Ramasamy Hari Vignesh, Kaliyappan Karthikeyan, Thangavel Ranjith, Seong Won Mo, Kang Kisuk, Chen Zhongwei, Lee Yun-Sung
School of Chemical Engineering, Chonnam National University , Gwang-ju 500-757, Republic of Korea.
Department of Chemical Engineering, University of Waterloo , Waterloo, Ontario N2L 3G1, Canada.
J Phys Chem Lett. 2017 Oct 19;8(20):5021-5030. doi: 10.1021/acs.jpclett.7b02012. Epub 2017 Oct 2.
Despite their high specific capacity, sodium layered oxides suffer from severe capacity fading when cycled at higher voltages. This key issue must be addressed in order to develop high-performance cathodes for sodium ion batteries (SIBs). Herein, we present a comprehensive study on the influence of Al doping of Mn sites on the structural and electrochemical properties of a P2-NaMnAlCoO (x = 0, 0.02, or 0.05) cathode for SIBs. Detailed structural, morphological, and electrochemical investigations were carried out using X-ray diffraction, cyclic voltammetry, and galvanostatic charge-discharge measurements, and some new insights are proposed. Rietveld refinement confirmed that Al doping caused TMO octahedra (TM = transition metal) shrinkage, resulting in wider interlayer spacing. After optimizing the aluminum concentration, the cathode exhibited remarkable electrochemical performance, with better stability and improved rate performance. Electrochemical impedance spectroscopy (EIS) measurements were performed at various states of charge to probe the surface and bulk effects of Al doping. The material presented here exhibits exceptional stability over 100 cycles within a 1.5-4.3 V window and outperforms several other Mn-Co-based cathodes for SIBs. This study presents a facile method for designing structurally stable cathodes for SIBs.
尽管钠层状氧化物具有较高的比容量，但在较高电压下循环时会出现严重的容量衰减。为了开发用于钠离子电池（SIB）的高性能阴极，必须解决这一关键问题。在此，我们对P2-NaMnAlCoO（x = 0、0.02或0.05）型SIB阴极中Mn位点的Al掺杂对其结构和电化学性能的影响进行了全面研究。使用X射线衍射、循环伏安法和恒电流充放电测量进行了详细的结构、形态和电化学研究，并提出了一些新的见解。Rietveld精修证实，Al掺杂导致过渡金属氧化物（TM = 过渡金属）八面体收缩，从而使层间距变宽。优化铝浓度后，阴极表现出卓越的电化学性能，具有更好的稳定性和更高的倍率性能。在不同充电状态下进行了电化学阻抗谱（EIS）测量，以探究Al掺杂的表面和体相效应。本文介绍的材料在1.5 - 4.3 V窗口内经过100次循环表现出优异的稳定性，并且优于其他几种用于SIB的Mn-Co基阴极。本研究提出了一种设计用于SIB的结构稳定阴极的简便方法。
