“…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.…”