Reviving Cost-Effective Organic Cathodes in Halide-Based All-Solid-State Lithium Batteries

The evolution of inorganic solid electrolytes has revolutionized the field of sustainable organic cathode materials, particularly by addressing the dissolution problems in traditional liquid electrolytes. However, current sulfide-based all-solid-state lithium-organic batteries still face challenges such as high working temperatures, high costs, and low voltages. Here, we design an all-solid-state lithium battery based on a cost-effective organic cathode material phenanthrenequinone (PQ) and a halide solid electrolyte Li2ZrCl6. Thanks to the good compatibility between PQ and Li2ZrCl6, the PQ cathode achieved a high specific capacity of 248 mAh g-1 (96 % of the theoretical capacity), a high average discharge voltage of 2.74 V (vs. Li+/Li), and a good capacity retention of 95 % after 100 cycles at room temperature (25 °C). Furthermore, the interactions between the high-voltage carbonyl PQ cathode and both sulfide and halide solid electrolytes, as well as the redox mechanism of the PQ cathode in all-solid-state batteries, were carefully studied by a variety of advanced characterizations. We believe such a design and the corresponding investigations into the underlying chemistry give insights for the further development of practical all-solid-state lithium-organic batteries.

Molecule and Microstructure Modulations of Cyano-Containing Electrodes for High-Performance Fully Organic Batteries

Cyano-containing electrodes usually promise high theoretical potentials while suffering from uncontrollable self-dissolution and sluggish reaction kinetics. Herein, to remedy their limitations, an unprecedented core-shell heterostructured electrode of carbon nanotubes encapsulated in poly(1,4-dicyanoperfluorobenzene sulfide) (CNT@PFDCB) is rationally crafted via molecule and microstructure modulations. Specifically, the linkage of sulfide bridges of PFDCB prevents the active cyano groups from dissolving, resulting in a robust structure. The fluorinations modulate the electronic configurations in frontier orbitals, allowing higher electrical conductivity and elevated output voltage. Combined with the core-shell architecture to unlock the sluggish diffusion kinetics for both electrons and guest ions, the CNT@PFDCB exhibits an impressive capacity (203.5 mAh g-1), remarkable rate ability (127.6 mAh g-1 at 3.0 A g-1), and exceptional cycling stability (retaining 81.1 % capacity after 3000 cycles at 1.0 A g-1). Additionally, the Li-storage mechanisms regarding PFDCB are thoroughly revealed by in situ attenuated total reflection infrared spectroscopy, in situ Raman spectroscopy, and theoretical simulations, which involve the coordination interaction between Li ions and cyano groups and the electron delocalization along the conjugated skeleton. More importantly, a practical fully organic cell based on the CNT@PFDCB is well-validated that demonstrates a tremendous potential of cyanopolymer as the cathode to replace its inorganic counterparts.

Recycling Compatible Organic Electrode Materials Containing Amide Bonds for Use in Rechargeable Batteries

Organic rechargeable batteries that do not use any scarce heavy metals are candidates for the next generation of rechargeable batteries; although, it is not easy to realize both high capacity and long cycle life. Organic compounds linked by amide bonds are expected to have superior recycling properties after battery degradation, since they will become a single monomer upon hydrolysis. In this study, anthraquinone was chosen as a model redox active unit, and dimeric and trimeric compounds were synthesized, their cycle performances as electrode materials for use in rechargeable batteries were compared, and a trend in which oligomerization improves cycle properties was confirmed. Furthermore, quantum chemistry calculations suggest that oligomerization decreases solubility, which would support a longer life for oligomerized compounds. This methodology will lead to the development of organic rechargeable batteries with further environmental benefits.

