P. A. van Aken

Tin Nanoparticles Encapsulated in Porous Multichannel Carbon Microtubes: Preparation by Single-Nozzle Electrospinning and Application as Anode Material for High-Performance Li-Based Batteries

Tin nanoparticles encapsulated in porous multichannel carbon microtubes (denoted as SPMCTs) were prepared by carbonization of electrospun PAN-PMMA-tin octoate nanofibers fabricated using a single-nozzle electrospinning technique. This material exhibited excellent characteristics for lithium ion battery anode applications in terms of reversible capacities, cycling performance, and rate capability. Undertaking such a production configuration allows the long-existing problem of obtaining a high packing density of tin particles while retaining sufficient spare space to buffer the volume variation during lithium alloying and dealloying processes to be properly addressed. Furthermore, the porous carbon shell preserves both the mechanical and chemical stability of the function-active Sn metal, which also serves as a highly conductive medium allowing Li(+) to access.

Carbon-Coated Na3V2(PO4)3 Embedded in Porous Carbon Matrix: An Ultrafast Na-Storage Cathode with the Potential of Outperforming Li Cathodes

Sodium ion batteries are one of the realistic promising alternatives to the lithium analogues. However, neither theoretical energy/power density nor the practical values reach the values of Li cathodes. Poorer performance is expected owing to larger size, larger mass, and lower cell voltage. Nonetheless, sodium ion batteries are considered to be practically relevant in view of the abundance of the element Na. The arguments in favor of Li and to the disadvantage of Na would be completely obsolete if the specific performance data of the latter would match the first. Here we present a cathode consisting of carbon-coated nanosized Na3V2(PO4)3 embedded in a porous carbon matrix, which not only matches but even outshines lithium cathodes under high rate conditions. It can be (dis)charged in 6 s with a current density as high as 22 A/g (200 C), still delivering a specific capacity of 44 mAh/g, while up to 20 C, the polarization is completely negligible.

Mössbauer and ELNES spectroscopy of (Mg,Fe)(Si,Al)O3 perovskite: a highly oxidised component of the lower mantle

Abstract (Mg,Fe)(Si,Al)O3 perovskite samples with varying Fe and Al concentration were synthesised at high pressure and temperature at varying conditions of oxygen fugacity using a multianvil press, and were characterised using ex situ X-ray diffraction, electron microprobe, Mössbauer spectroscopy and analytical transmission electron microscopy. The Fe3+/ΣFe ratio was determined from Mössbauer spectra recorded at 293 and 80 K, and shows a nearly linear dependence of Fe3+/ΣFe with Al composition of (Mg,Fe)(Si,Al)O3 perovskite. The Fe3+/ΣFe values were obtained for selected samples of (Mg,Fe)(Si,Al)O3 perovskite using electron energy-loss near-edge structure (ELNES) spectroscopy, and are in excellent agreement with Mössbauer data, demonstrating that Fe3+/ΣFe can be determined with a spatial resolution on the order of nm. Oxygen concentrations were determined by combining bulk chemical data with Fe3+/ΣFe data determined by Mössbauer spectroscopy, and show a significant concentration of oxygen vacancies in (Mg,Fe)(Si,Al)O3 perovskite.

Hollow carbon nanospheres with a high rate capability for lithium-based batteries

