Developing Synchrotron-based Techniques for Characterising Anode/Electrolyte Interface in Li/Na Batteries

With the increasing demand for lower carbon emissions for the mitigation of global warming, Li/Na battery systems are becoming increasingly ubiquitous in both industries and our daily life. The development of electric vehicles (EV), hybrid electric vehicles (HEV) and mobile devices has put forward the requirements for Li/Na batteries with higher energy density, power density, safer and longer operation time. These factors are significantly affected by the interfacial behaviour at electrolyte/anode interface. Therefore, understanding the interface is very important in improving the performance of Li/Na battery systems. However, the direct characterization and investigation of the anode/electrolyte interface are hard due to the buried and heterogeneous nature of the interface. Owing to the wide energy range, high brightness and flux of the beam provided by synchrotron radiation, an unprecedented opportunity was present to obtain new insights into the material chemistry of the interface. The synchrotron-based techniques were used across the entire thesis, which could provide a deeper understanding of the interfacial behaviour between electrolyte and anode in Li/Na batteries. In the thesis, the main area of focus will include the application of ex situ and in situ synchrotron radiation-based techniques in the study of the anode/electrolyte interface in Li/Na batteries and the broader design of in situ cells. Based on these studies, the interface behaviour between anodes and different electrolyte systems in Li/Na batteries was investigated, especially the chemical evolution. The developed synchrotron radiation-based techniques and designed specialized in situ cells can be further utilized in understanding other battery systems, not limited to electrode/electrolyte interface but also changes in other components of cell configuration during the operation of batteries. In Chapter 4, two types of sp2 carbon-based polymer anode were synthesised which show similar chemical structures and different topological structures. The influence of the topological structures on the Li+ storage at the liquid electrolyte/anode interface was investigated by the Near-edge X-ray absorption fine structure (XANES) of C k edge. The potential of such polymer anode was proved by functionating with the -SO3H group, delivering a higher storage capacity. To further boost the energy density of Li-ion batteries by directing using Li metal anode, PEO-based composite polymer electrolytes with the addition of Lithium Bis(trifluoromethanesulphonyl)imide (LiTFSI) and Li6.4La3Zr1.4Ta0.6O12 (LLZTO) fillers were proposed in Chapter 5. The addition of fillers improves the ionic conductivity, electrochemical stability, and contact with Li metal. Combing with the electrochemical tests and in situ X-ray imaging techniques, the role of fillers on the interfacial behaviour between composite polymer electrolytes and Li anode was investigated. In Chapter 6, TiO2 incorporated Na3Zr2Si2PO12 (NZSP-TiO2) solid electrolyte was synthesised to inhibit the metal filament formation during plating at ceramic/metal anode interfaces. The NZSP-TiO2 electrolyte shows an improved density and better cycling stability. An in situ X-ray imaging experiment was designed to investigate the role of TiO2 on the electrochemical behaviour between solid electrolyte and Na metal anode during the cycles