The development of high-performance cathode materials for aluminum-ion batteries (AIBs) is hindered by the strong electrostatic interactions of Al3+ ions with host frameworks, leading to sluggish kinetics and structural degradation. Herein, nickel hexacyanoferrate (NiHCF) nanomaterials with rhombohedral (r-NiHCF) and cubic (c-NiHCF) phases are synthesized using a chelator-regulated solvothermal approach at 80 and 150 °C, respectively. The r-NiHCF exhibits a more ordered lattice with higher Na+ content, fewer Fe(CN)6 vacancies, and reduced water content, resulting in a larger specific surface area (58.34 vs 13.13 m2 g-1) and smaller particle size (37 vs 224 nm). Electrochemical tests reveal that r-NiHCF delivers twice the initial discharge capacity of c-NiHCF (128.8 vs 67.1 mAh g-1 at 0.4 A g-1) and maintains 77.1% capacity retention after 500 cycles. It also demonstrates superior rate performance (38.5 mAh g-1 at 2.0 A g-1) and a higher Al3+ diffusion coefficient (1.04 × 10-11 vs 2.99 × 10-13 cm2 s-1). Mechanistic studies confirm a highly reversible dual-redox behavior (Ni2+/Ni3+ and Fe2+/Fe3+) in r-NiHCF, facilitated by a phase transition that stabilizes the framework during cycling. This work highlights crystal phase engineering as a strategic approach to optimize Prussian blue analogue cathodes for high-performance multivalent-ion batteries.
Feng et al. (Sun,) studied this question.