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<p>The series of O3-type high-entropy layered oxides Na<sub>x</sub>Ti<sub>0.2</sub>Mn<sub>0.2</sub>Fe<sub>0.2</sub>Co<sub>0.2</sub>Ni<sub>0.2</sub>O<sub>2</sub> were prepared by the mechanochemically assisted solid-state synthesis and studied as cathode materials for sodium-ion batteries. The effect of sodium excess (0, 10, and 20%) on electrochemical performance was investigated. It has shown that the addition of 10 or 20% excess sodium leads to a deterioration in rate performance despite a slight increase in specific capacity at low cycling rates (below 2C). The increase in sodium content in Na<sub>x</sub>Ti<sub>0.2</sub>Mn<sub>0.2</sub>Fe<sub>0.2</sub>Co<sub>0.2</sub>Ni<sub>0.2</sub>O<sub>2</sub> results in a negative effect on the sodium ion diffusion coefficient as it was confirmed by <sup>23</sup>Na nuclear magnetic resonance and galvanostatic intermittent titration technique (GITT). The GITT and electrochemical impedance spectroscopy results show that NaTi<sub>0.2</sub>Mn<sub>0.2</sub>Fe<sub>0.2</sub>Co<sub>0.2</sub>Ni<sub>0.2</sub>O<sub>2</sub> without sodium excess exhibits weaker changes in Na<sup>+</sup> diffusion coefficient and charge transfer resistance during charge/discharge process, demonstrating improved kinetics during O3-P3 phase transition, while the samples with sodium excess showed a greater change in the Na<sup>+</sup> diffusion coefficient and charge transfer resistance. Therefore, NaTi<sub>0.2</sub>Mn<sub>0.2</sub>Fe<sub>0.2</sub>Co<sub>0.2</sub>Ni<sub>0.2</sub>O<sub>2</sub> demonstrates superior electrochemical performance at higher rates (75, 60, and 33 mAh·g<sup>−1</sup> at 5C, 10C, and 20C, respectively).</p> Graphical Abstract <p></p>

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The effect of sodium content on sodium diffusion in NaxTi0.2Mn0.2Fe0.2Co0.2Ni0.2O2 high-entropy layered oxide

  • 期刊论文

  • 发表日期：

    2025年1月9日

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  • Dmitry Z. Tsydypylov,
  • Arseny B. Slobodyuk,
  • Maria A. Kirsanova,
  • Nina V. Kosova

摘要

The series of O3-type high-entropy layered oxides NaxTi0.2Mn0.2Fe0.2Co0.2Ni0.2O2 were prepared by the mechanochemically assisted solid-state synthesis and studied as cathode materials for sodium-ion batteries. The effect of sodium excess (0, 10, and 20%) on electrochemical performance was investigated. It has shown that the addition of 10 or 20% excess sodium leads to a deterioration in rate performance despite a slight increase in specific capacity at low cycling rates (below 2C). The increase in sodium content in NaxTi0.2Mn0.2Fe0.2Co0.2Ni0.2O2 results in a negative effect on the sodium ion diffusion coefficient as it was confirmed by 23Na nuclear magnetic resonance and galvanostatic intermittent titration technique (GITT). The GITT and electrochemical impedance spectroscopy results show that NaTi0.2Mn0.2Fe0.2Co0.2Ni0.2O2 without sodium excess exhibits weaker changes in Na+ diffusion coefficient and charge transfer resistance during charge/discharge process, demonstrating improved kinetics during O3-P3 phase transition, while the samples with sodium excess showed a greater change in the Na+ diffusion coefficient and charge transfer resistance. Therefore, NaTi0.2Mn0.2Fe0.2Co0.2Ni0.2O2 demonstrates superior electrochemical performance at higher rates (75, 60, and 33 mAh·g−1 at 5C, 10C, and 20C, respectively).

Graphical Abstract