Experimental and theoretical studies on low-temperature molten salts

In this dissertation, we investigate several kinds of electrolyte materials for battery application. The optimized structures and cation affinities of a series of zeolitic fragments that mimic the charge sites in polyelectrolytes are evaluated using ab initio molecular orbital methods. A polymer host with higher dielectric constant—poly(ethylene malonate) and the corresponding lithium salt complexes were prepared. The 8:1 mixture has the maximum ionic conductivity 1.6 × 10−6 S/cm at 25°C. The strong interaction between the cations and polymer host may stiffen the polymer backbone, lowering the resulting ionic conductivities.; The ambient temperature alkali glassy salt adduct 1:1 NaN(CN)₂/AlCl ₃ is an amorphous material with a glass transition at 27°C and the glassy state persists for four weeks at room temperature. The room temperature ionic conductivity of the 1:1 Na salt adduct is 6.6 × 10−6 S/cm and the conductivity curves follow the Vogel-Tammann-Fulcher (VTF) equation, suggesting that ion transport is coupled to local motion in the glassy salt mixture system.; Another low temperature molten salt system LiI/AlCl₃ exhibits different properties. The 1:1 LiI/AlCl₃ adduct melts at 75°C and the Raman spectrum implies that various haloaluminates exist in the system. At room temperature, the 1:1 adduct has the highest ionic conductivity 2 × 10−6 S/cm. Molecular Dynamics simulation results suggest that several haloaluminates appear in the 1:1 LiI/AlCl₃ system. Ab initio calculations on the species predicted by MD simulations are in reasonable agreement with Raman spectra data.; The 1:1 LiSCN/AlCl₃ adduct exhibits a glass transition temperature at −20°C and decent room temperature conductivity at 4 × 10 −4 S/cm. Neutron diffraction is used to investigate the 1:1 LiSCN/AlCl₃ adduct. The results demonstrate that the aluminum atom is surrounded by three chlorine atoms and a nitrogen atom, indicating the existence of the AlCl₃NCS− anion, in which the NCS− coordinates to the Al center through nitrogen. Molecular orbital calculations using ab initio methods are also performed to study the optimized structures of the AlCl₃NCS − and its isomer, AlCl₃SCN− and indicate that AlCl₃NCS− anion is the major species in the 1:1 LiSCN/AlCl₃ adduct.