Low-current-density stability of vanadium-based cathodes for aqueous zinc-ion batteries

Engineering vanadium vacancies to accelerate ion kinetics for high performance zinc ion battery

Vanadium dioxide (VO2) has attracted significant attention in aqueous zinc ion batteries (AZIBs) owing to their desirable theoretical specific capacity originated from multiple electrons transfer reaction and special crystal structure. However, sluggish electrochemical kinetics leads to inferior electrochemical storage performance. Herein, rich vanadium vacancies were introduced in tunnel VO2 to boost Zn2+ diffusion, increasing charge storage capacity and lengthen lifespan. The structural analyses of X-ray diffraction data refinement and X-ray photoelectron spectroscopy confirm that vanadium vacancies adjust the valence of vanadium, simultaneously shrink unit cell, thus improving structural stability. Theoretical calculations and the corresponding electrochemical measurements elucidate vacancy diffusion mechanism effectively enhance Zn2+ diffusion and electron transfer by reduced Zn2+ migration barrier and charge transfer activation energy. The resulted vacancy-rich cathode exhibits an improved electrochemical stability and kinetics, yielding unprecedented cycling performance at low currents (332 mA h g-1 after 200 cycles at 0.1 A g-1) and excellent rate capability of 184 mA h g-1 at 20 A g-1 as well as long-term stability at 20 A g-1. This work is anticipated to promote the development of next generation AZIBs and offer distinguishing inspiration for design of electrode systems.

Water-Deficient Interface Induced via Hydrated Eutectic Electrolyte with Restrictive Water to Achieve High-Performance Aqueous Zinc Metal Batteries

The development of aqueous zinc metal batteries (AZMBs) is hampered by dendrites and side reactions induced by reactive H2O. In this study, a hydrated eutectic electrolyte with restrictive water consisting of zinc trifluoromethanesulfonate (Zn(OTf)2), 1,3-propanediol (PDO), and water is developed to improve the stability of the anode/electrolyte interface in AZMBs via the formation of a water-deficient interface. Additionally, PDO participates in the Zn2+ solvation structure and inhibits the movement of water molecules. PDO also preferentially adsorbs along the Zn (100) plane, thereby inducing the formation of the organic/inorganic SEI layer that enables the cycle life of a Zn//Zn symmetric cell to reach 3000 h at 1 mA cm-2 and 1 mAh cm-2. Further, interfacial modulation by the eutectic electrolyte improves the cycling stability of Zn//V2O5 and Zn//VO2 cells. Particularly, the specific capacity of a Zn//V2O5 cell with the eutectic electrolyte is 1.7 times that of a cell with the 2M Zn(OTf)2 electrolyte, with a capacity retention of 93% after 100 cycles at 0.5 A g-1. This study provides a new perspective on the electrolyte modification strategies for AZMBs, highlighting the potential of PDO-8 electrolyte in developing aqueous energy storage devices with excellent cycling stability.

The Role of Ion-Polaron Electrostatic Attraction on Zn2+ Migration in α-V2O5 for Zinc Ion Battery: Insights from First-Principles Calculations

The migration of Zn2+ ions is significantly more challenging compared to that of Li+ ions within the same crystalline framework, leading to poor rate performance of zinc-ion batteries (ZIBs). Compared to Li+, the slower migration rate of Zn2+ is vaguely attributed to the stronger electrostatic interaction induced by Zn2+. Herein, the rule of how the size of the migration channel and electrostatic interaction affect Zn2+ and Li+ migration in α-V2O5 has been systematically investigated by first-principle calculations. It is found that expanding the layer spacing can facilitate Zn2+ migration. Once the layer spacing surpasses a certain threshold, further expansion does not lead to a continued reduction in the migration barrier. The local structure distortions caused by electron small polarons would lead to a decrease in migration channel size, which should have increased the energy barrier for Li+ and Zn2+ migration. However, interestingly, the electron small polarons decrease the energy barriers, which would be attributed to the ion-polaron electrostatic attraction. The higher activation barriers for the migration of Zn2+ ions compared to those of Li+ ions can be rationalized by the specific ion-polaron electrostatic attraction for Zn2+. Moreover, the comparative strength of the polaron-ion electrostatic attraction for alkali and alkaline earth metal ions is unveiled. Overall, this study provides theoretical insights into the role of ion-polaron electrostatic attraction on ion migration.

