Introducing zinc ions into manganese-based Prussian blue for improving the structural stability of sodium-ion batteries

Manganese-based Prussian blue (MF-N) is a promising cathode material for sodium-ion batteries and has attracted wide-spread attention owing to its advantages of high specific capacity and low cost. However, the lattice channel instability of MF-N during sodium ion de-intercalation leads to drastic phase transitions, structural damage, particle cracking, and cyclic stability failure. Considering divalent zinc ions have a strong electrostatic interaction with the crystal structure of the cathode material and present no electrochemical activity in the corresponding electrochemical window, they can effectively stabilize the lattice channel and structure of MF-N. Thus, zinc ions are introduced into the structure of MF-N to replace sodium ions on the lattice channel using a co-precipitation method. The phases of manganese-based Prussian blue with zinc ions (MF-NZ) are cubic and tetragonal when sodium ions are completely extracted due to the presence of zinc ions supporting the lattice channel, which inhibits the complete phase transformation to the tetragonal phase and makes MF-NZ exhibit excellent structural stability. The MF-NZ cathode exhibits a capacity of 104.7 mA h g-1 even at 5C and retains a capacity of 88.1 mA h g-1 in 300 cycles at 1C, which is 133.7% and 113.8% higher than those of MF-N, respectively. This study provides a feasible strategy for minimizing structural destruction and improving the electrochemical performance of the MF-N cathode. The introduction of non-electrochemically active metal ions stabilizes the lattice channels of manganese-based Prussian blue.