Ling Fei

High Capacity MoO2/Graphite Oxide Composite Anode for Lithium-Ion Batteries.

Nanostructured MoO2/graphite oxide (GO) composites are synthesized by a simple solvothermal method. X-ray diffraction and transmission electron microscopy analyses show that with the addition of GO and the increase in GO content in the precursor solutions, MoO3 rods change to MoO2 nanorods and then further to MoO2 nanoparticles, and the nanorods or nanoparticles are uniformly distributed on the surface of the GO sheets in the composites. The MoO2/GO composite with 10 wt % GO exhibits a reversible capacity of 720 mAh/g at a current density of 100 mA/g and 560 mAh/g at a high current density of 800 mA/g after 30 cycles. The improved reversible capacity, rate capacity, and cycling performance of the composites are attributed to synergistic reaction between MoO2 and GO.

SBA-15 confined synthesis of TiNb2O7 nanoparticles for lithium-ion batteries

Unlike most conventional anode materials, the newly developed TiNb2O7 (TNO) does not form a solid electrolyte interface (SEI) layer, which makes it safe for high power requiring lithium-ion batteries. In this paper, we demonstrated an SBA-15 confined synthetic approach to prepare TNO nanoparticles (S-TNO) with a small particle size around 10 nm and a large BET surface area of 79.5 m(2) g(-1). It is worth mentioning that this is the smallest size reported so far for TNO. In contrast, the TNO (L-TNO) synthesized without SBA-15 has a particle size above 100 nm and a BET surface area of only 4.3 m(2) g(-1). The S-TNO shows better lithium-ion storage properties than L-TNO. The excellent electrochemical performance of S-TNO is attributed to its small crystalline size, which not only provides a larger effective area for better contact between the electrode material and the electrolyte, but also reduces the rate-limiting Li diffusion path. Moreover, S-TNO shows a high Coulombic efficiency (above 98% over 300 cycles) and negligible increase of impedance after cycling, which confirms no SEI layer formation in the operational voltage (1-3 V) of TNO.

Instant gelation synthesis of 3D porous MoS2@C nanocomposites for lithium ion batteries

Three-dimensional (3D) nanoporous architectures, possessing high surface area, massive pores, and excellent structural stability, are highly desirable for many applications including catalysts and electrode materials in lithium ion batteries. However, the preparation of such materials remains a major challenge. Here, we introduce a novel method, instant gelation, for the synthesis of such materials. The as-prepared porous 3D MoS2@C nanocomposites, with layered MoS2 clusters or strips ingrained in porous and conductive 3D carbon matrix, indeed showed excellent electrochemical performance when applied as anode materials for lithium ion batteries. Its interconnected carbon network ensures good conductivity and fast electron transport; the micro-, and mesoporous nature effectively shortens the lithium ion diffusion path and provides room necessary for volume expansion. The large specific surface area is beneficial for a better contact between electrode materials and electrolyte.

Bismuth oxide: a new lithium-ion battery anode

Bismuth oxide directly grown on nickel foam (p-Bi2O3/Ni) was prepared by a facile polymer-assisted solution approach and was used directly as a lithium-ion battery anode for the first time. The Bi2O3 particles were covered with thin carbon layers, forming network-like sheets on the surface of the Ni foam. The binder-free p-Bi2O3/Ni shows superior electrochemical properties with a capacity of 668 mAh/g at a current density of 800 mA/g, which is much higher than that of commercial Bi2O3 powder (c-Bi2O3) and Bi2O3 powder prepared by the polymer-assisted solution method (p-Bi2O3). The good performance of p-Bi2O3/Ni can be attributed to higher volumetric utilization efficiency, better connection of active materials to the current collector, and shorter lithium ion diffusion path.

Two-Dimensional V2O5 Sheet Network as Electrode for Lithium-Ion Batteries

Two-dimensional V2O5 and manganese-doped V2O5 sheet network were synthesized by a one-step polymer-assisted chemical solution method and characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermal-gravimetric analysis, and galvanostatic discharge-charge analysis. The V2O5 particles were covered with thin carbon layers, which remained after decomposition of the polymer, forming a network-like sheet structure. This V2O5 network exhibits a high capacity of about 300 and 600 mA·h/g at a current density of 100 mA/g when it was used as a cathode and anode, respectively. After doping with 5% molar ratio of manganese, the capacity of the cathode increases from 99 to 165 mA·h/g at a current density of 1 A/g (∼3 C). This unique network structure provides an interconnected transportation pathway for lithium ions. Improvement of electrochemical performance after doping manganese could be attributed to the enhancement of electronic conductivity.

