Naphthoquinone-Based Composite Cathodes for Aqueous Rechargeable Zinc-Ion Batteries

Self-Charging Aqueous Zn//COF Battery with UltraHigh Self-Charging Efficiency and Rate

Self-charging zinc batteries that combine energy harvesting technology with batteries are candidates for reliable self-charging power systems. However, the lack of rational materials design results in unsatisfactory self-charging performance. Here, a covalent organic framework containing pyrene-4,5,9,10-tetraone groups (COF-PTO) is reported as a cathode material for aqueous self-charging zinc batteries. The ordered channel structure of the COF-PTO provides excellent capacity retention of 98% after 18 000 cycles at 10 A g-1 and ultra-fast ion transfer. To visually assess the self-charging performance, two parameters, namely self-charging efficiency (self-charging discharge capacity/galvanostatic discharge capacity, η) and average self-charging rate (total discharge capacity after cyclic self-charging/total cyclic self-charging time, ν), are proposed for performance evaluation. COF-PTO achieves an impressive η of 96.9% and an ν of 30 mAh g-1 self-charge capacity per hour in 100 self-charging cycles, surpassing the previous reports. Mechanism studies reveal the co-insertion of Zn2+ and H+ double ions in COF-PTO of self-charging zinc batteries. In addition, the C═N and C═O (on the benzene) in COF-PTO are ortho structures to each other, which can easily form metal heterocycles with Zn ions, thereby driving the forward progress of the self-charging reaction and enhancing the self-charging performance.

Fused Functional Organic Material with the Alternating Conjugation of Quinone-Pyrazine as Cathode for Aqueous Zinc Ion Batteries

Organic cathode materials for aqueous rechargeable zinc batteries (ARZBs) are rapidly gaining prominence, while the exploration of compounds with affordable synthesis, satisfactory electrochemical performance, and understandable mechanisms still remains challenging. In this study, 6,8,15,17-tetraaza-heptacene-5,7,9,14,16,18-hexaone (TAHQ) as an easily synthesized organic cathode material with novel quinone/pyrazine alternately conjugated molecule structure is presented. This organic electrode exhibits good capacity with highly reversible redox reactions, and the influence of multi-active structures on the Zn2+/H+ loading behavior is systematically investigated by ex situ spectroscopy, electrochemical tests, and computation. Both experimental and theoretical studies effectively address the Zn2+/H+ intercalation/deintercalation kinetics. Benefitting from the fused active functionalities, the assembled Zn//TAHQ battery displays a maximum discharge specific capacity of 254.3 mAh g-1 at 0.5 A g-1, and it maintains remarkable cycle performance with 71% capacity retention after 1000 cycles under 5 A g-1.

Entanglement Added to Cross-Linked Chains Enables Tough Gelatin-Based Hydrogel for Zn Metal Batteries

Currently, it is still challenging to develop a hydrogel electrolyte matrix that can successfully achieve a harmonious combination of mechanical strength, ionic conductivity, and interfacial adaptability. Herein, a multi-networked hydrogel electrolyte with a high entanglement effect based on gelatin/oxidized dextran/methacrylic anhydride, denoted as ODGelMA is constructed. Attribute to the Schiff base network formulation of ─RC═N─, oxidized dextran integrated gelatin chains induce a dense hydrophilic conformation group. Furthermore, addition of methacrylic anhydride through a grafting process, the entangled hydrogel achieves impressive mechanical features (6.8 MPa tensile strength) and high ionic conductivity (3.68 mS cm-1 at 20 °C). The ODGelMA electrolyte regulates the zinc electrode by circumventing dendrite growth, and showcases an adaptable framework reservoir to accelerate the Zn2+ desolvation process. Benefiting from the entanglement effect, the Zn anode achieves an outstanding average Coulombic efficiency (CE) of 99.8% over 500 cycles and cycling stability of 900 h at 5 mA cm-2 and 2.5 mAh cm-2. The Zn||I2 full cell yields an ultra-long cycling stability of 10 000 cycles with a capacity retention of 92.4% at 5 C. Furthermore, a 60 mAh single-layer pouch cell maintains a stable work of 350 cycles.

