[Liu, Chang; Li, Feng; Ma, Lai-Peng; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China.;Cheng, HM (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;cheng@imr.ac.cn

Advanced Materials for Energy Storage

Graphene-Like Two-Dimensional Materials

Metal Oxides and Oxysalts as Anode Materials for Li Ion Batteries

[Wu, Zhong-Shuai; Ren, Wencai; Wen, Lei; Gao, Libo; Zhao, Jinping; Chen, Zongping; Zhou, Guangmin; Li, Feng; Cheng, Hui-Ming] Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, Shenyang 110016, Peoples R China;Ren, WC (reprint author), Chinese Acad Sci, Inst Met Res, Shenyang Natl Lab Mat Sci, 72 Wenhua Rd, Shenyang 110016, Peoples R China;wcren@imraccn cheng@imraccn

Graphene Anchored with Co 3 O 4 Nanoparticles as Anode of Lithium Ion Batteries with Enhanced Reversible Capacity and Cyclic Performance

Despite the imminent commercial introduction of Li-ion batteries in electric drive vehicles and their proposed use as enablers of smart grids based on renewable energy technologies, an intensive quest for new electrode materials that bring about improvements in energy density, cycle life, cost, and safety is still underway. This Progress Report highlights the recent developments and the future prospects of the use of phases that react through conversion reactions as both positive and negative electrode materials in Li-ion batteries. By moving beyond classical intercalation reactions, a variety of low cost compounds with gravimetric specific capacities that are two-to-five times larger than those attained with currently used materials, such as graphite and LiCoO(2), can be achieved. Nonetheless, several factors currently handicap the applicability of electrode materials entailing conversion reactions. These factors, together with the scientific breakthroughs that are necessary to fully assess the practicality of this concept, are reviewed in this report.

Beyond Intercalation-Based Li-Ion Batteries: The State of the Art and Challenges of Electrode Materials Reacting Through Conversion Reactions

The flowerlike ZnO nanostructures, which consisted of swordlike ZnO nanorods, have been prepared by a cetyltrimethylammonium bromide (CTAB)-assisted hydrothermal process at low temperature (120 °C). The XRD pattern indicated that the flowerlike ZnO nanostructures were hexagonal. Furthermore, the SAED and HRTEM revealed that the swordlike ZnO nanorods were single crystal in nature and preferentially grew up along [001]. Finally, the mechanism for the CTAB-assisted hydrothermal synthesis of flowerlike ZnO nanostructures has been preliminarily explained by polar crystal growth theory and surfactant action theory.

Low temperature synthesis of flowerlike ZnO nanostructures by cetyltrimethylammonium bromide-assisted hydrothermal process

