Thorsten Gerdes

Commercial polyolefin separators for lithium-ion batteries (LIBs) exhibit only inadequate wettability and thermal stability. In large-scale production, high electrolyte uptake and wetting are essential to enable rapid electrolyte filling during battery assembly to reduce costs. In addition, it is imperative to develop separators with enhanced thermal stability for improved performance and safety. The focus of this study is the structure–property–performance relationship of separator coatings. Platelet-shaped glass particles are utilized as inorganic coating material for polyethylene (PE) separators. Styrene–butadiene rubber (SBR) was selected as binder due to its high thermal stability. Hybrid separators are prepared using a colloidal coating technology employing a water-based slurry. As the excessive use of binder in the coating can block pores, precise control of the binder content was essential to maintain battery performance. The resulting separators with an optimized binder content of 1 wt.% in the coating demonstrate high porosity, instantaneous wetting with electrolyte, and a 25 K increase in onset temperature for shrinkage. The utilization of glass platelets with an aspect ratio of 10 as coating material provided the best balance among processability, coating homogeneity, thermal stability, ionic conductivity, and cycling performance under the investigated processing conditions.

The formation of a crystallized surface layer, having a lower coefficient of thermal expansion (CTE) than the parent glass, can be exploited to place the glass surface under compression during cooling from crystallization temperature and hence improve mechanical properties. In our study, we focused on the understanding of the compositional dependency of the surface crystallization of quartz solid solutions (Qz‐ss) with potentially low CTE. Specifically, we investigated the crystallization of melt‐prepared soda–lime–silicate glasses with variable Al ₂ O ₃ content that were doped with lithium in exchange for sodium. Further, the role of ZnO and MgO in the crystallization was evaluated. Despite rather complex glass compositions, the observed cell parameters of the obtained Qz‐ss are close to the corresponding ternary Li ₂ O─Al ₂ O ₃ ─SiO ₂ (LAS) system. Further, a simple model was applied to predict the in‐plane stresses in the surface. For modeled compositions down to 5.5 mol% Al ₂ O ₃ , formation of a compressive layer for the complete range of the crystalline content can be observed. Our findings illustrate the potential of strengthening glasses through surface crystallization as an alternative to thermal‐ and chemical strengthening to make glass‐packaging more weight competitive. The results can help to optimize glass compositions that can be strengthened by this method.

The thermal characteristics and surface properties of battery separators are commonly modified by the incorporation of inorganic particles into a polymeric matrix material. At present, the particles employed are predominantly of an arbitrary shape. Herein, we demonstrate significantly improved battery safety features using a glass-based separator consisting of platelet-shaped particles. Glass is selected due to its temperature stability and the freedom of design that it offers when particles are formed directly from the melt. The influence of the particles’ aspect ratio and layer stacking on the electrochemical properties was analyzed, and a parametric study of glass particle layers as function of edge length and thickness was conducted. Particles with an excessively high aspect ratio impede the Li⁺ diffusion pathway, thereby negatively affecting the performance and stability of the battery cell. Conversely, if the aspect ratio is insufficient, a deterioration in cell performance can be observed, particularly at elevated C-rates, due to the high specific surface area of the particles. Hence, the utilization of particles with a moderate aspect ratio of about 10 and a thickness of around 1 µm is proposed to ensure optimum performance.

Direct atomization of a free-flowing glass melt was carried out using a high-speed flame with the aim of producing tiny, self-expanding glass melt droplets to form hollow glass microspheres. Atomization experiments were carried out using a specially adapted free-fall atomizer in combination with a high-power gas burner to achieve sufficient temperatures to atomize the melt droplets and to directly expand them into hollow glass spheres. In addition, numerical simulations were carried out to investigate non-measurable parameters such as hot gas velocities and temperatures in the flame region by the finite volume-based software Star CCM+^® (v. 2022.1.1), using the Reynolds-Averaged Navier–Stokes (RANS) turbulence and the segregated flow model. To calculate the combustion process, the laminar flamelet method was used. The experiments and simulations indicated that a maximum gas velocity of about 170 m/s was achieved at the point of atomization in the flame. The particle size distribution of the atomized glass droplets, either solid or hollow, ranged from 2 µm to 4 mm. Mean particle sizes in the range of 370 µm to 650 µm were highly dependent on process parameters such as gas velocity. They were in good agreement with theoretically calculated median diameters. The formation of hollow glass microspheres with the proposed concept could be demonstrated. However, only a small fraction of hollow glass spheres was found to be formed. These hollow spheres had diameters up to 50 µm and, as expected, a thin wall thickness.

Renovation of old buildings plays a key role in the sustainable energy transition because they are often poorly insulated and, therefore, lose a lot of heat through walls and ceilings. An important measure of renovation is façade insulation. Established and widely used materials include rigid expanded polystyrene (EPS) and extruded polystyrene (XPS) insulation boards. However, these boards do not easily follow the form of non-planar surfaces such as individually formed, ornamented, or bent façades. Furthermore, fire protection of these boards requires the addition of, for example, hazardous brominated flame retardants that impede recycling. This paper investigates a novel alternative insulating composite plaster. It is purely inorganic and can be applied easily by casting or wet spraying to any wall or ceiling element. The composite material consists of only two components: micro hollow glass microspheres as the insulating light component and calcium sulfoaluminate cement as the binder. Various compositions containing these components were cast, hydraulically set, and characterized with respect to microstructure, phase development during hydration, and thermal conductivity. With an increasing amount of hollow glass spheres, the density decreased to less than 0.2 g·cm⁻¹, and the thermal conductivity reached 0.04 to 0.05 W·m⁻¹K⁻¹, fulfilling the demands of building insulation.

