Monoclinic\nBimetallic Prussian Blue Analog Cathode\nwith High Capacity and Long Life for Advanced Sodium Storage

Abstract

Prussian\nblue analogs (PBAs) are regarded as promising cathode\nmaterials for sodium-ion batteries (SIBs), but most of them suffer\nfrom an incompatibility between capacity and structural stability.\nHerein, an innovative disodium ethylenediaminetetraacetate (Na₂EDTA)-assisted hydrothermal method is proposed to synthesize\nmonoclinic Fe-substituted Ni-rich PBA (H-PBA) cathodes for Na-ion\nstorage. The as-designed H-PBA cathode combines the merits of the\nlow strain of a Ni-based PBA framework and the enhanced capacity of\nN–Fe³⁺/Fe²⁺ redox sites. It can achieve\nsuperior sodium-storage performance in terms of capacity, rate capability,\nand cycle stability. Moreover, <i>ex situ</i> measurements\nreveal that solid solution (2.0–3.0 V) and phase-transition\n(3.0–4.0 V) reactions occur during the charge/discharge process\nto allow almost 1.5 Na⁺ storage in the H-PBA lattice. Meanwhile,\nthe H-PBA//NaTi₂(PO₄)₃@C full cell\nalso delivers remarkable electrochemical properties. Prospectively,\nthis work would promote the practical application of SIBs in grid-scale\nelectric energy storage.