Structure and magnetotransport properties of epitaxial nanocomposite La0.67Ca0.33MnO3:SrTiO3 thin films grown by a chemical solution approach

Epitaxial La0.67Ca0.33MnO3:SrTiO3 (LCMO:STO) composite thin films have been grown on single crystal LaAlO3(001) substrates by a cost effective polymer-assisted deposition method. Both x-ray diffraction and high-resolution transmission electron microscopy confirm the growth of epitaxial films with an epitaxial relationship between the films and the substrates as (002)film||(002)sub and [202]film||[202]sub. The transport property measurement shows that the STO phase significantly increases the resistivity and enhances the magnetoresistance (MR) effect of LCMO and moves the metal-insulator transition to lower temperatures. For example, the MR values measured at magnetic fields of 0 and 3 T are −44.6% at 255 K for LCMO, −94.2% at 125 K for LCMO:3% STO, and −99.4% at 100 K for LCMO:5% STO, respectively.

Nickel substituted LiMn2O4 cathode with durable high-rate capability for Li-ion batteries

Spinel LiMn2−xNixO4 (x = 0, 0.1, 0.2) nanoparticles were prepared through a simple one-step polymer-assisted chemical solution method. When x = 0.1, the cathode exhibited the best durable rate capability, with 100% of the capacity retained (∼100 mAh g−1) after 400 cycles at 10 C current rate. The excellent cyclability and rate capability originate from the thin carbon layer automatically formed from incomplete depolymerisation of polymers and the improved conductivity due to the nickel dopant. The improved conductivity was confirmed by less polarization at high current rate.

Chemical Solution Deposition of Epitaxial Metal‐Oxide Nanocomposite Thin Films

Epitaixial metal-oxide nanocomposite films, which possess interesting multifunctionality, have found applications in a wide range of devices. However, such films are typically produced by using high-vacuum equipment, like pulse-laser deposition, molecular-beam epitaxy, and chemical vapor deposition. As an alternative approach, chemical solution methods are not only cost-effective but also offer several advantages, including large surface coating, good control over stoichiometry, and the possible use of dopants. Therefore, in this Personal Account, we review the chemistry behind several of the main solution-based approaches, that is, sol-gel techniques, metal-organic decomposition, chelation, polymer-assisted deposition, and hydrothermal methods, including the seminal works that have been reported so far, to demonstrate the advantages and disadvantages of these different routes.

Enhancement of Low-field Magnetoresistance in Self-Assembled Epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 Composite Films via Polymer-Assisted Deposition.

Polymer-assisted deposition method has been used to fabricate self-assembled epitaxial La0.67Ca0.33MnO3:NiO and La0.67Ca0.33MnO3:Co3O4 films on LaAlO3 substrates. Compared to pulsed-laser deposition method, polymer-assisted deposition provides a simpler and lower-cost approach to self-assembled composite films with enhanced low-field magnetoresistance effect. After the addition of NiO or Co3O4, triangular NiO and tetrahedral Co3O4 nanoparticles remain on the surface of La0.67Ca0.33MnO3 films. This results in a dramatic increase in resistivity of the films from 0.0061 Ω•cm to 0.59 Ω•cm and 1.07 Ω•cm, and a decrease in metal-insulator transition temperature from 270 K to 180 K and 172 K by the addition of 10%-NiO and 10%-Co3O4, respectively. Accordingly, the maximum absolute magnetoresistance value is improved from −44.6% to −59.1% and −52.7% by the addition of 10%-NiO and 10%-Co3O4, respectively. The enhanced low-field magnetoresistance property is ascribed to the introduced insulating phase at the grain boundaries. The magnetism is found to be more suppressed for the La0.67Ca0.33MnO3:Co3O4 composite films than the La0.67Ca0.33MnO3:NiO films, which can be attributed to the antiferromagnetic properties of the Co3O4 phase. The solution-processed composite films show enhanced low-field magnetoresistance effect which are crucial in practical applications. We expect our polymer-assisted deposited films paving the pathway in the field of hole-doped perovskites with their intrinsic colossal magnetoresistance.

Preparation of Mesoporous Silica-Supported Palladium Catalysts for Biofuel Upgrade

We report the preparation of two hydrocracking catalysts Pd/CoMoO4/silica and Pd/CNTs/CoMoO4/silica (CNTs, carbon nanotubes). The structure, morphologies, composition, and thermal stability of catalysts were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, transmission electron microscopy (TEM), energy-dispersive X-ray (EDX), and thermogravimetric analysis (TGA). The catalyst activity was measured in a Parr reactor with camelina fatty acid methyl esters (FAMEs) as the feed. The analysis shows that the palladium nanoparticles have been incorporated onto mesoporous silica in Pd/CoMoO4/silica or on the CNTs surface in Pd/CNTs/CoMoO4/silica catalysts. The different combinations of metals and supports have selective control cracking on heavy hydrocarbons.