Multimodal tumor treatment settings consisting of radiotherapy and immunomodulating agents such as immune checkpoint inhibitors are more and more commonly applied in clinics. In this context, the immune phenotype of tumor cells has a major influence on the anti-tumor immune response as well as the composition of the tumor microenvironment. A promising approach to further boost anti-tumor immune responses is to add hyperthermia (HT), i.e., heating the tumor tissue between 39 °C to 45 °C for 60 min. One key technique is the use of radiative hyperthermia systems. However, knowledge is limited as to how the frequency of the used radiative systems affects the immune phenotype of the treated tumor cells. By using our self-designed in vitro hyperthermia system, we compared cell death induction and expression of immune checkpoint molecules (ICM) on the tumor cell surface of murine B16 melanoma and human MDA-MB-231 and MCF-7 breast cancer cells following HT treatment with clinically relevant microwaves at 915 MHz or 2.45 GHz alone, radiotherapy (RT; 2 × 5 Gy or 5 × 2 Gy) alone or in combination (RHT). At 44 °C, HT alone was the dominant cell death inductor with inactivation rates of around 70% for B16, 45% for MDA-MB-231 and 35% for MCF-7 at 915 MHz and 80%, 60% and 50% at 2.45 GHz, respectively. Additional RT resulted in 5–15% higher levels of dead cells. The expression of ICM on tumor cells showed time-, treatment-, cell line- and frequency-dependent effects and was highest for RHT. Computer simulations of an exemplary spherical cell revealed frequency-dependent local energy absorption. The frequency of hyperthermia systems is a newly identified parameter that could also affect the immune phenotype of tumor cells and consequently the immunogenicity of tumors.

A new type of separator for lithium-ion batteries (LIBs) has been developed using ultrathin micrometer-sized sodium borosilicate glass platelets coated directly on a battery electrode with a water-based binder. The coating process is described in detail, demonstrating coating thicknesses of the glass separator of less than 50 µm. The high-temperature stability has been investigated and it has been shown that the separator is dimensionally stable to at least 600 °C. With regard to the electrochemical performance, full-cell tests on graphite || lithium iron phosphate cells showed a very good behavior, according to which comparable properties of the electrode/separator compound to a commercial polymer-based separator were achieved. This glass separator/electrode composite shows an interesting property profile and is a temperature-stable alternative to conventional polymer-based separators.

In this paper, the dynamic mechanic and optical properties of composites made of Polyvinyl Butyral (PVB) and Micro Glass Flakes (MGF) with matching refractive indices (RIs) are investigated. The composite is produced by a slurry-based process using additional blade casting and lamination. It can be shown that a high degree of ordering of the MGF in the polymer matrix can be achieved with this method. This ordering, combined with the platelet-like structure of the MGF, leads to very efficient strengthening of the PVB with increasing content of the MGF. By carefully adjusting the RIs of the polymer, it is shown that haze is reduced to below 2%, which has not been achieved with irregular fillers or glass fibers.

Tetrafluoroethylene (TFE) and hexafluoropropylene (HFP) are the most common monomers for the synthesis of fluoropolymers at industrial scale. Currently, TFE is produced via multistep pyrolysis of chlorodifluoromethane (R22), resulting in a high energy demand and high amounts of waste acids, mainly HCl and HF. In this study, a new chlorine-free process for producing TFE and HFP in a microreactor is presented, starting from partially fluorinated alkanes obtained from electrochemical fluorination (ECF). In the microreactor, high conversion rates of CHF₃, which is used as a surrogate of partly fluorinated ECF streams, and high yields of fluoromonomers could be achieved. The energy saving and the environmental impact are shown by a life cycle assessment (LCA). The LCA confirms that the developed process has economical as well as ecological benefits, and is thus an interesting option for future industrial production of fluoroalkenes.

In this study, we introduce a through-plane electrochemical measurement cell for proton conducting polymer membranes (PEM) with the ability to vary temperature and humidity. Model Nafion and 3M membranes, as well as anisotropic composite membranes, were used to compare through plane and in plane conductivity. Electrochemical impedance spectroscopy (EIS) was applied to evaluate the proton conductivity of bare proton exchange membranes. In the Nyquist plots, all membranes showed a straight line with an angle of 60–70 degrees to the Z’-axis. Equivalent circuit modeling and linear extrapolation of the impedance data were compared to extract the membrane resistance. System and cell parameters such as high frequency inductance, contact resistance and pressure, interfacial capacitance were observed and instrumentally minimized. Material-related effects, such as swelling of the membranes and indentation of the platinum mesh electrodes were examined thoroughly to receive a reliable through-plane conductivity. The received data for model Nafion and 3M membranes were in accordance with literature values for in-plane and through-plane conductivity of membrane electrode assemblies. Anisotropic composite membranes underlined the importance of a sophisticated measurement technique that is able to separate the in-plane and through-plane effects in polymer electrolytes.