High-Density and Robust Charge Storage with Poly(anthraquinone-substituted norbornene) for Organic Electrode-Active Materials in Polymer–Air Secondary Batteries

Initiating a High-Rate and Stable Aqueous Air Battery by Using Organic N-Heterocycle Anode

Alkaline metal-air batteries are advantageous in high voltage, low cost, and high safety. However, metal anodes are heavily eroded in strong alkaline electrolytes, causing serious side reactions including dendrite growth, passivation, and hydrogen evolution. To address this limitation, we successfully synthesized an organic N-heterocycle compound (NHCC) to serve as an alternative anode. This compound not only exhibits remarkable stability but also possesses a low redox potential (-1.04 V vs. Hg/HgO) in alkaline environments. To effectively complement the low redox potential of the NHCC anode, we designed a dual-salt highly concentrated electrolyte (4.0 M KOH+10.0 M KCF3 SO3 ). This electrolyte expands the electrochemical stability window to 2.3 V through the robust interaction between the O atom in H2 O molecule with the K+ of KCF3 SO3 (H-O⋅⋅⋅KCF3 SO3 ). We further demonstrated the K+ uptaken/extraction storage mechanism of NHCC anodes. Consequently, the alkaline aqueous NHCC anode-air batteries delivers a high battery voltage of 1.6 V, high-rate performance (101.9 mAh g-1 at 100 A g-1 ) and long cycle ability (30,000 cycles). Our work offers a molecular engineering strategy for superior organic anode materials and develops a novel double superconcentrated conductive salt electrolyte for the construction of high-rate, long-cycle alkaline aqueous organic anode-air batteries.

Anthraquinone-Based Silicate Covalent Organic Frameworks as Solid Electrolyte Interphase for High-Performance Lithium-Metal Batteries

Lithium (Li)-metal batteries (LMBs) possess the highest theoretical energy density among current battery designs and thus have enormous potential for use in energy storage. However, the development of LMBs has been severely hindered by safety concerns arising from dendrite growth and unstable interphases on the Li anode. Covalent organic frameworks (COFs) incorporating either redox-active or anionic moieties on their backbones have high Li-ion (Li+) conductivities and mechanical/chemical stabilities, so are promising for solid electrolyte interphases (SEIs) in LMBs. Here, we synthesized anthraquinone-based silicate COFs (AQ-Si-COFs) that contained both redox-active and anionic sites via condensation of tetrahydroxyanthraquinone with silicon dioxide. The nine Li+-mediated charge/discharge processes enabled the AQ-Si-COF to demonstrate an ionic conductivity of 9.8 mS cm-1 at room temperature and a single-ion-conductive transference number of 0.92. Computational studies also supported the nine Li+ mechanism. We used AQ-Si-COF as the solid electrolyte interphase on the Li anode. The LMB cells with a LiCoO2 cathode attained a maximum reversible capacity of 188 mAh g-1 at 0.25 C during high-voltage operation. Moreover, this LMB cell demonstrated suppressed dendrite growth and stable cyclability, with its capacity decreasing by less than 3% up to 100 cycles. These findings demonstrate the effectiveness of our redox-active and anionic COFs and their practical utility as SEI in LMB.

Anthraquinone-Quinizarin Copolymer as a Promising Electrode Material for High-Performance Lithium and Potassium Batteries

The growing demand for cheap, safe, recyclable, and environmentally friendly batteries highlights the importance of the development of organic electrode materials. Here, we present a novel redox-active polymer comprising a polyaniline-type conjugated backbone and quinizarin and anthraquinone units. The synthesized polymer was explored as a cathode material for batteries, and it delivered promising performance characteristics in both lithium and potassium cells. Excellent lithiation efficiency enabled high discharge capacity values of >400 mA g^-1 in combination with good stability upon charge-discharge cycling. Similarly, the potassium cells with the polymer-based cathodes demonstrated a high discharge capacity of >200 mAh g^-1 at 50 mA g^-1 and impressive stability: no capacity deterioration was observed for over 3000 cycles at 11 A g^-1, which was among the best results reported for K ion battery cathodes to date. The synthetic availability and low projected cost of the designed material paves a way to its practical implementation in scalable and inexpensive organic batteries, which are emerging as a sustainable energy storage technology.

