Crystal structure engineering of Prussian blue through a double-acting chelating agent for energy storage devices

Abstract

Sodium-ion batteries (SIBs) are emerging as a viable alternative to lithium-ion batteries. Iron-based Prussian blue, as a cathode material for SIBs, offers the advantages of low cost and high capacity; however, its rapid crystallization can affect the sodium content and structural integrity. This work employs aspartic acid as both an acidulant and a chelating agent. Compared to the sole use of chelating agents, aspartic acid not only reduces the release rate of Fe²⁺ from the direction of acidity control but also chelates with Fe²⁺ through its two carboxylic groups. This dual action allows for a significant reduction in the synthesis rate of Prussian blue with only a minimal amount of aspartic acid, while also decreasing the internal moisture content and lattice defects within the crystals, thereby greatly reducing the amount of chelating agent used. The prepared PBAsp-3 sample exhibits a high discharge capacity of 141.42 mA h g⁻¹ at 50 mA g⁻¹ and retains 81.81% of its capacity after 450 cycles at 500 mA g⁻¹, making it a low-cost, high-capacity, and high-cycling cathode material for sodium-ion batteries.