Na_1.51Fe[Fe(CN)₆]_0.87·1.83H₂O Hollow Nanospheres via Non‐Aqueous Ball‐Milling Route to Achieve High Initial Coulombic Efficiency and High Rate Capability in Sodium‐Ion Batteries

Abstract

Prussian blue analogues (PBAs) have attracted extensive attention as cathode materials in sodium‐ion batteries (SIBs) due to their low cost, high theoretical capacity, and facile synthesis process. However, it is of great challenge to control the crystal vacancies and interstitial water formed during the aqueous co‐precipitation method, which are also the key factors in determining the electrochemical performance. Herein, an antioxidant and chelating agent co‐assisted non‐aqueous ball‐milling method to generate highly‐crystallized Na2‐xFe[Fe(CN)6]y with hollow structure is proposed by suppressing the speed and space of crystal growth. The as‐prepared Na2‐xFe[Fe(CN)6]y hollow nanospheres show low vacancies and interstitial water content, leading to a high sodium content. As a result, the Na‐rich Na1.51Fe[Fe(CN)6]0.87·1.83H2O hollow nanospheres exhibit a high initial Coulombic efficiency, excellent cycling stability, and rate performance via a highly reversible two‐phase transition reaction confirmed by in situ X‐ray diffraction. It delivers a specific capacity of 124.2 mAh g−1 at 17 mA g−1, presenting ultra‐high rate capability (84.1 mAh g−1 at 3400 mA g−1) and cycling stability (65.3% capacity retention after 1000 cycles at 170 mA g−1). Furthermore, the as‐reported non‐aqueous ball‐milling method could be regarded as a promising method for the scalable production of PBAs as cathode materials for high‐performance SIBs.

Defect‐Healing Induced Monoclinic Iron‐Based Prussian Blue Analogs as High‐Performance Cathode Materials for Sodium‐Ion Batteries

“…As shown in Figure S1 (Supporting Information), the as-prepared Fe-HCF-5 product is light blue while the Fe-HCF-1 prepared without Na 4 P 2 O 7 appears dark blue, indicating that part of the Fe 2+ of Fe-HCF-1 was oxidized and resulted in less Na + content inside the crystal framework. [22] Meanwhile, sodium pyrophosphate can greatly slow down the growth of grains, thus significantly improving the crystallinity of the product (Figure S2, Supporting Information).…”

Reforming Magnet Waste to Prussian Blue for Sustainable Sodium-Ion Batteries

“…As a chelating agent, sodium citrate can effectively control the release of Fe 2+ , thus slowing down the rate of crystallization nucleation and prolonging the time of crystal growth. 37 Since the aciddissolved waste liquid is a strong acid solution, NaOH is used to adjust the pH. The Fe 2+ in the waste liquid can better complex with citrate at a pH value of about 5.…”

Low-cost Prussian blue analogues for sodium-ion batteries and other metal-ion batteries

“…As for in situ Raman spectroscopy, it could identify the valence state evolution of Fe during cycling processes, because it is sensitive to the cyanide stretching mode [ ν (CN)] vibration of the chemical state of iron. 39,104…”

“…In the research for eligible cathode materials for sodium-ion batteries (SIBs) and other MIBs, a large number of compounds have been studied including transition-metal oxides (TMOs), 32–35 polyanionic materials, 36 organic compounds, 37 and Prussian blue analogues (PBAs). 38–40 Although TMOs have significant advantages in terms of specific capacity and working voltage, they still suffer from continuous capacity fading during cycling caused by complex and excessive phase transitions. The reversible specific capacities of polyanionic materials are generally below 120 mA h g −1 due to their heavy molar weights.…”