Tackling the Challenges of Aqueous Zn-Ion Batteries via Polymer-Derived Strategies

Zn-ion batteries (ZIBs) have gathered unprecedented interest recently benefiting from their intrinsic safety, affordability, and environmental benignity. Nevertheless, their practical implementation is hampered by low rate performance, inferior Zn2+ diffusion kinetics, and undesired parasitic reactions. Innovative solutions are put forth to address these issues by optimizing the electrodes, separators, electrolytes, and interfaces. Remarkably, polymers with inherent properties of low-density, high processability, structural flexibility, and superior stability show great promising in tackling the challenges. Herein, the recent progress in the synthesis and customization of functional polymers in aqueous ZIBs is outlined. The recent implementations of polymers into each component are summarized, with a focus on the inherent mechanisms underlying their unique functions. The challenges of incorporating polymers into practical ZIBs are also discussed and possible solutions to circumvent them are proposed. It is hoped that such a deep analysis could accelerate the design of polymer-derived approaches to boost the performance of ZIBs and other aqueous battery systems as they share similarities in many aspects.

Unveiling Organic Electrode Materials in Aqueous Zinc-Ion Batteries: From Structural Design to Electrochemical Performance

Aqueous zinc-ion batteries (AZIBs) are one of the most compelling alternatives of lithium-ion batteries due to their inherent safety and economics viability. In response to the growing demand for green and sustainable energy storage solutions, organic electrodes with the scalability from inexpensive starting materials and potential for biodegradation after use have become a prominent choice for AZIBs. Despite gratifying progresses of organic molecules with electrochemical performance in AZIBs, the research is still in infancy and hampered by certain issues due to the underlying complex electrochemistry. Strategies for designing organic electrode materials for AZIBs with high specific capacity and long cycling life are discussed in detail in this review. Specifically, we put emphasis on the unique electrochemistry of different redox-active structures to provide in-depth understanding of their working mechanisms. In addition, we highlight the importance of molecular size/dimension regarding their profound impact on electrochemical performances. Finally, challenges and perspectives are discussed from the developing point of view for future AZIBs. We hope to provide a valuable evaluation on organic electrode materials for AZIBs in our context and give inspiration for the rational design of high-performance AZIBs.

Non-Metal Ion Storage in Zinc-Organic Batteries

Zinc-organic batteries (ZOBs) are receiving widespread attention as up-and-coming energy-storage systems due to their sustainability, operational safety and low cost. Charge carrier is one of the critical factors affecting the redox kinetics and electrochemical performances of ZOBs. Compared with conventional large-sized and sluggish Zn2+ storage, non-metallic charge carriers with small hydrated size and light weight show accelerated interfacial dehydration and fast reaction kinetics, enabling superior electrochemical metrics for ZOBs. Thus, it is valuable and ongoing works to build better ZOBs with non-metallic ion storage. In this review, versatile non-metallic cationic (H+, NH4 +) and anionic (Cl-, OH-, CF3SO3 -, SO4 2-) charge carriers of ZOBs are first categorized with a brief comparison of their respective physicochemical properties and chemical interactions with redox-active organic materials. Furthermore, this work highlights the implementation effectiveness of non-metallic ions in ZOBs, giving insights into the impact of ion types on the metrics (capacity, rate capability, operation voltage, and cycle life) of organic cathodes. Finally, the challenges and perspectives of non-metal-ion-based ZOBs are outlined to guild the future development of next-generation energy communities.

