Anionic Co-insertion Charge Storage in Dinitrobenzene Cathodes for High-Performance Aqueous Zinc-Organic Batteries

Ladder-Type Redox-Active Polymer Achieves Ultra-Stable and Fast Proton Storage in Aqueous Proton Batteries

A ladder-type rigid-coplanar polymer with highly ordered molecular arrangement has been designed via a covalent cycloconjugation conformational strategy. Benefitting from the extended π-electron delocalization in the highly aromatic ladder-type polymeric backbone, the prepared polymer exhibits fast intra-chain charge transport along the polymeric chain, realizing extraordinary proton-storage capability in aqueous proton batteries.Affordable and safe aqueous proton batteries (APBs) with unique "Grotthuss mechanism," are very significant for advancing carbon neutrality initiatives. While organic polymers offer a robust and adaptable framework that is well-suited for APB electrodes, the limited proton-storage redox capacity has constrained their broader application. Herein, a ladder-type polymer (PNMZ) has been designed via a covalent cycloconjugation conformational strategy that exhibits optimized electronic structure and fast intra-chain charge transport within the high-aromaticity polymeric skeleton. As a result, the polymer exhibits exceptional proton-storage redox kinetics, which are evidenced by in-operando monitoring techniques and theoretical calculations. It achieves a remarkable proton-storage capacity of 189 mAh g-1 at 2 A g-1 and excellent long-term cycling stability, with approximately 97.8 % capacity retention over 10,000 cycles. Finally, a high-performance all-polymer APB device has been successfully constructed with a desirable capacity retention of 99.7 % after 6,000 cycles and high energy density of 56.3 Wh kg-1.

Regulating the Porosity and Bipolarity of Polyimide-Based Covalent Organic Framework for Advanced Aqueous Dual-Ion Symmetric Batteries

The all-organic aqueous dual-ion batteries (ADIBs) have attracted increasing attention due to the low cost and high safety. However, the solubility and unstable activity of organic electrodes restrict the synergistic storage of anions and cations in the symmetric ADIBs. Herein, a novel polyimide-based covalent organic framework (labeled as NTPI-COF) is constructed, featured with the boosted structure stability and electronic conductivity. Through regulating the porosity and bipolarity integrally, the NTPI-COF possesses hierarchical porous structure (mesopore and micropore) and abundant bipolar active centers (C═O and C─N), which exhibits rapid dual-ion transport and storage effects. As a result, the NTPI-COF as the electrodes for ADIBs deliver a high reversible capacity of 109.7 mA h g-1 for Na+ storage and that of 74.8 mA h g-1 for Cl- storage at 1 A g-1, respectively, and with a capacity retention of 93.2% over 10 000 cycles at 10 A g-1. Additionally, the all-organic ADIBs with symmetric NTPI-COF electrodes achieve an impressive energy density of up to 148 W h kg-1 and a high power density of 2600 W kg-1. Coupling the bipolarity and porosity of the all-organic electrodes applied in ADIBs will further advance the development of low-cost and large-scale energy storage.

Constructing a Janus Catholyte/Cathode Structure: A New Strategy for Stable Zn-Organic Batteries

Organic materials are promising candidates for the electrodes of aqueous zinc-ion batteries due to their nonmetallic nature, environmental friendliness, and cost-effectiveness. However, they often suffer from significant dissolution during the charge-discharge process, which poses a major hurdle to their practical applications. Inspired by membrane-less organelles in cells, a simple and versatile strategy is proposed-constructing a Janus catholyte/cathode structured electrode based on liquid-liquid phase separation, in which redox-active organic molecules are confined in the liquid state within the activated carbon, thereby eliminating the volume effect and preventing their diffusion into the electrolyte. The customization of phase separation systems by leveraging the hydrophobicity/hydrophilicity differences of various anions is successfully demonstrated. This approach allows for precise regulation of ion cluster/coordination structures, enabling the confinement of active substances while ensuring efficient ion transport. Consequently, the as-constructed Zn||Janus catholyte/cathode cells exhibit superior reversible rate capacity (186 mA h g-1 at 5.0 A g-1) and remarkable cycling performance (retention of 72.5% after 12 000 cycles). The strategy in building Janus catholyte/cathode structured electrodes breaks free from the limitations imposed by traditional solid-state electrodes, offering tremendous opportunities for exploring diverse advanced battery systems.

