Assembly of 12-Tungstovanadate-Templated Nanocage and Nanocomposites with Single-Walled Carbon Nanotubes as Anodes in Lithium-Ion Batteries

Self-Assembly of Polyoxometalate-Resorcin[4]arene-Based Inorganic-Organic Complexes: Metal Ion Effects on the Electrochemical Performance of Lithium Ion Batteries

With their adjustable structures and diverse functions, polyoxometalate (POM)-resorcin[4]arene-based inorganic-organic complexes are a kind of potential multifunctional material. They have potential applications for lithium ion batteries (LIBs). However, the relationship between different coordinated metal ions and electrochemical performance has rarely been investigated. Here, three functionalized POM-resorcin[4]arene-based inorganic-organic materials, [Co₂ (TMR4 A)₂ (H₂ O)₁₀ ][SiW₁₂ O₄₀ ]⋅2 EtOH⋅4.5 H₂ O (1), [Ni₂ (TMR4 A)₂ (H₂ O)₁₀ ][SiW₁₂ O₄₀ ]⋅4 EtOH⋅13 H₂ O (2), and [Zn₂ (TMR4 A)₂ (H₂ O)₁₀ ][SiW₁₂ O₄₀ ]⋅2 EtOH⋅2 H₂ O (3), have been synthesized. Furthermore, to enhance the conductivities of these compounds, 1-3 were doped with reduced graphene oxide (RGO) to give composites 1@RGO-3@RGO, respectively. As anode materials for LIBs, 1@RGO-3@RGO can deliver very high discharge capacities (1445.9, 1285.0 and 1095.3 mAh g^-1 , respectively) in the initial run, and show discharge capacities of 898, 665 and 651 mAh g^-1 , respectively, at a current density of 0.1 A g^-1 over 100 runs. More importantly, the discharge capacities of 319, 283 and 329 mAh g^-1 were maintained for 1@RGO-3@RGO even after 400 cycles at large current density (1 A g^-1 ).

Polyoxometalate-Templated Cobalt-Resorcin[4]arene Frameworks: Tunable Structure and Lithium-Ion Battery Performance

By employing a bowl-like tetra(benzimidazole)resorcin[4]arene (TBR4A) ligand, two new polyoxometalate-templated metal-organic frameworks (POMOFs), [Co₈Cl₁₄(TBR4A)₆]·3[H_3.3SiW₁₂O₄₀]·10DMF·11EtOH·20H₂O (1) and [Co₃Cl₂(TBR4A)₂(DMF)₄]·[SiW₁₂O₄₀]·2EtOH·3H₂O (2), have been prepared under solvothermal conditions (DMF = N,N'-dimethylformamide). 1 shows a 2D cationic layer, whereas 2 exhibits a 3D framework. Remarkably, the Keggin POMs in 1 and 2 were located in the cavities formed by two bowl-like resorcin[4]arenes in sandwich fashions. Their framework structures were highly dependent on the coordination modes of the TBR4A ligands. To increase the conductivity of POMOFs, the samples of 1 and 2 were loaded on the conductive polypyrrole-reduced graphene oxide (PPy-RGO) via ball milling (1@PG and 2@PG). Then, the obtained composites experienced calcination at a proper temperature to produce 1@PG-A and 2@PG-A. The resulting 1@PG-A and 2@PG-A composites, with improved conductivities, uniform sizes and micropores, exhibited promising electrochemical performance for lithium-ion batteries. We herein proposed a size-controlled route for the rational fabrication of functional POMOFs and their usage in energy fields.

A New Family of Polyoxometalates: Tris-functionalized Lindqvist-Type Hexatungstovanadates

We successfully designed and obtained a new family of polyoxometalates (POMs) containing mixed-metal elements and a trialkoxyl (TRIS) ligand via a very simple one-pot process under mild condition. Single-crystal X-ray diffraction revealed that this family belongs to compact Lindqvist-type hexatungstovanadates. In particular, the hydroxyl-containing product can be further functionalized through esterification. Not only does this work open a broad door for unusual POM clusters involving vanadium and tungsten atoms in the future, but also the design concept of this work also provides new insight for the synthesis and further exploration of POMs.