PhD Thesis Presentation: In situ synchrotron radiation investigation of charge compensation and phase evolution mechanisms in Li2FeSiO4 electrodes

PhD Candidate

Zachary Arthur

Abstract

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 [1]. 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 [2]. 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 [3]. 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 [4] 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 [5].

Examination Committee:

• Dr. Robert Wickham, Chair
• Dr. De-Tong Jiang, Advisor
• Dr. Paul Rowntree
• Dr. Dmitriy Soldatov
• Dr. Xueliang Sun, External Examiner (University of Western Ontario)
   

1. McBreen, J., The application of synchrotron techniques to the study of lithium-ion batteries. Journal of Solid State Electrochemistry, 2009. 13(7): p. 1051-1061.
2. 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.
3. 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.
4. Lu, X., et al., Rate-dependent phase transitions in Li2FeSiO4 cathode nanocrystals. Scientific Reports, 2015. 5: p. 8599.
5. 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.