Flexible Aqueous Supercapacitors for Long Cycle-Life Using Electrode with Multiple Active C═S Sites

Even though a few organic materials have attracted considerable attention for energy storage applications, their dissolution in the electrolyte during the charging-discharging processes presents a formidable challenge to their long-term performance. In this work, according to the principle of like dissolves like, non-polar trithiocyanuric acid (TCA) can effectively inhibit dissolution in an aqueous electrolyte, hence prolonging the cycle life. Moreover, theoretical calculations suggest that TCA lowers lowest unoccupied molecular orbital (LUMO) energy level, thereby promoting reaction kinetics. The CV curves of TCA maintain a rectangular structure even at a high scan rate of 1000 mV s‒1 and exhibit a remarkable capacitance retention rate of 93.1% after 50,000 cycles. Asymmetric flexible supercapacitors utilizing the TCA exhibit an impressive energy density. Moreover, they maintain 94.2% of their capacitance after undergoing 80,000 cycles. Their integration with perovskite solar cells to facilitate the rapid storage of photogenerated charges enables efficient solar energy utilization, providing a practical solution for capturing and storing renewable energy.

Designing Heterodiatomic Carbon Hydrangea Superstructures via Machine Learning-Regulated Solvent-Precursor Interactions for Superior Zinc Storage

Carbon superstructures with exquisite morphologies and functionalities show appealing prospects in energy realms, but the systematic tailoring of their microstructures remains a perplexing topic. Here, hydrangea-shaped heterodiatomic carbon superstructures (CHS) are designed using a solution phase manufacturing route, wherein machine learning workflow is applied to screen precursor-matched solvent for optimizing solvent-precursor interaction. Based on the established solubility parameter model and molecular growth kinetics simulation, ethanol as the optimal solvent stimulates thermodynamic solubilization and growth of polymeric intermediates to evoke CHS. Featured with surface-active motifs and consecutive charge transfer paths, CHS allows high accessibility of zincophilic sites and fast ion migration with low energy barriers. A anion-cation hybrid charge storage mechanism of CHS cathode is disclosed, which entails physical alternate uptake of Zn2+/CF3SO3 - ions at electroactive sites and chemical bipedal redox of Zn2+ ions with carbonyl/pyridine motifs. Such a beneficial electrochemistry contributes to all-round improvement in Zn-ion storage, involving excellent capacities (231 mAh g-1 at 0.5 A g-1; 132 mAh g-1 at 50 A g-1), high energy density (152 Wh kg-1), and long-lasting cyclability (100 000 cycles). This work expands the design versatilities of superstructure materials and will accelerate experimental procedures during carbon manufacturing through machine learning in the future.

High-Performance Azo Cathodes Enabled by N-Heteroatomic Substitution for Zinc Batteries with a Self-Charging Capability

Redox-active azo compounds are emerging as promising cathode materials due to their multi-electron redox capacity and fast redox response. However, their practical application is often limited by low output voltage and poor thermal stability. Herein, we use a heteroatomic substitution strategy to develop 4,4'-azopyridine. This modification results in a 350 mV increase in reduction potential compared to traditional azobenzene, increasing the energy density at the material level from 187 to 291 Wh kg-1. The introduced heteroatoms not only raise the melting point of azo compounds from 68 °C to 112 °C by forming an intermolecular hydrogen-bond network but also improves electrode kinetics by reducing energy band gaps. Moreover, 4,4'-azopyridine forms metal-ligand complexes with Zn2+ ions, which further self-assemble into a robust superstructure, acting as a molecular conductor to facilitate charge transfer. Consequently, the batteries display a good rate performance (192 mAh g-1 at 20 C) and an ultra-long lifespan of 60,000 cycles. Notably, we disclose that the depleted batteries spontaneously self-charge when exposed to air, marking a significant advancement in the development of self-powered aqueous systems.

Insight into Anionic Discrepancies in Bipolar Poly(Thionine) Organic Cathodes for Aqueous Zinc Ion Batteries

Electroactive organic electrode materials exhibit remarkable potential in aqueous zinc ion batteries (AZIBs) due to their abundant availability, customizable structures, sustainability, and high reversibility. However, the research on AZIBs has predominantly concentrated on unraveling the storage mechanism of zinc cations, often neglecting the significance of anions in this regard. Herein, bipolar poly(thionine) is synthesized by a simple and efficient polymerization reaction, and the kinetics of different anions are investigated using poly(thionine) as the cathode of AZIBs. Notably, poly(thionine) is a bipolar organic polymer electrode material and exhibits enhanced stability in aqueous solutions compared to thionine monomers. Kinetic analysis reveals that ClO4 - exhibits the fastest kinetics among SO4 2-, Cl-, and OTF-, demonstrating excellent rate performance (109 mAh g-1 @ 0.5 A g-1 and 92 mAh g-1 @ 20 A g-1). Mechanism studies reveal that the poly(thionine) cathode facilitates the co-storage of both anions and cations in Zn(ClO4)2. Furthermore, the lower electrostatic potential of ClO4 - influences the strength of hydrogen bonding with water molecules, thereby enhancing the overall kinetics in aqueous electrolytes. This work provides an effective strategy for synthesizing high-quality organic materials and offers new insights into the kinetic behavior of anions in AZIBs.

