A Review on In Situ Microscopic Understandings of Dendritic Zinc Growth in Aqueous Zinc Ion Batteries

Recent advances in interfacial modification of zinc anode for aqueous rechargeable zinc ion batteries

Construction of stable Zn metal anode by inorganic functional protective layer toward long-life aqueous Zn-ion battery

Aqueous rechargeable zinc-ion batteries (ZIBs) have attracted considerable attention as one of the most promising energy storage systems for the grid-scale application owing to the natural merits of metallic Zn, including a high theoretical capacity, suitable redox potential, low cost, high safety, and eco-friendliness. However, the existing aqueous ZIBs are far from satisfying the requirements of practical applications. Significant challenges hindering the further development of ZIBs come from the low utilization and poor cycling stability of cathodes and limited reversibility of Zn anodes associated with dendrite growth, corrosion, and passivation. To date, enormous efforts have been devoted to developing high-performance cathode materials, reliable electrolytes, and stable Zn anodes to achieve ZIB with high energy and power densities and long cycle life. These progresses have been reviewed in this dissertation. Regarding the main issues of ZIBs, the dissertation covered both the cathode and anode to comprehensively improve the electrochemical performance of ZIBs. For the cathode, high-performance manganese oxide-based cathode materials have been developed by in-situ electrochemical activation of MnS, and rational design of hierarchical core-shell MnO2@carbon nanofiber structures. To further understand the underlying reasons for the enhanced electrochemical performance, the charge storage mechanisms of manganese oxide-based cathodes in ZIBs have been in-depth investigated. With respect to the Zn anode, a thin polyvinyl alcohol (PVA) coating layer on the Zn anode has enabled dendrite-free, long-life aqueous Zn batteries by effectively regulating the interfacial ion diffusion and inducing the homogeneous Zn nucleation and deposition of stacked plates with preferentially crystallographic orientation along (002)Zn planes. This work is expected to provide facile and low-cost approaches for developing high-performance, cost-effective, and stable aqueous ZIBs and shed light on a new mechanistic understanding of manganese oxide-based cathodes.

In situ constructing a porous organic component-zincophilic Cu clusters layer on zinc anode for high performance aqueous zinc ion batteries

Aqueous zinc-ion batteries (ZIBs) have received much attention because of their high safety, low pollution, and satisfactory energy density (840 mAh g−1), which is important for the research of new energy storage devices. However, problems such as short cell cycle life and low coulombic efficiency (CE) of zinc (Zn) anodes due to disorderly growth of Zn dendrites and side reactions of hydrogen corrosion have delayed the practical application of ZIBs. In this work, a new “self-growth” method is proposed to build a robust and homogeneous three-dimensional (3D) nanoporous structure of tin (Sn)-coated Zn anodes (ZSN) in just 10 min by a simple and fast reaction, which can largely raise the surface area of the electrode plate. The ZSN not only provides abundant Zn nucleation sites, but also reduces the corrosion current, thus alleviating the self-corrosion of the electrolyte, reducing the occurrence of hydrogen precipitation side reactions, and effectively inhibiting the growth of Zn dendrites during cycling. Thus, a symmetric cell with a ZSN anode can be stabilized with very low voltage hysteresis (30 mV) for 480 h of stable plating/stripping cycles and can operate well for 200 h even at high current densities of 10 mA cm−2. Supercapacitors and button cells were assembled, respectively, to verify the performance of ZSN electrodes in different energy storage tools. The ZSN||AC supercapacitor exhibited superior capacity (75 mAh g−1) and high reversibility (98% coulombic efficiency) at a current density of 2 A g−1. With a MnVO (MVO) electrode as the cathode, the ZSN||MVO full cell presents excellent cycling stability with a capacity retention of 95.4% after 500 cycles at 2 A g−1, which far exceeds that of the bare Zn cell.

Rechargeable aqueous zinc‐ion batteries (AZBs), with their high theoretical capacity, low cost, safety, and environmental friendliness, have risen as a promising candidate for next‐generation energy storage. Despite the fruitful progress in cathode material research, the electrochemical performance of the AZB remains hindered by the physical and chemical instability of the Zn anode. The Zn anode suffers from dendrite growth and chemical reactions with the electrolyte, leading to efficiency decay and capacity loss. Recently, significant effort has been dedicated to regulating the Zn anode. Electrolyte manipulation, including tailoring the salt, additives, or concentration, is a useful strategy as the electrolyte strongly influences the anode's failure processes. It is thus worthwhile to gain an in‐depth understanding of these electrolyte‐dependent regulation mechanisms. With this in mind, this review first outlines the two main issues behind Zn anode failure, dendrite growth, and side reactions. Subsequently, an understanding of the electrolyte tailoring strategy, namely, the influence of the salt, additive, and concentration on the Zn anode, is provided. We conclude by summarizing the future prospects of the Zn metal anode and potential electrolyte‐based solutions.

