Suppressing Cation Migration and Reducing Particle Cracks in a Layered Fe-Based Cathode for Advanced Sodium-Ion...

Sodium-ion batteries have huge potential in large-scale energy storage applications. Layered Fe-based oxides are one of the desirable cathode materials due to abundance in the earth crust and high activity in electrochemical processes. However, Fe-ion migration to Na layers is one of the major hurdles leading to irreversible structural degradation. Herein, it is revealed that distinct Fe-ion migration in cycling NaFeO₂ (NFO) should be mainly responsible for the strong local lattice strain and resulting particle cracks, all of which results in the deterioration of electrochemical performance. More importantly, a strategy of Ru doping could effectively suppress the Fe-ion migration and then reduce the local lattice strain and the particle cracks, finally to greatly enhance the sodium storage performance. Atomic-scale characterization shows that NFO electrode after cycling presents the intense lattice strain locally, accompanied by the remarkable particle cracks. Whereas, Ru-doped NFO electrode maintains the well-ordered layered structure by inhibiting the Fe-O distortion, so as to eliminate the resulting side effect. As a result, Ru-doped NFO could greatly improve the comprehensive electrochemical performance by delivering a reversible capacity of 120 mA h g^-1 , about 80% capacity retention after 100 cycles. The findings provide new insights for designing high-performance electrodes for sodium-ion batteries.