Revealing Hydrogen Bond Effect in Rechargeable Aqueous Zinc-Organic Batteries

The surrounding hydrogen bond (H-bond) interaction around the active sites plays indispensable functions in enabling the organic electrode materials (OEMs) to fulfill their roles as ion reservoirs in aqueous zinc-organic batteries (ZOBs). Despite important, there are still no works could fully shed its real effects light on. Herein, quinone-based small molecules with a H-bond evolution model has been rationally selected to disclose the regulation and equilibration of H-bond interaction between OEMs, and OEM and the electrolyte. It has been found that only a suitable H-bond interaction could make the OEMs fully liberate their potential performance. Accordingly, the 2,5-diaminocyclohexa-2,5-diene-1,4-dione (DABQ) with elaborately designed H-bond structure exhibits a capacity of 193.3 mAh g-1 at a record-high mass loading of 66.2 mg cm-2 and 100 % capacity retention after 1500 cycles at 5 A g-1. In addition, the DABQ//Zn battery also possesses air-rechargeable ability by utilizing the chemistry redox of proton. Our results put forward a specific pathway to precise utilization of H-bond to liberate the performance of OEMs.

Recent Progress on Rechargeable Zn-X (X=S, Se, Te, I2, Br2) Batteries

Recently, aqueous Zn-X (X=S, Se, Te, I2, Br2) batteries (ZXBs) have attracted extensive attention in large-scale energy storage techniques due to their ultrahigh theoretical capacity and environmental friendliness. To date, despite tremendous research efforts, achieving high energy density in ZXBs remains challenging and requires a synergy of multiple factors including cathode materials, reaction mechanisms, electrodes and electrolytes. In this review, we comprehensively summarize the various reaction conversion mechanism of zinc-sulfur (Zn-S) batteries, zinc-selenium (Zn-Se) batteries, zinc-tellurium (Zn-Te) batteries, zinc-iodine (Zn-I2) batteries, and zinc-bromine (Zn-Br2) batteries, along with recent important progress in the design and electrolyte of advanced cathode (S, Se, Te, I2, Br2) materials. Additionally, we investigate the fundamental questions of ZXBs and highlight the correlation between electrolyte design and battery performance. This review will stimulate an in-deep understanding of ZXBs and guide the design of conversion batteries.

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.

A High-Energy Tellurium Redox-Amphoteric Conversion Cathode Chemistry for Aqueous Zinc Batteries

Rechargeable aqueous zinc batteries are potential candidates for sustainable energy storage systems at a grid scale, owing to their high safety and low cost. However, the existing cathode chemistries exhibit restricted energy density, which hinders their extensive applications. Here, a tellurium redox-amphoteric conversion cathode chemistry is presented for aqueous zinc batteries, which delivers a specific capacity of 1223.9 mAh gTe -1 and a high energy density of 1028.0 Wh kgTe -1. A highly concentrated electrolyte (30 mol kg-1 ZnCl2) is revealed crucial for initiating the Te redox-amphoteric conversion as it suppresses the H2O reactivity and inhibits undesirable hydrolysis of the Te4+ product. By carrying out multiple operando/ex situ characterizations, the reversible six-electron Te2-/Te0/Te4+ conversion with TeCl4 is identified as the fully charged product and ZnTe as the fully discharged product. This finding not only enriches the conversion-type battery chemistries but also establishes a critical step in exploring redox-amphoteric materials for aqueous zinc batteries and beyond.

Multielectron Redox-Bipolar Tetranitroporphyrin Macrocycle Cathode for High-Performance Zinc-Organic Batteries

Bipolar organics fuse the merits of n/p-type redox reactions for better Zn-organic batteries (ZOBs), but face the capacity plafond due to low density of active units and single-electron reactions. Here we report multielectron redox-bipolar tetranitroporphyrin (TNP) with quadruple two-electron-accepting n-type nitro motifs and dual-electron-donating p-type amine moieties towards high-capacity-voltage ZOBs. TNP cathode initiates high-kinetics, hybrid anion-cation 10e- charge storage involving four nitro sites coordinating with Zn2+ ions at low potential and two amine species coupling with SO4 2- ions at high potential. Consequently, Zn||TNP battery harvests high capacity (338 mAh g-1), boosted average voltage (1.08 V), and outstanding energy density (365 Wh kg-1 TNP). Moreover, the extended π-conjugated TNP macrocycle achieves anti-dissolution in electrolytes, prolonging the battery life to 50,000 cycles at 10 A g-1 with 71.6 % capacity retention. This work expands the chemical landscape of multielectron redox-bipolar organics for state-of-the-art ZOBs.

