Molecular recognition effect enabled by novel crown ether as macrocyclic host towards highly reversible Zn anode

"Water-In-Oil" Electrolyte Enabled by Microphase Separation Regulation for Highly Reversible Zinc Metal Anode

The sustained hydrogen evolution and zinc (Zn) dendrite growth greatly impede the practical application of low-cost aqueous Zn metal batteries (ZMBs). Herein, for the first time, a microphase separation strategy is proposed to construct a ″water-in-oil (W/O) electrolyte to endow durable ZMBs. As validated by theoretical modeling and experimental characterizations, the unique reverse micelle structure within the electrolyte not only disrupts water hydrogen bonding and efficiently inhibits the water consumption at Zn anode, but also undergoes directed movement and reversible demulsification under electric field, thus enhancing the anode desolvation kinetics and inhibiting the interfacial side reactions. Owing to the simultaneous regulation of water molecules in both electrolyte bulk and anode interface, this W/O electrolyte achieves a high Zn plating/stripping Coulombic efficiency of 99.76% over 6000 cycles, and maintains an extend lifespan in Zn||V10O24·12H2O (VOH) cells with negligible hydrogen evolution and dendrite formation. These key findings are expected to promote the electrolyte engineering toward reversible ZMBs.

Sulfurized Composite Interphase Enables a Highly Reversible Zn Anode

The stability and reversibility of Zn anode can be greatly improved by in situ construction of solid electrolyte interphase (SEI) on Zn surface via a low-cost design strategy of ZnSO4 electrolyte. However, the role of hydrogen bond acceptor -SO3 accompanying ZnS formation during SEI reconstruction is overlooked. In this work, we have explored and revealed the new role of -SO3 and ZnS in the in situ formed sulfide composite SEI (SCSEI) on Zn anode electrochemistry in ZnSO4 aqueous electrolytes. Structure characterization and DFT demonstrate that the introduction of -SO3 can not only reduce the dehydration energy of [Zn(H2O)6]2+, but also enhance the stability of the ZnS/Zn interface and homogenize the ZnS/Zn interface electric field, thereby significantly improving the dynamic kinetics and uniform deposition of Zn2+. Owing to the synergistic effect of ZnS and -SO3, a high cycling stability of 1500 h with a cumulative-plated capacity of 7.5 Ah cm-2 at 10 mA cm-2 has been achieved within the symmetrical cell. Furthermore, the full cell with NH4V4O10 cathode exhibits outstanding cyclic stability, exceeding 2000 cycles at 5 A g-1 and maintaining a Coulombic efficiency of 100 %. These new insights into anionic synergistic strategy could significantly enhance the practical application of zinc-ion batteries.

Organic Electrolyte Additives for Aqueous Zinc Ion Batteries: Progress and Outlook

Aqueous zinc ion batteries (AZIBs) are considered one of the most prospective new-generation electrochemical energy storage devices with the advantages of high specific capacity, good safety, and high economic efficiency. Nevertheless, the enduring problems of low Coulombic efficiency (CE) and inadequate cycling stability of zinc anodes, originating from dendrites, hydrogen precipitation and passivation, are closely tied to their thermodynamic instability in aqueous electrolytes, which significantly shortens the cycle life of the battery. Electrolyte additives can solve the above difficulties and are important for the advancement of affordable and reliable AZIBs. Organic electrolyte additives have attracted widespread attention due to their unique properties, however, there is a lack of systematic discussion on the performance and mechanism of action of organic electrolyte additives. In this review, a comprehensive overview of the application of organic electrolyte additives in AZIBs is presented. The role of organic electrolyte additives in stabilizing zinc anodes is described and evaluated. Finally, further potential directions and prospects for improving and directing organic electrolyte additives for AZIBs are presented.

Regulation of Zn2+ Solvation Configuration in Aqueous Batteries via Selenium-Substituted Crown Ether Engineering

The efficient utilization of the metallic Zn in rechargeable aqueous Zn-ion batteries (RAZBs) struggle to suffer from parasitic Zn dendrite formation, hydrogen evolution reactions as well as severe interfacial degradation at high areal capacity loadings. This study thus proposes to employ the modified crown ether as an aqueous electrolyte additive to regulate the Zn2+ desolvation kinetic and facilitates the horizontally oriented (002) deposition of Zn, extending the lifespan of both the symmetric cell and full cell models. Specifically, zincophilic cyano and hydrophobic selenium atoms are incorporated into the crown ether supramolecule to enhance Zn2+ coordination and desolvation capability. The addition of 4-cyanobenzo-21-crown-7-selenium at a low concentration of 0.5 wt.% effectively mitigates hydrogen evolution and Zn corrosion caused by water, promoting the oriented deposition of Zn2+. The Zn||V2O5 full cell prototype, assembled with the areal capacity loadings of 2 mAh cm-2 and N/P ratio of 2.95, exhibits negligible capacity fading at 2.0A g-1 for 300 cycles, highlighting the commercial feasibility of supramolecular macrocycles additive for practical RAZBs applications.

