چكيده لاتين
Lithium-ion batteries, despite advantages such as high energy density, face serious safety problems due to their flammable and volatile organic electrolytes. Ionic liquids have been introduced as safer alternatives with thermal stability and a wide voltage window, but their high viscosity limits their pure application. A practical solution is the addition of controlled amounts of ionic liquids to conventional electrolytes. This method transfers the positive properties of ionic liquids to the battery by improving thermal stability, reducing the risk of combustion, and expanding the voltage window, without the viscosity problem disrupting its performance. Consequently, this approach establishes a balance between safety and efficiency and provides a path for the development of safer and more efficient lithium-ion batteries. In this thesis, the primary objective is to identify suitable ionic liquids as additives in lithium-ion battery electrolytes. For this purpose, selected combinations of ionic liquids were studied using Density Functional Theory (DFT) calculations to determine their HOMO and LUMO energy levels. In the experimental section, various ionic liquids were synthesized based on theoretical foundations and were identified and confirmed through tests such as infrared spectroscopy, nuclear magnetic resonance, thermogravimetric analysis, and X-ray diffraction. Furthermore, to achieve novel ionic liquid compounds, LiBOB and NaBOB salts were successfully synthesized and characterized. The ionic liquids BmimHSO4, BmimPF6, BmimBr, BmimBOB, HNMP-HSO4, HNMP-H2PO4, 1,3di BmimBr, 1,3 di BmimBOB, and the deep eutectic solvents LiNO3-EG and LiNO3-Gly were synthesized and/or investigated in this research.The synthesized ionic liquids were examined using LSV and EIS electrochemical tests to determine their working potential window, their conditions of use as an additive or as an electrolyte, and their conductivity under different applied voltage conditions. Furthermore, the validity of the EIS data was assessed using the Kramers-Kronig test. Among the synthesized ionic liquids, BmimPF6 and 1,3 di BmimBOB, due to their large potential window, can be used as the electrolyte for lithium-ion batteries. Also, other ionic liquids such as BmimHSO4 are oxidized or reduced sooner than common electrolyte solvents, which allows them to be incorporated into the SEI and CEI layers and improve these layers.
