Yingqiang Wu

Facile synthesis of a Co3O4-carbon nanotube composite and its superior performance as an anode material for Li-ion batteries

In this work, we report a facile method for the synthesis of a Co3O4–functionalized carbon nanotube (Co3O4–f-CNT) composite via the growth of Co3O4 nanoparticles on the surface of functionalized carbon nanotubes (f-CNTs) by thermal decomposition of cobalt nitrate hexahydrate in ethanol. The composite consists of 13% carbon nanotubes and 87% Co3O4 nanoparticles by weight, and all the Co3O4 particles grew compactly along the carbon nanotube axis with a highly uniform dispersion. When used as an anode material for rechargeable lithium ion batteries, the composite manifested high capacities and excellent cycling performance at high and low current rates. The discharge capacity was 719 mA h g−1 at the 2nd cycle and 776 mA h g−1 at the 100th cycle. Even at a current density of 1 A g−1, the specific capacity still remained at about 600 mA h g−1. This superior electrochemical performance was attributed to the unique nanostructure of the composite. Because almost all of the Co3O4 nanoparticles were immobilized on the surface of f-CNTs, physical aggregation of nanoparticles was avoided during the charge–discharge processes. Furthermore, the good mechanical flexibility of f-CNTs can readily alleviate the massive volume expansion/shrinkage associated with a conversion reaction electrode. Finally, f-CNTs are highly conductive matrices for electrons due to their high conductivity, which can shorten the diffusion path for electrons.

One-step hydrothermal synthesis of SnS2/graphene composites as anode material for highly efficient rechargeable lithium ion batteries

SnS2/graphene nanosheets (SnS2/GNS) composites were synthesized by a one-step hydrothermal method. The composites exhibit remarkably improved Li-storage ability with a good cycling life and high capability superior to that of the pure SnS2 counterpart due to a synergic effect between the graphene and SnS2 nanosheets.

Fine control of titania deposition to prepare C@TiO2 composites and TiO2 hollow particles for photocatalysis and lithium-ion battery applications

In this study, an effective method of slow hydrolization of metal alkoxide (e.g., Ti(C4H9O)4) in an ethanol–water system was systematically investigated and used to finely control the deposition of titania on carbon colloids. A model of adsorption–hydrolization of precursors during the coating process was rationally built for the first time to interpret the usability of the method and facilitate its further extension. Using this strategy, titania in the form of supported nanocrystals or layers on carbon colloids (TiO2/C, C@TiO2) was successfully tailored. Meanwhile, finely dispersed hollow TiO2 nanoparticles with shells consisting of different crystalline structures were also prepared by varying the calcination conditions after removing the carbon cores. More importantly, the effects of the crystalline and nano/macrostructures of the as-prepared TiO2 samples in photocatalysis and lithium-ion battery applications were analyzed in detail. The preliminary results show that anatase–rutile TiO2 hollow particles demonstrate a higher catalytic activity in the photo-degradation of rhodamine B than anatase TiO2 hollow particles, powders, and P25. However, in the case of Li-ion battery applications, the anatase TiO2 hollow particles exhibited better performance as anode materials with high capacities of around 190 mA h g−1, 140 mA h g−1, and 120 mA h g−1 at current densities of 60 mA g−1, 120 mA g−1, and 300 mA g−1, respectively, accompanied by stable cyclability.

CO2–expanded ethanol chemical synthesis of a Fe3O4@graphene composite and its good electrochemical properties as anode material for Li-ion batteries

