Revealing nanoscale lithiation and dissolution pathways by in situ cryogenic electron microscopy

• Main Author: Tiukalova, Elizaveta
• Other Authors: Martial Duchamp
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Materials::Energy materials
• Online Access: https://hdl.handle.net/10356/160591
• Institution: Nanyang Technological University

Materials for energy storage and conversion devices are of high importance to meet future industrial energy demands. Detailed understanding of chemical processes occurring at the solid/liquid interfaces and alterations of the structure at the atomic scale is critical for the design and development of future devices. This Ph.D. work focuses on two central systems of particular relevance for energy applications, i.e., LiNi0.5Mn1.5O4 Li ion battery cathode material and two catalysts (La2LiIrO6, ZnCo1.2Ni0.8O4) for the oxygen evolution reaction (OER) applications. Through a deep understanding of the evolution of the structure at the local atomic scale, the overall aim is to get insights into the atomic structure property relationship to improve our understanding and provide information that will help develop materials capable of higher capacity, longer lifetime, and overall better performance. During operation, electrochemical reactions introduce structural and chemical changes to the active materials that are not necessarily reversible. These alterations cause degradation of the device performance and limit their lifetime. A detailed understanding of the correlation between electrochemical processes and atomic scale transformations is essential to improve the performance of the devices. Owing to its high resolution transmission electron microscopy (TEM) based imaging and spectroscopic analysis is able to provide unique information that is not available with other methods. In addition, with the recent development of dedicated in situ and operando TEM capabilities, it is possible to observe structural changes under the application of external stimuli such as at cryogenic temperature or presence of a liquid electrolyte, allowing to study dynamical processes in their native operation environment. The development of in situ cryogenic temperature stages for materials science applications has opened up many new possibilities, including learning new information about beam sensitive materials that are challenging to characterize with conventional room temperature imaging at the atomic level. This Ph.D. work focuses on three material systems studied in detail under various HR(S)TEM and spectroscopy methods: LiNi0.5Mn1.5O4 as a promising cathode material, ZnCo1.2Ni0.8O4 and La2LiIrO6 as catalysts for OER. It was found that LiNi0.5Mn1.5O4 material transforms from spinel into rocksalt phase during TEM imaging at room temperature. It is demonstrated that the implementation of TEM studies at cryogenic temperature helps to delay the radiation damage, allowing to reveal new insights into the process of charge/discharge of the LiNi0.5Mn1.5O4 cathode. During the oxygen evolution reaction, complex surface reconstruction was observed on two catalysts, La2LiIrO6 and ZnCo1.2Ni0.8O4, at the atomic scale, including dissolution of atomic elements and formation of new phases. The novelties consist of the studying of these beam sensitive materials under operando or in situ conditions, including cryo temperature in a TEM experiments, in order to understand the pristine atomic scale behavior of the above systems. As a result, the information obtained is used to reveal the actual structural modification happening at the atomic scale as a result of electrochemical reactions.