Ultra-High Mass-Loading Cathode for Aqueous Zinc-Ion Battery Based on Graphene-Wrapped Aluminum Vanadate Nanobelts

Scalable fabrication of free-standing and integrated electrodes with commercial level of areal capacity for aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) present a highly promising avenue for the deployment of grid-scale energy storage systems. However, the electrodes fabricated through conventional methodologies not only suffer from insufficient mass loadings, but also are susceptible to exfoliation under deformations. Herein, a scalable and cost-effective freezing-thawing method is developed to construct free-standing and integrated electrode, comprising H11Al2V6O23.2, carboxymethyl cellulose, and carbon nanotubes. Benefiting from the synergistic effect of these components, the resultant electrode exhibits superior flexibility and robustness, large tensile strength, exceptional electrical conductivity, and favorable electrolyte wettability. Under a large mass loading of 8 mg cm-2 (corresponding to a negative/positive electrode capacity ratio of 2.09), the electrode achieves remarkable capacity of 345.2 mAh/g (2.76 mAh cm-2) at 0.2 A/g and maintains 235.2 mAh/g (1.88 mAh cm-2) at 4 A/g, while sustaining an impressive capacity retention of 97.7 % over 5000 cycles. These considerably outperform conventional electrodes employing traditional binders. Even at an elevated mass loading of 14 mg cm-2 or when operated at a low temperature of - 30 °C, the electrode continues to deliver excellent electrochemical performance (e.g., extraordinary areal capacity of 4.32 mAh cm-2). In addition, the electrode owns outstanding tolerance to external forces. This research contributes to our understanding of the pivotal challenges within the realm of AZIB technology.

Separator Design Strategies to Advance Rechargeable Aqueous Zinc Ion Batteries

With the increasing demand for low-cost and high-safety portable batteries, aqueous zinc-ion batteries (ZIBs) have been regarded as a potential alternative to the lithium-ion batteries, bringing about extensive research dedicated in the exploration of high-performance and highly reversible ZIBs. Although separators are generally considered as non-active components in conventional research on ZIBs, advanced separators designs seem to offer effective solutions to the majority of issues within ZIBs system. These issues encompass concerns related to the zinc anode, cathode, and electrolyte. Initially, we delve into the origins and implications of various inherent problems within the ZIBs system. Subsequently, we present the latest research advancements in addressing these challenges through separators engineering. This includes a comprehensive, detailed exploration of various strategies, coupled with instances of advanced characterizations to provide a more profound insight into the mechanisms that influence the separators. Finally, we undertake a multi-criteria evaluation, based on application standards for diverse substrate separators, while proposing guiding principles for the optimal design of separators in zinc batteries. This review aims to furnish valuable guidance for the future development of advanced separators, thereby nurturing progress in the field of ZIBs.

Converting commercial Bi2O3 particles into Bi2O2Se@Bi4O8Se nanosheets for "rocking chair" zinc-ion batteries

The development of a low-cost, high-capacity, and insertion-type anode is key for promoting "rocking chair" zinc-ion batteries. Herein, commercial Bi2O3 (BiO) particles are transformed into Bi2O2Se@Bi4O8Se (BiOSe) nanosheets through a simple selenylation process. The change in morphology from commercial BiO particle to BiOSe nanosheet leads to an increased specific surface area of the material. The enhanced electronic/ionic conductivity results in its excellent electrochemical kinetics. Ex situ XRD and XPS tests prove the intercalation-type mechanism of BiO and BiOSe as well as the superior electrochemical reversibility of BiOSe compared to BiO. Furthermore, the H+/Zn2+ co-insertion mechanism of BiOSe is revealed. This makes BiOSe to have low discharge plateaus of 0.38/0.68 V, a high reversible capacity of 182 mA h g-1 at 0.1 A g-1, and a long cyclic life of 500 cycles at 1 A g-1. Besides, the BiOSe//MnO2 "rocking chair" zinc-ion battery offers a high capacity of ≈90 mA h g-1 at 0.2 A g-1. This work provides a reference for turning commercial material into high-performance anode for "rocking chair" zinc-ion batteries.

Effectively Modulating Oxygen Vacancies in Flower-Like δ-MnO2 Nanostructures for Large Capacity and High-Rate Zinc-Ion Storage

In recent years, manganese-based oxides as an advanced class of cathode materials for zinc-ion batteries (ZIBs) have attracted a great deal of attentions from numerous researchers. However, their slow reaction kinetics, limited active sites and poor electrical conductivity inevitably give rise to the severe performance degradation. To solve these problems, herein, we introduce abundant oxygen vacancies into the flower-like δ-MnO2 nanostructure and effectively modulate the vacancy defects to reach the optimal level (δ-MnO2-x-2.0). The smart design intrinsically tunes the electronic structure, guarantees ion chemisorption-desorption equilibrium and increases the electroactive sites, which not only effectively accelerates charge transfer rate during reaction processes, but also endows more redox reactions, as verified by first-principle calculations. These merits can help the fabricated δ-MnO2-x-2.0 cathode to present a large specific capacity of 551.8 mAh g-1 at 0.5 A g-1, high-rate capability of 262.2 mAh g-1 at 10 A g-1 and an excellent cycle lifespan (83% of capacity retention after 1500 cycles), which is far superior to those of the other metal compound cathodes. In addition, the charge/discharge mechanism of the δ-MnO2-x-2.0 cathode has also been elaborated through ex situ techniques. This work opens up a new pathway for constructing the next-generation high-performance ZIBs cathode materials.

