N-Doping-Induced Amorphization for Achieving Ultrastable Aqueous Zinc-Ion Batteries

Vanadium-based oxides, known for their high capacity and low cost, have garnered significant attention as promising cathode candidates in aqueous zinc-ion batteries. Nonetheless, their poor rate performance and limited durability in aqueous electrolytes present a challenge to the realistic implementation of vanadium-based aqueous zinc-ion batteries. Here, we synthesized nitrogen-doped V2O3@C (N-V2O3@N-C) via ammonia treatment of V2O3@C derived from vanadium-based metal-organic framework (V-MOF), aiming to achieve outstanding rate and cycling performance. The N-V2O3@N-C electrode exhibits notable in situ self-transformation into an amorphous state. Density functional theory calculations reveal that the distorted N-V2O3 structure and uneven charge distribution result in the creation of an amorphous state. As expected, Zn/N-V2O3@N-C aqueous zinc-ion batteries can achieve remarkable specific capacity (349.0 mAh g-1 at 0.1 A g-1), along with impressive rate performance, showcasing a capacity of 253.5 mAh g-1 at 5 A g-1 and exceptional durability at 5 A g-1 (96.4% after 1350 cycles). The employed induced amorphization approach offers novel perspectives for designing high-performance cathodes that exhibit both sturdy structures and extended cycling lifespans.

Unlocking Double Redox Reaction of Metal-Organic Framework for Aqueous Zinc-Ion Battery

Metal-organic frameworks (MOFs) show wide application as the cathode of aqueous zinc-ion batteries (AZIBs) in the future owning to their high porosity, diverse structures, abundant species, and controllable morphology. However, the low energy density and poor cycling stability hinder the feasibility in practical application. Herein, an innovative strategy of organic/inorganic double electroactive sites is proposed and demonstrated to obtain extra capacity and enhance the energy density in a manganese-based metal-organic framework (Mn-MOF-74). Simultaneously, its energy storage mechanism is systematically investigated. Moreover, profiting from the coordination effect, the Mn-MOF-74 features with stable structure in ZnSO4 electrolyte. Therefore, the Zn/Mn-MOF-74 batteries exhibit a high energy density and superior cycling stability. This work aids in the future development of MOFs in AZIBs.

Constructing Highly Stable Zinc Metal Anodes via Induced Zn(002) Growth

The nonuniform electric field at the surface of a zinc (Zn) anode, coupled with water-induced parasitic reactions, exacerbates the growth of Zn dendrites, presenting a significant impediment to large-scale energy storage in aqueous Zn-ion batteries. One of the most convenient strategies for mitigating dendrite-related issues involves controlling crystal growth through electrolyte additives. Herein, we present thiamine hydrochloride (THC) as an electrolyte additive capable of effectively stabilizing the preferential deposition of the Zn(002) plane. First-principles calculations reveal that THC tends to adsorb on Zn(100) and Zn(101) planes and is capable of inducing the deposition of Zn ion onto the (002) plane and the preferential growth of the (002) plane, resulting in a flat and compact deposition layer. A THC additive not only effectively suppresses dendrite growth but also prevents the generation of side reactions and hydrogen evolution reaction. Consequently, the Zn||Zn symmetric battery exhibits long-term cycling stability of over 3000 h at 1 mA cm-2/1 mAh cm-2 and 1000 h at 10 mA cm-2/10 mAh cm-2. Furthermore, the NH4V4O10||Zn full battery also displays excellent cycling stability and a high reversible capacity of 210 mAh g-1 after 1000 cycles at 1 A g-1, highlighting a significant potential for practical applications.

Multifunctionalized Supramolecular Cyclodextrin Additives Boosting the Durability of Aqueous Zinc-Ion Batteries

The poor cycling stability of aqueous zinc-ion batteries hinders their application in large-scale energy storage due to uncontrollable dendrite growth and harmful hydrogen evolution reactions. Here, we designed and synthesized an electrolyte additive, N-methylimidazolium-β-cyclodextrin p-toluenesulfonate (NMI-CDOTS). The cations of NMI-CD+ are more easily adsorbed on the abrupt Zn surface to regulate the deposition of Zn2+ and reduce dendrite generation under the combined action of the unique cavity structure with abundant hydroxyl groups and the electrostatic force. Meanwhile, p-toluenesulfonate (OTS-) is able to change the Zn2+ solvation structure and suppress the hydrogen evolution reaction by the strong interaction of Zn2+ and OTS-. Benefiting from the synergistic role of NMI-CD+ and OTS-, the Zn||Zn symmetric cell exhibits superior cycling performance as high as 3800 h under 1 mA cm-2 and 1 mA h cm-2. The Zn||V2O5 full battery also shows a high specific capacity (198.3 mA h g-1) under 2.0 A g-1 even after 1500 cycles, and its Coulomb efficiency is nearly 100% during the charging and discharging procedure. These multifunctional composite strategies open up possibilities for the commercial application of aqueous zinc-ion batteries.

One-Stone-for-Two-Birds Strategy for VSe2 to Enable High Capacity and Long-Life Zinc Storage

Based on a specific zinc storage mechanism and excellent electronic conductivity, transition metal dichalcogenides, represented by vanadium diselenide, are widely used in aqueous zinc-ion battery (AZIB) energy storage systems. However, most vanadium diselenide cathode materials are presently limited by low specific capacity and poor cycling life. Herein, a simple hydrothermal process has been proposed for obtaining a vanadium diselenide cathode for an AZIB. The interaction of defects and crystal planes enhances zinc storage capacity and reduces the migration energy barrier. Moreover, abundant lamellar structure greatly increases reaction sites and alleviates volume expansion during the electrochemical process. Thus, the as-obtained vanadium diselenide AZIB exhibits an excellent reversible specific capacity of 377 mAh g-1 at 1 A g-1, and ultralong cycle stability of 291 mAh g-1 after 3200 cycles, with a nearly negligible capacity loss. This one-stone-for-two-birds strategy would be expected to be applied to large-scale synthesis of a high-performance zinc-ion battery cathode in the future.

The Construction of Anion-Induced Solvation Structures in Low-concentration Electrolyte for Stable Zinc Anodes

Aqueous zinc-ion batteries (ZIBs) are promising large-scale energy storage devices because of their low cost and high safety. However, owing to the high activity of H2O molecules in electrolytes, hydrogen evolution reaction and side reactions usually take place on Zn anodes. Herein, additive-free PCA-Zn electrolyte with capacity of suppressing the activity of free and solvated H2O molecules was designed by selecting the cationophilic and solventophilic anions. In such electrolyte, contact ion-pairs and solvent-shared ion-pairs were achieved even at low concentration, where PCA- anions coordinate with Zn2+ and bond with solvated H2O molecules. Simultaneously, PCA- anions also induce the construction of H-bonds between free H2O molecules and them. Therefore, the activity of free and solvated H2O molecules is effectively restrained. Furthermore, since PCA- anions possess a strong affinity with metal Zn, they can also adsorb on Zn anode surface to protect Zn anode from the direct contact of H2O molecules, inhibiting the occurrence of water-triggered side reactions. As a result, plating/stripping behavior of Zn anodes is highly reversible and the coulombic efficiency can reach to 99.43 % in PCA-Zn electrolyte. To illustrate the feasibility of PCA-Zn electrolyte, the Zn||PANI full batteries were assembled based on PCA-Zn electrolyte and exhibited enhanced cycling performance.

Solvothermal Guided V2O5 Microspherical Nanoparticles Constructing High-Performance Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries have attracted a lot of attention owing to their cost effectiveness and plentiful resources, but less research has been conducted on the aspect of high volumetric energy density, which is crucial to the space available for the batteries in practical applications. In this work, highly crystalline V2O5 microspheres were self-assembled from one-dimensional V2O5 nanorod structures by a template-free solvothermal method, which were used as cathode materials for zinc-ion batteries with high performance, enabling fast ion transport, outstanding cycle stability and excellent rate capability, as well as a significant increase in tap density. Specifically, the V2O5 microspheres achieve a reversible specific capacity of 414.7 mAh g-1 at 0.1 A g-1, and show a long-term cycling stability retaining 76.5% after 3000 cycles at 2 A g-1. This work provides an efficient route for the synthesis of three-dimensional materials with stable structures, excellent electrochemical performance and high tap density.

