Heng Lai

Carbon Nanohorns As a High-Performance Carrier for MnO2 Anode in Lithium-Ion Batteries

MnO(2) nanoflakes coated on carbon nanohorns (CNHs) has been synthesized via a facile solution method and evaluated as anode for lithium-ion batteries. By using CNHs as buffer carrier, MnO(2)/CNH composite displays an excellent capacity of 565 mA h/g measured at a high current density of 450 mA/g after 60 cylces.

Surface modification of LiNi1/3Co1/3Mn1/3O2 with Cr2O3 for lithium ion batteries

Cr2O3-coated LiNi1/3Co1/3Mn1/3O2 cathode materials were synthesized by a novel method. The structure and electrochemical properties of prepared cathode materials were measured using X-ray diffraction (XRD), scanning electron microscopy (SEM), charge-discharge tests, cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The measured results indicate that surface coating with 1.0 wt% Cr2O3 does not affect the LiNi1/3Co1/3Mn1/3O2 crystal structure (α-NaFeO2) of the cathode material compared to the pristine material, the surfaces of LiNi1/3Co1/3Mn1/3O2 samples are covered with Cr2O3 well, and the LiNi1/3Co1/3Mn1/3O2 material coated with Cr2O3 has better electrochemical performance under a high cutoff voltage of 4.5 V. Moreover, at room temperature, the initial discharging capacity of LiNi1/3Co1/3Mn1/3O2 material coated with 1.0 wt.% Cr2O3 at 0.5C reaches 169 mAh·g−1 and the capacity retention is 83.1% after 30 cycles, while that of the bare LiNi1/3Co1/3Mn1/3O2 is only 160.8 mAh·g−1 and 72.5%. Finally, the coated samples are found to display the improved electrochemical performance, which is mainly attributed to the suppression of the charge-transfer resistance at the interface between the cathode and the electrolyte.

Nano-crystalline FeOOH mixed with SWNT matrix as a superior anode material for lithium batteries

Nano-crystalline FeOOH particles (5∼10 nm) have been uniformly mixed with electric matrix of single-walled carbon nanotubes (SWNTs) for forming FeOOH/SWNT composite via a facile ultrasonication method. Directly using the FeOOH/SWNT composite (containing 15 wt% SWNTs) as anode material for lithium battery enhances kinetics of the Li+ insertion/extraction processes, thereby effectively improving reversible capacity and cycle performance, which delivers a high reversible capacity of 758 mAh·g−1 under a current density of 400 mA·g−1 even after 180 cycles, being comparable with previous reports in terms of electrochemical performance for FeOOH anode. The good electrochemical performance should be ascribed to the small particle size and nano-crystalline of FeOOH, as well as the good electronic conductivity of SWNT matrix.

Electrochemical properties of carbon-coated LiFePO4 and LiFe0.98Mn0.02PO4 cathode materials synthesized by solid-state reaction

Olivine structured LiFePO4/C (lithium iron phosphate) and Mn2+-doped LiFe0.98Mn0.02PO4/C powders were synthesized by the solid-state reaction. The effects of manganese partial substitution and different carbon content coating on the surface of LiFePO4 were considered. The structures and electrochemical properties of the samples were measured by X-ray diffraction (XRD), cyclic voltammetry (CV), charge/discharge tests at different current densities, and electrochemical impedance spectroscopy (EIS). The electrochemical properties of LiFePO4 cathodes with x wt.% carbon coating (x= 3, 7, 11, 15) at γ =0.2C, 2C (1C= 170 mAh·g−1) between 2.5 and 4.3 V were investigated. The measured results mean that the LiFePO4 with 7 wt.% carbon coating shows the best rate performance. The discharge capacity of LiFe0.98Mn0.02PO4/C composite is found to be 165 mAh·g−1 at a discharge rate, γ = 0.2C, and 105 mAh·g−1 at γ =2C, respectively. After 10 cycles, the discharge capacity has rarely fallen, while that of the pristine LiFePO4/C cathode is 150 mAh·g−1 and 98 mAh·g−1 at γ=0.2 and 2C, respectively. Compared to the discharge capacities of both electrodes above, the evident improvement of the electrochemical performance is observed, which is ascribed to the enhancement of the electronic conductivity and diffusion kinetics by carbon coating and Mn2+-substitution.

