Electrolyte and Additive Engineering for Zn Anode Interfacial Regulation in Aqueous Zinc Batteries

Dynamic Modulation of Keto-Enol Tautomerism in Electrolytes for Aqueous Zinc Batteries

The reversibility of zinc (Zn) anode is subject to adverse reactions. Herein we design a dynamic modulation strategy via enol-keto tautomerism to inhibit the side reactions, thus improving the reversibility of the Zn anode. Density functional theory calculations and experimental results demonstrate the keto form of additives can be adsorbed on the Zn anode, inhibiting dendrite growth, while the enol form can serve as a bidentate ligand to participate in the construction of solvation sheath for Zn2+, enhancing the kinetics of Zn2+ transport, simultaneously suppressing water activity and reducing HER and corrosion. Consequently, the Zn anode with optimal electrolyte additive achieves high reversibility, where Zn||Zn symmetric cells operate over 4000 h at 10 mA cm-2/10 mAh cm-2, and Zn||Cu asymmetric cells have a life for 930 h at 10 mA cm-2/10 mAh cm-2. Further, this dynamic modulation enables Zn||V2O5 full cells to work over 5000 cycles with a capacity retention of 83% at 5 A g-1, and the Zn||Br2 pouch cells deliver a high capacity of ∼180 mAh. This study offers an original perspective on the dynamic regulation of electrolytes for Zn anode.

Porphyrinic N4 channels of zinc ions for the electrochemical reversibility of zinc plating/stripping

A Zn2+-coordinated porphyrinic artificial solid-electrolyte interphase (αSEI) layer, named [Zn]PP-4COO-(Zn), was developed to improve the reversibility of zinc metal plating/stripping in aqueous zinc-ion batteries (ZIBs). Inspired by nitrogen-terminating sites of biological molecules coordinating and transporting zinc in zinc metabolic processes, the αSEI layer was designed with zinc ions connecting porphyrinic building blocks to form two-dimensional clathrate sheets and stacking xy-plane sheets along the z-axis to allow N4 cages to align and form porphyrinic N4 channels for zinc transport. The [Zn]PP-4COO-(Zn) αSEI layer was Zn2+-conductive and structurally durable during repeated stripping/plating. Zinc ions traveled through the porphyrinic αSEI layer along the N4 channels via (1) desolvation, (2) coordination to two nitrogens of the first clathrate sheet, (3) passing through distorted N4 cages, (4) moving to inter-plane N4 (two nitrogens from the first sheet and two nitrogens from the second sheet), (5) consecutive transport to next inter-plane N4, and (6) metal nucleation on zinc metal foil during plating. Zinc ions coming from electrolytes along the N4 channels were plated preferentially along the (002) plane, ensuring the non-dendritic growth of zinc metal for supporting plating/stripping reversibility to guarantee cycling durability. The porphyrinic N4 zinc-ion channels kept the zinc symmetric cells healthy even after 1500 times repeated plating/stripping during 3000 h operation.

Design of asymmetric electrolytes for aqueous zinc batteries

Aqueous Zn batteries are gaining increasing research attention in the energy storage area due to their intrinsic safety, potentially low cost and environmental friendliness; however, the zinc dendrite formation, zinc corrosion, passivation and the hydrogen evolution reaction induced by water at the anode side, and materials dissolution as well as intrinsic poor reaction kinetics at cathode side in aqueous systems, seriously shorten the cycling life and decrease energy density of batteries and greatly hinder their development. Recent advancements in asymmetric electrolytes with various functions are promising to overcome such challenges for zinc batteries at the same time. It has been proved that the applications of asymmetric electrolytes show significant contributions in the field of zinc-based batteries in suppressing side reactions while maintaining electrochemical performance to satisfy both anode and cathode. Therefore, this perspective summarizes recent advancements in asymmetric electrolytes' design and applications for zinc batteries and outlines opportunities and future challenges, expecting continued research attention in this area.

