New insights into designing high-rate performance cathode materials for sodium ion batteries by enlarging the slab-spacing of the Na-ion diffusion layer

• Published in: Journal of materials chemistry. A, Materials for energy and sustainability Materials for energy and sustainability, 2016-01, Vol.4 (9), p.3453-3461
• Main Authors: Li, Zheng-Yao, Gao, Rui, Zhang, Jicheng, Zhang, Xiuling, Hu, Zhongbo, Liu, Xiangfeng
• Format: Article
• Language: English
• Subjects: Cathodes; Density; Diffusion layers; Electric batteries; Expansion; Nickel; Sodium; Stability
• ISSN: 2050-7488; 2050-7496
• DOI: 10.1039/c5ta10589g

Recently, the design and synthesis of high performance cathode materials for sodium ion batteries have attracted great interest. In this study, we propose a novel strategy to design high-rate performance cathode materials for sodium ion batteries through enlarging the d -spacing of the Na-ion diffusion layer. More importantly, some new insights into the expansion mechanism of the interplanar spacing for Na 0.67 Mn 0.8 Ni 0.1 Mg 0.1 O 2 induced by Ni and Mg co-doping and the resulting high-rate capability have been presented for the first time. We find that Mg and Ni co-doping leads to the shortening of the TM-O (TM = transition metal) bond lengths and the shrinkage of the TMO 6 octahedrons, which might be largely responsible for the expansion of the interplanar spacing of the Na-ion diffusion layer. In comparison with Na 0.67 Mn 0.8 Ni 0.2 O 2 and Na 0.67 Mn 0.8 Mg 0.2 O 2 , Mg and Ni co-doped Na 0.67 Mn 0.8 Ni 0.1 Mg 0.1 O 2 has a higher Na-ion diffusion coefficient and can deliver around 160, 145, 133 and 124 mA h g −1 at 24, 48, 120 and 240 mA g −1 , respectively. In particular, at the high current densities of 480 (2C), 1200 (5C) and 1920 mA g −1 (8C), MMN can still offer reversible capacities of 110, 66 and 37 mA h g −1 , respectively. In addition, the cycling stability has also been enhanced via Mg and Ni co-doping at the same time, which means that Mg and Ni co-doping also has a positive effect on the stability of the layered structure. We propose new insights into designing high-rate performance cathode materials for sodium-ion batteries through enlarging the interplanar spacing.