Long Cycle-Life Ca Batteries with Poly(anthraquinonylsulfide) Cathodes and Ca-Sn Alloy Anodes

Calcium (Ca) batteries are attractive post-lithium battery technologies, due to their potential to provide high-voltage and high-energy systems in a sustainable manner. We investigated herein 1,5-poly(anthraquinonylsulfide) (PAQS) for Ca-ion storage with calcium tetrakis(hexafluoroisopropyloxy)borate Ca[B(hfip)4 ]2 [hfip=OCH(CF3 )2 ] electrolytes. It is demonstrated that PAQS could be synthesized in a cost-effective approach and be processed environmentally friendly into the electrodes. The PAQS cathodes could provide 94 mAh g-1 capacity at 2.2 V vs. Ca at 0.5C (1C=225 mAh g-1 ). However, cycling of the cells was severely hindered due to the fast degradation of the metal anode. Replacing the Ca metal anode with a calcium-tin (Ca-Sn) alloy anode, the PAQS cathodes exhibited long cycling performance (45 mAh g-1 at 0.5C after 1000 cycles) and superior rate capability (52 mAh g-1 at 5C). This is mainly ascribed to the flexible structure of PAQS and good compatibility of the alloy anodes with the electrolyte solutions, which allow reversible quinone carbonyl redox chemistry in the Ca battery systems. The promising properties of PAQS indicate that further exploration of the organic cathode materials could be a feasible direction towards green Ca batteries.

Self-Reinforced Inductive Effect of Symmetric Bipolar Organic Molecule for High-Performance Rechargeable Batteries

Herein, the self-reinforced inductive effect derived from coexistence of both p- and n-type redox-active motifs in a single organic molecule is presented. Molecular orbital energy levels of each motif are dramatically tuned, which leads to the higher oxidation and the lower reduction potentials. The self-reinforced inductive effect of the symmetric bipolar organic molecule, N,N'-dimethylquinacridone (DMQA), is corroborated, by both experimental and theoretical methods. Furthermore, its redox mechanism and reaction pathway in the Li+ -battery system are scrutinized. DMQA shows excellent capacity retention at the operating voltage of 3.85 and 2.09 V (vs Li+ /Li) when used as the cathode and anode, respectively. Successful operation of DMQA electrodes in a symmetric all-organic battery is also demonstrated. The comprehensive insight into the energy storage capability of the symmetric bipolar organic molecule and its self-reinforced inductive effect is provided. Thus, a new class of organic electrode materials for symmetric all-organic batteries as well as conventional rechargeable batteries can be conceived.

Polyimides as Promising Cathodes for Metal-Organic Batteries: A Comparison between Divalent (Ca2+, Mg2+) and Monovalent (Li+, Na+) Cations

Ca- and Mg-based batteries represent a more sustainable alternative to Li-ion batteries. However, multivalent cation technologies suffer from poor cation mass transport. In addition, the development of positive electrodes enabling reversible charge storage currently represents one of the major challenges. Organic positive electrodes, in addition to being the most sustainable and potentially low-cost candidates, compared with their inorganic counterparts, currently present the best electrochemical performances in Ca and Mg cells. Unfortunately, organic positive electrodes suffer from relatively low capacity retention upon cycling, the origin of which is not yet fully understood. Here, 1,4,5,8-naphthalenetetracarboxylic dianhydride-derived polyimide was tested in Li, Na, Mg, and Ca cells for the sake of comparison in terms of redox potential, gravimetric capacities, capacity retention, and rate capability. The redox mechanisms were also investigated by means of operando IR experiments, and a parameter affecting most figures of merit has been identified: the presence of contact ion-pairs in the electrolyte.

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.

Recent Advances in Polymers for Potassium Ion Batteries

Potassium-ion batteries (KIBs) are considered to be an effective alternative to lithium-ion batteries (LIBs) due to their abundant resources, low cost, and similar electrochemical properties of K+ to Li+, and they have a good application prospect in the field of large-scale energy storage batteries. Polymer materials play a very important role in the battery field, such as polymer electrode materials, polymer binders, and polymer electrolytes. Here in this review, we focus on the research progress of polymers in KIBs and systematically summarize the research status and achievements of polymer electrode materials, electrolytes, and binders in potassium ion batteries in recent years. Finally, based on the latest representative research of polymers in KIBs, some suggestions and prospects are put forward, which provide possible directions for future research.