Combining Structural Modification and Electrolyte Regulation to Enable Long-Term Cyclic Stability of MoO3-x @TiO2 as Cathode for Aqueous Zn-Ion Batteries

Orthorhombic MoO3 (α-MoO3 ) with multivalent redox couple of Mo6+ /Mo4+ and layered structure is a promising cathode for rechargeable aqueous Zn-ion batteries (AZIBs). However, pure α-MoO3 suffers rapid capacity decay due to the serious dissolution and structural collapse. Meanwhile, the growth of byproduct and dendrite on the anode also lead to the deterioration of cyclic stability. This article establishes the mechanism of proton intercalation into MoO3 and proposes a joint strategy combining structural modification with electrolyte regulation to enhance the cyclic stability of MoO3 without sacrificing the capacity. In ZnSO4 electrolyte with Al2 (SO4 )3 additive, TiO2 coated oxygen-deficient α-MoO3 (MoO3-x @TiO2 ) delivers a reversible capacity of 93.2 mA h g-1 at 30 A g-1 after 5000 cycles. The TiO2 coating together with the oxygen deficiency avoids structural damage while facilitating proton diffusion. Besides, the additive of Al2 (SO4 )3 , acting as a pump, continuously supplements protons through dynamic hydrolysis, avoiding the formation of Zn4 SO4 (OH)6 ·xH2 O byproducts at both MoO3-x @TiO2 and Zn anode. In addition, Al2 (SO4 )3 additive facilitates uniform deposition of Zn owing to the tip-blocking effect of Al3+ ion. The study demonstrates that the joint strategy is beneficial for both cathode and anode, which may shed some light on the development of AZIBs.

Few-Atomic-Layered Co-Doped BiOBr Nanosheet: Free-Standing Anode with Ultrahigh Mass Loading for "Rocking Chair" Zinc-Ion Battery

Insertion host materials are considered as a candidate to replace metallic Zn anode. However, the high mass loading anode with good electrochemical performances is reported rarely. Herein, a few-atomic-layered Co-doped BiOBr nanosheet (Co-UTBiOBr) is prepared via one-step hydrothermal method and a free-standing flexible electrode consisting of Co-UTBiOBr and CNTs is designed. Ultrathin nanosheet (3 atomic layers) and CNTs accelerate Zn²⁺ and electron transfer respectively. The Co-doping is conducive to the reduced Zn²⁺ diffusion barrier, the improved volume expansion after Zn²⁺ intercalation, and the enhanced electronic conductivity of BiOBr, verified by experimental and theoretical studies. An insertion-conversion mechanism is proposed according to ex situ characterizations. Benefiting from many advantages, Co-UTBiOBr displays a high capacity of 150 mAh g^-1 at 0.1 A g^-1 and a long-term cyclic life with ≈100% capacity attention over 3000 cycles at 1 A g^-1 . Remarkably, excellent electrochemical performances are maintained even at an ultrahigh mass loading of 15 mg cm^-2 . Co-UTBiOBr//MnO₂ "rocking chair" zinc-ion battery exhibits a stable capacity of ≈130 mAh g^-1 at 0.2 A g^-1 during cyclic test and its flexible quasi-solid-state battery shows outstanding stability under various bending states. This work provides a new idea for designing high mass loading anode.

Highly Loaded and Binder-Free Molybdenum Trioxide Cathode Material Prepared Using Multi-Arc Ion Plating for Aqueous Zinc Ion Batteries

Aqueous zinc-ion batteries (ZIBS) are becoming more popular as the use of energy storage devices grows, owing to advantages such as safety and an abundant zinc supply. In this study, molybdenum powder was loaded directly on carbon fiber cloth (CFC) via multi-arc ion plating to obtain Mo@CFC, which was then oxidatively heated in a muffle furnace for 20 min at 600 °C to produce high mass loading α-MoO₃@CFC (α-MoO₃ of 12-15 mg cm^-2). The cells were assembled with α-MoO₃@CFC as the cathode and showed an outstanding Zn²⁺ storage capacity of 200.8 mAh g^-1 at 200 mA g^-1 current density. The capacity retention rate was 92.4 % after 100 cycles, along with an excellent cycling performance of 109.8 mAh g^-1 following 500 cycles at 1000 mA g^-1 current density. Subsequently, it was shown that CFC-loaded α-MoO₃ cathode material possessed significantly improved electrochemical performance when compared to a cell constructed from commercial MoO₃ using conventional slurry-based electrode methods. This work presents a novel yet simple method for preparing highly loaded and binder-free cathodic materials for aqueous ZIBs. The results suggest that the highly loaded cathode material with a high charge density may be potentially employed for future flexible device assembly and applications.