In this work, we have developed a new method to synthesize a Fe3O4@graphene (Fe3O4@GN) composite. First, the precursor was synthesized through the decomposition of ferric nitrate in the presence of graphene oxide in the mixed solvent of CO2–expanded ethanol. Then, the precursor was converted to the Fe3O4@GN composite via thermal treatment in N2 atmosphere. With the help of the CO2–expanded ethanol, Fe3O4 nanoparticles were coated on the surface of GN completely and uniformly with high loading. However, it is difficult to load Fe3O4 particles onto the surface of GN and most of the Fe3O4 particles were deviated away from GN and aggregated to form larger units in pure ethanol. When used as anode for Li-ion batteries (LIBs), the Fe3O4@GN composite with a graphene content of 25 wt% synthesized in CO2–expanded ethanol manifested excellent charge–discharge cycling stability and rate performance compared with the sample synthesized in ethanol. Such improved electrochemical performances should be attributed to the intimate contact between the GN and Fe3O4 nanoparticles in the composite. Since the present method does not need tedious pre-treatment, surfactant, or precipitate, it is a green or sustainable technology and the solvents could be recycled easily after simple phase separation. This facile method can be extended to the synthesis of other metal oxide composites, which are expected to have good performance as anode materials for LIBs and other applications.

CO2-assisted template synthesis of porous hollow bi-phase γ-/α-Fe2O3 nanoparticles with high sensor property

In this contribution, monodisperse porous hollow bi-phase γ-/α-Fe2O3 nanoparticles were successfully fabricated based on hard-template method with using carbon colloids as sacrificial templates. A new concept of assembling one kind of metal oxide with different crystalline structures into a single shell was presented for the first time. The critical procedure of coating carbon cores with a uniform layer of oxide was performed in CO2-expanded ethanol, which is a versatile way to produce high-quality hollow oxide nanoparticles. The formation of the novel bi-phase shell was achieved through combining the reduction ability of carbon cores under inert calcination atmosphere and the unique chemical composition of intermediate-shell formed in CO2-expanded ethanol. The porous hollow γ-/α-Fe2O3 nanoparticles with an average diameter of 99 nm not only possess combined properties of γ-Fe2O3 and α-Fe2O3, but also have a large specific surface area of 93.7 m2 g−1 and a high pore volume of 1.056 cm3 g−1, enabling them to have widespread applications in sensors, catalysis, magnetic and electrochemical areas, etc. Herein, such hollow bi-phase γ-/α-Fe2O3 nanoparticles were utilized to prepare a sensor device, and intriguingly it shows higher sensitivity and selectivity to ethanol than γ-Fe2O3 powders and many other porous α-Fe2O3 materials reported recently. The probable sensor mechanism of hollow γ-/α-Fe2O3 nanoparticles was discussed in detail.

Assembling metal oxide nanocrystals into dense, hollow, porous nanoparticles for lithium-ion and lithium–oxygen battery application

New dense hollow porous (DHP) metal oxide nanoparticles that are smaller than 100 nm and composed of Co3O4, FeOx, NiO and MnOx were prepared by densely assembling metal oxide nanocrystals based on the hard-template method using a carbon colloid as a sacrificial core. These nanoparticles are quite different from the traditional particles as their hollow interior originates from the stacking of nanocrystals rather than a spherical shell. The DHP nanoparticles preserve the intriguing properties of nanocrystals and possess desirable surface area and pore volume that enhance the active surface, which ultimately benefits applications such as lithium-ion batteries. The DHP Co3O4 nanoparticles demonstrated an enhanced capacity of 1168 mA h g(-1) at 100 mA g(-1)vs. 590 mA h g(-1) of powders and stable cycling performance greater than 250 cycles when used as an anode material. Most importantly, the electrochemical performance of DHP Co3O4 nanoparticles in a lithium-O2 battery was also investigated for the first time. A low charge potential of ∼4.0 V, a high discharge voltage near 2.74 V and a long cycle ability greater than 100 cycles at a delivered capacity of 2000 mA h g(-1) (current density, 200 mA g(-1)) were observed. The performances were considerably improved compared to recent results of mesoporous Co3O4, Co3O4 nanoparticles and a composite of Co3O4/RGO and Co3O4/Pd. Therefore, it would be promising to investigate such properties of DHP nanoparticles or other hollow metal (oxide) particles for the popular lithium-air battery.

