A High-Voltage Zn-Organic Battery Using a Nonflammable Organic Electrolyte

Recent advances in zinc-ion dehydration strategies for optimized Zn-metal batteries

Aqueous Zn-metal batteries have attracted increasing interest for large-scale energy storage owing to their outstanding merits in terms of safety, cost and production. However, they constantly suffer from inadequate energy density and poor cycling stability due to the presence of zinc ions in the fully hydrated solvation state. Thus, designing the dehydrated solvation structure of zinc ions can effectively address the current drawbacks of aqueous Zn-metal batteries. In this case, considering the lack of studies focused on strategies for the dehydration of zinc ions, herein, we present a systematic and comprehensive review to deepen the understanding of zinc-ion solvation regulation. Two fundamental design principles of component regulation and pre-desolvation are summarized in terms of solvation environment formation and interfacial desolvation behavior. Subsequently, specific strategy based distinct principles are carefully discussed, including preparation methods, working mechanisms, analysis approaches and performance improvements. Finally, we present a general summary of the issues addressed using zinc-ion dehydration strategies, and four critical aspects to promote zinc-ion solvation regulation are presented as an outlook, involving updating (de)solvation theories, revealing interfacial evolution, enhancing analysis techniques and developing functional materials. We believe that this review will not only stimulate more creativity in optimizing aqueous electrolytes but also provide valuable insights into designing other battery systems.

Self-templating synthesis strategy of oxygen-doped carbon from unique wasted pulping liquid directly as a cathode material for high-performance zinc ion hybrid capacitors

Affinity and storage capacity for zinc ions of the electrode materials are crucial factors on the properties of zinc ion hybrid capacitors (ZHICs). Wasted pulping liquor with abundant carbohydrates, lignin and inorganic matter served as a unique precursor to produce embedded oxygen-doped hierarchical porous carbon directly through a one-step carbonization process in this investigation. In carbonization process, lignin can serve effectively as the carbon framework, carbohydrates not only act as sacrificial templates but also offer a plentiful oxygen source which can increase the affinity for Zn2+, and sodium-containing inorganic substances plays a role as hard templates to optimize the pore structure. The resulting porous carbon under carbonization temperature of 800 °C shows a high specifical area of 2186 m2g-1 with oxygen content of 4.8 %, which can reduce the adsorption energy of Zn2+ from -0.16 eV to -0.32 eV through electrochemical techniques and density functional theory (DFT) calculations, the incorporation of oxygen was demonstrated to enhance the adsorption and desorption kinetics of Zn2+, suggesting a bright future for application in the domain of energy storage. The resulting ZIHC assembly showcases a notable energy density of 84.6 Wh kg-1 at a power density of 359 W kg-1. Remarkably, even after 10,000 charge and discharge cycles, it exhibits exceptional cycle stability with retaining 86.56 % of its capacity. Consequently, this approach provides fresh insights for exploring the facile and commercial fabrication of biomass-derived cathodes for ZIHCs, thereby propelling the progress of eco-friendly energy storage devices.

Organic Electrode Materials for Energy Storage and Conversion: Mechanism, Characteristics, and Applications

ConspectusLithium ion batteries (LIBs) with inorganic intercalation compounds as electrode active materials have become an indispensable part of human life. However, the rapid increase in their annual production raises concerns about limited mineral reserves and related environmental issues. Therefore, organic electrode materials (OEMs) for rechargeable batteries have once again come into the focus of researchers because of their design flexibility, sustainability, and environmental compatibility. Compared with conventional inorganic cathode materials for Li ion batteries, OEMs possess some unique characteristics including flexible molecular structure, weak intermolecular interaction, being highly soluble in electrolytes, and moderate electrochemical potentials. These unique characteristics make OEMs suitable for applications in multivalent ion batteries, low-temperature batteries, redox flow batteries, and decoupled water electrolysis. Specifically, the flexible molecular structure and weak intermolecular interaction of OEMs make multivalent ions easily accessible to the redox sites of OEMs and facilitate the desolvation process on the redox site, thus improving the low-temperature performance, while the highly soluble nature enables OEMs as redox couples for aqueous redox flow batteries. Finally, the moderate electrochemical potential and reversible proton storage and release of OEMs make them suitable as redox mediators for water electrolysis. Over the past ten years, although various new OEMs have been developed for Li-organic batteries, Na-organic batteries, Zn-organic batteries, and other battery systems, batteries with OEMs still face many challenges, such as poor cycle stability, inferior energy density, and limited rate capability. Therefore, previous reviews of OEMs mainly focused on organic molecular design for organic batteries or strategies to improve the electrochemical performance of OEMs. A comprehensive review to explore the characteristics of OEMs and establish the correlation between these characteristics and their specific application in energy storage and conversion is still lacking.In this Account, we initially provide an overview of the sustainability and environmental friendliness of OEMs for energy storage and conversion. Subsequently, we summarize the charge storage mechanisms of the different types of OEMs. Thereafter, we explore the characteristics of OEMs in comparison with conventional inorganic intercalation compounds including their structural flexibility, high solubility in the electrolyte, and appropriate electrochemical potential in order to establish the correlations between their characteristics and potential applications. Unlike previous reviews that mainly introduce the electrochemical performance progress of different organic batteries, this Account specifically focuses on some exceptional applications of OEMs corresponding to the characteristics of organic electrode materials in energy storage and conversion, as previously published by our groups. These applications include monovalent ion batteries, multivalent ion batteries, low-temperature batteries, redox flow batteries with soluble OEMs, and decoupled water electrolysis employing organic electrodes as redox mediators. We hope that this Account will make an invaluable contribution to the development of organic electrode materials for next-generation batteries and help to unlock a world of potential energy storage applications.