Microcrystalline Hybridization Enhanced Coal-Based Carbon Anode for Advanced Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are regarded as a kind of promising candidate for large-scale energy storage technology. The development of advanced carbon anodes with high Na-storage capacity and initial Coulombic efficiency (ICE) from low cost, resources abundant precursors is critical for SIBs. Here, a carbon microcrystalline hybridization route to synthesize hard carbons with extensive pseudo-graphitic regions from lignite coal with the assistance of sucrose is proposed. Employing the cross-linked interaction between sucrose and lignite coal to generate carbon-based hybrid microcrystalline states, the obtained hard carbons possess pseudo-graphitic dominant phases with large interlayer spaces that facilitate Na ion's storage and transportation, as well as fewer surface defects that guarantee high ICE. The LCS-73 with an optimum cross-link demonstrates the highest Na-storage capacity of 356 mAh g^-1 and an ICE of 82.9%. The corresponding full-cell delivers a high energy density of 240 Wh kg^-1 (based on the mass of anode and cathode materials) and excellent rate capability of 106 mAh g^-1 at 10 C in addition to outstanding cycle performance with 80% retention over 500 cycles at 2 C. The proposed work offers an efficient route to develop high-performance, low-cost carbon-based anode materials with potential application for advanced SIBs.

Dual intercalation of inorganics-organics for synergistically tuning the layer spacing of V2O5·nH2O to boost Zn2+ storage for aqueous zinc-ion batteries

Possessing a 2D zinc-ion transport channel, layered vanadium oxides have become good candidates as cathode materials for aqueous rechargeable zinc-ion batteries (ARZIBs). Tuning the lamellar structure of vanadium oxides to enhance their zinc-ion storage is a great challenge. In the present study, we proposed and investigated a "co-intercalation mechanism" in which Mg²⁺ and polyaniline (PANI) were simultaneously intercalated into the layers of hydrated V₂O₅ (MgVOH/PANI) by a one-step hydrothermal method. Inorganic-organic co-intercalation could tune the layer spacing of VOH, and this combination played a synergistic role in enhancing the zinc-ion storage in MgVOH/PANI. It showed an extremely large layer spacing of 14.2 Å, specific capacity of up to 412 mA h g^-1 at 0.1 A g^-1, and the capacity retention rate could reach 98% after 1000 cycles. PANI itself has a zinc-storage capacity, and Mg²⁺ intercalated with PANI can improve the conductivity of the material and enhance its stability. Further first-principles calculations clearly revealed the structural changes and improved electrochemical performance of vanadium oxides. This method of inorganic and organic co-regulation of the VOH structure opens a new strategy for tuning the lamellar structure of layered materials to boost their electrochemical performances.

A Comprehensive Understanding of Interlayer Engineering in Layered Manganese and Vanadium Cathodes for Aqueous Zn-ion Batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) hold a budding technology for large-scale stationary energy storage devices due to their inherent safety, cost-effectiveness, eco-friendly, and acceptable electrochemical performance. However, developing a cathode material with fast kinetics and durable structural stability for Zn 2+ intercalation is still an arduous challenge. Compared with other cathode materials, layered manganese/vanadium (Mn/V) oxides that feature merits of adjustable interlayer spacing and considerable specific capacity have attracted much interest in AZIBs. However, the intrinsic sluggish reaction kinetics, inferior electrical conductivity, and notorious dissolution of active materials still obstruct the realization of their full potentials. Interlayer engineering of pre-intercalation is regarded as an effective solution to overcome these problems. In this review, we start from the crystal structure and reaction mechanism of layered Mn/V oxide cathodes to critical issues and recent progress in interlayer engineering. Finally, some future perspectives are outlined for the development of high-performance AZIBs.

Phosphate interphase reinforced amorphous vanadium oxide cathode materials for aqueous zinc ion batteries

Phosphate interphase of anisotropy amorphous vanadium oxide (VO-PO@CNPs) can prevent structural reorganization and enrich ions diffusion paths for aqueous zinc ion batteries cathode materials. VO-PO@CNPs cathodes appear a high initial...

A rapid in situ electrochemical transformation of the biphase Zn3(OH)2V2O7·2H2O/NH4V4O10 composite for high capacity and long cycling life aqueous rechargeable zinc ion batteries

The Zn3(OH)2V2O7·2H2O/NH4V4O10 nanobelts transform into Zn3V2O7(OH)2-based materials by an in situ electrochemical conversion, which act as an active cathode for high capacity aqueous zinc ion batteries.