Achieving Long-Cycle-Life Zinc-Ion Batteries through a Zincophilic Prussian Blue Analogue Interphase

The practical application of rechargeable aqueous zinc-ion batteries (ZIBs) has been severely hindered by detrimental dendrite growth, uncontrollable hydrogen evolution, and unfavorable side reactions occurring at the Zn metal anode. Here, we applied a Prussian blue analogue (PBA) material K2Zn3(Fe(CN)6)2 as an artificial solid electrolyte interphase (SEI), by which the plentiful -C≡N- ligands at the surface and the large channels in the open framework structure can operate as a highly zincophilic moderator and ion sieve, inducing fast and uniform nucleation and deposition of Zn. Additionally, the dense interface effectively prevents water molecules from approaching the Zn surface, thereby inhibiting the hydrogen-evolution-resultant side reactions and corrosion. The highly reversible Zn plating/stripping is evidenced by an elevated Coulombic efficiency of 99.87% over 600 cycles in a Zn/Cu cell and a prolonged lifetime of 860 h at 5 mA cm-2, 2 mAh cm-2 in a Zn/Zn symmetric cell. Furthermore, the PBA-coated Zn anode ensures the excellent rate and cycling performance of an α-MnO2/Zn full cell. This work provides a simple and effective solution for the improvement of the Zn anode, advancing the commercialization of aqueous ZIBs.

Towards More Sustainable Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are considered as the promising candidates for large-scale energy storage because of their high safety, low cost and environmental benignity. The large-scale applications of AZIBs will inevitably result in a large amount of spent AZIBs, which not only induce the waste of resources, but also pose environmental risks. Therefore, sustainable AZIBs have to be considered to minimize the risk of environmental pollution and maximize the utilization of spent compounds. Herein, this minireview focuses on the sustainability of AZIBs from material design and recycling techniques. The structure and degradation mechanism of AZIBs are discussed to guide the recycling design of the materials. Subsequently, the sustainability of component materials in AZIBs is further analysed to pre-evaluate their recycling behaviors and mentor the selection of more sustainable component materials, including active materials in cathodes, Zn anodes, and aqueous electrolytes, respectively. According to the features of component materials, corresponding green and economic approaches are further proposed to realize the recycling of active materials in cathodes, Zn anodes and electrolytes, respectively. These advanced technologies endow the recycling of component materials with high efficiency and a closed-loop control, ensuring that AZIBs will be the promising candidates of sustainable energy storage devices. This review will offer insight into potential future directions in the design of sustainable AZIBs.

Achieving Dendrite-Free Zinc Metal Anodes via Molecule Anchoring and lon-Transport pumping

The potential for scale-up application has been acknowledged by researchers for rechargeable aqueous zinc-ion batteries (ZIBs). Nonetheless, the progress of the development is significantly impeded due to the instability of the interface between the zinc anode and electrolyte. Herein, efficient and environmentally benign valine (Val) were introduced as aqueous electrolyte additive to stabilize the electrode/electrolyte interface (EEI) via functional groups in additive molecules, thus achieving reversible dendrite-free zinc anode. The amino groups present in Val molecules have a strong ability to adsorb on the surface of zinc metal, enabling the construction of anchored molecular layer on the surface of zinc anodes. The strongly polar carboxyl groups in Val molecules can act as ion-transport pumps to capture zinc ions in the electric double layer (EDL) through coordination chemistry. Therefore, this reconstructed EEI could modulate the zinc ion flux and simultaneously suppress side reactions and dendritic growth of Zn. Consequently, a long stable cycling up to 1400 h at a high current density of 20 mA cm-2 is achieved. Additionally, Zn//V2O5 full cell with Val additive exhibit enhanced cyclability, retaining 77 % capacity after 3000 cycles, displaying significant potential in promoting the commercialization of ZIBs.

The Compatibility of COFs Cathode and Optimized Electrolyte for Ultra-Long Lifetime Rechargeable Aqueous Zinc-Ion Battery

Rechargeable aqueous zinc-ion batteries (RAZIBs) are attractive due to their affordability, safety, and eco-friendliness. However, their potential is limited by the lack of high-capacity cathodes and compatible electrolytes needed for reliable performance. Herein, we have presented a compatibility strategy for the development of a durable and long-lasting RAZIBs. The covalent organic frameworks (COFs) based on anthraquinone (DAAQ-COF) is created and utilized as the cathode, with zinc metal serving as the anode. The electrolyte is made up of an aqueous solution containing zinc salts at various concentrations. The COF cathode has been designed to be endowed with a rich array of redox-active groups, enhancing its electrochemical properties. Meanwhile, the electrolyte is formulated using triflate anions, which have exhibited superiority over sulfate anions. This strategy lead to the development of an optimized COF cathode with fast charging capability, high Coulombic efficiency (nearly 100 %) and long-term cyclability (retention rate of nearly 100 % at 1 A g-1 after 10000 cycles). Moreover, through experimental analysis, a co-insertion mechanism involving Zn2+ and H+ in this cathode is discovered for the first time. These findings represent a promising path for the advancement of organic cathode materials in high-performance and sustainable RAZIBs.

A 2.4 V Aqueous Zinc-Ion Battery Enabled by the Photoelectrochemical Effect of a Modified BiOI Photocathode: Shattering the Shackle of the Electrochemical Window of an Aqueous Electrolyte

Aqueous zinc-ion batteries emerge as a promising energy storage system with merits of high security, abundance, and being environmentally benign. But the low operating voltages of aqueous electrolytes restrict their energy densities. Previous reports have mostly focused on modifying the electrolytes to enlarge the operating voltages of aqueous zinc-ion batteries. However, either extra-expensive salts or potential safety hazards of organic additives are considered to be adverse for practical large-scale applications. Here, a proof-of-concept to enlarge the operating voltage of an aqueous zinc-ion battery by incorporating a well-designed semiconductor photocathode is proposed, which produces a photovoltage (Vph) across the semiconductor/liquid junction (SCLJ) interface to elevate the output voltage of zinc-ion battery under irradiation. The operating voltage of an aqueous zinc-ion battery can be markedly raised from 1.78 (thermodynamic limit) to 2.4 V when a BiOI nanoflake array photocathode with good surface modification is introduced, achieving a round-trip efficiency of 114.3% and a 34.8% increase of energy density compared to the theoretical value. The successive ionic layer adsorption and reaction modified surface effectively passivates surface trap defects of the BiOI photocathode and thus enlarges its Vph from 60 to 240 mV under irradiation. This study provides a design to enlarge the output voltages of aqueous zinc-ion batteries and other energy storage systems, providing insight into widening the voltage window, which is that the operating voltages are determined by photocathode under irradiation and not restricted by the electrochemical stability window of dilute aqueous electrolytes.

Vanadium Oxide Cathode Coinserted by Ni2+ and NH4+ for High-Performance Aqueous Zinc-Ion Batteries

Vanadium-based oxides have garnered significant attention as cathode materials for aqueous zinc-ion batteries (AZIBs) because of their high theoretical capacity and low cost. However, the limited reaction kinetics and poor long-term cycle stability hinder their widespread application. In this paper, we propose a novel approach by coinserting Ni2+ and NH4+ ions into V2O5·3H2O, i.e., NNVO. Structural characterization shows that the coinsertion of Ni2+ and NH4+ not only extends the interlayer spacing of V2O5·3H2O but also significantly promotes the transport kinetics of Zn2+ because of the synergistic "pillar" effect of Ni2+ and NH4+, as well as the increased oxygen vacancies that effectively lower the energy barrier for Zn2+ insertion. As a result, the AZIBs with an NNVO electrode exhibit a high capacity of 398.1 mAh g-1 (at 1.0 A g-1) and good cycle stability with 89.1% capacity retention even after 2000 cycles at 5.0 A g-1. At the same time, a highly competitive energy density of 262.9 Wh kg-1 is delivered at 382.9 W kg-1. Considering the simple scheme and the resultant high performance, this study may provide a positive attempt to develop high-performance AZIBs.

