Ion-exchange surface modification enhances cycling stability and kinetics of sodium manganese hexacyanoferrate cathode in sodium-ion batteries

Sodium manganese hexacyanoferrate (NaMnHCF) with low cost and high energy density is a promising cathode in Na-ion batteries (NIBs); however, the Jahn-teller effect of Mn3+ and large amounts of Fe(CN)(6)(4-) defects significantly reduces the cycling life of the battery. Here, we introduce a chemically less soluble and structurally more stable layer to the NaMnHCF surface with a simple ion-exchange method to mitigate the irreversible structural change and side reactions associated with both the low-spin Fe-II(-)/Fe-III and the high-spin Mn-II/Mn(III )redox. The NaMnHCF cathode treated in Cu2+ solution shows much better cycling stability (80 vs. 30 mA h(-1) after 1000 cycles at 1 C) and rate performance than the unmodified NaMnHCF. The as-proposed chemical ion-exchange is a well-compatible and low-cost technology to realize surface modification of NaMnHCF and other hexacyanoferrates, which is of great significance for the development of high-performance NIB cathodes. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

By introducing a chemically less soluble and structurally more stable layer to the surface of NaMnHCF through a simple ion-exchange method, the irreversible structural changes and side reactions associated with the cathode in cycling process can be mitigated. The NaMnHCF cathode treated in Cu2+ solution exhibits much better cycling stability and rate performance than the unmodified NaMnHCF, demonstrating the great potential of this low-cost chemical ion-exchange technology for surface modification of high-performance NIB cathodes.