Na-ion conduction, and correlations between Na-ion conduction pathways and crystal structure have been investigated as a function of temperature in the layered battery material Na2Ni2TeO6 by impedance spectroscopy and neutron diffraction, respectively. The impedance data reveal an ionic conductivity 2x10-4 S/m at 323 K which strongly enhances with increasing temperature and attains a high value of ~ 0.03 S/m at 423 K. The temperature dependent conductivity data show an Arrhenius type behavior with average activation energy (Ea) of ~ 0.58(3) eV for T > 383 K. By employing soft-bond valence sum analysis of the neutron diffraction patterns we experimentally demonstrate the site-specific Na-ion conductions, through visualization of microscopic sodium-ion conduction pathways, and verify the recent theoretical results of Molecular dynamic simulation. Our results reveal two-dimensional Na-ion conduction pathways that are confined within the ab planes of Na layers. Crystal structural study indicates that the layered structure involving Na ion layers is responsible for high ionic conductivity, and the local crystallographic environment of Na ion sites is responsible for site-specific conductivity. Our study further reveals that up to 500 K, the ionic conduction is governed by the Na ions located at the Na1 and Na2 sites, whereas, all the Na ions located at the three Na-sites contribute to the conduction process above 500 K. Our neutron diffraction study also establishes that the crystal structure of Na2Ni2TeO6 is stable at least up to 725 K (the highest measured temperature), however, with an anisotropic thermal expansion (c/a ~ 3).
High-Voltage Honeycomb Layered Oxide Positive Electrodes for Rechargeable Sodium Batteries
丰富的自然资源、令人印象深刻的化学特性和经济可行性重新点燃了可充电钠（Na）电池的吸引力，使其成为满足不断增长的能源需求、环境可持续性和能源独立性的实用解决方案。然而，可行的正极材料的稀缺仍然是该技术实现的巨大障碍。在本文中，我们探索蜂窝层状氧化物采用的组合物Na $_2$ Ni $_{2-x}$ Co $_x$ TeO $_6$（$x = 0, 0.25$和$0.50$）作为可行的正极（阴极）材料的可充电钠电池在室温和高温下使用离子液体。通过标准的恒电流评估和分析，我们证明在Na $_2$ Ni $_2$ TeO $_6$中用钴取代镍导致放电电压增加到接近$4$ V（相对于Na $^+$ / Na）对于Na $_2$ Ni $_{2-x}$ Co $_x$ TeO $_6$族蜂窝状层状氧化物材料，其超过了促进Na离子脱离的大多数层状氧化物正极材料所获得的平均电压。我们还验证了在高温下操作期间Na $_2$ Ni $_{2-x}$ Co $_x$ TeO $_6$蜂窝状层状氧化物内的增加的动力学，这导致可再充电Na电池的可逆容量增加。这项研究支持的同源过渡金属原子掺杂的蜂窝结构的Na $_2$ Ni $_2$ TeO $_6$除了作为一个明智的路线，以提高类似的层状氧化物的电化学性能的高温操作。
M\textbf{\textit{O}}enes family materials with Dirac nodal loop, strong light-harvesting ability, long carrier lifetime and conduction-band valley spin splitting
