Microstructural evolution and electrochemical performance of vanadium based nanostructured cathodes

Sarbada, Venkata Siva Varun
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Hull, Robert, 1959-
Watson, Bruce
Duquette, David J.
Chakrapani, Vidhya
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Materials engineering
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First, thermal annealing experiments are carried out to understand the crystallization process of amorphous films deposited from LiV3O8 targets as a function of annealing atmosphere (vacuum, Ar and O2), temperature and film thickness to optimize processing conditions for crystallizing stoichiometric LiV3O8 thin films. In ultra-thin films (c.50-150 nm), depending on the annealing atmosphere and temperature, delithiated phases such as V2O5, V2O3 and VO2 are generated, but not the desired LiV3O8 stoichiometry. Li depth composition profiles using Nuclear Reaction Analysis (NRA) indicate that the Li losses from these thin films are due to Li diffusion into the substrate and/or surface losses of volatile oxide., limiting the ability to maintain the Li concentration required for forming desired/expected Li-V-O phases (in this case LiV3O8) intended for battery applications. X-ray diffraction, NRA, focused ion beam (FIB) and transmission electron microscope (TEM) analysis show that thicker Li-V-O films (1.3 μm) do form the LiV3O8 phase within the interior of the film upon annealing in an Ar environment (~300°C, 30 mins), but formed the Li-deficient Li0.3V2O5 phase at the film surface. When the crystallization experiments are carried out inside the TEM to understand the microstructural evolution, electron-beam irradiation is also observed to alter the crystallization process, forming reduced vanadium oxides- VO2, V4O7 and V2O3. This is determined to be due to accelerated removal of lithium by knock-on damage and oxygen by electron-stimulated desorption caused by an interatomic auger decay.
August 2019
School of Engineering
Dept. of Materials Science and Engineering
Rensselaer Polytechnic Institute, Troy, NY
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