Abstract:
For large-scale application of lithium-ion batteries in electric vehicles and grid-scale storage, it has been of great interest to develop cost-effective hydrothermal/solvothermal synthesis methods for preparing high-energy electrodes. But solution-based reactions are mostly carried out in a sealed autoclave and therefore the reactor is a black box - the inputs and outputs are known, but little is known about intermediate phases and reaction pathways. Real-time probing of synthesis reactions can provide the details of reaction process, elucidating intermediate phases and how temperature, pressure, time and the precursor concentration affect the reaction pathways, and eventually the final product. To this end, new in-situ reactors and relevant techniques have been developed and applied for studying solvothermal synthesis of high-energy cathodes, olivines (LiFexMn1-xPO4), copper vanadates (Cu-V-O), and V-based phosphates (Li-V-PO4), using time-resolved synchrotron X-ray diffraction (XRD). Quantitative analysis of XRD patterns was performed via a rigorous Rietveld refinement procedure to extract the structural parameters, such as lattice constants, bond lengths and effective coordination numbers of crystalline phases, and their evolution as a function of reaction time and temperature. In addition, structural and electrochemical characterization were performed, via XRD, XAS and TEM-EELS, for gaining insights into lithium reaction mechanisms and possible limitations to the cycling stability of the synthesized electrodes. We show the development of in-situ methods provides access to a wide range of solvothermal synthesis reactions, and in a combination with structure-property characterization of synthesized materials, eventually enables rational design and synthesis of battery electrodes of desired phases and material properties.
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