Aqueous Rechargeable Zn-Iodine Batteries: Issues, Strategies and Perspectives

The static aqueous rechargeable Zn-Iodine batteries (ARZiBs) have been studied extensively because of their low-cost, high-safety, moderate voltage output, and other unique merits. Nonetheless, the poor electrical conductivity and thermodynamic instability of the iodine cathode, the complicated conversion mechanism, and the severe interfacial reactions at the Zn anode side induce their low operability and unsatisfactory cycling stability. This review first clarifies the typical configuration of ARZiBs with a focus on the energy storage mechanism and uncovers the issues of the ARZiBs from a fundamental point of view. After that, it categorizes the recent optimization strategies into cathode fabrication, electrolyte modulation, and separator/anode modification; and summarizes and highlights the achieved progress of these strategies in advanced ARZiBs. Given that the ARZiBs are still at an early stage, the future research outlook is provided, which hopefully may guide the rational design of advanced ARZiBs.

Carbonate Ester-Based Electrolyte Enabling Rechargeable Zn Battery to Achieve High Voltage and High Zn Utilization

Owing to the high H2O activity, the aqueous electrolyte in the Zn battery exhibits a narrow electrochemical window and inevitable hydrogen evolution reaction, limiting the anode utilization ratio and performance at high voltage. Carbonate ester, the well-developed electrolyte solvent in Li-ion batteries, exhibits aprotic properties and high anodic stability. However, its use in Zn metal batteries is limited due to the low solubility of Zn salts in carbonate esters. Herein, we propose a carbonate ester-based electrolyte (EC:DMC:EMC = 1:1:1 wt %), which contains a new Zn salt (Zn(BHFip)2) characterized by low cost, easy synthesis, and excellent aprotic solvent solubility. The BHFip- anion assists in forming Zn2+ conductive SEI on the anode and decomposes at high voltage to generate a protective CEI layer on the cathode. The Zn//Zn symmetric cell using such electrolyte achieves a remarkable Zn utilization ratio of 91% for 125 h, which has rarely been reported before. Furthermore, the Zn//LiMn2O4 full cell with an average operation voltage of 1.7 V demonstrates reliable cycling for 135 cycles with an N/P ratio of 1:1. In addition, the Zn//LiNi0.5Mn1.5O4 full cell exhibits a high discharge median voltage exceeding 2.2 V for 280 cycles, with the high voltage plateau (above 2 V) constituting 82% of the total capacity.

Recent progress in critical electrode and electrolyte materials for flexible zinc-ion batteries

With the increasing popularity of flexible and wearable electronic devices, the demand for power supplies that can be easily bent or worn is also rapidly growing. However, traditional lithium ion batteries are difficult to adapt to complex wearable devices because of their unsatisfactory flexibility and thickness as well as safety issues. Zinc-ion batteries have several advantages, including low redox potential, high theoretical capacity, high safety, and abundant reserves. These features make flexible zinc-ion batteries (FZIBs) an ideal wearable energy storage device candidate. The electrochemical performance and mechanical deformability of FZIBs were pivotally determined based on the properties of their electrode and electrolyte. Herein, we summarize some recent advances from 2015 to 2023 in the design and preparation of various electrode and electrolyte materials for FZIBs with controllable morphology and structure, excellent mechanical property, and enhanced electrochemical performance. Moreover, efforts to explore the potential practical applications of FZIBs have also been considered. Finally, we present and discuss current challenges and opportunities for the development of high-performance FZIBs.

