Electrochemical Performance Of Samples Research Articles

Synthesis and electrochemical performance of LiV3O8/polythiophene composite as cathode materials for lithium ion batteries

LiV3O8/polythiophene (LiV3O8/PTh) composite has been chemically synthesized via an in-situ oxidative polymerization method. The structure and morphology of the samples have been characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). LiV3O8/PTh composite shows a single phase in the XRD pattern, but the existence of PTh has been confirmed by FTIR spectra. HRTEM images show that an uniform PTh layer with a thickness of 3–5 nm covered on the surface of LiV3O8. Electrochemical performance of samples has been characterized by the charge/discharge test, cyclic voltammetry (CV), electrochemical impedance spectroscopic studies (EIS) and galvanostatic intermittent titration technique (GITT). The LiV3O8/PTh composite exhibits much better electrochemical performance than bare LiV3O8. The initial discharge capacities of 15 wt.% LiV3O8/PTh composite are 213.3 and 200.3 mAh g−1 with almost no capacity retention after 50 cycles at current densities of 300 and 900 mA g−1, respectively. PTh could enhance electronic conductivity, decrease the charge transfer resistance, increase the lithium diffusion coefficient, and thus improve cycling performance of LiV3O8. All these results demonstrate that the LiV3O8/PTh composite has a promising application as cathode material for lithium ion batteries.

Doping Effects on the Crystal Structure and Electrochemical Performance of LiFePO4/C

LiFe0.98M0.02PO4/C (M = Mg, Ni, Co, Sr) composite materials were prepared by solid‐state synthesis method using Fe2O3 as one of the starting materials. The structures and electrochemical performance of samples were carried out by means of XRD, SEM, TEM, and constant‐current charge–discharge method. The results showed that the ion doping did not change the crystal structure and morphology of LiFePO4. Unit‐cell volume gradually increased, which was good for embedding and disembedding of Li+, and improving conductivity and charge–discharge performance. The electrical conductivity of powders was increased by carbon coating and ion doping. The initial discharge capacity of Ni2+‐doped sample reached 156.6 mA·h/g and 149.4 mA·h/g at 0.2C and 1C rate. After 30 cycles, the capacity retention rate was still 98.8% and 97.2%.

A Fe2O3 nanoparticle/carbon aerogel composite for use as an anode material for lithium ion batteries

A Fe2O3 nanoparticle/carbon aerogel composite (Fe2O3/CA) is prepared from a carbon aerogel prepared by a sol–gel process by a simple soaking in a Fe(NO3)3 solution and subsequent heat treatment at 600°C. Thermal gravimetric analysis, X-ray diffraction, scanning and transmission electron microscopy, energy dispersive X-ray analysis and X-ray photoelectron spectroscopy are used to characterize the products. The electrochemical performance of samples with different Fe2O3 content is evaluated. The optimal sample Fe2O3/CA-60 exhibits a good capacity retention of 916 and 617mAhg−1 for the 1st and 100th cycle, respectively, which is much better than that of pure Fe2O3 and CA. The improved cycling performance, specific capacity and rate capability of Fe2O3/CA is mainly attributed to the synergistic effects of the nanoporous network skeleton of CA and the uniformly dispersed Fe2O3 nanoparticles.

Preparation and Performance of LiFePO<sub>4</sub>/C Using Fe<sub>2</sub>O<sub>3</sub> as Starting Material

To improve the electrochemical performance of LiFePO4, LiFePO4/C composite materials were prepared by solid-state synthesis method with Fe2O3 as one of the starting materials. The phase composition, microstructure and morphology of samples were determined by X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical performance of samples were characterized by constant current charge-discharge method. The results show that the prepared samples have the single phase, and the carbon coating lead to no change of the crystal structure of LiFePO4. The sample with carbon content of 10wt% shows the best electrochemical properties. Its initial discharge capacity is 144.6 mA·h /g at 0.2C rate. After 30 cycles the capacity remains 131.4 mA·h /g, and the capacity retention rate is 91%.

Study on the preparation and electrochemical performance of rare earth doped nano-Ni(OH) 2

Multiphase nano-Ni(OH) 2 doped with Y or La was prepared by supersonic co-precipitation method. The crystal morphology, structure and particle size were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD) and particle size distribution (PSD). The electrochemical performance of samples was investigated by electrochemical workstation and battery tested system. The results indicated that micro-morphology and grain size were changed with the changing of supersonic power, pH values and doping elements. The morphology of Y doped sample was from the flake-like to the needle-like with the increase of supersonic power; Particles were from quasi-spherical particles into needle-like with the increase of pH values; As the supersonic power increased, the proportion of α-Ni(OH) 2 increased initially and then decreased. pH value was very important to the formation of crystalline phase. Lower pH value was beneficial to the formation of α-Ni(OH) 2. However, the pH values had a slight effect on the reaction reversibility. Complex electrodes were prepared by mixing 8 wt.% nickel hydroxides with commercial micro-size spherical nickel. The discharge capacity of electrodes increased initially and then decreased with the increase of supersonic power. When the supersonic power was 60 W and the pH value was 9, the sample had the largest discharge capacity (358 mAh/g) at 0.5 C rate, which was 122.7 and 76 mAh/g higher than the spherical nickel electrode and La doped sample electrode, respectively.

Preparation and performance of ZnO nanoparticle aggregation with porous morphology

ZnO nanoparticle aggregations with porous morphology were prepared by the direct precipitation of Zn(OH) 2 coats on the surface of Zn powders, and succedent calcination of Zn/Zn(OH) 2 composites. The coating and calcination reaction mechanism was given to explain the formation of the novel structure. The samples were characterized by X-ray diffraction, energy-disperse X-ray spectrometry, scanning electron microscopy and ultraviolet–visible spectrometry. It was found that ZnO nanoparticle aggregations were irregular porous microspheres consisting of ZnO nanoparticles with hexagonal wurtzite structure, and the diameters of bores in the microspheres ranged from tens to hundreds nanometers. The gas sensing properties of the samples were investigated. Sensors based on the samples showed high sensitivity and short response time to the H 2S gas. These characteristics make the sensors to be excellent potential candidates for detecting H 2S. The electrochemical performance of samples as anode materials for Li-ion battery was also investigated.

Technical optimization of LiFePO4 preparation by water quenching treatment

A technique of combination of vacuum firing and water quenching was applied to the synthesis of LiFePO4 powder. The sample was prepared by heating the pre-decomposed precursor mixtures sealed in vacuum quartz-tube, followed by water quenching at the sintering temperature. The synthetic conditions were optimized by orthogonal experiment. The results indicate that the fast quenching treatment can avoid the overgrowth of single crystal and improve its availability ratio of active material. The sintering temperature has the greatest effect on the electrochemical performance of sample. Next is the molar ratio of Li to Fe and the sintering time, respectively. The samples prepared in the optimized technical condition has the highest reversible discharge specific capacity of 149.8 mA·h/g.