Low‐Cost K₄Fe(CN)₆ as a High‐Voltage Cathode for Potassium‐Ion Batteries

Abstract

Potassium-ion batteries (KIBs) are of interest for large-scale electrical energy storage, owing to the abundance of K resources and potential high energy density. Low-cost cathodes with high performance are crucial for KIBs. Herein, K Fe(CN) is shown to be a low-cost and high-voltage cathode for KIBs. It can deliver a high voltage of approximately 3.6 V and a discharge capacity of 65.5 mAh g with a lifespan of 400 cycles of discharge and charge. This is attributed to the strong σ bonds between C atoms and Fe and to the reduced particle size and good contact with conductive carbon brought about by ball milling, which benefit both the K ion and the electronic conduction. The [Fe(CN) ] redox couple is found to be responsible for charge compensation upon reversible extraction/insertion of K from/into K Fe(CN) . The high voltage and stability of K Fe(CN) will make it a promising low-cost cathode for KIBs and encourage more investigations into high-performance cathode materials.

Carbon foam with microporous structure for high performance symmetric potassium dual-ion capacitor

“…Meanwhile, potassium-ion storage systems, including potassium-ion batteries (PIBs) and potassium-ion capacitors (PICs), are also attracting widespread attention for the high natural abundance of potassium resources [35][36][37][38][39] . PIBs can provide a high energy density comparable with LIBs because that the standard electrode potential of K ( −2.93 V vs. SHE) is close to that of Li ( −3.04 V vs. SHE), which are considered to be one of the most promising alternatives [40][41][42] .…”

A fluoroxalate cathode material for potassium-ion batteries with ultra-long cyclability

“…As the size of K + (1.38 Å) is much larger than Na + (1.02 Å) and Li + (0.76 Å) 25 , large migration channels and stable crystal structures are essential for K ion migration, which raises a great challenge to develop suitable cathodes. Among the cathode materials reported for KIBs , Prussian blue analogs (PBAs) have received most intensive studies with good capacity and favorable cycling stability because of their 3D open framework structures 14,[31][32][33][34][35][48][49][50] . For instance, Goodenough et al reported a cyanoperovskite K x MnFe(CN) 6 (0 ≤ x ≤ 2) cathode for KIBs, delivering a stable discharge capacity of~100 mAh g −1 and a capacity retention of 91% over 100 cycles 33 .…”

Next-Generation Cathode Materials for Non-aqueous Potassium-Ion Batteries

“…In addition, the upper cutoff voltage allowed for most K-layered oxides is limited due to the structural instability and the concomitant capacity loss at deep charge [5,[23][24][25]27]. For example, when depotassiating K x MnO 2 and K y CrO 2 to x < 0.2 and y < 0.4, respectively, the crystallinity of electrodes is significantly reduced [5,27] The specific capacity of K-PBAs is slightly lower than that of Na-PBAs because of the heavier K + ions; nevertheless, their higher voltages result in competitive specific energies ( Figure 3b) [8][9][10][33][34][35][36][37][38][39]. There are two known factors that contribute to the voltage difference: (1) the lower anode potential for K + /K than for Na + /Na, and (2) according to density functional theory [40], the interaction between alkali ions and the metal-organic framework strengthens with alkali size, which stabilizes the discharged products and results in an increasing intercalation potential from Li + to Na + (Figure 3e) [10].…”