High‐Efficiency Na‐Storage Performance of a Nickel‐Based Ferricyanide Cathode in High‐Concentration Electrolytes for Aqueous Sodium‐Ion Batteries

Abstract

Nickel‐based ferricyanides have attracted much attention as cathode materials for aqueous sodium‐ion batteries, owing to their room‐temperature synthesis and open structural framework. However, factors affecting their electrochemical performance are still not clear. Herein, the effect of electrolyte concentrations on electrochemical properties of the ferricyanide cathode has been investigated by combining cyclic voltammetry, charge/discharge tests, and electrochemical impedance microscopy. It is found that high‐concentration electrolyte can not only raise the working potential, owing to increased activity of Na+ ions, but also increase the initial coulombic efficiency due to suppression of side reactions. The optimized electrolyte enables it cycling with an initial coulombic efficiency of 99.3 %, excellent high‐rate capability (68.1 mAh g−1 at 0.5 C and 63.1 mAh g−1 at 10 C), and outstanding cycling stability (96.3 % capacity retention after 1000 cycles at 10 C). The finding indicates that designing high‐concentration electrolytes is an effective strategy to improve electrochemical performance of ferricyanide cathodes for aqueous sodium‐ion batteries.

Nickel‐Substituted Copper Hexacyanoferrate as a Superior Cathode for Aqueous Sodium‐Ion Batteries

“…The high capacity retention of more than 90 % at 10 C relative to the capacity at 0.5 C suggests outstanding high‐rate capability. This is attributed to the unique open‐framework structure of Prussian‐blue analogues, which allows ultrafast charge‐transfer and ionic‐diffusivity ,. In addition, it renders excellent cycling performance (Figure b), with a capacity retention of 96 % after 1000 cycles at 10 C. Table compares the electrochemical performance of the cathode materials presented in this work and previous reports.…”

“…As reported, the electrochemical stability window of concentrated NaClO 4 electrolyte (17 mol Kg −1 ) can be widen to 2.8 V, which enables aqueous Na 2 MnFe(CN) 6 /NaTi 2 (PO 4 ) 3 battery working reversibly . The NaClO 4 electrolyte with concentrations of more than 6 M can achieve high‐efficiency Na‐storage performance of nickel‐based hexacyanoferrates . However, electrochemical properties of Ni‐substituted copper hexacyanoferrates in high‐concentration electrolytes are lack of being investigated.…”

Carbon‐Coated Na2.2V1.2Ti0.8(PO4)3 Cathode with Excellent Cycling Performance for Aqueous Sodium‐Ion Batteries

“…Recently, it was reported that 35 M NaFSI‐based aqueous electrolyte showed a wide electrochemical window up to 2.6 V. 6 M NaClO 4 aqueous electrolyte enabled NaNi [Fe(CN) 6 ] exhibiting unexpectedly high initial Coulombic efficiencies of 99.3 % and excellent cycling stability with 96.3 % retention after 1000 cycles . Therefore, designing Ti substitution and high‐concentration electrolyte would be an effective strategy to reach excellent electrochemical performance of Na 3–x V 2–x Ti x (PO 4 ) 3 cathode for aqueous SIBs.…”

Recent research progresses in ether‐ and ester‐based electrolytes for sodium‐ion batteries

“…Electrolytes in SIBs can be generally classified into five common types: organic electrolytes, ionic liquids (ILs), aqueous electrolytes, solid polymer electrolytes, and inorganic solid electrolytes . Among these electrolytes, organic electrolytes, especially those based on esters and ethers, are the most commonly used electrolytes in SIBs, due to their merits of relatively high ionic conductivity as well as superior wettability toward both the porous separators and the electrodes.…”