High Discharge Capacity and Ultra-Fast-Charging Sodium Dual-Ion Battery Based on Insoluble Organic Polymer Anode and Concentrated Electrolyte

Sodium-based dual-ion batteries have shown great promise for large-scale energy storage applications due to their wide operating voltages, environmental friendliness, abundant sodium resources, and low cost, which are widely investigated by researchers. However, the development of high-performance anode materials is a key requirement for the realization of such electrochemical energy storage systems at the practical application level. Carbonaceous anode materials based on intercalation/deintercalation mechanisms typically exhibit low discharge capacities, while metal-based materials based on conversion or alloying reactions show unsatisfactory stability in performance. On the contrary, organic materials display high theoretical capacities due to their flexible molecular structure designability and stable cyclic performance with fast reaction kinetics based on the unique enolization reaction. Herein, we report an organic polymer anode material of polyimide (PNTO), combined with a high-concentration electrolyte; the sodium-based dual-ion battery system constructed exhibits outstanding electrochemical performance. The full battery shows an ultra-high specific discharge capacity of 293.2 mAh g-1 and can be cycled stably for 3200/5600/4100 cycles at ultra-high rates of 60/120/150 C without degradation. Furthermore, the dual-ion battery system demonstrates an extremely low self-discharge rate of 0.03% h-1 and superior fast-charging-slow-discharging performance. It is one of the best performances reported up to now for a dual-ion full battery based on an organic polymer anode. This novel battery system design strategy will facilitate the advancement of high-performance organic-based dual-ion batteries and is expected to be a promising candidate for large-scale energy storage applications.

Progress on Polymer Dielectrics for Electrostatic Capacitors Application

Polymer dielectrics are attracting increasing attention for electrical energy storage owing to their advantages of mechanical flexibility, corrosion resistance, facile processability, light weight, great reliability, and high operating voltages. However, the dielectric constants of most dielectric polymers are less than 10, which results in low energy densities and limits their applications in electrostatic capacitors for advanced electronics and electrical power systems. Therefore, intensive efforts have been placed on the development of high-energy-density polymer dielectrics. In this perspective, the most recent results on the all-organic polymer dielectrics are summarized, including molecular structure design, polymer blends, and layered structured polymers. The challenges in the field and suggestions for future research on high-energy-density polymer dielectrics are also presented.

Molecular engineering of dihydroxyanthraquinone-based electrolytes for high-capacity aqueous organic redox flow batteries

Aqueous organic redox flow batteries (AORFBs) are a promising technology for large-scale electricity energy storage to realize efficient utilization of intermittent renewable energy. In particular, organic molecules are a class of metal-free compounds that consist of earth-abundant elements with good synthetic tunability, electrochemical reversibility and reaction rates. However, the short cycle lifetime and low capacity of AORFBs act as stumbling blocks for their practical deployment. To circumvent these issues, here, we report molecular engineered dihydroxyanthraquinone (DHAQ)-based alkaline electrolytes. Via computational studies and operando measurements, we initially demonstrate the presence of a hydrogen bond-mediated degradation mechanism of DHAQ molecules during electrochemical reactions. Afterwards, we apply a molecular engineering strategy based on redox-active polymers to develop capacity-boosting composite electrolytes. Indeed, by coupling a 1,5-DHAQ/poly(anthraquinonyl sulfide)/carbon black anolyte and a [Fe(CN)₆]^3−/4− alkaline catholyte, we report an AORFB capable of delivering a stable cell discharge capacity of about 573 mAh at 20 mA/cm² after 1100 h of cycling and an average cell discharge voltage of about 0.89 V at the same current density.

Aqueous organic redox flow batteries are affected by short cycle life and low capacity. Here, the authors develop composite dihydroxyanthraquinone/polymer anolytes capable of improving the cycling stability and discharge capacity of aqueous organic redox flow batteries.

