Organic Electrode Materials Research Articles

Covalent organic frameworks as electrode materials for rechargeable metal‐ion batteries

AbstractCovalent organic frameworks (COFs), as a class of crystalline porous polymers, featuring designable structures, tunable frameworks, well‐defined channels, and tailorable functionalities, have emerged as promising organic electrode materials for rechargeable metal‐ion batteries in recent years. Tremendous efforts have been devoted to improving the electrochemical performance of COFs. However, although significant achievements have been made, the electrochemical behaviors of developed COFs are far away from the desirable performance for practical batteries owing to intrinsic problems, such as poor electronic conductivity, the trade‐off relationship between capacity and redox potential, and unfavorable micromorphology. In this review, the recent progress in the development of COFs for rechargeable metal‐ion batteries is presented, including Li, Na, K, and Zn ion batteries. Various research strategies for improving the electrochemical performance of COFs are summarized in terms of the molecular‐level design and the material‐level modification. Finally, the major challenges and perspectives of COFs are also discussed in the aspect of large‐scale production and electrochemical performance improvements.

Validating the reversible redox of alkali-ion disulfonyl-methanide as organic positive electrode materials

Alkali-ion reservoir organic positive electrode materials with high redox potential emerge as promising candidates for rocking-chair batteries. Despite recent major advances on coordinated Li-enolates and conjugated Li-sulfonamides, alike chemistries remain rare with clearly enormous room to explore and investigate. Herein, we report a new high-voltage redox functionality for alkali-ion storage based on aromatic di-sulfonyl methanide. The versatile paradigm chemistry of di-alkali p-phenylene-bis-diethylsulfonyl methanide (denoted as A2-p-TESO2, where A = Li+, Na+, K+) displays high voltage (3.13 vs Li+/Li), a two-electron reversible redox in both liquid phase and solid phase electrochemistry. A2-p-TESO2 also shows great stability under ambient air conditions in their alkali-ion reservoir states. This work not only suggests a new charge storage mechanism for organic batteries but also highlights the versatility of organic chemistry in designing new redox functionalities for next-generation organic rechargeable batteries.

Electrolytes in Organic Batteries.

Organic batteries using redox-active polymers and small organic compounds have become promising candidates for next-generation energy storage devices due to the abundance, environmental benignity, and diverse nature of organic resources. To date, tremendous research efforts have been devoted to developing advanced organic electrode materials and understanding the material structure-performance correlation in organic batteries. In contrast, less attention was paid to the correlation between electrolyte structure and battery performance, despite the critical roles of electrolytes for the dissolution of organic electrode materials, the formation of the electrode-electrolyte interphase, and the solvation/desolvation of charge carriers. In this review, we discuss the prospects and challenges of organic batteries with an emphasis on electrolytes. The differences between organic and inorganic batteries in terms of electrolyte property requirements and charge storage mechanisms are elucidated. To provide a comprehensive and thorough overview of the electrolyte development in organic batteries, the electrolytes are divided into four categories including organic liquid electrolytes, aqueous electrolytes, inorganic solid electrolytes, and polymer-based electrolytes, to introduce different components, concentrations, additives, and applications in various organic batteries with different charge carriers, interphases, and separators. The perspectives and outlook for the future development of advanced electrolytes are also discussed to provide a guidance for the electrolyte design and optimization in organic batteries. We believe that this review will stimulate an in-depth study of electrolytes and accelerate the commercialization of organic batteries.

