The electrochemical community around the world is focusing heavily on sodium-ion batteries R&D due to the huge abundance of sodium and need for large scale deployment of safe and inexpensive batteries for the electrical grid energy storage. We report on the characterization of model parameters such as ionic diffusivity and interfacial kinetics, for a potential sodium-ion battery cathode material, Na_2-xFe₃(PO₄)₃, using experimental and computational investigations. The Na_2-xFe₃(PO₄)₃ structure is characterized by two distinct one-dimensional (1-D) Na diffusion channels. Density Functional Theory (DFT) calculation reveals that Na is first fully removed from one of the channels followed by the subsequent removal of Na from the second channel. The experimental investigation reveals that, in the beginning of Na removal at 0 ≤ x ≤ 0.5; the sodium ion diffusivity is of the order of ~10⁻¹¹ cm²s⁻¹ and then slightly decreases. This is further confirmed by comparing the calculated sodium diffusion barriers along the individual 1-D channels as well as between the channels. Nevertheless, the exchange current density slowly increases up to x = 1.0 and remains quite constant thereafter. The magnitude of exchange current density is very low suggesting that the interfacial kinetics are the rate limiting factor. The obtained results suggest that Na_2-xFe₃(PO₄)₃ could achieve better rate performance with long cycling stability through engineering of the particle morphology and microstructure.

由于钠的丰度很高，并且需要大规模部署安全廉价的电池来存储电网能量，因此世界各地的电化学界都将重点放在钠离子电池的研发上。我们使用实验和计算研究报告了潜在的钠离子电池正极材料Na _2-x Fe ₃（PO ₄）₃的模型参数（如离子扩散率和界面动力学）的表征。Na _2-x Fe ₃（PO ₄）₃该结构的特征在于两个不同的一维（1-D）Na扩散通道。密度泛函理论（DFT）计算表明，首先从一个通道中完全去除了Na，然后从第二个通道中去除了Na。实验研究表明，从0≤x≤0.5的Na去除开始。钠离子扩散率约为〜10 ^-11 cm ² s ^-1然后略有下降。通过比较沿各个1-D通道以及通道之间的钠扩散势垒，可以进一步确认这一点。但是，交换电流密度缓慢增加到x = 1.0，此后保持相当恒定。交换电流密度的幅度非常低，表明界面动力学是速率限制因素。所得结果表明，Na _2-x Fe ₃（PO ₄）₃可通过对粒子的形态和微观结构进行工程设计而获得更好的速率性能，并具有较长的循环稳定性。