Key to High Performance Ion Hybrid Capacitor: Weakly Solvated Zinc Cations

Zinc ion hybrid capacitors suffer from lack of reversibility and dendrite formation. An electrolyte, based on a solution of a zinc salt in acetonitrile and tetramethylene sulfone, allows smooth zinc deposition with high coulombic efficiency in a Zn||stainless steel cell (99.6% for 2880 cycles at 1.0 mA cm-2 , 1.0 mAh cm-2 ). A Zn||Zn cell operates stably for at least 7940 h at 1.0 mA cm-2 with an area capacity of 10 mAh cm-2 , or 648 h at 90% depth of discharge and 1 mA cm-2 , 9.0 mAh cm-2 . Molecular dynamics simulations reveal the reason for the excellent reversibility: The zinc cation is only weakly solvated than in pure tetramethylene sulfone with the closest atoms at 3.3 to 3.8 Å. With this electrolyte, a zinc||activated-carbon hybrid capacitor exhibits an operating voltage of 2.0 to 2.5 V, an energy-density of 135 Wh kg-1 and a power-density of 613 W kg-1 at 0.5 A g-1 . At the very high current-density of 15 A g-1 , 29.3 Wh kg-1 and 14 250 W kg-1 are achieved with 81.2% capacity retention over 9000 cycles.

The Construction of Binary Phase Electrolyte Interface for Highly Stable Zinc Anodes

Metal zinc is a promising anode candidate of aqueous zinc-ion batteries due to high theoretical capacity, low cost, and high safety. However, it often suffers from hydrogen evolution reaction (HER), dendrite growth, and formation of by-products. Herein, a triethyl phosphate (TEP)/H2 O binary phase electrolyte (BPE) interface is developed by introducing TEP-based electrolyte-wetted hydrophobic polypropylene (PP) separator onto the Zn anode surface. The equilibrium of the BPE interface depends on the comparable surface tensions of H2 O-based and TEP-based electrolytes on hydrophobic PP separator surfaces. The BPE interface induces Zn2+ solvation structure conversion from [Zn(H2 O)x ]2+ to [Zn(TEP)n (H2 O)y ]2+ , where most solvated H2 O molecules are removed. In [Zn(TEP)n (H2 O)y ]2+ , the residual H2 O molecules can be further constrained by the formation of H bonds between TEP and H2 O molecules. Consequently, the ionization of solvated H2 O molecules is effectively suppressed, and HER and by-products are effectively restricted on Zn anode surfaces in BPE. As a result, Zn anodes exhibit a high Coulombic efficiency of 99.12% and superior cycling performance of 6000 h, which is much higher than the case in single-phase aqueous electrolytes. To illustrate the feasibility of BPE in full cells, the Zn/Alx V2 O5 batteries are assembled based on the BPE and exhibited enhanced cycling performance.

A High-Potential Bipolar Phenothiazine Derivative Cathode for Aqueous Zinc Batteries

Aqueous zinc ion batteries (AZIBs) are gaining popularity as advanced energy storage devices that are economical, safe, and use resource-abundant storage options. In this study, we have synthesized a bipolar phenothiazine organic scaffold known as 3,7-bis(melaminyl)phenothiazin-5-ium iodide (PTDM), which is obtained by undergoing nucleophilic substitution through phenothiazinium tetraiodide hydrate (PTD) and melamine. Electrochemical results indicate that PTDM can act as a high-potential cathode material for rechargeable AZIBs. In detail, the aqueous PTDM//Zn full cell exhibits a high average voltage of approximate 1.13 V, along with a specific capacity of 118.3 mAh g-1 at 0.1 A g-1 . Furthermore, this demonstrated cell displays moderate long-term cycling stability over 6400 cycles, which is encouraging and suggests potential for developing advanced organic electrode materials for rechargeable AZIBs.