Predicting the Solubility of Organic Energy Storage Materials Based on Functional Group Identity and Substitution Pattern

Organic electrode materials (OEMs) provide sustainable alternatives to conventional electrode materials based on transition metals. However, the application of OEMs in lithium-ion and redox flow batteries requires either low or high solubility. Currently, the identification of new OEM candidates relies on chemical intuition and trial-and-error experimental testing, which is costly and time intensive. Herein, we develop a simple empirical model that predicts the solubility of anthraquinones based on functional group identity and substitution pattern. Within this statistical scaffold, a training set of 18 anthraquinone derivatives allows us to predict the solubility of 808 quinones. Internal and external validations show that our model can predict the solubility of anthraquinones in battery electrolytes within log S ± 0.7, which is a much higher accuracy than existing solubility models. As a demonstration of the utility of our approach, we identified several new anthraquinones with low solubilities and successfully demonstrated their utility experimentally in Li-organic cells.

Application of 2D MXene in Organic Electrode Materials for Rechargeable Batteries: Recent Progress and Perspectives

AbstractOrganic electrode materials (OEMs) are emerging green power because of the promising advantages such as environmental friendliness, abundant sources, easy recycling, and structural diversity. However, several inherent issues, including low electronic conductivity, dissolution of active materials, and particle pulverization restrict their practical application. MXene, as a novel 2D material has exhibited enormous potential to solve the issues of OEMs due to its high conductivity, unique structure, exceptional mechanical property, and abundant surface groups. Up to now, various effective strategies have been presented and achieved positive effects, such as constructing heterojunction structures, in situ assembly, dip‐coating, preparing free‐standing MXene paper, etc. Nonetheless, comprehensive review of the progress and status is rare. Herein, an overview of the application of MXene in organic electrode materials for rechargeable batteries is systematically put forward. Meanwhile, recent progress and future development directions are presented. This review can serve as a guide for future research.

An Insoluble Amino-Functionalized Hexaazatriphenylene as Stable Organic Cathode in Lithium-Ion Batteries

Organic electrode materials have received increasing attention in rechargeable batteries due to their earth abundance and variable structures. However, the practical application of most organic electrode materials is limited by the high solubility in the electrolyte. Herein, an insoluble amino-functionalized hexaazatriphenylene (defined as HATN-[NH2]3) in the electrolyte is developed as stable organic cathode material for lithium-ion batteries (LIBs). The resultant HATN-[NH2]3 electrode achieves a high reversible capacity of 192.5 mAh g−1 at a current density of 0.05 A g−1. Remarkably, the electrode exhibits almost no capacity fade after 500 cycles at 0.5 A g−1. The high stability can be ascribed to insoluble property caused by hydrogen bonds between HATN-[NH2]3 molecules. Moreover, density functional theory calculations suggest that amino functionalization can reduce the band gap of HATN, in favor of improved conductivity and thus enhanced rate performance. This work offers a simple but efficient strategy to develop stable organic electrode materials in LIBs and beyond.

Oxygen activity excited thiophene-diketopyrrolopyrrole-based organic molecules as anode for lithium-ion batteries with enhanced interfacial storage capacity and long cycling capability

In this work, we synthesized various thiophene-diketopyrrolopyrrole-based (DPP-2T-based) molecules by Knoevenagel condensation and halogenation reaction, which applied DPP-2T-based small molecules as anode for lithium-ion batteries (LIBs) for the first time. We studied the different substituents on battery performance and explored the charge–discharge mechanism for DPP-2T-based molecules. DPP-2T-based molecules exhibit different electrochemical properties by substituting various groups at nitrogen positions, where DPP-2T-TA (tert-butyl acetate) electrode possesses better capacity and long-term cycle performance than that of DPP-2T-H (no substitution) and DPP-2T-C6 (hexane) electrode. DPP-2T-TA electrode present an unusual upward tendency for its discharge specific capacity during cycling, which displays that of 530 mAh/g (1000 mA g−1) after 2000 cycles and the capacity retention reaches up to 142.5 %. It is better than those of DPP-2T-H (439 mAh/g, 108.1 %) and DPP-2T-C6 (423 mAh/g, 113.1 %) electrode, which is ascribed to oxygen activity excitation in tert-butyl acetate. This moment, the energy density and power density of DPP-2T-TA electrode are 346 Wh kg−1 and 699 W kg−1, respectively. To further explain this phenomenon, we used many ex-situ measurgin methods such as differential specific capacity (dQ/dV) curves, scanning electron microscope (SEM), Fourier transform infrared (FT-IR) spectrometer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and natural bond orbital (NBO) analysis to characterize the detailed lithiation/delithiation process of DPP-2T-TA electrode. The results suggest that the unusual capacity amplification for DPP-2T-TA electrode attributed to lithium-ions inserted into unsaturated carbons and increases its interfacial storage capacity. We believe that the synthesis of DPP-2T-based organic molecules can provide a novel strategy for the development of organic electrode materials for LIBs.

