Alexander Michaelis’s research while affiliated with Technische Universität Dresden and other places

WC-Ni hardmetals, especially with the addition of Cr, are the first choice for wear parts in a corrosive environment. Despite Ni being studied as a metallic binder matrix in hardmetals for as long as Co, the mechanical properties achieved have consistently fallen behind those of their cobalt-containing counterparts. Due to the rapidly increasing demand for Co, its substitution is of increasing importance. In this study, various alloying elements that do not form strong carbides were systematically investigated as part of a binary Ni-based binder system for hardmetals. Solid and liquid phase sintering were compared by using field assisted sintering and a conventional SinterHIP furnace. The obtained hardmetals were analysed in terms of their microstructure, phases, sintering behaviour, and mechanical properties. The metals manganese, iron, and copper, as well as the metalloids silicon and germanium, were evaluated as additional binder constituents. Hardmetals with a binary Ni-based binder alloy were successfully prepared. The combination with Mn or Si showed the potential to significantly lower the necessary sintering temperature. In particular, Mn proved to be the most effective grain growth inhibitor among the investigated alloying elements.

Zero‐excess sodium metal solid‐state batteries offer improved safety, lower cost, higher energy density, and reduced resource dependency compared to today's lithium‐ion technology. This study demonstrates the fabrication of zero‐excess electrodes with unprecedented stability during plating/stripping cycles. The fabrication process involves the sputter deposition of 20 nm metallic seed layers – zinc, silver, indium, or tin – onto NASICON (Na3.4Zr2Si2.4P0.6O12) ceramic separators, followed by the sputter deposition of a 30 μm copper current collector. The favorable influence of these seed layers on the in‐situ formation of the sodium|NASICON interface is examined through nucleation and cycling experiments, with a sodium metal reservoir serving as the non‐limiting counter electrode. Due to alloy formation the seed layers – particularly tin – stabilize sodium nucleation and cycling substantially and reduce dendrite formation compared to reference cells with bare copper current collectors. Sodium loss during cycling is primarily attributed to local cracking of the current collector and its partial delamination from the NASICON. Compared to polished NASICON, a roughened surface reduces the resistance e. g. of the counter electrode 200‐fold to approx. 1 Ωcm² at 3 MPa and suppresses delamination further.

Binder Jetting (BJT), a powder-based additive manufacturing technology, has been shown to be a fast and reproducible green shaping process for many different metals. Due to its high productivity and versatility in material processing, BJT is gaining increasing importance in the manufacturing sector. It can also be used for the production of WC-Co hardmetals, a primary ceramic-based composite often used for tools and wear parts. Five different BJT printers from four different manufacturers were evaluated to assess their effectiveness and feasibility in producing hardmetals based on the same WC-12 wt.% Co starting powders. The analysis focused on comparing the properties of the resulting hardmetals, as well as evaluating the printing performance. The results show that all tested BJT printers are fundamentally well suited for producing green hardmetal parts, which can achieve full density after sintering. This work highlights the potential of BJT technology in hardmetal manufacturing for tool production.

Cathode formulation, which describes the amount of cathode active material (CAM), conductive additives (CAs), and binder within a cathode compound, is decisive for the performance metrics of lithium-ion battery (LIB) cells. The direct measurement of electronic resistance can be an enabler for more time- and cost-efficient cathode formulation improvements. Within this work, we correlate the electronic resistance with the electrochemical performance of cathodes. Two different high Nickel NCM cathode materials and numerous CAs are used to validate the findings. A detailed look into the resistance reduction potential of carbon black (CB) and single-walled carbon nanotubes (SWCNT) and their mixtures is made. Finally, an impact estimation of cathode formulation changes on LIB key performance factors, such as energy density and cost, is shown.

The introduction of the European Green Deal has triggered various legislative projects that will require product manufacturers inside and outside the European Union (EU) to ensure compliance with the new regulatory framework. As this is a complex task we present a methodology that manufacturers can use to derive a strategic focus for future product development to fully comply with and prioritise regulatory requirements. Further, the method helps to assess the difficulty of achieving compliance. A case study is employed to examine the applicability of the methodology to the EU Battery Regulation. Consequently, the extent to which a currently available battery would comply with the 121 requirements was investigated. The method revealed a number of hot spots requiring immediate action. It therefore helps stakeholders to identify key issues that need to be addressed in future battery development and to classify them according to their importance.

Increasing the specific capacity and rate performance of thiophosphate composite cathodes is a major challenge in solid-state battery development. Understanding the charge transport kinetics and rate-limiting mechanisms within the cathode is key towards efficient optimization. Herein, we use quantitative analysis of chronoamperometric rate performance data to differentiate between resistive and diffusive rate limitations of NCM811—Li6PS5Cl cathodes with different morphology and composition. We substantiate our findings with separate measurements of the effective ionic conductivity and Li⁺ diffusion coefficients using impedance spectroscopy and GITT techniques, respectively. Increasing the active material to solid electrolyte ratio is found to increase diffusive limitations, which originate from the small contact area between the active material and solid electrolyte. The diffusive limitation is especially pronounced for single crystal NCM811 cathodes at over 84% AM. Employing fine particle catholyte significantly increases the contact area, alleviates the diffusive limitation, and increases rate performance. These results provide guidelines towards bringing the solid-state battery performance levels closer to practical targets.