Nonconjugated Redox-Active Polymers: Electron Transfer Mechanisms, Energy Storage, and Chemical Versatility

The storage of electric energy in a safe and environmentally friendly way is of ever-growing importance for a modern, technology-based society. With future pressures predicted for batteries that contain strategic metals, there is increasing interest in metal-free electrode materials. Among candidate materials, nonconjugated redox-active polymers (NC-RAPs) have advantages in terms of cost-effectiveness, good processability, unique electrochemical properties, and precise tuning for different battery chemistries. Here, we review the current state of the art regarding the mechanisms of redox kinetics, molecular design, synthesis, and application of NC-RAPs in electrochemical energy storage and conversion. Different redox chemistries are compared, including polyquinones, polyimides, polyketones, sulfur-containing polymers, radical-containing polymers, polyphenylamines, polyphenazines, polyphenothiazines, polyphenoxazines, and polyviologens. We close with cell design principles considering electrolyte optimization and cell configuration. Finally, we point to fundamental and applied areas of future promise for designer NC-RAPs.

A Quinone-Based Cathode Material for High-Performance Organic Lithium and Sodium Batteries

With the increased application of batteries in powering electric vehicles as well as potential contributions to utility-scale storage, there remains a need to identify and develop efficient and sustainable active materials for use in lithium (Li)- and sodium (Na)-ion batteries. Organic cathode materials provide a desirable alternative to inorganic counterparts, which often come with harmful environmental impact and supply chain uncertainties. Organic materials afford a sustainable route to active electrodes that also enable fine-tuning of electrochemical potentials through structural design. Here, we report a bis-anthraquinone-functionalized s-indacene-1,3,5,7(2H,6H)-tetraone (BAQIT) synthesized using a facile and inexpensive route as a high-capacity cathode material for use in Li- and Na-ion batteries. BAQIT provides multiple binding sites for Li- and Na-ions, while maintaining low solubility in commercial organic electrolytes. Electrochemical Li-ion cells demonstrate excellent stability with discharge capacities above 190 mAh g-1 after 300 cycles at a 0.1C rate. The material also displayed excellent high-rate performance with a reversible capacity of 142 mAh g-1 achieved at a 10C rate. This material affords high power capabilities superior to current state-of-the-art organic cathode materials, with values reaching 5.09 kW kg-1. The Na-ion performance was also evaluated, exhibiting reversible capacities of 130 mAh g-1 after 90 cycles at a 0.1C rate. This work offers a structural design to encourage versatile, high-power, and long cycle-life electrochemical energy-storage materials.

Redox Donor-Acceptor Conjugated Microporous Polymers as Ultralong-Lived Organic Anodes for Rechargeable Air Batteries

Herein, we explore a new redox donor-acceptor conjugated microporous polymer (AQ-CMP) by utilizing anthraquinone and benzene as linkers via C-C linkages and demonstrate the first use of CMP as ultralong-lived anodes for rechargeable air batteries. AQ-CMP features an interconnected octupole network, which affords not only favorable electronic structure for enhanced electron transport and n-doping activity compared to linear counterpart, but also high density of active sites for maximizing the formula-weight-based redox capability. This coupled with highly cross-linked and porous structure endows AQ-CMP with a specific capacity of 202 mAh g^-1 (96 % of theoretical capacity) at 2 Ag^-1 and ≈100 % capacity retention over 60000 charge/discharge cycles. The assembled CMP-air full cell shows a stable and high capacity with full capacity recovery after only refreshing cathodes, while the decoupled electrolyte and cathode design boosts the discharge voltage and voltage efficiency to ≈1 V and 87.5 %.