Ultraviolet-Assisted Printing of Flexible Solid-State Zn-Ion Battery with a Heterostructure Electrolyte

Flexible solid-state Zn-ion batteries (ZIBs) have garnered considerable attention for next-generation power sources, but the corrosion, dendrite growth, and interfacial problems severely hinder their practical applications. Herein, a high-performance flexible solid-state ZIB with a unique heterostructure electrolyte is facilely fabricated through ultraviolet-assisted printing strategy. The solid polymer/hydrogel heterostructure matrix not only isolates water molecules and optimizes electric field distribution for dendrite-free anode, but also facilitates fast and in-depth Zn2+ transport in the cathode. The in situ ultraviolet-assisted printing creates cross-linked and well-bonded interfaces between the electrodes and the electrolyte, enabling low ionic transfer resistance and high mechanical stability. As a result, the heterostructure electrolyte based ZIB outperforms single-electrolyte based cells. It not only delivers a high capacity of 442.2 mAh g-1 with long cycling life of 900 cycles at 2 A g-1 , but also maintains stable operation under mechanical bending and high-pressure compression in a wide temperature range (-20 °C to 100 °C).

Electrolyte for High-Energy- and Power-Density Zinc Batteries and Ion Capacitors

Growth of dendrites, limited coulombic efficiency (CE), and the lack of high-voltage electrolytes restrict the commercialization of zinc batteries and capacitors. These issues are resolved by a new electrolyte, based on the zinc(II)-betaine complex [Zn(bet)₂ ][NTf₂ ]₂ . Solutions in acetonitrile (AN) avoid dendrite formation. A Zn||Zn cell operates stably over 10 110 h (5055 cycles) at 0.2 mA cm^-2 or 110 h at 50 mA cm^-2 , and has an area capacity of 113 mAh cm^-2 at 80% depth of discharge. A zinc-graphite battery performs at 2.6 V with a midpoint discharge-voltage of 2.4 V. The capacity-retention at 3 A g^-1 (150 C) is 97% after 1000 cycles and 68% after 10 000 cycles. The charge/discharge time is about 24 s at 3.0 A g^-1 with an energy density of 49 Wh kg^-1 at a power density of 6864 W kg^-1 based on the cathode. A zinc||activated-carbon ion-capacitor (coin cell) exhibits an operating-voltage window of 2.5 V, an energy density of 96 Wh kg^-1 with a power density of 610 W kg^-1 at 0.5 A g^-1 . At 12 A g^-1 , 36 Wh kg^-1 , and 13 600 W kg^-1 are achieved with 90% capacity-retention and an average CE of 96% over 10 000 cycles. Quantum-chemical methods and vibrational spectroscopy reveal [Zn(bet)₂ (AN)₂ ]²⁺ as the dominant complex in the electrolyte.

H2 O Activity Adjustment by Hydrogen Bonding Enables High-Performance Zn-Organic Battery

The advantages of low cost and high safety of zinc (Zn) metal have attracted much attention on its application in batteries, but H₂ O-induced issues of hydrogen evolution reaction (HER), Zn corrosion, and Zn dendrites formation limit the application. Here, a strategy of adjusting H₂ O activity was provided by adding glycerol (GL) and acetonitrile (AN) into aqueous electrolyte to form hydrogen bonds between organic solvents and H₂ O, which alleviated the Zn corrosion. Furthermore, molecular dynamics (MD) simulation indicated that GL could exclude H₂ O from the Zn²⁺ solvation shell, thus preventing undesired HER and Zn dendrites formation. Therefore, the corresponding Zn//Zn symmetrical cell showed a ultralong lifespan (1300 h). Then, a Zn-organic battery with 3,7-dimorpholino-phenothiazin-5-ium iodide (FD28) cathode was fabricated by using such electrolyte. Interestingly, the reduced H₂ O activity also ensured the stable operation of organic cathode, and thus the full cell showed superior cycle stability for over 9000 cycles (≈1100 h), which is superior to previous reports. Moreover, such electrolyte owns novel properties of nonflammability, great weatherability, and low freezing point, thus boosting the practicality of the battery.

Rapidly Photocurable Solid-State Poly(ionic liquid) Ionogels For Thermally Robust and Flexible Electrochromic Devices

Formation of ionogels through in situ polymerization can effectively improve electrolyte processability; however, the curing process has been slow and oxygen-sensitive. Considering the low oxygen solubility of poly(ionic liquid)s (PILs), in situ polymerized ionogels are designed to realize excellent electrolytes. Herein, two in situ polymerized ionogels (PIL A & PIL B) are formulated, and they can be rapidly photocured within a minute. The ionogels are highly transparent, stretchable, and exhibit excellent physicochemical stability, including thermal, electrochemical, and air stability, allowing them to perform in various conditions. Benefitting from these properties, two high-performance electrochromic devices (ECDs) are assembled, with iron-centered coordination polymer (FeCP) and tungsten oxide (P-WO₃ ) electrochromic materials, achieving high color contrast (45.2% and 56.4%), fast response time (1.5/1.9 and 1.7/6.4 s), and excellent cycling endurance (>90% retention over 3000 cycles). Attributed to the thermal robustness of the ionogels, the ECDs can also be operated over a wide temperature range (-20 to 100 °C). With the use of deformable substrates (e.g., ultrathin ITO glass), curved electrochromic eye protector and flexible electrochromic displays are realized, highlighting their potential use in futuristic wearables.