Direct carbonization of cellulose toward hydroxyl-rich porous carbons for pseudocapacitive energy storage

Designing carbon materials with specific oxygen-containing functional groups is very attractive for the precise decoration of carbon electrode materials and the basic understanding of specific charge storage mechanisms, which contributes to the further development of high-performance carbon materials for energy storage and conversion applications. In this contribution, a hydroxyl-rich micropore-dominated porous carbon material was obtained by direct carbonization of cellulose. The content of oxygen atoms in hydroxyl form in the obtained carbon is nearly 6 at.%. With the pyrolysis temperature changed, the macroscopic morphology, the specific surface area, surface functional groups, and graphitization degree of the carbon materials were changed strongly. Besides, the carbon material obtained with a carbonization temperature of 900 °C (C9) showed enhanced specific capacitance in sulfuric acid, sodium hydroxide, and sodium sulfate aqueous electrolytes, which mainly originates from the contribution of pseudocapacitance. The pseudocapacitance mainly depends on the presence of surface hydroxyl functional groups. Besides, the pseudocapacitance value of C9 material in neutral electrolytes (151.34 F g-1) is about twice that in acidic (75.9 F g-1) and alkaline (75.78 F g-1) electrolytes.

Sulfonyl Molecules Induced Oriented Lithium Deposition for Long-Term Lithium Metal Batteries

Dendrites growth and unstable interfacial Li+ transport hinder the practical application of lithium metal batteries (LMBs). Herein, we report an active layer of 2,4,6-trihydroxy benzene sulfonyl fluorine on copper substrate that induces oriented Li+ deposition and generates highly crystalline solid-electrolyte interphase (SEI) to achieve high-performance LMBs. The lithiophilic -SO2 - groups of highly crystalline SEI accept the rapidly transported Li+ ions and form a dense inner layer of LiF and Li3 N, which regulate Li+ plating morphology along the (110) crystal surface toward dendrite-free Li anode. Thus, Li||Cu cells with lithiophilic SEI achieve an average deposition efficiency of 99.8 % after 700 cycles, and Li||Li cells operate well for 1100 h. Besides, Li||LiNi0.8 Co0.1 Mn0.1 O2 cells with modified SEI exhibit a capacity retention that is 14 times than that of conventional SEI. Even at -60 °C, Li||Cu cells reach stable deposition efficiency of 83.2 % after 100 cycles.

In situ Nafion-nanofilm oriented (002) Zn electrodeposition for long-term zinc-ion batteries

Dendrite growth and parasitic reactions of a Zn metal anode in aqueous media hinder the development of up-and-coming Zn-ion batteries. Optimizing the crystal growth after Zn nucleation is promising to enable stable cyclic performance of the anode, but directly regulating specific crystal plane growth for homogenized Zn electrodeposition remains highly challenging. Herein, a perfluoropolymer (Nafion) is introduced into an aqueous electrolyte to activate a thermodynamically ultrastable Zn/electrolyte interface for long-term Zn-ion batteries. The low adsorption energy (-2.09 eV) of Nafion molecules on Zn metal ensures the in situ formation of a Nafion-nanofilm during the first charge process. This ultrathin artificial solid electrolyte interface with zincophilic -SO3- groups guides the directional Zn2+ electrodeposition along the (002) crystal surface even at high current density, yielding a dendrite-free Zn anode. The synergic Zn/electrolyte interphase electrochemistry contributes an average coulombic efficiency of 99.71% after 4500 cycles for Zn‖Cu cells, and Zn‖Zn cells achieve an ultralong lifespan of over 7000 h at 5 mA cm-2. Besides, Zn‖MnO2 cells operate well over 3000 cycles. Even at -40 °C, Zn‖Zn cells achieve stable Zn2+ plating/stripping for 1200 h.