Critical roles of metal–organic frameworks in improving the Zn anode in aqueous zinc-ion batteries

Due to their cost‐effectiveness, high safety, and environmental friendliness, aqueous zinc‐ion batteries (AZIBs) are among the most promising technologies for next‐generation energy storage systems. Nonetheless, dendrite growth, hydrogen evolution, and corrosion at zinc (Zn) anode severely hinder their practical application. In this study, a combination of molecular self‐assembly engineering, squeegee coating, and air spraying process is employed to create a superhydrophobic and highly flexible artificial solid‐electrolyte‐interface layer on Zn anode (denoted as SFM/Zn). Self‐assembled monolayer of triethoxy‐3‐aminopropylsilane optimizes Zn2+ migration kinetics. The superhydrophobic interface, formed by polydimethylsiloxane (PDMS) and trimethoxy(octadecyl)silane (OTS)‐modified nanosilicon dioxide particles, inhibits water‐related side reactions. Furthermore, the highly flexible PDMS serves as a dynamic adaptive interface for Zn anode, effectively alleviating the “tip effect”. Consequently, the SFM/Zn||SFM/Zn symmetrical cells enable reversible and stable Zn plating/stripping at both ultralow current density (0.2 mA cm−2) and ultrahigh current density (45 mA cm−2). The assembled Zn‐vanadium (SFM/Zn||NH4V4O10) cell deliver stable average Coulombic efficiency (nearly 100%) and ultralong cycling stability (135.5 mAh g−1 after 500 cycles at 5 A g−1 and 173.2 mAh g−1 after 1000 cycles at 2 A g−1). This innovative superhydrophobic three‐layered strategy sheds new light on designing highly durable Zn anode for high‐performance AZIBs.

Aqueous zinc ion batteries (AZIBs) are promising candidates for next-generation energy storage systems due to their low cost, high safety, and environmental friendliness. As the critical component, Zn metal with high theoretical capacity (5855 mAh cm-3), low redox potential (-0.763 V vs standard hydrogen electrode), and low cost has been widely applied in AZIBs. However, the low Zn utilization rate (ZUR) of Zn metal anode caused by the dendrite growth, hydrogen evolution, corrosion, and passivation require excess Zn installation in current AZIBs, thus leading to increased unnecessary battery weight and decreased energy density. Herein, approaches to the historical progress toward high ZUR AZIBs through the perspective of electrolyte optimization, anode protection, and substrate construction are comprehensively summarized, and an in-depth understanding of ZUR is highlighted. Specifically, the main challenges and failure mechanisms of Zn anode are analyzed. Then, the persisting issues and promising solutions in the reaction interface, aqueous electrolyte, and Zn anode are emphasized. Finally, the design of 100% ZUR AZIBs free of Zn metal is presented in detail. This review aims to provide a better understanding and fundamental guidelines on the high ZUR AZIBs design, which can shed light on research directions for realizing high energy density AZIBs.