Over the past decades, a worldwide effort has been made to search for alternative anode materials of lithium batteries for improving their energy density and safety. It has been found that 3d transition metal oxides such as nickel oxide, cobalt oxide, and iron oxide exhibit reversible capacities about three times larger than those of graphite (372 mAh g) at a relative low potential, which greatly spurs the rapid development in this field. Among them, cobalt oxides (Co3O4 and CoO) have shown the highest capacity (700 mAh g) and best cycle performance (93.4 % of initial capacity was retained after 100 cycles), compared with nickel oxide (NiO) and iron oxides (Fe2O3 and Fe3O4). [3] In recent years, the nanostructured materials have attracted great interest in the application of anode or cathode materials for lithium batteries because of their high surface-to-volume ratio and short path length for Li transport. As a result, it is believed that the Co3O4 nanomaterials can exhibit the superior Li-battery performance. Previously, several Co3O4 nanostructures such as nanoparticles, nanowires, and nanotubes were prepared by different methods. Among them, the nanotubes have been considered one of the most promising structures for lithium batteries due to their higher surface-to-volume ratio than other one-dimensional nanostructures such as nanowires and more difficult for aggregation in comparison with nanoparticles. By far, there is little literature about the synthesis and application of Co3O4 nanotubes for lithium batteries. For example, Chen et al. synthesized the Co3O4 nanotubes via the anodic aluminum oxide (AAO) template route and applied them for lithium batteries with the capacity of about 800 mAh g at the current density of 50 mA g. However, there are some disadvantages for the AAO template assisted approach to synthesize metal oxide nanotubes, which restrict their application in Libattery. Firstly, the mass production of metal oxide nanotubes prepared by such an approach is impracticable, which is one of the bottlenecks for their wide applications. Secondly, it is very difficult to completely remove the nanoporous alumina template. Thirdly, the diameters of metal oxide nanotubes prepared by such an approach are usually larger than 100 nm. Recently, carbon nanotubes (CNTs) have been considered to be an ideal template for the synthesis of metal oxide nanotubes due to the mass production, being easily removed and small diameter. For example, Liu et al. reported the synthesis of Fe2O3/CNTs core-shell nanostructures and polycrystalline Fe2O3 nanotubes by supercritical fluids approach using CNTs as templates. Unfortunately, the high temperature and pressure were needed in this approach. In addition, metal oxide/ CNTs core-shell nanostructures and metal oxide nanotubes were also achieved by CNT-template assisted chemical vapor deposition (CVD), which operated at high temperature and, moreover, only deposited oxides on the top surface of CNTs. Furthermore, metal oxide/CNTs core-shell nanostructures were also fabricated by chemical precipitation method. However, the formation of metal oxide nanoparticles in the solution or metal oxide with very large grain size on the surface of CNTs was inevitable in this approach, which made it difficult to form metal oxide nanotubes after oxidation of CNTs. Very recently, we have developed a novel approach to synthesizing the porous and polycrystalline In2O3 nanotubes by layer-by-layer assembly on CNT templates in combination with subsequent calcinations, which exhibit superior gas sensing performance. Herein, we report a novel sonochemistry method to synthesizing CNTs-CoOx nanocables derived from Co4(CO)12 clusters on CNT templates at room temperature and subsequent transformation into uniform porous Co3O4 nanotubes by the calcination. Moreover, the assynthesized porous Co3O4 nanotubes have been applied in anode materials for lithium batteries, which exhibit the superior performance and thus promising application. Firstly, Co4(CO)12 and CNTs were mixed in hexane and sonicated for 1 h at room temperature. During the sonication, Co4(CO)12 can be readily decomposed to Co and CO, as shown in Reaction 1. Secondly, Co atom can be rapidly oxidized into CoOx due to the oxygen atmosphere in the solution, as illustrated in Reaction 2. Thirdly, CoOx with positive charge can be compactly deposited on the surface of CNTs C O M M U N IC A IO N

Porous Co3O4 Nanotubes Derived From Co4(CO)12 Clusters on Carbon Nanotube Templates : A Highly Efficient Material For Li-Battery Applications