Revisiting the Structure and Electrochemical Performance of Poly(o-phenylenediamine) as an Organic Cathode Material

Poly(o-phenylenediamine) (PoPDA) has been recognized as a low-cost electroactive organic material and studied as a cathode for aqueous zinc batteries or as an anode for nonaqueous lithium batteries. However, there remains a lot of confusion about its synthesis, structure, and electrochemical application. Especially, the previously studied PoPDA samples were mostly synthesized at room temperature, which were proved by us to be just a dimer, that is, 2,3-diaminophenazine (DAPZ). By various characterization methods including elemental analysis and mass spectrometry, we verified that the product synthesized at high temperature, PoPDA-H, was a polymer based on DAPZ as the structural repeat unit and with some imperfect substitutes (OH and NH₃⁺CH₃COO^-). Based on the reversible redox reaction of phenazine units and the stable polymer structure within 1.3-3.8 V vs Li⁺/Li, PoPDA-H was more appropriate to be applied as a cathode rather than as an anode for lithium batteries. It achieved a high energy density of 490 Wh kg^-1 (2.12 V × 231 mAh g^-1) at 50 mA g^-1 and a high cycling stability (79%@1000th cycle) at 500 mA g^-1, both of which were comparable to previously reported expensive pyrazine- and carbonyl-based polymers. This work clarifies many misunderstandings of PoPDA, which is important to its further development toward practical application in energy-storage devices.

Benzoquinone-Pyrrole Polymers as Cost-Effective Cathodes toward Practical Organic Batteries

Organic cathode materials (OCMs) for rechargeable Li and Na batteries show great advantages in resource sustainability and huge potential in electrochemical performance but suffer from dissolution problems and costly synthesis. Herein, for the first time, we investigated the copolymer of benzoquinone (BQ) and pyrrole (Py), namely, poly(benzoquinone-pyrrole) (PBQPy), as an OCM for Li batteries. The low-cost raw materials and solvent-free synthesis provide PBQPy much brighter prospects in large-scale production compared to other carbonyl-based polymer cathode materials. Nevertheless, PBQPy showed one of the best electrochemical performances among all OCMs, including excellent energy density (2.32 V × 255 mAh g^-1 = 592 Wh kg^-1), rate capability (79%@2000 mA g^-1), and cycling stability (81%@1000th cycle). By introducing poly(benzoquinone-methyl pyrrole) for comparison, as well as employing density functional theory calculations and various characterizations for in-depth understanding, the synthesis mechanism, polymer structure, electrochemical behavior, and redox mechanism were clearly clarified. It is believed that this work will encourage more efforts to develop cost-effective OCMs toward practical organic batteries.

Poly(Anthraquinonyl Sulfide)/CNT Composites as High-Rate-Performance Cathodes for Nonaqueous Rechargeable Calcium-Ion Batteries

Calcium-ion batteries (CIBs) are considered as promising alternatives in large-scale energy storage due to their divalent electron redox properties, low cost, and high volumetric/gravimetric capacity. However, the high charge density of Ca²⁺ contributes to strong electrostatic interaction between divalent Ca²⁺ and hosting lattice, leading to sluggish kinetics and poor rate performance. Here, in situ formed poly(anthraquinonyl sulfide) (PAQS)@CNT composite is reported as nonaqueous calcium-ion battery cathode. The enolization redox chemistry of organics has fast redox kinetics, and the introduction of carbon nanotube (CNT) accelerates electron transportation, which contributes to fast ionic diffusion. As the conductivity of the PAQS is enhanced by the increasing content of CNT, the voltage gap is significantly reduced. The PAQS@CNT electrode exhibits specific capacity (116 mAh g^-1 at 0.05 A g^-1 ), high rate capacity (60 mAh g^-1 at 4 A g^-1 ), and an initial capacity of 82 mAh g^-1 at 1 A g^-1 (83% capacity retention after 500 cycles). The electrochemical mechanism is proved to be that the PAQS undergoes reduction reaction of their carbonyl bond during discharge and becomes coordinated by Ca²⁺ and Ca(TFSI)⁺ species. Computational simulation also suggests that the construction of Ca²⁺ and Ca(TFSI)⁺ co-intercalation in the PAQS is the most reasonable pathway.

