In this work, the P2-type layered material Na_2/3[Ni_1/3Ti_2/3]O₂ was studied as a promising bi-functional electrode material for sodium-ion batteries. To assess the electrochemical performance of this material, we investigated the diffusion mechanism as well as ionic and electronic conductivity with a combination of experimental and computational techniques. The quasi-elastic neutron scattering (QENS) experiments and first-principles molecular dynamics (FPMD) simulations were performed to identify the diffusion mechanism. The QENS data showed that Na ion diffusion can be well described by the Singwi–Sjölander jump diffusion model, where the obtained mean jump length matched the distances between the neighboring edge-share and face-share Na sites. FPMD predicted diffusivity values similar to those from QENS. The computed composition dependence of ionic and electronic conductivity of Na_x[Ni_1/3Ti_2/3]O₂ suggested that electronic conductivity changes significantly when x deviates from 2/3 as the redox couple of Ni and Ti is activated, while the change of ionic conductivity with x is relatively small.

中文翻译：

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P2-Nax [Ni1 / 3Ti2 / 3] O2中的钠离子动力学：准弹性中子散射与第一性原理分子动力学的组合

在这项工作中，P2型层状材料Na _2/3 [Ni _1/3 Ti _2/3 ] O ₂作为一种有前景的用于钠离子电池的双功能电极材料，已被研究。为了评估这种材料的电化学性能，我们结合了实验和计算技术，研究了扩散机理以及离子和电子电导率。进行了准弹性中子散射（QENS）实验和第一性原理分子动力学（FPMD）模拟，以确定扩散机理。QENS数据表明，Singwi–Sjölander跃迁扩散模型可以很好地描述Na离子的扩散，在该模型中，获得的平均跃迁长度与相邻的边缘共享Na点和面部共享Na位点之间的距离相匹配。FPMD预测的扩散率值与QENS相似。Na _x的离子和电子电导率的计算组成依赖性[Ni _1/3 Ti _2/3 ] O ₂提示，当x和2/3偏离时，由于激活Ni和Ti的氧化还原对，电子电导率会发生显着变化，而离子电导率随x的变化相对较小。