Sodium salt effect on hydrothermal carbonization of biomass: a catalyst for carbon-based nanostructured materials for lithium-ion battery applications

The salt effect of NaxA (A = SO42−, Cl−, NO3−, etc.) on the hydrothermal carbonization of biomass is reported. It is a new catalyst and recyclable template to more simply and effectively prepare carbon-based materials, such as porous carbon-coated anode materials (e.g., Fe3O4@porous-C) in lithium-ion battery applications with enhanced performance.

A new strategy for finely controlling the metal (oxide) coating on colloidal particles with tunable catalytic properties

In this contribution, we present an efficient, versatile and green strategy for finely controlling the metal (oxide) coating on core particles through in situ reaction of precursors in CO2 expanded ethanol without using any precipitants. It not only avoids the formation of free metal (oxide) and/or naked cores, but also permits individual dispersion of all the resultant particles without aggregation. With this method, the composition, thickness, uniformity, and structure of the metal (oxide) shell could be precisely controlled. A wide variety of unreported high-quality core-shell particles with a shell consisting of highly dispersed metal (oxide) nanocrystals or nanoalloys, such as C@Ni, CoO/C, C@Ni&Co and C@Ni&Pd particles have been fabricated, and the properties of the resultant particles were precisely tailored, such as the promising catalytic performance obtained over Ni/C and C@Ni particles in the hydrogenation of nitrobenzene. The present coating strategy is more simple and precisely controllable compared to the conventional deposition method and it is suitable for most precursors and even for multi-component materials, enabling the fabrication of nanostructured materials more easily and precisely.

Trace Amounts of Water-Induced Distinct Growth Behaviors of NiO Nanostructures on Graphene in CO2-Expanded Ethanol and Their Applications in Lithium-Ion Batteries

In this work, we have developed a new method to grow NiO nanomaterials on the surface of graphene nanosheets (GNSs). The morphologies of NiO nanomaterials grown on GNSs could be tailored by trace amounts of water introduced into the mixed solvents of CO2-expanded ethanol (CE). Small and uniform Ni-salt nanoparticles (Ni-salt-NPs) were grown on the surface of graphene oxide (GO) through the decomposition of nickel nitrate directly in CE. However, when trace amounts of water were introduced into the mixed solvents, Ni-salt nanoflakes arrays (Ni-salt-NFAs) were grown on the surface of GO with almost perpendicular direction. After thermal treatment in N2 atmosphere, these Ni-salt @GO composites were converted to NiO@GNSs composites. The forming mechanisms of the NiO-NPs@GNSs and NiO-NFAs@GNSs were discussed by series comparative experiments. The presence of the trace amounts of water affected the chemical composition and structure of the precursors formed in CE and the growth behaviors on the surface of GNSs. When used as anode materials for lithium-ion batteries, the NiO-NPs@GNSs composite exhibited better cycle and rate performance compared with the NiO-NFAs@GNSs.

Coating of Al2O3 on layered Li(Mn1/3Ni1/3Co1/3)O2 using CO2 as green precipitant and their improved electrochemical performance for lithium ion batteries

Abstract Li(Mn 1/3 Ni 1/3 Co 1/3 )O 2 cathode materials were fabricated by a hydroxide precursor method. Al 2 O 3 was coated on the surface of the Li(Mn 1/3 Ni 1/3 Co 1/3 )O 2 through a simple and effective one-step electrostatic self-assembly method. In the coating process, a NHCO 3 -H 2 CO 3 buffer was formed spontaneously when CO 2 was introduced into the NaAlO 2 solution. Compared with bare Li(Mn 1/3 M 1/3 Co 1/3 )O 2 , the surface-modified samples exhibited better cycling performance, rate capability and rate capability retention. The Al 2 O 3 -coated Li(Mn 1/3 Ni 1/3 Co 1/3 )O 2 electrodes delivered a discharge capacity of about 115 mAh·g −1 at 2 A·g −1 , but only 84 mAh·g −1 for the bare one. The capacity retention of the Al 2 O 3 -coated Li(Mn 1/3 Ni 1/3 Co 1/3 )O 2 was 90.7% after 50 cycles, about 30% higher than that of the pristine one.