Electrolytes for Multivalent Metal-Ion Batteries: Current Status and Future Prospect

Electrochemical energy storage has experienced unprecedented advancements in recent years and extensive discussions and reviews on the progress of multivalent metal-ion batteries have been made mainly from the aspect of electrode materials, but relatively little work comprehensively discusses and provides an outlook on the development of electrolytes in these systems. Under this circumstance, this Review will initially introduce different types of electrolytes in current multivalent metal-ion batteries and explain the basic ion conduction mechanisms, preparation methods, and pros and cons. On this basis, we will discuss in detail the research and development of electrolytes for multivalent metal-ion batteries in recent years, and finally, critical challenges and prospects for the application of electrolytes in multivalent metal-ion batteries will be put forward.

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

Highly active and stable cathodes are critical for aqueous Zn-organic batteries with high capacity, fast redox kinetics, and long life. We herein report para-, meta-, and ortho-dinitrobenzene (p-, m-, and o-DB) containing two successive two-electron processes, as cathode materials to boost the battery performance. Theoretical and experimental studies reveal that nitro constitutional isomerism is key to zincophilic activity and redox kinetics. p-DB hosted in carbon nanoflower harvests a high capacity of 402 mAh g^-1 and a superior stability up to 25 000 cycles at 5 A g^-1 , giving a Zn-organic battery with a high energy density of 230 Wh kg^-1 . An anionic co-insertion charge storage mechanism is proposed, entailing a two-step (de)coordination of Zn(CF₃ SO₃ )⁺ with nitro oxygen. Besides, dinitrobenzene can be electrochemically optimized by side group regulation via implanting electron-withdrawing motifs. This work opens a new window to design multielectron nitroaromatics for Zn-organic batteries.

Surface Transformation Enables a Dendrite-Free Zinc-Metal Anode in Nonaqueous Electrolyte

Significant challenges remain in developing rechargeable zinc batteries mainly because of reversibility problems on zinc-metal anodes. The dendritic growth and hydrogen evolution on zinc electrodes are major obstacles to overcome in developing practical and safe zinc batteries. Here, a dendrite-free and hydrogen-free Zn-metal anode with high Coulombic efficiency up to 99.6% over 300 cycles is realized in a newly designed nonaqueous electrolyte, which comprises an inexpensive zinc salt, zinc acetate, and a green low-cost solvent, dimethyl sulfoxide. Surface transformation on Cu substrate plays a critical role in facilitating the dendrite-free deposition process, which lowers the diffusion energy barrier of the Zn atoms, leading to a uniform and compact thin film for zinc plating. Furthermore, in situ electrochemical atomic force microscopy reveals the plating process via a layer-by-layer growth mechanism and the stripping process through an edge-dissolution mechanism. In addition, Zn||Mo₆ S₈ full cells exhibit excellent electrochemical performance in terms of cycling stability and rate capability. This work presents a new opportunity to develop nonaqueous rechargeable zinc batteries.

A Binary Hydrate-Melt Electrolyte with Acetate-Oriented Cross-Linking Solvation Shells for Stable Zinc Anodes

Aqueous zinc-ion batteries (ZIBs) with low cost and high safety are promising energy-storage devices. However, ZIBs with metal Zn anodes usually suffer from low coulombic efficiency and poor cycling performance due to the occurrence of side reactions on the Zn anodes. Here, a binary hydrate-melt ZnCl₂ /Zn(OAc)₂ electrolyte is designed to suppress the hydrogen evolution reaction and by-product formation on Zn anodes by adjusting the Zn²⁺ solvation structure. In the solvation structure of the hydrate-melt ZnCl₂ /Zn(OAc)₂ electrolyte, the carboxylate group in OAc^- will coordinate with the Zn²⁺ , which will weaken the interaction between Zn²⁺ and H₂ O molecules to achieve higher ionization energy of H₂ O molecules. Simultaneously, these carboxylate groups of OAc^- can serve as H-bond acceptors to construct H-bonds with H₂ O molecules in their neighboring solvation structures, forming a cross-linking H-bond network. Such a cross-linking H-bond network further suppresses the water activity in ZnCl₂ /Zn(OAc)₂ electrolyte. As a result, in such an electrolyte, the side reactions are effectively restricted on Zn anodes and thus Zn anodes can achieve a high coulombic efficiency of 99.59% even after cycling. To illustrate the feasibility of the ZnCl₂ /Zn(OAc)₂ electrolyte in aqueous ZIBs, Zn||p-chloranil cells are assembled based on the ZnCl₂ /Zn(OAc)₂ electrolyte. The resultant Zn||p-chloranil cells exhibit enhanced cycling performance compared with the cases with a conventional ZnSO₄ electrolyte.