High‐Resolution Mass Spectroscopy for Revealing the Charge Storage Mechanism in Batteries: Oxamide Materials as an Example

The pursuit of high‐performance electrode materials is highly desired to meet the demand of batteries with high energy and power density. However, a deep understanding of the charge storage mechanism is always challenging, which limits the development of advanced electrode materials. Herein, high‐resolution mass spectroscopy (HR‐MS) is employed to detect the evolution of organic electrode materials during the redox process and reveal the charge storage mechanism, by using small molecular oxamides as an example, which have ortho‐carbonyls and are therefore potential electrochemical active materials for batteries. The HR‐MS results adequately proved that the oxamides could reversibly store lithium ions in the voltage window of 1.5–3.8 V. Upon deeper reduction, the oxamides would decompose due to the cleavage of the C–N bonds in oxamide structures, which could be proved by the fragments detected by HR‐MS, 1H NMR, and the generation of NH3 after the reduction of oxamide by Li. This work provides a strategy to deeply understand the charge storage mechanism of organic electrode materials and will stimulate the further development of characterization techniques to reveal the charge storage mechanism for developing high‐performance electrode materials.

Noncovalent interactions engineering construct the fast-kinetics organic cathode for room/low-temperature aqueous zinc-ion battery

Electroactive organic electrode materials are receiving increasing attention in aqueous zinc-ion batteries (AZIBs). However, the insufficient electrical conductivity, sluggish kinetics and intrinsic soluble trait of organic molecules still hinder their application as the electrode material. Here, a carbonyl compound, dibenzo[b,i]thian threne-5,7,12,14-tetraone (DTT) is tightly wrapping by reduced graphene oxide (r-GO) with noncovalent interactions to obtain DTT@r-GO organic cathode material. Benefiting from the π-π coupling, the composite electrode delivers higher surface area, enhanced electron/ion transportation and stable structure, which exhibits superior rate performance (259.1 mAh g−1 at 0.1 A g-1 and 117.7 mAh g−1 at 10 A g−1) and considerable calendar life (4000 cycles with 100 % capacity retention at 10 A g−1). Electrochemical testing and ex-situ analysis prove CO can act as a strong electron donor together with co-accommodation of Zn2+/H+, theoretical calculation confirms the favorable two-step Zn storage configuration during the charge storage process. Furthermore, these AZIBs can steadily power electronic devices at −50 °C, as well as retain a high reversible capacity of 199.5 mAh g−1 at 50 mA g−1 and 100 % capacity retention after 3700 cycles at −20 °C. The work is believed to broaden the insight into noncovalent interactions and inspire the organic electrochemical materials.

Reversible multi-electron redox chemistry of organic salt as anode for high-performance Li-ion/dual-ion batteries

Organic electrode materials are attracting increasing attention for rechargeable secondary batteries because of their low cost, high capacity, nontoxic and environmentally friendly. Herein, we report an excellent anode of a novel organic hexalithium salt of mellitic acid (Li6C12O12) for lithium-ion battery (LIB)/dual-ion battery (DIB). A combination of electrochemical and spectroscopic studies verifies a reversible coordination reaction mechanism based on carboxylic carbonyl and Li+ ions. Li6C12O12 delivers large reversible capacities of 730 mA h g−1 at 0.21 A/g and 372 mA h g−1 even at 2 A/g. Furthermore, the Li6C12O12 electrode enables LiFePO4//Li6C12O12 full LIB and graphite//Li6C12O12 full DIB to exhibit high capacity and good cycling stability. This work presents a new perspective on designing and tailoring organic electrode materials to build high-performance lithium-ion batteries/dual-ion batteries.