Hydrogen/Electron Amphiphilic Bi-Functional Water Molecular Inactivator-Assisted Interface Stabilization in Highly Reversible Zn Metal Batteries

Continuous hydrogen-bond-network in aqueous electrolytes can lead to uncontrollable hydrogen transfer, and combining the interfacial parasitic electron consumption cause the side reaction in aqueous zinc metal batteries (AZMBs). Herein, hydrogen/electron amphiphilic bi-functional 1,5-Pentanediol (PD) molecule was introduced to stabilize the electrode/electrolyte interface. Stronger proton affinity of -OH in PD can break bulk-H2O hydrogen-bond-network to inhibit the activity of water, and electron affinity can enhance electron acceptation capability, which ensures that PD is preferentially bound to electrode material over H2O. Besides, the participation of PD in the Zn2+ solvation structure reduces water content at the solid-liquid interface and promotes uniform deposition process by optimizing Zn2+ de-solvation energy. Accordingly, dense and vertical zinc texture based on intrinsic steric hindrance effect of PD and formed SEI protective layer to induce stable Zinc anode-electrolyte interface. Moreover, an organic-inorganic shielding water layer was formed at the cathode side to suppress vanadium dissolution in vanadium Oxide. Consequently, Zn//Zn symmetric cell could cycle for more than 5600 hours at 1 mAh cm-2@1 mA cm-2 (more than 250 hours at 50 °C). Besides, the VO2 and I2 cathode all achieved stable cycling performance and former pouch cell could reach average capacity of 0.13 Ah.

Minimizing Zn Loss Through Dual Regulation for Reversible Zinc Anode Beyond 90% Utilization Ratio

Large-scale energy storage devices experience explosive development in response to the increasing energy crisis. Zinc ion batteries featuring low cost, high safe, and environment friendly are considered promising candidates for next-generation energy storage devices. However, their practical application suffers from the limited anode lifespan under a high zinc utilization ratio, which can be attributed to aggravated Zn loss caused by zinc conversion reactions and "dead" Zn. Herein, n-propyl alcohol is reported to stabilize the Zn anode under the high depth of discharge through dual regulation of water activity inhibition and zinc-ion plating regulation. The modified electrolyte exhibits a 76.43% cut in corrosion current benefited from low water activity and benefits SEI surface. The "dead" Zn content is also reduced by 26 times as a result of dendrite-free zinc ion plating. Thus, the highly reversible zinc plating/stripping with 99.62% CE is achieved for ≈3600 cycles. Moreover, the lifespan of Zn/Zn cells is greatly increased even under a high depth of discharge (310 h, 90%DOD and 120 h, 95.18% DOD). In Zn/NH4V4O10 full cells, the improved anode reversibility enables a remarkable capacity retention of 92.16% after 400 cycles with a low N/P ratio of 2.5.

Electrochemically and chemically in-situ interfacial protection layers towards stable and reversible Zn anodes

Aqueous zinc metal batteries (AZMBs) have received widespread attention for large-scale sustainable energy storage due to their low toxicity, safety, cost-effectiveness. However, the technology and industrialization of AZMBs are greatly plagued by issues of Zn anode such as persistent dendrites and parasitic side reactions, resulting in rapid capacity degradation or battery failure. Electrochemically or chemically in-situ interfacial protection layers have very good self-adaption features for stability and reversibility of Zn anodes, which can also be well matched to current battery manufacturing. However, the in-situ interfacial strategies are far from the practical design for effective Zn anodes. Therefore, a targeted academic discussion that serves the development of this field is very urgent. Herein, the comprehensive insights on electrochemically and chemically in-situ interfacial protection layers for Zn anode were proposed in this review. It showcased a systematic summary of research advances, followed by detailed discussions on electrochemically and chemically in-situ interfacial protection strategies. More importantly, several crucial issues facing in-situ interfacial protection strategies have been further put forward. The final section particularly highlighted a systematic and rigorous scheme for precise designing highly stable and reversible in-situ interface for practical zinc anodes.

Engineering of Charge Density at the Anode/Electrolyte Interface for Long-Life Zn Anode in Aqueous Zinc Ion Battery

The aqueous zinc ion battery emerges as the promising candidate applied in large-scale energy storage system. However, Zn anode suffers from the issues including Zn dendrite, Hydrogen evolution reaction and corrosion. These challenges are primarily derived from the instability of anode/electrolyte interface, which is associated with the interfacial charge density distribution. In this context, the recent advancements concentrating on the strategies and mechanisms to regulate charge density at the Zn anode/electrolyte interface are summarized. Different characterization techniques for charge density distribution have been analysed, which can be applied to assess the interfacial zinc ion transport. Additionally, the charge density regulations at the Zn anode/electrolyte interface are discussed, elucidating their roles in modulating electrostatic interactions, electric field, structure of solvated zinc ion and electric double layer, respectively. Finally, the perspectives and challenges on the further research are provided to establish the stable anode/electrolyte interface by focusing on charge density modifications, which is expected to facilitate the development of aqueous zinc ion battery.