Manipulating Zn Metal Texture with Guided Zincophilic Sites via Electrochemical Stripping for Dendrite-Free Zn Anodes

Constructing a three-dimensional (3D) structure along with Zn (002) texture selective exposure is a promising strategy to tackle the issues faced by Zn metal anodes. Herein, for the first time, we proposed an electrochemical stripping strategy to achieve controlled modification of the texture and microstructure of zinc foils in one step, building a hierarchical structure with (002) texture preferred exposed Zn (SZ). The SZ with favorable zincophilic properties not only can reduce the concentration polarization at the interface but also allow Zn to grow horizontally on the edge of the (002) texture by guiding the adsorption sites for Zn2+. Moreover, the honeycomb-like structure is beneficial to rearrange the distribution of the Zn2+ flux as well as alleviating stress changes during cycling. Thus, the SZ||Cu cell exhibits excellent stability with a Coulombic efficiency of 99.76% over 1800 cycles. The SZ||NaV3O8·xH2O cell with inconspicuous self-discharge effect maintains a high areal capacity of 3.67 mA h cm-2 even after 700 cycles with a low N/P ratio of 3.6. This work achieves texture architecture and structure designing on Zn foils simultaneously by metallurgical electrochemical methods and opens up a potential strategy to implement the practicality of zinc metal anodes.

Optimizing Interplanar Spacing, Oxygen Vacancies and Micromorphology via Lithium-Ion Pre-Insertion into Ammonium Vanadate Nanosheets for Advanced Cathodes in Aqueous Zinc-Ion Batteries

Ammonium vanadates, featuring an N─H···O hydrogen bond network structure between NH4 + and V─O layers, have become popular cathode materials for aqueous zinc-ion batteries (AZIBs). Their appeal lies in their multi-electron transfer, high specific capacity, and facile synthesis. However, a major drawback arises as Zn2+ ions tend to form bonds with electronegative oxygen atoms between V─O layers during cycling, leading to irreversible structural collapse. Herein, Li+ pre-insertion into the intermediate layer of NH4 V4 O10 is proposed to enhance the electrochemical activity of ammonium vanadate cathodes for AZIBs, which extends the interlayer distance of NH4 V4 O10 to 9.8 Å and offers large interlaminar channels for Zn2+ (de)intercalation. Moreover, Li+ intercalation weakens the crystallinity, transforms the micromorphology from non-nanostructured strips to ultrathin nanosheets, and increases the level of oxygen defects, thus exposing more active sites for ion and electron transport, facilitating electrolyte penetration, and improving electrochemical kinetics of electrode. In addition, the introduction of Li+ significantly reduces the bandgap by 0.18 eV, enhancing electron transfer in redox reactions. Leveraging these unique advantages, the Li+ pre-intercalated NH4 V4 O10 cathode exhibits a high reversible capacity of 486.1 mAh g-1 at 0.5 A g-1 and an impressive capacity retention rate of 72% after 5,000 cycles at 5 A g-1 .

Versatile MXenes for Aqueous Zinc Batteries

Aqueous zinc-ion batteries (AZIBs) are gaining popularity for their cost-effectiveness, safety, and utilization of abundant resources. MXenes, which possess outstanding conductivity, controllable surface chemistry, and structural adaptability, are widely recognized as a highly versatile platform for AZIBs. MXenes offer a unique set of functions for AZIBs, yet their significance has not been systematically recognized and summarized. This review article provides an up-to-date overview of MXenes-based electrode materials for AZIBs, with a focus on the unique functions of MXenes in these materials. The discussion starts with MXenes and their derivatives on the cathode side, where they serve as a 2D conductive substrate, 3D framework, flexible support, and coating layer. MXenes can act as both the active material and a precursor to the active material in the cathode. On the anode side, the functions of MXenes include active material host, zinc metal surface protection, electrolyte additive, and separator modification. The review also highlights technical challenges and key hurdles that MXenes currently face in AZIBs.

Advances in Aqueous Zinc Ion Batteries based on Conversion Mechanism: Challenges, Strategies, and Prospects

Recently, aqueous zinc-ion batteries with conversion mechanisms have received wide attention in energy storage systems on account of excellent specific capacity, high power density, and energy density. Unfortunately, some characteristics of cathode material, zinc anode, and electrolyte still limit the development of aqueous zinc-ion batteries possessing conversion mechanism. Consequently, this paper provides a detailed summary of the development for numerous aqueous zinc-based batteries: zinc-sulfur (Zn-S) batteries, zinc-selenium (Zn-Se) batteries, zinc-tellurium (Zn-Te) batteries, zinc-iodine (Zn-I2 ) batteries, and zinc-bromine (Zn-Br2 ) batteries. Meanwhile, the reaction conversion mechanism of zinc-based batteries with conversion mechanism and the research progress in the investigation of composite cathode, zinc anode materials, and selection of electrolytes are systematically introduced. Finally, this review comprehensively describes the prospects and outlook of aqueous zinc-ion batteries with conversion mechanism, aiming to promote the rapid development of aqueous zinc-based batteries.

Preferred Orientation Deposition via Multifunctional Gel Electrolyte with Molecular Anchor Enabling Highly Reversible Zn Anode

The high activity of water molecules results in a series of awful parasitic reaction, which seriously impede the development of aqueous zinc batteries. Herein, a new gel electrolyte with multiple molecular anchors is designed by employing natural biomaterials from chitosan and chlorophyll derivative. The gel electrolyte firmly anchors water molecules by ternary hydrogen bonding to reduce the activity of water molecules and inhibit hydrogen evolution reaction. Meanwhile, the multipolar charged functional groups realize the gradient induction and redistribution of Zn2+ , which drives oriented Zn (002) plane deposition of Zn2+ and then achieves uniform Zn deposition and dendrite-free anode. As a result, it endows the Zn||Zn cell with over 1700 h stripping/plating processes and a high efficiency of 99.4% for the Zn||Cu cell. In addition, the Zn||V2 O5 full cells also exhibit capacity retention of 81.7% after 600 cycles at 0.5 A g-1 and excellent long-term stability over 1600 cycles at 2 A g-1 , and the flexible pouch cells can provide stable power for light-emitting diodes even after repeated bending. The gel electrolyte strategy provides a reference for reversible zinc anode and flexible wearable devices.

An Industrially Applicable Passivation Strategy for Significantly Improving Cyclability of Zinc Metal Anodes in Aqueous Batteries

The cycling instability of metallic Zn anodes hinders the practicability of aqueous Zn-ion batteries, though aqueous Zn-ion batteries may be the most credible alternative technology for future electrochemical energy storage applications. Commercially available trivalent chromium conversion films (TCCF) are successfully employed as robust artificial interphases on Zn metal anodes (ZMAs). Fabricated through a simple immersion method, the TCCF-protected Zn (TCCF@Zn) electrode enables a superlow nucleation overpotential for Zn plating of 6.9 mV under 1 mA cm-2 , outstanding Coulombic efficiency of 99.7% at 3 mA cm-2 for 1600 cycles in Zn||Cu asymmetric cells and superior cyclability in symmetric Zn||Zn batteries at 0.2, 2, and 5 mA cm-2 for 2500 h and 10 mA cm-2 for 1200 h. More importantly, the TCCF@Zn||V2 O5 full cell exhibits a specific capacity of 118.5 mAh g-1 with a retention of 53.4% at 3 A g-1 for 3000 cycles, which is considerably larger than that of the pristine Zn||V2 O5 full cell (59.7 mAh g-1 with a retention of 25.7%). This study demonstrates a highly efficient and low-cost surface modification strategy derived from an industrially applicable trivalent chromium passivation technique aimed at obtaining dendrite-free ZMAs with high reversibility for practical Zn batteries in the near future.

