Ultrafast Zn2+ Intercalation and Deintercalation in Vanadium Dioxide

High-Voltage and Super-Stable Aqueous Sodium-Zinc Hybrid Ion Batteries Enabled by Double Solvation Structures in Concentrated Electrolyte

Aqueous sodium-zinc hybrid ion batteries are attracting extensive attention due to high energy density, low cost, and environmental friendliness. Unfortunately, there are still some drawbacks associated with the low voltage and cycle performance degradation that limit their practical application. Here, a concentrated aqueous electrolyte with solvation-modulated Zn²⁺ is reported that reduces the hydrogen evolution reaction on the surface of Zn metal, avoiding the generation of ZnO and uneven deposition. Accordingly, the Zn anode exhibits 1600 h Zn plating/stripping and ≈99.96% Coulombic efficiency after 700 cycles. In addition, solvation-modulated Na⁺ promotes the excellent structural stability of zinc hexacyanoferrate (ZnHCF) due to the rhombohedral-rhombohedral rather than rhombohedral-cubic phase transition. A ZnHCF//Zn full cell delivers an average voltage of 1.76 V and 98% capacity retention after 2000 cycles at 5 C rates.

An Artificial Polyacrylonitrile Coating Layer Confining Zinc Dendrite Growth for Highly Reversible Aqueous Zinc-Based Batteries

Aqueous rechargeable zinc-metal-based batteries are an attractive alternative to lithium-ion batteries for grid-scale energy-storage systems because of their high specific capacity, low cost, eco-friendliness, and nonflammability. However, uncontrollable zinc dendrite growth limits the cycle life by piercing the separator, resulting in low zinc utilization in both alkaline and mild/neutral electrolytes. Herein, a polyacrylonitrile coating layer on a zinc anode produced by a simple drop coating approach to address the dendrite issue is reported. The coating layer not only improves the hydrophilicity of the zinc anode but also regulates zinc-ion transport, consequently facilitating the uniform deposition of zinc ions to avoid dendrite formation. A symmetrical cell with the polymer-coating-layer-modified Zn anode displays dendrite-free plating/stripping with a long cycle lifespan (>1100 h), much better than that of the bare Zn anode. The modified zinc anode coupled with a Mn-doped V2 O5 cathode forms a stable rechargeable full battery. This method is a facile and feasible way to solve the zinc dendrite problem for rechargeable aqueous zinc-metal batteries, providing a solid basis for application of aqueous rechargeable Zn batteries.

Electrochemically Induced Phase Transition in V3 O7 · H2 O Nanobelts/Reduced Graphene Oxide Composites for Aqueous Zinc-Ion Batteries

V₃ O₇ ·H₂ O nanobelts/reduced graphene oxide (rGO) composites (weight ratio: 86%/14%) are synthesized by a microwave approach with a high yield (85%) through controlling pH with acids. The growth mechanisms of the highly crystalline nanobelts (average diameter: 25 nm; length: ≈20 µm; oriented along the [101] direction) have been thoroughly investigated, with the governing role of the acid upon the morphology and oxidation state of vanadium disclosed. When used as the ZIB cathode, the composite can deliver a high specific capacity of 410.7 and 385.7 mAh g^-1 at the current density of 0.5 and 4 A g^-1 , respectively, with a high retention of the capacity of 93%. The capacity of the composite is greater than those of V₃ O₇  · H₂ O, V₂ O₅ nanobelts, and V₅ O₁₂  · 6H₂ O film. Zinc ion storage in V₃ O₇ ·H₂ O/rGO is mainly a pseudocapacitive behavior rather than ion diffusion. The presence of rGO enables outstanding cycling stability of up to 1000 cycles with a capacity retention of 99.6%. Extended cycling shows a gradual phase transition, that is, from the original orthorhombic V₃ O₇  · H₂ O to a stable hexagonal Zn₃ (VO₄ )₂ (H₂ O)_2.93 phase, which is a new electrochemical route found in V₃ O₇ materials. This phase transition process provides new insight into the reactions of aqueous ZIBs.

Novel aluminum vanadate as a cathode material for high-performance aqueous zinc-ion batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) have garnered widespread attention as a new large-scale energy storage candidate owing to their low cost and high theoretical capacity. Because of the unique divalent state of Zn²⁺and the existence of a strong electrostatic repulsion phenomenon, researchers are currently focusing on how to prepare high-performance cathode materials. In this study, we synthesized aluminum vanadate (AlV₃O₉) as a cathode material for AZIBs using a solvothermal method. Al³⁺acted as a pillar in the resultant structure and stabilized it. Furthermore, this large interlayer spacing enhanced the ion diffusion coefficient and accelerated the ion transport process. Because of these advantages, the AlV₃O₉(AVO) cathode exhibited excellent electrochemical performance, including a high capacity of 421.0 mA h g^-1at 0.1 A g^-1and a stable rate capability of 348.2 mA h g^-1at 1 A g^-1. Moreover, it exhibited a specific capacity of 202 mA h g^-1even at a high current density of 3 A g^-1(the capacity retention rate reached 84.38% after 1600 cycles). The prepared ZIBs presented a high power density of 366.6 W kg^-1at an energy density of 286 W h kg^-1. These extraordinary results indicate the great application potential of AVO as a cathode material for AZIBs.