The development of rechargeable lithium batteries is one of the success stories of modern materials science. They are currently used in a wide range of portable electronic devices because of their high energy density. Even though the performance of the batteries has been already been considerably enhanced in the last decades, further improvement of both their energy density and power density is to be aimed for. Carbonaceous materials are of tremendous interest in energy storage applications and are widely used as electrode materials in lithium batteries but also in electrochemical double layer capacitors. Carbon represents perhaps the most versatile base material, particularly in view of the huge variety of carbon materials that exists. These show large differences in crystallinity, chemical composition, and microstructure; all of which are features that the lithium storage mechanism shows sensitivity towards. In a rather broad definition, carbons can be classified as graphitic or nongraphitic. Graphite is the dominant anode material in today’s commercial rechargeable batteries because of its low cost, high stability, and low electrode potential relative to lithium metal. However, the low theoretical capacity of graphite (372 mAhg 1 for the nominal composition LiC6) and relatively low lithium diffusion coefficient (10 –10 10 cm s ), markedly influenced by the staging phenomenon, restrict its use for future battery applications in, for example, electric vehicles). 12] Nongraphitic carbons have recently attracted a great deal of attention because of their higher lithium storage capabilities compared to graphite, as defects are thought to provide large excess capacities. 8] Recent research efforts have therefore been devoted to the exploration of disordered carbonaceous materials that possess a high energy density. Kaskhedikar and Maier have provided a summary of various possible mechanisms of excess lithium storage in disordered carbon as compared to perfect graphite. Beside varying the properties of the bulk material, tuning of the particle size and morphology are important tools to optimize electrochemical performance. Zhou et al. reported the use of an ordered mesoporous carbon prepared by nanocasting from an ordered silica template as negative electrode in lithium-ion batteries. A high reversible capacity, up to 1100 mAhg , could be reached. Hierarchically porous carbon monoliths reported by Hu et al. showed even better storage properties, particularly at high rates. Very recently, Han et al. synthesized hollow carbon spheres with graphic structure. A good rate capability of 133 mAhg 1 at 10 C was achieved. The studies cited above demonstrate that a well-defined morphology is an important requirement for effectively improving the electrochemical properties of carbonaceous materials. Taking the high inherent electronic conductivities of carbonaceous materials into consideration, the reduced lithium diffusion path length as well as the large electrode/electrolyte contact area are the factors that lead to improved performance. In this context hollow nanospheres are unique materials, and their special shape, permeability, and high surface area permit applications in important fields such as energy storage, catalysis, drug release, and others. In this Communication, we propose the use of a novel nanocarbon architecture as lithium-ion battery anode material : an ensemble of monodisperse hollow carbon nanospheres synthesized via a combined polystyrene latex/hydrothermal carbonization templating approach. The carbon nanospheres employed here have a diameter of ca. 100 nm whilst the shell thickness is ca. 12 nm. We report herein that the unique structural combination offered by these sustainable carbon nanomaterials, that is, a hollow interior and a thin carbon shell, leads to a lithium-ion battery anode material with excellent cycling performance and superior rate capability. The hollow carbon nanospheres were prepared by using the established technique of hydrothermal carbonization of monosaccharide in the presence of spherical polystyrene latex nanoparticle templates. Briefly, an aqueous dispersion of polymer latexes of the desired size (D = 100 nm) is mixed with d-glucose acting as the carbon precursor. The system is then heated at 180 8C for 20 h. After reaction termination, the carbonaceous product is recovered, followed by washing and drying. To remove the thermally labile polymer template and simultaneously improve the level of structural order and conductivity in the carbonaceous shell, the composite material was heated to 1000 8C under an inert atmosphere. Electron microscopy analysis of the carbon nanosphere anode material revealed that the product consisted of uniform hollow nanospheres, neatly interconnected and demonstrating a near-perfect replication of the shape and size features of the [a] Dr. K. Tang, Prof.Dr. J. Maier Max Planck Institute for Solid State Research Heisenbergstr. 1, 70569 Stuttgart (Germany) Fax: + 49 (0)711 689 1722 E-mail : k.tang@fkf.mpg.de [b] Dr. R. J. White, Dr. M.-M. Titirici Max Planck Institute for Colloids and Interfaces Am Muehlenberg, 14476 Golm (Germany) Fax: + 49 331 567 9502 E-mail : robin.white@mpikg.mpg.de [c] X. Mu, Prof.Dr. P. A. van Aken Max Planck Institute for Intelligent Systems Heisenbergstr. 3, 70569 Stuttgart (Germany) Supporting Information for this article is available on the WWW under http://dx.doi.org/10.1002/cssc.201100609.

