Hydrophobic Two-Dimensional Layered Superstructure of a Polyoxometalate Cluster as the Cathode Material for Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries hold promise for sustainable energy storage, yet challenges in finding high-performance cathode materials persist. Polyoxovanadates (POVs) are emerging as potential candidates due to their structural diversity and robust redox activity. Despite their potential, issues like dissolution in electrolytes, structural degradation, and byproduct accumulation persist. This work introduces a POV-based hydrophobic two-dimensional (2D) layered superstructure that addresses these challenges. The hydrophobic nature minimizes POV dissolution, enhancing structural stability and inhibiting phase transitions during cycling. The 2D arrangement ensures a larger surface area and improved electronic conductivity, resulting in faster kinetics and higher specific capacity. The superstructure demonstrates improved cycle life and an increased operating voltage, marking a significant advancement in POV-based cathode materials for aqueous zinc-ion batteries.

Synergistic Cation-π Interactions and PEDOT-Based Protective Double-Layer for High Performance Zinc Anode.

Ensuring effective and controlled zinc ion transportation is crucial for functionality of the solid electrolyte interphase (SEI) and overall performance in zinc-based battery systems. Herein the first-ever demonstration of incorporate cation-π interactions are provided in the SEI to effectively facilitate uniform zinc ion flux. The artificial SEI design involves the immobilization of 4-amino-p-terphenyl (TPA), a strong amphiphilic cation-π interaction donor, as a monolayer onto a conductive poly(3,4-ethylenedioxythiophene) (PEDOT) matrix, which enable the establishment of a robust network of cation-π interactions. Through a carefully-designed interfacial polymerization process, a high-quality, large-area, robust is achieved, thin polymeric TPA/PEDOT (TP) film for the use of artificial SEI. Consequently, this interphase exhibits exceptional cycling stability with low overpotential and enables high reversibility of Zn plating/stripping. Symmetrical cells with TP/Zn electrodes can be cycled for more than 3200 hours at 1 mA cm-2 and 1 mAh cm-2 . And the asymmetric cells can cycle 3000 cycles stably with a high Coulomb efficiency of 99.78%. Also, under the extreme conditions of lean electrolyte and low N/P ratio, the battery with TP protective layer can still achieve ultra-stable cycle.

In Situ Grown Coordination-Supramolecular Layer Holding 3D Charged Channels for Highly Reversible Zn Anodes.

Dynamic reversible noncovalent interactions make supramolecular framework (SF) structures flexible and designable. A three-dimensional (3D) growth of such frameworks is beneficial to improve the structure stability while maintaining unique properties. Here, through the ionic interaction of the polyoxometalate cluster, coordination of zinc ions with cationic terpyridine, and hydrogen bonding of grafted carboxyl groups, the construction of a 3D SF at a well-crystallized state is realized. The framework can grow in situ on the Zn surface, further extending laterally into a full covering without defects. Relying on the dissolution and the postcoordination effects, the 3D SF layer is used as an artificial solid electrolyte interphase to improve the Zn-anode performance. The uniformly distributed clusters within nanosized pores create a negatively charged nanochannel, accelerating zinc ion transfer and homogenizing zinc deposition. The 3D SF/Zn symmetric cells demonstrate high stability for over 3000 h at a current density of 5 mA cm-2.

Pure Amorphous and Ultrathin Phosphate Layer with Superior Ionic Conduction for Zinc Anode Protection.

Fast and uniform ion transport within the solid electrolyte interphase (SEI) is considered a crucial factor for ensuring the long-term stability of metal electrodes. In this study, we present the fabrication of ultrathin artificial interphases consisting of a zinc phosphate nanofilm with pure amorphous characteristics and a surfactant overlayer. The thickness of the interphases can be precisely controlled within the range of a few tens of nanometers. We explore the impact of artificial SEI structure, including thickness and crystallinity, on its protective capabilities. The pure amorphous phosphate layer with optimized nanoscale thickness is found to provide an abundance of short and isotropic ion migration pathways and a low diffusion energy barrier. These features facilitate rapid and homogeneous Zn2+ transportation, resulting in compact and planar zinc deposition. Meanwhile, the hydrophobic alkyl moieties of the overlayer prevent disassociation of water at the interface. As a result, this nanofilm endures ultralong cycling stability with a low overpotential and enables high Zn plating/stripping reversibility. The Zn||MnO2 full cell shows a stable cycle life for 700 cycles under practical conditions of lean electrolyte, high areal capacity cathode, and limited Zn excess. These findings provide insights into the design and optimization of SEI layers for protection of metal anodes.

Two-Dimensional Organic-Inorganic Heterostructure as a Multifunctional Protective Layer for High Performance Zinc Metal Anode.