Engineering Interlayer Space of Vanadium Oxide by Pyridinesulfonic Acid-Assisted Intercalation of Polypyrrole Enables Enhanced Aqueous Zinc-Ion Storage

By adjusting the structure of vanadium oxides, their electrochemical performances as cathode materials for aqueous rechargeable zinc-ion batteries (ARZIBs) can be improved effectively. Due to the layered structure and high specific capacity of V₂O₅, many guests (like metal ions and conducting polymers) intercalated and regulated the structure to enhance its electrochemical properties. Polypyrrole (PPy) has attracted people's attention due to its good conductive ability. However, the intercalation of PPy into a lamellar structure of hydrated V₂O₅ (VOH) has rarely been achieved as a cathode material for ARZIBs. Herein, we developed a pyridinesulfonic acid (PSA)-assisted approach to intercalate PPy into the interplanar spacing of VOH under acidic conditions, and the sample is denoted as VOH-PPy (PSA). The presence of protic acid can improve the electrical conductivity of the polymer and enhance the oxidation of VOH, making the polymerization of pyrrole easier. Furthermore, the nitrogen-containing groups in PSA can interact with vanadium to further expand the layer space of VOH, and the sulfonic groups can facilitate the polymerization of pyrrole. The addition of the PSA results in an ultralarge interlayer spacing of 15.8 Å. VOH-PPy (PSA) delivers an excellent specific capacity of up to 422 mAh·g^-1 at 0.1 A·g^-1 and a stable cycle performance of 165 mAh·g^-1 after 5000 cycles at 10 A·g^-1. This work not only realizes PPy expanding the lamellar structure of VOH but also provides feasibility for improving the electrochemical properties of VOH as a cathode material for ARZIBs by intercalating conductive polymers.

High-Performance Aqueous Zinc Batteries Based on Organic/Organic Cathodes Integrating Multiredox Centers

Organic cathode materials with redox-active sites and flexible structure are promising for developing aqueous zinc ion batteries with high capacity and large output power. However, the energy storage of most organic hosts relies on the coordination/incoordination reaction between Zn²⁺ /H⁺ and a single functional group, which result in inferior capacity, low discharge platform, and structural instability. Here, the lead is taken in in situ electrodepositing stable poly(1,5-naphthalenediamine, 1,5-NAPD) as interlayer and excellent conductive poly(para-aminophenol, pAP) skin onto nanoporous carbon in sequence for the structural optimization of organic/organic cathodes, designated as C@multi-layer polymer. In situ analyses, electrochemical measurements, and theoretical calculation prove that both CO and CN active groups can act as a strong electron donor as well as Zn²⁺ host during the discharging process. Benefiting from the synergistic effect of the double organic layers, C@multi-layer polymer delivers high capacity, long lifespan, and excellent capacity reservation even at large discharge current and commercial mass loading (>10 mg cm^-2 ). Introducing multiredox centers into one organic composites will provide new insights into designing advanced Zn-organic batteries.

Tailoring double-layer aromatic polymers with multi-active sites towards high performance aqueous Zn-organic batteries

Unlike most reported organic-inorganic cathodes, the organic-organic zinc hosts can fully exploit the flexible structures and various redox chemistries of the organics. Herein, nanoporous carbon electrodeposited with a wrapped poly(meta-aminophenol, 3-AP) sandwich layer and a good conductive poly(para-aminophenol, 4-AP) skin, designated as a C@poly(3-AP)/poly(4-AP) cathode, has been synthesized for the first time via a novel two-step electrodeposition method. The synergistic effect of the double-layer polymers endows the C@poly(3-AP)/poly(4-AP) cathode with an ultrahigh specific capacity, excellent rate performance and long-term lifespan that are superior to those of the pristine C@poly(3-AP) and C@poly(4-AP) electrodes. Also, the strong electron donor capabilities of the multiple active sites (CO and CN) in the hetero-structural organic cathode can exhibit symmetrical bending to host inserted Zn ions during the discharge process, which opens up new opportunities to construct advanced Zn-organic batteries.

Tremella-like Hydrated Vanadium Oxide Cathode with an Architectural Design Strategy toward Ultralong Lifespan Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising systems for energy storage due to their operational safety, low cost, and environmental friendliness. However, the development of suitable cathode materials is plagued by the sluggish dynamics of Zn²⁺ with strong electrostatic interaction. Herein, an Al³⁺-doped tremella-like layered Al_0.15V₂O₅·1.01H₂O (A-VOH) cathode material with a large pore diameter and high specific surface area is demonstrated to greatly boost electrochemical performance as ZIB cathodes. Resultant ZIBs with a 3 M Zn(CF₃SO₃)₂ electrolyte deliver a high specific discharge capacity of 510.5 mAh g^-1 (0.05 A g^-1), and an excellent energy storage performance is well maintained with a specific capacity of 144 mAh g^-1 (10 A g^-1) even after ultralong 10,000 cycles. The decent electrochemical performance roots in the novel tremella-like structure and the interlayer of Al³⁺ ions and water molecules, which could improve the electrochemical reaction kinetics and structural long cycle stability. Furthermore, the assembled coin-type cells could power a light-emitting diode (LED) lamp for 2 days. We believed that the design philosophy of unique morphology with abundant active sites for Zn²⁺ storage will boost the development of competitive cathodes for high-performance aqueous batteries.

