Anton Bruckner; eine Monographie von Hans Tessmer.

"Bibliographie" : p. [129]-141

New Insights into the Behavior of Polycarbonate-Based Lithium Salt Containing Electrolytes Regarding Thermal Long-Term and Electrochemical Stability

For lithium ion batteries solid-state electrolytes like polymers gained more and more attention in the last years, especially due to safety reasons. Polyethylene oxide (PEO) based systems are still state of the art. One of its major drawbacks is the highly crystalline structure, which inhibits fast migration of lithium ions and results in a low transference number and low conductivity [1]. Recently, polycarbonate based polymer electrolytes gained some interest [2,3]. Polycarbonates were assumed to show weaker ion-dipole interactions in contrast to PEO, given rise to higher transference numbers [2]. With suitable additives and high salt concentrations, higher ionic conductivities were reported at moderate temperatures (>60 °C) [3].Nevertheless, there is still a lack of knowledge concerning long-term performance of the polycarbonate-salt-mixtures as electrolytes in terms of thermal stability in the temperature range of solid-state batteries. Therefore, we prepared lithium salt containing polycarbonate samples using either solution casting with additional removal of the solvent or the hot press method. We examined the behavior of polycarbonate salt mixtures over a period of time at given temperatures. Investigation methods such as differential scanning calorimetry (DSC), nuclear magnetic resonance spectroscopy (NMR) and electrochemical impedance spectroscopy (EIS) were used. The results of the experiments indicate that e. g. the mixture LiTFSI in polyethylene carbonate (PEC) suffers from a salt catalyzed decomposition for longer times whereas polypropylene carbonate (PPC) is stable.Furthermore, candidates with good thermal long-term stability (e. g. PPC/LiTFSI) were analyzed concerning their ionic conductivity and their electrochemical stability window. If necessary, improvements were made to increase the electrochemical stability (e. g. down to lithium stripping / plating) or the conductivity by use of different additives, e.g. plasticizers and SEI additives

Melt Electrowriting of Amphiphilic Physically Crosslinked Segmented Copolymers

Various (AB)$_{n}$ and (ABAC)$_{n}$ segmented copolymers with hydrophilic and hydrophobic segments are processed via melt electrowriting (MEW). Two different (AB)$_{n}$ segmented copolymers composed of bisurea segments and hydrophobic poly(dimethyl siloxane) (PDMS) or hydrophilic poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEG-PPO) segments, while the amphiphilic (ABAC)$_{n}$ segmented copolymers consist of bisurea segments in the combination of hydrophobic PDMS segments and hydrophilic PPO-PEG-PPO segments with different ratios, are explored. All copolymer compositions are processed using the same conditions, including nozzle temperature, applied voltage, and collector distance, while changes in applied pressure and collector speed altered the fiber diameter in the range of 7 and 60 µm. All copolymers showed excellent processability with MEW, well-controlled fiber stacking, and inter-layer bonding. Notably, the surfaces of all four copolymer fibers are very smooth when visualized using scanning electron microscopy. However, the fibers show different roughness demonstrated with atomic force microscopy. The non-cytotoxic copolymers increased L929 fibroblast attachment with increasing PDMS content while the different copolymer compositions result in a spectrum of physical properties