Hu Shejun

The Roles of Intermediate Phases of Li-Si Alloy as Anode Materials for Lithium-Ion Batteries

Abstract An ab initio method of the first-principles plane-wave pseudopotentials based on the density functional theory has been used to calculate the physical character and electrochemical performance of various alloy phases in Li-Si alloy. The results show that besides the growth of solid electrolyte interphase (SEI), the formation of Li 12 Si 7 alloy phase also partly leads to the initial irreversible capacity loss. In addition, the pure silicon thin film electrode was prepared by the radio frequency (RF) magnetic sputtering on copper foil collector as anode materials. The structural and electrochemical characteristics of Li-Si alloy were examined using X-ray diffraction (XRD), cyclic voltammogram (CV) and repeatedly constant current charge/discharge (CC). The results show that the first irreversible capacity loss is very large and amorphous structure can accommodate the large volume expansions and improve cyclic performance.

One-pot Synthesis of Nano-NiFe 2 O 4 Pinning on the Surface of the Graphite Composite as Superior Anodes for Li-ion Batteries

Abstract Nickel ferrite and related materials have recently received considerable attention as potential anode in lithium-ion batteries for their high theoretical specific capacities. To overcome low intrinsic electronic conductivity and large volume expansion during the Li insertion/extraction process, in this work, nano-NiFe2O4 pinning on the surface of the graphite composite was prepared by a hydrothermal method. As the superior anode material, the as-obtained nano-NiFe2O4/graphite composite demonstrates high capacity and excellent cycle stability. An initial specific discharge capacity of approximate 1478 mAh·g−1 and a reversible specific capacity of approximate 1109 mAh·g−1 after 50 cycles at a current density of 100 mA·g−1 are reached. When the charging current is increased to 1000 mA·g−1, it also delivers a charge capacity of 750 mAh·g−1. The excellent performances are attributed to the special structure of NiFe2O4 nanoparticles pinning on the surface of the graphite, especially the enhanced electronic conductivity and area specific capacitance during the cycling process.

Study of Lithium storage properties of the Sn-Ni alloys prepared by magnetic sputtering technology

Nano-level Sn-Ni alloy thin-film electrode materials prepared by magnetic sputtering technology are characterized with X-ray diffraction (XRD), atom force microscopy (AFM) and scanning electron microscopy (SEM). The charge/discharge and cyclic voltammograms (CV) of the films electrodes are tested by the battery testing system of high precision. The results indicate that the materials prepared by direct current (DC) and radio frequency (RF) methods differ greatly in their performance. Ni3Sn2 alloy phase constitutes the main components prepared by DC method, the particles on the surface are tiny and show steady cycling performance, the deficiency is that they have low initial efficiency and small discharge capacity of 72% and 108 mA·h/g, respectively. Contrary to the former, Ni3Sn4 alloy phase constitutes the main components prepared by RF method, the particles on the surface appear comparatively larger, their discharge capacity did not decline in the first 15 times, keeping above 500 mA·h/g, but began to decline after 15 times.

Optical Emission Spectroscopy of Electron Cyclotron Resonance-Plasma Enchanced Metalorganic Chemical Vapor Deposition Process for Deposition of GaN Film

An investigation was made into the nitrogen-trimethylgallium mixed electron cyclotron resonance (ECR) plasma by optical emission spectroscopy (OES). The ECR plasma enhanced metalorganic chemical vapour deposition technology was adopted to grow GaN film on an α-Al2O3 substrate. X-ray diffraction (XRD) analyses showed that the peak of GaN (0002) was at 2θ = 34.48°, being sharper and more intense with the increase in the N2: trimethylgallium(TMG) flow ratio. The results demonstrate that the electron cyclotron resonance-plasma enchanced metalorganic chemical vapor deposition (ECR-MOPECVD) technology is evidently advantageous for the deposition of GaN film at a low growth temperature.

Spatial Distribution of ECR Plasma Density in ECR-PECVD Reaction Chamber

The spatial distribution of Electron Cyclotron Resonance (ECR) plasma in the ECR-Plasma Enhanced Metalorganic Chemical Vapour Deposition (ECR-PECVD) reaction chamber is diagnosed by a Langmuir probe. The uniformity is also investigated. The results show that the ECR plasma in the upper region of the reaction chamber under the influence of magnetic field has poor radial and axial uniformity. However, the plasma in the downstream region of the reaction chamber has fine radial uniformity. This excellent uniform plasma in the downstream has extensive application in plasma process.