Aqueous Rechargeable Zn-ion Batteries: Strategies for Improving the Energy Storage Performance

The growing demand for the renewable energy storage technologies stimulated the quest for efficient energy storage devices. In recent years, the rechargeable aqueous zinc-based battery technologies are emerging as a compelling alternative to the lithium-based batteries owing to safety, eco-friendliness, and cost-effectiveness. Among the zinc-based energy devices, rechargeable zinc-ion batteries (ZIBs) are drawing considerable attention. However, they are plagued with several issues, including cathode dissolution, dendrite formation, etc.. Despite several efforts in the recent past, ZIBs are still in their infant stages and have yet to reach the stage of large-scale production. Finding stable Zn²⁺ intercalation cathode material with high operating voltage and long cycling stability as well as dendrite-free Zn anode is the main challenge in the development of efficient zinc-ion storage devices. This Review discusses the various strategies, in terms of the engineering of cathode, anode and electrolyte, adopted for improving the charge storage performance of ZIBs and highlights the recent ZIB technological innovations. A brief account on the history of zinc-based devices and various cathode materials tested for ZIB fabrication in the last five years are also included. The main focus of this Review is to provide a detailed account on the rational engineering of the electrodes, electrolytes, and separators for improving the charge storage performance with a future perspective to achieving high energy density and long cycling stability and large-scale production for practical application.

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.

Toward a High-Performance Aqueous Zinc Ion Battery: Potassium Vanadate Nanobelts and Carbon Enhanced Zinc Foil

Aqueous rechargeable zinc ion batteries are promising candidates for grid-scale applications owing to their low cost and high safety. However, they are plagued by the lack of suitable cathode and anode materials. Herein, we report on potassium vanadate (KVO) nanobelts as a promising cathode for an aqueous zinc ion battery, which shows a high discharge capacity of 461 mA h g^-1 at 0.2 A g^-1 and exhibits a capacity retention of 96.2% over 4000 cycles at 10 A g^-1. Furthermore, to enhance the energy efficiency in an aqueous zinc ion battery, a facile and effective method on the anode is demonstrated. The energy efficiency increases from 47.5% for Zn//KVO coupled with the zinc foil anode to 66.5% for AB-Zn//KVO coupled with an acetylene black film improved zinc foil anode at 10 A g^-1. The remarkable electrochemical performance makes AB-Zn//KVO a strong candidate for a high-performance aqueous zinc ion battery.

Superior-Performance Aqueous Zinc-Ion Batteries Based on the In Situ Growth of MnO2 Nanosheets on V2CTX MXene

Mn-based aqueous zinc-ion batteries (ZIBs) are promising candidate for large-scale rechargeable energy storage because of easy fabrication, low cost, and high safety. Nevertheless, the commercial application of Mn-based cathode is hindered by the challenging issues of low rate capability and poor cyclability. Herein, a manganese-vanadium hybrid, K-V₂C@MnO₂ cathode, featured with MnO₂ nanosheets uniformly formed on a V₂CT_X MXene surface, is elaborately designed and synthesized by metal-cation intercalation and following in situ growth strategy. Benefiting from the hybrid structure with high conductivity, abundant active sites, and the synergistic reaction of Mn²⁺ electrodeposition and inhibited structural damage of MnO₂, K-V₂C@MnO₂ shows excellent electrochemical performance for aqueous ZIBs. Specifically, it presents the high specific capacity of 408.1 mAh g^-1 at 0.3 A g^-1 and maintains the specific capacity of 119.2 mAh g^-1 at a high current density of 10 A g^-1 in a long-term cycle of up to 10000 cycles. It is superior to almost all reported Mn-based cathodes for ZIBs in the aqueous electrolyte. The superior electrochemical performance suggests that the Mn-based cathode materials designed in this work can be a rational approach to be applied for high-performance ZIBs cathodes.

Unravelling V6O13 Diffusion Pathways via CO2 Modification for High-Performance Zinc Ion Battery Cathode

Vanadium-based oxide is widely investigated as a zinc ion battery (ZIB) cathode due to its ability to react reversibly with Zn²⁺. Despite its successful demonstration, modification with simple molecules has shown some promise in enhancing the performance of ZIBs. Thus, this presents an immense opportunity to explore simple molecules that can dramatically improve the electrochemical performance of electrodes. Thus, the effect of CO₂ modification is studied in this work by decomposing oxalic acid within a hydrated V₆O₁₃ framework. Based on the collective results, the presence of CO₂ drastically lowers the relative energy of Zn²⁺ diffusion through the pathways by forming weak electrostatic interactions between O_CO2 and Zn²⁺. This leads to an enlarged diffusion contribution, which consequently results in enhanced stability and better rate performance. The as-synthesized CO₂-V₆O₁₃ electrode delivers one of the highest specific capacities reported for vanadium-based oxides of ca. 471 mAh g^-1. Furthermore, an excellent cyclic stability of 80% capacity retention after 4000 cycles at 2 A g^-1 is recorded for CO₂-V₆O₁₃, which suggests the importance of simple molecules in the material framework toward the enhancement of ZIB cathode performance.