Polyaniline-expanded the interlayer spacing of hydrated vanadium pentoxide by the interface-intercalation for aqueous rechargeable Zn-ion batteries

The metal ions or conductive macromolecules intercalated hydrated vanadium oxides for aqueous Zn-ion batteries (AZIBs) have received increasing attention in recent years. The strategy for the preparation of the intercalated hydrated vanadium oxides has been achieved great advances but is still a huge challenge. In this contribution, we develop an interface-intercalation method to synthesize the polyaniline-intercalated hydrated vanadium pentoxide (V₂O₅·nH₂O), denoted as PANI-VOH, as the cathode materials for AZIBs. The prepared PANI-VOH exhibits a 3D sponge-like morphology and the surface area of 190 m²·g^-1. The interlayer spacing of VOH is expanded to be 14.1 Å, which provides a lot of channels for the rapidly reversible (de)intercalation of Zn²⁺ ions. The coin-typed Zn//PANI-VOH battery shows the specific discharge capacity of 363 mAh·g^-1 at 0.1 A·g^-1 and stable cycling performance. Furthermore, the specific capacity remains 131 mAh·g^-1 after 2000 cycles at 5 A·g^-1, and the energy density is calculated to be 275 Wh·kg^-1 at 78 W·kg^-1 on the mass of PANI-VOH. The achieved values are comparable to or even much higher than that of the most state-of-the-art V-based cathode materials for AZIBs. The PANI intercalation can shorten the pathways and facilitate the transports for the migration of ions and electrons. Our finding guides a novel strategy for the intercalation of PANI into the layered materials to adjust their interlayer spacing, which exhibits super ions migration efficiency, as the cathode materials for AZIBs and even other multivalent ions batteries.

Saccharin Anion Acts as a "Traffic Assistant" of Zn2+ to Achieve a Long-Life and Dendritic-Free Zinc Plate Anode

Due to the great advantages of low cost, high capacity, and excellent safety, the Zn metal is a promising candidate material for rechargeable aqueous battery systems. However, its practical applications have been restricted by the uncontrollable dendrite growth and electrode side reactions (such as corrosion, passivation, and hydrogen evolution reactions) during the plating process. Herein, we reveal that the dendrite growth would expose the electrode to more highly active tips, exacerbating the passivation of the electrode and the decomposition of the electrolyte by in situ optical microscopies. We propose a low-cost, nontoxic, low-concentration (less than 1 g/L), and effective electrolyte additive, saccharin sodium, which can guide an even Zn deposition without obvious electrode side reactions in the charge/discharge process. The saccharin anion acts as a "traffic assistant" of Zn²⁺ and demonstrates its great potential for practical application. The assembled Zn symmetrical battery shows an excellent cycling performance at a high current density and capacity (an extremely long cycle life over 3800 h is obtained at 5 mA/cm² and 8 mA h/cm², and 20 mA/cm² and 5 mA h/cm² show a lifetime over 800 h), and the full cell (coupled to an AC electrode) presents a stable cycle life with a capacity retention of 86.4% even after 8000 cycles at 5 mA/cm². The saccharin sodium proposed in this work is promising to solve the anode problems in advanced Zn batteries.

Carbon Quantum Dots Promote Coupled Valence Engineering of V2 O5 Nanobelts for High-Performance Aqueous Zinc-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have acquired the researchers' curiosity owing to their harmlessness, cost effectiveness and high theoretical capacity of Zn anode. However, desirable cathode materials with high-capacity and high-rate are still scarce. In this work, the formation of carbon quantum dots induced vanadium pentoxide nanobelts was demonstrated via a facile one-step hydrothermal method for ZIBs. It exhibited an excellent Zn ion storage capacity of 460 mA h g^-1 at 0.1 A g^-1 , superior rate capability and stable cycling performance (above 85 % capacity retention over 1500 cycles at 4 A g^-1 ). The electrochemical kinetics and zinc ion storage mechanism were also considered. An efficient architecture-coupled valence engineering in the hybrid cathode was proposed to improve the electric conductivity, Zn ion diffusion rate, and cycling stability for ZIBs. This work may be a great motivation for further research on V₂ O₅ or other vanadium-based materials for high-performance ZIBs.

