Characterization methods of organic electrode materials

The development of novel organic electrode materials is of great significance for improving the reversible capacity and cycle stability of rechargeable batteries.Before practical application,it is essential to characterize the electrode materials to study their structures,redox mechanisms and electrochemical performances.In this review,the common characterization methods that have been adopted so far are summarized from two aspects:experimental characterization and theoretical calculation.The experimental characterization is introduced in detail from structural characterization,electrochemical characterization and electrode reaction chara cterization.The experimental purposes and working principles of various experimental characterization methods are briefly illustrated.As the auxilia ry means,theoretical calculation provides the theoretical basis for characterizing the electrochemical reaction mechanism of organic electrode materials.Through these characterizations,we will have a deep understanding about the material structures,electrochemical redox mechanisms,electrochemical properties and the relationships of structure-property.It is hoped that this review would help researchers to select the suitable characterization methods to analyze the structures and performances of organic electrode materials quickly and effectively.

Organic Electrode Materials for Non-aqueous K-Ion Batteries

The demands for high-performance and low-cost batteries make K-ion batteries(KIBs) considered as promising supplements or alternatives for Li-ion batteries(LIBs). Nevertheless, there are only a small amount of conventional inorganic electrode materials that can be used in KIBs, due to the large radius of K^+ ions. Diff erently, organic electrode materials(OEMs) generally own sufficiently interstitial space and good structure flexibility, which can maintain superior performance in K-ion systems. Therefore, in recent years, more and more investigations have been focused on OEMs for KIBs. This review will comprehensively cover the researches on OEMs in KIBs in order to accelerate the research and development of KIBs. The reaction mechanism, electrochemical behavior, etc., of OEMs will all be summarized in detail and deeply. Emphasis is placed to overview the performance improvement strategies of OEMs and the characteristic superiority of OEMs in KIBs compared with LIBs and Na-ion batteries.

Advanced organic electrode materials for aqueous rechargeable batteries

Organic electrode materials take advantages of potentially sustainable production and structural tunability compared with present commercial inorganic electrode materials.However,their applications in traditional rechargeable batteries with nonaqueous electrolytes suffer from the premature failure and safety concerns.In comparison,aqueous rechargeable batteries based on organic electrode materials have received extensive attentions in recent years for low-cost and sustainable energy storage systems due to their inherent safety.This review aims to provide a comprehensive summary on the recent progress in advanced organic electrode materials for aqueous rechargeable batteries.We start from the overview of working principles and general design strategies of organic electrode materials in aqueous rechargeable batteries.Then the research advances of organic electrode materials in various aqueous rechargeable batteries are highlighted in terms of charge carriers(monovalent ions,multivalent ions,and anions).We emphasized the characteristics of organic electrode materials in various charge carriers.Finally,the critical challenges and future efforts of aqueous organic rechargeable batteries are discussed.More organic electrode materials with better electronic conductivity and fast reaction kinetics are still needed to build advanced aqueous batteries for commercial applications.

Small-molecule organic electrode materials for rechargeable batteries

Small-molecule organic electrode materials(SMOEMs)have shown tremendous potential as cathodes or anodes for various rechargeable batteries including lithium and sodium batteries,due to their easy material availability,high structure designability,attractive theoretical capacity,and wide adaptability to counterions.However,they suffer from the severe dissolution problem and the subsequent shuttle effect in nonaqueous electrolytes,which cause the poor cycling stability and Coulombic efficiency.To satisfy the demands on the energy density and cycling stability simultaneously,the molecular structures of SMOEMs need to be rationally designed,and extrinsic approaches including electrode engineering and electrolyte optimizations can be further conducted.In this review,we summarize the fundamental knowledge about SMOEMs,including their working principles and applications,structure classifications,molecular structure design methods,and extrinsic optimization strategies.Moreover,we also provide some original insights aiming at guiding the research and development of SMOEMs in a more scientific and practical way.In brief,SMOEMs are facing huge opportunities and challenges as candidates to enable the next-generation of efficient,sustainable,and green rechargeable batteries.

