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In this paper, we report a simple sol–gel method for the synthesis of a composite containing reduced graphene oxide (R-GO) embedded within nano LiFePO 4 particles for a lithium-ion battery cathode. This composite has an effective electron pathway and a highly meso-porous structure as compared to conventional LiFePO 4 . Highly conductive R-GO, together with the meso-porosity results in a material that has good electronic conductivity and high electrolyte permeability. Electrodes fabricated from the composite exhibited excellent performance when evaluated as lithium-ion battery cathodes, including compared to pristine LiFePO 4 . The electrode of the R-GO composite exhibits excellent rate capabilities of 125 mAh g −1 at 10 C, whereas pristine LiFePO 4 could deliver only 81.5 mAh g −1 at the same condition. It also achieves an improved cyclability with capacity retention ratios of 92.48% after 200 cycles at 10 C, as well.

The nitrate-form of Ca–Fe-layered double hydroxide (Ca–Fe-LDH) was synthesized via co-precipitation method, and its phosphate-intercalates were prepared by ion-exchange reaction. According to X-ray diffraction analysis, the Ca–Fe-LDH–NO3− compound and its H2PO4−-intercalate showed hexagonal layered structures, whereas the ion-exchange reaction with HPO42− caused a frustration of the layer ordering of LDH. Fe K-edge X-ray absorption spectroscopy clearly demonstrated that the Ca–Fe-LDH lattice with trivalent iron ions was well-maintained after the ion-exchange with HPO42− and H2PO4−. Under acidic conditions, phosphate ions were slowly released from the Ca–Fe-LDH lattice and the simultaneous release of hydroxide caused the neutralization of acidic media. Fitting analysis based on kinetic models indicated a heterogeneous diffusion process of phosphates and a distinct dependence of release rate on the charge of phosphates. This study strongly suggested that Ca–Fe-LDH is applicable as bifunctional vector for slow release of phosphate fertilizer and for the neutralization of acid soil.

1D nanorods/nanowires of manganese oxides with different crystal structures and morphologies were prepared and characterized to understand the influence of the Mn valence in the solid-state precursor on the electrochemical activity of these nanomaterials and to elucidate the mechanism responsible for the excellent activity of β-MnO2 nanorods as well. According to powder X-ray diffraction analyses, treating manganese oxide precursors that have an oxidation state of ≤+3 with persulfate ions under hydrothermal conditions yields manganese oxides with the β-MnO2 structure. In contrast, the use of a LiMn2O4 precursor with a higher Mn valence leads to the formation of the α-MnO2-structured manganese oxide. Electron microscopic studies clearly show a 1D nanorod-type morphology for the β-MnO2 material, whereas a 1D nanowire-type morphology with a higher aspect ratio is observed for the α-MnO2 material. The diameter of the β-MnO2 nanorods decreases as the Mn valence in the precursors becomes smaller. According to e...

The porous hierarchical assembly of lithium-rich Li1+xMnO 3-δ 2D nanoplates as well as isolated 0D nanocrystalline homologues has been synthesized via lithiation reactions of nanostructured manganese oxides under hydrothermal conditions. According to powder X-ray diffraction and electron microscopy, a hydrothermal LiOH treatment for nanostructured δ-MnO2 precursor produces a lithium-rich Li 1+xMnO3-δ phase with the nanoworm-like hierarchically assembled 2D nanoplate morphology. After the lithiation reaction under identical conditions, the 1D nanowires of the α-MnO2 precursor are transformed into the 0D nanoparticles of the Li 1+xMnO3-δ phase. The Mn K-edge X-ray absorption spectroscopic analysis for the lithiated materials clearly demonstrated that tetravalent manganese ions are stabilized in octahedral sites of a Li 2MnO3-type layered structure composed of edge-shared MnO6/LiO6 octahedra. From electrochemical measurements, it was found that the lithiated Li1+xMnO3-δ nanostructured materials show much superior electrode performance over the precursor manganese oxides and bulk lithium-rich manganate. The powder X-ray diffraction analyses for the electrochemically cycled derivatives clearly demonstrated that the improvement of electrode performance after lithiation can be attributed to the phase transformation to the Li-rich Li 1+xMnO3-δ phase with high structural stability. On the basis of the present experimental findings, we are able to conclude that the present phase transformation route provides a new method not only to synthesize nanostructured lithium-rich manganese oxides with controllable dimensionality and morphology but also to improve the electrode performance of nanostructured manganese oxides Refereed/Peer-reviewed