Analysis of the Ordering Effects in Anthraquinone Thin Films and Its Potential Application for Sodium Ion Batteries

The ordering effects in anthraquinone (AQ) stacking forced by thin-film application and its influence on dimer solubility and current collector adhesion are investigated. The structural characteristics of AQ and its chemical environment are found to have a substantial influence on its electrochemical performance. Computational investigation for different charged states of AQ on a carbon substrate obtained via basin hopping global minimization provides important insights into the physicochemical thin-film properties. The results reveal the ideal stacking configurations of the individual AQ-carrier systems and show ordering effects in a periodic supercell environment. The latter reveals the transition from intermolecular hydrogen bonding toward the formation of salt bridges between the reduced AQ units and a stabilizing effect upon the dimerlike rearrangement, while the strong surface-molecular interactions in the thin-film geometries are found to be crucial for the formed dimers to remain electronically active. Both characteristics, the improved current collector adhesion and the stabilization due to dimerization, are mutual benefits of thin-film electrodes over powder-based systems. This hypothesis has been further investigated for its potential application in sodium ion batteries. Our results show that AQ thin-film electrodes exhibit significantly better specific capacities (233 vs 87 mAh g-1 in the first cycle), Coulombic efficiencies, and long-term cycling performance (80 vs 4 mAh g-1 after 100 cycles) over the AQ powder electrodes. By augmenting the experimental findings via computational investigations, we are able to suggest design strategies that may foster the performance of industrially desirable powder-based electrode materials.

Polymer-Based Batteries-Flexible and Thin Energy Storage Systems

Batteries have become an integral part of everyday life-from small coin cells to batteries for mobile phones, as well as batteries for electric vehicles and an increasing number of stationary energy storage applications. There is a large variety of standardized battery sizes (e.g., the familiar AA-battery or AAA-battery). Interestingly, all these battery systems are based on a huge number of different cell chemistries depending on the application and the corresponding requirements. There is not one single battery type fulfilling all demands for all imaginable applications. One battery class that has been gaining significant interest in recent years is polymer-based batteries. These batteries utilize organic materials as the active parts within the electrodes without utilizing metals (and their compounds) as the redox-active materials. Such polymer-based batteries feature a number of interesting properties, like high power densities and flexible batteries fabrication, among many more.

Amorphous flexible covalent organic networks containing redox-active moieties: a noncrystalline approach to the assembly of functional molecules

The organization states of functional molecules have a significant impact on the properties of materials. A variety of approaches have been studied to obtain well-organized molecular assemblies. The present work shows a new non-organized state of isolated and dispersed functional molecules in amorphous flexible covalent organic networks. Redox-active quinone molecules are embedded in the amorphous network polymers. Consecutive reactions between benzoquinone (BQ) and linker molecules generate random network structures through polymerization at different rates and in multiple directions. The low-crystalline stackings of the amorphous network polymers facilitate the formation of nanoflakes through exfoliation in dispersion media. Enhanced electrochemical performances, one of the highest specific capacities in recent studies, were achieved by efficient redox reactions of the quinone moiety. The present noncrystalline approach, low-crystalline stacking of designer amorphous covalent organic networks, can be applied to construct similar nanostructured polymer materials containing functional units.

Conducting Redox Polymer as a Robust Organic Electrode-Active Material in Acidic Aqueous Electrolyte towards Polymer-Air Secondary Batteries

Organic materials receive increasing attention as environmentally benign and sustainable electrode-active materials. We present a conducting redox polymer (CRP) based on poly(3,4-ethylenedioxythiophene) with naphthoquinone pendant group, which is formed from a stable suspension of a trimeric precursor and an oxoammonium cation as oxidant. This suspension allows us to easily coat the polymer onto a current collector, opening up use of roll-to-roll processing or ink-jet printing for electrode preparation. The CRP showed a full capacity of 76 mAh g^-1 even at a high C rate of 100 C in acidic aqueous electrolyte. These properties make the CRP a promising candidate as anode-active material; a polymer-air secondary battery was fabricated with the CRP as anode, a conventional Pt/C catalyst as cathode, and sulfuric acid aqueous solution as electrolyte. This battery yielded a discharge voltage of 0.50 V and showed good cycling stability with 97 % capacity retention after 100 cycles and high rate capabilities up to 20 C.