Tailored porous framework materials for advancing lithium-sulfur batteries

Despite great promise as next-generation high-capacity energy storage devices, lithium-sulfur batteries still face technical challenges in long-term cyclability. With their porous structures and facile synthesis, metal-organic frameworks (MOFs) are tunable platforms for understanding polysulfide redox and can serve as effective sulfur hosts for lithium-sulfur batteries. This feature article describes our design strategies to tailor MOF properties such as polysulfide affinity, ionic conductivity, and porosity for promoting active material utilization and charge transport efficiency. We also present engineering approaches for implementing MOF-based sulfur cathodes for lithium-sulfur batteries with high volumetric density and under low temperature operation. Our studies provide fundamental insights into sulfur-host interactions and polysulfide electrochemistry in the presence of porous matrices, inspiring future designs of advanced batteries.

Interfacial Self-assembly of Organics/MXene Hybrid Cathodes Toward High-Rate-Performance Sodium Ion Batteries

Conjugated quinones are promising cathode materials for sodium-ion batteries. However, the contemporary primary conjugated quinones cathodes still hold to limited capacity, poor rate performance and low cyclability, due to the poor electronic and ionic conductivity. Herein, a series of high-performance conjugated-quinones@MXene hybrid cathodes is constructed by an in situ polymerization-assembly strategy based on the hydrogen bond and S-Ti interaction. The PAQS@Ti₃C₂T_x MXene hybrid, as a typical example, exhibits sandwiched structure with intimate PAQS@MXene contact, resulting in efficient interfacial mass transfer. The assembled MXene is able to build interconnected conductive channels in the hybrid cathodes for continuous and fast electrons/ions transport, which is verified by both the experimental results and density functional theory (DFT) calculations. As a result, the optimal PAQS@MXene hybrid electrode delivers excellent electrochemical performances with high capacity (∼242 mA h g^-1 at 100 mA g^-1), superior fast-charge/discharge ability (∼148 and 121 mA h g^-1 at 5 and 10 A g^-1, respectively), and ultralong cycle life (capacity as high as 57 mA h g^-1 after 9000 cycles at 5 A g^-1), which are more superior to that of the pure PAQS electrodes. Besides, the analogous PPTS@Ti₃C₂T_x MXene hybrid cathode also shows better performances compared to the pure materials.

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.

Novel Hybrid Polymer Composites Based on Anthraquinone and Eco-Friendly Dyes with Potential for Use in Intelligent Packaging Materials

This study aimed to present the influence of bio-based and anthraquinone dyes and their combinations on the optical properties of ethylene-propylene (EPM) composites after thermo-oxidative and climatic aging. Therefore, the chosen polymer was filled with a natural, plant-origin flavonoid—quercetin, and with two commercial anthraquinone dyes (C.I. Solvent Yellow 163 and C.I. Solvent Red 207). The manufactured polymer composites were subjected to accelerated aging tests: weathering and thermo-oxidation, respectively. Examination of the materials’ properties indicated that the combination of synthetic and natural dyes can result in better resistance to oxidizing agents and higher thermal stability of ethylene-propylene products. Moreover, color change of quercetin-containing samples due to exposure to simulated atmospheric conditions could be a promising solution for use as aging indicators in intelligent packaging materials that will inform about the ongoing degradation process. Another interesting finding is that these samples exhibited good fungistatic activity against Candida albicans yeast and Aspergillus niger mold. Overall, this novel solution based on hybrid polymer composites containing natural and commercial dyes is a more environmentally friendly alternative to traditional materials used in the plastic packaging industry with better and more desirable properties.

Secondary Bonding Channel Design Induces Intercalation Pseudocapacitance toward Ultrahigh-Capacity and High-Rate Organic Electrodes

