“Anions‐in‐Colloid” Hydrated Deep Eutectic Electrolyte for High Reversible Zinc Metal Anodes

Abstract

AbstractZn metal as a promising anode for aqueous batteries suffers from severe zinc dendrites, anion‐related side reactions, hydrogen evolution reaction (HER) and narrow electrochemical stable window (ESW). Herein, an “anions‐in‐colloid” hydrated deep eutectic electrolyte consisting of Zn(ClO4)2 ⋅ 6H2O, β‐cyclodextrin (β‐CD), and H2O with mass ratio of 7 : 4.5 : 3 (ACDE‐3) is designed to improve the stability of zinc anode. The ACDE‐3 reconfigures the hydrogen‐bond (HB) network and regulates the solvation shell. More importantly, the hydroxyl‐rich β‐cyclodextrins (β‐CDs) in ACDE‐3 self‐assemble into micelles, in which the steric effect between adjacent β‐CDs in micelles restricts the movement of anions. This unique “anions‐in‐colloid” structure enables the eutectic system with a high Zn2+ transference number (tZn2+) of 0.84. Thus, ACDE‐3 inhibits the formation of dendrite, prevents the anion‐involved side reactions, suppresses the HER, and enlarges the ESW to 2.32 V. The Zn//Zn symmetric cell delivers a long lifespan of 900 hours at 0.5 mA cm−2, and the Zn//Cu half cells have a high average columbic efficiency (ACE) of 97.9 % at 0.5 mA cm−2 from cycle 15 to 200 with a uniform and compact zinc deposition. When matched with a poly(1,5‐naphthalenediamine) (poly(1, 5‐NAPD)) cathode, the full battery with a low negative/positive capacity (N/P) ratio of 2 can still cycle steadily for 200 cycles at a current density of 1.0 A g−1. Additionally, this electrolyte has been proven to be operative over a wide temperature range from −40 °C to 40 °C.