Organic electrode materials and carbon/small-sulfur composites for affordable, lightweight and sustainable batteries.

Redox-active organic/polymeric materials and carbon/small-sulfur composites are promising electrode materials for developing affordable, lightweight, and sustainable batteries because of their low cost, abundance, low carbon footprint, and flexible structural tunability. This feature article summarized the key aspects of the research related to organic batteries and Li-S batteries (LSBs) based on organic/polymeric/sulfur materials for next-generation sustainable energy storage. An in-depth discussion for organic electrode materials in alkali-ion, multivalent metal, all-solid-state, and redox flow batteries is provided. State-of-the-art LSBs under high mass loading and lean electrolyte conditions for practical applications is also covered. The challenges, reaction mechanisms, strategies, approaches, and developments of organic batteries and LSBs are discussed to offer guidance for rational structure design and performance optimization. This feature article will contribute to the development and commercialization of affordable, lightweight, and sustainable batteries.

Iodine doping induced activation of covalent organic framework cathodes for Li-ion batteries.

Covalent organic frameworks (COFs) are considered as promising candidate organic electrode materials for lithium-ion batteries (LIBs) because of their relatively high capacity, ordered nanopores, and limited solubility in electrolyte. However, the practical capacity of COF materials is mainly affected by their low electronic/ionic conductivity and the deep-buried active sites inside the COFs. Here, we synthesize an iodine doped β-ketoenamine-linked COF (2,6-diaminoanthraquinone and 1,3,5-triformylphloroglucinol, denoted as COF-I) by a facile one-pot solvothermal reaction. The introduction of iodine can make the COF more lithiophilic inside and exhibit high intrinsic ion/electron transport, ensuring more accessible active sites of the COFs. Consequently, when used as the cathode of LIBs, COF-I demonstrates a high initial discharge capacity of 140 mA h g-1 at 0.2 A g-1, and excellent cycling stability with 92% capacity retention after 1000 cycles. Furthermore, a reversible capacity of 95 mA h g-1 at 1.0 A g-1 is also achieved after 300 cycles. Our study provides a facile way to develop high-performance COF electrode materials for LIB applications.

Two-dimensional polymer nanosheets as a high-performance organic anode for sodium-ion batteries.

Organic compounds have become a potentially important choice for a new generation of energy-storage electrode materials due to their designability, flexibility, green sustainability, and abundance. However, the applications of organic electrode materials are still limited because of their dissolution in electrolytes and low electrical conductivity, which in turn cause poor cycling stability. Here, for the first time, we report 2-amino-4-thiazole-acetic acid (ATA) and its sodium salt, sodium 2-amino-4-thiazol-derived polymer (PATANa), as an anode. The PATANa showed a two-dimensional (2D) nanosheet structure, offering a larger contact area with the electrolyte and a shorter ion-migration path, which improved the ion-diffusion kinetics. The polymer showed excellent cycling stability and outstanding rate capability when tested as an anode for sodium-ion batteries (SIBs). It could deliver a high reversible specific capacity of 303 mA h g-1 at 100 mA g-1 for 100 cycles and maintain a high discharge capacity of 190 mA h g-1 after 1000 long cycle numbers even at a high current density of 1000 mA g-1. This approach of salinizing the polymer opens a new way to develop anode materials for sodium-ion batteries.

Boosting the zinc storage of a small-molecule organic cathode by a desalinization strategy.