Sulfur-Defect-Induced TiS1.94 as a High-Capacity and Long-Life Anode Material for Zinc-Ion Batteries

Aqueous zinc-ion batteries (ZIBs) are competitive among the elective candidates for electrochemical energy storage systems, but the intrinsic drawbacks of zinc metal anodes such as dendrites and corrosion severely hinder their large-scale application. Developing alternative anode materials capable of high reversibility and stability for storing Zn2+ ions is a feasible approach to circumvent the challenge. Herein, a sulfur-defect-induced TiS1.94 (D-TiS1.94) as a promising intercalation anode material for ZIBs is designed. The abundant Zn2+-storage active sites and lower Zn2+ migration barrier induced by sulfur defects endow D-TiS1.94 with a high capacity for Zn2+-storage (219.1 mA h g-1 at 0.05 A g-1) and outstanding rate capability (107.3 mA h g-1 at 5 A g-1). In addition, a slight volume change of 8.1% is identified upon Zn2+ storage, which favors a prolonged cycling life (50.3% capacity remaining in 1500 cycles). More significantly, the D-TiS1.94||ZnxMnO2 full battery demonstrates a high discharge capacity of 155.7 mA h g-1 with a capacity retention of 59.8% in 400 cycles. It has been estimated that the high-capacity, low-operation voltage, and long-life D-TiS1.94 can be a promising component of the ZIB anode material family, and the strategy proposed in this work will provide guidance to the defect engineering of high-performance electrode materials toward energy storage applications.

An Organic Molecular Cathode Composed of Naphthoquinones Bridged by Organodisulfide for Rechargeable Lithium Battery

Organic electrodes that embrace multiple electron transfer and efficient redox reactions are desirable for green energy storage batteries. Here, a novel organic electrode material is synthesized, i.e., 2, 2'-((disulfanediylbis (4, 1-phenylene)) bis(azanediyl)) bis (naphthalene-1, 4-dione) (MNQ), through a simple click reaction between common carbonyl and organosulfur compounds and demonstrate its application potential as a high-performance cathode material in rechargeable lithium batteries. MNQ exhibits the aggregation effect of redox-active functional groups, the advantage of fast reaction kinetics from molecular structure evolution, and the decreased solubility in aprotic electrolytes resulting from intermolecular interactions. As expected, the MNQ electrode exhibits a high initial discharge capacity of 281.2 mA h g-1 at 0.5 C, equivalent to 97.9% of its theoretical capacity, and sustains stable long-term cycling performance of over 1000 cycles at 1 C. This work adds a new member to the family of organic electrode materials, providing performance-efficient organic molecules for the design of rechargeable battery systems, which will undoubtedly spark great interest in their applications.

Lewis Acid-Catalyzed Benzannulation of Vinyloxiranes with 3-Formylchromones or 1,4-Quinones for Diversely Functionalized 2-Hydroxybenzophenones, 1,4-Naphthoquinones, and Anthraquinones

A facile and convenient protocol for the regioselective construction of functionalized 2-hydroxybenzophenones is described. This protocol involves the Sc(OTf)3/BF3·OEt2-catalyzed benzannulation of 2-vinyloxirans with 3-formylchromone, which involves cascade in situ diene formation, [4 + 2] cycloaddition, elimination, and ring-opening strategies. Moreover, it provides an expedited synthetic pathway to access biologically intriguing 1,4-naphthoquinones and anthraquinones including vitamin K3 and tectoquinone. The synthesized compounds also hold potential for use as UV filters and show promise as chemosensors for Cu2+ and Mg2+ ions.

Long Cycle Life for Rechargeable Lithium Battery using Organic Small Molecule Dihydrodibenzo[c,h][2,6]naphthyridine-5,11-dione as a Cathode after Isoindigo Pigment Isomerization

Sustainability and adaptability in structural design of the organic cathodes present promises for applications in alkali metal ion batteries. Nevertheless, a formidable challenge lies in their high solubility in organic electrolytes, particularly for small molecular materials, impeding cycling stability and high capacity. This study focuses on the design and synthesis of organic small molecules, the isomers of (E)-5,5'-difluoro-[3,3'-biindolinylidene]-2,2'-dione (EFID) and 3,9-difluoro-6,12-dihydrodibenzo [c, h][2,6]naphthyridine-5,11-dione (FBND). While EFID, characterized by a less π-conjugated structure, exhibits subpar cycling stability in lithium-ion batteries (LIBs), intriguingly, another isomer, FBND, demonstrates exceptional capacity and cycling stability in LIBs. FBND delivers a remarkable capacity of 175 mAh g-1 at a current density of 0.05 A g-1 and maintains excellent cycling stability over 2000 cycles, retaining 90% of its initial capacity. Furthermore, an in-depth examination of redox reactions and storage mechanisms of FBND are conducted. The potential of FBND is also explored as an anode in lithium-ion batteries (LIBs) and as a cathode in sodium-ion batteries (SIBs). The FBND framework, featuring extended π-conjugated molecules with an imide structure compared to EFID, proves to be an excellent material template to develop advanced organic small molecular cathode materials for sustainable batteries.

