Yingbin Lin

Ferromagnetism of Co-doped TiO2 films prepared by plasma enhanced chemical vapour deposition (PECVD) method

Ti1−xCoxO2 polycrystalline films have been prepared on Si(0 0 1) substrates by the plasma enhanced chemical vapour deposition technique at 280 °C without using any carrier gas. All the films show room-temperature ferromagnetic behaviours and no ferromagnetic clusters are detected by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy, Raman and superconducting quantum interference device measurements as the doping concentration is lower than 4%. In addition, the formation of non-ferromagnetic CoTiO3 under heavy doping is considered to be responsible for the degradation of magnetization in Ti1−xCoxO2 polycrystalline films. Furthermore, saturated magnetization of Ti1−xCoxO2 films is found to decrease with the increasing duration of oxygen-plasma processing, indicating that the oxygen vacancies in the films play an important role in the generation of ferromagnetic Ti1−xCoxO2 films.

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.

Hierarchical flower-like NiCo2O4@TiO2 hetero-nanosheets as anodes for lithium ion batteries

Flower-like NiCo2O4 consisting of nanosheets are synthesized by hydrothermal technique and subsequently surface-modified with a TiO2 ultrathin layer by a hydrolysis process at low temperature. It is found that NiCo2O4@TiO2 exhibits superior electrochemical performances over NiCo2O4 in terms of rate capability and cyclability. After 60 cycles at 100 mA g−1, NiCo2O4@TiO2 showed 78% capacity retention compared with 57% for bare NiCo2O4. Analysis from the electrochemical measurements indicates that the improved electrochemical performances of NiCo2O4@TiO2 might be attributed to a higher lithium diffusion rate, smaller charge-transfer resistance and more structural stability. Kelvin probe force microscopy measurements reveal that NiCo2O4@TiO2 has a lower work function than those of the pristine one, which help to facilitate electron transfer in composites. In addition, the electric field between NiCo2O4 and TiO2 resulting from the difference in work functions is also expected to enhance the electrochemical performances.

Enhanced electrochemical properties and thermal stability of LiNi1/3Co1/3Mn1/3O2 by surface modification with Eu2O3

Layered LiNi1/3Co1/3Mn1/3O2 cathode material is synthesized via a sol-gel method and subsequently surface-modified with Eu2O3 layer by a wet chemical process. The effect of Eu2O3 coating on the electrochemical performances and thermal stability of LiNi1/3Co1/3Mn1/3O2@Eu2O3 cells is investigated systematically by the charge/discharge testing, cyclic voltammograms, AC impedance spectroscopy, and DSC measurements, respectively. In comparison, the Eu2O3-coated sample demonstrates better electrochemical performances and thermal stability than that of the pristine one. After 100 cycles at 1C, the Eu2O3-coated LiNi1/3Co1/3Mn1/3O2 cathode demonstrates stable cyclability with capacity retention of 92.9xa0%, which is higher than that (75.5xa0%) of the pristine one in voltage range 3.0–4.6xa0V. Analysis from the electrochemical measurements reveals that the remarkably improved performances of the surface-modified composites are mainly ascribed to the presence of Eu2O3-coating layer, which could efficiently suppress the undesirable side reaction and increasing impedance, and enhance the structural stability of active material.

The Phase Evolution and Physical Properties of Binary Copper Oxide Thin Films Prepared by Reactive Magnetron Sputtering

P-type binary copper oxide semiconductor films for various O2 flow rates and total pressures (Pt) were prepared using the reactive magnetron sputtering method. Their morphologies and structures were detected by X-ray diffraction, Raman spectrometry, and SEM. A phase diagram with Cu2O, Cu4O3, CuO, and their mixture was established. Moreover, based on Kelvin Probe Force Microscopy (KPFM) and conductive AFM (C-AFM), by measuring the contact potential difference (VCPD) and the field emission property, the work function and the carrier concentration were obtained, which can be used to distinguish the different types of copper oxide states. The band gaps of the Cu2O, Cu4O3, and CuO thin films were observed to be (2.51 ± 0.02) eV, (1.65 ± 0.1) eV, and (1.42 ± 0.01) eV, respectively. The resistivities of Cu2O, Cu4O3, and CuO thin films are (3.7 ± 0.3) × 103 Ω·cm, (1.1 ± 0.3) × 103 Ω·cm, and (1.6 ± 6) × 101 Ω·cm, respectively. All the measured results above are consistent.

Suppression of degradation for lithium iron phosphate cylindrical batteries by nano silicon surface modification

Nano-scale silicon particles were successfully decorated uniformly on a LiFePO4@C electrode through utilization of spray technique. The electrochemical measured results indicate that the Si surface modification results in improved electrochemical performances for commercial 18u2006650 cylindrical batteries, especially at elevated temperature, which is attributed to the fact that Si introduction can enable the LiFePO4 electrodes to suppress cylindrical battery degradation. Based on the analysis of structural characterization, it is revealed that the battery cathode with Si modification retains a better LiFePO4 phase and exhibits less Li+ loss. In addition, the negative electrode of the battery contains a better graphite carbon structure and a thinner thickness of SEI film due to Si decoration. Furthermore, the related high-temperature aging and degradation mechanisms of the batteries were discussed.

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.

Ab initio study of ferromagnetism in N doped ZnO and its stabilization by Li co-doping

Spin-resolved electronic properties of N doped ZnO is investigated from ab initio calculations based on density functional theory (DFT). It is found that single N atom at O site in ZnO becomes spin polarized with its many neighboring atoms with a total magnetic moment of 1.0 muB. Band structure of ZnO doped with 6.25% of N shows a half metallic character with hole states in the minority channel. Though the ferromagnetic coupling is weak in the system, Li co-doping greatly enhance the ferromagnetism. The results of our calculations suggest the possibility of fabricating ZnO based DMS by (N, Li) co-doping.