Publikationen

Using low-melting-point electrolytes could overcome various key challenges of low-cost sodium-based liquid metal batteries (Na-LMBs), e.g. high rates of self-discharge and degradation of structural materials, by lowering their operating temperatures. Molten halide salts are considered promising electrolyte candidates for Na-LMBs due to their high stability and electrical conductivity. In this work, thermodynamic simulation via FactSageTM and thermal analysis via e.g. Differential Scanning Calorimeter (DSC) were carried out to explore the NaI-LiI-KI system, since it could be a promising electrolyte for Na-LMBs due to its low melting point and Na solubility. The results show that the eutectic NaI-LiI-KI performs as a pseudo-binary salt with a melting point of ˜290 &ring;C. In this pseudo-binary salt, the solubility of NaI in the eutectic LiI-KI is ˜7 mol%. Using the eutectic NaI-LiI-KI electrolyte, Na-LMBs could be operated at < 350 &ring;C. Moreover, the Na solubility and Na+ conductivity of the eutectic NaI-LiI-KI electrolyte, which are vital to the battery performance, were estimated by calculation based on the literature data. Additionally, its applicability and economy were also discussed based on cost pre-analysis of salt materials, salt treatment and structural materials regarding salt corrosivity.

Electrochemical co-deposition of gallium and titanium on copper and gold substrates from the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate was investigated in the temperature range from 25 &ring;C to 140 &ring;C. Crystalline gallium-titanium alloys were obtained by annealing the deposits at 800 &ring;C for 16 h. X-ray diffraction performed on the annealed specimens confirmed the formation of crystalline phases. In situ quartz crystal microbalance experiments gave further insight into the initial stages of gallium-titanium co-deposition. One can tune the composition of the films by changing the deposition potential or the deposition technique. Gallium rich films with more than 60 wt% were obtained by potentiostatic depositions at 140 &ring;C. We could show that no elemental titanium can be electrodeposited from bis(cyclopentadienyl)titanium(IV) bis(trifluoromethanesulfonate) in 1-butyl-1-methyl- pyrrolidinium trifluoromethanesulfonate. The addition of GaCl 3 to the electrolyte facilitated the reduction of Ti(IV) species.

Planning the design and discussing the results are routine tasks carried out daily by researchers all over the world. This study is focused on making these stages of research time- and cost-efficient without affecting the reliability of the data. Following the principles of the Taguchi method brings such a result. This approach ensures the quality of research by optimisation of the experimental procedure. In the presented work, the Taguchi method solves an exemplary research problem of the corrosion process of aluminium current collector in lithium-ion batteries. Operating factors selected for the optimisation include temperature (25, 35, 45&ring;C), the volume ratio of ethylene carbonate to diethyl carbonate in the solvent (1:1, 1:2, 1:4), and type of lithium salt (LiPF6, LiTFSI, LiBOB). Using three operating factors with three levels of variability requires data assembly in an orthogonal array L9 with nine experimental runs in total. In this study, the Taguchi approach is validated by performing a full-factorial procedure of twenty-seven individual experiments. The response of tested systems is analysed by cyclic voltammetry and electrochemical impedance spectroscopy, which enables the evaluation of corrosion parameters in each experimental run. The assessed parameters indicate the intensity of the aluminium corrosion depending on the operating conditions. These conditions cause unwanted variance, which accelerates corrosion and lowers the life expectancy of lithium-ion batteries. The Taguchi signal-to-noise-ratio analysis reveals that the most significant variation is caused by the lithium salt in the electrolyte (S/N LiBOB ≥ LiPF6 > LiTFSI). Temperature and alkyl carbonates play a secondary role. The Taguchi prediction method is also consistent with the full-factorial approach, which warrants reliability.