“Water‐in‐Deep Eutectic Solvent” Electrolytes for High‐Performance Aqueous Zn‐Ion Batteries

Abstract

Aqueous Zn‐ion batteries have been considered as promising alternatives to Li‐ion batteries due to their abundant reserves, low price, and high safety. However, Zn anode shows poor reversibility and cycling stability in most conventional aqueous electrolytes. Here, a new type of aqueous Zn‐ion electrolyte based on ZnCl2–acetamide deep eutectic solvent with both environmental and economic friendliness has been prepared. The water molecule introduced in the “water‐in‐deep eutectic solvent” electrolyte could reduce the Zn2+ desolvation energy barrier by regulating Zn2+ solvation structure to promote uniform Zn nucleation. Zn anode shows improved electrochemical performance (≈98% Coulombic efficiency over 1000 cycles) in the electrolyte whose molar ratio of ZnCl2:acetamide:H2O is 1:3:1. The assembled full battery composed of phenazine cathode and Zn anode could stably cycle over 10 000 cycles with a high capacity retention of 85.7%. Overall, this work offers new insights into exploring new green electrolyte systems for Zn‐ion batteries.

Hydrated Deep Eutectic Electrolytes for High‐Performance Zn‐Ion Batteries Capable of Low‐Temperature Operation

“…These results are superior to recently reported Zn symmetrical cells with DEEs (Table S1, Supporting Information). [25][26][27]29] Scanning electron microscopy (SEM) was used to investigate the morphology of the Zn electrodes in the Zn|AE|Zn and Zn|Z6S|Zn cells after 50 cycles. The Zn electrode from the cycled Zn|AE|Zn cell was rough and porous, indicating severe corrosion due to the AE (Figure 3d).…”

“…For example, Lewis acids (e.g., Li + , Na + , and Zn 2+ ), can be mixed with Lewis bases (e.g., succinonitrile, acetamide, and urea) to produce DEEs. [ 22,24–27 ] In that context, Qiu et al. reported an acetamide/ZnTFSI‐based DEE, which effectively suppressed dendrite growth and side reactions on ZMA.…”

“…[ 29 ] Water molecules in Zn(ClO 4 ) 2 ·6H 2 O form a unique water‐in‐DEE structure, which is contributory to enhancing ionic conductivity, reducing electrolyte viscosity, and promoting Zn 2+ desolvation on ZMA, as revealed by in‐depth simulations and experiments. [ 27 ] Moreover, water molecules are bound in a eutectic network, resulting in delayed oxidation/reduction and a large electrochemical window for DEE. Last, DEE has a wide operating temperature window, ranging from −40 °C to room temperature (RT).…”

Synergistic Effect of Cation and Anion for Low-Temperature Aqueous Zinc-Ion Battery

“…Deep eutectic solvents (DES), as a kind of "green" solvent, have been studied to protect the Zn metal anode for AZIBs [17][18][19]. Meanwhile, it also exhibits a certain antifreezing property due to the interaction with water molecules.…”

Eutectic electrolyte based on N-methylacetamide for highly reversible zinc–iodine battery

“…Deep eutectic solvent, a eutectic mixture of Lewis/Brønsted acidic anion and alkaline cation, is a new type of ionic liquid that can maintain thermal stability at room temperature. 23,24 While used as electrolytes for zinc-based batteries, it was found that anodic zinc revealed a more stable plating/stripping process, but the disadvantage of poor Zn 2+ diffusion efficiency caused by low electron conductivity and high viscosity was also prominent. 25 The extra addition of small molecular cosolvents ( e.g.…”