Building electrode/electrolyte interphases in aqueous zinc batteries via self-polymerization of electrolyte additives

Aqueous zinc batteries offer promising prospects for large-scale energy storage, yet their application is limited by undesired side reactions at the electrode/electrolyte interface. Here, we report a universal approach for the in situ building of an electrode/electrolyte interphase (EEI) layer on both the cathode and the anode through the self-polymerization of electrolyte additives. In an exemplified Zn||V2O5·nH2O cell, we reveal that the glutamate additive undergoes radical-initiated electro-polymerization on the cathode and polycondensation on the anode, yielding polyglutamic acid-dominated EEI layers on both electrodes. These EEI layers effectively mitigate undesired interfacial side reactions while enhancing reaction kinetics, enabling Zn||V2O5·nH2O cells to achieve a high capacity of 387 mAh g-1 at 0.2 A g-1 and maintain >96.3% capacity retention after 1500 cycles at 1 A g-1. Moreover, this interphase-forming additive exhibits broad applicability to varied cathode materials, encompassing VS2, VS4, VO2, α-MnO2, β-MnO2 and δ-MnO2. The methodology of utilizing self-polymerizable electrolyte additives to construct robust EEI layers opens a novel pathway in interphase engineering for electrode stabilization in aqueous batteries.

Novel in situ SEI fabrication on Zn anodes for ultra-high current density tolerance enabled by electrical excitation–conjugation of iminoacetonitriles

Electroplating enriched IDAN on zinc surface, forming IDA to complex with Zn2+, thus creating an in situ SEI. This SEI optimized Zn2+ transport, shielded water molecules, and stabilized the anode interface, enhancing long-term performance.

Constructing Quasi-Single Ion Conductors by a β-Cyclodextrin Polymer to Stabilize Zn Anode

Aqueous Zn-ion batteries (AZIBs) are promising for the next-generation large-scale energy storage. However, the Zn anode remains facing challenges. Here, we report a cyclodextrin polymer (P-CD) to construct quasi-single ion conductor for coating and protecting Zn anodes. The P-CD coating layer inhibited the corrosion of Zn anode and prevented the side reaction of metal anodes. More important is that the cyclodextrin units enabled the trapping of anions through host-guest interactions and hydrogen bonds, forming a quasi-single ion conductor that elevated the Zn ion transference number (from 0.31 to 0.68), suppressed the formation of space charge regions and hence stabilized the plating/striping of Zn ions. As a result, the Zn//Zn symmetric cells coated with P-CD achieved a 70.6 times improvement in cycle life at high current densities of 10 mA cm-2 with 10 mAh cm-2. Importantly, the Zn//K1.1V3O8 (KVO) full-cells with high mass loading of cathode materials and low N/P ratio of 1.46 reached the capacity retention of 94.5 % after 1000 cycles at 10 A g-1; while the cell without coating failed only after 230 cycles. These results provide novel perspective into the control of solid-electrolyte interfaces for stabilizing Zn anode and offer a practical strategy to improve AZIBs.

Simultaneous Inhibition of Vanadium Dissolution and Zinc Dendrites by Mineral-Derived Solid-State Electrolyte for High-Performance Zinc Metal Batteries

Designing solid electrolyte is deemed as an effective approach to suppress the side reaction of zinc anode and active material dissolution of cathodes in liquid electrolytes for zinc metal batteries (ZMBs). Herein, kaolin is comprehensively investigated as raw material to prepare solid electrolyte (KL-Zn) for ZMBs. As demonstrated, KL-Zn electrolyte is an excellent electronic insulator and zinc ionic conductor, which presents wide voltage window of 2.73 V, high ionic conductivity of 5.08 mS cm-1, and high Zn2+ transference number of 0.79. For the Zn//Zn cells, superior cyclic stability lasting for 2200 h can be achieved at 0.2 mA cm-2. For the Zn//NH4V4O10 batteries, stable capacity of 245.8 mAh g-1 can be maintained at 0.2 A g-1 after 200 cycles along with high retention ratio of 81 %, manifesting KL-Zn electrolyte contributes to stabilize the crystal structure of NH4V4O10 cathode. These satisfying performances can be attributed to the enlarged interlayer spacing, zinc (de)solvation-free mechanism and fast diffusion kinetics of KL-Zn electrolyte, availably guaranteeing uniform zinc deposition for zinc anode and reversible zinc (de)intercalation for NH4V4O10 cathode. Additionally, this work also verifies the application possibility of KL-Zn electrolyte for Zn//MnO2 batteries and Zn//I2 batteries, suggesting the universality of mineral-based solid electrolyte.

