Synthesis of New‐Phased VOOH Hollow “Dandelions” and Their Application in Lithium‐Ion Batteries

Abstract

Large-scale self-assembly of meso-, micro-, and nanostructured building components with highly specific morphology and novel properties are of great interest to chemists and material scientists. Remarkable progress has been made in the self-assembly of highly organized building blocks of metals, [1] semiconductors, [2] copolymers, [3] organic-inorganic hybrid materials, [4] and biomaterials [5] based on different driving mechanisms. However, controlling the assembly of primary building units, for example flakes, into curved hollow structures is still a challenge for materials self-assembly.[6] The ability to assemble primary units into hollow structures is in great demand by scientists not only because of the role this plays in better understanding the concept of self-assembly with artificial building blocks but also for its great potential for technological applications. [7] Vanadium oxides, in which the vanadium is known to exist in a wide range of oxidation states, from +2, as in VO, to +5, as in V 2 O 5 , have been extensively studied as a well-known kind of transition-metal oxide because they have unique electrical and optical properties. [8] Regarding the V 5+ and V 4+ oxides, various nanostructures (e.g., nanotubes, nanowires, nanofibers, nanobelts, nanorods, and mesoporous structures) have already been synthesized by a variety of methods, [9] including reverse-micelle transition, the sol-gel process, hydrothermal treatment, and electrochemical deposition. As expected, the various nanostructures of V 4+and V 5+ oxides lead to a wide variety of potential applications, including sensors, [10] optical switching devices, [11] optical datastorage media, [12] and electrode materials for Li secondary batteries.[13] By contrast, there are only limited reports concerning the synthesis of V 3+ oxide nanostructures and their interesting properties, [14] and thus it still remains a challenge to develop simpler and versatile approaches to V 3+ oxide nanostructures.In this communication, we describe a simple hydrothermal method to organize as-formed building blocks of flakes into VOOH hollow curved architectures by means of the "aggregation-then-growth" process: 1) freshly formed VOOH monomers aggregate around the gas/liquid interface to form hollow VOOH spheres and 2) the in situ formed building units of flakes continue to grow during the following hydrothermal process. This one-pot hierarchical organizing scheme relies primarily on the N 2 gas bubbles produced in the reaction process, representing another way of organizing flake building blocks into hollow curved architectures; this is different from previously reported ways using, for example, emulsified soft templates, hydrophobic attraction, or the solid templates resulting from variation of the chemical composition of the building units.[15] The as-obtained VOOH hollow "dandelions", a new-phased and unique V 3+ oxide nanostructure, offer the first opportunity to investigate the Li + charge-and-discharge electrochemical properties for V 3+ oxides.Important info...

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