Publication News

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3rd August 2018

Degradation Mechanisms in an All-Solid-State Lithium-Ion Battery

Research by the Peter Bruce Group and collaborators at University of Giessen as reported in ACS Applied Materials & Interfaces provides an insight to the degradation mechanism in an All-Solid-State Lithium-Ion Battery. All-solid-state batteries (ASSBs) show great potential for providing high power and energy densities with enhanced battery safety. While new solid electrolytes (SEs) have been developed with high enough ionic conductivities, SSBs with long operational life are still rarely reported. Therefore, on the way to high-performance and long-life ASSBs, a better understanding of the complex degradation mechanisms, occurring at the electrode/electrolyte interfaces is pivotal. While the lithium metal/solid electrolyte interface is receiving considerable attention due to the quest for high energy density, the interface between the active material and solid electrolyte particles within the composite cathode is arguably the most difficult to solve and study. In this work, multiple characterization methods are combined to better understand the processes that occur at the LiCoO2 cathode and the Li10GeP2S12 solid electrolyte interface. Indium and Li4Ti5O12 are used as anode materials to avoid the instability problems associated with Li-metal anodes. Capacity fading and increased impedances are observed during long-term cycling. Postmortem analysis with scanning transmission electron microscopy, electron energy loss spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy show that electrochemically driven mechanical failure and degradation at the cathode/solid electrolyte interface contribute to the increase in internal resistance and the resulting capacity fading. These results suggest that the development of electrochemically more stable SEs and the engineering of cathode/SE interfaces are crucial for achieving reliable SSB performance.

Device logic

16th July 2018

Device-level photonic memories and logic applications using phase-change materials

Photonics is believed to be one of the best candidates for a future computing system, which can perform data storage and processing in an optical manner at extremely high speed and with unprecedented bandwidth. However, it’s essential yet difficult to build the electronic counterparts, such as non-volatile memories and logic devices, in optical manner. Researchers from the Advanced Nanoscale Engineering group, collaborated with University of Exeter (UK), University of Muenster (Germany) and Massachusetts Institute of Technology (USA) reported their latest results on integrated photonic memories and logic devices based on phase-change materials in Advanced Materials. Phase-change materials (PCMs), widely used in rewritable optical discs and phase-change memory applications, show a substantial difference in both electronic and optical properties between the amorphous and crystalline states. In photonic memory implementations, the authors developed an optical pulse width modulation (PWM) technic, successfully achieving multi-level and non-volatile photonic memories with complete random accessibility. Furthermore, they demonstrated programmable optical logic devices with logic “OR” and “NAND” achieved on just a single photonic memory device. Their study provides a practical and elegant technique to optically program multiple functions in photonic phase-change devices for future computing applications.


23rd June 2018

Halide double perovskites for water splitting

Since their discovery in 2016, halide double perovskites that are based on combinations of monovalent and trivalent cations, have been thoroughly investigated as potential lead-free alternatives to lead halide perovskites. In a recent study published in Applied Physics Letters,  researchers George Volonakis and Feliciano Giustino, considered applications beyond photovoltaics and found that the lead-free double perovskites Cs2BiAgCl6, Cs2BiAgBr6, Cs2SbAgCl6 and Cs2InAgCl6 may open new opportunities in solar-driven photocatalytic water splitting. Using first-principles calculations they report on the stability of different surface terminations of the newly synthesised double perovskites, and also report their absolute energy levels. The energy levels of Cs2BiAgCl6 and Cs2BiAgBr6 are matching the redox potential of water. While, Cs2SbAgCl6 and Cs2InAgCl6 could also be suitable for either hydrogen evolution or water evolution. Futher details are in the AIP journal feature article press release.


22nd June 2018

Maximising the resolving power of the scanning tunneling microscope

Research by the Surface Nanoscience group and collaborators at Trinity College Dublin as reported in open access Advanced Structural and Chemical Imaging demonstrates that a significant improvement in the resolving power of the STM is achieved through automated distortion correction and multi-frame averaging. We demonstrate the approximately square-root relationship improvement in signal-to-noise ratio upon image averaging, a sub-picometre precision height measurement, and the automated identification of chiral unit cells on a surface. These automated tools, which do not require prior knowledge of the surface structure, promise to facilitate more rapid and higher-precision studies of surfaces, making full use of the experimentalists recorded data sets. This advance allows a new study of surface pico-science to be developed where subtle variations in surface structure can now be seen, that hitherto were not detected because they were buried in noise.

Electrical percolation through a discontinuous Au nanoparticle film

21st June 2018

Electrical percolation through a discontinuous Au nanoparticle film

Researchers in the Surface Nanoscience Group report in Applied Physics Letters evidence of stepwise control of resistivity in thin gold layers. When a thin gold film is deposited the electrical resistance of the film decreases from fully resistive at the start of deposition to close to the bulk resistance for thicker films. We’ve found that, instead of a smooth decrease, this resistance change occurs in discrete steps. The steps are attributed to conduction through newly formed electrical pathways in the discontinuous film being created as more gold is deposited. Scanning electron microscopy images confirm the discontinuous nature of the films and show that thicker layers are more connected. Annealing such films causes them to dewet, decreasing the number of conductive pathways and causing a stepwise increase in the resistance of the film. This control over the electrical resistance of the layer as well as the size and separation of the particles opens up new opportunities for various applications of discontinuous metal films.


