Interstitial Water Improves Structural Stability of Iron Hexacyanoferrate for High-Performance Sodium-Ion Batteries
Jianwei Hu, Hongwei Tao, Manlin Chen, Zhuchan Zhang, Shengling Cao, Yi Shen, Kai Jiang, Min Zhou
Abstract
Prussian blue analogues (PBAs) are considered one of the promising cathodes for sodium-ion batteries because of their low cost and tunable structure. As an intrinsic characteristic, the influence of structured water in PBAs on the electrochemical properties is still controversial. Herein, low-vacancy iron hexacyanoferrate with different interstitial water contents is synthesized through the citric acid-assisted single iron source method. Ex situ Fourier transform infrared and X-ray diffraction characterization reveals that the interstitial water can stably exist in the Prussian blue framework during repeated cycling. The long-standing interstitial water can reduce the volume change during the Na+ insertion/extraction process, resulting in improved cycling stability. Thanks to the low Fe(CN)64– vacancies and pillar role of interstitial water in the crystal framework, the HW-PB exhibits a high reversible capacity of 117 mAh g–1 and excellent long cycle performance with a capacity retention of 91% after 1380 cycles. This work broadens the understanding of the relationship between the interstitial water in PBAs and Na-storage performances, providing guidance for the precise synthesis of high-quality PBAs.