The zinc ion concentration dynamically regulated by an ionophore in the outer Helmholtz layer for stable Zn anode

The Zn dendrite limits the practical application of aqueous zinc-ion batteries in the large-scale energy storage systems. To suppress the growth of Zn dendrites, a zinc ionophore of hydroxychloroquine (defined as HCQ) applied in vivo treatment is investigated as the electrolyte additive. HCQ dynamically regulates zinc ion concentration in the outer Helmholtz layer, promoting even Zn plating at the anode/electrolyte interface. This is evidenced by the scanning electron microscopy, which delivers planar Zn plating after cycling. It is further supported by the X-ray diffraction spectroscopy, which reveals the growth of Zn (002) plane. Additionally, the reduced production of H2 during Zn plating/stripping is detected by the in-situ differential electrochemical mass spectrometry (DEMS), which shows the resistance of Zn (002) to hydrogen evolution reaction. The mechanism of dynamic regulation for zinc ion concentration is demonstrated by the in-situ optical microscopy. The hydrated zinc ion can be further plated more rapidly to the uneven location than the case in other regions, which is resulted from the dynamic regulation for zinc ion concentration. Therefore, the uniform Zn plating is formed. A cycling life of 1100 h is exhibited in the Zn||Zn symmetric cell at 1.6 mA cm-2 with the capacity of 1.6 mAh cm-2. The Zn||Cu battery exhibits a cycling life of 200 cycles at 4 mA cm-2 with a capacity of 4 mAh cm-2 and the average Coulombic efficiency is larger than 99 %. The Zn||VO2 battery with HCQ modified electrolyte can operate for 1500 cycles at 4 A g-1 with a capacity retention of 90 %. This strategy in the present work is wished to advance the development of zinc-ion batteries for practical application.

Concentration polarization induced phase rigidification in ultralow salt colloid chemistry to stabilize cryogenic Zn batteries

The breakthrough in electrolyte technology stands as a pivotal factor driving the battery revolution forward. The colloidal electrolytes, as one of the emerging electrolytes, will arise gushing research interest due to their complex colloidal behaviors and mechanistic actions at different conditions (aqueous/nonaqueous solvents, salt concentrations etc.). Herein, we show "beyond aqueous" colloidal electrolytes with ultralow salt concentration and inherent low freezing points to investigate its underlying mechanistic principles to stabilize cryogenic Zn metal batteries. Impressively, the "seemingly undesired" concentration polarization at the interface would disrupt the coalescence stability of the electrolyte, leading to a mechanically rigid interphase of colloidal particle-rich layer, positively inhibiting side reactions on either side of the electrodes. Importantly, the multi-layered pouch cells with cathode loading of 10 mg cm-2 exhibit undecayed capacity at various temperatures, and a relatively high capacity of 50 mAh g-1 could be well maintained at -80 °C.

Regulation of Zn2+ Solvation Configuration in Aqueous Batteries via Selenium-Substituted Crown Ether Engineering

The efficient utilization of the metallic Zn in rechargeable aqueous Zn-ion batteries (RAZBs) struggle to suffer from parasitic Zn dendrite formation, hydrogen evolution reactions as well as severe interfacial degradation at high areal capacity loadings. This study thus proposes to employ the modified crown ether as an aqueous electrolyte additive to regulate the Zn2+ desolvation kinetic and facilitates the horizontally oriented (002) deposition of Zn, extending the lifespan of both the symmetric cell and full cell models. Specifically, zincophilic cyano and hydrophobic selenium atoms are incorporated into the crown ether supramolecule to enhance Zn2+ coordination and desolvation capability. The addition of 4-cyanobenzo-21-crown-7-selenium at a low concentration of 0.5 wt.% effectively mitigates hydrogen evolution and Zn corrosion caused by water, promoting the oriented deposition of Zn2+. The Zn||V2O5 full cell prototype, assembled with the areal capacity loadings of 2 mAh cm-2 and N/P ratio of 2.95, exhibits negligible capacity fading at 2.0A g-1 for 300 cycles, highlighting the commercial feasibility of supramolecular macrocycles additive for practical RAZBs applications.

Engineering Interlayer Space and Composite of Square-Shaped V2O5 by PVP-Assisted Polyaniline Intercalation and Graphene for Aqueous Zinc-Ion Batteries

V2O5 undergoes irreversible phase transition and collapse of layered structure during the Zn2+ insertion/extraction, which severely limits its application as a cathode for aqueous zinc-ion batteries (AZIBs). Herein, a synergistic strategy of conductive polyaniline insertion and graphene composite was proposed to boost the Zn2+ storage performance of the V2O5 cathode. A square-shaped polyaniline (PANI)-intercalated and graphene-composited vanadium oxide (GO/PANI-PVP/V2O5) structure was successfully synthesized via an in situ oxidation/insertion polymerization combined with a hydrothermal method. The results showed that PANI intercalation and the composite of graphene combined with layered V2O5, enabling reversible intercalation of Zn2+/H+. The insertion of conjugated PANI not only increases the lattice spacing of V2O5, providing a channel for rapid transport of Zn2+, but also increases the storage sites for charges through doping/dedoping processes and redox conversion reactions. GO/PANI-PVP/V2O5 delivers an excellent specific capacity (495 mA h g-1 at 0.1 A g-1), wonderful rate capability (208 mA h g-1 at 30 A g-1), and good cycling stability (93% after 4000 cycles). Our results provide a new approach for adjusting the valence states, interlayer spacing, and rational design of organic-inorganic compound materials for different functional materials.