Spatial Structure Design of Thioether-Linked Naphthoquinone Cathodes for High-Performance Aqueous Zinc-Organic Batteries

Organic electrode materials (OEMs) have gathered extensive attention for aqueous zinc-ion batteries (AZIBs) due to their structural diversity and molecular designability. However, the reported research mainly focuses on the design of the planar configuration of OEMs and does not take into account the important influence of the spatial structure on the electrochemical properties, which seriously hamper the further performance liberation of OEMs. Herein, this work has designed a series of thioether-linked naphthoquinone-derived isomers with tunable spatial structures and applied them as the cathodes in AZIBs. The incomplete conjugated structure of the elaborately engineered isomers can guarantee the independence of the redox reaction of active groups, which contributes to the full utilization of active sites and high redox reversibility. In addition, the position isomerization of naphthoquinones on the benzene rings changes the zincophilic activity and redox kinetics of the isomers, signifying the importance of spatial structure on the electrochemical performance. As a result, the 2,2'-(1,4-phenylenedithio) bis(1,4-naphthoquinone) (p-PNQ) with the smallest steric hindrance and the most independent redox of active sites exhibits a high specific capacity (279 mAh g-1 ), an outstanding rate capability (167 mAh g-1 at 100 A g-1 ), and a long-term cycling lifetime (over 2800 h at 0.05 A g-1 ).

Non-Metallic NH4 + /H+ Co-Storage in Organic Superstructures for Ultra-Fast and Long-Life Zinc-Organic Batteries

Compared with Zn2+ storage, non-metallic charge carrier with small hydrated size and light weight shows fast dehydration and diffusion kinetics for Zn-organic batteries. Here we first report NH4 + /H+ co-storage in self-assembled organic superstructures (OSs) by intermolecular interactions of p-benzoquinone (BQ) and 2, 6-diaminoanthraquinone (DQ) polymer through H-bonding and π-π stacking. BQ-DQ OSs exhibit exposed quadruple-active carbonyl motifs and super electron delocalization routes, which are redox-exclusively coupled with high-kinetics NH4 + /H+ but exclude sluggish and rigid Zn2+ ions. A unique 4e- NH4 + /H+ co-coordination mechanism is unravelled, giving BQ-DQ cathode high capacity (299 mAh g-1 at 1 A g-1 ), large-current tolerance (100 A g-1 ) and ultralong life (50,000 cycles). This strategy further boosts the capacity to 358 mAh g-1 by modulating redox-active building units, giving new insights into ultra-fast and stable NH4 + /H+ storage in organic materials for better Zn batteries.

Design and synthesis of п-conjugated aromatic heterocyclic materials with dual active sites and ultra-high rate performance for aqueous zinc-organic batteries

Acid anhydride cathode materials garner considerable interest for aqueous zinc ion batteries (AZIBs) due to ideal specific capacity and structural diversity, however, serious solubility leads to capacity degradation. Herein, 1,4,5,8-naphthalene tetracarboxylic acid dianhydride - 2,3-diamino phenothiazine (NTDP) featuring multiple active sites (6 with CN and 2 with CO) and large π-conjugated backbone, was designed and synthesized utilizing solid-phase method. The smallest energy gap (ΔE) and the lowest LUMO levels (against monomers) induced by multiple active sites and п-conjugated backbone with high aromaticity, NTDP exhibited excellent specific capacity (307.5 mA h g-1 under 0.05 A/g), ultrahigh rate performance (194.9 mA h g-1 under 20 A/g) and impressive cycling stability (190.0 mA h g-1 over 9000 cycles with a capacity retention of 91.2 % at 15 A/g). The reversible Zn2+ insertion/removal mechanism on multiple active centers (CO and CN) was proposed through XPS, FT-IR, and Raman. The specific capacity of the NTDP//zinc flexible cell was 112.6 mA h g-1 at 3 A/g under various folding angles (45°, 90°, 135°, and 180° bends), suggesting its practical potential for flexible devices. This work will offer opportunities for the rational design of battery structures.

Polymer Coating with Balanced Coordination Strength and Ion Conductivity for Dendrite-Free Zinc Anode