15th June 2018

Improving the specific energy of the Li-ion battery with new cathode material

Research by the Peter Bruce Group and collaborators at Japan Synchrotron Radiation Research Institute (JASRI) and Uppsala University as reported in Energy & Environmental Science explains that the greatest barrier to improving the specific energy of the Li-ion battery is the cathode. While Si offers a route to increase the capacity at the anode this needs to be balanced by higher energy storage cathodes. The capacity of the cathode is limited by storing electrons on the transition metal ions alone, such as in LiMn2O4, where electrons are stored on the Mn 3+/4+ redox couple. There is a great deal of interest in increasing charge storage in transition metal oxide cathodes beyond the limit of transition metal redox activity. While redox reactions on sulfur in transition metal sulfides are well known only recently has O redox activity in transition metal oxides been recognised. They report a new intercalation cathode material, a lithium manganese oxyfluoride based on Li2MnO2F, with a high capacity to store charge by invoking redox activity on the Mn cations and O anions. It has a disordered rocksalt structure, which avoids the structural changes and consequent severe changes in voltage observed for O-redox layered transition metal oxide cathodes during the 1st cycle.


15th June 2018

Strategy for making bicontinuous conducting composite materials in a controllable fashion

Research by the Peter Bruce Group and collaborators at University of Edinburgh as reported in Materials Horizons  suggests a general strategy for making bicontinuous conducting composite materials in a controllable fashion. Their approach begins with a bicontinuous interfacially jammed emulsion gel (bijel) fabricated from a pre-mix containing a salt, here bis(trifluoromethane)sulfonimide lithium salt (LiTFSI). The resulting structure has interpenetrating ionic conducting and non-conducting domains composed of an ethylene carbonate (EC)-rich phase and a p-xylene (xylene)-rich phase of roughly equal volumes. This is the first time that bijel fabrication has been carried out using a pair of partially miscible liquids whose phase behaviour has been modified due to the addition of salt. Diffusing polystyrene (PS) into the xylene-rich phase enables the facile formation of a PS-filled bijel in place of a multi-step polymerization of added monomers. Drying the bijel results in the selective removal of xylene, reducing the total sample volume without compromising the morphology of the EC domain. Electrochemical impedance spectroscopy of the composite electrolytes confirms the existence of ion conducting pathways.


15th June 2018

Crossover from lattice to plasmonic polarons of a spin-polarised electron gas in ferromagnetic EuO

Doped oxides can host a wealth of fascinating physical properties driven by strong many-body interactions, such as the dressing of electrons into polaronic quasiparticles from the interaction with bosonic excitations of the system. Besides the more conventional lattice polarons produced by the coupling to the crystal phonons, plasmonic polarons may form when conduction electrons couple with the collective plasmon excitations of their own Fermi sea.
Combining angle-resolved photoemission experiments with first-principles calculations, Fabio Caruso, Carla Verdi and Feliciano Giustino, in collaboration with the group of Phil King at the University of St Andrews, report the observation of lattice and plasmonic polarons in the doped ferromagnetic semiconductor EuO. These findings, published in a paper in the journal Nature Communications, suggest interesting opportunities for tailoring charge carrier properties in dilutely doped semiconductors.


4th June 2018

Magnetic edge states and coherent manipulation of graphene nanoribbons

Graphene has been called the wonder material, and its mechanical and electric properties never cease to amaze. Theory predicts that it could show magnetic properties too, if we could control the geometry of ist edges at the single-atom level. Such magnetic graphene would allow testing some very fundamental assumptions about graphene, and yield excellent building blocks for quantum computing machines. Now this theoretical prediction has become true: chemists and physicists have joined forces to create atomically-perfect graphene nanoribbons in huge quantities. In addition to validating and disproving a number of fundamental theoretical proposals, they found out that the quantum properties of the new material are actually astonishingly promising, yielding coherence times good for quantum operations at room temperature already without any type of optimization. Such results, when single-electron transport is realized with similar nanoribbons, could usher a new era quantum electronic devices. 

Details of recent findings are reported in Nature by Professor Lapo Bogani and co-workers.

Predicting Perovskites

12th May 2018

The geometric blueprint of perovskites

Perovskites constitute one of the most versatile and chemically diverse families of crystals. In perovskites the same structural template supports a staggering variety of properties, from metallic, insulating, and semiconducting behavior to superconducting, ferroelectric, ferromagnetic, and multiferroic phases. Approximately 2,000 perovskites are currently known, including those used in high performance solar cells as discovered in Oxford in 2012.  Researchers Marina Filip and Feliciano Giustino report in PNAS and the Oxford Science Blog a library of compositions predicting the existence of 90,000 new perovskites by combining elementary geometric ideas with high-throughput data analytics. These predictions hopefully will lead to the realization of entirely new functional materials for electronics, lighting, energy, sensors, and detectors. 

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