The automotive industry aims for the highest possible driving range (highest energy density) in combination with a fast charge ability (highest power density) of electric vehicles. With both targets being intrinsically contradictory, it is important to understand and optimize resistances within lithium-ion battery (LIB) electrodes. In this study, the properties and magnitude of electronic resistance contributions in LiMn0.7Fe0.3PO4 (LMFP)- and LiNixCoyMnzO2 (NCM, x = 0.88~0.90, x + y + z = 1)-based electrodes are comprehensively investigated through the use of different measurement methods. Contact resistance properties are characterized via electrochemical impedance spectroscopy (EIS) on the example of LMFP cathodes. The EIS results are compared to a two-point probe as well as to the results obtained using a novel commercial 46-point probe system. The magnitude and ratio of contact resistance and compound electronic resistance for LMFP- and NCM-based cathodes are discussed on the basis of the 46-point probe measurement results. The results show that the 46-point probe yields significantly lower resistance values than those in EIS studies. Further results show that electronic resistance values in cathodes can vary over several orders of magnitude. Various influence parameters such as electrode porosity, type of current collector and the impact of solvent soaking on electronic resistance are investigated.

Li-In electrodes are widely applied as counter electrodes in fundamental research on Li-metal all-solid-state batteries. It is commonly assumed that the Li-In anode is not rate limiting, i.e. the measurement results are expected to be representative of the investigated electrode of interest. However, this assumption is rarely verified, and some counterexamples were recently demonstrated in literature. Herein, we fabricate Li-In anodes in three different ways and systematically evaluate the electrochemical properties in two- and three-electrode half-cells. The most common method of pressing Li and In metal sheets together during cell assembly resulted in poor homogeneity and low rate performance, which may result in data misinterpretation when applied for investigations on cathodic phenomena. The formation of a Li-poor region on the separator side of the anode is identified as a major kinetic bottleneck. An alternative fabrication of a Li-In powder anode resulted in no kinetic benefits. In contrast, preparing a composite from Li-In powder and sulfide electrolyte powder alleviated the kinetic limitation, resulted in superior rate performance, and minimized the impedance. The results emphasize the need to fabricate optimized Li-In anodes to ensure suitability as a counter electrode in solid-state cells.

This paper deals with the separate electrochemical recovery of transition metals from battery black liquor. In a first approach, the authors investigated a model waste electrolyte mainly consisting of Cu, Co, Ni, and Mn in an acidic solvent, using citric acid as a complexing agent. An open porous Inconel® foam had been included as an electrode to benefit from the increased active surface area. Under the selected operation conditions, Cu was completely recovered, presenting almost 100% purity, while, in the case of Co, the purity was 96%, and a remanent concentration of about 1.2 g L−1 could still be determined.

In recent years, the growing electric vehicle market has increased the need for cost efficient and high energy materials for batteries drastically. Tin and tin oxide materials bear great potential as anode materials for Li-Ion batteries due to low cost and high theoretical capacity. Nevertheless, the development of commercial tin anodes has so far been hindered due to several drawbacks related to high volume expansion during operation leading to fast cell degradation. To circumvent these issues, nanostructured electrodes can be applied to mitigate volume changes. Typically, the production process of such electrodes is challenging, leading to high cost and issues in terms of scalability. Electrochemical processes, such as the electrolytic oxidation of tin, has been found a promising alternative to fabricate nanostructured electrodes. The additive-free tin oxide anodes obtained from this process exhibit high gravimetric and volumetric capacity, excellent rate capability as well as promising cycle life. The morphology and microstructure have high impact on the rate capability and cycling stability of tin oxide anodes. Since structural properties can be precisely adjusted by controlling the electrochemical oxidation process, a deeper understanding of the structure-property relationship is needed to optimize the production process and pave the way for commercialization. Herein an in-depth characterization of nanostructured tin oxide anodes formed by electrochemical oxidation is presented. The rate capability and the cycling stability are investigated by means of electrochemical measurements in battery cells. Operando electrochemical dilatometry is used to investigate the thickness change of the anodes during cycling (cell breathing). In-situ XRD measurements are applied to elucidate the reaction mechanism. The anodes are carefully analyzed by SEM/EDS at different state of lithiation to understand the impact of volume changes on the inner porosity and morphology. Finally, the cycling stability of tin oxide anodes is improved by applying an electrochemical prelithiation step. Therefore, the impact of different prelithiation regimes on the cycling stability is evaluated in full cells. The results contribute to the understanding of electrochemical behavior of nanostructured tin oxide anodes and the derivation of optimal design criteria adjusted by electrochemical surface engineering.