Decorating Zn anodes with functionalized polymers is considered as an effective strategy to inhibit dendrite growth. However, this normally brings extra interfacial resistance rendering slow reaction kinetics of Zn2+ . Herein, a poly(2-vinylpyridine) (P2VP) coating with modulated coordination strength and ion conductivity for dendrite-free Zn anode is reported. The P2VP coating favors a high electrolyte wettability and rapid Zn2+ migration speed (Zn2+ transfer number, tZn 2+ = 0.58). Electrostatic potential calculation shows that P2VP mildly coordinates with Zn2+ (adsorption energy = -0.94 eV), which promotes a preferential deposition of Zn along the (002) crystal plane. Notably, the use of partially (26%) quaternized P2VP (q-P2VP) further reduces the interfacial resistance to 126 Ω, leading to a high ion migration speed (tZn 2+ = 0.78) and a considerably low nucleation overpotential (18 mV). As a result of the synergistic effect of mild coordination and partial electrolysis, the overpotential of the q-P2VP-decorated Zn anode retains at a considerably low level (≈46 mV) over 1000 h at a high current density of 10 mA cm-2 . The assembled (NH4 )2 V6 O16 ·1.5H2 O || glass fiber || q-P2VP-Zn full cell reveals a lower average capacity decay rate of only 0.018% per cycle within 500 cycles at 1 A g-1 .

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.

Intramolecular Hydrogen Bond Improved Durability and Kinetics for Zinc-Organic Batteries

Organic compounds have the advantages of green sustainability and high designability, but their high solubility leads to poor durability of zinc-organic batteries. Herein, a high-performance quinone-based polymer (H-PNADBQ) material is designed by introducing an intramolecular hydrogen bonding (HB) strategy. The intramolecular HB (C=O⋯N-H) is formed in the reaction of 1,4-benzoquinone and 1,5-naphthalene diamine, which efficiently reduces the H-PNADBQ solubility and enhances its charge transfer in theory. In situ ultraviolet-visible analysis further reveals the insolubility of H-PNADBQ during the electrochemical cycles, enabling high durability at different current densities. Specifically, the H-PNADBQ electrode with high loading (10 mg cm-2) performs a long cycling life at 125 mA g-1 (> 290 cycles). The H-PNADBQ also shows high rate capability (137.1 mAh g-1 at 25 A g-1) due to significantly improved kinetics inducted by intramolecular HB. This work provides an efficient approach toward insoluble organic electrode materials.

Activating Organic Electrode via Trace Dissolved Organic Molecules

Organic electrode materials have gained attention for their tunable structures and sustainability, but their low electronic conductivity requires the use of large amounts of carbon additives (30 wt %) and low mass loadings (<2 mg cm-2) in electrodes. Here, we synthesize dibenzo[b,i]phenazine-5,7,12,14-tetrone (DPT) as a cathode active material for an aqueous Zn battery and find that Zn2+ storage dominates the cathode reaction. This battery demonstrates high capacity (367 mAh g-1), high-rate performance, and superlong life (12000 cycles). Remarkably, despite DPT's insulative nature, even with a high mass loading (10 mg cm-2) and only 10 wt % carbon additives, the DPT-based cathode exhibits promising performance due to trace dissolved discharge product (DPTx-). During discharge, the DPT is reduced to trace amounts of dissolved DPTx- at the cathode surface, which in turn reduces the remaining solid DPT as a redox mediator. Furthermore, dissolution-redeposition results in the reduction of DPT size and the formation of pores, further activating the electrode.

Guiding Zn Uniform Deposition with Polymer Additives for Long-lasting and Highly Utilized Zn Metal Anodes

The parasitic side reaction on Zn anode is the key issue which hinders the development of aqueous Zn-based energy storage systems on power-grid applications. Here, a polymer additive (PMCNA) engineered by copolymerizing 2-methacryloyloxyethyl phosphorylcholine (MPC) and N-acryloyl glycinamide (NAGA) was employed to regulate the Zn deposition environment for satisfying side reaction inhibition performance during long-term cycling with high Zn utilization. The PMCNA can preferentially adsorb on Zn metal surface to form a uniform protective layer for effective water molecule repelling and side reaction resistance. In addition, the PMCNA can guide Zn nucleation and deposition along 002 plane for further side reaction and dendrite suppression. Consequently, the PMCNA additive can enable the Zn//Zn battery with an ultrahigh depth of discharge (DOD) of 90.0 % for over 420 h, the Zn//active carbon (AC) capacitor with long cycling lifespan, and the Zn//PANI battery with Zn utilization of 51.3 % at low N/P ratio of 2.6.

