This study clarifies, for the first time, that misplacement of Cr³⁺ ions at the Na⁺ site plays a more important role in dictating the specific capacity and capacity retention over cycles of O3-NaCrO₂ cathodes than the Na–O bond length and the NaO₂ interlayer spacing do. It is shown that O3-NaCrO₂ crystals with a lower degree of misplacement of Cr³⁺ ions at Na sites and a longer Na–O bond length have higher specific capacity, better capacity retention, and smaller cell impedance. Furthermore, O3-NaCrO₂ crystals with a high degree of cation mixing at the Na plane exhibit the formation of some monoclinic O′3-NaCrO₂ crystals over 300 charge/discharge cycles between NaCrO₂ and Na_0.5CrO₂ formulas, whereas the rhombohedral structure of O3-NaCrO₂ crystals with a low degree of cation mixing at the Na plane is fully reversible. The effects of structural defects discovered in this study are interpreted based on the interference of Cr ions in Na transport on the Na plane and gradual migration of Cr ions to the Na plane during cycles. The insights established in this study will provide guidance in rational design and synthesis of NaCrO₂ cathode materials with high specific capacity and long-term cycle stability in the future.

中文翻译：

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通过结构缺陷控制增强NaCrO ₂的电化学性能

这项研究首次阐明，在Na ⁺位点上Cr ³⁺离子的错位在决定O3-NaCrO ₂阴极循环的比容量和容量保持率方面比Na-O键长和用NaO _2进行层间间距。结果表明，在Na位点具有较低的Cr ³⁺离子错位程度和较长的Na-O键长度的O3-NaCrO ₂晶体具有更高的比容量，更好的容量保持率和更小的电池阻抗。此外，在Na平面上具有高度阳离子混合的O3-NaCrO ₂晶体表现出一些单斜O'3-NaCrO ₂的形成。在NaCrO ₂和Na _0.5 CrO ₂分子式之间的300个充/放电循环中，这些晶体具有完全可逆性，而在Na平面上具有低阳离子混合度的O3-NaCrO ₂晶体的菱形结构是完全可逆的。本研究中发现的结构缺陷的影响是基于Cr离子在Na平面上的Na传输中的干扰以及在循环过程中Cr离子逐渐迁移到Na平面上来解释的。这项研究中建立的见解将为未来高比容量和长期循环稳定性的NaCrO ₂正极材料的合理设计和合成提供指导。