Adv. Funct. Mater. 2019, 29, 1902392 In the initially published version of this article, the authors inadvertently omitted mention and citations to related work. The following text is included as part of the Introduction: In this work, we investigated and contrasted alkali ion (Li, Na, and K) intercalation properties in KxVPO4F (x ∼ 0) by a combined experimental and computational study. Related work has been done by Fedotov et al. and Nikitina et al. Fedotov et al. demonstrated that depotassiated KxVPO4F (x ∼ 0.15) can intercalate Li ions reversibly, and found that Li ions occupy under-coordinated sites, compared to K sites. Later, alkali ion diffusivity in KxVPO4F (x ∼ 0.5) and RbxVPO4F (x ∼ 0.5) was investigated and compared by Nikitina et al. and Fedotov et al., respectively. These authors found that K migration along the c-axis has a low barrier (≈200 meV) and the Li ion diffusivity is lower than for Na and K ions in the KxVPO4F (x ∼ 0.5) structure despite its smaller ionic size. There are some differences between the Fedotov et al.'s compound and ours in the voltage profile, which is attributable to different V-oxidation and O/F between the two as previously discussed. In addition, we removed all the K from KxVPO4F in our work in order not to have interaction between the inserted alkali (Li and Na) and the remaining K. The authors apologize for any inconvenience or misunderstanding that this error may have caused.

This work compares the intercalation of K, Na, and Li in KxVPO4F (x ∼ 0). The KxVPO4F (x ∼ 0) cathode delivers reversible capacities of ≈90–100 mAh g−1 in K, Na, and Li cells, at an average voltage of ≈4.33 V for K, ≈3.98 V for Na, and ≈3.96 V for Li. This is so far the highest average voltage known for a K-intercalation cathode. The lower voltage of Li insertion compared to Na is attributable to undercoordinated Li ions in the KxVPO4F (x ∼ 0) framework. While the material shows high rate capability for all the alkali ions, Li migration in KxVPO4F (x ∼ 0) is more difficult than with Na and K. This work suggests that a large cavity is not always good for insertion of alkali ions and cathode materials need to be suitably tailored to each intercalating ion species.