Organic-Inorganic Superlattices of Vanadium Oxide@Polyaniline for High-Performance Magnesium-Ion Batteries

Rechargeable magnesium batteries (RMBs) have attracted significant attention owing to the high energy density and economic viability. However, the lack of suitable cathode materials, owing to the high polarizability of divalent Mg-ion and slow Mg-ion diffusion, hinders the development of RMBs. V₂ O₅ is a promising RMBs cathode material, but its limited interlayer spacing is unfavorable for the rapid diffusion of Mg²⁺ , demonstrating unsatisfactory electrochemical performance. In this study, the superlattices of V₂ O₅ and polyaniline (PANI) with expanded interlayer spacing are assembled as the cathode material for RMBs. The intercalation of PANI in the interlayer region of V₂ O₅ significantly improves the reversible capacities, Mg²⁺ diffusion kinetics, and cycling performance of the PVO cathode. Furthermore, RMBs with PVO as the cathode and Mg metal as the anode deliver high specific capacities. The introduced polyaniline layer not only expands the interlayer spacing of V₂ O₅ , but also increases the electrical conductivity. Moreover, ex situ XRD characterization indicates that PVO does not undergo obvious phase transformation with the continuous insertion of Mg²⁺ , which may be ascribed to the π-conjugated chains of PANI that give flexibility to the structure to improve cycling stability. This study demonstrates that designing organic-inorganic superlattices is an efficient strategy for developing high-performance cathode materials for RMBs.

Interface Engineering via Ti3C2Tx MXene Electrolyte Additive toward Dendrite-Free Zinc Deposition

Zinc metal batteries have been considered as a promising candidate for next-generation batteries due to their high safety and low cost. However, their practical applications are severely hampered by the poor cyclability that caused by the undesired dendrite growth of metallic Zn. Herein, Ti₃C₂T_x MXene was first used as electrolyte additive to facilitate the uniform Zn deposition by controlling the nucleation and growth process of Zn. Such MXene additives can not only be absorbed on Zn foil to induce uniform initial Zn deposition via providing abundant zincophilic-O groups and subsequently participate in the formation of robust solid-electrolyte interface film, but also accelerate ion transportation by reducing the Zn²⁺ concentration gradient at the electrode/electrolyte interface. Consequently, MXene-containing electrolyte realizes dendrite-free Zn plating/striping with high Coulombic efficiency (99.7%) and superior reversibility (stably up to 1180 cycles). When applied in full cell, the Zn-V₂O₅ cell also delivers significantly improved cycling performances. This work provides a facile yet effective method for developing reversible zinc metal batteries.

Inorganic Colloidal Electrolyte for Highly Robust Zinc-Ion Batteries

Zinc-ion batteries (ZIBs) is a promising electrical energy storage candidate due to its eco-friendliness, low cost, and intrinsic safety, but on the cathode the element dissolution and the formation of irreversible products, and on the anode the growth of dendrite as well as irreversible products hinder its practical application. Herein, we propose a new type of the inorganic highly concentrated colloidal electrolytes (HCCE) for ZIBs promoting simultaneous robust protection of both cathode/anode leading to an effective suppression of element dissolution, dendrite, and irreversible products growth. The new HCCE has high Zn²⁺ ion transference number (0.64) endowed by the limitation of SO₄^2-, the competitive ion conductivity (1.1 × 10^-2 S cm^-1) and Zn²⁺ ion diffusion enabled by the uniform pore distribution (3.6 nm) and the limited free water. The Zn/HCCE/α-MnO₂ cells exhibit high durability under both high and low current densities, which is almost 100% capacity retention at 200 mA g^-1 after 400 cycles (290 mAh g^-1) and 89% capacity retention under 500 mA g^-1 after 1000 cycles (212 mAh g^-1). Considering material sustainability and batteries' high performances, the colloidal electrolyte may provide a feasible substitute beyond the liquid and all-solid-state electrolyte of ZIBs.

In Situ Electrochemical Transformation Reaction of Ammonium-Anchored Heptavanadate Cathode for Long-Life Aqueous Zinc-Ion Batteries

Rechargeable aqueous zinc-ion batteries (ZIBs) are promising portable and large-scale grid energy storage devices, as they are safe and economical. However, developing suitable ZIB cathode materials with excellent cycling performance characteristics remains a challenging task. Here, ammonium heptavanadate (NH₄)₂V₇O₁₆·3.2H₂O (NHVO) nanosquares with mixed-valence V⁵⁺/V⁴⁺ as a cathode are developed for high-performance ZIBs. The layered NHVO shows a capacity of 362 mA h g^-1 at 0.05 A g^-1, with a high energy density of 263.5 W h kg^-1. It exhibits an initial specific capacity of 250.7 mA h g^-1 at a current density of 4 A g^-1 and retains 255 mA h g^-1 capacity after 1000 charge/discharge cycles. The V₇O₁₆-based cathode was demonstrated with a phase transition to the V₂O₅-based cathode upon initial cycling. Moreover, the in situ generated V₂O₅-based cathodes show excellent electrochemical properties, which provide a different perspective on the electrochemical reaction of cathode materials for aqueous ZIBs.

