Dual-Site Spin State Modulation in Iron-Based Prussian Blue Cathode Enabling Improved Sodium Storage.
basic_science · Level V
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- Record sourced from PubMed, PMID 42687672.
- Also identified by DOI 10.1002/adma.74904.
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Abstract
Prussian blue (PB) and its analogues are promising cathode materials for sodium-ion batteries (SIBs), yet their practical application is hindered by uncontrolled [Fe(CN)<sub>6</sub>] vacancies and interstitial water, which lead to unsatisfactory cycling stability and capacity utilization. Herein, we report a ligand engineering strategy to simultaneously modulate the spin states of both low-spin (LS) and high-spin (HS) Fe sites in PB. By introducing ─CN vacancies and terminal ─NH<sub>2</sub> groups via a pentacyanide precursor, a modified PB (denoted as PPB) is achieved. Spectroscopic and computational analyses confirm a dual-site spin transition in which both LS and HS Fe sites predominantly convert into an intermediate-spin (IS) state. As a result, the PPB cathode exhibits impressive rate capability (129 and 92 mAh g<sup>-1</sup> at 0.05 and 2 A g<sup>-1</sup>, respectively) and cycling stability (70% retention after 4000 cycles at 2 A g<sup>-1</sup>), significantly outperforming the routine hexacyanide-based PB. Density functional theory calculations reveal that the ─NH<sub>2</sub> groups serve as preferential adsorption sites for Na<sup>+</sup>, while ─CN vacancies lower the migration barrier, which collectively enhance the Na<sup>+</sup> storage kinetics. This work presents a prudent ligand engineering strategy for designing high-performance cathode materials through deliberate spin state manipulation.