Advanced electrolytes for high-performance aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) have garnered significant attention in the realm of large-scale and sustainable energy storage, primarily owing to their high safety, low cost, and eco-friendliness. Aqueous electrolytes, serving as an indispensable constituent, exert a direct influence on the electrochemical performance and longevity of AZIBs. Nonetheless, conventional aqueous electrolytes often encounter formidable challenges in AZIB applications, such as the limited electrochemical stability window and the zinc dendrite growth. In response to these hurdles, a series of advanced aqueous electrolytes have been proposed, such as "water-in-salt" electrolytes, aqueous eutectic electrolytes, molecular crowding electrolytes, and hydrogel electrolytes. This comprehensive review commences by presenting an in-depth overview of the fundamental compositions, principles, and distinctive characteristics of various advanced aqueous electrolytes for AZIBs. Subsequently, we systematically scrutinizes the recent research progress achieved with these advanced aqueous electrolytes. Furthermore, we summarizes the challenges and bottlenecks associated with these advanced aqueous electrolytes, along with offering recommendations. Based on the optimization of advanced aqueous electrolytes, this review outlines future directions and potential strategies for the development of high-performance AZIBs. This review is anticipated to provide valuable insights into the development of advanced electrolyte systems for the next generation of stable and sustainable multi-valent secondary batteries.

A Comprehensive Review of the Mechanism and Modification Strategies of V2O5 Cathodes for Aqueous Zinc-Ion Batteries

Aqueous zinc-ion batteries (AZIBs) have attracted wide attention due to their affordability, inherent safety, and environmental friendliness, recognized as one of the most ideal next generation energy storage systems. Vanadium-based cathodes have garnered significant interest in the field of AZIBs, presenting vast application prospects in stationary energy storage. Among them, layered vanadium pentoxide (V2O5) stands out a promising material due to its high theoretical capacity, drawing extensive research efforts. However, the research on V2O5 is greatly hindered by issues such as cathode material dissolution, low conductivity, and byproduct formation. Therefore, this review starts from the characteristics of V2O5 materials, summarizes the energy storage mechanism of Zn2+, and elucidates the main challenges faced by V2O5. Subsequently, current modification strategies are summarized based on these challenges, along with the relationships between the issues and strategies. Finally, further challenges and directions faced by each modification strategy are proposed. It is expected to provide researchers with information to quickly familiarize themselves with the current applications and inspiring prospects of V2O5 in AZIBs.

Regulating Zn2+ Migration-Diffusion Behavior by Spontaneous Cascade Optimization Strategy for Long-Life and Low N/P Ratio Zinc Ion Batteries

Parasitic side reactions and dendrite growth on zinc anodes are formidable issues causing limited lifetime of aqueous zinc ion batteries (ZIBs). Herein, a spontaneous cascade optimization strategy is first proposed to regulate Zn2+ migration-diffusion behavior. Specifically, PAPE@Zn layer with separation-reconstruction properties is constructed in situ on Zn anode. In this layer, well-soluble poly(ethylene oxide) (PEO) can spontaneously separation to bulk electrolyte and weaken the preferential coordination between H2O and Zn2+ to achieve primary optimization. Meanwhile, poor-soluble polymerized-4-acryloylmorpholine (PACMO) is reconstructed on Zn anode as hydrophobic flower-like arrays with abundant zincophilic sites, further guiding the de-solvation and homogeneous diffusion of Zn2+ to achieve the secondary optimization. Cascade optimization effectively regulates Zn2+ migration-diffusion behavior, dendrite growth and side reactions of Zn anode are negligible, and the stability is significantly improved. Consequently, symmetrical cells exhibit stability over 4000 h (1 mA cm-2). PAPE@Zn//NH4 +-V2O5 full cells with a high current density of 15 A g-1 maintains 72.2 % capacity retention for 12000 cycles. Even better, the full cell demonstrates excellent performance of cumulative capacity of 2.33 Ah cm-2 at ultra-low negative/positive (N/P) ratio of 0.6 and a high mass-loading (~17 mg cm-2). The spontaneous cascade optimization strategy provides novel path to achieve high-performance and practical ZIBs.

