Liujiang Xi

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.

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.

Hierarchical assembly of Ti(IV)/Sn(II) co-doped SnO2 nanosheets along sacrificial titanate nanowires: synthesis, characterization and electrochemical properties

Hierarchical assembly of Ti(IV)/Sn(II)-doped SnO₂ nanosheets along titanate nanowires serving as both sacrificial templates and a Ti(IV) source is demonstrated, using SnCl2 as a tin precursor and Sn(II) dopants and NaF as the morphology controlling agent. Excess fluoride inhibits the hydrolysis of SnCl2, promoting heterogeneous nucleation of Sn(II)-doped SnO₂ on the titanate nanowires due to the insufficient oxidization of Sn(II) to Sn(IV). Simultaneously, titanate nanowires are dissolved forming Ti(4+) species under the etching effect of in situ generated HF resulting in spontaneous Ti(4+) ion doping of SnO₂ nanosheets formed under hydrothermal conditions. Compositional analysis indicates that Ti(4+) ions are incorporated by substitution of Sn sites at a high level (16-18 at.%), with uniform distribution and no phase separation. Mössbauer spectroscopy quantified the relative content of Sn(II) and Sn(IV) in both Sn(II)-doped and Ti(IV)/Sn(II) co-doped SnO₂ samples. Electrochemical properties were investigated as an anode material in lithium ion batteries, demonstrating that Ti-doped SnO₂ nanosheets show improved cycle performance, which is attributed to the alleviation of inherent volume expansion of the SnO₂-based anode materials by substituting part of Sn sites with Ti dopants.

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.

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.

Layered Li2MnO3·3LiNi0.5−xMn0.5−xCo2xO2 microspheres with Mn-rich cores as high performance cathode materials for lithium ion batteries

Layered Li2MnO3·3LiNi0.5-xMn0.5-xCo2xO2 (x = 0, 0.05, 0.1, 0.165) microspheres with Mn-rich core were successfully synthesized by a simple two-step precipitation calcination method and intensively evaluated as cathode materials for lithium ion batteries. The X-ray powder diffractometry (XRD) results indicate that the growth of Li2MnO3-like regions is impeded due to the presence of cobalt (Co) in the material. The field-emission scanning electron microscopy (FESEM) data reveal the core-shell-like structure with a Mn-rich core in the as-prepared particles. The charge-discharge testing reveals that the capacity is markedly improved by adding Co. The activation of the cathode after Co doping becomes easier and can be accomplished completely when charged to 4.6 V at the C/40 rate in the initial cycle. Superior electrochemical performances are obtained for samples with x = 0.05 and 0.1. The corresponding initial discharge capacities are separately 281 and 285 mA h g(-1) at C/40 between 2 and 4.6 V at room temperature. After 250 cycles at C/2, the respective capacity retentions are 71.2% and 70.4%, which are better compared to the normal Li-excess Li2MnO3·3LiNi0.4Mn0.4Co0.2O2 sample with a uniform distribution of Mn element in the particles. The initial discharge capacities of both samples are approximately 250 mA h g(-1) at a rate of C/2 between 2 and 4.6 V at 55 °C after activation. Furthermore, the samples are investigated by electrochemical impedance spectroscopy (EIS) at room and elevated temperature, revealing that the key factor affecting electrochemical performance is the charge transfer resistance in the particles.

Facile synthesis of porous Li-rich layered Li[Li0.2Mn0.534Ni0.133Co0.133]O2 as high-performance cathode materials for Li-ion batteries

Lithium-rich layered metal oxides have drawn much recent attention due to their high rechargeable capacity of 250–300 mA h g−1. Herein, we report the synthesis of porous Li[Li0.2Mn0.534Ni0.133Co0.133]O2 metal oxide powders using a facile polymer-thermolysis method. X-ray powder diffractometry (XRD) results show that a well-crystallized layered structure was obtained when the calcination temperatures reach 800 °C. Pores in the range of 100–200 nm are observed using scanning electron microscopy (SEM). The porous Li[Li0.2Mn0.534Ni0.133Co0.133]O2 synthesized at 850 °C shows much superior electrochemical performance to the sample synthesized by the traditional coprecipitation-calcination method, with a high initial coulombic efficiency of 87% and initial discharge capacity of 245.4 mA h g−1 at 15 mA g−1 in the voltage window 2–4.6 V. A capacity retention of 81% was obtained after 300 cycles at 300 mA g−1. The higher capacity and improved rate performance of porous Li[Li0.2Mn0.534Ni0.133Co0.133]O2 can be predominantly attributed to enhanced Li+ intercalation kinetics resulting from the highly porous structure.