Organic materials offer great potential as electrodes for batteries due to their high theoretical capacity, flexible structural design, and easily accessible materials. However, one significant drawback of organic electrode materials is their tendency to dissolve in the electrolyte. Resazurin sodium salt (RSS) has demonstrated remarkable charge/discharge performance characterized by a voltage plateau and high capacity when utilized as a cathode in aqueous zinc-ion batteries (AZIBs). Unfortunately, the solubility of RSS as a sodium salt continues to pose challenges in AZIBs. In this study, we introduce an RSS-containing organic compound, triresazurin-triazine (TRT), with a porous structure prepared by a desalinization method from the RSS and 2,4,6-trichloro-1,3,5-triazine (TCT). This process retained active groups (carbonyl and nitroxide radical) while generating a highly conjugated structure, which not only inhibits the dissolution in the electrolyte, but also improves the electrical conductivity, enabling TRT to have excellent electrochemical properties. When evaluated as a cathode for AZIBs, TRT exhibits a high reversible capacity of 180 mA h g-1, exceptional rate performance (78 mA h g-1 under 2 A g-1), and excellent cycling stability with 65 mA h g-1 at 500 mA g-1 after 1000 cycles.

Unexpected Direct Synthesis of Tunable Redox-Active Benzil-Linked Polymers via the Benzoin Reaction.

Strategies for the sustainable synthesis of redox-active organic polymers could lead to next-generation organic electrode materials for electrochemical energy storage, electrocatalysis, and electro-swing chemical separations. Among redox-active moieties, benzils or aromatic 1,2-diones are particularly attractive due to their high theoretical gravimetric capacities and fast charge/discharge rates. Herein, we demonstrate that the cyanide-catalyzed polymerization of simple dialdehyde monomers unexpectedly leads to insoluble redox-active benzil-linked polymers instead of the expected benzoin polymers, as supported by solid-state nuclear magnetic resonance spectroscopy and electrochemical characterization. Mechanistic studies suggest that cyanide-mediated benzoin oxidation occurs by hydride transfer to the solvent, and that the insolubility of the benzil-linked polymers protects them from subsequent cyanolysis. The thiophene-based polymer poly(BTDA) is an intriguing organic electrode material that demonstrates two reversible one-electron reductions with monovalent cations such as Li+ and Na+ but one two-electron reduction with divalent Mg2+. As such, the tandem benzoin-oxidation polymerization reported herein represents a sustainable method for the synthesis of highly tunable and redox-active organic materials.

Organic Anode Materials for Lithium-Ion Batteries: Recent Progress and Challenges.

In the search for novel anode materials for lithium-ion batteries (LIBs), organic electrode materials have recently attracted substantial attention and seem to be the next preferred candidates for use as high-performance anode materials in rechargeable LIBs due to their low cost, high theoretical capacity, structural diversity, environmental friendliness, and facile synthesis. Up to now, the electrochemical properties of numerous organic compounds with different functional groups (carbonyl, azo, sulfur, imine, etc.) have been thoroughly explored as anode materials for LIBs, dividing organic anode materials into four main classes: organic carbonyl compounds, covalent organic frameworks (COFs), metal-organic frameworks (MOFs), and organic compounds with nitrogen-containing groups. In this review, an overview of the recent progress in organic anodes is provided. The electrochemical performances of different organic anode materials are compared, revealing the advantages and disadvantages of each class of organic materials in both research and commercial applications. Afterward, the practical applications of some organic anode materials in full cells of LIBs are provided. Finally, some techniques to address significant issues, such as poor electronic conductivity, low discharge voltage, and undesired dissolution of active organic anode material into typical organic electrolytes, are discussed. This paper will guide the study of more efficient organic compounds that can be employed as high-performance anode materials in LIBs.

Emerging Lithiated Organic Cathode Materials for Lithium-Ion Full Batteries.

