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Bragg Coherent Diffractive Imaging of Energy Storage and Conversion Materials

  • Author(s): Cela, Devin
  • Advisor(s): Shpyrko, Oleg G
  • et al.
Abstract

Nanoscale disorder plays an essential role in guiding material properties which promise to solve many global challenge. Two such challenges are renewable energy generation and storage. Among lithium-ion batteries, lithium rich layered oxides (LRLO) are one of the most promising class of cathode materials, delivering more than 50% capacity over leading commercial battery cathodes. In solar cells, a class of absorbers called hybrid organic-inorganic perovskites promise printable solar cells as efficient as the best silicon-wafer cells and at a fraction of the cost. A variety of challenges at the nanoscale, however, prevent the rapid commercialization of either. With imaging techniques limited in terms of sample environments, averaging over large ensembles of particles, or lacking adequate spatiotemporal resolution for studying the relevant physical processes, characterization has also remained a challenge. The majority of this thesis is on the use of operando Bragg coherent diffractive imaging (BCDI) for energy storage and conversion materials. Some figures and analysis also make use of traditional X-ray diffraction, ”ensemble” X-ray diffraction, density functional theory (DFT), and X-ray photon correlation spectroscopy (XPCS). I show that in LRLO cathodes there is a striking three-fold rotational symmetry of the displacement field, with this effect drastically reduced or eliminated in two compositions of classically layered oxides (CLO), respectively, as well as varying during the charge/discharge process. This finding illuminates the effects of surface strain on the bulk cathode physical structure, and thus its effect on the overall battery performance. I show that different annealing conditions of one CLO chemistry (called NCA) have counter-intuitive effects on the overall strain energy landscape and dislocation density. I also discuss measurements of different solar cell absorbers and the challenges they pose for BCDI. Lastly, I provide an experience-based guide for preparing these different classes of materials for measurement, and how to minimize X-ray beam damage.

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