Cations-Pillared and Polyaniline-Encapsulated Vanadate Cathode for High-Performance Aqueous Zinc-Ion Batteries

Layered vanadium-based oxides have emerged as highly promising candidates for aqueous zinc-ion batteries (AZIBs) due to their open-framework layer structure and high theoretical capacity among the diverse cathode materials investigated. However, the susceptibility to structural collapse during charge-discharge cycling severely hampers their advancement. Herein, we propose an effective strategy to enhance the cycling stability of vanadium oxides. Initially, the structural integrity of the host material is significantly reinforced by incorporating bi-cations Na+ and NH4 + as "pillars" between the V2O5 layers (NaNVO). Subsequently, surface coating with polyaniline (PA) is employed to further improve the conductivity of the active material. As anticipated, the assembled Zn//NaNVO@PA cell exhibits a remarkable discharge capacity of 492 mAh g-1 at 0.1 A g-1 and exceptional capacity retention up to 89.2 % after 1000 cycles at a current density of 5 A g-1. Moreover, a series of in-situ and ex-situ characterization techniques were utilized to investigate both Zn ions insertion/extraction storage mechanism and the contribution of polyaniline protonation process towards enhancing capacity.

Flash Joule Heating Synthesis of Layer-Stacked Vanadium Oxide/Graphene Hybrids within Seconds for High-Performance Aqueous Zinc-Ion Batteries

Vanadium oxides have been regarded as highly promising cathodes for aqueous zinc-ion batteries (ZIBs). However, obtaining high-performance vanadium oxide-based cathodes suitable for industrial application remains a significant challenge due to the need for cost-effective, straightforward, and efficient preparation methods. Herein, we present a facile and rapid synthesis of a composite cathode, consisting of layer-stacked VO2/V2O5 and graphene-like carbon nanosheets, in just 2.5 s by treating the commercial V2O5 powder via a flash Joule heating strategy. When employed as the cathode for ZIBs, the resulting composite delivers a comparable rate capacity of 459 mA h g-1 at 0.2 A g-1 and remarkable cycle stabilities of 355.5 mA h g-1 after 2500 cycles at 1.0 A g-1 and 169.5 mA h g-1 after 10,000 cycles at 10 A g-1, respectively. Further electrochemical analysis reveals that the impressive performance is attributed to the accelerated charge transfer and the alleviated structure degradation, facilitated by the abundant sites and a built-in electric field of the layer-stacked VO2/V2O5 heterostructure, as well as the excellent conductivity of graphene-like carbon nanosheets. This work introduces a unique approach for ultrafast and low-cost fabrication of high-performance vanadium oxide-based composite cathodes toward efficient ZIBs.

Anchored VN Quantum Dots Boosting High Capacity and Cycle Durability of Na3V2(PO4)3@NC Cathode for Aqueous Zinc-Ion Battery and Organic Sodium-Ion Battery

Na3V2(PO4)3 is a promising high-voltage cathode for aqueous zinc-ion batteries (ZIBs) and organic sodium-ion batteries (SIBs). However, the poor rate capability, specific capacity, and cycling stability severely hamper it from further development. In this work, Na3V2(PO4)3 (NVP) with vanadium nitride (VN) quantum dots encapsulated by nitrogen-doped carbon (NC) nanoflowers (NVP/VN@NC) are manufactured as cathode using in situ nitridation, carbon coating, and structural adjustment. The outer NC layer increases the higher electronic conductivity of NVP. Furthermore, VN quantum dots with high theoretical capacity not only improve the specific capacity of pristine NVP, but also serve as abundant "pins" between NVP and NC to strengthen the stability of NVP/VN@NC heterostructure. For Zn-ion storage, these essential characteristics allow NVP/VN@NC to attain a high reversible capacity of 135.4 mAh g-1 at 0.1 A g-1, and a capacity retention of 91% after 2000 cycles at 5 A g-1. Meanwhile, NVP/VN@NC also demonstrates to be a stable cathode material for SIBs, which can reach a high reversible capacity of 124.5 mAh g-1 at 0.1 A g-1, and maintain 92% of initial capacity after 11000 cycles at 5 A g-1. This work presents a feasible path to create innovative high-voltage cathodes with excellent reaction kinetics and structural stability.

Vanadium-Based Cathodes for Aqueous Zinc-Ion Batteries: Mechanisms, Challenges, and Strategies