Surface plasmon modes of a single silver nanorod: an electron energy loss study

We present an electron energy loss study using energy filtered TEM of spatially resolved surface plasmon excitations on a silver nanorod of aspect ratio 14.2 resting on a 30 nm thick silicon nitride membrane. Our results show that the excitation is quantized as resonant modes whose intensity maxima vary along the nanorods length and whose wavelength becomes compressed towards the ends of the nanorod. Theoretical calculations modelling the surface plasmon response of the silver nanorod-silicon nitride system show the importance of including retardation and substrate effects in order to describe accurately the energy dispersion of the resonant modes.

Direct imaging of surface plasmon resonances on single triangular silver nanoprisms at optical wavelength using low-loss EFTEM imaging.

Using low-loss energy-filtering transmission electron microscopy (EFTEM) imaging, we map surface plasmon resonances (SPRs) at optical wavelengths on single triangular silver nanoprisms. We show that EFTEM imaging combining high spatial sampling and high energy resolution enables the detection and for the first time, to the best of our knowledge, mapping at the nanoscale of an extra multipolar SPR on these nanoparticles. As illustrated on a 276.5 nm long nanoprism, this eigenmode is found to be enhanced on the three edges where it exhibits a two-lobe distribution.

Experimental realization of graded L10-FePt/Fe composite media with perpendicular magnetization

A concept is suggested and experimentally realized to fabricate graded media for ultrahigh density magnetic recording where the material parameters vary gradually in the interfacial region between the hard magnetic part and the soft magnetic part of epitaxial L10-FePt/Fe exchange spring nanocomposites with perpendicular magnetization. A graded interface between the L10-FePt phase and the Fe phase is formed by depositing part of the Fe layer at elevated temperatures. The existence of the graded interface is verified by electron energy-loss spectroscopy. The influence of the character of the graded interface on the magnetic properties is studied. With increasing thickness of the graded interface the coercivity continuously decreases, which can be used for a fine tuning of the coercivity of exchange spring composite media.

Toughening through nature-adapted nanoscale design

The extraordinary combination of strength and toughness attained by natures highly sophisticated structural design in nacre has inspired the synthesis of novel nanocomposites. In this context, the organic-inorganic hierarchical design of nacre has been mimicked. However, two key features of nacre, namely the scaling of the structural components and the low content of the organic phase, have not been replicated yet. Here, we present thin nanocomposite films with properly adjusted thicknesses of the organic and inorganic layers, as well as a microstructure that closely resembles that of nacre. These films, which are obtained by the combination of low-temperature chemical bath deposition of titania with layer-by-layer assembly of polyelectrolytes, exhibit enhancement in a fracture toughness by a factor of 4, combined with notable increase in hardness, while the Youngs modulus is largely preserved in comparison to the single titania layer. Our findings highlight the significance of the 10:1 inorganic/organic layer thickness ratio evolved by nature, and provide novel perspectives for the future development of efficient bioinspired thin films.

Tiny Li4Ti5O12 nanoparticles embedded in carbon nanofibers as high-capacity and long-life anode materials for both Li-ion and Na-ion batteries

Tiny Li4Ti5O12 nanoparticles embedded in carbon nanofibers (Li4Ti5O12@C hierarchical nanofibers) were synthesized using a scalable synthesis technique involving electrospinning and annealing in an Ar atmosphere for the purpose of using them as anode materials for high-capacity and high-rate-capability Li-ion and Na-ion batteries. The Li4Ti5O12@C hierarchical nanofibers exhibited high stable discharge capacities of about 145.5 mA h g(-1) after 1000 cycles at 10C for the Li-ion battery anode. For Na-ion storage performance, a reversible capacity of approximately 162.5 mA h g(-1) is stably maintained at 0.2C during the first 100 cycles.

Delithiation study of LiFePO4 crystals using electron energy-loss spectroscopy

There is still some controversy about the mechanisms responsible for the delithiation of LiFePO 4 . We studied the delithiation of both large single crystals and powder by electron energy-loss spectroscopy. It is shown that Li depletion leads to a change in the Fe valency, to an enhanced prepeak at the O K edge, and to a pronounced interband transition peak between 4 and 6 eV. Exploiting these spectral changes, the delithiation process was monitored, with the result that in the large single crystal, delithiation takes place by removal of Li from the surface-near region, whereas in small particles, Li is removed from the particle core.