Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
College of Material Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing 100190, China.
ACS Appl Mater Interfaces. 2023 Mar 8;15(9):11756-11764. doi: 10.1021/acsami.2c21608. Epub 2023 Feb 21.
Anionic redox is an effective way to increase the capacity of the cathode materials. NaMnO [Na[Mn□]O, □ for the transition metal (TM) vacancies] with native and ordered TM vacancies can conduct a reversible oxygen redox and be a promising high-energy cathode material for sodium-ion batteries (SIBs). However, its phase transition at low potentials (∼1.5 V vs Na/Na) induces potential decays. Herein, magnesium (Mg) is doped on the TM vacancies to form a disordered Mn/Mg/□ arrangement in the TM layer. The Mg substitution suppresses the oxygen oxidation at ∼4.2 V by reducing the number of the Na-O-□ configurations. Meanwhile, this flexible disordering structure inhibits the generation of the dissolvable Mn ions and mitigates the phase transition at ∼1.6 V. Therefore, the Mg doping improves the structural stability and its cycling performance in 1.5-4.5 V. The disordering arrangement endows NaMnMg□O with a higher Na diffusivity and improved rate performance. Our study reveals that oxygen oxidation is highly dependent on the ordering/disordering arrangements in the cathode materials. This work provides insights into the balance of anionic and cationic redox for enhancing the structural stability and electrochemical performance in the SIBs.
阴离子氧化还原是增加阴极材料容量的有效方法。具有本征和有序过渡金属（TM）空位的 NaMnO [Na[Mn□]O，□代表 TM 空位]可以进行可逆的氧氧化还原反应，是一种很有前途的钠离子电池（SIBs）高能阴极材料。然而，其在低电位（约 1.5 V vs Na/Na）下的相变会导致电位衰减。在此，镁（Mg）被掺杂到 TM 空位中，在 TM 层中形成无序的 Mn/Mg/□排列。Mg 取代通过减少 Na-O-□构型的数量来抑制约 4.2 V 处的氧氧化。同时，这种灵活的无序结构抑制了可溶解 Mn 离子的生成，并减轻了约 1.6 V 处的相变。因此，Mg 掺杂提高了其在 1.5-4.5 V 下的结构稳定性和循环性能。无序排列使 NaMnMg□O 具有更高的 Na 扩散率和改进的倍率性能。我们的研究表明，氧氧化高度依赖于阴极材料中的有序/无序排列。这项工作为平衡阴离子和阳离子氧化还原以提高 SIBs 的结构稳定性和电化学性能提供了新的思路。
