Novel tin-graphite composites as negative electrodes of Li-ion batteries

For the purpose of obtaining an improved performance of the graphite negative electrode of Li-ion batteries, a novel graphite-tin composite has been synthesized by reduction of tin chloride (SnCl₂) with KC₈ in THF medium. This composite contains nano-sized tin particles dispersed on the graphite surface and free tin aggregates. Lithium electrochemical insertion occurs both in graphite and in tin. An experimental reversible specific charge of 489 mA h g⁻¹ is found stable upon cycling. Such a value is lower than the maximum theoretical one of 609 mA h g⁻¹ suggesting that only a part of tin is involved in the lithium insertion/extraction process. This part of active tin responsible for the stable capacity could be that bound to graphite. To the contrary, free tin aggregates could contribute to an extra capacity that decreases upon cycling in relation with the volume changes that occurs during alloying/dealloying.     

Gramazio Kohler Research,Automated Diversity: New Morphologies of Vertical Urbanism

Automated fabrication techniques are currently largely confined to the production of discrete objects or building elements. To notch up the potential of robotics for architectural design, it is necessary to start to push the limits and experiment at a larger urban scale. Fabio Gramazio and Matthias Kohler are pioneers in this field. Here, with Jan Willmann , they describe the research that they are undertaking as part of the Future Cities Laboratory (FCL) located at the Singapore-ETH Centre for Global Environmental Sustainability (SEC) and ETH Zurich, in which robotic fabrication technologies are employed to realize 1:50 physical models of mixed-use high-rise structures that are unique in their spatial layouts.     

Glucose quantification in dried-down nanoliter samples using mid-infrared attenuated total reflection spectroscopy

The aim of this study was to determine the feasibility of minimally invasive glucose concentration measurement of a body fluid within the physiologically important range below 100 nL with a number of samples such as interstitial fluid, plasma, or whole blood using mid-infrared spectroscopy, but starting with preliminary measurements on samples of simple aqueous glucose solutions. The Fourier transform infrared spectrometer was equipped with a Golden Gate single reflection diamond attenuated total reflection (ATR) accessory and a room-temperature pyroelectric detector. As the necessary detection limits can be achieved only for dried samples within the spectrometric conditions realized by a commercial instrument, the work focused on the optimization of such ATR measurements. We achieved quantification of samples with volumes as low as 7 nL between 10 and 600 mg/dL. The standard error of prediction (SEP) for the concentration range 10-100 mg/dL is 3.2 mg/dL with full interval data between 1180 and 940 cm(-1). The performance of the prediction is given by a coefficient of variation of prediction (CV(pred) ) of 6.2%. When all samples within the whole concentration range are included, the SEP increases to 20.2 mg/dL, and hence the CV(pred) to 10.6% due to a nonlinear signal dependence on glucose concentration. A detection limit for glucose of 0.7 ng with a signal-to-noise ratio of 10 was obtained.     

γ-Butyrolactone-ethylene carbonate based electrolytes for lithium-ion batteries

-Butyrolactone-ethylene carbonate (BL-EC) mixtures have been investigated as electrolytes for Li-ion batteries using LiPF₆ and LiBF₄ as lithium salt. The thermal stability of the electrolytes in a large range of temperatures (–90 °C to 40 °C) have been studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). From the results of these experiments, the phase diagram of the BL-EC system has been determined. It is characterised by a eutectic point at –56.3 °C and a molar fraction in EC: x _EC = 0.1. A metastable compound has been demonstrated below –90 °C at x _EC = 0.4. Conductivity measurements of BL-EC solutions, in the presence of LiPF₆ and LiBF₄, indicate that LiPF₆ in the eutectic mixture is the most conducting electrolyte in the range of temperatures investigated (–30 °C to room temperature). Nevertheless, at low temperature, LiBF₄ based electrolytes compete well with LiPF₆, especially when the amount of EC in the mixture is as high as x _EC = 0.5. Moreover, recrystallisation of the salt below –20 °C is avoided when LiBF₄ is used as salt. A large increase in viscosity of the solvent mixture is observed when a salt is added, but the increase is lower for LiBF₄ than LiPF₆. When EC is added to BL at constant salt concentration (1 M), the conductivity of LiPF₆ solutions decreases more rapidly than LiBF₄ solutions. This has been attributed, at least partially, to the dissociating power of EC. The electrochemical windows of BL-EC (equimolar) mixtures in the presence of LiPF₆ and LiBF₄ are comparable but it is shown that the solvents oxidation rate at high potentials is lower when LiBF₄ is used.     

