News of the Institute and the groups@ICTM

Wilkening Group • Trimmel Group •  Gollas Group •  Slugovc Group

  A solid with liquid properties: new class of electrolytes for all-solid-state batteries

Replacing liquid electrolytes with a powerful solid would be a major breakthrough for all-solid-state batteries. In the new superionic conductor, studied by G. Hautier and Yuki Kato (Toyota Motor Europe) in collaboration with the Wilkening group, the very fast Li diffusion comes from a unique crystal structure which offers no strongly energetically favoured lattice sites leading to a so-called frustrated energy landscape: the ions are never "satisfied" where they sit. In this sense the ionic diffusion properties resemble those of a liquid. This specific diffusion mechanism could inspire the search for further materials offering the same feature. NMR helped us to characterize the two dynamic processes predicted by theory: the fast inter-ring and the even faster intra-ring Li ion hopping process.

https://www.cell.com/chem/fulltext/S2451-9294(19)30309-2

  Mechanism of singlet oxygen formation revealed - a major step for understanding metal oxygen batteries

Decarbonizing the energy system requires energy storage with large capacity but equally low economic and ecological footprint. Alkali metal-O2 batteries are considered outstanding candidates in this respect. However, they suffer from poor cycle life as a result of cathode degradation. Formation of the highly reactive singlet oxygen has been proposed to cause this degradation, but formation mechanisms have remained unclear. Here, Freunberger at al. have shown that the singlet oxygen source is the disproportionation of thermodynamically instable superoxide intermediates to the peroxides.
The revealed mechanism conclusively explains the strongly growing degree of degradation when going from K-O2 to Na-O2 and Li-O2 cells. A major consequence is that highly reversible cell operation of Li-O2 and Na-O2 cells requires them to form and decompose the peroxides without disproportionation. Achieving this requires finding new reaction routes. The publication lays the mechanistic foundation to fight singlet oxygen as the predominant source of degradation in metal-O2 cells.

  Rotations vs. Hopping Processes: Holy Grails in Chemistry

Ion dynamics in argyrodite-type solid-electrolytes was explored by 31P NMR spin-lattice relaxation. Far from being understood completely how rotational dynamics influence translational Li movements and vice versa. Look at our latest findings published in Chem. Mater.

Networking Event Energy Materials

On June 27th, 2019 a networking meeting on energy materials research at TU Graz took place (8:30 to about 18:00 in the lecture room H “Ulrich Santner” Kopernikusgasse 24).

The event was jointly organized by VARTA Micro Innovation GmbH and the lead-project Porous Materials @ Work and aimed at connecting the expertise of the many groups active in the field. Additionally, representatives of industries were present. The meeting consisted of talks (12+3 min) introducing the research fields, expertise and special equipment of the research groups, a poster session and ample time for networking.

  Ion dynamics in closo-borates

Ionic conduction mechanism in closo-borates for sodium ion batteries elucidated. A portfolio of methods (NMR, QENS, ESI) was needed to see the full picture. Great collaboration with EMPA, Université de Genève, PSI, and ETH. Link: paper Chem. Mater. 

  Electrochemistry of arylsilanes

Electrochemical properties of arlysilanes - new paper in Electrochemistry Communications; Hanzu and co-workers throw light on the fascinating properties of 11 arylsilanes, 2 of them synthesized for the first time. Link: paper EC 

  Ion dynamics in argyrodite-type thiophosphates

Li-bearing argyrodites play an important role as solid electrolytes for next-generation batteries. In a new publication, which appeared in RSC's PCCP, we report in detail on the complex interplay of local structures and ion dynamics. Importantly, also for the poor ion conductor Li6PS5I we found rapid ion dynamics on a local lenght scale. Link: paper in PCCP

  Ion dynamics in nanoglasses

Li ion diffusivity is, in general, faster in glassy materials than in the crystalline counterparts. In particular, this relation holds for compounds with the same chemical composition. If a glassy sample is mechanically treated in a high-energy ball mill a material is obtained with a lower diffusivity as compared to that in the original sample. Obviously, structural relaxation is responsible for the decrease observed. Via modulus spectroscopy we followed the change in electrical relaxation and identified two distinct relaxation rates which we attribute to the situation in the unmilled glass and to Li species being already influenced by mechanical treatment. Link: paper in JPCC 

Singlet oxygen quenching in battery devices

Singlet oxygen (1O2) causes a major fraction of parasitic chemistry during cycling of non-aqueous alkali metal-O2 batteries and also contributes to interfacial reactivity of transition-metal oxide intercalation compounds. Yet DABCOnium, the mono alkylated form of 1,4-diazabicyclo[2.2.2]octane (DABCO), is introduced in Angewandte Chemie as an efficient 1O2 quencher with an unusually high oxidative stability of ~4.2 V vs. Li/Li+. Previously known quenchers are strongly Lewis basic amines with too low oxidative stability. It is an ionic liquid, non-volatile, highly soluble in the electrolyte, and stable against superoxide and peroxide. The electrochemical stability covers the required range for metal-O2 batteries and greatly reduces 1O2 related parasitic chemistry as demonstrated for the Li-O2 cell.