Recent Progress of the Cathode Material Design for Aqueous Zn-Organic Batteries

Aqueous zinc-ion batteries (ZIBs) have emerged as the most promising candidate for large-scale energy storage due to their inherent safety, environmental friendliness, and cost-effectiveness. Simultaneously, the utilization of organic electrode materials with renewable resources, environmental compatibility, and diverse structures has sparked a surge in research and development of aqueous Zn-organic batteries (ZOBs). A comprehensive review is warranted to systematically present recent advancements in design principles, synthesis techniques, energy storage mechanisms, and zinc-ion storage performance of organic cathodes. In this review article, we comprehensively summarize the energy storage mechanisms employed by aqueous ZOBs. Subsequently, we categorize organic cathode materials into small-molecule compounds and high-molecular polymers respectively. Novel polymer materials such as conjugated polymers (CPs), conjugated microporous polymers (CMPs), and covalent organic frameworks (COFs) are highlighted with an overview of molecular design strategies and structural optimization based on organic cathode materials aimed at enhancing the performance of aqueous ZOBs. Finally, we discuss the challenges faced by aqueous ZOBs along with future prospects to offer insights into their practical applications.

Organic Zinc-Ion Battery: Planar, π-Conjugated Quinone-Based Polymer Endows Ultrafast Ion Diffusion Kinetics

A novel poly(phenazine-alt-pyromellitic anhydride) (PPPA) has been successfully designed and synthesized via a condensation polymerization strategy as promising cathode material in organic zinc-ion batteries. Electrochemical quartz crystal microbalance (EQCM), FTIR and XPS characterizations verify a reversible Zn²⁺ -coordination mechanism in our PPPA cathode. Intriguingly, an ultrahigh Zn²⁺ diffusion coefficient of 1.2×10^-7  cm²  s^-1 was found in this large π-conjugated system, which is the highest one among all organic cathode materials for zinc-ion batteries. Theoretical calculations reveal the extended π-conjugated plane in our PPPA sample results in a significant reduction on energy gap, effectively accelerating intramolecular electron transfer during charge/discharge process. Our finding provides insights to achieve high zinc-ion transport kinetics by a design strategy on planar polymer system.

Challenges and Perspectives of Organic Multivalent Metal-Ion Batteries

Rechargeable organic multivalent metal-ion batteries (MMIBs) have attracted a surge of interest as promising alternatives for large-scale energy storage applications because they can combine the advantages of both organic electrodes and multivalent metal-ion batteries. However, the development of organic MMIBs is hampered by many factors, which mean they lag far behind organic alkali-metal- (e.g., Li-, Na-, and K-) ion batteries. Herein, the challenges that are specifically faced by organic MMIBs are analyzed and the strategies that can probably solve such challenges are then discussed. As a special challenge that organic MMIBs are facing, the charge-storage mechanism is particularly underlined to deeply understand the structure-property relationships for guiding the future design of high-performance organic electrodes for MMIBs. The perspectives are thereby elaborated in this review with the outlook of practical applications of organic MMIBs.

