Monoclinic Bimetallic Prussian Blue Analog Cathode with High Capacity and Long Life for Advanced Sodium Storage

Prussian blue analogs (PBAs) are regarded as promising cathode materials for sodium-ion batteries (SIBs), but most of them suffer from an incompatibility between capacity and structural stability. Herein, an innovative disodium ethylenediaminetetraacetate (Na₂EDTA)-assisted hydrothermal method is proposed to synthesize monoclinic Fe-substituted Ni-rich PBA (H-PBA) cathodes for Na-ion storage. The as-designed H-PBA cathode combines the merits of the low strain of a Ni-based PBA framework and the enhanced capacity of N-Fe³⁺/Fe²⁺ redox sites. It can achieve superior sodium-storage performance in terms of capacity, rate capability, and cycle stability. Moreover, ex situ measurements reveal that solid solution (2.0-3.0 V) and phase-transition (3.0-4.0 V) reactions occur during the charge/discharge process to allow almost 1.5 Na⁺ storage in the H-PBA lattice. Meanwhile, the H-PBA//NaTi₂(PO₄)₃@C full cell also delivers remarkable electrochemical properties. Prospectively, this work would promote the practical application of SIBs in grid-scale electric energy storage.