A Layer-by-Layer Self-Assembled Bio-Macromolecule Film for Stable Zinc Anode

Side reactions on zinc metal (Zn) anodes are formidable issues that cause limited battery life of aqueous zinc-ion batteries (AZIBs). Here, a facile and controllable layer-by-layer (LbL) self-assembly technique is deployed to construct an ion-conductive and mechanically robust electrolyte/anode interface for stabilizing the Zn anode. The LbL film consists of two natural and biodegradable bio-macromolecules, chitosan (CS) and sodium alginate (SA). It is shown that such an LbL film tailors the solvation sheath of Zn ions and facilitates the oriented deposition of Zn. Symmetric cells with the four double layers of CS/SA ((CS/SA)4 -Zn) exhibit stable cycles for over 6500 h. The (CS/SA)4 -Zn||H2 V3 O8 coin cell maintains a specific capacity of 125.5 mAh g-1 after 14 000 cycles. The pouch cell with an electrode area of 5 × 7 cm2 also presents a capacity retention of 83% for over 500 cycles at 0.1 A g-1 . No obvious dendrites are observed after long cycles in both symmetric and full cells. Given the cost-effective material and fabrication, and environmental friendliness of the LbL films, this Zn protection strategy may boost the industrial application of AZIBs.

Suppressing Rampant and Vertical Deposition of Cathode Intermediate Product via PH Regulation Toward Large-Capacity and High-Durability Zn//MnO2 Batteries

Despite great prospects, Zn//MnO2 batteries suffer from rampant and vertical deposition of zinc sulfate hydroxide (ZSH) at the cathode surface, which leads to a significant impact on their electrochemical performance. This phenomenon is primarily due to the drastic increase in the electrolyte pH value upon discharging, which is closely associated with the electrodissolution of Mn-based active materials. Herein, the pH value change is effectively inhibited by employing an electrolyte additive with excellent pH buffering capability. As such, the formation of ZSH at the cathode is postponed, resulting in the deposition of ZSH in a horizontal arrangement. This strategy can significantly enhance the utilization efficiency of cathode active material, while also enabling a solid electrolyte interphase layer at the Zn anode to address low Zn stripping/plating reversibility. With the optimal electrolyte, the Zn//MnO2 battery realizes a 25.6% increase in the specific capacity at 0.2 A g-1 compared to that with the baseline electrolyte, great rate capability (161.6 mAh g-1 at 5 A g-1 ), and superior capacity retention (90.2% over 5,000 cycles). In addition, the pH buffering strategy is highly applicable in hydrogel electrolytes. This work underscores the importance of pH regulation for Zn//MnO2 batteries and provides enlightening insights.

A Layered Bi2 Te3 @PPy Cathode for Aqueous Zinc-Ion Batteries: Mechanism and Application in Printed Flexible Batteries

Low-cost, safe, and environmental-friendly rechargeable aqueous zinc-ion batteries (ZIBs) are promising as next-generation energy storage devices for wearable electronics among other applications. However, sluggish ionic transport kinetics and the unstable electrode structure during ionic insertion/extraction hamper their deployment. Herein, a new cathode material based on a layered metal chalcogenide (LMC), bismuth telluride (Bi2 Te3 ), coated with polypyrrole (PPy) is proposed. Taking advantage of the PPy coating, the Bi2 Te3 @PPy composite presents strong ionic absorption affinity, high oxidation resistance, and high structural stability. The ZIBs based on Bi2 Te3 @PPy cathodes exhibit high capacities and ultra-long lifespans of over 5000 cycles. They also present outstanding stability even under bending. In addition, here the reaction mechanism is analyzed using in situ X-ray diffraction, X-ray photoelectron spectroscopy, and computational tools and it is demonstrated that, in the aqueous system, Zn2+ is not inserted into the cathode as previously assumed. In contrast, proton charge storage dominates the process. Overall, this work not only shows the great potential of LMCs as ZIB cathode materials and the advantages of PPy coating, but also clarifies the charge/discharge mechanism in rechargeable ZIBs based on LMCs.

Ion-Molecule Co-Confining Ammonium Vanadate Cathode for High-Performance Aqueous Zinc-Ion Batteries

Vanadium-based cathode materials have attracted great attention in aqueous zinc-ion batteries (AZIBs). However, the inferior ion transport and cyclic stability due to the strong Coulomb interaction between Zn2+ and the lattice limit their further application. In this work, CO2 molecules are in situ embedded in the interlayer structure of NH4 V4 O10 by decomposing excess H2 C2 O4 ·2H2 O in the main framework, obtaining an ion-molecule co-confining NH4 V4 O10 for AZIB cathode material. The introduced CO2 molecules expanded the interlayer spacing of NH4 V4 O10 , broadened the diffusion channel of Zn2+ , and stabilized the structure of NH4 V4 O10 as the interlayer pillars together withNH 4 + ${\mathrm{NH}}_4^ + $ , which effectively improved the Zn2+ diffusion kinetics and cycle stability of the electrode. In addition, the binding betweenNH 4 + ${\mathrm{NH}}_4^ + $ and the host framework is stabilized via hydrogen bonds with CO2 molecules. NVO-CO2 -0.8 exhibited excellent specific capacity (451.1 mAh g-1 at 2 A g-1 ), cycle stability (214.0 mAh g-1 at 10 A g-1 after 1000 cycles) and rate performance. This work provides new ideas and approaches for optimizing vanadium-based materials with high-performance AZIBs.

Hydrogen Peroxide Tuned Morphology and Crystal Structure of Barium Vanadate-Based Nanostructures for Aqueous Zinc-Ion Storage Properties

Improving the layered-structure stability and suppressing vanadium (V) dissolution during repeated Zn2+ insertion/extraction processes are key to promoting the electrochemical stability of V-based cathodes for aqueous zinc (Zn)-ion batteries (AZIBs). In this study, barium vanadate (Ba2 V2 O7 , BVO) nanostructures (NSs) are synthesized using a facile hydrothermal method. The formation process of the BVO NSs is controlled by adjusting the concentration of hydrogen peroxide (H2 O2 ), and these NSs are employed as potential cathode materials for AZIBs. As the H2 O2 content increases, the corresponding electrochemical properties demonstrate a discernible parabolic trend, with an initial increase, followed by a subsequent decrease. Benefiting from the effect of H2 O2 concentration, the optimized BVO electrode with 20 mL H2 O2 delivers a specific capacity of 180.15 mA h g-1 at 1 A g-1 with good rate capability and a long-term cyclability of 158.34 mA h g-1 at 3 A g-1 over 2000 cycles. Thus, this study provides a method for designing cathode materials with robust structures to boost the electrochemical performance of AZIBs.

Design Strategy of High Stability Vertically Aligned RGO@V2O5 Heterostructure Cathodes for Flexible Quasi-Solid-State Aqueous Zinc-Ion Batteries

Among various cathodes for aqueous zinc-ion batteries (AZIBs), vanadium-based oxides have garnered significant attention in research circles owing to their exceptionally high theoretical specific capacity. However, the outstanding zinc storage capacity of vanadium pentoxide is constrained by its irreversible dissolution in an aqueous solution. Here, we propose a laser reduction of graphene oxide and construct a heterostructure of V2O5 coated with vertically aligned reduced graphene oxide (VrGO). The VrGO nanosheets effectively suppress the dissolution of V2O5 and provide channels for the efficient transport of zinc ions and electrons, so the electrochemical reaction kinetics of the electrode are improved. The AZIB based on the VrGO@V2O5 heterostructure cathode has a high specific capacity of 254.9 mAh g-1 at 0.2 A g-1 and excellent cycle stability with a capacity retention rate of 90.1% after 5000 cycles of charge and discharge. When assembled into a flexible quasi-solid-state AZIB, the capacity of the device is reduced by only 2% after 1000 bending cycles, showing good potential for wearable applications. This work provides a reliable strategy for designing flexible AZIB with high electrochemical performance and structural stability.

