The Electron Capture in 163^{163} Ho Experiment - a Short Update

The definition of the absolute neutrino mass scale is one of the main goals of the Particle Physics today. The study of the end-point regions of the β- and electron capture (EC) spectrum offers a possibility to determine the effective electron (anti-)neutrino mass in a completely model independent way, as it only relies on the energy and momentum conservation. The ECHo (Electron Capture in 163Ho) experiment has been designed in the attempt to measure the effective mass of the electron neutrino by performing high statistics and high energy resolution measurements of the 163 Ho electron capture spectrum. To achieve this goal, large arrays of low temperature metallic magnetic calorimeters (MMCs) implanted with with 163Ho are used. Here we report on the structure and the status of the experiment

Scanning Tunneling Microscopy and spectroscopy on YBa2Cu3O7: new light on the subgap states

The mechanism underlying high temperature superconductivity continues to challenge our understanding. Scanning tunneling spectroscopy (STM) has historically been one of the prime techniques to tackle superconductivity in conventional BCS materials, providing key insight into the pairing mechanism. Here we present a new set of tunneling spectra obtained on YBCO single crystals. Our new results are twofold: Firstly, we have observed low energy electronic states that previously have been associated with the vortex core in HTS, to be present everywhere on the sample surface, both inside and outside vortices. This fact suggests that these features have a more general origin and are not specific signatures of the vortex core. Secondly, we have found these low energy states to be modulated in space, with a nematic order

Inside the electrode: Looking at cycling products in Li/O2 batteries

This work investigates the impact of electrochemical reactions and products on discharge capacity and cycling stability with electrolytes based on two common solvents – tetraethylene glycol dimethyl ether (TEGDME) and dimethyl sulfoxide (DMSO). Although the DMSO-based electrolyte exhibits better initial electrochemical properties compared to that based on TEGDME, e.g., higher discharge capacity and potential, the use of TEGDME results in a significantly better cycling stability. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) investigations of the gas diffusion electrodes (GDE) after first discharge reveal a considerable difference in discharge product morphology. With DMSO as solvent one high-potential reduction process leads to the formation of crystalline lithium peroxide (Li2O2) particles on the cathode surface area. SEM imaging of GDE cross-sections depicts that the (non-crystalline) product film formation at lower potentials during discharge with the TEGDME-based electrolyte results in a GDE pore clogging close to the O2 inlet, so that gas transport is hindered and the discharge ends at an earlier point. The higher cycling stability with LiTFSI/TEGDME, however, is attributed to (i) the apparently complete recovery of the GDE active surface by recharge and (ii) different parasitic reactions resulting in the formation of side product particles rather than films.acceptedVersio

High capacity Mg batteries based on surface-controlled electrochemical reactions

Mg batteries are one of several new battery technologies expected to partially substitute lithium-based batteries in the future due to the lower cost and higher safety. However, the development of Mg batteries has been greatly hindered by the sluggish Mg migration kinetics in the solid state. Here, we exploit a high performance cathode for Mg battery based on a tailored nanocomposite, synthesized by in-situ growth of nanocrystalline Mn3O4 on graphene substrates, which provides high reversible capacities (~ 220 mA h g−1 at 15.4 mA g−1 and ~ 80 mA h g−1 at 1.54 A g−1), good rate performance (high reversibility at various current rates), and excellent cycling stability (no capacity decay after 700 hundred cycles). The magnesiation mechanism in our cell system has been identified as a combination of capacitive processes and diffusion-controlled reactions involving electrolyte solvents. Characterization is performed by ex-situ transmission electron microscopy (TEM)/scanning TEM (STEM), energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS) and X-ray photoelectron spectroscopy (XPS) in addition to quantitative kinetics analysis. Exploiting the high-performance capacitive-type electrodes, where the specific capacity is limited by the kinetics of surface processes and not by bulk Mg ion diffusion governing the properties of conventional intercalation-type electrodes, could reveal a new approach to developing commercially viable Mg batteries.acceptedVersio

Inside the electrode: Looking at cycling products in Li/O2 batteries

This work investigates the impact of electrochemical reactions and products on discharge capacity and cycling stability with electrolytes based on two common solvents – tetraethylene glycol dimethyl ether (TEGDME) and dimethyl sulfoxide (DMSO). Although the DMSO-based electrolyte exhibits better initial electrochemical properties compared to that based on TEGDME, e.g., higher discharge capacity and potential, the use of TEGDME results in a significantly better cycling stability. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) investigations of the gas diffusion electrodes (GDE) after first discharge reveal a considerable difference in discharge product morphology. With DMSO as solvent one high-potential reduction process leads to the formation of crystalline lithium peroxide (Li2O2) particles on the cathode surface area. SEM imaging of GDE cross-sections depicts that the (non-crystalline) product film formation at lower potentials during discharge with the TEGDME-based electrolyte results in a GDE pore clogging close to the O2 inlet, so that gas transport is hindered and the discharge ends at an earlier point. The higher cycling stability with LiTFSI/TEGDME, however, is attributed to (i) the apparently complete recovery of the GDE active surface by recharge and (ii) different parasitic reactions resulting in the formation of side product particles rather than films

