Quantitative electron diffraction tomography for structure characterization of cathode materials for Li-ion batteries
2 July 2018
Campus Groenenborger, U0.24 - Groenenborgerlaan 171 - 2020 Antwerpen (route: UAntwerpen, Campus Groenenborger
Organization / co-organization:
Department of Physics
Joke Hadermann & Artem Abakumov
PhD defence Olesia Karakulina - Faculty of Science, Department of Physics
Rechargeable batteries play an important role in the development of renewable energy and the decrease of air pollution. The battery is a dynamic system, which converts electricity into chemical energy and vice versa by oxidation/reduction reactions. Understanding these processes is crucial, because they define the electrochemical properties. In case of Li-ion batteries, the active compound of the positive battery electrode (cathode) is an inorganic phase, which consists of a framework or a layered structure filled with Li-ions. During cycling, Li-ions are reversibly extracted and inserted. How the inorganic structure adapts to the variation in Li content has a crucial impact on the battery performance. It is challenging to characterize the crystal structure variations due to complex nature of the cathodes, which contain the active cathode material as well as several amorphous additives. The most wide-spread laboratory technique for the structure determination, powder X-ray diffraction (PXRD), does not always allow refining fine structural details for such mixed compounds. Therefore, state-of-the-art large diffraction facilities such as synchrotron and neutron sources are currently used to solve this problem.
An alternative method is proposed in this thesis, which is quantitative electron diffraction using a transmission electron microscope (TEM). Electron diffraction tomography (EDT) was developed a bit more than a decade ago. It allows obtaining crystallographic information from a single submicrometer crystal without prior knowledge. Therefore, multiphase samples can be successfully investigated. Also it allows to detect light atoms such as Li, however successful refinement of their occupancies has not been shown so far in literature. Therefore, the aim of this thesis is to investigate the possibility to use EDT for the complete structure characterization of cathode materials including the refinement of Li occupancies and also to investigate their degradation mechanisms upon electrochemical cycling using ex situ and in situ TEM.