The formation mechanism and atomic arrangement of one-dimensional (1D) nanostructured titanates have been systematically investigated with combinative spectroscopic and microscopic analyses. First of all, the influence of the interlayer distances of the lepidocrocite-type titanate precursor on the formation efficiency of 1D nanobelts has been studied, clearly demonstrating that the increase of basal spacing upon the protonation does not promote the formation of 1D nanostructures. This finding did not support the previously proposed exfoliation mechanism of the layered titanate precursor. Of special interest is that the poor efficiency of the protonated titanate as a precursor could be enhanced by Fe substitution, underscoring the importance of precursor dissolution. According to time-dependent electron microscopic analyses, the hydrothermal alkali treatment initially gave rise not only to a decrease in the particle size of the precursor but also to the formation of 1D titanate nanobelts with lepidocrocite...

Mesoporous iron oxide-layered titanate nanohybrids have been synthesized through a reassembling reaction between exfoliated titanate nanosheets and iron hydroxide nanoclusters, in which an electrostatic attraction between both nanosized species could be achieved at low pH of 1.5. The formation of the layer-by-layer ordered heterostructure with the repeating unit of 1.33 nm was clearly evidenced by powder X-ray diffraction and transmission electron microscopic analysis. According to Fe K-edge X-ray absorption spectroscopy, the hybridized iron oxide crystallizes with loosely packed network of three edge-shared FeO6 octahedra units. N2 adsorption−desorption isotherm and diffuse reflectance UV−vis measurements clearly demonstrated that the present iron oxide-layered titanate nanohybrids showed greatly expanded surface areas with mesopores (∼190−230 m2g−1) and narrow bandgap energies (∼2.3 eV), which are of crucial importance in creating a visible light-active photocatalyst. The test of photocatalytic activity...

Cr-substituted β-Mn1-xCrxO2 nanowires with nonaggregated morphology have been synthesized by the chemical oxidation of layered LiMn0.9Cr0.1O2 microcrystals under hydrothermal conditions at elevated temperature. According to powder X-ray diffraction analysis, a persulfate treatment at 200 °C gives rise to a unique transformation from a monoclinic-layered structure to a pyrolusite- (β-MnO2-) type structure. Electron microscopic analyses clearly demonstrated that the oxidized derivative consists of well-separated single-crystalline nanowires with a diameter of ∼30 nm and a length of several micrometers. Mn K-edge and Cr K-edge X-ray absorption spectroscopy and chemical analysis provide straightforward evidence for the substitution of chromium ions for the manganese sites of the pyrolusite-structured manganese oxide nanowires. Of special importance is that the present Cr-substituted β-MnO2-type nanowires show promising electrode performance for Li+ ion batteries, superior to those of pristine LiMn0.9Cr0.1O2, ...

LiNi 1− x Ti x O 2 (0 ≤ x ≤ 0.1) compounds have been synthesized by a direct molten-salt method that uses a eutectic mixture of LiNO 3 and LiOH salts. According to X-ray diffraction analysis, these materials have a well-developed layered structure (R3-m) and are an isostructure of LiNiO 2 . The LiNi 1− x Ti x O 2 (0 ≤ x ≤ 0.1) compounds have average particle sizes of 1–5 μm depending on the amount of Ti salt. Charge–discharge tests show that a LiNi 1− x Ti x O 2 (0 ≤ x ≤ 0.1) cathode prepared at 700 °C has an initial discharge capacity as high as 171 mA h g −1 and excellent capacity retention in the range 4.3–2.8 V at a current density of 0.2 mA cm −2 .

Olivine structure LiFePO 4 /C composite powders are synthesized as cathode materials for Li-ion batteries via a conventional solid-state reaction. Improvement in electrochemical performance has been achieved by using poly(vinyl alcohol) as the carbon sources for the as-prepared materials. The influence of the heat treatment on the physical and the electrochemical properties of LiFePO 4 /C materials is investigated. To examine the effect of added carbon content on the properties of materials, a one-step heat treatment has been employed with control of the PVA content in the precursor. Six samples were prepared with 0, 1, 3, 5, 10 and 30 wt.% PVA added to the raw materials. The particle size of LiFePO 4 decreases as the carbon content increases. Materials with medium carbon contents have a small charge-transfer resistance and thus exhibit superior electrochemical performance. Interestingly, for a LiFePO 4 /C composite with a low PVA content, an unusual plateau at 4.3 V is observed. It is considered that this is due to the Fe 3+ /Fe 4+ redox reaction of Fe 3+ compounds that are present as an impurity. For samples with a high PVA amount, a thicker carbon coating provides an obstacle to improve the electrochemical properties.

