Rechargeable lithium-ion batteries are essential to portable electronic devices. Owing to the rapid development of such equipment there is an increasing demand for lithium-ion batteries with high energy density and long cycle life. For high energy density, the electrode materials in the lithium-ion batteries must possess high specific storage capacity and coulombic efficiency. Graphite and LiCoO 2 are normally used and have high coulombic efficiencies (typically >90%) but rather low capacities (372 and 145 mAhg -1 , respectively). [1][2][3][4][5] Various anode materials with improved storage capacity and thermal stability have been proposed for lithium-ion batteries in the last decade. Among these, silicon has attracted great interest as a candidate to replace commercial graphite materials owing to its numerous appealing features: it has the highest theoretical capacity (Li 4.4 Siº4200 mAhg ) of all known materials, and is abundant, inexpensive, and safer than graphite (it shows a slightly higher voltage plateau than that of graphite as shown in Figure S1, and lithiated silicon is more stable in typical electrolytes than lithiated graphite [6]).The practical use of Si powders as a negative electrode in lithium-ion batteries is, however, still hindered by two major problems: the low intrinsic electric conductivity and severe volume changes during Li insertion/extraction processes, leading to poor cycling performance. [7][8][9][10][11][12][13][14][15][16][17][18][19][20] Tremendous efforts have been made to overcome these problems by decreasing the particle size, [7, 8a,b] using silicon-based thin films and silicon-metal alloys, [9,10, 20] dispersing silicon into an inactive/ active matrix, [11][12][13][14][15][16][17][18][19] and coating with carbon as well as using different electrolyte systems. [15, 20] In these approaches a variety of composites of active and inactive materials have been widely exploited in which the inactive component plays a structural buffering role to minimize the mechanical stress induced by huge volume change of active silicon, thus preventing the deterioration of the electrode integrity. [11][12][13][14][15][16][17][18][19] Recent work has demonstrated that anodes made of silicon/ carbon composites can combine the advantageous properties of carbon (long cycle life) and silicon (high lithium-storage capacity) to improve the overall electrochemical performance of the anode for lithium-ion batteries. [8c,9b, 11-13,15-17] In contrast to these rather complicated high-temperature processes we report here a new, simple, and green methodology for the simultaneous coating of preformed silicon nanoparticles in a one-step procedure with a thin layer of SiO x and carbon by the hydrothermal carbonization of glucose. This Si@SiO x /C nanocomposite with a typical core/shell structure, which was further modified by electrochemical in situ generation of a passivated layer, shows remarkably improved lithium-storage performance in terms of high reversible lithium-storage capacity (º1100 mAhg -1 ), ex...

For the past decade, nanostructuring has been becoming one of the most powerful means to improve electrochemical performance of electrode materials in terms of both energy and power densities in rechargeable lithium-based energystorage devices which have a wide range of promising applications in portable electronic devices and in powering electric vehicles. [1][2][3][4][5][6] Nanostructuring is very helpful in improving the electroactivity of electrode materials (e.g. Li storage in nanostructured TiO 2 [6c, 7] and MnO 2 [8] with rutile structure), in improving the cycle life of electrode materials (e.g. Li storage in nanostructured Ni-Sn [3a] and Si [9] ), and especially in improving discharge/charge rate capability of electrode materials. [1, 3a, 6e,f, 10] Very recently, an optimized nanostructure design of electrode materials for high-power and high-energy lithium-ion batteries was proposed.[6e,f] The major characteristic tool is the introduction of hierarchical mixed-conducting networks (that is, networks that can conduct both ions and electrons). These networks involve the combination of both the nano-and microscale materials through which the effective diffusion length for both electrons and ions is reduced to only several nanometers. The concept was realized by the synthesis of mesoporous TiO 2 :RuO 2 and C-LiFePO 4 :RuO 2 nanocomposite electrodes which show high rate capabilities when used as the anode and cathode materials for lithium batteries. The key to its success is both the preparation of mesopores which render the electrolyte diffusion into the bulk of the electrode material facile and hence provide fast transport channels for the conductive ions (e.g., solvated Li + ions), and the coating of pore channels by a good electronic conductor-the oxide RuO 2 -that enables fast electronic transport pathway. However, RuO 2 is an expensive material, a cost-effective alternate is desired for such nanostructure. Carbon is one of the best choices because of its high electronic conductivity, good lithium permeation, and electrochemical stability. The carbon-coating technique is widely applied in a variety of electrode materials. [9a,10g, 11-13] However, the synthesis of such nanocomposites is complicated and the thickness of carbon shell needs to be controlled to a few nanometers and the porosity required for Li migration through this layer must be obtained.Herein, we propose the use of a nanoarchitectured electrode composed of an efficient mixed-conducting network (Figure 1 a), in which carbon tube-in-tube (CTIT) serves as "electronic wire" which provides the electrons to the active materials and the specifically designed tube diameter of the CTIT allows for easy electrolyte access. Such a nanostructure provides both an electronic pathway and a lithium-ion pathway which are essential for a high rate rechargeable lithium battery. We also show that CTIT can be employed as a nanoreactor for the synthesis nanomaterials, by exploiting its multiple channels and the possibility of confining reagents within t...

We report the synthesis, characterization, and catalytic performance of Fe-Co alloy nanoparticles inside the tubular channel of carbon nanotubes. The homogeneous distributions of Fe and Co in the isolated nanoparticles were evidenced confidentially by bulk and surface structural and compositional characterizations, that is, scanning electron microscopy, high-resolution transmission electron microscope in combination with elemental mapping by energy dispersive X-ray spectroscopy and electron energy-loss spectroscopy, powder X-ray diffraction, and X-ray photoelectron spectroscopy. We also demonstrate for the first time an unusual synergism in alloy catalysis. The alloy nanoparticles with widely varying Co/Fe ratio are kept as active as Co for the H 2 production from NH 3 decomposition. The stability of Co was significantly improved by alloying with Fe. We expect our experimental method to be a general approach to elucidate the synergism phenomenon in alloy catalysis.

Soot particulate collected from a Euro III heavy duty diesel engine run under black smoke conditions was investigated using thermogravimetry, transmission electron microscopy, electron energy loss spectroscopy, and X-ray photoelectron spectroscopy. The characterization results are compared with those of commercial carbon black. The onset temperature toward oxidation of the diesel engine soot in 5% O2 is 150 degrees C lower than that for carbon black. The burn out temperature for the diesel engine soot is 60 degrees C lower than that of the carbon black. The soot primary particles exhibit a core-shell structure. The shell of the soot particles consists of homogeneously stacked basic structure units. The commercial carbon lamp black is more graphitized than the diesel engine soot, whereas the diesel engine soot contains more carbon in aromatic nature than the carbon black and is highly surface-functionalized. Our findings reveal that technical carbon black is not a suitable model for the chemistry of the diesel engine soot.

Carbon samples are being investigated with thermogravimetry, infrared spectroscopy and transmission electron microscopy. We focus on a spark discharge soot, soot from a heavy-duty diesel engine, soot from a diesel engine in black smoking conditions and a furnace carbon black from Degussa. The aim of this study is to correlate reactivity towards oxygen, functional groups and nanostructure. It is found that the amount of defects as well as the functionalisation plays an important role in the onset of combustion in the thermogravimetric experiments. Clear differences in reactivity towards oxidation are observed.