VO2(B)@carbon fiber sheet as a binder-free flexible cathode for aqueous Zn-ion batteries

A flexible VO2(B)@CFS electrode exhibits a high capacity and a long cycle life for zinc-ion batteries.

VO2 Nanostructures for Batteries and Supercapacitors: A Review

Vanadium dioxide (VO₂ ) received tremendous interest lately due to its unique structural, electronic, and optoelectronic properties. VO₂ has been extensively used in electrochromic displays and memristors and its VO₂ (B) polymorph is extensively utilized as electrode material in energy storage applications. More studies are focused on VO₂ (B) nanostructures which displayed different energy storage behavior than the bulk VO₂ . The present review provides a systematic overview of the progress in VO₂ nanostructures syntheses and its application in energy storage devices. Herein, a general introduction, discussion about crystal structure, and syntheses of a variety of nanostructures such as nanowires, nanorods, nanobelts, nanotubes, carambola shaped, etc. are summarized. The energy storage application of VO₂ nanostructure and its composites are also described in detail and categorically, e.g. Li-ion battery, Na-ion battery, and supercapacitors. The current status and challenges associated with VO₂ nanostructures are reported. Finally, light has been shed for the overall performance improvement of VO₂ nanostructure as potential electrode material for future application.

Potentiodynamics of the Zinc and Proton Storage in Disordered Sodium Vanadate for Aqueous Zn-Ion Batteries

A rechargeable Zn-ion battery is a promising aqueous system, where coinsertion of Zn²⁺ and H⁺ could address the obstacles of the sluggish ionic transport in cathode materials imposed by multivalent battery chemistry. However, there is a lack of fundamental understanding of this dual-ion transport, especially the potentiodynamics of the storage process. Here, a quantitative analysis of Zn²⁺ and H⁺ transport in a disordered sodium vanadate (NaV₃O₈) cathode material has been reported. Collectively, synchrotron X-ray analysis shows that both Zn²⁺ and H⁺ storages follow an intercalation storage mechanism in NaV₃O₈ and proceed in a sequential manner, where intercalations of 0.26 Zn²⁺ followed by 0.24 H⁺ per vanadium atom occur during discharging, while reverse dynamics happens during charging. Such a unique and synergistic dual-ion sequential storage favors a high capacity (265 mA h g^-1) and an energy density (221 W h kg^-1) based on the NaV₃O₈ cathode and a great cycling life (a capacity retention of 78% after 2000 cycles) in Zn/NaV₃O₈ full cells.

Hierarchical Multicavity Nitrogen-Doped Carbon Nanospheres as Efficient Polyselenide Reservoir for Fast and Long-Life Sodium-Selenium Batteries

Sodium-selenium (Na-Se) battery has been emerging as one of the most prospective energy storage systems owing to their high volumetric energy density and cost effectiveness. Nevertheless, the shuttle effect of sodium polyselenide (NaPSe) and sluggish electrochemical reaction kinetics present the main bottlenecks for its practical implementation. Herein, a new Se host of 3D nitrogen-doped hierarchical multicavity carbon nanospheres (3D NHMCs) is designed and synthesized via a facile self-sacrifice templating strategy. The 3D NHMCs are verified to hold a favorable structure of a hollow macropore core and numerous micro/mesopores hollow shell for hosting Se, which can not only maximize Se utilization and alleviate the volumetric expansion but also promote the electrical/ionic conductivity and electrolyte infiltration. Moreover, the abundant self-functionalized surfaces as an efficient NaPSe scavenger via robust physical-chemical dual blocking effects demonstrate high-efficiency in situ anchoring-diffusion-conversion of NaPSe, rendering rapid reaction kinetics and remarkable suppressive shuttle effect, as evidenced by systematic experimental analysis and density functional theory calculations. As a result, the high-Se-loading 3D NHMCs/Se cathode exhibits an ultrahigh volumetric capacity (863 mAh cm^-3 ) and rate capability (377 mAh g^-1 at 20 C) and unexceptionable stability over 2000 cycles at 2 C.

Dendrites in Zn-Based Batteries

Aqueous Zn batteries that provide a synergistic integration of absolute safety and high energy density have been considered as highly promising energy-storage systems for powering electronics. Despite the rapid progress made in developing high-performance cathodes and electrolytes, the underestimated but non-negligible dendrites of Zn anode have been observed to shorten battery lifespan. Herein, this dendrite issue in Zn anodes, with regard to fundamentals, protection strategies, characterization techniques, and theoretical simulations, is systematically discussed. An overall comparison between the Zn dendrite and its Li and Al counterparts, to highlight their differences in both origin and topology, is given. Subsequently, in-depth clarifications of the specific influence factors of Zn dendrites, including the accumulation effect and the cathode loading mass (a distinct factor for laboratory studies and practical applications) are presented. Recent advances in Zn dendrite protection are then comprehensively summarized and categorized to generate an overview of respective superiorities and limitations of various strategies. Accordingly, theoretical computations and advanced characterization approaches are introduced as mechanism guidelines and measurement criteria for dendrite suppression, respectively. The concluding section emphasizes future challenges in addressing the Zn dendrite issue and potential approaches to further promoting the lifespan of Zn batteries.