Organic electrode materials have application potential in lithium batteries owing to their high capacity, abundant resources, and structural designability. However, most reported organic cathodes are at oxidized states (namely unlithiated compounds) and thus need to couple with Li-rich anodes. In contrast, lithiated organic cathode materials could act as a Li reservoir and match with Li-free anodes such as graphite, showing great promise for practical full-battery applications. Here we summarize the synthesis, stability, and battery applications of lithiated organic cathode materials, including synthetic methods, stability against O2 and H2 O in air, and strategies to improve comprehensive electrochemical performance. Future research should be focused on new redox chemistries and the construction of full batteries with lithiated organic cathodes and commercial anodes under practical conditions. This Minireview will encourage more efforts on lithiated organic cathode materials and finally promote their commercialization.

A voltage control strategy to improve the cycling stability of organic electrode materials: The case of para-dinitrobenzene

Small-molecule organic cathode materials (SMOCMs) with high energy density are promising for various energy storage devices including rechargeable lithium batteries, but it is a huge challenge to simultaneously satisfy the demand of cycling stability. Herein, by taking nitro-based para-dinitrobenzene (pDNB) as an example, we propose a simple but effective voltage control strategy to improve the cycling stability, without energy density decrease or cost increase of the system as for many other complicated solutions. The highly reversible two-electron redox reaction of pDNB provides it full utilization of the theoretical capacity (319 mAh g−1) and high discharge plateau at 2.65 V vs Li+/Li, and thus an outstanding energy density of 850 Wh kg−1. Different voltage windows of 1.8/2.4–3.4/3.8 V are applied to test the cycling performance, and 2.4–3.8 V is selected as the optimized one endowing a high capacity retention of 86 % after 100 cycles (as a contrast, only 8 % within 1.8–3.4 V). Various electrochemical analyses and ex-situ characterization methods reveale that the influence is not in the depth of discharge/charge, but in the dissolution–redepostion behavior of active material and thus the electrode structure evolution. This work provides not only a novel strategy to improve the cycling stability of SMOCMs, but also a new perspective to understand the capacity fading mechanism of them.

Effects of Position and Quantity of the Cyano Group in Organic Electrode Materials on Electrochemical Performance

AbstractRecently, organic cathodes have received wide attention as eco‐friendly and sustainable materials for aqueous Zn‐organic batteries. However, the low voltage limits its further development and the related optimization strategies are rarely reported. Herein, three HATN‐based cathode materials containing cyano groups (named O3CN, P3CN, and P6CN) are proposed to reveal the role of cyano groups. The number of cyano groups was positively correlated with the potential, and the position of cyano groups would affect the ion mobility through the steric effect. Furthermore, the cyano group also reduces the solubility of the materials in water, greatly improving the cycle stability under low current density. As a result, the average voltage increased from 0.48 V for HATN to 0.73 V for P6CN, and the capacity retained 88.2 % after 5000 cycles at 5 A g−1. This study provides a systematic reference for the improvement of the voltage of organic cathode materials in the future.

Nine‐Electron Transfer of Binder Synergistic π‐d Conjugated Coordination Polymers as High‐Performance Lithium Storage Materials

AbstractTo solve the problems such as the dissolution and the poor conductivity of organic small molecule electrode materials, we construct π‐d conjugated coordination polymer Ni‐DHBQ with multiple redox‐active centers as lithium storage materials. It exhibits an ultra‐high capacity of 9‐electron transfers, while the π‐d conjugation and the laminar structure inside the crystal ensure fast electron transport and lithium ion diffusion, resulting in excellent rate performance (505.6 mAh g−1 at 1 A g−1 after 300 cycles). The interaction of Ni‐DHBQ with the binder CMC synergistically inhibits its dissolution and anchors the Ni atoms, thus exhibiting excellent cycling stability (650.7 mAh g−1 at 0.1 A g−1 after 100 cycles). This work provides insight into the mechanism of lithium storage in π‐d conjugated coordination polymers and the synergistic effect of CMC, which will contribute to the molecular design and commercial application of organic electrode materials.