Efficient Suppression of Dendrites and Side Reactions by Strong Electrostatic Shielding Effect via the Additive of Rb2 SO4 for Anodes in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have attracted considerable attention due to their low cost and environmental friendliness. However, the rampant dendrite growth and severe side reactions during plating/stripping on the surface of zinc (Zn) anode hinder the practicability of AZIBs. Herein, an effective and non-toxic cationic electrolyte additive of Rb2 SO4 is proposed to address the issues. The large cation of Rb+ is preferentially adsorbed on the surface of Zn metal to induce a strong shielding effect for realizing the lateral deposition of Zn2+ ions along the Zn surface and isolating water from Zn metal to effectively inhibit side reactions. Consequently, the Zn||Zn symmetric cell with the addition of 1.5 mm Rb2 SO4 can cycle more than 6000 h at 0.5 mA cm-2 /0.25 mAh cm-2 , which is 20 times longer than that without Rb2 SO4 . Besides, the Zn||Cu asymmetric cell with Rb2 SO4 achieves a very high average Coulombic efficiency of 99.16% up to 500 cycles. Moreover, the electrolyte with Rb2 SO4 well matches with the VO2 cathode, achieving high initial capacity of 412.7 mAh g-1 at 5 A g-1 and excellent cycling stability with a capacity retention of 71.6% at 5 A g-1 after 500 cycles for the Zn//VO2 full cell.

High Entropy Oxides Modulate Atomic-Level Interactions for High-Performance Aqueous Zinc-Ion Batteries

The strong electrostatic interaction between high-charge-density zinc ions (112 C mm-3 ) and the fixed crystallinity of traditional oxide cathodes with delayed charge compensation hinders the development of high-performance aqueous zinc-ion batteries (AZIBs). Herein, to intrinsically promote electron transfer efficiency and improve lattice tolerance, a revolutionary family of high-entropy oxides (HEOs) materials with multipath electron transfer and remarkable structural stability as cathodes for AZIBs is proposed. Benefiting from the unique "cock-tail" effect, the interaction of diverse type metal-atoms in HEOs achieves essentially broadened d-band and lower degeneracy than monometallic oxides, which contribute to convenient electron transfer and one of the best rate-performances (136.2 mAh g-1 at 10.0 A g-1 ) in AZIBs. In addition, the intense lattice strain field of HEOs is highly tolerant to the electrostatic repulsion of high-charge-density Zn2+ , leading to the outstanding cycling stability in AZIBs. Moreover, the super selectability of elements in HEOs exhibits significant potential for AZIBs.

Dendrite-Free Zn Anode Endowed by Facile Al-Complex Coating for Long-Cycled Aqueous Zn-Ion Batteries

Side reactions and dendrite growth on the zinc metal anode surface seriously damage the shelf life and calendar life of Zn-based batteries. Here, an Al-complexed artificial interfacial layer is constructed on the Zn surface (denoted as Al-complex@Zn) by a low-cost, facile, and scalable chemical method. The Al-complex interfacial layer improves the wettability of the electrolyte. Meanwhile, the Al-complex layer not only inhibits the side reaction by a physical barrier on the Zn surface but also regulates the zinc-ion flux to realize the uniform deposition of Zn2+. The Zn//Zn symmetric cell with an Al-complex layer has realized an ultralong cycle life of 2400 h and an extremely low polarization voltage of 20 mV (1 mA cm-2, 0.5 mAh cm-2), surpassing those reported in most literature. Furthermore, when an Al-complex@Zn//NaV3O8·1.5H2O (NVO) full cell is assembled, a high capacity retention of 92.5% is achieved over 1000 cycles at a current density of 4 A g-1. This work provides a facile and low-cost strategy on the modification of zinc anode to realize long-cycled aqueous Zn-ion batteries.

Covalent Organic Frameworks in Aqueous Zinc-Ion Batteries

The development and utilization of green renewable energy are imperative with the aggravation of environmental pollution and energy crisis. In recent years, the exploration of electrochemical energy storage systems has gradually become a research hotspot in energy. Among them, aqueous zinc-ion batteries (ZIBs) have progressively developed into highly competitive and efficient energy storage devices owing to their inherent safety, natural abundance, and higher theoretical capacity. However, the practical application of ZIBs suffers from the limitation of challenges such as the absence of proper cathode materials and the unavoidable zinc dendrites and side reactions of Zn anode. Covalent organic frameworks (COFs) are an attractive class of electrode materials due to their inherent advantages, like structural designability, high stability, and ordered-open channels, bestowing them with great potential to overcome the problems of ZIBs. In this review, we concentrate on the discussion of designed strategies of COFs applied to ZIBs. Furthermore, the methods of using COFs to solve the challenging problems of cathode development, anode modification, and electrolyte optimization for ZIBs are summarized. Finally, the existing difficulties, solution measures, and prospects of COFs for ZIBs applications are discussed. Our commentary hopes to serve as a valuable reference for developing COFs-based ZIBs.

Proton Self-Doped Polyaniline with High Electrochemical Activity for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries are promising energy storage devices due to their low cost, good ionic conductivity, and high safety. Conductive polyaniline is a promising cathode because of its redox activity, but because the neutral electrolyte protonates only weakly, it displays limited electrochemical activity. A polyaniline cathode is developed with proton self-doping from manganese metal-organic frameworks (Mn-MOFs) that alleviates the deprotonation and electrochemical activity concerns arising during the charge/discharge process. The MOFs carboxyl group provides protons to prevent deprotonation and allows the polyaniline to reach a high zinc storage redox activity. The proton self-doped polyaniline cathode has a superior specific capacity (273 mAh g-1 at 0.5 A g-1 ), a high rate property (154 mAh g-1 at 20 A g-1 ), and excellent cyclability retention (87% over 4000 cycles at 15 A g-1 ). This research provides fresh insight into the development of innovative polymers as cathode materials for high-performance AZIBs.

Boosting Material Utilization via Direct Growth of Zn2 (V3 O8 )2 on the Carbon Cloth as a Cathode to Achieve a High-Capacity Aqueous Zinc-Ion Battery

Aqueous zinc-ion batteries (AZIBs) have attracted the attention of researchers because of their high theoretical capacity and safety. Among the many vanadium-based AZIB cathode materials, zinc vanadate is of great interest as a typical phase in the dis-/charge process. Here, a remarkable method to improve the utilization rate of zinc vanadate cathode materials is reported. In situ growth of Zn2 (V3 O8 )2 on carbon cloth (CC) as the cathode material (ZVO@CC) of AZIBs. Compared with the Zn2 (V3 O8 )2 cathode material bonded on titanium foil (ZVO@Ti), the specific capacity increases from 300 to 420 mAh g-1 , and the utilization rate of the material increases from 69.60% to 99.2%. After the flexible device is prepared, it shows the appropriate specific capacity (268.4 mAh g-1 at 0.1 A g-1 ) and high safety. The method proposed in this work improves the material utilization rate and enhances the energy density of AZIB and also has a certain reference for the other electrochemical energy storage devices.

Uniform zinc-ion deposition regulated by thin sulfonated poly(ether ketone) layer for Stabilizing Zn anodes

Aqueous zinc-ion batteries (AZIBs) have been getting lots of attention in the field of large scale energy storage owing to their low cost, large capacity and excellent safety. However, Zn anodes have serious dendritic growth and corrosion hydrogen evolution issues, which hinder their further application. Herein, a simple drop-coating technique was used to build a thin sulfate poly(ether ketone) (SPEEK) solid-electrolyte interphase (SEI) on the surface of the Zn anode to address these issues. The sulfonated group (-SO3-） in SPEEK can provide rich coordination sites for Zn2+, controlling the uniform deposition of Zn2+. Therefore, the polymer SEI can block electrolytes and homogenize the Zn2+flux, resulting that the modified Zn (SPEEK@Zn) anode could effectively limit the formation of dendrites and side reactions. At a current density of 0.5 mA cm-2, SPEEK@Zn electrodes can maintain an ultra-long plating/stripping cycle life of 1000 h. Full batteries based on SPEEK@Zn have more superior cycle stability than the bare ones. This approach offers a straightforward and scalable remedy for high-performance Zn anode batteries.

