A high rate and stability cathode material for half/full sodium-ion batteries: Nb-substituted NaNi1/3Mn1/3−xFe1/3NbxO2 layered oxides

Abstract

O3 layered oxide cathode materials have infinite development potential in sodium ion batteries (SIBs), but complex phase transitions usually result in poor rate capacity. In this study, NaNi1/3Mn1/3−xFe1/3NbxO2 (NFM-Nb x, x = 0, 0.01, 0.02) precursor were synthesized through ball-milling spray drying method. The structure morphology characterization confirmed that Nb was successfully doped into the material and replaced part of Mn in the transition metal. The chemical valence analysis shows that Nb doping promoted the reduction of Mn4+ to Mn3+, and the increase of Mn3+ improved the ionic conductivity. NFM-Nb 0.01 significantly improved long cycle stability and rate capacity, the capacity of NFM-Nb 0.01 at 1 C and 5 C were 125.4 and 115.5 mAh g−1, respectively, and the corresponding cycle retention rate maintained 83. 81% and 83.12%. NFM-Nb 0.01 has a 25.06% higher capacity retention rate than NFM after 100 cycles at 1 C in the voltage range 2–4.3 V. For full-cell, NFM-Nb 0.01//HC delivered the capacity of 79.4 mAh g−1 at 10 C after 200 cycles and kept 71.16% cycle retention. The results of ex-situ XRD further investigated Nb-substitution enhanced the structure recoverability of cathode materials. The failure analysis result showed that Nb substitution is beneficial to stabilize the layered structure of materials, improve the cycling performance under high voltage.