Ting Fang

Improving the Electrochemical Performance of LiCoO2 Cathode by Nanocrystalline ZnO Coating

The cycle life of LiCoO 2 cathodes cycled at a high cutoff voltage can be largely improved by surface modification with ZnO coating. The bright-field transmission electron microscopy (TEM) images and selected area diffraction patterns of as-coated LiCoO 2 particles reveal the existence of continuous ZnO films with a 10-nm thickness deposited on LiCoO 2 surfaces, indicating a Li-Zn-O phase formed on the surface region. Besides high-voltage cycleability, cycle-life degradation caused by inappropriate conductive carbon can also be moderated by ZnO coating. Furthermore, the rate capability at high current density can also be notably improved. The role ZnO coating played in the charge-discharge process is discussed from the viewpoint of surface chemistry with the aid of data from scanning electron microscopy, TEM, energy-dispersive X-ray, and impedance spectra. Moreover, the correlation between electrochemical performance and surface properties of ZnO-coated LiCoO 2 is explored.

Electrochemical Properties of Nanosize Ni–Sn–P Coated on MCMB Anode for Lithium Secondary Batteries

Tin-based alloy/carbonaceous composite materials are attractions for Li-ion rechargeable batteries because of their high capacity. A novel Ni-Sn-P mesocarbon microbead (MCMB) composite material for lithium-ion batteries was prepared by an electroless plating method. On the basis of X-ray color mapping analysis by electron probe microanalyzer, the nanosize Ni-Sn-P was precipitated not only on the surface but in the interior of MCMB powders. The Ni-Sn-P/MCMB composite anode exhibited large capacity (418 mAh/g in the tenth cycle) and the coulombic efficiency of the Ni-Sn-P/MCMB anode is as high as 98% even after the twenty-fifth cycle. In addition, the Ni-Sn-P/MCMB composite anode showed a significant improvement in electrochemical performance. Therefore, the Ni-Sn-P/MCMB provides a new type of anode material for lithium-ion batteries with an enhanced capacity.

The Microstructural Evolution of Mn3O4 Hausmannite during Autoxidation

Mn3O4 hausmannite, which is a normal spinel with the Mn2+ in the tetrahedral site and the Mn3+ in the tetrahedral site, is one of the most stable manganese oxides. Variation in the valence of Mn ions (2+, 3+ and 4+) contributes to several different structures of manganese oxides. The autoxidation of precipitated manganese hydroxide in an alkaline solution is a practical approach to synthesize hausmannite (Mn3O4) at low temperature. During the process, the particle size and morphology of derived products were totally different from the precursors even though nanometer-sized Mn(OH)2 crystals were fabricated at first. It was observed that the variation was resulted from the accumulation of produced Mn3O4 crystallites which departed from the original crystals. This study has not only discussed the influence of reactant concentrations on the particle size and morphology of derived powders, but also revealed the morphological transformation of crystals involved in autoxidation with the aid of electron micrographs

LiCoO2 Cathode Material Coated with Nano-Crystallized ZnO by Sol-Gel Method

LiCoO2 spinel is one of the most promising cathode materials for Li-ion batteries. However, the capacity fading is aggravated at high voltage, resulting from cathode degradation and electrolyte decomposition owing to over-charging. To improve structural stability, surface modification is an effective method. In this study, nano-crystallized ZnO was coated on the surface of commercial LiCoO2 powders via sol-gel method. The correlation among the amount of coated ZnO, microstructure of modified cathode and the cycling behavior of surface-treated LiCoO2 powders is discussed. Moreover, the effects of cycling for cathodes with as-derived powders on the phase and morphology are also considered. The surface morphology observed from the scanning electron microscope (SEM) images shows that nano-crystallized and spherical ZnO particles with an average size of about 20 nm have developed after coating. The size of ZnO nanocrystallites is related to the initial concentration of Zn2+ cations. In comparing the characteristics of bare and coated LiCoO2 powders, improvement in cyceability of the ZnO-coated cathode is explored. It is confirmed that Zn2+ ions diffuse into the surface region of LiCoO2 particles. To reveal the effects of Zone coating on enhancing the electrochemical properties of LiCoO2 cathode during charge and discharge, the morphological differences between the cathode material before and after cycling are discussed.

Preparation of Sn-Coated Mesophase Graphite Powders by Carbothermal Reduction

Recently, combination of ductile carbonaceous materials with the metallic Sn has received a great deal of interest to be a novel anode material for lithium ion batteries, because of their higher capacity than the conventional graphite anodes and better cycleability than the pure Sn anodes. Electrochemical performance of the Sn/C composite anodes is influenced by the material system, particle size and size distribution of Sn as well as the amount of deposited Sn. This study revealed that a favorable Sn/C composite anode exhibited reduced size and uniformly distributed tin particles. The crystal structure, morphology and elemental distribution were analyzed by XRD patterns, SEM and EPMA, respectively. The carbothermal-reducted Sn/Mesophase graphite powder (MGP) composite anodes exhibited much higher capacity than the bare MGP, and the initial efficiency was also much higher than the metallic tin anode in literatures.

Novel Composite Anode Containing Tin Compounds and Carbonaceous Materials for Li-Ion Batteries

Tin-based compounds/carbonaceous materials composite anodes for Li-ion rechargeable batteries attracted much attention because of their high capacity and improved cycleability. Two novel Sn compounds/mesophase graphite powders (MGP) composite materials for lithium-ion batteries were prepared by the electroless plating method. The electroless-plated composite anodes exhibited much higher capacity than the bare MGP without appreciable fading. The capacity retention after 20 cycles of the Sn-P-O/MGP and Sn-P-Ni/MGP composites was 82.4% and 94.3%, respectively, of their highest capacity. Therefore, introducing Ni into the composite anodes could effectively improve the cycling stability.

Synthesis of Well-Crystallized Manganese Oxide from Precipitation: Effect of Introducing Carbonate Anions

Powdery hausmannite (Mn3O4) is of interest in many industrial and technological applications. It is widely used as reactive catalysts, raw material of humidity sensors, and the cathode oxides of Li-ion secondary batteries. In this study, sub-micron and nano-meter sized Mn3O4 powders are prepared by an efficient method at room temperature. Mn(OH)2 nanocrystalsare commonly precipitated at first and then oxidized in the alkaline solution containing excess OH- anions. However, conventionally prepared Mn3O4 powders by the above process are ill-crystallized. To enhance the crystallinity of fabricated powders, CO3 2- anions are introduced into the process. The modified autoxidation method is practical to fabricate low-cost and high grade powders of Mn3O4. Advantages of the modified method are confirmed by both the electron micrographs and XRD patterns of synthesized powders. It is revealed that particle size of the products is in the sub-micron meter range, and the particle morphology can be adjusted by altering the precipitation sequence.