Electrolyte Concentration Regulation Boosting Zinc Storage Stability of High-Capacity K0.486V2O5 Cathode for Bendable Quasi-Solid-State Zinc Ion Batteries

Vanadium-based cathodes have attracted great interest in aqueous zinc ion batteries (AZIBs) due to their large capacities, good rate performance and facile synthesis in large scale. However, their practical application is greatly hampered by vanadium dissolution issue in conventional dilute electrolytes. Herein, taking a new potassium vanadate K_0.486V₂O₅ (KVO) cathode with large interlayer spacing (~ 0.95 nm) and high capacity as an example, we propose that the cycle life of vanadates can be greatly upgraded in AZIBs by regulating the concentration of ZnCl₂ electrolyte, but with no need to approach "water-in-salt" threshold. With the optimized moderate concentration of 15 m ZnCl₂ electrolyte, the KVO exhibits the best cycling stability with ~ 95.02% capacity retention after 1400 cycles. We further design a novel sodium carboxymethyl cellulose (CMC)-moderate concentration ZnCl₂ gel electrolyte with high ionic conductivity of 10.08 mS cm^-1 for the first time and assemble a quasi-solid-state AZIB. This device is bendable with remarkable energy density (268.2 Wh kg^-1), excellent stability (97.35% after 2800 cycles), low self-discharge rate, and good environmental (temperature, pressure) suitability, and is capable of powering small electronics. The device also exhibits good electrochemical performance with high KVO mass loading (5 and 10 mg cm^-2). Our work sheds light on the feasibility of using moderately concentrated electrolyte to address the stability issue of aqueous soluble electrode materials.

“Double guarantee mechanism” of Ca2+-intercalation and rGO-integration ensures hydrated vanadium oxide with high performance for aqueous zinc-ion batteries

Ca²⁺-Intercalated hydrated V₂O₅/rGO (CaVOH/rGO) is synthesized via a facile hydrothermal process and applied as a cathode for ARZIBs with an admirable specific capacity (409 mA h g⁻¹ at 0.05 A g⁻¹) and excellent energy density (381 W h kg⁻¹).

Anode Materials for Aqueous Zinc Ion Batteries: Mechanisms, Properties, and Perspectives

Aqueous Zn-ion batteries (ZIBs) are promising safe energy storage systems that have received considerable attention in recent years. Based on the electrochemical behavior of Zn²⁺ in the charging and discharging process, herein we review the research progress on anode materials for use in aqueous ZIBs based on two aspects: Zn deposition and Zn²⁺ intercalation. To date, Zn dendrite, corrosion, and passivation issues have restricted the development of aqueous ZIBs. However, many strategies have been developed, including structural design, interface protection of the Zn anode, Zn alloying, and using polymer electrolytes. The main aim is to stabilize the Zn stripping/plating layer and limit side reactions. Zn²⁺-intercalated anodes, with a high Zn²⁺ storage capacity to replace the current metal Zn anode, are also a potential option. Finally, some suggestions have been put forward for the subsequent optimization strategy, which are expected to promote further development of aqueous ZIBs.

2D Sandwiched Nano Heterostructures Endow MoSe2 /TiO2- x /Graphene with High Rate and Durability for Sodium Ion Capacitor and Its Solid Electrolyte Interphase Dependent Sodiation/Desodiation Mechanism

Nano heterostructures relying on their versatile construction and the breadth of combined functionality have shown great potential in energy storage fields. Herein, 2D sandwiched MoSe₂ /TiO_{2- x} /graphene nano heterostructures are designed by integrating structural and functional effects of each component, aiming to address the rate capability and cyclic stability of MoSe₂ for sodium ion capacitors (SICs). These 2D nano heterostructures based on graphene platform can facilitate the interfacial electron transport, giving rise to fast reaction kinetics. Meanwhile, the 2D open structure induces a large extent of surface capacitive contribution, eventually leading to a high rate capability (415.2 mAh g^-1 @ 5 A g^-1 ). An ultrathin oxygen deficient TiO_{2- x} layer sandwiched in these nano heterostructures provides a strong chemical-anchoring regarding the products generated during the sodiation/desodiation process, securing the entire cyclic stability. The associated sodiation/desodiation mechanism is revealed by operando and ex situ characterizations, which exhibits a strong solid electrolyte interphase (SEI) dependence. The simulations verify the dependent sodiation products and enhanced heterostructural chemical-anchoring. Assembled SICs based on these nano heterostructures anode exhibit high initial Coulombic efficiency, energy/power densities, and long cycle life, shedding new light on the design of nano heterostructure electrodes for high performance energy storage application.

High-Capacity Layered Magnesium Vanadate with Concentrated Gel Electrolyte toward High-Performance and Wide-Temperature Zinc-Ion Battery

Aqueous zinc-ion batteries (ZIBs) have emerged as the most promising alternative energy storage system, but the development of a suitable cathode and the issues of Zn anodes have remained challenging. Herein, an effective strategy of high-capacity layered Mg_0.1V₂O₅·H₂O (MgVO) nanobelts together with a concentrated 3 M Zn(CF₃SO₃)₂ polyacrylamide gel electrolyte was proposed to achieve a durable and practical ZIB system. By adopting the designed concentrated gel electrolyte which not only inherits the high-voltage window and wide operating temperature of the concentrated electrolyte but also addresses the Zn dendrite formation problem, the prepared cathode exhibits an ultrahigh capacity of 470 mAh g^-1 and a high rate capability of 345 mAh g^-1 at 5.0 A g^-1, and the assembled quasi-solid-state ZIBs achieve 95% capacity retention over 3000 cycles as well as a wide operating temperature from -30 to 80 °C, demonstrating a promising prospect for large-scale energy storage. In situ X-ray diffraction, X-ray photoelectron spectroscopy, and thermogravimetric analysis (TGA) investigations also demonstrate a complex reaction mechanism for this cathode involving the (de)insertion of Zn²⁺, H⁺, and water molecules during cycling. The water molecules will reinsert into the interlayer and act as "pillars" to stabilize the host structure when Zn²⁺ is fully extracted.