Carboxyl-Substituted Organic Molecule Assembled with MXene Nanosheets for Boosting Aqueous Na+ Storage

Aqueous alkali-ion batteries have enormous promise as a kind of safe, reliable, and sustainable energy technologies for power supplies. Although organic molecules with tunable and diverse configurations are potential electroactive materials, their inadequate redox activity and electron affinity hinder the practical application for aqueous alkali-ion storage. Herein, a novel electron-withdrawing carboxyl-substituted dipyridophenazine (CDPPZ) organic molecule is designed and synthesized for aqueous Na+ storage. Significantly, the introduction of carboxyl functional groups not only serves as additional redox-active sites for reversible Na+ coordination, but also causes the rearrangement of intramolecular electron cloud density to reduce the energy level, thereby ensuring the high redox activity and superior electron affinity of the CDPPZ molecule. For portable electronics, a self-supporting, adhesive-free, and flexible CDPPZ@MXene electrode is further constructed by incorporating highly redox-active CDPPZ molecule with MXene nanosheets, which delivers a fast, stable, and unrivaled aqueous Na+ storage capability with a high reversible capacity of 172.6 mAh cm-3 and excellent redox stability over 4000 cycles. In situ dynamic analysis combined with theoretical calculations illustrates the Na+ storage mechanism and corresponding coordinated pathway. Finally, a high-performance flexible aqueous Na-ion battery is fabricated with exceptional energy/power density and remarkable cycling lifespan, further confirming its promising application prospect.

Aqueous Organic Batteries Using the Proton as a Charge Carrier

Benefiting from the merits of low cost, nonflammability, and high operational safety, aqueous rechargeable batteries have emerged as promising candidates for large-scale energy-storage applications. Among various metal-ion/non-metallic charge carriers, the proton (H+ ) as a charge carrier possesses numerous unique properties such as fast proton diffusion dynamics, a low molar mass, and a small hydrated ion radius, which endow aqueous proton batteries (APBs) with a salient rate capability, a long-term life span, and an excellent low-temperature electrochemical performance. In addition, redox-active organic molecules, with the advantages of structural diversity, rich proton-storage sites, and abundant resources, are considered attractive electrode materials for APBs. However, the charge-storage and transport mechanisms of organic electrodes in APBs are still in their infancy. Therefore, finding suitable electrode materials and uncovering the H+ -storage mechanisms are significant for the application of organic materials in APBs. Herein, the latest research progress on organic materials, such as small molecules and polymers for APBs, is reviewed. Furthermore, a comprehensive summary and evaluation of APBs employing organic electrodes as anode and/or cathode is provided, especially regarding their low-temperature and high-power performances, along with systematic discussions for guiding the rational design and the construction of APBs based on organic electrodes.

NH4 + Charge Carrier Coordinated H-Bonded Organic Small Molecule for Fast and Superstable Rechargeable Zinc Batteries

Organic small molecules as high-capacity cathodes for Zn-organic batteries have inspired numerous interests, but are trapped by their easy-dissolution in electrolytes. Here we knit ultrastable lock-and-key hydrogen-bonding networks between 2, 7-dinitropyrene-4, 5, 9, 10-tetraone (DNPT) and NH4 + charge carrier. DNPT with octuple-active carbonyl/nitro centers (H-bond acceptor) are redox-exclusively accessible for flexible tetrahedral NH4 + ions (H-bond donator) but exclude larger and rigid Zn2+ , due to a lower activation energy (0.14 vs. 0.31 eV). NH4 + coordinated H-bonding chemistry conquers the stability barrier of DNPT in electrolyte, and gives fast diffusion kinetics of non-metallic charge carrier. A stable two-step 4e- NH4 + coordination with DNPT cathode harvests a high capacity (320 mAh g-1 ), a high-rate capability (50 A g-1 ) and an ultralong life (60,000 cycles). This finding points to a new paradigm for H-bond stabilized organic small molecules to design advanced zinc batteries.

In Situ Electrochemical Activation of Hydroxyl Polymer Cathode for High-Performance Aqueous Zinc-Organic Batteries

The slow reaction kinetics and structural instability of organic electrode materials limit the further performance improvement of aqueous zinc-organic batteries. Herein, we have synthesized a Z-folded hydroxyl polymer polytetrafluorohydroquinone (PTFHQ) with inert hydroxyl groups that could be partially oxidized to the active carbonyl groups through the in situ activation process and then undertake the storage/release of Zn2+ . In the activated PTFHQ, the hydroxyl groups and S atoms enlarge the electronegativity region near the electrochemically active carbonyl groups, enhancing their electrochemical activity. Simultaneously, the residual hydroxyl groups could act as hydrophilic groups to enhance the electrolyte wettability while ensuring the stability of the polymer chain in the electrolyte. Also, the Z-folded structure of PTFHQ plays an important role in reversible binding with Zn2+ and fast ion diffusion. All these benefits make the activated PTFHQ exhibit a high specific capacity of 215 mAh g-1 at 0.1 A g-1 , over 3400 stable cycles with a capacity retention of 92 %, and an outstanding rate capability of 196 mAh g-1 at 20 A g-1 .

