X.M. Feng

Three-dimensional porous V2O5 cathode with ultra high rate capability

Three-dimensional (3D) porous vanadium pentoxide (V2O5) thin films were synthesized by electrostatic spray deposition followed by annealing at 350 °C in air. The interconnected pore networks facilitate the kinetics of lithium-ion diffusion and help the porous V2O5 with stable capacity, high energy efficiency and excellent rate capability as a cathode material for lithium batteries.

Structural transition and atomic ordering in the non-stoichiometric double perovskite Sr2FexMo2-xO6

The structural transition and atomic ordering of a new series of ordered double perovskite oxides Sr2FexMo2-xO6 (0.8 less than or equal to x less than or equal to 1.5) have been studied by X-ray powder diffraction (XRD). Rietveld refinement of the powder diffraction profiles indicates that the crystal structure of the compounds Sr2FexMo2-xO6 changes from a tetragonal I4/mmm lattice to a cubic Fm(3)over-bar-m lattice around x = 1.2 and the lattice parameters decrease slightly as Fe content increases. The degree of ordering in Sr2FexMo2-xO6 exhibits a maximal at x = 0.95 and decreases as x deviates from 0.95

Ultrathin Li4Ti5O12 Nanosheets as Anode Materials for Lithium and Sodium Storage

Ultrathin Li4Ti5O12 (LTO) nanosheets with ordered microstructures were prepared via a polyether-assisted hydrothermal process. Pluronic P123, a polyether, can impede the growth of Li2TiO3 in the precursor and also act as a structure-directing agent to facilitate the (Li1.81H0.19)Ti2O5·2H2O precursor to form the LTO nanosheets with the ordered microstructure. Moreover, the addition of P123 can suppress the stacking of LTO nanosheets during calcining of the precursor, and the thickness of the nanosheets can be controlled to be about 4 nm. The microstructure of the as-prepared ultrathin and ordered nanosheets is helpful for Li(+) or Na(+) diffusion and charge transfer through the particles. Therefore, the ultrathin P123-assisted LTO (P-LTO) nanosheets show a rate capability much higher than that of the LTO sample without P123 in a Li battery with over 130 mAh g(-1) of capacity remaining at the 64C rate. For intercalation of larger size Na(+) ions, the P-LTO still exhibits a capacity of 115 mAh g(-1) at a current rate of 10 C and a capacity retention of 96% after 400 cycles.

Lithium chromium oxide modified spinel LiCrTiO4 with improved electrochemical properties

Lithium chromium titanium oxide (LiCrTiO4) spinel powders are synthesized by an acrylic acid polymerization method. The lithium intercalation capacity of the LiCrTiO4 sample synthesized in air is about 150 mA h g−1, which is very close to its theoretical capacity (157 mA h g−1). In addition to its very good cycle performance similar to that of Li4Ti5O12, the LiCrTiO4 shows excellent rate performance with no obvious capacity loss at the current density from 1C to 10C rates. By means of Raman spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy, the LiCrTiO4 sample synthesized in air is found to contain a small amount of lithium chromium oxide (LiCrxOy, y > 1/2 + 3x/2) as an in situ produced modifier that can improve the conductivity of the electrode.

Chromium-Modified Li4Ti5O12 with a Synergistic Effect of Bulk Doping, Surface Coating, and Size Reducing.

Bulk doping, surface coating, and size reducing are three strategies for improving the electrochemical properties of Li4Ti5O12 (LTO). In this work, chromium (Cr)-modified LTO with a synergistic effect of bulk doping, surface coating, and size reducing is synthesized by a facile sol-gel method. X-ray diffraction (XRD) and Raman analysis prove that Cr dopes into the LTO bulk lattice, which effectively inhibits the generation of TiO2 impurities. Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) verifies the surface coating of Li2CrO4 on the LTO surface, which decreases impedance of the LTO electrode. More importantly, the size of LTO particles can be significantly reduced from submicroscale to nanoscale as a result of the protection of the Li2CrO4 surface layer and the suppression from Cr atoms on the long-range order in the LTO lattice. As anode material, Li4-xCr3xTi5-2xO12 (x = 0.1) delivers a reversible capacity of 141 mAh g(-1) at 10 °C, and over 155 mAh g(-1) at 1 °C after 1000 cycles. Therefore, the Cr-modified Li4Ti5O12 prepared via a sol-gel method has potential for applications in high-power, long-life lithium-ion batteries.