Aqueous zinc-ion batteries (AZIBs) have been investigated intensively as effective energy storage devices that are environmentally friendly, safe, and have a lower cost than current Li-ion batteries.[1-5] Being outstandingly safe due to usage of non-organic electrolyte, AZIBs could also be used as power supply for wearable electronics. This also put high standard requirements in terms of flexibility, stability and electrochemical performance to AZIBs. On the other hand, the general challenges, such as the formation of the dendrites on the Zn anodes, hydrogen evolution and side reactions, have been obstructing the practical application of AZIBs. In this presentation, a simple method to assemble quasi-solid-state Zn ion pouch cell with excellent mechanical performance, flexibility and electrochemical performance was developed, combining in-situ electrodeposition of MnO2 cathode and aramid nano fiber-based hydrogel with Zn plate as anode. In-situ and cycling measurements of the electrodeposition of MnO2 on carbon nanotube mat shows excellent capacitance and superior cycling stability. In addition, Kevlar derivatized aramid nanofiber-based hydrogel shows extremely strong strength when combined with polyvinyl alcohol, which prolonged the lifetime of the cell by preventing Zn dendrite growth largely.[5,6] Moreover, the method to assemble the AZIBs pouch cell enables us to optimize the process, decrease the steps, and save time effectively by taking advantage of hydrogel formation stage and avoiding conventional verbose slurry-casting-drying steps. This work paves an efficient path to assemble flexible and stable AZIBs pouch cells with high capacity and cycling stability.[1] Tang, Boya, et al. "Issues and opportunities facing aqueous zinc-ion batteries." Energy & Environmental Science 12.11 (2019): 3288-3304.[2] Li, Chang, et al. "Toward practical aqueous zinc-ion batteries for electrochemical energy storage." Joule 6.8 (2022): 1733-1738.[3] Yu, Feng, et al. "An aqueous rechargeable zinc-ion battery on basis of an organic pigment." Rare Metals 41.7 (2022): 2230-2236.[4] Lin, Yuexing, et al. "Dendrite-free Zn anode enabled by anionic surfactant-induced horizontal growth for highly-stable aqueous Zn-ion pouch cells." Energy & Environmental Science 16.2 (2023): 687-697.[5] Wang, Peng, and Petru Andrei. "High Performance Separator and Hydrogel Based on Aramid Fibers for Zn Ion Batteries." Electrochemical Society Meeting s 242. No. 4. The Electrochemical Society, Inc., 2022.[6] Xu, Lizhi, et al. "Water‐rich biomimetic composites with abiotic self‐organizing nanofiber network." Advanced Materials 30.1 (2018): 1703343.

In situ engineering of a hydrophobic–zincophilic interface toward long‐cycle stability of Zn metal anodes

Amphiphilic ionic liquid hydrogel electrolytes with high ionic conductivity towards dendrite-free ultra-stable aqueous zinc ion batteries

Biomass-derived polymer as a flexible “zincophilic–hydrophobic” solid electrolyte interphase layer to enable practical Zn metal anodes

The Zn anode in aqueous zinc-ion batteries (AZIBs) suffers from hydrogen evolution reaction (HER), by-product accumulation, and dendrite growth, severely restricting practical viability. To address these challenges concurrently, we propose a dynamic Zn2+-conductive protective layer strategy, which involves constructing an in situ ZnOHF layer on the Zn anode and incorporating F- into the electrolyte. Zn2+-conductivity and reducibility of ZnOHF layer guide uniform Zn nucleation and deposition, thereby inhibiting dendrite formation. Crucially, the addition of F- to the electrolyte enables the dynamic regeneration of the ZnOHF layer during cycling and the conversion of detrimental by-products into favorable ZnOHF. Additionally, HER is effectively suppressed by isolating the Zn anode from the aqueous electrolyte via ZnOHF interfacial layer, and decreasing water activity through F--induced elevation of electrolyte pH from 4.1 to 5. As a result, the protected Zn anode enables the symmetrical cell to operate stably for 3100h at 0.5 mA cm-2, and a full cell to retain 85% capacity after 4000 cycles at 10 A g-1. Moreover, a 90 cm2 pouch cell delivers an initial capacity of 240 mAh and maintains 70% capacity after 200 cycles, highlighting its practical viability. This work presents an effective and scalable interface engineering approach to realize durable Zn anodes for practical AZIBs.