Tuning electron delocalization of hydrogen-bonded organic framework cathode for high-performance zinc-organic batteries

Stable cathodes with multiple redox-active centres affording a high energy density, fast redox kinetics and a long life are continuous pursuits for aqueous zinc-organic batteries. Here, we achieve a high-performance zinc-organic battery by tuning the electron delocalization within a designed fully conjugated two-dimensional hydrogen-bonded organic framework as a cathode material. Notably, the intermolecular hydrogen bonds endow this framework with a transverse two-dimensional extended stacking network and structural stability, whereas the multiple C = O and C = N electroactive centres cooperatively trigger multielectron redox chemistry with super delocalization, thereby sharply boosting the redox potential, intrinsic electronic conductivity and redox kinetics. Further mechanistic investigations reveal that the fully conjugated molecular configuration enables reversible Zn2+/H+ synergistic storage accompanied by 10-electron transfer. Benefitting from the above synergistic effects, the elaborately tailored organic cathode delivers a reversible capacity of 498.6 mAh g-1 at 0.2 A g-1, good cyclability and a high energy density (355 Wh kg-1).

Tuning active sites for highly efficient bifunctional oxygen electrocatalysts of rechargeable zinc-air battery

High activity, excellent durability, and low-cost oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) bifunctional catalysts are highly required for rechargeable zinc (Zn)-air batteries. Herein, we designed an electrocatalyst by integrating the ORR active species of ferroferric oxide (Fe₃O₄) and the OER active species of cobaltous oxide (CoO) into the carbon nanoflower. By well regulating and controlling the synthesis parameters, Fe₃O₄ and CoO nanoparticles were uniformly inserted into the porous carbon nanoflower. This electrocatalyst can reduce the potential gap between the ORR and OER to 0.79 V. The Zn-air battery assembled with it exhibited an open-circuit voltage of 1.457 V, a stable discharge of 98 h, a high specific capacity of 740 mA h g^-1, a large power density of 137 mW cm^-2, as well as good charge/discharge cycling performance, exceeding the performance of platinum/carbon (Pt/C). This work provides references for exploring highly efficient non-noble metal oxygen electrocatalysts by tuning ORR/OER active sites.

Proton-Reservoir Hydrogel Electrolyte for Long-Term Cycling Zn/PANI Batteries in Wide Temperature Range

Advanced aqueous batteries are promising for next generation flexible devices owing to the high safety, yet still requiring better cycling stability and high capacities in wide temperature range. Herein, a polymeric acid hydrogel electrolyte (PAGE) with 3 M Zn(ClO₄ )₂ was fabricated for high performance Zn/polyaniline (PANI) batteries. With PAGE, even at -35 °C the Zn/Zn symmetrical battery can keep stable for more than 1 500 h under 2 mA cm^-2 , and the Zn/PANI battery can provide ultra-high stable specific capacity of 79.6 mAh g^-1 for more than 70 000 cycles at 15 A g^-1 . This can be mainly ascribed to the -SO₃ ^- H⁺ function group in PAGE. It can generate constant protons and guide the (002) plane formation to accelerate the PANI redox reaction kinetics, increase the specific capacity, and suppress the side reaction and dendrites. This proton-supplying strategy by polymeric acid hydrogel may further propel the development of high performance aqueous batteries.

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.

Integrated Construction Improving Electrochemical Performance of Stretchable Supercapacitors Based on Ant-Nest Amphiphilic Gel Electrolytes

Aqueous integrated stretchable supercapacitors (ISSCs) have attracted extensive attention due to the intrinsic safety in future wearable electronics. However, aqueous ISSCs usually suffer from low energy density and poor dynamic deformation stability owing to the conventional hydrogel electrolytes' narrow electrochemical stability window (ESW) and dissatisfied interface bonding. Herein, an ant-nest amphiphilic polyurethane hydro/organogel electrolyte (sAPUGE) with a wide ESW (≈2.2 V) and superb self-adhesion is prepared by electrospinning, which interacts with carbon-based stretchable electrodes for the construction of flame-retardant PU-based sAPUGE-ISSC. Benefitting from the synergistic effect of chemical bonding and mechanical meshing between the electrode and gel electrolyte interface, as-assembled sAPUGE-ISSC delivers a high energy density of 13.7 mWh cm^-3 (at a power density of 0.126 W cm^-3 ) and outstanding dynamic deformation stability (98.3% capacitance retention after 500 stretching cycles under 100% strain). This unique hydro/organogel electrolyte provides a pathway toward the next generation of wearable energy products in modern electronics.