An ultra-stable Mn-based Prussian blue compound effectively suppresses Jahn-Teller distortion as a superior cathode material for sodium-ion batteries

Among the potential cathode materials for sodium-ion batteries (SIBs), sodium manganese hexacyanoferrate (NaMHCF) has attracted great interest because of its open 3D framework, cost-effectiveness, and high voltage properties. However, NaMHCF synthesized by the conventional coprecipitation method has the disadvantages of high crystal water and high defects. Herein, through an effective regulation strategy, the strong chelation between organic complex manganese salt and Na4Fe(CN)6 can greatly slow down the nucleation rate of the coprecipitation reaction and prepare low defect, low water content, high crystallization cubic phase NaMHCF. In situ XRD analysis shows that the cubic phase NaMHCF has no phase transformation during repeated charge and discharge, which greatly reduced the deterioration of the cathode caused by Jahn-Teller (J-T) distortion of Mn3+. Moreover, ex situ XPS and time-of-flight secondary ion mass spectrometry (TOF-SIMS) verified that the cubic phase NaMHCF crystal structure has low water content and lattice defects, and shows superior cycle stability with a capacity retention rate of about 90% at 350 mA g-1 over 300 cycles and impressive rate performance, and can still work normally even in low temperature environments (-20 degrees C). This work has great potential in the research of high-performance cathode materials for sodium-ion batteries. By regulating the nucleation rate of the coprecipitation reaction, cubic NaMHCF was successfully prepared, which can effectively inhibit the Jahn-Teller effect and can work normally as the cathode of SIB even in low-temperature environments.