Organic electrode materials have shown extraordinary promise for green and sustainable electrochemical energy storage devices, but usually suffer from low specific capacity and poor rate capability, which is largely caused by inactive components and diffusion-controlled Li⁺ intercalation. Herein, high-rate Li⁺ intercalation pseudocapacitance in organic molecular crystals is achieved through introducing weak secondary bonding channels, far exceeding their theoretical capacity based on redox chemistry at functional groups. The authors' combined experimentally electrochemical characterization with first-principles calculations show that the heterocyclic organic molecule 2,2'-bipyridine-4,4'-dicarboxylic acid (BPDCA) crystal permits a four-electron redox reaction at conventional CO and CN groups and a six-electron intercalation pseudocapacitance along conjugated alkene hydrogen bonding channels (H₂ NC₅ H⋯OC(OH)) and heterocyclic aromatic stacking channels (C₅ H₃ N⋯NH₃ C₅ ). The BPDCA electrode delivers an ultrahigh reversible capacity of 1206 mAh g^-1 at 0.5 A g^-1 and an exceptional rate capability. A 4.8 V high-energy/power-density BPDCA anode-based hybrid Li-ion capacitor is thus realized. This work opens a new avenue for developing organic intercalation pseudocapacitive materials via secondary bonding structure design.

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 %.

Quinone-Enriched Conjugated Microporous Polymer as an Organic Cathode for Li-Ion Batteries

Among various organic cathode materials, C═O group-enriched structures have attracted wide attention worldwide. However, small organic molecules have long suffered from dissolving in electrolytes during charge-discharge cycles. π-Conjugated microporous polymers (CMPs) become one solution to address this issue. However, the synthesis strategy for CMPs with rich C═O groups and stable backbones remains a challenge. In this study, a novel CMP enriched with C═O units was synthesized through a highly efficient Diels-Alder reaction. The as-prepared CMP exhibited a fused carbon backbone and a semiconductive characteristic with a band gap of 1.4 eV. When used as an organic electrode material in LIBs, the insoluble and robust fused structure caused such CMPs to exhibit remarkable cycling stability (a 96.1% capacity retention at 0.2 A g^-1 after 200 cycles and a 94.8% capacity retention at 1 A g^-1 after 1500 cycles), superior lithium-ion diffusion coefficient (5.30 × 10^-11 cm² s^-1), and excellent rate capability (95.8 mAh g^-1 at 1 A g^-1). This study provided a novel synthetic method for fabricating quinone-enriched fused CMPs, which can be used as LIB cathode materials.

Electronic Conductive Inorganic Cathodes Promising High-Energy Organic Batteries

The electrochemical utilization of organic electrode materials (OEMs) is highly dependent on an excess amount of inactive carbon at the expense of low packing density and energy density. In this work, the challenges by substituting inactive carbon with electronic conductive inorganic cathode (ECIC) materials, which are endowed with high electronic conductivity to transport electrons for redox reactions of the whole electrodes, high ion-storage capacity to act as secondary active materials, and strong affinity with OEMs to inhibit their dissolution, are addressed. Combining representative ECICs (TiS₂ and Mo₆ S₈ ) with organic electrode materials (perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) and hexaazatrinaphthalene (HATN)) simultaneously achieves high capacity, low porosity, lean electrolyte, and thus high energy density. High gravimetric and volumetric energy densities of 153 Wh kg^-1 and 200 Wh L^-1 are delivered with superior cycling stability in a 30 mA h-level Li/PTCDA-TiS₂ pouch cell. The proof-of-concept of organic-ECIC electrodes is also successfully demonstrated in monovalent Na, divalent Mg, and trivalent Al batteries, indicating their feasibility and generalizability. With the discovery of more ECIC materials and OEMs, it is anticipated that the proposed organic-ECIC system can result in further improvements at cell level to compete with transition metal-based Li-ion batteries.

Review on organosulfur materials for rechargeable lithium batteries

Organic electrode materials have been considered as promising candidates for the next generation rechargeable battery systems due to their high theoretical capacity, versatility, and environmentally friendly nature. Among them, organosulfur compounds have been receiving more attention in conjunction with the development of lithium-sulfur batteries. Usually, organosulfide electrodes can deliver a relatively high theoretical capacity based on reversible breakage and formation of disulfide (S-S) bonds. In this review, we provide an overview of organosulfur materials for rechargeable lithium batteries, including their molecular structural design, structure related electrochemical performance study and electrochemical performance optimization. In addition, recent progress of advanced characterization techniques for investigation of the structure and lithium storage mechanism of organosulfur electrodes are elaborated. To further understand the perspective application, the additive effect of organosulfur compounds for lithium metal anodes, sulfur cathodes and high voltage inorganic cathode materials are reviewed with typical examples. Finally, some remaining challenges and perspectives of the organosulfur compounds as lithium battery components are also discussed. This review is intended to serve as general guidance for researchers to facilitate the development of organosulfur compounds.

