Matthias Busse

This article examines contacting by means of ultrasonic welding between a cast aluminum winding and a copper conductor of a wheel hub drive for a passenger car. The effect of thermal stress on the formation and growth of intermetallic phases (IMC) in the contact is analyzed. By using microscopy, the growth constant under the specific load conditions can be identified with the help of the parabolic time law and offer a possibility for predicting the service life of the corresponding contacts. As a result, it can be stated that the increase in electrical resistance of the present contact at load temperatures of 120 °C, 150 °C, and 180 °C does not reach a critical value. The growth rates of the IMC also show no critical tendencies at the usual operating temperatures (120 °C and 150 °C, e.g., at 150 °C = 4.59 × 10⁻⁷ μm²/s). The activation energy calculated using the Arrhenius plot of 155 kJ/mol (1.61 eV) can be classified as high in comparison to similar studies. In addition, it was found that future investigations of the IMC growth of corresponding electrical contacts should rather be carried out with electric current. The 180 °C sample series were carried out in the oven and with electric current; the samples in the oven did not show clear IMC, while the samples exposed to electric current already showed IMC under the microscope.

For all-solid-state batteries, the particle size distribution of the solid electrolyte is a critical factor. Small particles are preferred to obtain a high active mass loading of cathode active material and a small porosity in composite cathodes. In this work, the influence of the solid fraction in the wet-chemical synthesis of β-Li₃PS₄ in tetrahydrofuran (THF) is investigated. The solid fraction is varied between 50 and 200 mg/mL, and the obtained samples are evaluated using X-ray diffraction, SEM and electrochemical impedance measurements. The sizes of the resulting particles show a significant dependency on the solid fraction, while a good ionic conductivity is maintained. For the highest concentration, the particle sizes do not exceed 10 µm, but for the lowest concentration, particles up to ~73 µm can be found. The ionic conductivities at room temperature are determined to be 0.63 ± 0.01 × 10⁻⁴ S/cm and 0.78 ± 0.01 × 10⁻⁴ S/cm for the highest and lowest concentrations, respectively. These findings lead to an improvement towards the production of tailored sulfide solid electrolytes.

New energy systems such as all-solid-state battery (ASSB) technology are becoming increasingly important today. Recently, researchers have been investigating the transition from the lab-scale production of ASSB components to a larger scale. Poly(ethylene oxide) (PEO) is a promising candidate for the large-scale production of polymer-based solid electrolytes (SPEs) because it offers many processing options. Hence, in this work, the thermal processing route for a PEO-Lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) SPE in the ratio of 20:1 (EO:Li) is investigated using kneading experiments. Here, we clearly show the sensitivity of PEO during thermal processing, especially for high-molecular-weight PEO (M_w = 600,000 g mol⁻¹). LiTFSI acts as a plasticizer for low-molecular-weight PEO (M_w = 100,000 g mol⁻¹), while it amplifies the degradation of high-molecular-weight PEO. Further, LiTFSI affects the thermal properties of PEO and its crystallinity. This leads to a higher chain mobility in the polymer matrix, which improves the flowability. In addition, the spherulite size of the produced PEO electrolytes differs from the molecular weight. This work demonstrates that low-molecular-weight PEO is more suitable for thermal processing as a solid electrolyte due to the process stability. High-molecular-weight PEO, especially, is strongly influenced by the process settings and LiTFSI.

Metal foam inserts are known for their high potential for weight and vibration reduction in composite gear wheels. However, most metal foams do not meet the strength requirements mandatory for the transfer of sufficiently high levels of torque by the gears. Syntactic iron and steel foams offer higher strength levels than conventional two-phase metal foams, thus making them optimum candidates for such inserts. The present study investigates to what extent surface hardening treatments commonly applied to gear wheels can improve the mechanical properties of iron-based syntactic foams. Experiments performed thus focus on case hardening treatments based on carburizing and carbonitriding, with subsequent quenching and tempering to achieve surface hardening effects. Production of samples relied on the powder metallurgical metal injection molding (MIM) process. Syntactic iron foams containing 10 wt.% of S60HS hollow glass microspheres were compared to reference materials without such filler. Following heat treatments, the samples’ microstructure was evaluated metallographically; mechanical properties were determined via hardness measurements on reference samples and 4-point bending tests, on both reference and syntactic foam materials. The data obtained show that case hardening can indeed improve the mechanical performance of syntactic iron foams by inducing the formation of a hardened surface layer. Moreover, the investigation indicates that the respective thermo-chemical treatments can be applied to composite gear wheels in exactly the same way as to monolithic ones. In the surface region modified by the treatment, martensitic microstructures were observed, and as consequence, the bending limits of syntactic foam samples were increased by a factor of three.

