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Na-rich Prussian white NaMHCF was prepared by regulating precursors water content based on a mechanochemical protocol. Its interstitial water can be further reduced by rising drying temperature and thus the electrochemical performance was greatly improved.
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•Na-rich Prussian white cathodes were synthesized via a mechanochemical protocol.•Precursors crystal water plays an important role for the formation of NaMHCF.•The interstitial H2O can be greatly reduced via increasing drying temperature.•NaMHCF with less interstitial H2O shows an improved stability and rate capacity.•NaMHCF/NaTi2(PO4)3 shows a high-rate capacity and ultra-stable cycle performance.
Prussian blue analogs (PBAs) with rigid open framework are promising low-cost and easily prepared cathodes for Na-ion batteries. However, their electrochemical performances are hindered from the crystal vacancies and interstitial water in a traditional aqueous co-precipitation process. Herein, we explore a solvent-free mechanochemical protocol to prepare a monoclinic Na1.94Mn[Fe0.99(CN)6]0.95·□0.05·1.92H2O via regulating the crystal water in precursors. The interstitial water of NaMHCF can be further reduced through increasing the drying temperature. Ex-situ XRD confirms that the monoclinic phase transformed to the rhombohedral structure during the first cycle, and a highly reversible multi-phase evolution among rhombohedral, cubic, and Na-poor phase upon Na+ (de)intercalations occurred from the second cycle on. Finally, it delivers a specific capacity of 168.8 mA h g−1 with a stable average voltage of 3.44 V at 10 mA g−1, showing ultra-high rate capability (127 mA h g−1 at 2000 mA g−1) and cycling stability (87.6% capacity retention after 100 cycles at 100 mA g−1) for half cells. For the full cell of NaMHCF/NaTi2(PO4)3, it can deliver an ultra-stable cycle performance, retaining 84% capacity after 500 cycles at 100 mA g−1. Our work provides a facile avenue to prepare monoclinic NaMHCF with low water and vacancies for high-performance Na-ion batteries.