Anhydride-Based Compound with Tunable Redox Properties as Advanced Organic Cathodes for High-Performance Aqueous Zinc-Ion Batteries

Organic materials with multiple active sites and flexible structural designs are becoming popular for use in aqueous zinc-ion batteries (AZIBs). However, their applicability is limited due to the low specific capacity and poor cycle stability originating from the introduction of inactive units and high solubility. Herein, three organic molecules with tunable redox properties were synthesized using anhydride (PMDA, 1,2,4,5-benzenetetracarboxylic anhydride-1,2-diaminoanthraquinone, NTCDA, 1,4,5,8-naphthalenetetracarboxylic dianhydride-1,2-diaminoanthraquinone, and PTCDA, 3,4,9,10-perylenetetracarboxylic dianhydride-1,2-diaminoanthraquinone, referred to as PM12, NT12, and PT12) in the solid-phase method. Density functional theory (DFT) simulations and experiments identified that NT12 exhibits superior electrochemical performance compared with PM12 and PT12 because of the low energy gap and large aromatic conjugated structure. They demonstrated specific capacities of 106.7, 192.9, and 124.9 mA h g-1 at 0.05 A g-1, respectively. Especially, NT12 displayed excellent initial specific capacity (85.4 mA h g-1 at 1 A g-1) and remarkable capacity retention (64.1% for 3000 cycles) due to dual active centers (C═N and C═O). The all-NT12 full-cell also had excellent performance (127.1 mA h g-1 under 1 A g-1 and 80.6% over 200 cycles). The organic compounds synthesized in this work have potential applications of AZIBs, highlighting the importance of molecular design to develop the next generation of advanced materials.

Effect of Fluoride Atoms on the Electrochemical Performance of Tetracyanoquinodimethane(TCNQ) Electrodes in Zinc-ion Batteries

Tetracyanoquinodimethane (TCNQ) electrode material has achieved excellent performance in aqueous zinc-ion batteries (AZIBs). However, fundamental understanding about effect of substitutes on electrochemical performance of TCNQ remain unknown. In this work, the effects of fluorine (F) as an electron-absorbing group on the structure, morphology and electrochemical performance of TCNQ and storage mechanism of TCNQ in AZIBs are discussed. Theoretical calculation proves that the introduction of fluorine atoms decreases lowest unoccupied molecular orbital (LUMO) energy of TCNQ thus affect the redox potential. Electrochemical performance of TCNQ/Fluoro-7,7,8,8-tetracyanoquinodimethane (FTCNQ)/2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4 TCNQ) is evaluated from 25 °C to -20 °C in AZIBs. Results tend out that with the increasing substituents of F on TCNQ molecular, their stability in AZIBs decrease. Dipole moment calculation further shows that the introduction of fluorine atoms is inconducive to the stability of the electrode material in aqueous solution. Ex-situ characterization demonstrate that electron withdrawing groups do not change the REDOX center of TCNQ electrode materials. Our work provides a new thought for the selection of the electrode material in AZIBs.

Polyvinylpyrrolidone-Intercalated Mn0.07 VOx toward High Rate and Long-Life Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are expected to be an attractive alternative in advanced energy storage devices due to large abundance and dependable security. Nevertheless, the undesirable energy density and operating voltage still hinder the development of AZIBs, which is intimately associated with the fundamental properties of the cathode. In this work, polyvinylpyrrolidone (PVP) intercalated Mn0.07 VOx (PVP-MnVO) with a large interlayer spacing of 13.5 Å (against 12.5 Å for MnVO) synthesized by a facile hydrothermal method is adopted for the cathode in AZIBs. The experimental results demonstrate that PVP-MnVO with expanded interlayer spacing provides beneficial channels for the rapid diffusion of Zn2+ , resulting in a high discharge capacity of 402 mAh g-1 at 0.1 A g-1 , superior to that of MnVO (275 mAh g-1 at 0.1 A g-1 ). Meanwhile, the PVP molecule remains in the layer structure as a binder/pillar, which can maintain its structural integrity well during the charging/discharging process. Consequently, PVP-MnVO cathode exhibits superior rate capability and cycling stability (89% retention after 4300 cycles at 10 A g-1 ) compared to that of MnVO (≈51% retention over 500 cycles at 2 A g-1 ). This work proposes a new approach to optimize the performance of vanadium-based electrode materials in AZIBs.

Heterostructured Interface Enables Uniform Zinc Deposition for High-Performance Zinc-Ion Batteries

Zinc metal has considerable potential as a high-energy anode material for aqueous batteries due to its high theoretical capacity and environmental friendliness. However, dendrite growth and parasitic reactions at the electrode/electrolyte interface remain two serious problems for the Zn metal anode. Here, the heterostructured interface of ZnO rod array and CuZn5 layer is fabricated on the Zn substrate (ZnCu@Zn) to address these two issues. The zincophilic CuZn5 layer with abundant nucleation sites ensures the initial uniform Zn nucleation process during cycling. Meanwhile, the ZnO rod array grown on the surface of the CuZn5 layer can guide the subsequent homogeneous Zn deposition via spatial confinement and electrostatic attraction effects, leading to the dendrite-free Zn electrodeposition process. Consequently, the derived ZnCu@Zn anode exhibits an ultra-long lifespan of up to 2500 h with symmetric cells at the current density and capacity of 0.5 mA cm-2 /0.5 mA h cm-2 . Besides, a remarkable cyclability (75% retention for 2500 cycles at 2 A g-1 ) is achieved in the ZnCu@Zn||MnO2 full cell with a capacity of 139.7 mA h g-1 . This heterostructured interface with specific functional layers provides a feasible strategy for the design of high-performance metal anodes.

Nitrate Radical Induced "Two in One" Interface Engineering toward High Reversibility of Zn Metal Anode

Advanced interfacial engineering performs a forceful modulation effect on Zn2+ plating/stripping with simultaneous inhibition of hydrogen evolution reaction, chemical corrosion, and dendrite growth, which is responsible for high reversibility of Zn anode. Herein, a "two in one" interface engineering is developed to improve the reversibility of Zn anode, in which multi-functional Zn5 (NO3 )2 (OH)8 ·2H2 O layer and preferential Zn (002) texture are constructed simultaneously. Due to nucleophilicity to Zn2+ arising from electronegativity, the layer can accelerate the desolvation process of [Zn (H2 O)6 ]2+ and transfer kinetics of Zn2+ ions, leading to uniform nucleation and effective inhibition of water-induced side reactions. Meanwhile, the latter is beneficial to guiding   Zn (002)-preferred orientation deposition with compact structure. Consequently, the Zn electrodes with such complementary interface modulation exhibit prominent reversibility. With an area capacity of 1 mAh cm-2 at 1 mA cm-2 , the symmetric cell operates steadily for 4000 h. Highly reversible Zn anode is maintained even at 50 mA cm-2 . For full cells coupled with MnO2 cathode, impressive rate capability and cycling stability with a high capacity beyond 100 mAh g-1 at 1 A g-1 after 2000 cycles are achieved. The results provide new insights into Zn anodes with high reversibility for next-generation aqueous zinc ion batteries.

Mg2+ Ion Pre-Insertion Boosting Reaction Kinetics and Structural Stability of Ammonium Vanadates for High-Performance Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) attract much attention owing to their high safety, environmentally friendliness and low cost. However, the unsatisfactory performance of cathode materials is one of the unsolved important factors for their widespread application. Herein, we report NH4 V4 O10 nanorods with Mg2+ ion preinsertion (Mg-NHVO) as a high-performance cathode material for AZIBs. The preinserted Mg2+ ions effectively improve the reaction kinetics and structural stability of NH4 V4 O10 (NHVO), which are confirmed by electrochemical analysis and density functional theory calculations. Compared with pristine NHVO, the intrinsic conductivity of Mg-NHVO is improved by 5 times based on the test results of a single nanorod device. Besides, Mg-NHVO could maintain a high specific capacity of 152.3 mAh g-1 after 6000 cycles at the current density of 5 A g-1 , which is larger than that of NHVO (only exhibits a low specific capacity of 30.5 mAh g-1 at the same condition). Moreover, the two-phase crystal structure evolution process of Mg-NHVO in AZIBs is revealed. This work provides a simple and efficient method to improve the electrochemical performance of ammonium vanadates and enhances the understanding about the reaction mechanism of layered vanadium-based materials in AZIBs.