Scalable Synthesis of Manganese-Doped Hydrated Vanadium Oxide as a Cathode Material for Aqueous Zinc-Metal Battery

Rechargeable aqueous zinc-metal batteries (ZMBs) are considered as potential energy storage devices for stationary applications. Despite the significant developments in recent years, the performance of ZMBs is still limited due to the lack of advanced cathode materials delivering high capacity and long cycle life. In this work, we report a low-temperature and scalable synthesis method following a surfactant-assisted route for preparing manganese-doped hydrated vanadium oxide (MnHVO-30) and its application as the cathode material for ZMB. The as-prepared material possesses a porous architecture and expanded interlayer spacing. Therefore, the MnHVO-30 cathode offers fast and reversible insertion of Zn²⁺ ions during the charge/discharge process and delivers 341 mAh g^-1 capacity at 0.1 A g^-1. Moreover, the MnHVO-30||Zn cell retains 82% of its initial capacity over 1200 stability cycles, which is higher compared to that of the undoped system. Besides, a quasi-solid-state home-made pouch cell with an area of 3.3 × 1.6 cm² and 3.6 mg cm^-2 loading is assembled, achieving 115 mAh g^-1 capacity over 100 stability cycles. Therefore, this work provides an easy and attractive way for preparing efficient cathode materials for aqueous ZMBs.

Stabilized Rechargeable Aqueous Zinc Batteries Using Ethylene Glycol as Water Blocker

Addressing the cost concerns and safety of zinc metal has stimulated research on mild aqueous Zn-metal batteries. However, their application is limited by dendrite formation and H₂ evolution on the Zn anode. Here, ethylene glycol (EG) is proposed as additional water blocker to form localized high-concentration electrolyte for aqueous Zn batteries. This unique solvation structure inhibits hydrate formation and facilitates close association of Zn²⁺ and SO₄ ^2- , which alleviates undesired H₂ evolution and enables dendrite-free Zn plating/stripping. Accordingly, a Zn//PQ-MCT (phenanthrenequinone macrocyclic trimer) full cell with such electrolyte exhibits a very long cycling life (more than 8000 cycles). Furthermore, this EG-based aqueous electrolyte is non-flammable and inexpensive and prevents evaporation of water when open to the atmosphere, endowing aqueous Zn batteries with excellent safety performance and easy operability in practical applications.

Intercalation Pseudocapacitive Zn2+ Storage with Hydrated Vanadium Dioxide toward Ultrahigh Rate Performance

The weak van der Waals interactions enable ion-intercalation-type hosts to be ideal pseudocapacitive materials for energy storage. Here, a methodology for the preparation of hydrated vanadium dioxide nanoribbon (HVO) with moderate transport pathways is proposed. Out of the ordinary, the intercalation pseudocapacitive reaction mechanism is discovered for HVO, which powers high-rate capacitive charge storage compared with the battery-type intercalation reaction. The main factor is that the defective crystalline structure provides suitable ambient spacing for rapidly accommodating and transporting cations. As a result, the HVO delivers a fast Zn²⁺ ion diffusion coefficient and a low Zn²⁺ diffusion barrier. The electrochemical results with intercalation pseudocapacitance demonstrate a high reversible capacity of 396 mAh g^-1 at 0.05 A g^-1 , and even maintain 88 mAh g^-1 at a high current density of 50 A g^-1 .

Vanadium-Based Materials: Next Generation Electrodes Powering the Battery Revolution?

ConspectusAs the world transitions away from fossil fuels, energy storage, especially rechargeable batteries, could have a big role to play. Though rechargeable batteries have dramatically changed the energy landscape, their performance metrics still need to be further enhanced to keep pace with the changing consumer preferences along with the increasing demands from the market. For the most part, advances in battery technology rely on the continuing development of materials science, where the development of high-performance electrode materials helps to expand the world of battery innovation by pushing the limits of performance of existing batteries. This is where vanadium-based compounds (V-compounds) with intriguing properties can fit in to fill the gap of the current battery technologies.The history of experimenting with V-compounds (i.e., vanadium oxides, vanadates, vanadium-based NASICON) in various battery systems, ranging from monovalent-ion to multivalent-ion batteries, stretches back decades. They are fascinating materials that display rich redox chemistry arising from multiple valency and coordination geometries. Over the years, researchers have made use of the inherent ability of vanadium that undergoes metamorphosis between different coordination polyhedra accompanied by transitions in the oxidation state for reversible intercalation/insertion of more than one guest ions without breaking the structure apart. Such infinitely variable properties endow them with a wide range of electronic and crystallographic structures. The former attribute varies from insulators to metallic conductors while the latter feature gives rise to layered structures or 3D open tunnel frameworks that allow facile movement of a wide range of metal cations and guest species along the gallery. Accompanied by a growing stringent requirements for energy storage applications, most V-compounds face difficulty in resolving the problems of their own lack competitiveness mostly due to their intrinsically low ionic/electronic conductivity. The key to producing vanadium-based electrodes with the desired performance characteristics is the ability to fabricate and optimize them consistently to realize certain specifications through effective engineering strategies for property modulation.In this Account, we aim to provide a comprehensive article that correlates the fundamental of charge storage mechanism to crystallographic forms and design principle for V-compounds. More importantly, the essential roles played by engineering strategies in the property modulation of V-compounds are pinpointed to further explain the rationale behind their anomalous behavior. Apart from that, we further summarize the key theoretical and experimental results of some representative examples for tuning of properties. On the other hand, advances in characterization techniques are now sufficiently mature that they can be relied upon to understand the reaction mechanism of V-compounds by tracing real-time transformation and structural changes at the atomic scale during their working state. The mechanistic insights covered in this Account could be used as a fundamental guidance for several key strategies in electrode materials design in terms of dimension, morphology, composition, and architecture that govern the rate and degree of chemical reaction.