Ether-Water Hybrid Electrolyte Contributing to Excellent Mg Ion Storage in Layered Sodium Vanadate

Magnesium ion batteries have potential for large-scale energy storage. However, the high charge density of Mg²⁺ ions establishes a strong intercalation energy barrier in host materials, causing sluggish diffusion kinetics and structural degradation. Here, we report that the kinetic and dissolution issues connected to cathode materials can be resolved simultaneously using a tetraethylene glycol dimethyl ether (TEGDME)-water hybrid electrolyte. The lubricating and shielding effect of water solvent could boost the swift transport of Mg²⁺, contributing to a high diffusion coefficient within the sodium vanadate (NaV₈O₂₀·nH₂O) cathode. Meanwhile, the organic TEGDME component can coordinate with water to diminish its activity, thus providing the hybrid electrolyte with a broad electrochemical window of 3.9 V. More importantly, the TEGDME preferentially amassed at the interface, leading to a robust cathode electrolyte interface layer that suppresses the dissolution of vanadium species. Consequently, the NaV₈O₂₀·nH₂O cathode achieved a specific capacity of 351 mAh g^-1 at 0.3 A g^-1 and a long cycle life of 1000 cycles in this hybrid electrolyte. A mechanism study revealed the reversible interaction of Mg²⁺ during cycles. This organic water hybrid electrolyte is effective for overcoming the difficulty of multivalent ion storage.

From room temperature to harsh temperature applications: Fundamentals and perspectives on electrolytes in zinc metal batteries

As one of the most competitive candidates for the next-generation energy storage systems, the emerging rechargeable zinc metal battery (ZMB) is inevitably influenced by beyond-room-temperature conditions, resulting in inferior performances. Although much attention has been paid to evaluating the performance of ZMBs under extreme temperatures in recent years, most academic electrolyte research has not provided adequate information about physical properties or practical testing protocols of their electrolytes, making it difficult to assess their true performance. The growing interest in ZMBs is calling for in-depth research on electrolyte behavior under harsh practical conditions, which has not been systematically reviewed yet. Hence, in this review, we first showcase the fundamentals behind the failure of ZMBs in terms of temperature influence and then present a comprehensive understanding of the current electrolyte strategies to improve battery performance at harsh temperatures. Last, we offer perspectives on the advance of ZMB electrolytes toward industrial application.

Non-flammable, dilute, and hydrous organic electrolytes for reversible Zn batteries

Rechargeable Zn batteries hold great practicability for cost-effective sustainable energy storage but suffer from irreversibility of the Zn anode in aqueous electrolytes due to parasitic H₂ evolution, corrosion, and dendrite growth. Herein, we report a non-flammable, dilute, and hydrous organic electrolyte by dissolving low-cost hydrated Zn(ClO₄)₂·6H₂O in trimethyl phosphate (TMP), which homogenizes plating/stripping and enables in situ formation of a Zn₃(PO₄)₂–ZnCl₂-rich interphase to stabilize the Zn anode. A dilute 0.5 m Zn(ClO₄)₂·6H₂O/TMP electrolyte featuring a H₂O-poor Zn²⁺-solvation sheath and low water activity enables significantly enhanced Zn reversibility and a wider electrochemical window than the concentrated counterpart. In this formulated electrolyte, the Zn anode exhibits a high efficiency of 99.5% over 500 cycles, long-term cycling for 1200 h (5 mA h cm⁻² at 5 mA cm⁻²) and stable operation at 50 °C. The results would guide the design of hydrous organic electrolytes for practical rechargeable batteries employing metallic electrode materials.

A non-flammable, dilute, and hydrous organic electrolyte can homogenize Zn plating/stripping, suppress water decomposition, and form organic–inorganic hybrid interphase on Zn, thus contributing to highly reversible Zn metal batteries.

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.