FeFe(CN)₆ Nanocubes as a Bipolar Electrode Material in Aqueous Symmetric Sodium‐Ion Batteries

Abstract

Bipolar materials, which work as both the cathode and anode materiali na queous sodium-ionb atteries, have advantages over aqueous electrolytes such as the low cost of sodium and high convenience of the material processing. However,t he availablem aterials are greatly limited. Herein, Prussian blue FeFe(CN) 6 nanocubesw ere successfully synthesized by using a modifiedc o-precipitation method. Owingt ot he well-separated redox reactions, fair cycling stability and rate capability of FeFe(CN) 6 ,i tc ould be developed as ab ipolar material in an aqueous sodium-ion battery.T he as-obtained full battery exhibits good cycling stabilitya nd rate capability.I tw as ablet o deliver ac apacity of 32 mA hg À1 at 20 C, 76 %o ft he capacity at 2C.A fter 200 cycles at 2C,9 7% of the initial capacity was maintained for this battery,which suggests good cycling stability.

Perovskite-related ReO3-type structures

“…Conversely, a counter example would be the iron-ruthenium PBA, (Fe 4 [Ru(CN) 6 ] 3 •18H 2 O),182 which was examined in part for its potential magnetic behavior but found to display no ordering above 1.8 K. This material, however, is interesting as it demonstrates the effect of electron localization when compared to its Prussian Blue parent and potassium intercalated sibling (K 1.2 Ru 3.6 [Ru(CN) 6 ] 3 ), as the ironruthenium compound has decreased electrical conductivity and blue shifted optical intervalence charge transfer (IVCT) transitions.Many PBA materials have also been explored for their potential applications in sodium ion batteries,189 but work in this area has been hampered by low capacity utilization and poor cyclability. In the case of Fe[Fe(CN) 6 ], the use of nanoparticles overcame these drawbacks, giving rise to a device with good kinetics, capacity and lifetime190,191 (we note that this strategy also worked for FeF 3 , as discussed earlier). There has also been work on both lithium192 and potassium193 batteries with Fe[Fe(CN) 6 ].Finally, we would like to mention a very recent report of the first examples of thiocyanates with the ReO 3 structure 194.…”

Hexacyanoferrate‐Type Prussian Blue Analogs: Principles and Advances Toward High‐Performance Sodium and Potassium Ion Batteries

“…Among the viable KIB anodes, graphite gives a higher full‐cell voltage (3.4‒3.5 V) [ 29,86 ] than K 2 TP (2.7‒3.3 V) [ 208 ] and super P (2.5 V). [ 120 ] As to the aqueous batteries for both AM ions, the voltage output is lower than that of nonaqueous batteries, lying in the range of 0.6‒1.7 V for different anodes such as NaTi 2 (PO 4 ) 3 , [ 123 ] active carbon, [ 20 ] FeHCFs, [ 225–227 ] and MnMn(CN) 6 . [ 13,16 ] The operation current density of the aqueous full cells can be higher than normally used in nonaqueous batteries, which can readily reach several A g ‒1 as a compensation as the low voltage and capacity.…”

Prussian Blue Analogs for Rechargeable Batteries

“…Hereby, the authors suppressed the process at high voltage. FeHCF was also used as bipolar material, which works as both the cathode and anode materials in a battery ( Zhang et al., 2017b ). The as-obtained full aqueous battery exhibited a capacity of 32 mAh g −1 at 20 C. Wang et al.…”