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Disorder and Order in the Conversion Mechanism of Metal Oxides in Lithium-ion Batteries

Periodic Reporting for period 1 - DisorMetox (Disorder and Order in the Conversion Mechanism of Metal Oxides in Lithium-ion Batteries)

Reporting period: 2018-08-01 to 2020-07-31

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.
Progress of the Activities:
a. The fellow has learnt how to code using Fortran and how to write programs for scientific calculation and data analysis. Beamtime applications were successful and materials for battery application were successfully prepared and measured as planned. Robust data analysis and interpretation were performed using the new programming skill that the fellow has acquired during the fellowship.
b. The fellow has received training from the university by taking language and IT courses. He has also received significant career training by the host (Prof Andrew Goodwin) in writing scientific article and job applications, as well as the training for career interview – the fellow was selected in the final round of interview for a lectureship position.
c. The researcher worked closely with internal group members in the host group. On the one hand, he has enhanced his analytical skills in crystallography study; on the other hand, his knowledge and experience of battery research has benefited the host group by expanding the group’s research domains.
d. Difficulties concerning materials preparation for OBJ 1 were encountered at the beginning of the fellowship. The fellow has readjusted the objectives based on the feasibility of the original OBJ 1 and the significance of the new preliminary results for OBJ 2.

Results:
a. New reaction pathway of metal oxides and fluorides were discovered which significantly improved the fundamental knowledge of these materials’ reaction mechanisms as electrode materials.
b. Two publications are in the revision, with one additional publication in preparation.
c. New methodology to study heterogeneous electrode reaction was developed, which requires no a priori knowledge of the number and the nature of various phases within the mixture.
d. The study was based on high-quality data obtained from awarded beamtime in synchrotron facilities.

Exploitation and dissmination:
The fellow has attended a series of conferences in fields of crystallography and batteries to present his work and results, including: Winter crystallography 2018, International Battery Association 2019, and European Crystallography Meeting 2019. He has also been invited to give seminars at Complutense University of Madrid 2019 and Shanghai Jiaotong University 2020. Two publications are in revision, one publication is still in preparation. EU funding through MSCA action are acknowledged in all his presentation and publication.
The fellow has significantly strengthened his analytical skill and fundamental knowledge in the local structure study of materials with complex structures. Using this skill, a variety of analytical methods including Monte Carlo (MC) simulation and non-negative matrix factorisation (NMF) were developed (with the support of Prof Andrew Goodwin’s group). These methods constituted the key diagnostic tool to study the complex crystal structure involved in the phase behaviours of the measured metal oxides, which has the potential to become a very important tool to study complex electrode materials in the future.

The significance of the research achievements in this fellowship is reflected by the influence of the renewed understanding of the functionality of binary metal oxides and fluorides on the battery community. These materials are commonly perceived as “conversion” materials and are therefore believed to have intrinsically slow kinetic performance. However, the new mechanistic understanding of these materials shows that their kinetic performance can be theoretically improved. This result would promote renewed interests from researchers to revisit these cost-effective materials for future battery application, and eventually to enhance their energy capacity for practical use. 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.