2020 Roadmap on Zinc Metal Batteries

Towards Superior Aqueous Zinc-Ion Batteries: The Insights of Artificial Protective Interfaces

Aqueous zinc ion batteries (AZIBs) with metallic Zn anode have the potential for large-scale energy storage application due to their cost-effectiveness, safety, environmental-friendliness, and ease of preparation. However, the concerns regarding dendrite growth and side reactions on Zn anode surface hamper the commercialization of AZIBs. This review aims to give a comprehensive evaluation of the protective interphase construction and provide guidance to further improve the electrochemical performance of AZIBs. The failure behaviors of the Zn metal anode including dendrite growth, corrosion, and hydrogen evolution are analyzed. Then, the applications and mechanisms of the constructed interphases are introduced, which are classified by the material species. The fabrication methods of the artificial interfaces are summarized and evaluated, including the in-situ strategy and ex-situ strategy. Finally, the characterization means are discussed to give a full view for the study of Zn anode protection. Based on the analysis of this review, a stable and high-performance Zn anode could be designed by carefully choosing applied material, corresponding protective mechanism, and appropriate construction technique. Additionally, this review for Zn anode modification and construction techniques for anode protection in AZIBs may be helpful in other aqueous metal batteries with similar problems.

MOF-modified dendrite-free gel polymer electrolyte for zinc-ion batteries

Zinc-ion batteries are promising candidates for large-scale energy storage, and gel polymer electrolytes (GPEs) play an important role in zinc-ion battery applications. Metal-organic frameworks (MOFs) are characterized by large specific surface areas and ordered pores. This highly ordered microporous structure provides a continuous transport channel for ions, thus realizing the high-speed transmission of ions. In this paper, an MOF-modified dendrite-free GPE was designed. The incorporation of MOF particles not only reduces the crystallinity of the polymer, increases the motility of the molecular chains, and facilitates the transfer of Zn2+, but also attracts anions to reduce polarization during electrochemical reactions. It was shown that this MOF-modified gel polymer electrolyte has a higher ionic conductivity compared to other PVDF-based polymer electrolytes (approximate range of 2 × 10-4 to 3 × 10-3 S cm-1), with a very high conductivity (1.63 mS cm-1) even at -20 °C. The Zn/Zn symmetric cell could maintain operation for more than 3600 h at a current density of 1 mA cm-2, and SEM showed that the MOF-modified gel electrolyte had uniform Zn2+ deposition.

Zinc ion Batteries: Bridging the Gap from Academia to Industry for Grid-Scale Energy Storage

Zinc ion batteries (ZIBs) exhibit significant promise in the next generation of grid-scale energy storage systems owing to their safety, relatively high volumetric energy density, and low production cost. Despite substantial advancements in ZIBs, a comprehensive evaluation of critical parameters impacting their practical energy density (Epractical) and calendar life is lacking. Hence, we suggest using formulation-based study as a scientific tool to accurately calculate the cell-level energy density and predict the cycling life of ZIBs. By combining all key battery parameters, such as the capacity ratio of negative to positive electrode (N/P), into one formula, we assess their impact on Epractical. When all parameters are optimized, we urge to achieve the theoretical capacity for a high Epractical. Furthermore, we propose a formulation that correlates the N/P and Coulombic efficiency of ZIBs for predicting their calendar life. Finally, we offer a comprehensive overview of current advancements in ZIBs, covering cathode and anode, along with practical evaluations. This Minireview outlines specific goals, suggests future research directions, and sketches prospects for designing efficient and high-performing ZIBs. It aims at bridging the gap from academia to industry for grid-scale energy storage.

Microfluidics in environmental analysis: advancements, challenges, and future prospects for rapid and efficient monitoring

Microfluidic devices have emerged as advantageous tools for detecting environmental contaminants due to their portability, ease of use, cost-effectiveness, and rapid response capabilities. These devices have wide-ranging applications in environmental monitoring of air, water, and soil matrices, and have also been applied to agricultural monitoring. Although several previous reviews have explored microfluidic devices' utility, this paper presents an up-to-date account of the latest advancements in this field for environmental monitoring, looking back at the past five years. In this review, we discuss devices for prominent contaminants such as heavy metals, pesticides, nutrients, microorganisms, per- and polyfluoroalkyl substances (PFAS), etc. We cover numerous detection methods (electrochemical, colorimetric, fluorescent, etc.) and critically assess the current state of microfluidic devices for environmental monitoring, highlighting both their successes and limitations. Moreover, we propose potential strategies to mitigate these limitations and offer valuable insights into future research and development directions.