MXene-Boosted Imine Cathodes with Extended Conjugated Structure for Aqueous Zinc-Ion Batteries

Organic molecules have been considered promising energy-storage materials in aqueous zinc-ion batteries (ZIBs), but are plagued by poor conductivity and structural instability because of the short-range conjugated structure and low molecular weight. Herein, an imine-based tris(aza)pentacene (TAP) with extended conjugated effects along the CN backbones is proposed, which is in situ injected into layered MXene to form a TAP/Ti₃ C₂ T_x cathode. Theoretical and electrochemical analyses reveal a selective H⁺ /Zn²⁺ co-insertion/extraction mechanism in TAP, which is ascribed to the steric effect on the availability of active CN sites. Moreover, Ti₃ C₂ T_x , as a conductive scaffold, favors fast Zn²⁺ diffusion to boost the electrode kinetics of TAP. Close electronic interactions between TAP and Ti₃ C₂ T_x preserve the structural integrity of TAP/Ti₃ C₂ T_x during the repeated charge/discharge. Accordingly, the TAP/Ti₃ C₂ T_x cathode delivers a high reversible capacity of 303 mAh g^-1 at 0.04 A g^-1 in aqueous ZIBs, which also realizes an ultralong lifetime over 10 000 cycles with a capacity retention of 81.6%. Furthermore, flexible Zn||TAP/Ti₃ C₂ T_x batteries with a quasi-solid-state electrolyte demonstrate potential application in wearable electronic devices. This work offers pivotal guidance to create highly stable organic electrodes for advanced ZIBs.

Long-Life Aqueous Zinc-Ion Batteries of Organic Iminodianthraquinone/rGO Cathode Assisted by Zn2+ Binding with Adjacent Molecules

Organic compounds have been extensively used as zinc-ion battery (ZIB) cathodes due to their high capacities and outstanding properties. Nevertheless, poor electrical conductivity limits their developments. RGO (reduced graphene oxide) can well interact with organic compounds through π-π stacking for furnishing capacious ion diffusion paths and active sites to enhance conductivity and capacity. Herein, a 1,1'-iminodianthraquinone (IDAQ)/rGO composite is utilized as cathode of ZIBs, demonstrating ultrahigh stability with 96% capacity retention after 5000 cycles. Zn2+ and H+ synergetic mechanism in IDAQ/rGO has been deeply discussed by ex situ analysis and theoretical calculation. Consequently, the structure of IDAQ2(H+)6(Zn2+) is the most probable product after discharging progress. Prospectively, the IDAQ/rGO material with excellent stability and good performance would provide new insights into designing advanced ZIBs.

An Anti-Aromatic Covalent Organic Framework Cathode with Dual-Redox Centers for Rechargeable Aqueous Zinc Batteries

Covalent organic frameworks (COFs) are promising cathode candidates with high structural stability. However, they contain redox inactive linkages and experience low redox potential. Herein, a full anti-aromatic microporous COF cathode material of TAQ-BQ is designed for aqueous zinc batteries. The anti-aromatic conjugation effectively lowers the energy level of the lowest unoccupied molecular orbital as revealed by theoretical calculations, which corresponds to an elevated redox potential. Besides, the structure contains imino active sites at the linkages, in addition to carbonyl at the active parts. As a result, the TAQ-BQ cathode exhibits a voltage of 1.53 V/1.54 V and between 1.35 and 0.45 V in zinc cells. It delivers 208 mAh g^-1 capacity at 0.1 A g^-1 and maintains 136 mAh g^-1 at 2 A g^-1. Stable cycling is realized for 1000 cycles with 87% capacity retention. The co-de/insertion of Zn²⁺ and protons is identified for energy storage. Our work reveals the promises of COF cathode materials for aqueous zinc batteries.

Enhancing the kinetics of vanadium oxides via conducting polymer and metal ions co-intercalation for high-performance aqueous zinc-ions batteries

Aqueous zinc-ions batteries with low cost, reliable safety, high theoretical specific capacity and eco-friendliness have captured conspicuous attention in large-scale energy storage. However, the developed cathodes often suffer from low electrical conductivity and sluggish Zn²⁺ diffusion kinetics, which severely hampers the development of aqueous zinc-ions batteries. Herein, we successfully prepare Mg/PANI/V₂O₅•nH₂O (MPVO) nanosheets through conducting polymers (polyaniline) and metal ions (Mg²⁺) co-intercalated strategy and systematically explore its electrochemical performance as cathode materials for aqueous zinc-ion batteries. Benefitting from the synergistic effect of polyaniline and Mg²⁺ co-intercalated, the MPVO exhibits larger interlayer spacing and higher electrical conductivity than the single guest intercalation, which significantly enhances the electrochemical kinetics. As a consequence, the MPVO cathodes deliver superior specific capacity, rate capability and long-term cycling performance. Moreover, multiple characterizations and theoretical calculations are executed to expound the relevant mechanism.Therefore, this work provides a novel thought for the design of high-performance cathode materials for aqueous ZIBs.