Facilitating Oriented Dense Deposition: Utilizing Crystal Plane End-Capping Reagent to Construct Dendrite-Free and Highly Corrosion-Resistant (100) Crystal Plane Zinc Anode

Dendrite growth and corrosion issues have significantly hindered the usability of Zn anodes, which further restricts the development of aqueous zinc-ion batteries (AZIBs). In this study, a zinc-philic and hydrophobic Zn (100) crystal plane end-capping reagent (ECR) is introduced into the electrolyte to address these challenges in AZIBs. Specifically, under the mediation of 100-ECR, the electroplated Zn configures oriented dense deposition of (100) crystal plane texture, which slows down the formation of dendrites. Furthermore, owing to the high corrosion resistance of the (100) crystal plane and the hydrophobic protective interface formed by the adsorbed ECR on the electrode surface, the Zn anode demonstrates enhanced reversibility and higher Coulombic efficiency in the modified electrolyte. Consequently, superior electrochemical performance is achieved through this novel crystal plane control strategy and interface protection technology. The Zn//VO2 cells based on the modified electrolyte maintained a high-capacity retention of ≈80.6% after 1350 cycles, corresponding to a low-capacity loss rate of only 0.014% per cycle. This study underscores the importance of deposition uniformity and corrosion resistance of crystal planes over their type. And through crystal plane engineering, a high-quality (100) crystal plane is constructed, thereby expanding the range of options for viable Zn anodes.

Amphipathic Phenylalanine-Induced Nucleophilic-Hydrophobic Interface Toward Highly Reversible Zn Anode

Aqueous Zn2+-ion batteries (AZIBs), recognized for their high security, reliability, and cost efficiency, have garnered considerable attention. However, the prevalent issues of dendrite growth and parasitic reactions at the Zn electrode interface significantly impede their practical application. In this study, we introduced a ubiquitous biomolecule of phenylalanine (Phe) into the electrolyte as a multifunctional additive to improve the reversibility of the Zn anode. Leveraging its exceptional nucleophilic characteristics, Phe molecules tend to coordinate with Zn2+ ions for optimizing the solvation environment. Simultaneously, the distinctive lipophilicity of aromatic amino acids empowers Phe with a higher adsorption energy, enabling the construction of a multifunctional protective interphase. The hydrophobic benzene ring ligands act as cleaners for repelling H2O molecules, while the hydrophilic hydroxyl and carboxyl groups attract Zn2+ ions for homogenizing Zn2+ flux. Moreover, the preferential reduction of Phe molecules prior to H2O facilitates the in situ formation of an organic-inorganic hybrid solid electrolyte interphase, enhancing the interfacial stability of the Zn anode. Consequently, Zn||Zn cells display improved reversibility, achieving an extended cycle life of 5250 h. Additionally, Zn||LMO full cells exhibit enhanced cyclability of retaining 77.3% capacity after 300 cycles, demonstrating substantial potential in advancing the commercialization of AZIBs.

Toward Simultaneous Dense Zinc Deposition and Broken Side-Reaction Loops in the Zn//V2 O5 System

The Zn//V2 O5 system not only faces the incontrollable growth of zinc (Zn) dendrites, but also withstands the cross-talk effect of by-products produced from the cathode side to the Zn anode, inducing interelectrode talk and aggravating battery failure. To tackle these issues, we construct a rapid Zn2+ -conducting hydrogel electrolyte (R-ZSO) to achieve Zn deposition modulation and side reaction inhibition in Zn//V2 O5 full cells. The polymer matrix and BN exhibit a robust anchoring effect on SO4 2- , accelerating Zn2+ migration and enabling dense Zn deposition behavior. Therefore, the Zn//Zn symmetric cells based on the R-ZSO electrolyte can operate stably for more than 1500 h, which is six times higher than that of cells employing the blank electrolyte. More importantly, the R-ZSO hydrogel electrolyte effectively decouples the cross-talk effects, thus breaking the infinite loop of side reactions. As a result, the Zn//V2 O5 cells using this modified hydrogel electrolyte demonstrate stable operation over 1,000 cycles, with a capacity loss rate of only 0.028 % per cycle. Our study provides a promising gel chemistry, which offers a valuable guide for the construction of high-performance and multifunctional aqueous Zn-ion batteries.