Gan Liang

Reduced graphene oxide modified Li2FeSiO4/C composite with enhanced electrochemical performance as cathode material for lithium ion batteries.

Reduced graphene oxide modified Li2FeSiO4/C (LFS/(C+rGO)) composite is successfully synthesized by a citric-acid-based sol-gel method and evaluated as cathode material for lithium ion batteries. The LFS/(C+rGO) shows an improved electronic conductivity due to the conductive network formed by reduced graphene oxide nanosheets and amorphous carbon in particles. Electrochemical impedance spectroscopy results indicate an increased diffusion coefficient of lithium ions (2.4 × 10(-11) cm(2) s(-1)) for LFS/(C+rGO) electrode. Compared with LFS with only amorphous carbon, the LFS/(C+rGO) electrode exhibits higher capacity and better cycling stability. It delivers a reversible capacity of 178 mAh g(-1) with a capacity retention ratio of 94.5% after 40 cycles at 0.1 C, and an average capacity of 119 mAh g(-1) at 2 C. The improved performance can be contributed to the reduced crystal size, good particle dispersion, and the improved conductive network between LFS particles.

Absorption distribution of an optical beam focused into a turbid medium.

The focusing of light into a turbid medium was studied with Monte Carlo simulations. Focusing was found to have a significant effect on the absorption distribution in turbid media when the depth of the focal point (the distance between the focal point and the surface of the turbid media) was less than or comparable with the transport mean free path. Focusing could significantly increase the peak absorption and narrow the absorption distribution. As the depth of the focal point increased, the peak absorption decreased, and the depth of peak absorption increased initially but quickly reached a plateau that was less than the transport mean free path. A refractive-index-mismatched boundary between the ambient medium and the turbid medium deteriorated the focusing effect, increased the absorption near the boundary, lowered the peak absorption, and broadened the absorption distribution.

Systematic investigation on Cadmium-incorporation in Li2FeSiO4/C cathode material for lithium-ion batteries

Cadmium-incorporated Li2FeSiO4/C composites have been successfully synthesized by a solid-state reaction assisted with refluxing. The effect and mechanism of Cd-modification on the electrochemical performance of Li2FeSiO4/C were investigated in detail by X-ray powder diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectra, transmission electron microscopy, positron annihilation lifetime spectroscopy and Doppler broadening spectrum, and electrochemical measurements. The results show that Cd not only exists in an amorphous state of CdO on the surface of LFS particles, but also enters into the crystal lattice of LFS. Positron annihilation lifetime spectroscopy and Doppler broadening spectrum analyses verify that Cd-incorporation increases the defect concentration and the electronic conductivity of LFS, thus improve the Li+-ion diffusion process. Furthermore, our electrochemical measurements verify that an appropriate amount of Cd-incorporation can achieve a satisfied electrochemical performance for LFS/C cathode material.

Superior rate performance of Li3V2(PO4)3 co-modified by Fe-doping and rGO-incorporation

Reduced graphene oxide (rGO) incorporated Li3V1.94Fe0.06(PO4)3/C cathode materials were successfully prepared by a sol–gel method. Compared with Li3V2(PO4)3/C and single rGO-incorporated Li3V2(PO4)3/C, the rGO-incorporated Li3V1.94Fe0.06(PO4)3/C electrode has the highest initial capacity of 164.4 mA h g−1 with a capacity retention ratio of 83.5% after 100 cycles at 1C. When charged/discharged for 1000 cycles at 5C, it exhibits a prominent capacity of 129.3 mA h g−1 with a capacity retention ratio of 91.5% and a very low capacity fading of 0.0085% per cycle. The superior electrochemical performance of Fe-doped and rGO-incorporated Li3V2(PO4)3 can contribute to the reduced particle size, the improved electronic conductivity, and the increased Li-ion diffusion coefficient. We believe this novel co-modification with Fe-doping and rGO-incorporation is an efficient way for Li3V2(PO4)3 and any other polyanion cathode materials to realize their application in power lithium ion battery.

Experimental results on the Kondo system (Ce, La)Ni2Sn2

Abstract Structural, transport, magnetic and Ce-L 3 X-ray absorption measurements on CeNi 2 Sn 2 are discussed. Our results indicate that this system is a Kondo heavy fermion system with Fermi liquid behavior, and with the possible occurrence of antiferromagnetic order at low temperature. Moreover, evidence in the structural and magnetic data support the possibility of an annealing induced distortion in this material.

