Parks, Andrew2025-05-142025-05-142025-05-14http://hdl.handle.net/10393/50485https://doi.org/10.20381/ruor-31125Current liquid-based electrolytes face challenges meeting future energy storage demands due to safety issues and low volumetric energy density. Solid-state electrolytes (SSE) represent the next frontier of battery innovation, offering significant improvements in thermal and electrochemical stability while inhibiting risks such as dendrite formation and thermal runaway. Despite these advantages, SSEs show a lot of challenges hindering their widespread adoption. Garnet-type SSEs are not very robust, and polymer SSEs have low conductivity despite their good processability. Composite solid electrolytes (CSEs) containing both garnet fillers and polymer are a good compromise with good mechanical and greater conductive properties. However, CSEs introduce new complications, such as filler agglomeration and poor compatibility with the polymer matrix, often due to filler surface contaminants such as lithium carbonate. This study investigates the role played by the size, morphology and quantity of lithium lanthanum zirconia oxide (Li₇La₃Zr₂O₁₂, LLZO) garnet-based CSEs to improve their functionality and electrochemical performance. The effects of garnet morphology, particle size, and content were explored using advanced characterization techniques, including FTIR, XRD, SEM, TGA, DSC, as well as mechanical testing and electrochemical impedance spectroscopy to evaluate the structural, mechanical and ionic properties of these CSE. The results demonstrate that CSEs using optimized LLZO spherical filler achieved an ionic conductivity as high as 10⁻⁵ S/cm at room temperature and 10⁻⁴ at 60 °C, which meets the minimum requirement for battery operation. SEM analysis further revealed that spherical LLZO exhibits superior dispersion over the commercial counterparts. Furthermore, this thesis investigated the modification of the surface chemistry of LLZO through acid treatment to improve its compatibility with the polymer and LiFTSI, as well as improve the ionic conductivity of the CSE. Varying types and concentrations of acidic solutions have been used to remove carbonates and hydroxides from the LLZO's surface. Surface characterization techniques, such as XRD, FTIR, Raman and XPS, were employed to evaluate the effects of the acid treatments on the garnet's crystal structure and ability to remove unwanted contaminants. Notably, acid-washing solutions proved ineffective at eliminating Li₂CO₃. However, acid-washing did show some surface removal of Li₂CO₃ and caused no damage to the cubic phase of the garnet. These findings contribute to the advancement of solid-state batteries, paving the way for safer and more efficient energy storage solutions.enAttribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/Lithiun-Ion BatteriesSolid State BatteriesComposite Solid ElectrolyteLLZOThesis