Cathode Evolution Track for Evaluating Commercial Lithium-Ion Battery Attenuation through Ar Ion Beam Cutting

Abstract

The cathode is crucial for lithium-ion (Li-ion) batteries, and its corresponding investigation is also a hot issue in the scientific research and engineering field. The textile of the active particles and interface of the cathode components determine the rate capability and lifetime of the Li-ion batteries. To study the interface, it is vital and necessary to obtain and track the real cross section of the cathode, which can reflect the real state of each part of the cathode and the combination between them. In this work, an optimized Ar ion beam cutting has been employed to prepare both contamination-free and stress-free cross sections of the commercial Li-ion battery cathode for the first time. As seen from the scanning electron microscopy (SEM) images, the as-prepared cross section of the above cathode is flat with full exposure of the inner textile of cathode active particles. It can be inferred that there exists a Co element accumulation region in the original Li-ion battery cathode in the form of LiCoO2 (rhombohedral) according to the X-ray diffraction (XRD) and transmission electron microscopy (TEM) results. Moreover, along with Li-ion battery aging, it can be found that cathode expansion and disappearance of the Co element accumulation region occur, indicating that the collapse of the LiCoO2 (rhombohedral) structure reduces the sites of Li-ion storage and destroys the conductive network of the electrodes, thus resulting in the decrease of the voltage plateau and capacity attenuation of the Li-ion batteries. The present work could provide a good avenue by tracking the cathode evolution to evaluate the Li-ion battery attenuation during cycling performance.