Layered lithium cobalt nitrides: A new class of lithium intercalation compounds

Lithium cobalt nitrides Li_3−2xCo_xN (0.1 ≤ x ≤ 0.44) have been prepared and investigated as negative electrode in the 1/0.02 V potential window. The evolution of the unit cell parameters and unit cell volume with the Co content show a solid solution behaviour. Whatever the Co content, all these nitrides are electroactive with a single step around 0.6 V/0.7 V for the discharge and charge processes, respectively. The electrochemical behaviour observed is typical of a Li intercalation compound and involves the Co²⁺/Co⁺ redox couple in the interlayer plane combined with the reversible accommodation of Li⁺ ions in the cation vacancies located in Li₂N⁻ layers. XRD experiments performed after discharge, charge and cycling tests clearly indicate the hexagonal layered structure of the host lattice is maintained. This intercalation process explains the excellent capacity retention found after 50 cycles. A specific capacity of 180 mAh g⁻¹ at C/20 and 130 mAh g⁻¹ at C/5 rate (100 mA cm⁻²) is achieved for Li_2.23Co_0.39N. ac impedance measurements have allowed to characterize the kinetics of the reaction.     

Lithium insertion into new graphite-antimony composites

Metal-based composites are under investigation as possible negative-electrode materials in lithium-ion batteries. In this paper, we present a new composite material constituted of antimony particles dispersed on graphite. The antimony-graphite compound is prepared by antimony pentachloride reduction with KC₈ in tetrahydrofuran. The high reversible capacity of 420 mAh g⁻¹ and the good stability suggest that the association of antimony with graphite allows not only to improve reversible capacity but also to prevent the metal from particle pulverisation generally occurring during lithium alloying.     

Recrystallization and grain growth of nanocomposite Ti–B–N coatings

Nanocomposite Ti–B–N coatings with different chemical composition were prepared by non-reactive co-sputtering of a segmented TiN–TiB₂ target. The coatings investigated are primarily composed of nanocrystalline TiN and TiB₂ phases. Increasing boron content results in a decreasing grain size from approximately 6 to 2 nm. During a thermal treatment of such coatings solely recovery and recrystallization with subsequent grain growth would appear, since the two phases are in thermodynamic equilibrium. Differential scanning calorimetry (DSC) and X-ray diffraction analysis were used to investigate the recrystallization behavior and subsequent grain growth of the nanocomposite Ti–B–N coatings. On heating the coating samples, which were removed chemically from their low alloyed steel substrates, an exothermal peak appeared during the DSC measurements indicating grain growth. From the onset temperature of this peak the recrystallization temperature was found which increases with increasing boron content from 1032 to 1070 °C. Activation energies for grain growth are obtained from Kissinger plots and yield values decreasing from 7.9 to 4.4 eV with increasing boron content. After heat treatment up to 1400 °C during the DSC measurements the coatings showed grain sizes within the range of 15–30 nm. It was found that the highest recrystallization temperature does not imply the highest activation energy for grain growth.     

Der konstruktive Entwurf Keramischer Bauteile

The Design of Ceramic Components It is expected that engineering ceramics will be used for components outside the traditional fields of applications for ceramics. Some of the basic methods of production engineering practiced with metals are compared to the production of ceramics. Here the reasons for certain restrictions in designing with ceramics can be detected. Information is given about some basic properties, tolerances and literature discussing the design with ceramics.     

Werkstoffkundliche Basis für die Konstruktion mit Ingenieurkeramik

Fundamental Properties for the Design with Engineering Ceramics Within the class of technical ceramics a new group of high quality materials has been developed, called “engineering ceramics”. A definition is given, some of their properties and future applications for mechanical design are pointed out. Comparing to the fundamental properties and definitions known for metallic materials the distinctions and different approach for the design with engineering ceramics are discussed.