Low-Temperature and High-Performance Vanadium-Based Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries have attracted attention due to their low cost and high safety. Unfortunately, dendrite growth, hydrogen evolution reactions, cathodic dissolution, and other problems are more serious; not only that, but also the cathodic and anodic materials' lattices contract when the temperature drops, and charge transfer and solid phase diffusion become slow, seriously aggravating dendrite growth. At present, there are few studies on the low-temperature system, and studies on retaining high specific capacity are even more rare. Herein, ethylene glycol (EG) and manganese sulfate (MSO) are selected as additives, and the manganese vanadate (MVO) cathode is used to find a high-performance solution at low temperature. MVO can provide higher specific capacity and better structural stability than MnO2 to adapt to a low-temperature environment. At the same time, Mn2+ in MSO can produce a cationic shield covering the initial zinc tip at an appropriate concentration to avoid the tip effect and inhibit the dissolution of MVO. EG can not only reduce the freezing point of the electrolyte but also promote the desolvation of [Zn(H2O)6]2+. The synergistic effect of the three elements prevents the dissolution equilibrium of Mn2+ in MVO from fluctuating greatly due to the change of temperature. Therefore, when we use EG@0.2 M MnSO4 + 2 M ZnSO4 (EG + 0.2Mn/2ZSO) electrolyte at -30 °C, the Zn||Zn batteries which used this type of electrolyte can remain 350 h at 1 mA cm-2 without failure. The Zn||Cu batteries can retain 100% Coulombic efficiency after more than 2000 cycles at 0.2 mA cm-2. The Zn||MVO battery can reach 231.13 mA h g-1 at its first cycle, and the capacity retention rate is still above 85% after 1000 cycles, which is higher than that of the existing low-temperature research system.

Enhancing the Performance of Reversible Zn Deposition by Ultrathin Polyelectrolyte Coatings

Modifying the surfaces of zinc and other metallic substrates is considered an effective strategy to enhance the reversibility of the zinc deposition and stripping processes. While a variety of surface modification strategies have been explored, their ability to be practically implemented is not always trivial due to the associated high costs and complexity of the proposed techniques. In this study, we showcase a straightforward method for preparing ultrathin polyelectrolyte coatings using polydiallyldimethylammonium chloride (PDDA) and polyethylenimine (PEI). The coatings, characterized by their electrostatic charge and hydrophobicity, suppress side reactions and even out the electrodeposition process across the substrate surface. The PDDA-coated anodes demonstrate significantly reduced voltage hysteresis, uniform zinc morphology, improved self-discharge rates, and an impressive Coulombic efficiency exceeding 99% over prolonged cycling. Our findings highlight the potential that such cost-effective and straightforward surface treatments could be widely applied in Zn metal-based batteries.

Failure Mechanism, Electrolyte Design, and Electrolyte/Electrode Interface Regulation for Low-Temperature Zinc-Based Batteries

With more renewable energy developed to satisfy the human need in the energy crisis, electricity storage is critical in power utilization and storage. Due to its high safety, high nature reserve, and high energy density, the zinc-based battery is drawing increasing attention. Together with the expansion of human activities, the low-temperature battery is developed to satisfy the power demand in extreme environments, and as a critical component, electrolytes shall have a low freezing point and satisfying electrochemical properties in cold conditions. In this review, the development of low-temperature electrolytes for zinc-based batteries will be comprehensively introduced. First, the failure mechanism of zinc-based battery at low temperature will be illustrated. Second, five main types of low-temperature electrolytes will be introduced in detail. Finally, the regulation of electrolyte/electrode surface at low temperature will be discussed. This review aims to provide a guideline for low-temperature electrolyte design from the perspective of molecular behavior regulation.

Monolithic Phosphate Interphase for Highly Reversible and Stable Zn Metal Anode

Zinc metal battery (ZMB) is promising as the next generation of energy storage system, but challenges relating to dendrites and corrosion of the zinc anode are restricting its practical application. Here, to stabilize Zn anode, we report a controlled electrolytic method for a monolithic solid-electrolyte interphase (SEI) via a high dipole moment solvent dimethyl methylphosphonate (DMMP). The DMMP-based electrolytes can generate a homogeneous and robust phosphate SEI (Zn₃ (PO₄ )₂ and ZnP₂ O₆ ). Benefiting from the protecting impact of this in situ monolithic SEI, the zinc electrode exhibits long-term cycling of 4700 h and a high Coulombic efficiency 99.89 % in Zn|Zn and Zn|Cu cell, respectively. The full V₂ O₅ |Zn battery with DMMP-H₂ O hybrid electrolyte exhibits a high capacity retention of 82.2 % following 4000 cycles under 5 A g^-1 . The first success in constructing the monolithic phosphate SEI will open a new avenue in electrolyte design for highly reversible and stable Zn metal anodes.