Nitrogen-Doped Hierarchical Porous Carbon-Promoted Adsorption of Anthraquinone for Long-Life Organic Batteries

Organic quinone molecules are attractive electrochemical energy storage devices because of their high abundance, multielectron reactions, and structural diversity compared with transition metal-oxide electrode materials. However, they have problems like poor cycle stability and low rate performance on account of the inherent low conductivity and high solubility in the electrolyte. Solving these two key problems at the same time can be challenging. Herein, we demonstrate that using a nitrogen-doped hierarchical porous carbon (NC) with mixed microporous/low-range mesoporous can greatly alleviate the shuttle effect caused by the dissolution of organic molecules in the electrolyte through physical binding and chemisorption, thereby improving the electrochemical performances. Lithium-ion batteries based on the anthraquinone (AQ) electrode exhibit dramatic capacity decay (5.7% capacity retention at 0.2 C after 1000 cycles) and poor rate performance (14.2 mA h g^-1 at 2 C). However, the lithium-ion battery based on the NC@AQ cathode shows excellent cycle stability (60.5% capacity retention at 0.2 C after 1000 cycles, 82.8% capacity retention at 0.5 C after 1000 cycles), superior rate capability (152.9 mA h g^-1 at 2 C), and outstanding energy efficiency (98% at 0.2 C). Our work offers a new approach to realize the next-generation organic batteries for long life and high rate performance.

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.

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.

Single-Molecule Dye Organics with Multielectron Redox Processes as Cathode Materials for Lithium Secondary Batteries

Dissolution loss is the biggest issue for an organic electrode material, and nowadays the most popular strategy to avoid it is to synthesize a polymer or add a large amount of conductive carbon. In this study, the issue is addressed by using monomolecular organics with a relatively long chain and large size. A dye composed of quinones and a carbazole is proposed as the cathode material for a Li secondary battery. The unique structure of more than three quinones joined by a carbazole bridge improves the cycling stability significantly. In addition to the widely known enolization reaction of the quinone moiety, extra anion-doping capacity is supplied by the carbazole moiety. As a result of the multiple active sites, multielectron redox transfer and remarkable capacity enhancement are realized by using Vet Yellow 3RT dye material. It shows a stable capacity up to 340 mAh g^-1 within 300 cycles. XRD, X-ray photoelectron spectroscopy, and electrochemical measurements were used to confirm the reactivity of the carbonyl group and the N-heterocycle toward Li⁺ and PF₆ ^- , respectively. In this work, a new application of this dye material is revealed, providing a new avenue to address the dissolution loss and capacity breakthrough of organic batteries.

Redox Mechanisms in Li and Mg Batteries Containing Poly(phenanthrene quinone)/Graphene Cathodes using Operando ATR-IR Spectroscopy

The redox reaction mechanism of a poly(phenanthrene quinone)/graphene composite (PFQ/rGO) was investigated using operando attenuated total reflection infrared (ATR-IR) spectroscopy during cycling of Li and Mg batteries. The reference phenanthrene quinone and the Li and Mg salts of the hydroquinone monomers were synthesized and their IR spectra were measured. Additionally, IR spectra were calculated using DFT. A comparison of all three spectra allowed us to accurately assign the C=O and C-O- vibration bands and confirm the redox mechanism of the quinone/Li salt of hydroquinone, with radical anion formation as the intermediate product. PFQ/rGO also showed exceptional performance in an Mg battery: A potential of 1.8 V versus Mg/Mg2+ , maximum capacity of 186 mAh g-1 (335 Wh kg-1 of cathode material), and high capacity retention with only 8 % drop/100 cycles. Operando ATR-IR spectroscopy was performed in a Mg/organic system, revealing an analogous redox mechanism to a Li/organic cell.