Dendrite growth and side reactions of Zn metal anodes remain unresolved obstacles for practical application of aqueous Zn ion batteries. Herein, a two-dimensional (2D) organic-inorganic heterostructure with controlled thickness was constructed as a protective layer for a Zn metal anode. The reduction of uniformly distributed polyoxometalate in the layer causes a negative charge density gradient, which can accelerate zinc ion transfer, homogenize zinc deposition, and shield sulfates at the electrode interface, while the exposed hydrophobic alkyl chain of the layer can isolate the direct contact of water with the Zn anode. As a result of the synergetic effect, this 2D organic-inorganic heterostructure enables high Zn plating/stripping reversibility, with high average Coulombic efficiencies of 99.97% for 3700 cycles at 2 mA cm-2. Under high Zn utilization conditions, a high areal-capacity full cell with hundreds of cycles was demonstrated.

Stabilizing Interface pH by Mixing Electrolytes for High-Performance Aqueous Zn Metal Batteries.

Aqueous zinc metal batteries with mild acidic electrolytes are considered promising candidates for large-scale energy storage. However, the Zn anode suffers from severe Zn dendrite growth and side reactions due to the unstable interfacial pH and the absence of a solid electrolyte interphase (SEI) protective layer. Herein, a novel and simple mixed electrolyte strategy is proposed to address these problems. The mixed electrolytes of 2 M ZnSO4 and 2 M Zn (CF3 SO3 )2 can efficiently buffer the interfacial pH and induce the in situ formation of the organic-inorganic SEI layer, which eliminates dendrite growth and prevents side reactions. As a result, Zn anodes in mixed electrolyte exhibit a lifespan enhancement over 400 times, endure stable cycling over 270 h at a high DOD of 62% and achieve high Zn plating/stripping reversibility with an average CE of 99.5% for 1000 cycles at 1 mA cm-2 . The findings pave the way for developing practical electrolyte systems for Zn batteries.

Cations Modulated Assembly of Triol-Ligand Modified Cu-Centered Anderson-Evans Polyanions.

Counter-cations are essential components of polyoxometalates (POMs), which have a distinct influence on the solubility, stabilization, self-assembly, and functionality of POMs. To investigate the roles of cations in the packing of POMs, as a systematic investigation, herein, a series of triol-ligand covalently modified Cu-centered Anderson-Evans POMs with different counter ions were prepared in an aqueous solution and characterized by various techniques including single-crystal X-ray diffraction. Using the strategy of controlling Mo sources, in the presence of triol ligand, NH4+, Cu2+ and Na+ were introduced successfully into POMs. When (NH4)6Mo7O24 was selected, the counter cations of the produced POMs were ammonium ions, which resulted in the existence of clusters in the discrete state. Additionally, with the modulation of the pH of the solutions, the modified sites of triol ligands on the cluster can be controlled to form δ- or χ-isomers. By applying MoO3 in the same reaction, Cu2+ ions served as linkers to connect triol-ligand modified polyanions into chains. When Na4Mo8O26 was employed as the Mo source to react with triol ligands in the presence of CuCl2, two 2-D networks were obtained with {Na4(H2O)14} or {{Na2(H2O)4} sub-clusters as linkers, where the building blocks were δ/δ- and χ/χ-isomers, respectively. The present investigation reveals that the charges, sizes and coordination manners of the counter cations have an obvious influence on the assembled structure of polyanions.

{VMo9O31[RC(CH2O)3]}6-: the first class of triol ligand covalently-decorated Keggin-type polyoxomolybdates.

Three trivacant polyoxomolybdates were constructed, presenting the first class of triol ligand covalently-decorated Keggin-type clusters through C-O-Mo bonds. The introduction of the organic component enhanced the stability of the cluster in the solid state with the leaving of active sites at the lacunary position.

Supramolecular interaction-induced assemblies of polyanions and 2-aminopyridinium in two polyoxometalate-based hybrids.

Organic-inorganic hybrids consisting of organic cations and polyanions are promising functional materials due to their various compositions and structures. An important aspect of these materials is the interactions between the organic and inorganic components, which not only produce the final structures, but also influence the properties. Here, we investigated the interactions between organic cations and polyanions using protonated 2-aminopyridinium (Hap) as the cation, and successfully obtained two polyoxometalate-based hybrids, namely (C5H7N2)4[Mo8O26], (I), and (C5H7N2)2[NiMo6O16(OH)2{CH3C(CH2O)3}2]·4H2O, (II). In the crystal structure of (I), every Hap cation links with two polyanions by donating one or two N-H...O hydrogen bonds, and every polyanion is surrounded by eight Hap cations via terminal or bridging O atoms. Conversely, in compound (II), every Hap cation only links with one polyanion decorated by a triol ligand; this organic-inorganic component further assembles via uncoordinated water molecules. In the extended structures, Hap plays a key role, not only providing a counter charge, but also acting as `glue' linking polyanions in the role of hydrogen-bond donors. In both compounds, as the nodes of the supramolecular network, the polyanions exhibit an ordered two-dimensional arrangement due to strong hydrogen bonds and electrostatic interactions between the organic and inorganic parts. The electrochemistry of compound (I) shows that redox sourcing from polyanions is a surface-controlled process. Conversely, the magnetic behaviour of compound (II) indicates dominant antiferromagnetic properties.