The effect of addition of the redox mediator dimethylphenazine on the oxygen reaction in porous carbon electrodes for Li/O2 batteries

Secondary Li–O2 batteries are promising due to their potentially high theoretical energy density. However, both the discharge (oxygen reduction reaction, ORR) and the recharge reaction (oxygen evolution reaction, OER) are associated with high irreversible losses, and multiple side reactions, depending on the electrolyte of choice. Addition of redox mediators is currently considered a promising route to combat the challenges of the highly irreversible ORR/OER. In this work, the effect of addition of the redox mediator 5,10-dimethylphenazine (DMPZ) on the capacity and reversibility of the oxygen reaction is investigated in porous carbon electrodes. The electrolytes are based on tetraethylene glycol dimethyl ether (TEGDME) as solvent, and either Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as salt, or a combination of LiTFSI and LiNO3 salt, alternatively dimethyl sulfoxide (DMSO) as solvent, with LiTFSI salt. The addition of DMPZ results in a significant improvement of the reversibility of the ORR/OER reactions for electrolytes based on LiTFSI in DMSO, and LITFSI + LiNO3 in TEGDME. This is attributed to a depression of the side reactions limiting the recharge reaction in these electrolytes. Post mortem analyses by XRD, SEM, as well as FIB-SEM investigations of cross sections, are used to characterize the products from the side reactions

Edge/basal/defect ratios in graphite and their influence on the thermal stability of lithium ion batteries

Raw graphite can be processed industrially in large quanta but for the graphite to be useful in lithium ion batteries (LIB's) certain parameters needs to be optimized. Some key parameters are graphite morphology, active surface area, and particle size. These parameters can to some extent be manipulated by surface coatings, milling processes and heat treatment in various atmospheres. Industrial graphite materials have been investigated for use as anode material in LIB's and compared with commercial graphite. These materials have been exposed to two different milling processes, and some of these materials were further heat treated in nitrogen atmosphere above 2650 °C. Brunauer-Emmett-Teller (BET) theory combined with density functional theory (DFT) has been employed to study the ratio of basal to non-basal plane and to determine the relative amount of defects. Thermal properties have been investigated with differential scanning calorimetry (DSC). High ethylene carbonate (EC) content improved the thermal stability for graphite with high amount of edge/defect surface area, but showed no improvement of graphite with lower amount of edge/defects. High irreversible capacity loss (ICL) combined with low surface area improved the thermal properties. DFT combined with ICL could potentially be used as a tool to predict thermal stability

High interfacial charge storage capability of carbonaceous cathodes for Mg batteries

A rechargeable Mg battery where the capacity mainly originates from reversible reactions occurring at the electrode/electrolyte interface efficiently avoids the challenge of sluggish Mg intercalation encountered in conventional Mg batteries. The interfacial reactions in a cell based on microwave-exfoliated graphite oxide (MEGO) as the cathode and all phenyl complex (APC) as electrolyte are identified by quantitative kinetics analysis as a combination of diffusion-controlled reactions involving ether solvents (esols) and capacitive processes. During magnesiation, esols in APC electrolytes can significantly affect the electrochemical reactions and charge transfer resistances at the electrode/electrolyte interface and thus govern the charge storage properties of the MEGO cathode. In APC–tetrahydrofuran (THF) electrolyte, MEGO exhibits a reversible capacity of ∼220 mAh g–1 at 10 mA g–1, while a reversible capacity of ∼750 mAh g–1 at 10 mA g–1 was obtained in APC-1,2-dimethoxyethane (DME) electrolyte. The high capacity improvement not only points to the important role of the esols in the APC electrolytes but also presents a Mg battery with high interfacial charge storage capability as a very promising and viable competitor to the conventional intercalation-based batteries.acceptedVersio

Electrochemical impedance spectroscopy of a porous graphite electrode used for Li-ion batteries with EC/PC based electrolytes

Electrochemical impedance spectroscopy has been employed to investigate different electrolyte compositions used for lithium-ion batteries. Diffusion coefficients in ethylene carbonate (EC) was estimated to be in order of 10-7-10-11 cm2/s, depending on the state of charge (SOC), and propylene carbonate (PC) based electrolytes has been estimated to be in the order 10-10-10-11 cm2/s. Lithium bis(oxalato) borate (LiBOB) was used as an additive in the PC electrolytes to prevent exfoliation