The research in storage and conversion of energy is an everlasting process. The use of fuel cells is very tempting but up to now there are still several conceptual challenges to overcome. Especially, the requirement of liquid water causes difficulties due to the temperature limit. Therefore, imidazoles and triazoles are increasingly investigated in a manifold of experimental and theoretical publications as they are both very promising in overcoming this problem. Recently, triazoles were found to be superior to imidazoles in proton conduction. An ab-initio molecular dynamics simulation of pure triazole phases for investigating the behavior of both tautomer species of the triazole molecule has never been done. In this work, we investigate the structural and dynamical properties of two different solid phases and the liquid phase at two different temperatures. We are able to show how the distinct tautomers contribute to the mechanism of proton conduction, to compute dynamical properties of the four systems and to suggest a mechanism of reorientation in solid phase.

Abstract:We analyse the initial stages of cluster formation of polyphilic additive molecules which are solvated in a dipalmitoylphosphatidylcholine (DPPC) lipid bilayer. Our polyphilic molecules comprise an aromatic (trans-bilayer) core domain with (out-of-bilayer) glycerol terminations, complemented with a fluorophilic and an alkyl side chain, both of which are confined within the aliphatic segment of the bilayer. Large-scale molecular dynamics simulations (1 µs total duration) of a set of six of such polyphilic additives reveal the initial steps towards supramolecular aggregation induced by the specific philicity properties of the molecules. For our intermediate system size of six polyphiles, the transient but recurrent formation of a trimer is observed on a characteristic timescale of about 100 ns. The alkane/perfluoroalkane side chains show a very distinct conformational distribution inside the bilayer thanks to their different philicity, despite their identical anchoring in the trans-bilayer segment of the polyphile. The diffusive mobility of the polyphilic additives is about the same as that of the surrounding lipids, although it crosses both bilayer leaflets and tends to self-associate.

Abstract:We investigated the effect of fluorinated molecules on dipalmitoylphosphatidylcholine (DPPC) bilayers by force-field molecular dynamics simulations. In the first step, we developed all-atom force-field parameters for additive molecules in membranes to enable an accurate description of those systems. On the basis of this force field, we performed extensive simulations of various bilayer systems containing different additives. The additive molecules were chosen to be of different size and shape, and they included small molecules such as perfluorinated alcohols, but also more complex molecules. From these simulations, we investigated the structural and dynamic effects of the additives on the membrane properties, as well as the behavior of the additive molecules themselves. Our results are in good agreement with other theoretical and experimental studies, and they contribute to a microscopic understanding of interactions, which might be used to specifically tune membrane properties by additives in the future.

In recent years, lithium-ion batteries (LIBs) are widely used in electric vehicles (EVs) and mobile energy storage devices (ESDs), which has led to higher requirements for energy density. To fulfill these requirements, tremendous attention has been paid to design advanced LIBs with various silicon active materials as alternative negative electrodes to replace graphite (372 mAh g-1) due to their high theoretical gravimetric capacity (4200 mA h g-1).[1,2] However, silicon as potential anode material suffers from huge volume changes during charging and discharging and has a poor electronic conductivity which negatively impacts the long-term performance and prevents high silicon contents from practical application.[3] Additionally, an unstable crystalline silicon structure tends to pulverization during the (de)lithiation process.[4] To compensate the volume changes, alleviate pulverization and maintain high electronic conductivity, silicon-doped graphite composites with protecting coating layers are a promising approach. In this context, phosphazene compounds are investigated concerning their silicon protecting properties in silicon-doped graphite composites. In detail electrochemical performance measurements in pouch full-cells (NCM523||SiOx/C), supressing gas formation properties and post-mortem analyzes were carried out to characterize phosphazene compounds as additive materials. The introduction of the dual-additive approach in state-of-the-art electrolytes leads to synergistic effects between FEC and phosphazene compounds which accelerate the durability of silicon particles and results in enhanced electrochemical performance. Reference: [1]Zuo X, Zhu J, Muller‐Buschbaum P, Cheng Y, Silicon based lithium‐ion battery anodes: a chronicle perspective review, Nano Energy, 2017, 31, 113‐143. [2]Jimenez A. R., Klöpsch R., Wagner R., Rodehorst U. C., Kolek M., Nölle R., Winter M., Placke T., A step toward high-energy silicon-based thin film lithium ion batteries, ACS Nano, 2017, 11, 5, 4731-4744. [3] Berla A. L., Lee S. W., Ryu I., Cui Y., Nix W. D., Robustness of amorphous silicon during the initial lithiation/delithiation cycle, Journal of power sources, 2014, 258, 253-259. [4] Casimir A., Zhang H., Ogoke O., Amine J. C., Lu J., Wu G., Silicon-based anodes for lithium-ion batteries: Effectiveness of materials synthesis and electrode preparation, Nano Energy, 2016, 27, 359-376.