Sodium ion batteries offer an inexpensive alternative to lithium ion batteries, particularly for large-scale applications such as grid storage that do not require fast charging rates and high power output. Moreover, the use of polyanionic structures as cathode materials afford incredibly high structural stability relative to layered transition metal oxides that can undergo a structural collapse upon full removal of the charge carrying ions. Sodium iron fluorophosphate, Na₂FePO₄F, has demonstrated its viability as a potential cathode material for sodium ion batteries, having a robust framework even after multiple charge-discharge cycles. Although solid-state NMR has traditionally been an excellent method for the determination of local structure and dynamic properties of cathode materials during the electrochemical cycling process, reliable assignment of the ²³Na chemical shifts resulting from the paramagnetic hyperfine interaction can be difficult when using only empirical rules. Here we present the use of density functional theory calculations to assign the experimentally observed NMR shifts to the crystallographic sites in Na₂FePO₄F, where it is found that the results do not agree with the previously reported assignment based upon simple geometry arguments. Furthermore, we report the justification of the proposed desodiation mechanism in Na₂FePO₄F on the basis of theoretical arguments, in good agreement with experimental NMR results reported previously.

钠离子电池是锂离子电池的廉价替代品，特别是对于不需要快速充电速率和高功率输出的大规模应用（例如电网存储）。而且，相对于层状过渡金属氧化物而言，使用聚阴离子结构作为阴极材料提供了极高的结构稳定性，该层状过渡金属氧化物在完全去除载流子离子时会发生结构塌陷。氟磷酸钠铁，Na ₂ FePO ₄F已经证明了其作为钠离子电池潜在的阴极材料的可行性，即使在多次充放电循环之后，也具有坚固的骨架。尽管传统上固态NMR是测定电化学循环过程中阴极材料的局部结构和动力学性质的出色方法，但仅使用经验法则，很难确定顺磁超精细相互作用导致的²³ Na化学位移的可靠分配规则。在这里，我们介绍使用密度泛函理论计算将实验观察到的NMR位移分配给Na ₂ FePO _4中的晶体学位点F，根据简单的几何参数发现结果与先前报告的分配不一致。此外，我们在理论观点的基础上报告了在Na ₂ FePO ₄ F中提出的脱氮机理的合理性，与先前报道的实验NMR结果非常吻合。