Boosted H+ Intercalation Enables Ultrahigh Rate Performance of the δ-MnO2 Cathode for Aqueous Zinc Batteries

H+ intercalation, as a critical battery chemistry, enables electrodes' high rate performance due to the fast diffusion kinetics of H+. In this work, more water molecules are introduced into δ-MnO2 by the protonation of δ-MnO2 with abundant oxygen vacancies. Benefiting from the structure with a close arrangement of water molecules in interlayers, the Grotthuss transport of proton is achieved in the energy storage of the δ-MnO2 cathode. As a result, the δ-MnO2 cathode exhibits an ultrahigh rate performance with a capacity of 368.1 mAh g-1 at 0.5 A g-1 and 83.4 mAh g-1 at 50 A g-1, which has a capacity retention of 73% after 1100 cycles at 10 A g-1. The study of the storage mechanism reveals that the Grotthuss intercalation of proton predominates the storage process, which empowers the cathode with high rate performance.

Synthesis of Nitrogen-Doped KMn8 O16 with Oxygen Vacancy for Stable Zinc-Ion Batteries

The development of MnO₂ as a cathode for aqueous zinc-ion batteries (AZIBs) is severely limited by the low intrinsic electrical conductivity and unstable crystal structure. Herein, a multifunctional modification strategy is proposed to construct N-doped KMn₈ O₁₆ with abundant oxygen vacancy and large specific surface area (named as N-KMO) through a facile one-step hydrothermal approach. The synergetic effects of N-doping, oxygen vacancy, and porous structure in N-KMO can effectively suppress the dissolution of manganese ions, and promote ion diffusion and electron conduction. As a result, the N-KMO cathode exhibits dramatically improved stability and reaction kinetics, superior to the pristine MnO₂ and MnO₂ with only oxygen vacancy. Remarkably, the N-KMO cathode delivers a high reversible capacity of 262 mAh g^-1 after 2500 cycles at 1 A g^-1 with a capacity retention of 91%. Simultaneously, the highest specific capacity can reach 298 mAh g^-1 at 0.1 A g^-1 . Theoretical calculations reveal that the oxygen vacancy and N-doping can improve the electrical conductivity of MnO₂ and thus account for the outstanding rate performance. Moreover, ex situ characterizations indicate that the energy storage mechanism of the N-KMO cathode is mainly a H⁺ and Zn²⁺ co-insertion/extraction process.

Hexagonal WO3/3D Porous Graphene as a Novel Zinc Intercalation Anode for Aqueous Zinc-Ion Batteries

Aqueous Zn-ion batteries (ZIBs) have acquired great attention because of their high safety and environmentally friendly properties. However, the uncontrollable Zn dendrites and the irreversibility of electrodes seriously affect their practical application. Herein, hexagonal WO₃/three-dimensional porous graphene (h-WO₃/3DG) is investigated as an intercalation anode for ZIBs. As a result, the h-WO₃/3DG//Zn half-battery shows excellent electrochemical performance with a high capacity of 115.6 mAh g^-1 at 0.1 A g^-1 and 89% capacity retention at 2.0 A g^-1 after 10 000 cycles. The reason could be that the crystalline structure of WO₃, which has hexagonal channels, with a diameter of 5.36 Å, much higher than the diameter of Zn²⁺ (0.73 Å), accelerating the insertion/extraction of Zn ions. A zinc metal-free full battery using h-WO₃/3DG as the anode and ZnMn₂O₄/carbon black (ZnMn₂O₄/CB) as the cathode is constructed, exhibiting an initial capacity of 66.8 mAh g^-1 at 0.1 A g^-1 corresponding to an energy density of 73.5 W h kg^-1 (based on the total mass of anode and cathode-active materials) and a capacity retention of 76.6% after 1000 cycles at 0.5 A g^-1. This work demonstrates the high potential of hexagonal WO₃ as an advanced intercalation anode material for Zn metal-free batteries and may inspire new ideas for the development of other intercalation anode hosts for ZIBs.

