Structurally Compatible Anion Substitution for the Enhanced NASICON-Na<sub>4</sub>Mn<sub>1.5</sub>Fe<sub>1.5</sub>(PO<sub>4</sub>)<sub>2</sub>P<sub>2</sub>O<sub>7</sub> Cathode.
basic_science · Level V
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- Record sourced from PubMed, PMID 40916203.
- Also identified by DOI 10.1021/acsnano.5c08681.
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Abstract
The integration of Mn in Na<sub>4</sub>Mn<sub>1.5</sub>Fe<sub>1.5</sub>(PO<sub>4</sub>)<sub>2</sub>P<sub>2</sub>O<sub>7</sub> (NMFPP) enhances the energy density but compromises the Na<sup>+</sup> mobility and structural stability due to limited electron hopping and pronounced Jahn-Teller effects. To address this, a structurally compatible anionic substitution strategy is implemented by partially replacing PO<sub>4</sub><sup>3-</sup> with bulkier and less electronegative SiO<sub>4</sub><sup>4-</sup> groups. The reinforced cathode exhibits enhanced rate performance, which is attributed to lattice expansion induced by the larger SiO<sub>4</sub><sup>4-</sup> units, thereby facilitating Na<sup>+</sup> diffusion and reducing impedance during charge-discharge processes, as supported by GITT and DRT analyses. In addition, the improved cycling stability results from the lower electronegativity of Si, which enables SiO<sub>4</sub><sup>4-</sup> to accommodate local charge redistribution without triggering structural collapse, as evidenced by reduced lattice volume fluctuations observed in <i>in situ</i> XRD. Consequently, Na<sub>4</sub>Mn<sub>1.5</sub>Fe<sub>1.5</sub>(PO<sub>4</sub>)<sub>1.95</sub>(SiO<sub>4</sub>)<sub>0.05</sub>P<sub>2</sub>O<sub>7</sub> achieves a capacity retention of up to 85.42% for 500 cycles at 1 C and 80.54% over 1500 cycles at 5 C. These findings highlight anion substitution as a promising strategy for optimizing polyanionic frameworks toward high-performance sodium-ion batteries.