Ion Tunnel Matrix Initiated Oriented Attachment for Highly Utilized Zn Anodes

Metallic zinc is an ideal anode for aqueous energy storage; however, Zn anodes suffer from nonhomogeneous deposition, low reversibility, and dendrite formation; these lead to an overprovision of zinc metal in full cells. Herein, oriented-attachment-regulated Zn stacking initiated through a trapping-then-planting process with a high zinc utilization rate (ZUR) is reported. Due to the isometric topology features of cubic-type Prussian blue analog (PBA), the initial Zn plating occurs at specific sites with equal spacing of ≈5 Å in the direction perpendicular to the substrate; the trace amount of zinc ions trapped in tunnel matrix provides nuclei for the oriented attachment of Zn (002) deposits. As a result, the PBA-decorated substrate delivers high reversibility of dendrite-free zinc plating/stripping for more than 6600 cycles (1320 h) and achieves an average Coulombic efficiency (CE) of 99.5% at 5 mA cm-2 with 100% ZUR. Moreover, the anode-limited full cell with a low negative-positive electrode ratio (N/P) of 1.2 can be operated stably for 360 cycles, displaying an energy density of 214 Wh kg-1 ; this greatly exceeds commercial aqueous batteries. This work provides a proof of concept design of metal anodes with a high utilization ratio and a practical method for developing high-energy-density batteries.

High-Performance Aqueous Zinc-Ion Batteries Based on Multidimensional V2 O3 Nanosheets@Single-Walled Carbon Nanohorns@Reduced Graphene Oxide Composite and Optimized Electrolyte

The drawbacks of poor electronic conductivity and structural instability during the cycling process limit the electrochemical property of vanadium-based cathode materials for aqueous zinc-ion batteries. In addition, continuous growth and accumulation of zinc dendrites can puncture the separator and cause an internal short circuit in the battery. In this work, a unique multidimensional nanocomposite is designed by a facile freeze-drying method with subsequent calcination, consisting of V₂ O₃ nanosheets and single-walled carbon nanohorns (SWCNHs) crosslinked together and wrapped by reduced graphene oxide (rGO). The multidimensional structure can largely enhance the structural stability and electronic conductivity of the electrode material. Besides, additive Na₂ SO₄ in the ZnSO₄ aqueous electrolyte not only prevents the dissolution of cathode materials but also suppresses the Zn dendrite growth. After considering the influence of additive concentration on ionic conductivity and electrostatic force for electrolyte, V₂ O₃ @SWCNHs@rGO electrode delivers a high initial discharge capacity of 422 mAh g^-1 at 0.2 A g^-1 and a high discharge capacity of 283 mAh g^-1 after 1000 cycles at 5 A g^-1 in 2 m ZnSO₄ + 2 m Na₂ SO₄ electrolyte. Experimental techniques reveal that the electrochemical reaction mechanism can be expressed as the reversible phase transformation between V₂ O₅ and V₂ O₃ with Zn₃ (VO₄ )₂ .

Design of Ti4+/Zr4+ as Dual-Supporting Sites in Na3V2(PO4)3 for the Advanced Aqueous Zinc-Ion Battery Cathode

The development of aqueous zinc-ion batteries (AZIBs) still faces a huge challenge due to poor cycling stability and slow kinetics of the cathode material. In this work, we report an advanced cathode of Ti⁴⁺/Zr⁴⁺ as dual-supporting sites in Na₃V₂(PO₄)₃ with an expanded crystal structure, exceptional conductivity, and superior structural stability for AZIBs, which exhibits fast Zn²⁺ diffusion and excellent performance. The results of AZIBs afford remarkably high cycling stability (91.2% retention rate over 4000 cycles) and exceptional energy density (191.3 W h kg^-1), outperforming most Na⁺ superionic conductor (NASICON)-type cathodes. Furthermore, different in/ex situ characterization techniques and theoretical studies reveal the reversible storage mechanism of Zn²⁺ in an optimal Na_2.9V_1.9Ti_0.05Zr_0.05(PO₄)₃ (NVTZP) cathode and demonstrate that Na⁺ defects together with Ti⁴⁺/Zr⁴⁺ sites can intrinsically contribute to the high electrical conductivity and low Na⁺/Zn²⁺ diffusion energy barrier of NVTZP. Moreover, the flexible soft-packaged batteries further demonstrate a superior capacity retention rate of 83.2% after 2000 cycles from the perspective of practicality.

The Effect of Oxygen Vacancies on the Diffusion Characteristics of Zn(II) Ions in the Perovskite SrTiO3 Layer: A Computational Study

A highly polar perovskite SrTiO₃ (STO) layer is considered as one of the promising artificial protective layers for the Zn metal anode of aqueous zinc-ion batteries (AZIBs). Although it has been reported that oxygen vacancies tend to promote Zn(II) ion migration in the STO layer and thereby effectively suppress Zn dendrite growth, there is still a lack of a basic understanding of the quantitative effects of oxygen vacancies on the diffusion characteristics of Zn(II) ions. In this regard, we comprehensively studied the structural features of charge imbalances caused by oxygen vacancies and how these charge imbalances affect the diffusion dynamics of Zn(II) ions by utilizing density functional theory and molecular dynamics simulations. It was found that the charge imbalances are typically localized close to vacancy sites and those Ti atoms that are closest to them, whereas differential charge densities close to Sr atoms are essentially non-existent. We also demonstrated that there is virtually no difference in structural stability between the different locations of oxygen vacancies by analyzing the electronic total energies of STO crystals with the different vacancy locations. As a result, although the structural aspects of charge distribution strongly rely on the relative vacancy locations within the STO crystal, Zn(II) diffusion characteristics stay almost consistent with changing vacancy locations. No preference for vacancy locations causes isotropic Zn(II) ion transport inside the STO layer, which subsequently inhibits the formation of Zn dendrites. Due to the promoted dynamics of Zn(II) ions induced by charge imbalance near the oxygen vacancies, the Zn(II) ion diffusivity in the STO layer monotonously increases with the increasing vacancy concentration ranging from 0% to 16%. However, the growth rate of Zn(II) ion diffusivity tends to slow down at relatively high vacancy concentrations as the imbalance points become saturated across the entire STO domain. The atomic-level understanding of the characteristics of Zn(II) ion diffusion demonstrated in this study is expected to contribute to developing new long-life anode systems for AZIBs.

Improving the Cycling Stability of Aqueous Zinc-Ion Batteries by Preintercalation of Polyaniline in Hydrated Vanadium Oxide

This paper reports the synthesis and characterization of hydrated vanadium oxide (VOH) and chemically preintercalated polyanilines in VOH, labeled as PAVO-H as the cathode material for aqueous zinc-ion batteries. Synthesized PAVO-H has a high surface area and rod-shaped morphology. PAVO-H has an increased interlayer distance of 13.36 Å. PAVO-H offers high specific capacities of 330 and 225 mAh g^-1 at 50 mA g^-1 and 4 A g^-1 of current densities, respectively, with a 92% capacity retention rate of over 3000 cycles. The preintercalation of polyaniline is likely to catalyze the redox reaction and facilitate and simplify transport kinetics. It is also possible that the preintercalation of polyaniline permits the insertion of large hydrated Zn ions and reduces the formation of zinc basic salts.

Synergetic modulation on ionic association and solvation structure by electron-withdrawing effect for aqueous zinc-ion batteries

Aqueous zinc-ion batteries are emerging as one of the most promising large-scale energy storage systems due to their low cost and high safety. However, Zn anodes often encounter the problems of Zn dendrite growth, hydrogen evolution reaction, and formation of by-products. Herein, we developed the low ionic association electrolytes (LIAEs) by introducing 2, 2, 2-trifluoroethanol (TFE) into 30 m ZnCl2 electrolyte. Owing to the electron-withdrawing effect of -CF3 groups in TFE molecules, in LIAEs, the Zn2+ solvation structures convert from larger aggregate clusters into smaller parts and TFE will construct H-bonds with H2O in Zn2+ solvation structure simultaneously. Consequently, ionic migration kinetics are significantly enhanced and the ionization of solvated H2O is effectively suppressed in LIAEs. As a result, Zn anodes in LIAE display a fast plating/stripping kinetics and high Coulombic efficiency of 99.74%. The corresponding full batteries exhibit an improved comprehensive performance such as high-rate capability and long cycling life.

