The role of potassium ions in iron hexacyanoferrate as a cathode material for hybrid ion batteries

Abstract

The synthesis of Na x K y Fe[Fe(CN) 6 ] through a simple co-precipitation method and the application of these nanoparticles in sodium-ion batteries are presented. K 1.90 Fe[Fe(CN) 6 ] with a cubic structure shows low volumetric change during electrochemical cycling. It is clarified by ex-situ X-ray diffraction and cyclic voltammetry curves that K + influences the intercalation sites of the neighboring Na +. More significantly, this hexacyanoferrate delivers a high capacity of 137.0 mAh g − 1 at a current density of 14 mA g − 1 and superior cyclability with 94% capacity retention after 120 cycles, showing great promise for sodium-ion battery applications.

Ultrafine Prussian Blue as a High‐Rate and Long‐Life Sodium‐Ion Battery Cathode

“…From the aforementioned results, it is concluded that the ultrafine particle size and the mesoporous structure of FePBA/16 result in the fast Na + diffusion kinetics, and the high crystallinity guarantees the structural stability during the electrochemical process, thus leading to its excellent sodium storage performance. Interestingly, the electrochemical kinetic enhancement has also been observed for FePBAs by the solution method with particle size below 100 nm, suggesting that a size may take effect on other PBAs with size less than 100 nm, which needs to be further investigated in the future …”

Prussian Blue Analogs for Rechargeable Batteries

“…Chen et al. ( Liao et al., 2016 ) synthesized Na x K y Fe[Fe(CN) 6 ] and argued that K + influences the insertion sites of the neighboring Na + . Chen et al.…”

Engineering Fast Ion Conduction and Selective Cation Channels for a High‐Rate and High‐Voltage Hybrid Aqueous Battery

“…Figure 2a reveals CV curves of K-FeHCF tested in different aqueous electrolytes. [13] Thefirst-cycle galvanostatic voltage profiles of K-FeHCF are illustrated in Figure 2b.T here are two flat charge/discharge plateaus for both electrolyte K( + 0.87/ + 0.86 and + 0.25/ + 0.21 V) and mixed-ion electrolyte (+ 0.90/ + 0.88 and + 0.26/ + 0.18 V), while only one plateau which is centered at around 0V and slightly slanted could be discovered for electrolyte Na. [7] As for the case in electrolyte Na, apair of splitting redox peaks at about 0V is observed.…”

“…This phenomenon results from the special feature of Na + during its insertion/extraction processes,since there are two different sites for the Na + ion due to the smaller volume compared to that of K + .H owever,w hen there is K + neighboring,t he extra site for Na + would be forbidden, therefore as plit of redox peaks disappears in the mixed-ion electrolyte. [13] Thefirst-cycle galvanostatic voltage profiles of K-FeHCF are illustrated in Figure 2b.T here are two flat charge/discharge plateaus for both electrolyte K( + 0.87/ + 0.86 and + 0.25/ + 0.21 V) and mixed-ion electrolyte (+ 0.90/ + 0.88 and + 0.26/ + 0.18 V), while only one plateau which is centered at around 0V and slightly slanted could be discovered for electrolyte Na. This is consistent well with the CV results.T he first-cycle discharge capacity can reach 125 mAh g À1 ,which is comparable to other excellent aqueous battery systems with potassium iron (II) hexacyanoferrate cathodes, [14] when using electrolyte K + Na and the corresponding initial charge-discharge efficiencycould reach up to 96.5 %.…”