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.

Latest Advances in High-Voltage and High-Energy-Density Aqueous Rechargeable Batteries

Abstract

Aqueous rechargeable batteries (ARBs) have become a lively research theme due to their advantages of low cost, safety, environmental friendliness, and easy manufacturing. However, since its inception, the aqueous solution energy storage system has always faced some problems, which hinders its development, such as the narrow electrochemical stability window of water, poor percolation of electrode materials, and low energy density. In recent years, to overcome the shortcomings of the aqueous solution-based energy storage system, some very pioneering work has been done, which also provides a great inspiration for further research and development of future high-performance aqueous energy storage systems. In this paper, the latest advances in various ARBs with high voltage and high energy density are reviewed. These include aqueous rechargeable lithium, sodium, potassium, ammonium, zinc, magnesium, calcium, and aluminum batteries. Further challenges are pointed out.

Graphic Abstract

Aqueous can be better in terms of safety, friendliness, and energy density.

Recent Advances in the Rational Design and Synthesis of Two-Dimensional Materials for Multivalent Ion Batteries

With the increase of device requirements, rechargeable lithium-ion batteries are facing tremendous challenges in large-scale applications due to the high price and gradual shortage of lithium sources. In contrast, multivalent ion batteries, such as aluminum, magnesium, and zinc, are promising candidates for the next-generation energy-storage systems because of their high volumetric energy density, safe operation, and abundant reserves. The strong intercalation between multivalent ions and the host materials, however, will cause lower ion-diffusion kinetics and a poor discharge capacity. One of the main challenges is to search for a suitable cathode material with a high capacity and good structural stability to overcome the abovementioned problems. Two-dimensional layered materials, with characteristic unique structural features, good conductivity, and high electrochemically active surface, have attracted attention from researchers during the past decade. In this review, the design approach and synthetic procedures for the preparation of two-dimensional materials as cathodes for multivalent ion batteries, including interlayer engineering, two-dimensional heterostructures, pore/hole engineering, and heteroatom doping, are summarized. Meanwhile, the relationship between the design configuration and optimized electrochemical performance is rationally and systematically presented. Additionally, perspectives for the sustainable synthesis of cathode materials are proposed for multivalent metal-ion chemistry.

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.

NaV6O15 microflowers as a stable cathode material for high-performance aqueous zinc-ion batteries

Reversible aqueous zinc-ion batteries (ZIBs) have great potential for large-scale energy storage owing to their low cost and safety. However, the lack of long-lifetime positive materials severely restricts the development of ZIBs. Herein, we report NaV₆O₁₅ microflowers as a cathode material for ZIBs with excellent electrochemical performance, including a high specific capacity of ∼300 mA h g⁻¹ at 100 mA g⁻¹ and 141 mA h g⁻¹ maintained after 2000 cycles at 5 A g⁻¹ with a capacity retention of ∼107%. The high diffusion coefficient and stable tunneled structure of NaV₆O₁₅ facilitate Zn²⁺ intercalation/extraction and long-term cycle stability.

NaV₆O₁₅ microflowers were synthesized as a stable cathode material for aqueous zinc ion batteries, which show a high specific capacity and excellent long-term cycling performance.

High-Power and Ultralong-Life Aqueous Zinc-Ion Hybrid Capacitors Based on Pseudocapacitive Charge Storage

Rechargeable aqueous zinc-ion hybrid capacitors and zinc-ion batteries are promising safe energy storage systems. In this study, amorphous RuO2·H2O for the first time was employed to achieve fast and ultralong-life Zn2+ storage based on a pseudocapacitive storage mechanism. In the RuO2·H2O||Zn zinc-ion hybrid capacitors with Zn(CF3SO3)2 aqueous electrolyte, the RuO2·H2O cathode can reversibly store Zn2+ in a voltage window of 0.4-1.6 V (vs. Zn/Zn2+), delivering a high discharge capacity of 122 mAh g-1. In particular, the zinc-ion hybrid capacitors can be rapidly charged/discharged within 36 s with a very high power density of 16.74 kW kg-1 and a high energy density of 82 Wh kg-1. Besides, the zinc-ion hybrid capacitors demonstrate an ultralong cycle life (over 10,000 charge/discharge cycles). The kinetic analysis elucidates that the ultrafast Zn2+ storage in the RuO2·H2O cathode originates from redox pseudocapacitive reactions. This work could greatly facilitate the development of high-power and safe electrochemical energy storage.