ConspectusZinc-ion batteries (ZIBs) are highly promising for large-scale energy storage because of their safety, high energy/power density, low cost, and eco-friendliness. Vanadium-based compounds are attractive cathodes because of their versatile structures and multielectron redox processes (+5 to +3), leading to high capacity. Layered structures or 3-dimensional open tunnel frameworks allow easy movement of zinc-ions without breaking the structure apart, offering superior rate-performance. However, challenges such as dissolution and phase transformation hinder the long-term stability of vanadium-based cathodes in ZIBs. Although significant research has been dedicated to understanding the mechanisms and developing high-performance vanadium-based cathodes, uncertainties still exist regarding the critical mechanisms of energy storage and dissolution, the actual active phase and the specific optimization strategy. For example, it is unclear whether materials such as α-V2O5, VO2, and V2O3 serve as the active phase or undergo phase transformations during cycling. Additionally, the root cause of V-dissolution and the role of byproducts such as Zn3(OH)2V2O7·2H2O in ZIBs are debated.In this account, we aim to outline a clear and comprehensive roadmap for V-based cathodes in ZIBs. On the basis of our studies, we analyzed intrinsic crystal structures and their correlation with performance to guide the design of V-based materials with high-capacity and high-stability for ZIBs. Then, we revealed the underlying mechanisms of energy storage and instability, enabling more effective design and optimization of V-based cathodes. After identifying the key challenges, we proposed effective design principles to achieve high cycling performance of V-based cathodes and outlined future development directions toward their practical application. Vanadium-based compounds include [VO4] tetrahedrons, [VO5] square pyramids, and [VO6] octahedra, which are connected through a cocorner, coedge and coplane. The [VO4] tetrahedron is inactive, and the [VO5] square pyramid is unstable in aqueous solutions because water attacks the exposed vanadium, whereas stable [VO6] octahedra are desirable because of their ability to reduce from +5 to +3 with minimal structural distortion. Therefore, high-performance vanadium-based oxides in ZIBs should maintain intact [VO6] octahedra while avoiding [VO4] tetrahedra or [VO5] square pyramids. The energy storage mechanism involves H2O/H+/Zn2+ coinsertion. The existence of interlayer water in V-based cathodes significantly improves the rate and cycling performance by expanding galleries, screening Zn2+ electrostatically via solvation, reducing ion diffusion energy barriers, and increasing layer flexibility. The insertion of H+/Zn2+ and the instability of V-based cathodes lead to the formation of byproducts such as basic zinc salts (i.e., Zn4SO4(OH)6·nH2O) and dead vanadium (Zn3(OH)2V2O7·2H2O), whose reversibility strongly affects long-term stability. To increase the cycling stability of vanadium-based cathodes, strategies such as electrolyte modulation and coating have been proposed to decrease water attack on the surface of V-oxides, thereby affecting the formation of byproducts. Additionally, in situ electrochemical transformation, ion preintercalation, and ion exchange were explored to prepare intrinsically stable V-based cathodes with enhanced performance. Furthermore, future research should focus on revealing atomic-scale mechanisms through advanced in situ characterization and theoretical calculations, enhancing rate-performance by facilitating ion/electron diffusion, promoting cycling stability by developing highly stable cathodes and refining interface engineering, and scaling up vanadium-based cathodes for practical ZIB applications.

Promoting Preferential Zn (002) Deposition with a Low-Concentration Electrolyte Additive for Highly Reversible Zn-Ion Batteries

Aqueous zinc-ion batteries have promising potential as energy storage devices due to their low cost and environmental friendliness. However, their development has been hindered by zinc dendrite formation and parasitic side reactions. Herein, we introduce a low-concentration sodium benzoate (NaBZ) electrolyte additive to stabilize the electrode-electrolyte interface and promote deposition on the Zn (002) crystal plane. From experimental characterization and computational analyses, NaBZ was found to adsorb on the Zn surface and inhibit side reactions while guiding homogeneous Zn deposition on the (002) plane. Consequently, Zn|Zn symmetric cells with the NaBZ additive cycled stably for over 1000 h at a current density of 0.5 mA cm-2 and an areal capacity of 0.5 mAh cm-2, while Zn|Cu cells showed excellent reversibility with a Coulombic efficiency of 99.05%. Moreover, Zn|Na0.33V2O5 full cells achieve a high specific capacity of 124 mAh g-1 while cycling for 600 h at 2 A g-1. These findings present a low-cost electrolyte modification strategy for reversible zinc-ion batteries.

Transforming Undesired Corrosion Products into a Nanoflake-Array Functional Layer: A Gelatin-Assistant Modification Strategy for High Performance Zn Battery Anodes

As corrosion products of Zn anodes in ZnSO4 electrolytes, Zn4SO4 (OH)6·xH2O with loose structure cannot suppress persistent side reactions but can increase the electrode polarization and induce dendrite growth, hindering the practical applications of Zn metal batteries. In this work, a functional layer is built on the Zn anode by a gelatin-assistant corrosion and low-temperature pyrolysis method. With the assistant of gelatin, undesired corrosion products are converted into a uniform nanoflake array comprising ZnO coated by gelatin-derived carbon on Zn foil (denoted Zn@ZnO@GC). It is revealed that the gelatin-derived carbons not only enhance the electron conductivity, facilitate Zn2+ desolvation, and boost transport/deposition kinetics, but also inhibit the occurrence of hydrogen evolution and corrosion reactions on the zincophilic Zn@ZnO@GC anode. Moreover, the 3D nanoflake array effectively homogenizes the current density and Zn2+ concentration, thus inhibiting the formation of dendrites. The symmetric cells using the Zn@ZnO@GC anodes exhibit superior cycling performance (over 7000 h at 1 mA cm-2/1 mAh cm-2) and without short-circuiting even up to 25 mAh cm-2. The Zn@ZnO@GC||NaV3O8 full cell works stably for 5000 cycles even with a limited N/P ratio of ≈5.5, showing good application prospects.