Non-Electrode Components for Rechargeable Aqueous Zinc Batteries: Electrolytes, Solid-Electrolyte-Interphase, Current Collectors, Binders, and Separators

Rechargeable aqueous zinc batteries (AZBs) are one of the promising options for large-scale electrical energy storage owing to their safety, affordability and environmental friendliness. During the past decade, there have been remarkable advancements in the AZBs technology, which are achieved through intensive efforts not only in the area of electrode materials but also in the fundamental understandings of non-electrode components such as electrolytes, solid electrolyte interphase (SEI), current collectors, binders, and separators. In particular, the breakthroughs in the non-electrode components should not be underestimated in having enabled the AZBs to attain a higher energy and power density beyond that of the conventional AZBs, proving their critical role. In this article, the recent research progress is comprehensively reviewed with respect to non-electrode components in AZBs, covering the new-type of electrolytes that have been introduced, attempts for the tailoring of SEI, and the design efforts for multi-functional current collectors, binders and separators, along with the remaining challenges associated with these non-electrode components. Finally, perspectives are discussed toward future research directions in this field. This extensive overview on the non-electrode components is expected to guide and spur further development of high-performance AZBs.

Selenium Defect Boosted Electrochemical Performance of Binder-Free VSe2 Nanosheets for Aqueous Zinc-Ion Batteries

As a typical transition-metal dichalcogenides, vanadium diselenide (VSe₂) is a promising electrode material for aqueous zinc-ion batteries due to its metallic characteristics and excellent electronic conductivity. In this work, we propose a strategy of hydrothermal reduction synthesis of stainless-steel (SS)-supported VSe₂ nanosheets with defect (VSe_2-x-SS), thereby further improving the conductivity and activity of VSe_2-x-SS. Density functional theory calculations confirmed that Se defect can adjust the adsorption energy of Zn²⁺ ions. This means that the adsorption/desorption process of Zn²⁺ ions on VSe_2-x-SS is more reversible than that on pure SS-supported VSe₂ (VSe₂-SS). As a result, the Zn//VSe_2-x-SS battery showed more excellent electrochemical performance than Zn//VSe₂-SS. The VSe_2-x-SS electrode shows a good specific capacity of 265.2 mA h g^-1 (0.2 A g^-1 after 150 cycles), satisfactory rate performance, and impressive cyclic stability. In addition, we also have explored the energy-storage mechanism of Zn²⁺ ions in this VSe_2-x-SS electrode material. This study provides an effective strategy for the rational design of electrode materials for electrochemical energy-storage devices.

Facile and Scalable Synthesis of 3D Structures of V10O24·12H2O Nanosheets Coated with Carbon toward Ultrafast and Ultrastable Zinc Storage

Three-dimensional (3D) structures of V₁₀O₂₄·12H₂O nanosheets coated with carbon (denoted as V₁₀O₂₄@C) are facially and cost-effectively fabricated by reducing the V₂O₅-based aqueous solution with ethanol under hydrothermal conditions. By using the 3D V₁₀O₂₄@C as the cathode of zinc-ion batteries, the as-obtained 3D V₁₀O₂₄@C sample delivers excellent charge-discharge cycling capability, superior rate performance, and reasonable specific capacity, and a specific capacity of ca. 133.3 mA h g^-1 and a 94.1% capacity retention are achieved even after 10000 cycles at a high current density of 10 A g^-1 (∼80 C). Furthermore, it provides a facile and scalable approach to synthesize the 3D structures of pure-phased vanadium oxide nanosheets or other nanoscale metal oxides coated with carbon.

Dendrite-free Zn anodes enabled by functional nitrogen-doped carbon protective layers for aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries possess the merits of good environmental benignity, high operational safety and high energy density. Nevertheless, the practical application of zinc-ion batteries is severely obstructed by the inhomogeneous deposition of metallic Zn on the anode, which results in serious capacity fading, poor coulombic efficiency, and electrolyte consumption. Herein, we propose a simple strategy of constructing a functional nitrogen-doped carbon network coating layer on zinc foil for dendrite-free Zn stripping/plating. On one hand, the good conductivity of the artificial Zn/electrolyte interface can quickly balance the electric field and lower the nucleation overpotential. On the other hand, the porosity feature and functional groups of the protective layer can provide a fast Zn2+ transportation pathway and generate well-dispersed nucleation seeds. Therefore, the protective layer can effectively hamper the growth of metallic Zn dendrites and resist side reactions. The as-prepared N-C/Zn anode displays superior cycling stability (800 h at 2 mA cm-2 with the capacity of 2 mA h cm-2) and a satisfactory coulombic efficiency of 98.76% during the Zn stripping/plating process. A long cycle life and high specific capacity (162.10 mA h g-1 after 500 cycles at 2.0 A g-1) are also obtained for N-C/Zn||ZnSO4||V2O5 full cells. The strategy provides a facile and effective opportunity for constructing high-performance rechargeable aqueous zinc-ion batteries.