Mitigating voltage decay of O3-NaNi_1/3Fe_1/3Mn_1/3O₂ layered oxide cathode for sodium-ion batteries by incorporation of 5d metal tantalum

The cycling stability of O3-type NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) as a commercial cathode material for sodium ion batteries (SIBs) is still a challenge. In this study, the Ni/Fe/Mn elements are replaced successfully with tantalum (Ta) in the NFM lattice, which generated additional delocalized electrons and enhanced the binding ability between the transition metal and oxygen, resulting in suppressed lattice distortion during charging and discharging. This caused significant mitigation of voltage decay and improved cycle stability within the potential range of 2.0–4.2 V. The optimized Na(Ni_1/3Fe_1/3Mn_1/3)_0.97Ta_0.03O₂ sample achieved a reversible capacity of 162.6 mAh g⁻¹ at a current rate of 0.1 C and 73.2 mAh g⁻¹ at a high rate of 10 C. Additionally, the average charge/discharge potential retention reached 98% after 100 cycles, significantly mitigating the voltage decay. This work demonstrates a significant contribution towards the practical utilization of NFM cathodes in the SIBs energy storage field.