Scientific Events

Solid-state batteries (SSBs) promise to meet the increasing demand for safe, high-power, and high-capacity energy storage. SSBs with solid electrolytes (SEs) offer potential advantages over conventional lithium-ion batteries with liquid electrolytes. Their performance, however, strongly depends on the structure and composition of the various interfaces contained in the different materials, which also change upon electrochemical cycling. We use Scanning transmission electron microscopy (STEM), to quantify properties of interfaces in battery materials. When compared to image simulations, the information on the sample structure and composition derived from STEM data can be quantitative. Combining STEM with a fast, pixelated detector allows for the acquisition of a full diffraction pattern at each scan point. From this, four-dimensional STEM (4D-STEM) datasets are available, which can be used to generate different data, e.g. annular dark field (ADF) as well as (annular) bright field ((A)BF) images, angular resolved STEM (ARSTEM) or differential phase contrast (DPC) data. With the example of cathode, anode and different SE materials for battery applications (e.g., NCM, Si, LLZO, LATP), we track the formation of different phases of and defects within the materials in dependence on synthesis as well as cycling conditions of the material and derive ABF as well as BF images from 4D datasets. These are used to also obtain difference images (ABF-BF). It will be shown that the composition of the materials and especially the Lithium content can be derived from the contrast of the different atomic columns in the structure. This is possible by comparing the experimental data sets to state of the art multi-slice simulations. This contribution will summarize the material science aspects of the energy materials investigated but also elucidate the potential of quantitative 4D-STEM to investigate materials. [more]

Half-Heusler compounds exhibit significant potential in thermoelectric applications for power generation up to 1000 K, notwithstanding the substantial challenges posed by the cost of constituent elements and the imperative to augment the average thermoelectric figure-of-merit (zT_ave) for more practical applications. Overcoming these obstacles demands the advancement of high-performance p-type TaFeSb thermoelectric materials with diminished Ta content. This investigation systematically explores the quaternary-phase space encompassing Ta, Nb, V, and Ti to ascertain an optimal composition, namely Ta_0.42Nb_0.3V_0.15Ti_0.13FeSb. This composition is characterized by a remarkable reduction in Ta concentration coupled with an enhancement in zT, peaking at 1.23 at 973 K. Moreover, the integration of a high-mobility secondary phase, InSb, fosters enhancements in both the Seebeck coefficient and electrical conductivity, resulting in a 23% augmentation in the average power factor, while concurrently suppressing lattice thermal conductivity. The optimized composite, Ta_0.42Nb_0.3V_0.15Ti_0.13FeSb-(InSb)_0.015, achieves a peak zT value of 1.43 at 973 K and a zT_ave of 1 from 300 K to 973 K, thereby setting a precedent among p-type half-Heusler materials. Additionally, a single-leg device demonstrates a peak efficiency of approximately 8% under a temperature difference of 823 K vs. 303 K. These findings underscore the substantial potential of the proposed material design and fabrication methodologies in fostering efficient and sustainable thermoelectric applications. [more]

High entropy materials are materials with 5 or more principle components within crystalline lattices. High entropy metal chalcogenides are a recent (since 2016) development in this area that have shown exceptional promise in both thermoelectric energy conversion and electrocatalysis. However, these materials remain limited in both compositional range and characterisation. In this talk the compositional boundaries of high entropy metal sulfides will be explored, along with advanced and comprehensive characterisation techniques and our initial explorations into acidic hydrogen evolution electrocatalysis. [more]

Thermoelectric materials can realize waste heat recovery and solid-state refrigeration, providing sustainable solutions to the energy crisis and environmental pollution. The performance of thermoelectric materials is gauged by the transport of electrons and phonons. Materials with fast electron movement but slow phonon propagation would be ideal thermoelectrics. These transport behaviors of carriers are influenced by the intrinsic chemical bonding mechanism and structural defects of materials. Understanding the bonding and microstructures of materials is of paramount importance to improve their thermoelectric properties. Atom probe tomography (APT) provides a unique combination of characterizing chemical bonding and lattice defects, being a very powerful tool in the study of thermoelectric materials. It has been revealed that many of the high-performance thermoelectric chalcogenides utilize metavalent bonding (MVB), which can be distinguished from other bonding mechanisms by the unconventionally high value (>60%) of “probability of multiple events (PME)” measured by APT. Thus, many new compounds with high thermoelectric performance can be designed by tailoring their chemical bonds, and APT is an indispensable technique to corroborate the bonding transition. Owing to the high spatial and chemical resolution of APT, the local change of chemical bonding at defects such as grain boundaries and precipitates can also be detected by APT. This enables us to better understand the role of chemical bonding in regulating the electron and phonon transport across individual defects. The results in turn provide insights into the tailoring of thermoelectric properties by manipulating the local chemical bonds. For example, the thermoelectric properties of polycrystalline SnSe have been significantly improved by removing the stiff Sn-O bonds at the grain boundary as directly observed by APT. In contrast, the strong bonding connection between thermoelectric and interfacial materials enables a high-efficiency and durable thermoelectric device. Based on APT, in conjunction with other characterization techniques, we can explore some uncharted territories in the design of thermoelectric materials. [more]