The properties of a new cathode material of nano-sized TiO 2 -coated Ni powder for application in molten carbonate fuel cells (MCFCs) are investigated. The material is prepared by a sol–gel method. X-ray diffraction (XRD), field emission-scanning electron microscopy (FE-SEM) with energy dispersive X-ray analysis (EDAX), transmission electron microscopy (TEM) and Raman spectroscopy are employed to characterize the cathode material. The nano-sized TiO 2 particles are homogenously coated on the surface of the Ni powder. A stable LiTi 1− x Ni x O 2 phase is formed on the surface of the Ni powder during immersion in molten carbonate at 650 °C. The solubility of the TiO 2 -coated Ni cathode is about 50% lower compare with that of a pure Ni cathode.

Fluorine-doped nanocrystalline tin dioxide materials (F:SnO 2 ) have been successfully prepared by the sol–gel process from a single molecular precursor followed by a thermal treatment at 450–650 °C. The resulting materials were characterized by FTIR spectroscopy, powder X-ray diffraction, nitrogen adsorption porosimetry (BET) and transmission electron microscopy (TEM). The mean particle size increased from 5 to 20 nm and the specific surface area decreased from 123 to 37 m 2 /g as the temperature of heat treatment was risen from 450 to 650 °C. Fluorine-doped nanocrystalline SnO 2 exhibited capacity of 560, 502, and 702 mA h/g with 48%, 50%, and 40% capacity retention after 25 cycles between 1.2 V and 50 mV at the rate of 25 mA/g, respectively. In comparison, commercial SnO 2 showed an initial capacity of 388 mA h/g, with only 23% capacity retention after 25 cycles.

Chemically activated graphene ('activated microwave expanded graphite oxide', a-MEGO) was used as a cathode material for Li-ion hybrid supercapacitors. The performance of a-MEGO was first verified with Li-ion electrolyte in a symmetrical supercapacitor cell. Hybrid supercapacitors were then constructed with a-MEGO as the cathode and with either graphite or Li(4)Ti(5)O(12) (LTO) for the anode materials. The results show that the activated graphene material works well in a symmetrical cell with the Li-ion electrolyte with specific capacitances as high as 182 F g(-1). In a full a-MEGO/graphite hybrid cell, specific capacitances as high as 266 F g(-1) for the active materials at operating potentials of 4 V yielded gravimetric energy densities for a packaged cell of 53.2 W h kg(-1).

A simple approach has been developed for the synthesis of Pt nanoparticles with uniform diameters of approximately 2.9 nm supported on reduced graphene oxide (RG-O) platelets via a modified polyol method. Compared to Johnson Matthey (JM) Pt/C (75 wt % Pt) catalyst, the Pt/RG-O (70 wt % Pt) composite showed much higher electrochemical surface area, greater catalytic activity towards the oxygen reduction reaction (ORR), and significantly better single cell polarization performance. The maximum power density of the Pt/RG-O composite was about 128 mW cm−2, an 11% greater than the JM Pt/C commercial catalyst.

1D nanostructured manganese oxides are prepared by oxidation reaction of precursor LiMn(2-x)Cr(x)O(4) microcrystals under hydrothermal condition. The crystal structure and morphology of the obtained manganese oxides are strongly dependent on the reaction condition and the chemical composition of the precursors. The alpha-MnO(2) nanowires are prepared by reaction at 120 degrees C, and their aspect ratios decrease with the Cr content in the precursor. Treating precursors with persulfate ions at 160-180 C yields the beta-MnO(2) nanorods for the precursors LiMn(2-x)Cr(x)O(4) with lower Cr content and the alpha-MnO(2) nanowires for the precursors with higher Cr content. The structure dependence of the products on the Cr content in the precursors is related to the high octahedral site stabilization energy of Cr(3+) ions and/or to the increase of Mn valence state upon Cr substitution. The increase of Cr content in the precursors degrades the electrode performance for the manganates prepared at 160 degrees C but improves electrode activity for those prepared at 180 degrees C. This observation can be explained by the structural variation and chromium substitution of the hydrothermally treated manganates. We conclude that the use of spinel LiMn(2-x)Cr(x)O(4) as precursors provides an effective way to synthesize 1D nanostructured manganate with tailored crystal structure and morphology. Refereed/Peer-reviewed