Yang Yang,Honghao Deng,Liying Liu,Jiahong Pan,Ping Chen,Zhicong Shi
O3-type Cu/Fe/Mn-based layered oxides are regarded as promising cathode materials for sodium-ion batteries due to the abundance of elements in the Earth's crust and the imperative for large-scale energy storage. However, these materials still encounter some challenges, including low capacity and insufficient rate performance. In this study, Al-doped, cobalt-free, and nickel-free Na 0.9 Cu 0.18 Fe 0.3 Mn 0.52-x Al x O 2 (x = 0, 0.03, 0.05, 0.08) are successfully synthesized by using the solid-state method to introduce non-electrochemically active elements to stabilize the crystal structure and enhance the electrochemical performance. The impact of Al-doping is comprehensively analyzed by using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), galvanostatic intermittent titration technique (GITT), and electrochemical impedance spectroscopy (EIS). Al-doping effectively enhances the diffusion coefficient of Na + , reduces the Jahn-Teller effect caused by Mn 3+ and mitigates the transition from O3 to P3 phase. Finally, it stops the partial phase transitions from O3 to P3, which can be found in pristine oxide without Al-doping during charge-discharge cycling. Notably, the Na 0.9 Cu 0.18 Fe 0.3 Mn 0.47 Al 0.05 O 2 electrode exhibits a reversible capacity of 123.89 mAh g −1 at 0.1 C, a capacity retention rate of 91.1 % after 200 cycles at 1 C, and a discharge capacity of 66.36 mAh g −1 at a high rate of 5 C.
Zhe Xu,Haidi Yang,Xuesen Zhao,Runguo Zheng,Zhishuang Song,Zhiyuan Wang,Hongyu Sun,Yanguo Liu,Dan Wang
O3-NaNi1/3Fe1/3Mn1/3O2 has attracted much attention as a cathode for sodium-ion batteries, because of its low cost and high sodium-ion storage capacity. However, its slow Na+ diffusion kinetics and harmful P3–O3′ phase transition with severe bulk strain at high voltage leads to poor rate capability and fast capacity fading. Herein, we propose a multivariate doping strategy with Cu, Mg, and Ti ions to solve the above problems of the O3-NaNi1/3Fe1/3Mn1/3O2 cathode. The O3–Na(Ni1/3Fe1/3Mn1/3)0.9Cu0.03Mg0.02Ti0.05O2 (NFMCMT) cathode exhibits enlarged Na+ diffusion channels and a strengthened layered structure, which improves the Na+ diffusion kinetics, suppresses the harmful P3–O3′ phase transition at high voltages, and inhibits the intragranular fatigue cracks, leading to enhanced rate capability and cycling performance. As a result, the NFMCMT exhibits outstanding performance in the 2–4.1 V voltage window, delivers a discharge capacity of 151.2 mAh g–1 with the 81.5% capacity retention for 100 cycles at 0.1 C, and 83.1% capacity retention for 300 cycles at 5 C. Especially in the rate performance, the NFMCMT delivers a 115.6 mAh g–1 and 100.1 mAh g–1 discharge capacity even at 5 and 10 C. This work provides an effective multivariate doping strategy for development of high-performance layered oxide cathodes for sodium-ion batteries.
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