An Insoluble Anthraquinone Dimer with Near-Plane Structure as a Cathode Material for Lithium-Ion Batteries

Conjugated carbonyl-based organic electrode materials for lithium-ion batteries have gained increasing interests owing to their many advantages such as resource abundance and sustainable development. However, serious dissolution in organic liquid electrolytes is often encountered, resulting in inferior electrochemical performance such as poor cycling stability. Herein, a new molecular design strategy was developed to address the dissolution issue of 9,10-anthraquinone (AQ). An AQ dimer with near-plane molecular structure, 1,4-bis(9,10-anthraquinonyl)benzene (BAQB), was facilely synthesized. The near-plane structure was proved by DFT calculations. It was found that the obtained BAQB was insoluble in ether electrolyte. Compared to AQ, BAQB displayed remarkably enhanced cycling stability. After 100 cycles at 0.2 C, a high capacity retention of 91.6 % was achieved (195 mAh g^-1 ). BAQB also exhibited excellent rate performance (138 mAh g^-1 at 10 C). The results demonstrate the effectiveness of the near-plane molecular design concept. This work provides a new idea for rational molecular design to inhibit the dissolution of conjugated carbonyl-based organic electrode materials.

Benzoquinone- and Naphthoquinone-Bearing Polymers Synthesized by Ring-Opening Metathesis Polymerization as Cathode Materials for Lithium-Ion Batteries

Organic electrode materials have attracted great interest for next-generation lithium-ion batteries owing to their merits of low cost, resource sustainability, and environmental friendliness. Dissolution in organic electrolyte is one of critical factors that limit their development, and constructing corresponding polymers is an effective way to prevent it. Herein, the synthesis of benzoquinone- and naphthoquinone-bearing polymers by ring-opening metathesis polymerization of monomers with an exo-type four-membered ring between polymerizable norbornene and redox-active quinone units is reported. They exhibit significantly reduced solubility and clearly enhanced electrochemical performance. In particular, a high capacity (189.7 mAh g^-1 at 0.1 C, 1 C=216.1 mA g^-1 ), stable cycling (75.6 % capacity retention after 500 cycles at 2 C), and good rate capability (retaining 80.4 % from 0.1 to 2 C) were obtained for the naphthoquinone-bearing polymer, which stand out among naphthoquinone-bearing polymer electrode materials. This work offers rational molecular design and a new polymerization strategy to construct high-performance polymer electrode materials.

Poly(dihydroxybenzoquinone): its high-density and robust charge storage capability in rechargeable acidic polymer–air batteries

A rechargeable acidic polymer–air battery was firstly fabricated, which exhibited a long-lifetime of >500 cycles and high rate capabilities.

Reversible Hydrogen Releasing and Fixing with Poly(Vinylfluorenol) through a Mild Ir-Catalyzed Dehydrogenation and Electrochemical Hydrogenation

The radical polymerization of 2-vinylfluorenol, an alcohol derivative of vinylfluorene, gives poly(vinylfluorenol), which quantitatively releases hydrogen gas (≈110 mL per gram polymer at standard temperature and pressure) by simply warming at 100 °C with an iridium catalyst. A high population of fluorenol units in the polymer accomplishes a large formula-weight-based theoretical hydrogen density (1.0 wt%). The dehydrogenated ketone derivative, poly(vinylfluorenone), exhibits reversible negative-charge storage with a high density of 260 mAh g^-1 . The electrolytically reduced poly(vinylfluorenone) is momentarily hydrogenated in the presence of an electrolyte with water as the hydrogen source to be converted to the original poly(vinylfluorenol). The formed poly(vinylfluorenol) almost quantitatively evolves hydrogen gas similar to the starting poly(vinylfluorenol). Both hydrogen and charge storage with the organic fluorenol/fluorenone polymer suggest a new type of energy-storage configuration.