Sol-gel Synthesis and Electrochemical Properties of LiMn1.8Co0.2O4 Cathode Material

Spinel LiMn 1.8 Co 0.2 O 4 and LiMn 1.2 Co 0.2 Cr 0.6 O 4 compounds were prepared through sol-gel method using citric acid as a chelating agent. The structural and electrochemical properties of cathode compounds were investigated by mean of X-ray diffraction, cyclic voltammetry, galvanostatic charge-discharge test and AC impedance spectra systematically. It is found that the high rate discharge capability of electrodes is distinctly improved by chromium doping, indicating that Cr oxidation stabilized the spinel structure.

Electrochemical behaviour of Al-doped Li(Ni 0.5-x Al 2x Mn 0.5-x )O 2 with large Al content by the sol-gel method

Layered Li(Ni<inf>0.5-x</inf>Al<inf>2x</inf>Mn<inf>0.5-x</inf>)O<inf>2</inf> (x=0 and 0.1) (Mn/Ni = 1) were synthesized by sol-gel method using citric acid as a chelating agent. The Structure, electrochemical properties of prepared cathode materials were measured by means of X-ray diffraction, cyclic voltammetry, galvanostatic charge-discharge test and AC impedance spectra. The measured results indicate that, (1) the Al-doped sample has the better layered-structure; (2) compared to Li(Ni<inf>0.5</inf>Mn<inf>0.5</inf>)O<inf>2</inf>, the discharge capacity of Li(Ni<inf>0.4</inf>Al<inf>0.2</inf>Mn<inf>0.4</inf>)O<inf>2</inf> is evidently increased and reaches 160 mAhg⁻¹ between 2.8 and 4.2V at the rate of 20 mAg⁻¹; (3) Al ion in Li(Ni<inf>0.5-x</inf>Al<inf>2x</inf>Mn<inf>0.5-x</inf>)O<inf>2</inf> not only replaces Ni²⁺ as an active materal, but also can substitute Mn⁴⁺ used for supporting structure. Moreover, the electrochemical impedance spectra of the samples are also discussed.

Electrical transport properties and magnetoresistance of La 0.7 Sr 0.3 MnO 3 :xZn 1−y Co y O composites

The La_0.7Sr_0.3MnO₃:xZn_1-yCo_yO (x=0.0, 0.1, 0.2, 0.3, 0.4mo1, y=0.05) composites were prepared via a sol-gel process. The temperature dependence of the resistivity and magnetoresistance of the composites with different Zn_1-yCo_yO were investigated. X-ray diffraction reveals that both the compounds maintain their identities, that is, there is no evidence of reaction between the La_0.7Sr_0.3MnO₃ (LSMO) and Zn_0.95Co_0.50O. Magnetization is observed to decrease as the Zn_0.95Co_0.05 content is increased. Moreover, it is found that the change in MR is greater in the doped composites with x=0.1, 0.2, 0.3, as compared to pure LSMO. At the same time, on the addition of weak magnetic Zn_0.95Co_0.05O, the spin disorder is produced through the tunneling process at the grain boundaries and when a magnetic field is applied, the spin disorder is suppressed, resulting in a high MR at the low field 5 kOe.

Electrical Conductivity and Low-Field Magnetoresistance in La2/3(Ca0.60Ba0.40)1/3Mn1-xVxO3 Prepared by Sol-Gol

La2/3(Ca0.6Ba0.4)1/3Mn1-xVxO3 (x=0, 0.03, 0.05, 0.07, 0.10, 0.15, 0.20) nanoparticles were synthesized using sol-gel technology. The experimental results reveal that, (1) the substitution of V for Mn in La2/3(Ca0.6Ba0.4)1/3Mn1-xVxO3 lowers the Curie temperature TC and the metal–insulator transition temperature TMI; (2) there exists the evident difference between the TC and the TMI for different V substitution ratio; (3) the low-temperature tunneling magnetoresistance and maximum magnetoresistance near Tc increase with the enhancement of V-doping content. Based on the tunneling magnetoresistance model and the percolation model near Curie temperature, the experimental results are explained well.

The Influences of Size and Anisotropy Strength on Hysteresis Scaling for Anisotropy Heisenberg Multilayer Films

In this paper, we simulate the magnetization dynamic processes of the multilayer films, and calculate their hysteresis loop areas using Monte Carlo method. The simulated results indicate that, the size and anisotropy strength of the anisotropy multilayer films influence evidently the dynamic phase transition, and the phase transition temperature increases with enhancing values of the anisotropy constant and layer thickness. It is also found that, with increasing number of layers of films, the value of α decreases, while the magnitudes of β and γ increase. On the contrary, with increasing anisotropy strength, the value of α increases, while the magnitudes of β and γ reduce.