Proton Insertion Promoted a Polyfurfural/MnO2 Nanocomposite Cathode for a Rechargeable Aqueous Zn-MnO2 Battery

Rechargeable aqueous Zn-MnO₂ batteries using a mild electrolyte have attracted considerable interest because of their high output voltage, high safety, low cost, and environmental friendliness. However, poor cycling stability remains a significant issue for their applications. Equally, the energy storage mechanism involved is still controversial thus far. Herein, porous polyfurfural/MnO₂ (PFM) nanocomposites are prepared via a facile one-step method. When tested in a rechargeable aqueous Zn-MnO₂ cell, the PFM nanocomposites deliver high specific capacity, considerable rate performance, and excellent long-term cyclic stability. Based on the experimental results, the role of the hydrated basic zinc sulfate layer being linked to the cycling stability of the aqueous rechargeable zinc-ion batteries is revealed. The mechanistic details of the insertion reaction based on the H⁺ ion storage mechanism are proposed, which plays a crucial role in maintaining the cycling performance of the rechargeable aqueous Zn-MnO₂ cell. We expect that this work will provide an insight into the energy storage mechanism of MnO₂ in aqueous systems and pave the way for the design of long-term cycling stable electrode materials for rechargeable aqueous Zn-MnO₂ batteries.

Boosting Zn-Ion Storage Performance of Bronze-Type VO2 via Ni-Mediated Electronic Structure Engineering

Aqueous rechargeable zinc-ion batteries are emerging as attractive alternatives for post-lithium-ion batteries. However, their electrochemical performances are restricted by the narrow working window of materials in aqueous electrolytes. Herein, a Ni-mediated VO₂-B nanobelt [(Ni)VO₂] has been designed to optimize the intrinsic electronic structure of VO₂-B and thus achieve much more enhanced zinc-ion storage. Specifically, the Zn/(Ni)VO₂ battery yields a good rate capability (182.0 mA h g^-1 at 5 A g^-1) with a superior cycling stability (130.6 mA h g^-1 at 10 A g^-1 after 2000 cycles). Experimental and theoretical methods reveal that the introduction of Ni²⁺ in the VO₂ tunnel structure can effectively provide high surface reactivity and improve the intrinsic electronic configurations, thus resulting in good kinetics. Furthermore, H⁺ and Zn²⁺ cointercalation processes are determined via in situ X-ray diffraction and supported by ex situ characterizations. Additionally, quasi-solid-state Zn/(Ni)VO₂ soft-packaged batteries are assembled and provide flexibility in battery design for practical applications. The results provide insights into the interrelationships between the intrinsic electronic structure of the cathode and the overall electrochemical performance.

Graphene-like Vanadium Oxygen Hydrate (VOH) Nanosheets Intercalated and Exfoliated by Polyaniline (PANI) for Aqueous Zinc-Ion Batteries (ZIBs)

A new approach is employed to boost the electrochemical kinetics and stability of vanadium oxygen hydrate (VOH, V₂O₅·nH₂O) employed for aqueous zinc-ion battery (ZIB) cathodes. The methodology is based on electrically conductive polyaniline (PANI) intercalated-exfoliated VOH, achieved by preintercalation of an aniline monomer and its in situ polymerization within the oxide interlayers. The resulting graphene-like PANI-VOH nanosheets possess a greatly boosted reaction-controlled contribution to the total charge storage capacity, resulting in more material undergoing the reversible V⁵⁺ to V³⁺ redox reaction. The PANI-VOH electrode obtains an impressive capacity of 323 mAh g^-1 at 1 A g^-1, and state-of-the-art cycling stability at 80% capacity retention after 800 cycles. Because of the facile redox kinetics, the PANI-VOH ZIB obtains uniquely promising specific energy-specific power combinations: an energy of 216 Wh kg^-1 is achieved at 252 W kg^-1, while 150 Wh kg^-1 is achieved at 3900 W kg^-1. Electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) analyses indicate that with PANI-VOH nanosheets, there is a simultaneous decrease in the charge transfer resistance and a boost in the diffusion coefficient of Zn²⁺ (by a factor of 10-100) vs the VOH baseline. The strategy of employing PANI for combined intercalation-exfoliation may provide a broadly applicable approach for improving the performance in a range of oxide-based energy storage materials.

