Boosting the Kinetics and Stability of Zn Anodes in Aqueous Electrolytes with Supramolecular Cyclodextrin Additives

Abstract

The hydrophobic internal cavity and hydrophilic external surface of cyclodextrins (CDs) render promising electrochemical applications. Here, we report a comparative and mechanistic study on the use of CD molecules (α-, β-, and γ-CD) as electrolyte additives for rechargeable Zn batteries. The addition of α-CD in aqueous ZnSO 4 solution reduces nucleation overpotential and activation energy of Zn plating and suppresses H 2 generation. Computational, spectroscopic, and electrochemical studies reveal that α-CD preferentially adsorbs in parallel on the Zn surface via secondary hydroxyl groups, suppressing water-induced side reactions of hydrogen evolution and hydroxide sulfate formation. Additionally, the hydrophilic exterior surface of α-CD with intense electron density simultaneously facilitates Zn 2+ deposition and alleviates Zn dendrite formation. A formulated 3 M ZnSO 4 + 10 mM α-CD electrolyte enables homogenous Zn plating/stripping (average Coulombic efficiency ∼ 99.90%) at 1 mA cm −2 in Zn|Cu cells and a considerable capacity retention of 84.20% after 800 cycles in Zn|V 2 O 5 full batteries. This study provides insight into the use of supramolecular macrocycles to modulate and enhance the interface stability and kinetics of metallic anodes for aqueous battery chemistry.

Engineering a self-adaptive electric double layer on both electrodes for high-performance zinc metal batteries

“…S34, ESI †), revealing that the ImS additive has favorable charge transfer kinetics. 24 Similar results were also demonstrated at GITT with a high Zn 2+ diffusion coefficient 19 (Fig. 6d).…”

“…Apparently, when ImS/ZSO electrolyte was used, the cell delivered over 2100 plating/stripping cycles with an ultrahigh average CE of 99.9%, which further demonstrates the inhibitory effect of ImS additive on parasitic reactions. The CE of the Zn//Cu cell in ImS/ZSO electrolyte can still reach ∼99.8% after 200 cycles and even the current density and capacity are increased to 40 mA cm −2 and 10 mA h cm −2 , which outperform the current study 19,37,50–54 (Fig. 3i).…”

“…Furthermore, previous studies proved that the ZnS component probably originates from the reduction of SO 4 . 2–53…”

“…Various strategies have been employed to circumvent these drawbacks and improve the reversibility of the Zn anode, including designing Zn anode host substrates, [10][11][12] constructing artificial interface layers, [13][14][15][16] and using electrolyte additives. [17][18][19] In addition, some organic solvents can be used as co-solvents with water to regulate the solvated structure of Zn 2+ for uniform Zn deposition. However, most organic solvents are immiscible with water, requiring the use of high-cost Zn(CF 3 SO 3 ) 2 as the Zn salt.…”

Ultra‐Stable Aqueous Zinc Batteries Enabled by β‐Cyclodextrin: Preferred Zinc Deposition and Suppressed Parasitic Reactions

“…In particular, the cyclodextrin molecules have been recently reported as additives for zinc batteries to inhibit the hydrogen evolution reaction and dendrite growth, thereby, boosting Zn plating kinetics and consequently enhancing the cycling stability. [ 45 ] Compared with α‐CD (5.4 Å), β‐CD with a larger inner diameter (6.5 Å) ( Figure a) may provide robust regulation effect on the diffusion pathway and trapping of ions. [ 46 ] The experimental results show that β‐CD can improve the ionic conductivity with negligible effect on the pH of the electrolytes (Figure S1, Supporting Information).…”