The application of Synchrotron Radiation (SR) based techniques in the field of electrochemistry has been facilitated with the development of in situ or in operando experimental methods using reliable, consumable, x-ray transparent windows (e.g. Kapton, Mylar, Graphene and Silicon Nitride). Specifically, the two most popular SR approaches used for in situ electrochemical studies are: (1) x-ray absorption spectroscopy (XAS), which is used to infer oxidation state, ligand coordination and bond lengths; and (2) x-ray diffraction (XRD), which is used to probe long range crystallographic structure . To this end, a combined experimental setup capable of near simultaneous XRD & XANES measurements has been constructed at 06ID-1 at the Canadian Light Source for high throughput in situ studies of secondary batteries . To affirm the utility of this experimental setup one promising cathode material is Li2FeSiO4 (LFS), desirable for its low cost and high theoretical capacity (330mAh/g), was selected for characterization of structure-function relationships that define electrochemical performance. The ionic conduction and transport mechanisms of this material were previously not well understood, and have been elucidated using a combined XRD & XANES approach.
I begin by detailing the experimental setup, including ray-tracing and optical considerations for performing near simultaneous scattering and absorption experiments. This experimental setup is used to further understand the physicochemical behaviour of LFS; the validity of a solid-solution model is explored to describe the (de)intercalation processes in a mixed phase LFS cathode material using post-mortem samples . It is found that for the formation cycle, this process does indeed follow a solid-solution behaviour, but that phase instabilities lead to a more two-phase behaviour following repeated cycling. A fine-grained study of the 1 Li extraction process has was performed, and the charging rate-dependent performance of LFS  is understood to originate from varied crystal phase stabilities among different charging kinetics. During the aforementioned in situ studies, a subsequent phenomenon involving the spontaneous formation of a surface electrolyte interphase layer is identified, as well its apparent removal upon cycling is described .
- Dr. Robert Wickham, Chair Dr.
- De-Tong Jiang, Advisor
- Dr. Paul Rowntree
- Dr. Dmitriy Soldatov
- Dr. Xueliang Sun, External Examiner (University of Western Ontario)
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- Arthur, Z., et al., In situ XANES & XRD Study of interphasial reaction between uncharged Li 2 FeSiO 4 cathode and LiPF 6 -based electrolyte. Journal of Physics: Conference Series, 2016. 712(1): p. 012124.
- Lu, X., et al., Li-ion storage dynamics in metastable nanostructured Li2FeSiO4 cathode: Antisite-induced phase transition and lattice oxygen participation. Journal of Power Sources, 2016. 329: p. 355-363.
- Lu, X., et al., Rate-dependent phase transitions in Li2FeSiO4 cathode nanocrystals. Scientific Reports, 2015. 5: p. 8599.
- Arthur, Z., et al., Spontaneous reaction between an uncharged lithium iron silicate cathode and a LiPF6-based electrolyte. Chemical Communications, 2016. 52(1): p. 190-193.