Zhaorong Chang

Bubble-template-assisted synthesis of hollow fullerene-like MoS2 nanocages as a lithium ion battery anode material

Inorganic fullerene (IF)-like structured materials have attracted considerable attention for electrochemical energy storage and conversion. In this report, we describe a facile method of synthesizing IF-MoS2 hollow structures with a diameter of ∼100 nm by a facile solution-phase reduction process to obtain a hollow MoSx precursor under ambient pressures before subsequent annealing of the material at high temperatures to form IF-MoS2 nanocages. TEM images at different reaction stages reveal the hollow structure spontaneously arising in the novel “close-edge” nanocages under the assistance of an ammonia cation bubble template. When evaluated as an anode material for lithium ion batteries, ex situ characterization indicates that these IF-MoS2 hollow nanocages can provide large expandable spaces for volume changes occurring during the cycles. Such a highly desired structure offers remarkably improved lithium storage performance including high reversible capacity and good cycling behavior and high rate capability.

Effects of different methods of cobalt addition on the performance of nickel electrodes

Abstract Cobalt is an effective additive which is widely used in nickel electrodes. Three kinds of nickel electrodes with various cobalt levels are made with different methods of cobalt addition. The electrochemical properties, including charge–discharge characteristics of the nickel electrodes are investigated. It is found that the method used to add cobalt exerts a marked effect on electrode performance. Nickel electrodes with cobalt incorporated directly display excellent charge-discharge behaviour. By contrast, nickel electrodes co-precipitated with cobalt exhibit an adverse effect except at high-rate discharge.

Facile and Nonradiation Pretreated Membrane as a High Conductive Separator for Li-Ion Batteries.

Polyolefin membranes are widely used as separators in commercialized Li-ion batteries. They have less polarized surfaces compared with polarized molecules of electrolyte, leading to a poor wetting state for separators. Radiation pretreatments are often adopted to solve such a problem. Unfortunately, they can only activate several nanometers deep from the surface, which limits the performance improvement. Here we report a facile and scalable method to polarize polyolefin membranes via a chemical oxidation route. On the surfaces of pretreated membrane, layers of poly(ethylene oxide) and poly(acrylic acid) can easily be coated, thus resulting in a high Li-ion conductivity of the membrane. Assembled with this decorated separator in button cells, both high-voltage (Li1.2Mn0.54Co0.13Ni0.13O2) and moderate-voltage (LiFePO4) cathode materials show better electrochemical performances than those assembled with pristine polyolefin separators.

Influence of preparation conditions of spherical nickel hydroxide on its electrochemical properties

The influence of various conditions in spherical nickel hydroxide preparation on its electrochemical properties is studied. Experimental results show that several factors, such as pH and temperature, exert a great influence on the properties of the final product. Optimum conditions and reference data for preparing spherical nickel hydroxide with excellent properties are provided.

Synthesis and Characterization of Nonspherical LiCoO2 with High Tap Density by Two-Step Drying Method

Nonspherical LiCoO 2 powders have been synthesized using a two-step drying method. The tap density of the powder obtained is 3.06 g cm -3 , which is remarkably higher than that of spherical LiCoO 2 powders (only 2.40 g cm -3 ). The LiCoO 2 powder is also characterized by X-ray diffraction (XRD) and scanning electron microscopy. The XRD analysis shows that the material has a well-ordered layered structure. Initial charge and discharge capacities of 165 and 152 mAh g -1 are obtained between 3 and 4.2 V at a current of 0.2 C rate. The nonspherical LiCoO 2 cathode material demonstrates a stable cyclability over 50 charge-discharge cycling.

Synthesis of high-purity LiMn2O4 with enhanced electrical properties from electrolytic manganese dioxide treated by sulfuric acid-assisted hydrothermal method

Using sulfuric acid-assisted hydrothermal treatment, β-MnO2 particles were obtained from the electrolytic manganese dioxide (EMD). Via high-temperature solid-phase reactions, spinel lithium manganese oxides (LiMn2O4) were produced using the obtained β-MnO2 particles as precursor mixed with LiOH·H2O for the lithium-ion battery cathodes. Atomic absorption (AAS) shows that after the hydrothermal treatment, the contents of impurity ions, such as Na+, K+, Ca2+, and Mg2+, caused by the limitation of preparation technology of EMD are greatly reduced. X-ray diffraction and scanning electron microscopy show that β-MnO2 is highly alloyed consisting of nano sticks. Spinel lithium manganese (LiMn2O4) synthesized by the β-MnO2 precursor has high crystallinity with a well 111 face grow and presents a regular and micron-sized octagonal crystal. When used as cathode materials for lithium-ion batteries, LiMn2O4 synthesized by the β-MnO2 precursor has greater discharge capacity, better cycle performance, and better high-rate capability when compared with LiMn2O4 synthesized by the EMD precursor. Cyclic voltammetry and electrochemical impedance spectroscopy indicate that LiMn2O4 synthesized by the β-MnO2 precursor has better electrochemical reaction reversibility, greater peak current, higher lithium-ion diffusion coefficient, and lower electrochemical impedance.

