Wang Yuesheng, Xiao Ruijuan, Hu Yong-Sheng, Avdeev Maxim, Chen Liquan
Key Laboratory for Renewable Energy, Beijing Key Laboratory for New Energy Materials and Devices, Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
Bragg Institute, Australian Nuclear Science and Technology Organisation, Locked Bag 2001, Kirrawee DC NSW 2232, Australia.
Nat Commun. 2015 Apr 24;6:6954. doi: 10.1038/ncomms7954.
Most P2-type layered oxides exhibit Na(+)/vacancy-ordered superstructures because of strong Na(+)-Na(+) interaction in the alkali metal layer and charge ordering in the transition metal layer. These superstructures evidenced by voltage plateaus in the electrochemical curves limit the Na(+) ion transport kinetics and cycle performance in rechargeable batteries. Here we show that such Na(+)/vacancy ordering can be avoided by choosing the transition metal ions with similar ionic radii and different redox potentials, for example, Cr(3+) and Ti(4+). The designed P2-Na(0.6)[Cr(0.6)Ti(0.4)]O2 is completely Na(+)/vacancy-disordered at any sodium content and displays excellent rate capability and long cycle life. A symmetric sodium-ion battery using the same P2-Na(0.6)[Cr(0.6)Ti(0.4)]O2 electrode delivers 75% of the initial capacity at 12C rate. Our contribution demonstrates that the approach of preventing Na(+)/vacancy ordering by breaking charge ordering in the transition metal layer opens a simple way to design disordered electrode materials with high power density and long cycle life.
大多数P2型层状氧化物由于碱金属层中强烈的Na⁺-Na⁺相互作用和过渡金属层中的电荷有序化而呈现出Na⁺/空位有序超结构。电化学曲线中的电压平台所证明的这些超结构限制了可充电电池中Na⁺离子的传输动力学和循环性能。在此我们表明，通过选择具有相似离子半径和不同氧化还原电位的过渡金属离子，例如Cr³⁺和Ti⁴⁺，可以避免这种Na⁺/空位有序化。设计的P2-Na₀.₆[Cr₀.₆Ti₀.₄]O₂在任何钠含量下都是完全Na⁺/空位无序的，并表现出优异的倍率性能和长循环寿命。使用相同的P2-Na₀.₆[Cr₀.₆Ti₀.₄]O₂电极的对称钠离子电池在12C倍率下可提供初始容量的75%。我们的研究表明，通过打破过渡金属层中的电荷有序化来防止Na⁺/空位有序化的方法为设计具有高功率密度和长循环寿命的无序电极材料开辟了一条简单途径。
