Ruguang Ma

Growth of TiO2 nanorod arrays on reduced graphene oxide with enhanced lithium-ion storage

We demonstrate the synthesis of a sandwich-like nanocomposite by planting rutile TiO2 nanorods onto reduced graphene oxide (RGO) via a modified seed-assisted hydrothermal growth method. The synthetic process consists of functionalization of graphene oxide (GO), followed by hydrolytic deposition of TiO2 nanoparticles on GO and reduction, and finally hydrothermal growth of rutile TiO2 nanorods on RGO. The resultant nanocomposite, i.e. rutile TiO2 nanorod arrays on RGO (TONRAs–RGO), exhibits largely enhanced reversible charge–discharge capacity and rate capability compared to bare TiO2 nanorods (TONRs) due to its unique structure and superior conductivity. The rate performance of the nanocomposite is also better than that of anatase TiO2 nanoparticles. This study will inspire better design of RGO-based nanocomposites for high energy density lithium-ion battery applications.

Facile and rapid synthesis of highly porous wirelike TiO2 as anodes for lithium-ion batteries.

Highly porous wirelike TiO(2) nanostructures have been synthesized by a simple two-step process. The morphological and structural characterizations reveal that the TiO(2) wires typically have diameters from 0.4 to 2 μm, and lengths from 2 to 20 μm. The TiO(2) wires are highly porous and comprise of interconnected nanocrystals with diameters of 8 ± 2 nm resulting in a high specific surface area of 252 m(2) g(-1). The effects of experimental parameters on the structure and morphology of the porous wirelike TiO(2) have been investigated and the possible formation processes of these porous nanostructures are discussed. Galvanostatic charge/discharge tests indicate that the porous wirelike TiO(2) samples exhibit stable reversible lithium ion storage capacities of 167.1 ± 0.7, 152.1 ± 0.8, 139.7 ± 0.3, and 116.1 ± 1.1 mA h g(-1) at 0.5, 1, 2, and 5 C rates, respectively. Such improved performance could be ascribed to their unique porous and 1D nanostructures facilitating better electrolyte penetration, higher diffusion rate of electrons and lithium ion, and variation of accommodated volumes during the charge/discharge cycles.

Thermal evaporation-induced anhydrous synthesis of Fe3O4-graphene composite with enhanced rate performance and cyclic stability for lithium ion batteries.

We present a high-yield and low cost thermal evaporation-induced anhydrous strategy to prepare hybrid materials of Fe3O4 nanoparticles and graphene as an advanced anode for high-performance lithium ion batteries. The ~10-20 nm Fe3O4 nanoparticles are densely anchored on conducting graphene sheets and act as spacers to keep the adjacent sheets separated. The Fe3O4-graphene composite displays a superior battery performance with high retained capacity of 868 mA h g(-1) up to 100 cycles at a current density of 200 mA g(-1), and 539 mA h g(-1) up to 200 cycles when cycling at 1000 mA g(-1), high Coulombic efficiency (above 99% after 200 cycles), good rate capability, and excellent cyclic stability. The simple approach offers a promising route to prepare anode materials for practical fabrication of lithium ion batteries.

Fabrication of FeF3 nanocrystals dispersed into a porous carbon matrix as a high performance cathode material for lithium ion batteries

FeF3/C nanocomposites, where FeF3 nanocrystals had been dispersed into a porous carbon matrix, were successfully fabricated by a novel vapour–solid method in a tailored autoclave. Phase evolution of the reaction between the precursor and HF solution vapour under air and argon gas atmospheres were investigated. The results showed that the air in the autoclave played an important role in driving the reaction to form FeF3. The as-prepared FeF3/C delivered 134.3, 103.2 and 71.0 mA h g−1 of charge capacity at a current density of 104, 520, and 1040 mA g−1 in turn, exhibiting superior rate capability to the bare FeF3. Moreover, it displayed stable cycling performance, with a charge capacity of 196.3 mA h g−1 at 20.8 mA g−1. EIS and BET investigations indicated that the good electrochemical performance can be attributed to the good electrical conductivity and high specific surface area that result from the porous carbon matrix.

Solvothermal synthesis of monodisperse LiFePO4 micro hollow spheres as high performance cathode material for lithium ion batteries.

