Abstract
Zinc hexacyanoferrate (ZnHCF) which is a dimorphic (cubic or rhombohedral) Prussian blue analogue and can be intercalated by both monovalent and divalent ions,is a promising cathode material for rechargeable aqueous metal-ion batteries.In this paper, a simple co-precipitation method is developed to tune the particle morphology of ZnHCF by adjusting the dropping speed at room temperature. Three polyhedral ZnHCF particles, with cubooctahedral, truncated octahedral or octahedral shapes, are obtained at room temperature. Structural transformation from cubic phase of as-prepared ZnHCF to rhombohedral phase is observed by further dehydration of the sample at 70 °C, whereas the dehydrated ZnHCF crystals still hold the identical polyhedral shape as that of the cubic phase particles. Then the influence of shape and facets on electrochemical performance is studied for polyhedral ZnHCF with rhombohedral structure (RZnHCF). RZnHCF sample with cubooctahedral shape possesses the best rate capability and cyclic stability comparing with RZnHCF particles having truncated octahedral or octahedral shapes. Furthermore, the structure of cuboctahedron RZnHCF particles during electrochemical cycling has been monitored with ex situ X-ray diffraction to demonstrate the reversible zinc-ion intercalation mechanism.
Highlights
In recent years, Prussian blue analogues (PBAs) are widely studied in the energy storage systems as the electrode materials[19,20,21,22,23]
To investigate the influence of morphology on the electrochemical performance, we demonstrate a facile and general procedure for preparation of single-crystalline Zinc hexacyanoferrate (ZnHCF) polyhedrons by a simple co-precipitation method without capping agent
Three cubic phase ZnHCF samples with cubooctahedral, truncated octahedral or octahedral shapes are obtained at room temperature
Summary
Prussian blue analogues (PBAs) are widely studied in the energy storage systems as the electrode materials[19,20,21,22,23]. The structural diversity of MeHCFs makes it possible to design new high-performance divalent metal-ion RAMB, including aqueous zinc-ion battery. Compared to most of MeHCFs with cubic structure, ZnHCFs exhibit the rhombohedral structure in which the ZnN4 tetrahedras are linked to FeC6 octahedras via CN ligands to form a porous three-dimensional framework with large open sites where metal ions such as Na+, K+ and Cs+ and water molecules are located. Such a framework endows ZnHCFs with the possibility of acting as intercalation hosts for various cations. By controlling the reaction conditions, uniform ZnHCF particles with a series of regular morphologies were successfully prepared, and their relationship between exposed facets and electrochemical performance was proposed, which will give new insights into the design of high-performance RAMB based on PBAs
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