Atomic ordering and magnetic properties of non-stoichiometric double-perovskite Sr2FexMo2-xO6

The crystal structure and magnetic properties of a new series of ordered double-perovskite oxides Sr2FexMo2-xO6 (0.8 less than or equal to x less than or equal to 1.5) have been studied. The crystal structure changes from a tetragonal I4/mmm lattice to a cubic Fm (3) over barm lattice around x = 1.2. The degree of ordering in Sr2FexMo2-xO6 exhibits a maximal at x = 0.95 and decreases as x deviates from 0.95. The saturated magnetization increases from x = 0.8 to 0.95 and then decreases from x = 0.95 to 1.5. The Curie temperature exhibits an abrupt drop around x = 1.2, where the structural transition takes place. These complex behaviours are strongly correlated to antisite defect concentration in the compounds.

Metal–semiconductor transition in non-stoichiometric double perovskite Sr2FexMo2−xO6

The electronic transport properties of the ordered double perovskite oxides Sr2FexMo2-xO6 (0.8 less than or equal to x less than or equal to 1.5) have been investigated. In this system, the samples (x greater than or equal to 1.2) are semiconducting in the temperature range of 4.2 less than or equal to T less than or equal to 300 K. A metal-semiconductor transition occurs when x < 1.2 and the transition temperature T-MS decreases obviously as the Fe, content decreases. Rietveld refinement of the X-ray powder. diffraction profiles indicates that the crystal structure of the compounds Sr2FexMo2-xO6 changes from a tetragonal I4/mmm lattice to a cubic Fm (3) over barm lattice around x = 1.2

Crystal structures of compounds in the pseudobinary system Gd5Ge4-La5Ge4

Crystal structures of compounds at ambient temperature in the pseudobinary system Gd5Ge4-La5Ge4 were studied by X-ray powder diffraction (XRD). There exist three single-phase regions in this system. The crystal structure of Gd5Ge4, La5Ge4 and Gd3La2Ge4, which are prototype compounds in three phase regions, respectively, were reported. The Gd5Ge4 and La5Ge4 crystallize in the orthorhombic Sm5Ge4-type structure with space group Pnma. The ternary intermediate compound Gd3La2Ge4, which is determined for the first time, crystallizes in the monoclinic Gd5Si2Ge2-type structure with space group P112(1)/a. The Rietveld powder diffraction profile fitting technique was used for the refinement of crystal structure. The lattice parameters, atomic occupations, interatomic distances of the Gd5Ge4, La5Ge4 and Gd3La2Ge4 compounds were derived

A chromium oxide solution modified lithium titanium oxide with much improved rate performance

A simple surface modification of Li4Ti5O12 powder is made with an aqueous CrO3 solution to improve its electrochemical properties. At a high current rate of 30 C, the specific capacity of the Li4Ti5O12 increases by about 60% from its original 80 to 130 mA h g−1. After the modification with the CrO3 solution, a few surface phases including lithium chromate (Li2CrO4), Cr2O5 and anatase are found to co-exist in the final product. Among these three phases, Li2CrO4 and Cr2O5 can improve while anatase deteriorates the rate performance of Li4Ti5O12. The AC impedance spectra and electron spin resonance (ESR) spectra reveal that the improvement of rate performance is correlated with the presence of Ti3+, which can increase the conductivity of the Li4Ti5O12 sample. Lithium chromate (Li2CrO4) and Cr2O5 react with lithium to form lithium rich phases (Li3+xCrO4 and LiyCr2O5) of low potential, which stabilize Li7Ti5O12 with high electric conductivity and result in better rate performance. Besides improved rate performance, the cycle performance of the modified Li4Ti5O12 samples is almost at the same level with the original Li4Ti5O12, suggesting that this proposed modification method is efficient and harmless.

Mixing effects of light and heavy rare earths in the Laves phase compounds Nd1−xHRxCo2 (HR = Gd,Tb)

The mixing effects of light and heavy rare earths in cubic Laves phase compounds Nd1-xHRxCO2 (HR = Gd, Tb) have been investigated by means of x-ray powder diffraction and magnetic measurements. In Nd1-xTbxCo2, the saturation moment M-S exhibits in anomaly and could be ascribed to an abrupt jump of the Co moment at a critical concentration x approximate to 0.33, whereas, in Nd1-xGdxCo2, M-S does not show such an anomaly and a relatively simple magnetic behaviour is observed at x(c) approximate to 0.43. The different behaviours of these two systems can be understood by considering the structural distortion of a cubic unit cell at low temperature. A field-induced metamagnetic transition from weak ferrimagnetism to strong ferrimagnetism is observed in both systems. This can be interpreted by the evolution of magnetization with the help of percolation theory. The compensation points are observed in both systems, which are well explained within the two-sublattice model. A double peak of the AC susceptibility observed in Nd1-xTbxCo2 near x(0) approximate to 0.19 does not necessarily mean the occurrence of a first-order phase transition. The observed second-order magnetic phase transition near x(0) can be well described by Landau theory of the phase transition.