SiXu Deng

Preparation of Novel Three-Dimensional NiO/Ultrathin Derived Graphene Hybrid for Supercapacitor Applications

A new type of three-dimensional (3D) NiO/ultrathin derived graphene (UDG) hybrid on commercial Ni foam (NF) for a binder-free pseudocapacitor electrode is presented. NiO nanoflakes are in situ grown by a chemical bath deposition (CBD) technique on the free-standing 3D UDG/NF scaffold, which is first prepared by a simple nanocasting process consisting of hydrothermal reaction and subsequent thermal transformation. The 3D UDG/NF scaffold with interconnected network affords a high conductivity due to the high graphitization degree and efficiently facilitates the electron transport to NiO. Moreover, the 3D NiO/UDG/NF hybrid allows for a thinner 3D active material layer under the same loading density, which could shorten the diffusion paths of ions. The NiO/UDG/NF hybrid is directly used as a binder-free supercapacitor electrode, which exhibited significantly improved supercapacitor performance compared to the bare CBD prepared NiO/NF electrode.

Three-dimensional Co3O4/flocculent graphene hybrid on Ni foam for supercapacitor applications

A novel Co3O4/flocculent graphene (FG) hybrid on commercial Ni foam (NF) has been prepared. The unique flocculent graphene structure is prepared by combining a rapid filtering approach through Ni foam and a template method, in which the thermally expanded graphite is used as precursor and polystyrene (PS) microspheres are used as templates. The PS spheres play an important role in preventing the re-stacking of graphene nanosheets and the formation of flocculent graphene on NF. The PS spheres were first introduced as a guest material and were subsequently removed by calcination. The resulting free-standing FG/NF provides a three-dimensional and high conductivity scaffold for the hydrothermal growth of Co3O4 nanoclusters. The obtained Co3O4/FG/NF hybrid could be directly used as a binder-free supercapacitor electrode. Moreover, the Co3O4 nanoclusters on FG/NF scaffold exhibit improved specific capacitance of 1615 F g−1 compared to that of the bare NF. The 3D active material layer of Co3O4/FG/NF hybrid, high conductivity of 3D FG/NF scaffold and functional features of the Co3O4 nanocluster morphology synergistically result in an improved electrochemical performance.

Morphologically Controlled Synthesis of Porous Spherical and Cubic LaMnO3 with High Activity for the Catalytic Removal of Toluene

A morphology-controlled molten salt route was developed to synthesize porous spherical LaMnO3 and cubic LaMnO3 nanoparticles using the as-prepared porous Mn2O3 spheres as template. The porous LaMnO3 spheres with an average pore size of about 34.7 nm and the cubic LaMnO3 nanoparticles with a good dispersion were confirmed by scanning electron microscope, transmission electron microscope, and N2 adsorption-desorption measurements. The mechanism of morphological transformation from the porous spherical structure to the cubic particle in the molten salt was proposed. The porous spherical LaMnO3 and cubic LaMnO3 catalysts exhibited high catalytic performance for the combustion of toluene, and the latter performed better than the former. Under the conditions of toluene/oxygen molar ratio = 1/400 and space velocity = 20,000 h(-1), the temperature required for 10, 50, and 90% toluene conversion was 110, 170, and 220 °C over the cubic LaMnO3 catalyst, respectively. Based on the results of X-ray photoelectron spectroscopic and hydrogen temperature-programmed reduction characterization, we deduce that the higher surface Mn(4+)/Mn(3+) molar ratio and better low-temperature reducibility enhanced the catalytic performance of cubic LaMnO3. Taking the facile morphology-controlled synthesis and excellent catalytic performance into consideration, we believe that the well-defined morphological LaMnO3 samples are good candidate catalytic materials for the oxidative removal of toluene.

Research Progress in Improving the Rate Performance of LiFePO4 Cathode Materials

Olivine lithium iron phosphate (LiFePO4) is considered as a promising cathode material for high power-density lithium ion battery due to its high capacity, long cycle life, environmental friendly, low cost, and safety consideration. The theoretical capacity of LiFePO4 based on one electron reaction is 170 mAh g−1 at the stable voltage plateau of 3.5 V vs. Li/Li+. However, the instinct drawbacks of olivine structure induce a poor rate performance, resulting from the low lithium ion diffusion rate and low electronic conductivity. In this review, we summarize the methods for enhancing the rate performance of LiFePO4 cathode materials, including carbon coating, elements doping, preparation of nanosized materials, porous materials and composites, etc. Meanwhile, the advantages and disadvantages of above methods are also discussed.

Preparation and electrochemical properties of double-shell LiNi0.5Mn1.5O4 hollow microspheres as cathode materials for Li-ion batteries

Double-shell LiNi0.5Mn1.5O4 (LNMO-DS) hollow microspheres have been synthesized via a facile molten salt and annealing method. This method is a heating and cooling process with programmed control, which can promote the formation of a double-shell hollow microspherical structure and suppress rock-salt impurity phase. The LNMO-DS material with an average size of about 1 μm has outer and inner shells with thicknesses of all about 100 nm, which is confirmed by transmission electron microscopy (TEM). The double shell structures allow easy penetration of the electrolyte into the whole microspheres and buffer the large volume change of the electrode materials during Li ion intercalation/deintercalation processes. When applied as cathode materials for Li ion batteries, LNMO-DS exhibit high reversible capacity, excellent cycling and rate performances. The capacities remain at about 98.3% after 100 cycles (116.7 mA h g−1 at 0.5C). Furthermore, the favorable electrochemical performances of LNMO-DS are suitable for them to be used as the positive electrode in full cells.

The effects of supercritical carbon dioxide treatment on the morphology and electrochemical performance of LiFePO4 cathode materials

As cathode materials, LiFePO4 particles have been investigated after a supercritical carbon dioxide (scCO2) treatment. We first produced LiFePO4 through a hydrothermal method. Then, scCO2 was introduced to change the morphology of the particles. Three effects have been found after the scCO2 treatment; the breakup of the aggregated LiFePO4 platelets into separate plates, the purification of LiFePO4, and the formation of porous LiFePO4. Electrochemical measurements showed that the performance of LiFePO4 greatly improved after the scCO2 treatment. Finally, a theoretical model was used to explain the mechanism of the morphology change.