Tunable Layered (Na,Mn)V8O20·nH2O Cathode Material for High-Performance Aqueous Zinc Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) show promise for use in energy storage. However, the development of ZIBs has been plagued by the limited cathode candidates, which usually show low capacity or poor cycling performance. Here, a reversible Zn//(Na,Mn)V8O20·nH2O system is reported, the introduction of manganese (Mn) ions in NaV8O20 to form (Na,Mn)V8O20 exhibits an outstanding electrochemical performance with a capacity of 377 mA h g-1 at a current density of 0.1 A g-1. Through experimental and theoretical results, it is discovered that the outstanding performance of (Na,Mn)V8O20·nH2O is ascribed to the Mn2+/Mn3+-induced high electrical conductivity and Na+-induced fast migration of Zn2+. Other cathode materials derived from (Na,Mn)V8O20·nH2O by substituting Mn with Fe, Co, Ni, Ca, and K are explored to confirm the unique advantages of transition metal ions. With an increase in Mn content in NaV8O20, (Na0.33,Mn0.65)V8O20 ·nH2O can deliver a reversible capacity of 150 mA h g-1 and a capacity retention of 99% after 1000 cycles, which may open new opportunities for the development of high-performance aqueous ZIBs.

Building High Rate Capability and Ultrastable Dendrite-Free Organic Anode for Rechargeable Aqueous Zinc Batteries

Aqueous zinc-ion batteries (ZIBs) are an alternative energy storage system for large-scale grid applications compared with lithium-ion batteries, when the low cost, safety, and durability are taken into consideration. However, the reliability of the battery systems always suffers from the serious challenge of the large Zn dendrite formation and "dead Zn," thus bringing out the inferior cycling stability, and even cell shorting. Herein, a dendrite-free organic anode, perylene-3,4,9,10-tetracarboxylic diimide (PTCDI) polymerized on the surface of reduced graphene oxide (PTCDI/rGO) utilized in ZIBs is reported. Moreover, the theoretical calculations prove the reason for the low redox potential. Due to the protons and zinc ions coparticipant phase transfer mechanism and the high charge transfer capability, the PTCDI/rGO electrode provides superior rate capability (121 mA h g-1 at 5000 mA g-1, retaining the 95% capacity of that compared with 50 mA g-1) and a long cycling life span (96% capacity retention after 1500 cycles at 3000 mA g-1). In addition, the proton coparticipation energy storage mechanism of active materials is elucidated by various ex-situ methods.

Tuning the Kinetics of Zinc-Ion Insertion/Extraction in V2 O5 by In Situ Polyaniline Intercalation Enables Improved Aqueous Zinc-Ion Storage Performance

Rechargeable zinc-ion batteries (ZIBs) are emerging as a promising alternative for Li-ion batteries. However, the developed cathodes suffer from sluggish Zn²⁺ diffusion kinetics, leading to poor rate capability and inadequate cycle life. Herein, an in situ polyaniline (PANI) intercalation strategy is developed to facilitate the Zn²⁺ (de)intercalation kinetics in V₂ O₅ . In this way, a remarkably enlarged interlayer distance (13.90 Å) can be constructed alternatively between the VO layers, offering expediting channels for facile Zn²⁺ diffusion. Importantly, the electrostatic interactions between the Zn²⁺ and the host O^2- , which is another key factor in hindering the Zn²⁺ diffusion kinetics, can be effectively blocked by the unique π-conjugated structure of PANI. As a result, the PANI-intercalated V₂ O₅ exhibits a stable and highly reversible electrochemical reaction during repetitive Zn²⁺ insertion and extraction, as demonstrated by in situ synchrotron X-ray diffraction and Raman studies. Further first-principles calculations clearly reveal a remarkably lowered binding energy between Zn²⁺ and host O^2- , which explains the favorable kinetics in PANI-intercalated V₂ O₅ . Benefitting from the above, the overall electrochemical performance of PANI-intercalated V₂ O₅ electrode is remarkable improved, exhibiting excellent high rate capability of 197.1 mAh g^-1 at current density of 20 A g^-1 with capacity retention of 97.6% over 2000 cycles.

Constructing the Efficient Ion Diffusion Pathway by Introducing Oxygen Defects in Mn2O3 for High-Performance Aqueous Zinc-Ion Batteries

Mn-based cathodes are admittedly the most promising candidate to achieve the practical applications of aqueous zinc-ion batteries because of the high operating voltage and economic benefit. However, the design of Mn-based cathodes still remains challenging because of the vulnerable chemical architecture and strong electrostatic interaction that lead to the inferior reaction kinetics and rapid capacity decay. These intrinsic drawbacks need to be fundamentally addressed by rationally decorating the crystal structure. Herein, an oxygen-defective Mn-based cathode (Oc_u-Mn₂O₃) is designed via a doping low-valence Cu-ion strategy. The oxygen defect can modify the internal electric field of the material and enhance the substantial electrostatic stability by compensating for the nonzero dipole moment. With the merits of oxygen deficiency, the Oc_u-Mn₂O₃ electrode exhibits the significant diffusion coefficient in the range from 1 × 10^-6 to 1 × 10^-8, and good rate performance. In addition, the Oc_u-Mn₂O₃ maintains the highly reversible cyclic stability with the capacity retention of 88% over 600 cycles. The charge storage mechanism is explored as well, illustrating that the oxygen defects can improve the electrochemical active sites of H⁺ insertion, achieving a better charge-storage capacity than Mn₂O₃.