Structural Transformation by Crystal Engineering Endows Aqueous Zinc-Ion Batteries with Ultra-long Cyclability

Manganese oxide is a promising cathode material for aqueous zinc batteries. However, its weak structural stability, low electrical conductivity, and sluggish reaction kinetics lead to rapid capacity fading. Herein, a crystal engineering strategy is proposed to construct a novel MnO₂ cathode material. Both experimental results and theoretical calculations demonstrate that Al-doping plays a crucial role in phase transition and doping-superlattice structure construction, which stabilizes the structure of MnO₂ cathode materials, improves conductivity, and accelerates ion diffusion dynamics. As a result, 1.98% Al-doping MnO₂ (AlMO) cathode shows an incredible 15 000 cycle stability with a low capacity decay rate of 0.0014% per cycle at 4 A g^-1 . Additionally, it provides superior specific capacity of 311.2 mAh g^-1 at 0.1 A g^-1 and excellent rate performance (145.2 mAh g^-1 at 5.0 A g^-1 ). To illustrate the potential of 1.98%AlMO to be applied in actual practice, flexible energy storage devices are fabricated and measured. These discoveries provide a new insight for structural transformation via crystal engineering, as well as a new avenue for the rational design of electrode material in other battery systems.

How About Vanadium-Based Compounds as Cathode Materials for Aqueous Zinc Ion Batteries?

Aqueous zinc-ion batteries (AZIBs) stand out among many monovalent/multivalent metal-ion batteries as promising new energy storage devices because of their good safety, low cost, and environmental friendliness. Nevertheless, there are still many great challenges to exploring new-type cathode materials that are suitable for Zn²⁺ intercalation. Vanadium-based compounds with various structures, large layer spacing, and different oxidation states are considered suitable cathode candidates for AZIBs. Herein, the research advances in vanadium-based compounds in recent years are systematically reviewed. The preparation methods, crystal structures, electrochemical performances, and energy storage mechanisms of vanadium-based compounds (e.g., vanadium phosphates, vanadium oxides, vanadates, vanadium sulfides, and vanadium nitrides) are mainly introduced. Finally, the limitations and development prospects of vanadium-based compounds are pointed out. Vanadium-based compounds as cathode materials for AZIBs are hoped to flourish in the coming years and attract more and more researchers' attention.

2D VS2 @MXene Based Zinc Ion Batteries with SPANI-Contained Electrolyte Enables Dendrite-Free Anode for Stable Cycling

Regarded as one of the popular cathode materials in aqueous zinc ion batteries (ZIBs), VS₂ has unsatisfied cycling stability and relatively low capacity owing to its poor conductivity and low mechanical properties. To this regard, compositing VS₂ with high-conductive 2D transition metal carbide (MXene) has been an effective method recently. However, the Zn dendrite on the anode electrode derived from the uncontrollable sluggish migration of solvated Zn²⁺ /H₂ O ions seriously threatens the application safety of ZIB batteries. To effectively regulate the diffusion of zinc ions, in this work a conductive polymeric electrolyte of sulfonated polyaniline (SPANI) is added in the electrolyte solution. Under the Zn²⁺ /SPANI interactions confirmed by X-ray diffraction, Raman, and zeta potential experiments, the Zn²⁺ /H₂ O combination is weakened, and the deposition rate of Zn²⁺ is increased evaluated by the galvanostatic intermittent titration technique. Theoretical simulation shows that the electrostatic shielding by SPANI combining Zn^2- at the zinc/electrolyte interface has important contribution to the significant suppression of Zn dendrite. Accordingly, the fabricated VS₂ @MXene||ZnSO₄ +SPANI||Zn battery shows high capacity (368.0 mAh g^-1 at 0.1 A g^-1 ), which remains 96% after 5000 cyclic charge-discharge operations. This work develops an available strategic idea for suppressing growth of metallic dendrites to improve the ZIB performances.

Metal-Organic Framework-Based Materials in Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) are promising for large-scale energy storage systems due to their high safety, large capacity, cost-effectiveness, and environmental friendliness. However, their commercialization is currently hindered by several challenging issues, including cathode degradation and zinc dendrite growth. Recently, metal-organic frameworks (MOFs) and their derivatives have gained significant attention and are widely used in AZIBs due to their highly porous structures, large specific surface area, and ability to design frameworks for Zn²⁺ shuttle. Based on preceding contributions, this review aims to generalize two design principles for MOF-based materials in AZIBs: cathode preparation and anode protection. For cathode preparation, we mainly introduce novel MOF-based electrode materials such as pure MOFs, porous carbon materials, metal oxides, and their compounds, focusing on the analysis of the specific capacity of AZIBs. For anode protection, we systematically analyze MOF-based materials used as 3D Zn architecture, solid electrolyte interfaces, novel separators, and solid-state electrolytes, highlighting the improvement in the cyclic stability of Zn anodes. Finally, we propose the future development of MOF-based materials in AZIBs. Our work can give some clues for raising the practical application level of aqueous ZIBs.

Sodium Ion Pre-Intercalation of δ-MnO2 Nanosheets for High Energy Density Aqueous Zinc-Ion Batteries

With the merits of low cost, environmental friendliness and rich resources, manganese dioxide is considered to be a promising cathode material for aqueous zinc-ion batteries (AZIBs). However, its low ion diffusion and structural instability greatly limit its practical application. Hence, we developed an ion pre-intercalation strategy based on a simple water bath method to grow in situ δ-MnO₂ nanosheets on flexible carbon cloth substrate (MnO₂), while pre-intercalated Na⁺ in the interlayer of δ-MnO₂ nanosheets (Na-MnO₂), which effectively enlarges the layer spacing and enhances the conductivity of Na-MnO₂. The prepared Na-MnO₂//Zn battery obtained a fairly high capacity of 251 mAh g^-1 at a current density of 2 A g^-1, a satisfactory cycle life (62.5% of its initial capacity after 500 cycles) and favorable rate capability (96 mAh g^-1 at 8 A g^-1). Furthermore, this study revealed that the pre-intercalation engineering of alkaline cations is an effective method to boost the properties of δ-MnO₂ zinc storage and provides new insights into the construction of high energy density flexible electrodes.

Quantitative Regulation of Interlayer Space of NH4 V4 O10 for Fast and Durable Zn2+ and NH4 + Storage

Layered vanadium-based oxides are the promising cathode materials for aqueous zinc-ion batteries (AZIBs). Herein, an in situ electrochemical strategy that can effectively regulate the interlayer distance of layered NH₄ V₄ O₁₀ quantitatively is proposed and a close relationship between the optimal performances with interlayer space is revealed. Specifically, via increasing the cutoff voltage from 1.4, 1.6 to 1.8 V, the interlayer space of NH₄ V₄ O₁₀ can be well-controlled and enlarged to 10.21, 11.86, and 12.08 Å, respectively, much larger than the pristine one (9.5 Å). Among them, the cathode being charging to 1.6 V (NH₄ V₄ O₁₀ -C1.6), demonstrates the best Zn²⁺ storage performances including high capacity of 223 mA h g^-1 at 10 A g^-1 and long-term stability with capacity retention of 97.5% over 1000 cycles. Such superior performances can be attributed to a good balance among active redox sites, charge transfer kinetics, and crystal structure stability, enabled by careful control of the interlayer space. Moreover, NH₄ V₄ O₁₀ -C1.6 delivers NH₄ ⁺ storage performances whose capacity reaches 296 mA h g^-1 at 0.1 A g^-1 and lifespan lasts over 3000 cycles at 5 A g^-1 . This study provides new insights into understand the limitation of interlayer space for ion storage in aqueous media and guides exploration of high-performance cathode materials.