X-ray absorption measurements on Tl1−xBixSr2CuO5 and Tl0.5Bi0.5Sr2CaCu2O7 Valences of Bi, Tl and Cu

Abstract Near-edge X-ray absorption spectroscopy measurements of Bi and Tl L3-edges and Cu K-edge in a series of compounds Tl 1− x Bi x Sr 2 CuO 5 and Tl 0.5 Bi 0.5 Sr 2 CaCu 2 O 7 have been presented. The results provides strong evidence for the existence of mixed-valent Bi and Tl in these compounds. Moreover, the formal valence of copper in Tl 1− x Bi x Sr 2 CuO 5 and Tl 0.5 Bi 0.5 Sr 2 CaCu 2 O 7 appears to be much higher than 2+. It is suggested that the Tl(Bi) 6s band could cross the Fermi level, resulting in electronic correlations between the Tl(Bi)-O and Cu-O layers, which is significant in determining the physical properties of these compounds.

Reentrant Kondo‐mixed valent‐Kondo regime behavior with T in the 3d CeT2Si2 series

In intermetallic compounds of Ce involving late 3d, 4d, and 5d row transition metals (T), the Ce valence state increases with decreasing T‐d‐band electron count. Neifeld, et al. [Phys. Rev. B 32, 6928 (1985)] have recently shown (using extensive Ce‐L3‐edge measurements) that this trend is reversed for the Ce‐3d row compounds earlier than Co. This somewhat striking behavior is nowhere more apparent than in the ThCr2Si2 crystal structure series CeT2Si2 with T=Cu, Ni, Co, Fe, Mn, and (MnxCr1−x). In this paper, we will discuss the following: (1) the extension of this crystal structure to its stability limit in the T=(Mn,Cr) substituted system; (2), how this extension permits restoration of the Ce‐valence state to the Kondo local‐moment regime; (3) low‐temperature electrical resistivity measurements which support first the Kondo to mixed valent followed by mixed valent to Kondo regime passage with decreasing 3d electron count in this series; and (4) finally the apparent compatibility of the Ce‐Kondo effect wit...

High critical current of Cu-sheathed MgB/sub 2/ wire at 20 K

For large-scale electric power applications of MgB/sub 2/ wire, especially at AC environments, development of nonmagnetic sheath material is essential. In this study, Cu-sheathed MgB/sub 2/ wire was fabricated using the powder-in-tube method and ultra-fine Mg and B precursor prepared by high-energy ball milling. Lowering the annealing temperature and shortening the annealing time effectively limit the reaction between Mg and Cu. Critical current density of the wire annealed at 700/spl deg/C for 5 minutes is 4.3/spl times/10/sup 4/ A/cm/sup 2/ at 20 K and self-field. Adding excess Mg in precursor further enhances critical current to 250 A at 20 K and self-field. These results demonstrate the potential of Cu-sheathed MgB/sub 2/ wires for large-scale applications.

The confirmation of superconductivity in the BiSrCaCuO system

Abstract By exploring more than 30 compositions in a quaternary oxide system BiSrCaCuO, we have (1) confirmed the existance of superconductivity up to 114K and (2) located the composition range for the superconducting phase. Several compositions in the proximity of the BiSrCaCu compositions 6:5:3:6 and 2:2:1:2 revealed identical diffraction patterns, indicating a broad homogeneity range for the superconducting phase. The equilibrium phase exhibits a T C ∼ 86K. Depending upon the heat treatment conditions, multiple superconducting transitions at temperatures above and below 86K have been observed.

Investigation of Co-incorporated pristine and Fe-doped Li3V2(PO4)3 cathode materials for lithium-ion batteries

Monoclinic Li3V2(PO4)3/C (LVP/C) and Li3V1.95Fe0.05(PO4)3/C (LVFP/C) composites were successfully modified by cobalt incorporation. The effects of cobalt incorporation on the structure, morphology and electrochemical performance of the LVP/C and LVFP/C composites were systematically investigated. The results show that most Co exists in the form of CoO and forms a hybrid layer with the carbon coating on the surface of the LVP and LVFP particles; moreover, a small part of Co enters into the LVP or LVFP lattices due to atomic diffusion. Compared with LVP/C and LVFP/C, Co-incorporated samples exhibit better electrochemical performance. In particular, under the common effect of doping and a hybrid layer (carbon and metal oxides) coating, the LVFP/C-Co electrode displays a prominent initial capacity of 124.7 mA h g-1 and a very low capacity fading of ∼0.04% per cycle even after 500 cycles at 20 C. This novel co-modification method with cation doping and a hybrid layer (carbon and metal oxide) coating is a highly effective way to improve the electrochemical performance and has great potential to be easily used to modify other cathode materials with poor electrical conductivity.