Singlet oxygen in Li-O2 batteries

A joint undertaking of Korean, US American and Austrian researchers revealed singlet oxygen as the main reason for the gradual deactivation of redox mediators in lithium-oxygen batteries in an article in Nature Communications.
Non-aqueous lithium-oxygen batteries cycle by forming lithium peroxide during discharge and oxidizing it during recharge. The significant problem of oxidizing the solid insulating lithium peroxide can greatly be facilitated by incorporating redox mediators that shuttle electron-holes between the porous substrate and lithium peroxide. Redox mediator stability is thus key for energy efficiency, reversibility, and cycle life. It is shown that organic redox mediators are predominantly decomposed by singlet oxygen that forms during cycling. Their reaction with superoxide, previously assumed to mainly trigger their degradation, peroxide, and dioxygen, is orders of magnitude slower in comparison. Redox mediators must thus be designed for stability against singlet oxygen.

  Porous polymers - best mechanical properties in class

Researchers of the National Institute of Chemistry, Ljubljana and ICTM underlined in a recent publication in Polymer the unique mechanical properties of emulsion templated macroporous polymer foams consisting of poly(dicyclopentadiene). The recent work deals with the influence of surfactant loading on strengths and toughness of this kind of porous matter which can be considered as the strongest and toughest macroporous polymer foams available up to now.

  Nanostructured Composites, new paper in JPCC

Since the pioneering work of Liang in 1973 nano- or mesostructured composites consiting of an insulator and an ionically conducting phase act as model systems helpful to understand interfacial transport properties. (7)Li and (19)F NMR revealed details of the diffusion mechanism in LiF:alumina composites. Link to J. Phys. Chem. C    

  A Benzobis(thiazole)-Based Copolymer for Highly Efficient Non-Fullerene Polymer Solar Cells

In a collaborative publication of researchers of the Chinese Academy of Sciences, the South China Normal University, Austrian company Anton Paar GmbH and the Trimmel group non-fullerene polymer solar cells with a high efficiency of 13.3% were disclosed in Chemistry of Materials. The success is based on properly selecting and processing donor–acceptor pairs with suitable electronic properties and complementary optical absorption.   

  Proton diffusion in cubic LLZO, new paper in JPCC

A new paper has been published by the Rettenwander group about single-crystal X-ray diffraction to study the nature of Li+/H+ exchange in cubic Li7La3Zr2O12 (LLZO) garnets. On the basis of the proton concentration change over time (3 years), a spherical diffusion model was used to estimate the proton diffusion coefficient to be of the order of 2 × 10–17 m2/s. This diffusion coefficient is high enough to have a significant impact on both the cell performance and safety when LLZO is used as a protecting layer for Li metal anodes in Li-ion batteries that rely on liquid electrolytes. Link to JPCC.

  MSc/PhD positions available in the Wilkening/Hanzu group

We seek to fill a PhD student position (30 h/week) in our research group in the course of March 2019. Topics: Solid-State Chemistry and Electrochemistry, new solid electrolytes, safety of all-solid-state batteries, spectroscopic methods (NMR, impedance spectroscopy, GPCL, GITT, etc.) You have a M.Sc. degree, Diploma or equivalent in Inorganic/Analytical Chemistry, Physical Chemistry or related areas, strong interest in Solid-State Physical Chemistry and application-oriented research. Contact: wilkeningnoSpam@tugraz.at or hanzunoSpam@tugraz.at

  2D Fluorine Diffusion, new paper in PCCP

A new paper about 2D F anion diffusion in nanocrystalline RbSn2F5 that has been prepared by a mechanochemical approach is out. We used broadband conductivity spectroscopy and nuclear magnetic relaxation to show that F preferably diffuses between the Rb-Sn layers. Analyzing the NMR relaxation rates with a spectral density function developed for 2D diffusion yields a consistent picture about F dynamics. This spectral density function has been introduced by P. M. Richards in 1978. Link to PCCP.

  Another new paper on CuInS2...

...has been published by Thomas Rath et al. Dr. Rath assembled an interdisciplinary team for realizing his latest paper on ligand-free preparation of polymer/CuInS2 nanocrystal films and employing this strategy for improving the performance of solar cells. The work appeared as open access article in Journal of Materials Chemistry C.

  New paper on CuInS2 nanocrystals

The Trimmel group realized an new synthesis route towards copper indium sulfide (CuInS2) nanocrystals with a size of 3–4 nm and a chalcopyrite crystal structure starting from copper and indium xanthates as precursors in a hot injection synthesis performed at a temperature of 200 °C and used the material as acceptor in polymer/nanocrystal bulk heterojunction solar cells. The work has been published in New Journal of Chemistry as an open access arcticle.

Current events
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Next event organized also partly by the Wilkening group @ ICTM:

EUROMAT 2019 Stockholm
https://euromat2019.fems.eu/
PDF of the symposium

for more information see the homepage

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