A concentrated electrolyte for zinc hexacyanoferrate electrodes in aqueous rechargeable zinc-ion batteries

Abstract

Abstract. In this study, a concentrated electrolyte was applied in an aqueous rechargeable zinc-ion battery system with a zinc hexacyanoferrate (ZnHCF) electrode to improve the electrochemical performance by changing the hydration number of the zinc ions. To optimize the active material, ZnHCF was synthesized using aqueous solutions of zinc nitrate with three different concentrations. The synthesized materials exhibited some differences in structure, crystallinity, and particle size, as observed by X-ray diffraction and scanning electron microscopy. Subsequently, these well-structured materials were applied in electrochemical tests. A more than two-fold improvement in the charge/discharge capacities was observed when the concentrated electrolyte was used instead of the dilute electrolyte. Additionally, the cycling performance observed in the concentrated electrolyte was superior to that in the dilute electrolyte. This improvement in the electrochemical performance may result from a decrease in the hydration number of the zinc ions in the concentrated electrolyte.

Recent Progress in the Electrolytes of Aqueous Zinc‐Ion Batteries

“…At the earlier stage of developing neutral or mild acidic electrolytes, the aqueous Zn(NO 3 ) 2 solution was introduced in the aqueous Zn/CuHCF battery . The copper hexacyanoferrate (CuHCF) is a Prussian Blue Analog (PBA)‐based cathode material with an open framework structure.…”

“…[29] At the earlier stage of developing neutralo rm ild acidic electrolytes,t he aqueous Zn(NO 3 ) 2 solution was introduced in the aqueous Zn/CuHCF battery. [30] The copperh exacyanoferrate (CuHCF)i saPrussian Blue Analog (PBA)-based cathode material with an open framework structure. Owing to its unique crystal structure, the reversible Zn 2 + insertion/extraction is observed in the typical cubic CuHCF cathode.…”

Issues and rational design of aqueous electrolyte for Zn‐ion batteries

“…The salt concentration is also a key factor in the properties of the aqueous electrolyte. The higher salt concentration can effectively increase the Coulombic efficiency and operating stability of the battery by reducing water activity and the meliorative transport behavior of both cations and anions 31,32 . A novel ultra‐concentrated electrolyte named “water‐in‐salt” with Zn salt as the main component was proposed recently 33 .…”

“…The higher salt concentration can effectively increase the Coulombic efficiency and operating stability of the battery by reducing water activity and the meliorative transport behavior of both cations and anions. 31,32 A novel ultra-concentrated electrolyte named "water-in-salt" with Zn salt as the main component was proposed recently. 33 In this electrolyte, the Zn 2+ solvation sheath is composed of the anions in the Zn salt instead of water molecules.…”

Zn Metal Anodes for Zn-Ion Batteries in Mild Aqueous Electrolytes: Challenges and Strategies

“…When the corrosion process continues, the Zn anode surface becomes more uneven and unsafe because of the increased pressure inside the cell. A recent study demonstrated that some Zn salts (e.g., Zn(NO 3 ) 2 and Zn(ClO 4 ) 2 ) may play a negative role in the Zn corrosion reaction [ 95 ]. For example, in the early stages of corrosion in a neutral electrolyte, a strong oxidizing agent with NO 3 − anions leads to the corrosion of the Zn foil and cathode materials.…”