Food-Additive-Inspired Bifunctional Proton Buffering-Iron Capture Route to Low-Defect Prussian Blue Cathodes for Sodium-Ion Batteries

Abstract

The quest for sustainable and cost-effective energy storage systems has propelled the development of sodium-ion batteries. Iron-based Prussian blue (PB) and its analogues are among the most promising cathode candidates due to their open framework, facile sodium intercalation, and elemental abundance. However, their practical deployment is severely hampered by intrinsic structural imperfections. These defects, primarily in the form of hexacyanoferrate ([Fe(CN)6]) vacancies and interstitial water molecules, which lead to insufficient active sites and poor cycling stability. To mitigate these issues, conventional synthetic strategies often require harsh conditions to slow nucleation. In this study, a novel strategy inspired by food processing additives is developed for effective synthesis of low-defect PB, which employs a bifunctional organophosphate reagent to buffer proton and sequester Fe ions during preparation. This obviates harsh reaction conditions, guarantees a controlled release of H⁺ to promote ligand dissociation, leading to retarded nucleation, as well as limited Fe(CN)6 vacancies and interstitial water. The prepared Prussian blue cathode delivers enhanced cyclic stability in sodium-ion batteries, retaining 90% of its capacity after 1000 cycles at 5 C. This work presents a simple, sustainable, and scalable route to high-performance PB under mild conditions.