A microspherical, hollow LiFePO4 (LFP) cathode material with polycrystal structure was simply synthesized by a solvothermal method using spherical Li3PO4 as the self-sacrificed template and FeCl2·4H2O as the Fe(2+) source. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the LFP micro hollow spheres have a quite uniform size of ~1 μm consisting of aggregated nanoparticles. The influences of solvent and Fe(2+) source on the phase and morphology of the final product were chiefly investigated, and a direct ion exchange reaction between spherical Li3PO4 templates and Fe(2+) ions was firstly proposed on the basis of the X-ray powder diffraction (XRD) transformation of the products. The LFP nanoparticles in the micro hollow spheres could finely coat a uniform carbon layer ~3.5 nm by a glucose solution impregnating-drying-sintering process. The electrochemical measurements show that the carbon coated LFP materials could exhibit high charge-discharge capacities of 158, 144, 125, 101, and even 72 mAh g(-1) at 0.1, 1, 5, 20, and 50 C, respectively. It could also maintain 80% of the initial discharge capacity after cycling for 2000 times at 20 C.

Solvothermal synthesis of nano-LiMnPO4 from Li3PO4 rod-like precursor: reaction mechanism and electrochemical properties

A simple one-pot solvothermal approach is employed to synthesize LiMnPO4 (LMP) nanomaterials by using Li3PO4 nanorods and MnSO4·H2O as the precursors. Various experimental parameters, such as volume ratio of polyethylene glycol 600 (PEG600) to water, reactant feeding order, reaction time and pH value, are discussed. The phase and morphology changes of the product were characterized by XRD and TEM. A reaction mechanism is proposed based on the characteristic results. The charge–discharge properties show that the LMP nanomaterials synthesized at 180 °C for 4 h at a pH value of 6.46 followed by sintering with glucose at 600 °C for 3 h under argon atmosphere present the highest discharge capacity of 147 mA h g−1 at 0.05 C rate (i.e. 8.55 mA g−1 of current rate) under a galvanostatic charging–discharging mode, and it can retain 93% of the initial capacity of 46.6 mA h g−1 after cycling 200 times at 1 C rate. Cyclic voltammetry (CV) was also used to investigate the carbon coated LMP electrode.

Fabrication of LiF/Fe/Graphene nanocomposites as cathode material for lithium-ion batteries.

Homogeneous LiF/Fe/Graphene nanocomposites as cathode material for lithium ion batteries have been synthesized for the first time by a facile two-step strategy, which not only avoids the use of highly corrosive reagents and expensive precursors but also fully takes advantage of the excellent electronic conductivity of graphene. The capacity remains higher than 150 mA h g(-1) after 180 cylces, indicating high reversible capacity and stable cyclability. The ex situ XRD and HRTEM investigations on the cycled LiF/Fe/G nanocomposites confirm the formation of FeF(x) and the coexistence of LiF and FeF(x) at the charged state. Therefore, the heterostructure nanocomposites of LiF/Fe/Graphene with nano-LiF and ultrafine Fe homogeneously anchored on graphene sheets could open up a novel avenue for the application of iron fluorides as high-performance cathode materials for lithium-ion batteries.

Evaporation-induced synthesis of carbon-supported Fe3O4 nanocomposites as anode material for lithium-ion batteries

We report the high-yield preparation of carbon-supported superparamagnetic Fe3O4 nanocomposites (C–Fe3O4-NCs) using a simple evaporation-induced method. The Fe3O4 products consist of ∼3–10 nm nanocrystals uniformly embedded in a carbon matrix to assemble nanoparticles with a size range from 40 to 80 nm. It is shown that lithium-ion batteries (LIB) assembled from heat-treated C–Fe3O4-NCs present attractive characteristics including a high specific capacity of 752 mA h g−1 at a current rate of 0.2 C for the second discharge cycle as well as good cycling performances with ∼87% retained capacity after 100 cycles.

Rugated porous Fe3O4 thin films as stable binder-free anode materials for lithium ion batteries

Rugated porous Fe3O4 thin films were synthesized by a facile multi-pulse electrochemical anodization method. The fabricated Fe3O4 films are directly grown on Fe, featuring nano-channels with periodically rugated channel walls running throughout the film thickness direction. Electrochemical measurements show that the as-prepared Fe3O4 films readily serve as high-performance anode materials for lithium ion batteries with a specific capacity of 1100, 880 and 660 mA h g−1 at 0.1, 0.2, and 0.5 C, respectively, which compared favorably with the conventional straight-channel counterparts fabricated by DC anodization. Moreover, the cycling capability test of the novel electrode at 0.1 C for 100 cycles shows a steady charge/discharge platform, indicating a high cycling stability and structural robustness. The observed improvements of the rugated Fe3O4 films as lithium ion battery anode materials are attributed to their special periodic rugated nanostructures.

Large-scale fabrication of hierarchical α-Fe2O3 assemblies as high performance anode materials for lithium-ion batteries

Hierarchical flower- and cube-like α-Fe2O3 assemblies consisting of nanoparticles with sizes of around 150 nm have been successfully synthesized by a precipitation–calcination strategy. The as-prepared assemblies exhibit superior electrochemical performance, with respective reversible capacities of 570 and 675 mA h g−1 at 0.2 C after 100 cycles.