The fellow has spent two productive years in the hosting group and acquired important coding skill for data analysis to study materials with complex structures. Despite the interruption of COVID-19 which has led to a couple of awarded beamtime experiments unperformed during the timescale of fellowship, key objectives were all achieved, resulting in a few publications in revision and in preparation. Based on the preliminary experimental results, there was a slight adjustment of the objectives (OBJ) relative to ones of the DoA. As bulk metal oxides show very poor electrochemical performance and only nanostructured materials were active in batteries, it was challenging to study the size-dependent behaviour (OBJ1) given the lack of bulk material reference. However, these materials’ phase behaviours were found to show significantly different mechanism during conversion and reconversion processes (OBJ2). This renders a separate study of conversion and reconversion reaction more important for the battery community. Therefore, the original OB1 and OB2 were readjusted with the new OBJ1 focusing only on the conversion process, and the new OBJ2 only on the reconversion. In addition, the NMF methodology developed in this study was found important to investigate heterogeneous electrode materials for batteries. Therefore, a new OBJ3 was added in the course of fellowship to revisit the fellow’s previous work on metal fluorides.
The redefined new OBJ 1, OBJ 2 and OBJ3 were all fully achieved with two publication in revision for OB2 and OBJ3, respectively. A publication related to OBJ 1 is in preparation. The fellow has studied the reaction mechanisms of both binary metal oxides and fluorides and found that their phase behaviours are dominated by topochemical displacement reactions, instead of the reconstructive conversion pathways that are commonly believed to associate with these materials. The renewed mechanistic understanding of these materials is profound to the community because it suggests the kinetic performances of these materials - previously believed to be intrinsically slow as defined by the conversion mechanism - can be enhanced by employing displaced species with faster mobilities. This knowledge sheds light into future strategies to improve these materials' applicability into real-world devices and provides opportunities to make better and cheaper batteries, reflecting the significance to our society. This potential impact of the scientific achievement is in line with the objective of the EU commission to reduce emissions by at least 40% by 2030 – as part of the EU's 2030 climate and energy framework and contribution to the Paris Agreement.