Anodic Oxidation Strategy toward Structure-Optimized V2O3 Cathode via Electrolyte Regulation for Zn-Ion Storage

The lack of suitable cathodes is one of the key reasons that impede the development of aqueous zinc-ion batteries. Because of the inherently unsuitable structure and inferior physicochemical properties, the low-valent V₂O₃ as Zn²⁺ host could not be effectively discharged. Herein, we demonstrate that V₂O₃ (theoretical capacity up to 715 mAh g^-1) can be utilized as a high-performance cathode material by an in situ anodic oxidation strategy. Through simultaneously regulating the concentration of the electrolyte and the morphology of the V₂O₃ sample, the ultraefficient anodic oxidation process of the V₂O₃ cathode was achieved within the first charging, and the mechanism was also schematically investigated. As expected, the V₂O₃ cathode with a hierarchical microcuboid structure achieved a nearly two-electron transfer process, enabling a high discharging capacity of 625 mAh g^-1 at 0.1 A g^-1 (corresponding to a high energy density of 406 Wh kg^-1) and cycling stability (100% capacity retention after 10 000 cycles). This work not only sheds light on the phase transition process of low-valent V₂O₃ but also exploits a method toward design of advanced cathode materials.

Freestanding Potassium Vanadate/Carbon Nanotube Films for Ultralong-Life Aqueous Zinc-Ion Batteries

Among various energy storage devices, aqueous zinc-ion batteries (ZIBs) have captured great attention due to their high safety and low cost. One of the most promising cathodes of aqueous ZIBs is layered vanadium-based compounds. However, they often suffer from the capacity decaying during cycling. Herein, we prepared KV₃O₈·0.75H₂O (KVO) and further incorporated it into a single-walled carbon nanotube (SWCNT) network, achieving freestanding KVO/SWCNT composite films. The KVO/SWCNT cathodes exhibit a Zn²⁺/H⁺ insertion/extraction mechanism, resulting in fast kinetics of ion transfer. In addition, the KVO/SWCNT composite films possess a segregated network structure, which offers the fast kinetics of electron transfer and guarantees an intimate contact between KVO and SWCNTs during cycling. As a result, the resultant batteries deliver a high capacity of 379 mAh g^-1, excellent rate capability, and an ultralong cycle life up to 10,000 cycles with a high capacity retention of 91%. In addition, owing to the high conductivity and flexibility of KVO/SWCNT films, flexible soft-packaged ZIBs based on KVO/SWCNT film cathodes were assembled and displayed stable electrochemical performance at different bending states.

An Overview and Future Perspectives of Rechargeable Zinc Batteries

Aqueous rechargeable zinc-based batteries have sparked a lot of enthusiasm in the energy storage field recently due to their inherent safety, low cost, and environmental friendliness. Although remarkable progress has been made in the exploration of performance so far, there are still many challenges such as low working voltage and dissolution of electrode materials at the material and system level. Herein, the central tenet is to establish a systematic summary for the construction and mechanism of different aqueous zinc-based batteries. Details for three major zinc-based battery systems, including alkaline rechargeable Zn-based batteries (ARZBs), aqueous Zn ion batteries (AZIBs), and dual-ion hybrid Zn batteries (DHZBs) are given. First, the electrode materials and energy storage mechanism of the three types of zinc-based batteries are discussed to provide universal guidance for these batteries. Then, the electrode behavior of zinc anodes and strategies to deal with problems such as dendrite and passivation are recommended. Finally, some challenge-oriented solutions are provided to facilitate the next development of zinc-based batteries. Combining the characteristics of zinc-based batteries with good use of concepts and ideas from other disciplines will surely pave the way for its commercialization.

Impacts of Oxygen Vacancies on Zinc Ion Intercalation in VO2

The aqueous zinc ion battery has emerged as a promising alternative technology for large-scale energy storage due to its low cost, natural abundance, and high safety features. However, the sluggish kinetics stemming from the strong electrostatic interaction of divalent zinc ions in the host crystal structure is one of challenges for highly efficient energy storage. Oxygen vacancies (V_O^••), in the present work, lead to a larger tunnel structure along the b axis, which improves the reactive kinetics and enhances Zn-ion storage capability in VO₂ (B) cathode. DFT calculations further support that V_O^•• in VO₂ (B) result in a narrower bandgap and lower Zn ion diffusion energy barrier compared to those of pristine VO₂ (B). V_O^••-rich VO₂ (B) achieves a specific capacity of 375 mAh g^-1 at a current density of 100 mA g^-1 and long-term cyclic stability with retained specific capacity of 175 mAh g^-1 at 5 A g^-1 over 2000 cycles (85% capacity retention), higher than that of VO₂ (B) nanobelts (280 mAh g^-1 at 100 mA g^-1 and 120 mAh g^-1 at 5 A g^-1, 65% capacity retention).