The joining of plastic-based fiber composites and light metals is increasingly becoming the focus of lightweight construction applications. To date, conventional mechanical and adhesive joining techniques are still the predominant means to produce hybrid composites. The aim of this work was to create a hybrid composite of CFRP and aluminum in a novel way using the economic high-pressure die-casting process without the use of additional joining elements. The casting process implies the direct contact of molten metal (AlSi10MnMg) and thermally resistant polyetheretherketone (PEEK) under short-term temperatures of about 700 °C. The material and process parameters lead to a material transition that spatially separates the CFRP and the aluminum while guaranteeing a firm bond with lap shear strengths up to 22 MPa. This work structurally and chemically characterizes the interface between Al and PEEK in the hybrid composite. The results of the TEM investigations into the boundary region between PEEK and the AlSi10MnMg alloy show that both materials are locally joined without gaps. Furthermore, the chemical EDX, XPS and IR spectroscopy results indicate a tendency for the bond to form through the thermal alteration of the polymer and the associated modification of the bonding possibilities in the direct contact area.

Mechanical and electrochemical stability are key issues for large-scale production of solid state Li-ion batteries. Polymer electrolytes can provide good ionic conductivity, but mechanical strength needs to be improved. In this study, we investigate the correlation of mechanical and electrical properties of poly (ethylene oxide) (PEO)-based solid electrolytes for Li-ion batteries. The influence of alumina and LiClO₄ addition are investigated. Differential scanning calorimetry (DSC) is used to study the thermal behavior of salt-free and salt-containing samples and to identify the melting temperature. Dynamic mechanical analysis reveals the elastic properties as a function of temperature. Electrochemical properties are investigated using impedance spectroscopy. It is found that addition of alumina increases mechanical strength, while LiClO₄ decreases it. Addition of LiClO₄ and Al₂O₃ increases ionic conductivity and improves mechanical properties. However, there is no overlapping window of high mechanical strength and high ionic conductivity.

A LiMn₂O₄ (LMO) containing three-dimensional composite cathode was prepared by impregnation of carbon fiber paper with the oxide precursor sol. The sol consisted of the corresponding metal acetates, instead of nitrates in order to prevent the evolution of nitrous gases during the calcination. Poly(vinylpyrrolidone) served as chelating agent, which allows for a homogeneous distribution of the metal ions in the sol. Carbon fiber paper was soaked with the precursor sol and dried repeatedly up to the desired filling grade. After gelation of the precursor sol, the gel was converted to LMO at 450°C. At this temperature transformation of the amorphous gel into crystalline LMO was completed and in the same time it was possible to retain the carbon backbone without significant material damage. The carbon fiber matrix serves as the three-dimensional support for the LMO particles and current collector in the oxide/carbon composite. Microstructural characterization of the LMO/carbon composites revealed that LMO crystals were deposited directly onto the carbon fibers as well as in the voids between the fibers which results in a homogeneous distribution of active material throughout the cathode's bulk. Electrochemical properties of the composite cathodes were investigated as a function of the number of sol impregnation steps. It was noted that the specific capacity of the cathode increases with the number of fillings. Moreover, the irreversible capacity regarding the first charge/discharge cycles was greatly reduced. As proof-of-concept a lithium-ion battery cell containing dry solid polymer electrolyte was assembled and its electrochemical performance was evaluated for future solid-state battery application.

Integration of sensors into various kinds of products and machines provides access to in-depth usage information as basis for product optimization. Presently, this large potential for more user-friendly and efficient products is not being realized because (a) sensor integration and thus usage information is not available on a large scale and (b) product optimization requires considerable efforts in terms of manpower and adaptation of production equipment. However, with the advent of cloud-based services and highly flexible additive manufacturing techniques, these obstacles are currently crumbling away at rapid pace. The present study explores the state of the art in gathering and evaluating product usage and life cycle data, additive manufacturing and sensor integration, automated design and cloud-based services in manufacturing. By joining and extrapolating development trends in these areas, it delimits the foundations of a manufacturing concept that will allow continuous and economically viable product optimization on a general, user group or individual user level. This projection is checked against three different application scenarios, each of which stresses different aspects of the underlying holistic concept. The following discussion identifies critical issues and research needs by adopting the relevant stakeholder perspectives.