Structure-properties relationship for energy storage redox polymers: a review

Redox-active polymers among the energy storage materials (ESMs) are very attractive due to their exceptional advantages such as high stability and processability as well as their simple manufacturing. Their applications are found to useful in electric vehicle, ultraright computers, intelligent electric gadgets, mobile sensor systems, and portable intelligent clothing. They are found to be more efficient and advantageous in terms of superior processing capacity, quick loading unloading, stronger security, lengthy life cycle, versatility, adjustment to various scales, excellent fabrication process capabilities, light weight, flexible, most significantly cost efficiency, and non-toxicity in order to satisfy the requirement for the usage of these potential applications. The redox-active polymers are produced through organic synthesis, which allows the design and free modification of chemical constructions, which allow for the structure of organic compounds. The redox-active polymers can be finely tuned for the desired ESMs applications with their chemical structures and electrochemical properties. The redox-active polymers synthesis also offers the benefits of high-scale, relatively low reaction, and a low demand for energy. In this review we discussed the relationship between structural properties of different polymers for solar energy and their energy storage applications.

A Quinone Anode for Lithium-Ion Batteries in Mild Aqueous Electrolytes

Aqueous batteries could be potentially used for grid-scale energy storage owing to the use of nonflammable electrolytes and long cycle life. Recently, quinones have shown examples as redox-active materials in aqueous batteries under either strong acidic or basic conditions. However, a quinone-based battery with a less corrosive electrolyte is still rare. Given that quinone-based batteries are heavily influenced by the pH of electrolytes, we studied the influence of acid dissociation constants (pKa) of hydroquinones on their performance as solid electrode materials. We measured the pKa of anthracene-9,10-diol (AQH₂ ) and benzo[1,2-b:4,5-b']dithiophene-4,8-diol (BDTDH₂ ) from the Pourbaix diagrams of two para-quinone monomers [i.e., anthracene-9,10-dione (AQ) and benzo[1,2-b:4,5-b']dithiophene-4,8-dione (BDTD)]. Subsequently, their polymeric forms [i.e., poly(anthraquinonyl sulfide) (PAQS) and poly(benzo[1,2-b:4,5-b']dithiophene-4,8-dione-2,6-diyl sulfide) (PBDTDS)] were investigated as electrodes in aqueous lithium-ion cells. At pH 13, PAQS demonstrates a low capacity and poor cycle life, whereas PBDTDS shows a capacity of 196 mAh g^-1 and fade rates of 0.0038 % per cycle over 4200 cycles, 0.77 % per day over 21 days. The differences in capacity and cycle stability can be explained by the difference of corresponding pKa values. A full cell with the configuration of (-)PBDTDS|2.5 m Li₂ SO₄ (pH 13)|LiCoO₂ (+) shows a voltage of 1.08 V, a capacity of 72 mAh g^-1 and ≈99.9 % of Coulombic efficiency for 500 stable cycles.

Phendione-Transition-Metal Complexes with Bipolar Redox Activity for Lithium Batteries

1,10-Phenanthroline-5,6-dione (phendione)-based transition-metal complexes are known for their use in pharmacological and catalysis applications. However, their application in electrochemical energy storage has not been investigated thus far. Herein, the feasibility of employing phendione-transition-metal complexes was investigated for electrochemical charge storage by taking advantage of the reversible redox activity of both carbonyl groups and transition metal center, contributing to augmented charge storage. Interestingly, the chemistry of the counter ion in the studied complexes effectively tuned the solubility and improved the cycling stability. Although further studies are required to limit the solubility and active-species shuttle, this study explores the bottlenecks of phendione-transition-metal complexes as electrode materials for solid-electrode-format batteries.

Keto-enol tautomerization drives the self-assembly of leucoquinizarin on Au(111)

The self-assembly of leucoquinizarin molecules on Au(111) surfaces is shown to be characterized by the molecules mostly being in their keto-enolic tautomeric form, with evidence of their temporary switching to other tautomeric forms. This reveals a metastable chemistry of the assembled molecules, to be considered for their possible employment in the formation of more complex hetero-organic interfaces.