A chemically self-charging aqueous zinc-ion battery

Self-charging power systems integrating energy harvesting technologies and batteries are attracting extensive attention in energy technologies. However, the conventional integrated systems are highly dependent on the availability of the energy sources and generally possess complicated configuration. Herein, we develop chemically self-charging aqueous zinc-ion batteries with a simplified two-electrode configuration based on CaV₆O₁₆·3H₂O electrode. Such system possesses the capability of energy harvesting, conversion and storage simultaneously. It can be chemically self-recharged by the spontaneous redox reaction between the discharged cathode and oxygen from the ambient environment. Chemically self-recharged zinc-ion batteries display an initial open-circuit voltage of about 1.05 V and a considerable discharge capacity of about 239 mAh g⁻¹, indicating the excellent self-rechargeability. Impressively, such chemically self-charging zinc-ion batteries can also work well at chemical or/and galvanostatic charging hybrid modes. This work not only provides a route to design chemically self-charging energy storage, but also broadens the horizons of aqueous zinc-ion batteries.

Self-charging power systems integrating energy generation and storage are receiving consideration attention. Here the authors report an aqueous Zn-ion battery that can be self-recharged by the spontaneous redox reaction between cathode and oxygen from ambient environment without external power supply.

A High-Capacity Ammonium Vanadate Cathode for Zinc-Ion Battery

Given the advantages of being abundant in resources, environmental benign and highly safe, rechargeable zinc-ion batteries (ZIBs) enter the global spotlight for their potential utilization in large-scale energy storage. Despite their preliminary success, zinc-ion storage that is able to deliver capacity > 400 mAh g-1 remains a great challenge. Here, we demonstrate the viability of NH4V4O10 (NVO) as high-capacity cathode that breaks through the bottleneck of ZIBs in limited capacity. The first-principles calculations reveal that layered NVO is a good host to provide fast Zn2+ ions diffusion channel along its [010] direction in the interlayer space. On the other hand, to further enhance Zn2+ ion intercalation kinetics and long-term cycling stability, a three-dimensional (3D) flower-like architecture that is self-assembled by NVO nanobelts (3D-NVO) is rationally designed and fabricated through a microwave-assisted hydrothermal method. As a result, such 3D-NVO cathode possesses high capacity (485 mAh g-1) and superior long-term cycling performance (3000 times) at 10 A g-1 (~ 50 s to full discharge/charge). Additionally, based on the excellent 3D-NVO cathode, a quasi-solid-state ZIB with capacity of 378 mAh g-1 is developed.

Interfacial Engineering Coupled Valence Tuning of MoO3 Cathode for High-Capacity and High-Rate Fiber-Shaped Zinc-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have garnered the researchers' spotlight owing to its high safety, cost effectiveness, and high theoretical capacity of Zn anode. However, the availability of cathode materials for Zn ions storage is limited. With unique layered structure along the [010] direction, α-MoO₃ holds great promise as a cathode material for ZIBs, but its intrinsically poor conductivity severely restricts the capacity and rate capability. To circumvent this issue, an efficient surface engineering strategy is proposed to significantly improve the electric conductivity, Zn ion diffusion rate, and cycling stability of the MoO₃ cathode for ZIBs, thus drastically promoting its electrochemical properties. With the synergetic effect of Al₂ O₃ coating and phosphating process, the constructed Zn//P-MoO_{3- x} @Al₂ O₃ battery delivers impressive capacity of 257.7 mAh g^-1 at 1 A g^-1 and superior rate capability (57% capacity retention at 20 A g^-1 ), dramatically surpassing the pristine Zn//MoO₃ battery (115.8 mAh g^-1 ; 19.7%). More importantly, capitalized on polyvinyl alcohol gel electrolyte, an admirable capacity (19.2 mAh cm^-3 ) as well as favorable energy density (14.4 mWh cm^-3 ; 240 Wh kg^-1 ) are both achieved by the fiber-shaped quasi-solid-state ZIB. This work may be a great motivation for further research on molybdenum or other layered structure materials for high-performance ZIBs.

Aqueous zinc ion batteries: focus on zinc metal anodes

Despite the prevalence of lithium ion batteries in modern technology, the search for alternative electrochemical systems to complement the global battery portfolio is an ongoing effort. The search has resulted in numerous candidates, among which mildly acidic aqueous zinc ion batteries have recently garnered significant academic interest, mostly due to their inherent safety. As the anode is often fixed as zinc metal in these systems, most studies address the absence of a suitable cathode for reaction with zinc ions. This has led to aggressive research into viable intercalation cathodes, some of which have shown impressive results. However, many investigations often overlook the implications of the zinc metal anode, when in fact the anode is key to determining the energy density of the entire cell. In this regard, we aim to shed light on the importance of the zinc metal anode. This perspective offers a brief discussion of zinc electrochemistry in mildly acidic aqueous environments, along with an overview of recent efforts to improve the performance of zinc metal to extract key lessons for future research initiatives. Furthermore, we discuss the energy density ramifications of the zinc anode with respect to its weight and reversibility through simple calculations for numerous influential reports in the field. Finally, we offer some perspectives on the importance of optimizing zinc anodes as well as a future direction for developing high-performance aqueous zinc ion batteries.