Indium oxide (In2O3), as an n-type and wide-bandgap semiconductor, is of great interest for use in toxic-gas detectors, solar cells, and light-emitting diodes because of its high electrical conductivity and high transparency. In particular, In2O3 has been extensively applied in film-based chemical sensors for a long time. However, In2O3-film-based sensing devices possess several critical limitations such as a limited maximum sensitivity and high operation temperatures (200–600 °C). In2O3 nanostructured materials, possessing ultrahigh surface-to-volume ratios, are expected to be superior gas-sensor candidates that may overcome the fundamental limitations as mentioned above. Therefore, considerable efforts have been devoted to synthesizing In2O3 nanostructures such as nanoparticles, nanowires, nanotubes, and nanobelts. Among them, nanotubes are believed to be one of the most promising structures for chemical sensors because of their higher surface-to-volume ratios and, moreover, they do not aggregate as easily as nanoparticles. Up to now, template-assisted approaches have been widely used to synthesize metal oxide nanotubes. Metal oxide nanotubes prepared by template-assisted approaches possess higher surface-to-volume ratios than those prepared by template-free approaches because of their polycrystalline and porous structure, and, therefore, may display a more superior gas-sensor performance. As a result, owing to the simplicity in the synthesis of nanotubes and their availability, quite a few metal oxide nanotubes have been fabricated by nanoporous alumina template assisted approaches such as Ga2O3, In2O3, TiO2, and Fe2O3. [8] Nevertheless, there are some disadvantages in using nanoporous alumina as a template to synthesize metal oxide nanotubes. Firstly, mass production of metal oxide nanotubes by such an approach is impractical, which is one of the bottlenecks for their wide application. Secondly, it is very difficult to completely remove the nanoporous alumina template. Thirdly, the diameters of the prepared metal oxide nanotubes by such an approach are usually larger than 100 nm. Recently, carbon nanotubes (CNTs) have been considered to be an ideal template for the synthesis of metal oxide nanotubes, which can circumvent the disadvantages of nanoporous alumina as mentioned above. For example, Rao and co-workers first fabricated ZrO2, Al2O3, V2O5, SiO2, and MoO3 nanotubes by a metal-alkoxide-based sol–gel process using CNTs as templates in combination with subsequent calcination. However, the deliquescence, toxicity, and high cost of metal alkoxides, as well as the long reaction time, restrict the practical applications of this approach. Liu and co-workers reported the synthesis of Fe2O3/CNT core–shell nanostructures and polycrystalline Fe2O3 nanotubes by a supercritical-fluid-approach using CNTs as templates. Unfortunately, this approach needed to be carried out at high temperature and pressure. In addition, metal oxide/CNT core–shell nanostructures and metal oxide nanotubes have been obtained by CNT-template-assisted chemical vapor deposition (CVD), which was also carried out at high temperature and, moreover, only resulted in the deposition of oxides on the top surface of the CNTs. Metal oxide/CNT core–shell nanostructures were also fabricated by a chemical precipitation method. However, in this route, the formation of metal oxide nanoparticles in the solution or metal oxides with a very large grain size on the surface of the CNTs was inevitable, which made it difficult to form metal oxide nanotubes after oxidation of the CNTs. We report a novel and versatile approach to synthesize metal oxide nanotubes using layer-by-layer (LBL) assembly on the CNT templates in combination with subsequent calcination. LBL assembly is based on the electrostatic attraction between charged species and it has been widely used to synthesize polymeric multicomposites, inorganic and hybrid hollow spheres, polymer nanotubes, and core–shell nanostructures. We now present its use, for the first time, to synthesize metal oxide nanotubes including In2O3, NiO, SnO2, Fe2O3, and CuO. Of these, In2O3 nanotubes are used to illustrate the basic idea underlying the approach presented in this work. The as-synthesized In2O3 nanotubes were applied in an NH3 gas sensor operated at room temperature, which exhibits improved performance and thus promising applications. C O M M U N IC A IO N

Porous Indium Oxide Nanotubes: Layer-by-Layer Assembly on Carbon-Nanotube Templates and Application for Room-Temperature NH3 Gas Sensors

Different shapes of ZnO microcrystals have been achieved controllably by a capping-molecule-assisted hydrothermal process. The flowerlike, disklike, and dumbbell-like ZnO microcrystals of hexagonal phase have been obtained respectively using ammonia, citric acid (CA), and poly(vinyl alcohol) (PVA) as the capping molecules. Only a very strong UV emission at ∼380 nm is observed in the photoluminescence (PL) spectra of the three kinds of ZnO microcrystals, indicative of their high crystal quality. The formation mechanisms for the hydrothermally synthesized microcrystals in different morphologies have been phenomenologically presented.

Controllable growth of ZnO microcrystals by a capping-molecule-assisted hydrothermal process

Flower-like ZnO nanostructures, which consisted of sword-like ZnO nanorods, have been prepared by an organic-free hydrothermal process. The XRD pattern indicated that the flower-like ZnO nanostructures were hexagonal. The SAED and HRTEM experiments implied that the sword-like ZnO nanorods were single crystal in nature and preferentially grew up along the [001] direction. The effects of temperature, pH value and mineralizer on the morphology have been also investigated. It is considered that pH value is the main factor to influence the morphology because of its effect on the initial nuclei and growth environment of ZnO. Finally, the mechanism for organic-free hydrothermal synthesis of the flower-like ZnO nanostructure is discussed.

https://iopscience.iop.org/article/10.1088/0957-4484/15/5/037/pdf

Xiangyang Ma

Papers

Low temperature synthesis of flowerlike ZnO nanostructures by cetyltrimethylammonium bromide-assisted hydrothermal process

Porous Co3O4 Nanotubes Derived From Co4(CO)12 Clusters on Carbon Nanotube Templates : A Highly Efficient Material For Li-Battery Applications

Porous Indium Oxide Nanotubes: Layer-by-Layer Assembly on Carbon-Nanotube Templates and Application for Room-Temperature NH3 Gas Sensors

Controllable growth of ZnO microcrystals by a capping-molecule-assisted hydrothermal process

Synthesis of flower-like ZnO nanostructures by an organic-free hydrothermal process