Synchronous crystal growth and etching optimization of Prussian blue from a single iron-source as high-rate cathode for sodium-ion batteries

Abstract

Prussian blue (PB) and its analogues (PBAs) have been considered as promising cathodes for room temperature sodium-ion batteries (SIBs) because of their rigid open framework and low-cost synthesis. Herein, we have synthesized slight-etching PB cubes with low amounts of coordinated water and [Fe(CN)6] vacancies using an optimized hydrothermal method with the aid of acid. Interestingly, synchronous crystal growth and etching processes are observed, accompanied by recrystallization behaviors during the etching process. With the increasing acid amount, yield of the as-prepared PB improves greatly. The acid etching mechanism is further clarified. Notably, such one-step acid-etching hydrothermal approach can realize the rational composition and architecture design of PB. The correlation between physical properties and cell performance of PB is systematically investigated. The optimized PB cubes with slight surface etching deliver a high reversible specific capacity of 99 mA h g−1, a capacity retention of 79% for 500 cycles and 74 mA h g−1 at a high current density of 1500 mA g−1. Such superior rate capability and long cycle life are ascribed to the synergistic effects of the structure and morphology of PB, which possesses low amounts of coordinated water and [Fe(CN)6] vacancies, large unit cell volume, and slight-etching surface in the cubic structure, good crystallinity and uniform particle size distribution.