Investigation of Alkali‐Ion (Li, Na, and K) Intercalation in KxVPO4F (x ∼ 0) Cathode

• Published in: Advanced functional materials Vol. 29; no. 34
• Main Authors: Kim, Haegyeom, Ishado, Yuji, Tian, Yaosen, Ceder, Gerbrand
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc 01.08.2019
• Subjects: batteries; Cathodes; Electric potential; Electrode materials; Insertion; Intercalation; Lithium; Materials science; potassium; Sodium; Voltage
• ISSN: 1616-301X; 1616-3028
• DOI: 10.1002/adfm.201902392

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. This work investigates and compares the K, Na, and Li intercalation properties of the KxVPO4F (x ∼ 0) cathode. It demonstrates that large alkali‐ion migration channels are not always good for fast ion diffusion and thus cathode materials need to be suitably tailored to each intercalating ion species.