Ultralong-Life Cathode for Aqueous Zinc-Organic Batteries via Pouring 9,10-Phenanthraquinone into Active Carbon

Organic carbonyl electrode materials have shown a great potential in various rechargeable batteries but limited by the problems of poor cycling and rate performance owing to their high solubility in aqueous electrolytes and low conductivity. To address these problems, the 9,10-phenanthraquinone (PQ)@active carbon (AC) composite fabricated by melting PQ molecules into porous AC is considered as a superstable cathode material for aqueous zinc batteries. The introduction of AC improves the structural stability and restrains the PQ dissolution in an aqueous electrolyte. As a result, the PQ@AC composite electrode delivers a reversible discharge capacity of 150.0 mA h g^-1 at a current density of 0.1 A g^-1, and it also features an unprecedented cycling performance of 36 000 cycles with a capacity retention of 96.3% at 5 A g^-1. Moreover, the Zn²⁺ and H⁺ in an aqueous electrolyte are verified to co-insert into the PQ@AC composite electrode using various ex situ characterizations and electrochemical test. This strategy provides a new avenue for organic carbonyl compounds with quinone substructures to improve their electrochemical performance of other 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.

Yttrium Vanadium Oxide-Poly(3,4-ethylenedioxythiophene) Composite Cathode Material for Aqueous Zinc-Ion Batteries

The development of metal ion-intercalated active materials for excellent electrochemical performance in rechargeable aqueous zinc-ion batteries (AZIBs) is challenging. The structure instability and intrinsic electrostatic repulsion of the lattice framework cause structural breakdown and low-rate performance. In response to these problems, yttrium vanadium oxide-poly(3,4-ethylenedioxythiophene) (PEDOT@YVO) composite is reported as stable cathode material for AZIBs. The introduction of PEDOT in YVO nanorods improves the crystalline structure with an enlarged interplanar lattice spacing of 3.4 Å. The PEDOT@YVO composite electrode demonstrates effective electric conductivity and a higher initial specific capacity of 308.5 mAh g^-1 than that (125.5 mAh g^-1 ) of the pure YVO at 0.2 C rate. It also features a long-term stable discharge-charge cycle performance of 4000 cycles with a capacity retention of 79.2% at 1C rate, better than YVO (29.4 mAh g^-1 ). The oxygen vacancies and improved electrical conductivity of the composite account for the invigorated electrochemical performance. Consequently, this work reveals another avenue for constructing unique electrodes to enhance the electrochemical properties of AZIBs.

Recent Advances on Spinel Zinc Manganate Cathode Materials for Zinc-Ion Batteries

Zinc metal is abundant in nature, non-toxic, harmless, and cheap. Zinc-ion batteries (ZIBs) have also emerged as the times require, which has attracted scholars' research interest. In the zinc-ion batteries, the cathode material is indispensable. Manganese oxides are widely used in electrode materials because of their various valence states (+2, +3, +4, +7). ZnMn₂ O₄ (ZMO) is a mixed metal oxide with a spinel structure similar to LiMn₂ O₄ . Due to the synergistic effect of Zn and Mn, it has the advantages of high theoretical capacity. In recent years, researchers have gradually applied ZnMn₂ O₄ to zinc ion batteries. In order to obtain high-energy-density zinc ion batteries, it is also very important to match electrolytes with a wide operating voltage window and develop a highly reversible anode. In the first instance, we investigate the research progress of spinel ZnMn₂ O₄ as a reliable candidate material for zinc ion batteries. Later on, we review the optimization and modification measures of anode and electrolyte to improve the electrochemical properties of spinel ZnMn₂ O₄ . On this basis, we propose the reasonable research direction and development prospects for this material. It is hoped that there will be a help to researchers in this field.