UBC Theses and Dissertations
Li-La-Zr-O electrolytes for all-solid-state Li-ion batteries by solution/suspension plasma spray Koresh, Ido
All-solid-state Li-ion batteries (LIB) have been drawing growing attention among the scientific and industrial communities as they offer superior properties over the state-of-the-art liquid-electrolyte based LIB. The Li garnet-type oxides Li₇La₃Zr₂O₁₂ and amorphous Li-La-Zr-O (a-LLZO) are promising solid-state electrolytes (SSE) for all-solid-state LIB. There are several knowledge gaps related to this relatively new class of SSE that are yet to be explored. In this work, we investigated a novel approach to prepare thick films (about 10 to 60 µm thick) of this class of SSE by a solution/suspension plasma spray (SSPS) process. The SSPS process is an emerging thick films (10-500 µm) deposition technology. It offers several advantages that make it a promising low-cost, rapid and robust SSE production method. We studied how process parameters affect the film’s phase composition, Li number density and microstructure, which in turn alter the film’s Li-ion conductivity. The SSPS flexibility enabled us to study the Li-ion transport properties of amorphous Li-La-Zr-Nb-O (a-LLZNO) based thick films. The process was manipulated to alter a-LLZNO content in the films. The films that contained mostly a-LLZNO (~76 wt%) exhibited significantly different properties vs. mostly (~55 wt%) cubic Li₆.₇₅La₃Zr₁.₇₅Nb₀.₂₅O₁₂ (c-LLZNbO). The latter showed Li-ion conductivity of 4.1•10⁻⁵ S cm⁻¹ at 20 °C and activation energy of 0.49 eV. As the a-LLZNO became the main phase the transport properties shifted. The Li-ion conductivity decreased by a few orders of magnitude and the activation energy raised by 47 %. The conductivity spectra for these films showed a Jonscher power law behavior that was followed by superlinear power law behavior with a dimensionless exponent that was around 1.65. These behaviors were not observed for the c-LLZNbO based films and have not been reported earlier for a-LLZNO/a-LLZO phases. To improve the SSPS films’ Li-ion conductivity the c-LLZNbO stabilization process was investigated through post-deposition thermal treatment. We found that the process comprises two main transformations: a-LLZNO crystallization and La₂Zr₂O₇ to c-LLZNbO transformation that showed a large rate difference. Films that were treated at 700 °C for 2 h exhibited pure c-LLZNbO but the treatments also promoted significant microstructural changes that increased the films’ resistance.
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