of the same location before and after electrochemical testing to evaluate localized changes. Nanoscale lithium-ion distribution along with the electron beam dose effects on the nanoscale/atomic structure of layered NMC532 cathodes at various charge stages will be presented.