Enhanced performance of core-shell structured sodium manganese hexacyanoferrate achieved by self-limiting Na^(+)-Cs^(+)ion exchange for sodium-ion batteries

Sodium manganese hexacyanoferrate(NaMnHCF)is a promising cathode material for sodiumion batteries(SIBs)due to its low cost and high energy density.The Jahn-Teller effect of Mn,however,leads to the poor structural stability of NaMnHCF,resulting in undesired electrochemical performance.Herein,we developed a novel coating strategy and obtained a coreshell structured NaMnHCF through facile Na^(+)-Cs^(+)ion exchange,which naturally produced a robust and insoluble Cs-rich surface layer(CsMnHCF)with several nanometers in thickness on pristine NaMnHCF.It is shown that the Csrich surface plays a positive role in the stability of the NaMnHCF structure by prohibiting the leakage of crystal water,stabilizing the solid-liquid interfaces,and solidifying crystal structure.The electrochemical performance of the core-shell NaMnHCF is dramatically improved with a discharge capacity of 76.3 mAh·g^(-1)after 1000 cycles at 1.0 C and a reversible capacity of 87.0 mAh·g^(-1)at 10.0 C,which is much superior to that of the pristine NaMnHCF with only 26.6 mAh·g^(-1)after 400 cycles and 31 mAh·g^(-1)at 10.0 C.This work reports a new method for the synthesis of core-shell NaMnHCF and provides a novel perspective for the development of advanced NaMnHCF cathode for SIBs.

Preparation and Electrochemical Properties of Manganese Hexacyanoferrate Modified Glassy Carbon Electrode

A thin film of manganese hexacyanoferrate （MnHCF） was electrochemically formed on a glassy carbon （GC） electrode to prepare a chemically modified electrode （CME）. The mechanism of film formation of MnHCF and its growth process were investigated in detail by cyclic voltammetry. The results show that the stoichiometric composition of MnHCF is Mn^ⅢFe^Ⅲ（CN）6, an analogue of prussian yellow. There exist three clear-cut stages in the whole modification process and the last stage is indispensable to the fabrication of homogenized, stable MnHCF film and must last for an appropriate time. The surface morphology of MnHCF/GC electrode was characterized by scanning electron microscopy （SEM）, which further verified the effective deposition of MnHCF film on GC. The kinetic constants of MnHCF/GC electrode process were also evaluated. The resulting MnHCF film modified electrode presented good stability and high electrocatalytic activity toward the oxidation of H2O2, indicating that MnHCF film possesses function of catalase and can be expected for analytical purposes.