Synthesis and Electrochemical Properties of High Density LiNi0.8Co0.2 − x Ti x O2 for Lithium-Ion Batteries

LiNi 0.8 Co 0.2-x Ti x O 2 (0 ≤ x ≤ 0.1) powders with a high tap density have been successfully prepared using a eutectic molten salt of 0.62LiNO 3 -0.38LiOH, with a melting point of 175.7°C, and Co-doped Ni(OH) 2 and TiO 2 , where the ratio of Li/(Ni + Co + Ti) is controlled at 1.1:1. The tap density of the synthesized LiNi 0.8 Co 0.2-x Ti x O 2 reaches 3.17 g cm -3 . X-ray diffraction analysis shows that this material has a well-developed layered structure. Scanning electron microscopy indicates that the synthesized particles distribute evenly. Charge-discharge tests demonstrate that the LiNi 0.8 Co 0.15 Ti 0.05 O 2 cathode prepared at 800°C has an initial discharge capacity as high as 169 mAh g -1 and excellent capacity retention at a current density of 0.2 C in the range of 3.0-4.3 V. A capacity of 161 mAh g -1 is retained after 50 charge-discharge cycles, with a capacity retention of 95.3%.

Synthesis and Electrochemical Properties of High-Density LiNi0.8Co0.2O2 for the Lithium-Ion-Battery Cathode

LiNi 0.8 Co 0.2 O 2 powder with a tap density of 3.23 g cm -3 has been successfully prepared by a molten-salt synthesis method using a eutectic molten salt of 0.62LiNO 3 -0.38LiOH with a melting point of 175.7°C and Ni 0.8 Co 0.2 (OH) 2 , where the ratio of Li/(Ni + Co) is controlled at 1.1:1. X-ray diffraction analysis has shown that this material has a well-developed layered structure. Charge-discharge tests have shown that an LiNi 0.8 Co 0.2 O 2 cathode prepared at 800°C has an initial discharge capacity as high as 163 mAh g -1 and excellent capacity retention in the range of 3.0-4.3 V at a current density of 0.2 mA cm -2 .

Highly [010]-oriented self-assembled LiCoPO4/C nanoflakes as high-performance cathode for lithium ion batteries

In this article, highly [010]-oriented self-assembled LiCoPO4/C nanoflakes were prepared through simple and facile solution-phase strategies at low temperature and ambient pressure. The formation of 5-hydroxylmethylfurfural and levoglucosan via the dehydration of glucose during the reaction played a key role in mediating the morphology and structure of the resulting products. LiCoPO4 highly oriented along the (010)-facets exposed Li+ ion transport channels, facilitating ultrafast lithium ion transportation. In turn, the unique assembled mesoporous structure and the flake-like morphology of the prepared products benefit lithium ion batteries constructed using two-dimensional (2D) LiCoPO4/C nanoflakes self-assembles as cathodes and commercial Li4Ti5O12 as anodes. The tested batteries provide high capacities of 154.6 mA·h·g−1 at 0.1 C (based on the LiCoPO4 weight of 1 C = 167 mA·h·g−1) and stable cycling with 93.1% capacity retention after 100 cycles, which is outstanding compared to other recently developed LiCoPO4 cathodes.

Rapid microwave-assisted refluxing synthesis of hierarchical mulberry-shaped Na3V2(PO4)2O2F@C as high performance cathode for sodium & lithium-ion batteries

Unique hierarchical mulberry-shaped Na3V2(PO4)2O2F@C nanocomposite was fabricated by a rapid microwave-assisted low-temperature refluxing strategy. The V(acac)3 reverse micelle systems in the water-in-oil microemulsions played key roles in forming the self-assembly architectures. The prepared Na3V2(PO4)2O2F@C nanoparticles with the anisotropic growth along the [002] direction were in-situ encapsulated in carbon shells, which greatly contribute to fast Na+/e− transfer in electrodes. And the self-assemblies with high structure stability help to improve the cycle performance and mitigate voltage fading. The initial discharge capacity of Na3V2(PO4)2O2F@C as cathode for sodium ion batteries is about 127.9 mA h g−1 at 0.1 C. Besides, a high rate performance with a capacity of 88.1 mA h g−1 at 20 C has been achieved, and the capacity retains 82.1% after 2,000 cycles. In addition, the reaction kinetics and Na+ transportation mechanism of Na3V2(PO4)2O2F@C were preliminarily investigated by the ex situ X-ray diffraction, X-ray photoelectron spectroscopy and galvanostatic intermittent titration technique. More interestingly, when coupled with Li, the fabricated hybrid Li/Na-ion batteries also exhibit excellent rate and cycling performances. The proposed rapid refluxing strategy to synthesize mulberry-shaped Na3V2(PO4)2O2F@C opens up a new opportunity to develop high-performance electrode materials for the energy storage systems.摘要本论文采用快速微波辅助低温回流策略制备了桑椹形Na3V2(PO4)2O2F@C纳米复合材料. 研究表明微乳液中的V(acac)3反胶束体系 对该自组装结构的形成起到了关键作用. 制得的Na3V2(PO4)2O2F晶粒沿着[002]方向生长并被原位包封在碳壳中, 形成了高度稳定的自组装结构, 这不仅有利于Na+/e−的快速迁移, 而且能够有效改善电极材料的循环性能并抑制电压衰减. 作为钠离子电池正极材料, 在0.1C条件下, Na3V2(PO4)2O2F@C的初始放电容量约为127.9 mA h g−1. 在高倍率(20 C)条件下, 容量达88.1 mA h g−1, 2000次循环后容量保持率为 82.1%. 此外, 利用非原位X射线衍射, X射线光电子能谱和恒电流间歇滴定技术, 初步研究了Na3V2(PO4)2O2F@C在充放电过程中的反应机 理和Na+迁移机制. 同时, 在Li/Na离子混合电池当中, Na3V2(PO4)2O2F@C也表现出了优异的倍率和循环性能. 上述微波辅助低温回流合成 策略为开发高性能电化学储能材料开辟了新的途径.