Rhombohedral Potassium–Zinc Hexacyanoferrate as a Cathode Material for Nonaqueous Potassium-Ion Batteries

Abstract

Rhombohedral potassium–zinc hexacyanoferrate K1.88Zn2.88[Fe­(CN)6]2(H2O)5 (KZnHCF) synthesized using a precipitation method is demonstrated as a high-voltage cathode material for potassium-ion batteries (PIBs), exhibiting an initial discharge capacity of 55.6 mAh g–1 with a discharge voltage of 3.9 V versus K/K+ and a capacity retention of ∼95% after 100 cycles in a nonaqueous electrolyte. All K ions are extracted from the structure upon the initial charge process. However, only 1.61 out of 1.88 K ions per formula unit are inserted back into the structure upon discharge, and it becomes the reversible ion of the second cycle onward. Despite the large ionic size of K, the material exhibits a lattice-volume change (∼3%) during a cycle, which is exceptionally small among the cathode materials for PIBs. The distinct feature of the material seems to come from the unique porous framework structure built by ZnN4 and FeC6 polyhedra linked via the CN bond and a Zn/Fe atomic ratio of 3/2, resulting in high structural stability and cycle performance.

TMDs beyond MoS2 for Electrochemical Energy Storage

“…Thus, this lower cost current collector can be used both as anode and cathode . Considering that copper prices are more volatile in the market than aluminum, this relevant aspect may represent a competitive aspect driving down costs in large scale applications …”

Recent advances and perspective in metal coordination materials-based electrode materials for potassium-ion batteries

“…On the other hand, Zn-based PBA could usually present a higher discharge voltage (not lower than 3.9 V) than that of K/K ? in a non-aqueous electrolyte [81,82]. Although Zn-based PBA shows two pairs of redox peaks, only the C-coordinated Fe is electrochemically active [81][82][83].…”

“…in a non-aqueous electrolyte [81,82]. Although Zn-based PBA shows two pairs of redox peaks, only the C-coordinated Fe is electrochemically active [81][82][83]. The detailed intercalation mechanism is not understood clearly for the two redox couples with only one redox center.…”

Post‐Lithium‐Ion Battery Era: Recent Advances in Rechargeable Potassium‐Ion Batteries

“…It displayed a super long‐term lifetime of over 8000 cycles at 200 mA g −1 [125] . Additionally, cube‐shaped K 1.88 Zn 2.88 [Fe(CN) 6 ] 2 ⋅ 5 H 2 O was also demonstrated as a high‐voltage (3.9 V vs. K/K + ) cathode material for PIBs [126] . The groups of Solanki [127] and Fu [128] also found that Prussian green (Fe III Fe III (CN) 6 ) had outstanding K + ‐storage capabilities as a cathode material for PIBs.…”