Visualization of Heterogeneity in Materials for Lithium Batteries Using Micro X-ray Diffraction
thesisposted on 01.08.2021, 00:00 authored by Chao Li
The ultimate goal of this thesis is to establish correlations between local investigated properties and macroscopic electrochemical performance that affect the performance of batteries and inform their future design toward overcoming existing frontiers in the technology. X-ray diffraction (XRD) is a powerful characterization technique which has been extensively applied in the study of crystalline materials in many different fields, including pharmaceutical industry, forensic science, mineralogy, microelectronics industry, corrosion analysis even in glass industry. This thesis focuses on the design and the development of protocols to implement methods of XRD using microbeams to study local electrochemical phenomena relevant to cathode materials and solid electrolytes for batteries based on shuttling Li ions to store charge. With the resulting maps, heterogeneity at several length scales, and their associated chemical and physical properties, can be visualized and assessed both qualitatively and quantitatively. The μXRD mapping methods demonstrated in Chapter 3, was applied to evaluate the electrochemical performance of a complete NCA cathode by visualizing how the local distribution of states of charge after cycling is affected by storing the electrode under different conditions. The domains of different delithiation states revealed by the μXRD maps were consistent with the structural analysis based on the bulk powder XRD. By showing the local phase distribution, insight was revealed into the effects on the macroscopic transport of lithium ions of the formation of insulating impurities on the surface of NCA cathode during storage. Taking advantage of an extremely powerful X-ray source, a synchrotron, at Argonne National Laboratory, operando μXRD was developed and performed to map secondary particles in Chapter 4. The diffraction patterns of each mapping position revealed compositional gradients within single secondary particles of NCA during galvanostatic cycling, based on the comparison of the position and shape of selected diffraction peaks to reference data. The μXRD diffraction patterns were also compared with a previous study with the same technique to reveal the effect of cycling rates on the electrochemical behavior of NCA secondary particles. In Chapter 5, a novel μXRD mapping method with Laue diffraction at a synchrotron was successfully developed and applied to create deviatoric strain maps of garnet-typed solid state electrolytes compositionally derived from LLZO. These deviatoric strain maps helped to visualize the variation in microstructure within the solid electrolytes, which helped rationalize differences in local stability of lithium electrodeposition during cycling.