CNT Composite β-MnO2 with Fiber Cable Shape as Cathode Materials for Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) have developed into one of the most attractive materials for large-scale energy storage owing to their advantages such as high energy density, low cost, and environmental friendliness. Nevertheless, the sluggish diffusion kinetics and inherent impoverished conductivity affect their practical application. Herein, the β-MnO2 composited with carbon nanotubes (CNT@M) is prepared through a simple hydrothermal approach as a high-performance cathode for AZIBs. The CNT@M electrode exhibits excellent cycling stability, in which the maximum specific discharge capacity is 259 mA h g-1 at 3 A g-1, and there is still 220 mA h g-1 after 2000 cycles. The specific capacity is obviously better than that of β-MnO2 (32 mA h g-1 after 2000 cycles). The outstanding electrochemical performance of the battery is inseparable from the structural framework of CNT and inherent high conductivity. Furthermore, CNT@M can form a complex conductive network based on CNTs to provide excellent ion diffusion and charge transfer. Therefore, the active material can maintain a long-term cycle and achieve stable capacity retention. This research provides a reasonable solution for the reliable conception of Mn-based electrodes and indicates its potential application in high-performance AZIB cathode materials.

Engineering Interphasial Chemistry for Zn Anodes in Aqueous Zinc Ion Batteries

Aqueous zinc ion batteries (AZIBs) have emerged as promising candidates for large-scale energy storage systems during post lithium-ion era, drawing attention for their environmental-friendliness, cost-effectiveness, high safety, and minimal manufacturing constraints. However, the long-standing roadblock to their commercialization lies in the dendrite growth and parasitic reactions (hydrogen evolution reaction and water-induced corrosion) of the metallic zinc anode, which strongly depends on the complicated interphasial chemistries. This review, with a focus on optimizing the zinc anode/electrolyte interphase, begins by elucidating the intrinsic factor of zinc ions' migration, diffusion, nucleation, electro-crystallization, and growth of the zinc nucleus in AZIBs, along with the underlying scientific principles. Then the electrochemical theories pertinent to the plating behavior of the interphase is systematically clarified, thereby enriching the understanding of how anode structure and electrolyte design principles relate to the electrode interphase. Accordingly, the rational strategies emphasizing structural engineering of the zinc anode and electrolyte have been summarized and discussed in detail. The mechanisms, advances, drawbacks, and future outlook of these strategies are analyzed for the purpose of fabricating a chemically and electrochemically stable interphase. Finally, the challenging perspectives and major directions of zinc anode are proposed. This review is expected to shed light on developing high-performance Zn anodes for use in sustainable AZIBs.

Biomimetic Superstructured Interphase for Aqueous Zinc-Ion Batteries

The practical application of aqueous zinc-ion batteries (AZIBs) is greatly challenged by rampant dendrites and pestilent side reactions resulting from an unstable Zn-electrolyte interphase. Herein, we report the construction of a reliable superstructured solid electrolyte interphase for stable Zn anodes by using mesoporous polydopamine (2D-mPDA) platelets as building blocks. The interphase shows a biomimetic nacre's "brick-and-mortar" structure and artificial transmembrane channels of hexagonally ordered mesopores in the plane, overcoming the mechanical robustness and ionic conductivity trade-off. Experimental results and simulations reveal that the -OH and -NH groups on the surface of artificial ion channels can promote rapid desolvation kinetics and serve as an ion sieve to homogenize the Zn2+ flux, thus inhibiting side reactions and ensuring uniform Zn deposition without dendrites. The 2D-mPDA@Zn electrode achieves an ultralow nucleation potential of 35 mV and maintains a Coulombic efficiency of 99.8% over 1500 cycles at 5 mA cm-2. Moreover, the symmetric battery exhibits a prolonged lifespan of over 580 h at a high current density of 20 mA cm-2. This biomimetic superstructured interphase also demonstrates the high feasibility in Zn//VO2 full cells and paves a new route for rechargeable aqueous metal-ion batteries.

Ultra-thin amphiphilic hydrogel electrolyte for flexible zinc-ion paper batteries

The paper-like ZIBs can be folded and unfolded using the Miura folding technique, enhancing the areal energy density by a factor of 18.