An Ultrahigh Output Rechargeable Electrode of a Hydrophilic Radical Polymer/Nanocarbon Hybrid with an Exceptionally Large Current Density beyond 1 A cm-2

Facile charge transport by a hydrophilic organic radical-substituted polymer and the 3D current collection by a self-assembled mesh of single-walled carbon nanotube bundles lead to the operation of an ultrahigh-output rechargeable electrode. Exceptionally large current density beyond 1 A cm^-2 and high areal capacity around 3 mAh cm^-2 are achieved, which are 10^1-2 times larger than those of the previously reported so-called "ultrafast electrodes." A sub-millimeter-thick, flexible, highly safe organic redox polymer-based rechargeable device with an aqueous sodium chloride electrolyte is fabricated to demonstrate the superior performance.

Approaches to Electrolyte Solvent Selection for Poly-Anthraquinone Sulfide Organic Electrode Material

Organic materials such as polyanthraquinone sulfide (PAQS) are receiving increased attention as electrodes for energy storage systems owing to their good environmental compatibility, high rate capability, and large charge-storage capacity. However, one of their limitations is the solubility in organic solvents typically composing the electrolytes. Here, the solubility of PAQS was tested in 17 different solvents using UV/Vis spectroscopy. The results show that PAQS exhibits a very wide range of solubility according to the nature of the solvent and the obtained trend agrees well with the predictions from Hansen solubility analysis. Furthermore, the transport properties (conductivity, σ, and viscosity, η) of selected electrolytes composed of non-solubilising solvents with 1 m LiTFSI are compared and discussed in the temperature range from -40 °C to 80 °C. In the second part of this study, the electrochemical characterization of PAQS as electrode material in selected pure or mixture of solvents with 1 m LiTFSI as salt was made in half-cells by a galvanostatic method. In a methylglutaronitrile (2MeGLN)-based electrolyte that exhibits low solubility of PAQS, it appears that the capacity fade is intricately linked to the large irreversibility of the second step of the redox process. Although the standard cyclic carbonate solvents mixture (ethylene carbonate and propylene carbonate) led to rapid capacity fade in the initial 10-15 cycles owing to their high solubilising ability. Finally, it is shown that a pure linear alkylcarbonate (dimethyl carbonate) or binary mixture of ether-based (dioxolane/dimethoxy ethane) electrolyte is much more compatible for enhanced capacity retention in PAQS with more than 120 mAh g^-1 for 1000 cycles at 4 C.

The rise of organic electrode materials for energy storage

Organic electrode materials are very attractive for electrochemical energy storage devices because they can be flexible, lightweight, low cost, benign to the environment, and used in a variety of device architectures. They are not mere alternatives to more traditional energy storage materials, rather, they have the potential to lead to disruptive technologies. Although organic electrode materials for energy storage have progressed in recent years, there are still significant challenges to overcome before reaching large-scale commercialization. This review provides an overview of energy storage systems as a whole, the metrics that are used to quantify the performance of electrodes, recent strategies that have been investigated to overcome the challenges associated with organic electrode materials, and the use of computational chemistry to design and study new materials and their properties. Design strategies are examined to overcome issues with capacity/capacitance, device voltage, rate capability, and cycling stability in order to guide future work in the area. The use of low cost materials is highlighted as a direction towards commercial realization.

High-performance rechargeable aqueous Zn-ion batteries with a poly(benzoquinonyl sulfide) cathode

Aqueous Zn-ion batteries with a poly(benzoquinonyl sulfide) cathode show good electrochemical performance.

