Improved Electrochemical Performance of Fe-Substituted NaNi0.5Mn0.5O2 Cathode Materials for Sodium-Ion Batteries
2015
Yuan, Ding D. | Wang, Yan X. | Cao, Yu L. | Ai, Xin P. | Yang, Han X.
A series of O3-phase NaFeₓ(Ni₀.₅Mn₀.₅)₁–ₓO₂ (x = 0, 0.1, 0.2, 0.3, 0.4, and 1) samples with different Fe contents was prepared and investigated as high-capacity cathodic hosts of Na-ion batteries. The partial substitution of Ni and Mn with Fe in the O3-phase lattice can greatly improve the electrochemical performance and the structural stability. A NaFe₀.₂Mn₀.₄Ni₀.₄O₂ cathode with an optimized Fe content of x = 0.2 can deliver an initial reversible capacity of 131 mAh g–¹, a reversible capacity greater than 95% over 30 cycles, and a high rate capacity of 86 mAh g–¹ at 10 C in a voltage range of 2.0–4.0 V. The structural characterizations reveal that pristine NaMn₀.₅Ni₀.₅O₂ and Fe-substituted NaFe₀.₂Mn₀.₄Ni₀.₄O₂ lattices underwent different phase transformations from P3 to P3″ and from P3 to OP2 phases, respectively, at high voltage interval. The as-resulted OP2 phase by Fe substitution has smaller interslab distance (5.13 Å) than the P3″ phase (5.72 Å), which suppresses the co-insertion of the solvent molecules, the electrolyte anions, or both and therefore enhances the cycling stability in the high voltage charge. This finding suggests a new strategy for creating cycle-stable transition-metal oxide cathodes for high-performance Na-ion batteries.
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