Defects and Grain boundaries have a remarkable effect on the thermal and electrical transport properties of polycrystalline materials but are often ignored by prevailing physical theories. Grain boundaries and interfaces can adversely alter the properties of Power Electronics, Solar Cells, Batteries and Thermoelectrics such as interfacial electrical and thermal resistance (Kapitza resistance) and even an interfacial Seebeck effect. Interfacial thermal resistance limits the performance of power electronics because of overheating. New scanning thermal reflectance techniques can image the thermal resistance of interfaces and boundaries directly. The Thermal conductivity suppression at grain boundaries can even be imaged showing that different grain boundaries can have very different thermal resistances with high energy grain boundaries having more resistance and low energy boundaries having lower thermal resistance. Electrical grain boundary resistance can be so high in some thermoelectric materials it is the dominant property that limits zT. While small grains are usually considered beneficial for thermoelectric performance due to reduced thermal conductivity, Mg₃Sb₂ based thermoelectric materials, so far at least, contradict that trend. Indeed, atomic segregation has been recently observed at the nanometer scale in grain boundaries in many materials suggesting interfacial or complexion phases should be specifically considered when understanding nearly all thermoelectric materials. The concentration of point defects, such as vacancies, interstitial and substitutional atoms can now be predicted with DFT allowing defects to be included in phase diagram analysis for prediction of materials processing for particular properties. [more]

In recent decades, extensive efforts have been done to develop new and more efficient alternative energy sources, which can substitute conventional sources like gas, petrol, and carbon, have been made. Due to the increase in energy consumed by society, we not only need an alternative to conventional energy sources, but also a reduction in energy consumption. Therefore, it is necessary to investigate different methods for energy-recovery and energy-saving as such as thermoelectric materials and radiative coolers. The thermoelectric materials can convert heat into electricity and vice versa. The efficiency of these materials is related to the figure of merit (zT) and it is defined as zT=(σ·S²/k)·T, where σ is the electrical conductivity, S is the Seebeck coefficient, k is the thermal conductivity, and T is the absolute temperature. Nowadays, the application of inexpensive and scalable materials in the industry for thermoelectric applications has received great interest. In this sense electrodeposition is one of the most interesting techniques. It is performed at room temperature, so it is compatible with polymeric substrates, it does not require vacuum conditions, and it allows perfect control over the composition, morphology, and crystallographic structure. In this presentation, I will provide an overview of different thermoelectric materials such as Bi₂Te₃¹, CuNi², and Ag₂Se³ grown by electrodeposition and their thermoelectric properties. In the case of silver selenide, a thermoelectric power generator was produced and characterized. Radiative cooling is the process by which temperature decreases due to an excess of emitted radiation above absorber radiation. To achieve cooling, it is necessary to reduce and keep the temperature below the ambient air temperature. The requirements of radiative coolers to have maximum cooling power, to be able to reduce the temperature sufficiently, and to function 24 hours a day anywhere, are high solar reflectance and high infrared emittance, close to the atmosphere’s window (between 8 and 13μm wavelengths). Different approaches have been explored and porous nanostructures have shown the best results to this respect. In this sense, porous anodic aluminium oxide (AAO) nanostructures on Al was demonstrated to be a great candidate⁴. AAO is an amorphous material with an isotropic permittivity, a strong acoustic resonance absorption at the far IR (15 – 25 µm), and high transparency in the UV‑Vis‑NIR range. In this presentation, I will highlight the possibilities to use AAO nanostructure as radiative cooling. In addition, strcutural cellulose will be also analysed for the same purpose. [more]

Materials play a crucial role in driving the twin transition, a key strategy of the European Union to address current and future environmental challenges. Currently, improving the efficiency of solar cells and the capacity of battery storage is essential for achieving a Net Zero Carbon society, underlining the growing demand for innovative materials. Nanotechnology played a major role in development of the necessary hardware, such as sensors, data storage systems, and actuators, needed for advanced digital solutions. Still, the push to enhance performance and replace outdated technologies is accelerating the research into always-new materials and solutions. Performance-oriented development also expanded the range of metals utilized by humanity, leading to a scenario where a single smartphone necessitates a broader spectrum of elements than the entire biosphere [1], [2]. Due to the fast development, the raw materials for such technologies are changing by day - a pace that the supply chain cannot follow satisfactory. In addition, the environmental impact of raw materials production, especially metals, varies significantly. For example, steel production—accounting for 1.9 billion tons annually—contributes to 8% of global CO₂ emissions, but its per mass environmental footprint is one of the lowest (2 kg of CO₂ per kg of primary steel, and 0.7 kg of CO₂ when recycled). In contrast, the production of platinum, crucial element for hydrogen economy with a limited production of 200 t/y, is one of the most carbon-intensive (60 tons of CO₂ per kg of Pt). Limiting the challenge of the Green and digital revolutions to the simple cost-performance paradigm would be somehow repeating the mistake of the Oil Age during which the resource was considered as infinite and the impact on the environment had been long time neglected. Making the twin transition successful requires changing the mindset of innovators (from lower TRL) to a binary trade-off (price-performance) towards multi-criteria decision-making [3]. In the presentation, we will introduce a straightforward multi-criteria assessment methodology for evaluating the sustainability of metallic alloys. [more]