Molecular Engineering with Organic Carbonyl Electrode Materials for Advanced Stationary and Redox Flow Rechargeable Batteries

Organic carbonyl electrode materials that have the advantages of high capacity, low cost and being environmentally friendly, are regarded as powerful candidates for next-generation stationary and redox flow rechargeable batteries (RFBs). However, low carbonyl utilization, poor electronic conductivity and undesired dissolution in electrolyte are urgent issues to be solved. Here, we summarize a molecular engineering approach for tuning the capacity, working potential, concentration of active species, kinetics, and stability of stationary and redox flow batteries, which well resolves the problems of organic carbonyl electrode materials. As an example, in stationary batteries, 9,10-anthraquinone (AQ) with two carbonyls delivers a capacity of 257 mAh g^-1 (2.27 V vs Li⁺ /Li), while increasing the number of carbonyls to four with the formation of 5,7,12,14-pentacenetetrone results in a higher capacity of 317 mAh g^-1 (2.60 V vs Li⁺ /Li). In RFBs, AQ, which is less soluble in aqueous electrolyte, reaches 1 M by grafting -SO₃ H with the formation of 9,10-anthraquinone-2,7-disulphonic acid, resulting in a power density exceeding 0.6 W cm^-2 with long cycling life. Therefore, through regulating substituent groups, conjugated structures, Coulomb interactions, and the molecular weight, the electrochemical performance of carbonyl electrode materials can be rationally optimized. This review offers fundamental principles and insight into designing advanced carbonyl materials for the electrodes of next-generation rechargeable batteries.

A ketone/alcohol polymer for cycle of electrolytic hydrogen-fixing with water and releasing under mild conditions

Finding a safe and efficient carrier of hydrogen is a major challenge. Recently, hydrogenated organic compounds have been studied as hydrogen storage materials because of their ability to stably and reversibly store hydrogen by forming chemical bonds; however, these compounds often suffer from safety issues and are usually hydrogenated with hydrogen at high pressure and/or temperature. Here we present a ketone (fluorenone) polymer that can be moulded as a plastic sheet and fixes hydrogen via a simple electrolytic hydrogenation at −1.5 V (versus Ag/AgCl) in water at room temperature. The hydrogenated alcohol derivative (the fluorenol polymer) reversibly releases hydrogen by heating (80 °C) in the presence of an aqueous iridium catalyst. Both the use of a ketone polymer and the efficient hydrogen fixing with water as a proton source are completely different from other (de)hydrogenated compounds and hydrogenation processes. The easy handling and mouldable polymers could suggest a pocketable hydrogen carrier.

Using hydrogen efficiently requires safe carriers and reversible storage. Here, Nishide and others develop a ketone based polymer that can fix hydrogen by electrolytic hydrogenation in water and reversibly release it via heating and the use of an iridium catalyst.

Polymer-Based Organic Batteries

The storage of electric energy is of ever growing importance for our modern, technology-based society, and novel battery systems are in the focus of research. The substitution of conventional metals as redox-active material by organic materials offers a promising alternative for the next generation of rechargeable batteries since these organic batteries are excelling in charging speed and cycling stability. This review provides a comprehensive overview of these systems and discusses the numerous classes of organic, polymer-based active materials as well as auxiliary components of the battery, like additives or electrolytes. Moreover, a definition of important cell characteristics and an introduction to selected characterization techniques is provided, completed by the discussion of potential socio-economic impacts.

Poly(norbornyl-NDIs) as a potential cathode-active material in rechargeable charge storage devices

Two pendant-type naphthalene diimide (NDI) polymers bearing a polynorbornene backbone were prepared and their electrochemical properties explored.

Electrochemical current rectification with cross reaction at a TEMPO/viologen-substituted polymer thin-layer heterojunction

The electrochemical large current rectification was achieved in the bilayer system composed of the TEMPO- and viologen-containing polymer thin layers.

RAFT polymerization of an alkoxyamine bearing acrylate, towards a well-defined redox active polyacrylate

A new strategy for the synthesis of a well-defined redox active polymer, a polyacrylate bearing TEMPO, and its grafting onto a gold substrate is described.