Rechargeable battery is the leading energy storage option for renewable power sources such as solar, wind and tidal (Park, et al., 2019, Tarascon, 2010). Furthermore, everyone owns a device powered by a rechargeable battery. Most of these devices are powered by lithium ion batteries (LIBs) owing to their rechargeability and high-energy density (Shin, et al., 2019). However, the rechargeable battery will lose its ability to retain a charge over time, forcing the consumer to discard the battery or product, which ends up in landfills. Owing to the high chemical activity of Li and the toxicity and flammability of organic solvent-based electrolytes, LIBs cause alarming safety and environmental issues (Yang, et al., 2018). Although Na+/K+ batteries are possible alternatives, these technologies also utilize organic electrolytes. Hence, there is a huge motivation to explore a battery chemistry that is long lasting, environmentally friendly, and cost-efficient. Rechargeable batteries based on water-based electrolytes are a revolutionary alternative and hold a prominent place in the energy storage research community. Along with other advantages, water also has a higher ionic conductivity (1 S cm-1) than organic electrolytes (~10-2 – 10-3 S cm-1) which is ideal for high rate cycling of batteries (Fang, et al., 2018, Winter, et al., 2004).The development of rechargeable aqueous batteries is ongoing, and there are systems based on monovalent ions (e.g. K+) and multivalent ions (e.g. Al3+, Zn2+ and Mg2+) (Liu, et al., 2014, Zhang, et al., 2017). Multivalent systems are more desirable given that their multiple redox states promise high specific capacity and energy density. Among multivalent systems, the rechargeable zinc ion battery (ZIB) has a huge potential, owing to its large overpotential for hydrogen evolution reaction (HER) (Fang, et al., 2018, Xu, et al., 2012, Glatz, et al., 2020, Zeng, et al., 2019). Apart from that, Zn holds a number of advantages over others, namely: high Earth abundance (low cost), high theoretical capacity (820 mAh g-1), low redox potential (-0.762 V vs SHE) and nontoxicity (Blanc, et al., 2020). Clearly, the electrochemical stability of Zn in aqueous solutions enlightens an opportunity to develop a “green” rechargeable battery.The aqueous ZIB consists of three main components, the Zn anode, electrolyte (e.g. Zn salts, such as ZnSO4, ZnNO3 or Zn(CF3SO3) in water) (Zhang, et al., 2016) and the cathode material (layered transition metal oxides, metal sulphides, polyaniline compounds, Prussian blue analogues etc.) (Fang, et al., 2018). Most scientific contributions on ZIB are devoted to the development of high-capacity and stable cathode materials. Owing to the cost effectiveness, environmental friendliness, and high theoretical capacity, Mn and V-based layered oxides are popular as cathode materials (Xu, et al., 2012, Alfaruqi, et al., 2015, Zhang, et al., 2019, Wei, et al., 2019). However, due to the +2 charge of Zn, it can suffer severe electrostatic interactions with the layered host material resulting in sluggish charge transfer kinetics (Yang, et al., 2018). Incorporation of metal ions (Zn2+, Mg2+, Ca2+, Li+, Na+) or structural water molecules between layers can mitigate these interactions and improve structuralstability (Zeng, et al., 2019, Lewis, et al., 2022). Dissolution of cathode material in aqueous electrolytesis another issue, which is typically addressed by electrolyte optimization (Zhao, et al., 2019).When considering the anode, growth of Zn dendrites on the anode surface is a major bottleneckfor the expansion of ZIB (Zhao, et al., 2019), i.e. localized nucleation of Zn, further aggravated by thedeposition of new Zn at preformed crystals. These Zn dendrites lead to an internal short circuit of thebattery. Furthermore, as deposited highly active Zn surface can undergo side reactions (corrosion,HER), leading to by-products and low coulombic efficiency (Zhao, et al., 2018). There have been fourmain strategies to tackle these problems: (i) electrolyte optimization, (ii) Zn anode surfacemodification, (iii) 3D Zn host design, and (iv) electrochemical protocol development (Blanc, et al.,2020). Among these, the surface passivation of Zn anode with inorganic (ZnO, TiO2, CaCO3) (Kang,et al., 2018, Kim, et al., 2020, Zhao, et al., 2020, Xie, et al., 2020) and organic (polyamide, polyvinylbutyl) (Zhao, et al., 2019, Hao, et al., 2020) coatings is a promising new approach.Although there has been some progress, effective and practically viable approaches to retardZn dendrite growth are yet insufficient. The final fate of the electrodeposited Zn critically relies on theinitial nucleation pattern and nanoscale surface kinetics (Zhao, et al., 2019, White, et al., 2012).Researchers have recognized the importance of this and have analyzed the dendrite formation viatechniques such as ex-situ atomic force microscopy (AFM), scanning electron microscopy (SEM) andtransmission electron microscopy (TEM) (Song, et al., 2016), yet these “stop-and-go” methods restrictsthe study of dynamic processes in real-time. Operando techniques are necessary to observe theevolution of micro/nanostructure of Zn deposits as it happens, which would help to establish thedeposition kinetics and transfer dynamics at the Zn anode. Hence, advanced operando characterizationtools are expected to guide the development of safe, cost-effective, and environmentally friendlyaqueous batteries and supercapacitors for future grid scale energy storage.