Stress Release of Zincophilic N-Doped Carbon@Sn Composite on High-Curvature Surface of Zinc Foam for Dendrite-Free 3D Zinc Anode

Commercial 3D zinc foam anodes with high deposition space and ion permeation have shown great potential in aqueous ion batteries. However, the local accumulated stress from its high-curvature surface exacerbates the Zn dendrite issue, leading to poor reversibility. Herein, we have employed zincophilic N-doped carbon@Sn composites (N-C@Sn) as nano-fillings to effectively release the local stress of high curvature surface of 3D Zn foams toward dendrite-free anode in aqueous zinc ion battery (AZIB). These electronegative and conductive N-C@Sn nano-fillings as supporters can provide a highly zincophilic channel for initial Zn nucleation and reduce local current density for regulating Zn deposition. Uniform Zn deposition further assists homogenous stress distribution on the platting surface, which gives a positive feedback loop to improve anode reversibility. As a result, zinc foam with N-C@Sn composite (ZCSn Foam) symmetric cell achieves a long cycle lifespan of 1100h at 0.5 mA cm-2, much more than that of Zn Foam (∼80 h lifespan). The full cell ZCSn Foam||MnO2 exhibits remarkable reversibility with 67% retention after 1000 cycles at 0.8 A g-1 and 76% after 1600 cycles at 2 Ag-1. This 3D-constructing strategy may offer a promising and practical pathway for metal anode application.

High-Entropy-Inspired Multicomponent Electrical Double Layer Structure Design for Stable Zinc Metal Anodes

Regulating the electrical double layer (EDL) structure can enhance the cycling stability of Zn metal anodes, however, the effectiveness of this strategy is significantly limited by individual additives. Inspired by the high-entropy (HE) concept, we developed a multicomponent (MC) EDL structure composed of La3+, Cl-, and BBI anions by adding dibenzenesulfonimide (BBI) and LaCl3 additives into ZnSO4 electrolytes (BBI/LaCl3/ZnSO4). Specifically, La3+ ions accumulate within EDL to shield the net charges on the Zn surface, allowing more BBI anions and Cl- ions to enter this region. Consequently, this unique MC EDL enables Zn anodes to simultaneously achieve uniform electric field, robust SEI layer, and balanced reaction kinetics. Moreover, the synergistic parameter - a novel descriptor for quantifying collaborative improvement - was first proposed to demonstrates the synergistic effect between BBI and LaCl3 additives. Benefitting from these advantages, Zn metal anodes achieved a high reversibility of 99.5 % at a depth of discharge (DoD) of 51.3 %, and Zn|MnO2 pouch cells exhibited a stable cycle life of 100 cycles at a low N/P ratio of 2.9.

Additives for Aqueous Zinc-Ion Batteries: Recent Progress, Mechanism Analysis, and Future Perspectives

Aqueous zinc-ion batteries (ZIBs) stand out as a promising next-generation electrochemical energy storage technology, offering notable advantages such as high specific capacity, enhanced safety, and cost-effectiveness. However, the application of aqueous electrolytes introduces challenges: Zn dendrite formation and parasitic reactions at the anode, as well as dissolution, electrostatic interaction, and by-product formation at the cathode. In addressing these electrode-centric problems, additive engineering has emerged as an effective strategy. This review delves into the latest advancements in electrolyte additives for ZIBs, emphasizing their role in resolving the existing issues. Key focus areas include improving morphology and reducing side reactions during battery cycling using synergistic effects of modulating anode interface regulation, zinc facet control, and restructuring of hydrogen bonds and solvation sheaths. Special attention is given to the efficacy of amino acids and zwitterions due to their multifunction to improve the cycling performance of batteries concerning cycle stability and lifespan. Additionally, the recent additive advancements are studied for low-temperature and extreme weather applications meticulously. This review concludes with a holistic look at the future of additive engineering, underscoring its critical role in advancing ZIB performance amidst the complexities and challenges of electrolyte additives.

Understanding the Role of Zinc Hydroxide Sulfate and its Analogues in Mildly Acidic Aqueous Zinc Batteries: A Review

Mildly acidic aqueous zinc batteries (AZBs) have attracted tremendous attention for grid storage applications with the expectation to tackle the issues of Li-ion batteries on high cost and poor safety. However, the performance, particularly energy density and cycle stability of AZBs are still unsatisfactory when compared with LIBs. To help the development of AZBs, a lot of effort have been made to understand the battery reaction mechanisms and precedent microscopic and spectroscopic analyses have shown flake-like large particles of zinc hydroxide sulfate (ZHS) and its analogues formed on the surfaces of cathodes and anodes in sulfate and other electrolyte systems during cycling. However, because of the complexity of the thermodynamics and kinetics of aqueous reactions to understand different battery conditions, controversies still exist. This article will review the roles of ZHS discussed in recent representative references aiming to shine light on the fundamental mechanisms of AZBs and pave ways to further improve the battery performance.