Impact of Ti and Zn Dual-Substitution in P2 Type Na<sub>2/3</sub> Ni<sub>1/3</sub> Mn<sub>2/3</sub> O<sub>2</sub> on Ni-Mn and Na-Vacancy Ordering and Electrochemical Properties.
basic_science · Level V
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- Record sourced from PubMed, PMID 37058281.
- Also identified by DOI 10.1002/adma.202300714.
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Abstract
High-entropy layered oxide materials containing various metals that exhibit smooth voltage curves and excellent electrochemical performances have attracted attention in the development of positive electrode materials for sodium-ion batteries. However, a smooth voltage curve can be obtained by suppression of the Na<sup>+</sup> -vacancy ordering, and therefore, transition metal slabs do not need to be more multi-element than necessary. Here, the Na<sup>+</sup> -vacancy ordering is found to be disturbed by dual substitution of Ti<sup>IV</sup> for Mn<sup>IV</sup> and Zn<sup>II</sup> for Ni<sup>II</sup> in P2-Na<sub>2/3</sub> [Ni<sub>1/3</sub> Mn<sub>2/3</sub> ]O<sub>2</sub> . Dual-substituted Na<sub>2/3</sub> [Ni<sub>1/4</sub> Mn<sub>1/2</sub> Ti<sub>1/6</sub> Zn<sub>1/12</sub> ]O<sub>2</sub> demonstrates almost non-step voltage curves with a reversible capacity of 114 mAh g<sup>-1</sup> and less structural changes with a high crystalline structure maintained during charging and discharging. Synchrotron X-ray, neutron, and electron diffraction measurements reveal that dual-substitution with Ti<sup>IV</sup> and Zn<sup>II</sup> uniquely promotes in-plane Ni<sup>II</sup> -Mn<sup>IV</sup> ordering, which is quite different from the disordered mixing in conventional multiple metal substitution.