Turning Berlin green frameworks into cubic crystals for cathodes with high-rate capability

Abstract

Prussian blue analogues (PBAs) have been considered as promising host frameworks for charge carriers because of their well-defined diffusion channel along the <100> direction. Among PBA families, Berlin green (BG)...

Synergistic effect of a Berlin green framework for highly efficient moisture-electric energy transformation

“…The presence of XRD peaks corresponding to the (200), (220), (400), and (420) planes indicates that the crystalline structure of the BG particles is face-centered cubic. 17–19 Fig. 1c and d show the cross-sectional SEM image and corresponding EDS elemental mapping image of the BGC–NC bilayer with thicknesses of 0.2 mm (NC) and 1.1 mm (BGC).…”

“…BG, an oxidized form of Prussian blue (PB), is cost-effective, easily synthesized, and chemically modifiable. 16,17 The BG-based MPG was prepared by stacking a BG/graphene oxide (GO)/cellulose nanofiber (CNF) (hereinafter abbreviated as BGC) composite layer on a NaCl/CNF (NC) composite layer. The adsorption of moisture onto the NC layer causes the sodium ions to dissociate and spontaneously diffuse toward the BGC layer because of the ion concentration gradient.…”

Effect of the Interaction between Transition Metal Redox Center and Cyanide Ligand on Structural Evolution in Prussian White Cathodes

“…The diatomic nature of the cyanide anion in the X site endows PBAs having larger interstitial cavities (up to ∼4.5 Å) with open frameworks for the carrier ions in the A site, , making them more attractive than typical oxide and phosphate materials used in lithium-ion batteries (LIBs) for storing various monovalent/bivalent/trivalent charge carriers. − Furthermore, the well-defined ion diffusion channel along the ⟨100⟩ direction in PBAs enable high rate capability, which is crucial for the actual operation of large-scale energy storage systems in electric vehicles and stationary power supplies where quick charging is highly demanded . The B site is regularly occupied by C-coordinated low-spin (LS) TM ions (R site) and N-coordinated high-spin (HS) TM ions (P site) (Figure a). − Therefore, depending on the selection of TM in the R and P sites, PBAs exhibited distinguished electrochemical performance from the viewpoint of operating voltage, specific capacity, and reversibility. − Interestingly, the amount ( x ) of carrier ions occupying the A site determines the oxidation state of TM ions, varying the phase and structure of PBAs such as Berlin green (BG; x = 0), Prussian blue (PB; x = 1), and Prussian white (PW; x = 2). , Moreover, with carrier ions being fully populated on the A site (i.e., x = 2), the interaction between the carrier ions and cyanide anion becomes stronger, causing lattice distortion from the cubic phase ( x = 0 and 1, Fm 3̅ m ) to the monoclinic or rhombohedral phase ( x = 2, P 2 1 / n or R 3̅) in such a way that the carrier ions tend to move away from each other. − Furthermore, the interstitial water molecules [ y (H 2 O)] are readily crystallized over the A and R sites because rapid crystallization leads to the formation of Fe­(CN) 6 vacancies, which may considerably deteriorate the key battery performance. ,, To overcome this issue, several synthetic protocols have been developed to reduce the crystallization rate (such as citrate-assisted crystallization − and N 2 bubbling). The proposed synthetic protocols could efficiently suppress the formation of Fe­(CN) 6 vacancies.…”

“…17 phase and structure of PBAs such as Berlin green (BG; x = 0), Prussian blue (PB; x = 1), and Prussian white (PW; x = 2). 20,21 Moreover, with carrier ions being fully populated on the A site (i.e., x = 2), the interaction between the carrier ions and cyanide anion becomes stronger, causing lattice distortion from the cubic phase (x = 0 and 1, Fm3̅ m) to the monoclinic or rhombohedral phase (x = 2, P2 1 /n or R3̅ ) in such a way that the carrier ions tend to move away from each other. 22−28 Furthermore, the interstitial water molecules [y(H 2 O)] are readily crystallized over the A and R sites because rapid crystallization leads to the formation of Fe(CN) 6 vacancies, which may considerably deteriorate the key battery performance.…”