Perspectives on the Redox Chemistry of Organic Electrode Materials in Lithium Batteries

Organic electrode materials have attracted much attention for lithium batteries because of their high capacity,flexible designability,and environmental friendliness.Understanding the redox chemistry of organic electrode materials is essential for optimizing electrochemical performance and designing new molecules.This review aims to summarize the redox chemistry of different organic electrode materials in lithium batteries,including carbonyl compounds,conductive polymers,organosulfur compounds,organic radicals,imine compounds,compounds with superlithiation ability,and azo compounds.The discussions are focused on the evolution of their molecular and crystal structures during discharge/charge processes utilizing various characterization approaches.To date,carbonyl compounds based on the conversion between C=O and C-OLi have been proven to be one of the most promising organic electrode materials for lithium batteries.Future works should pay more attention to the detection of redox intermediates through operando techniques and the further combination of theoretical calculations.This review provides insights into the redox chemistry of organic electrode materials in lithium batteries.

Nanostructured organic electrode materials grown on graphene with covalent-bond interaction for high-rate and ultra-long-life lithium-ion batteries

Nanostructured organic tetralithium salts of 2,5-dihydroxyterephthalic acid （Li4C8H2O6） supported on graphene were prepared via a facile recrystallization method. The optimized composite with 75 wt.% Li4C8H2O6 was evaluated as an anode with redox couples of Li4C8H2O6/Li6C8H2O6 and as a cathode with redox couples of Li4C8H2O6/Li2C8H2O6 for Li-ion batteries, exhibiting a high-rate capability （10 C） and long cycling life （1,000 cycles）. Moreover, in an all-organic symmetric Li-ion battery, this dual-function electrode retained capacities of 191 and 121 mA.h·g-1 after 100 and 500 cycles, respectively. Density functional theory calculations indicated the presence of covalent bonds between Li4CsH206 and graphene, which affected both the morphology and electronic structure of the composite. The special nanostructures, high electronic conductivity of graphene, and covalent-bond interaction between Li4C8H2O6 and graphene contributed to the superior electrochemical properties. Our results indicate that the combination of organic salt molecules with graphene is useful for obtaining high-performance organic batteries.

A precise theoretical method for high-throughput screening of novel organic electrode materials for Li-ion batteries

Organic electrode materials have gained significant attention due to their flexibility,lightweight characteristics,abundant resources in nature,and low CO_(2) emission.It's urgently needed for setting up an accurate high-throughput screening theoretical scheme that could find out possible candidates of electrode materials.Currently,the error between the theoretical potentials calculated by the PBE-D2(DFT-D2,dispersion-corrected density functional theory)method and the experimental values is larger than 12%.Thus,it's essential to finding a more accurate method.In the present work,hybrid functionals and vdW correction methods are applied to investigate six reported organic electrode materials for Li-ion batteries.The results show that the hybrid functional combined with the D2 dispersion corrected method,i.e.,HSE06-D2(Heyd,Scuseria,and Ernzerhof,dispersion-corrected),is able to predict the potential of the organic material precisely with an average error of approximately 5%.This method occupies much hardware resources and being very time consuming,but it could be applied as the final ultrafine step in the high-throughput screening program.

Structural Isomers:Small Change with Big Difference in Anion Storage

Organic electrode materials are promising for batteries.However,the reported organic electrodes are often facing the challenges of low specific capacity,low voltage,poor rate capability and vague charge storage mechanisms,etc.Isomers are good platform to investigate the charge storage mechanisms and enhance the performance of batteries,which,however,have not been focused in batteries.Herein,two isomers are reported for batteries.As a result,the isomer tetrathiafulvalene(TTF)could store two monovalent anions reversibly,deriving an average discharge voltage of 1.05 V and a specific capacity of 220 mAh g−1 at a current density of 2 C.On the other hand,the other isomer tetrathianaphthalene could only reversibly store one monovalent anion and upon further oxidation,it would undergo an irreversible solid-state molecular rearrangement to TTF.The molecular rearrangement was confirmed by electrochemical performances,X-ray diffraction patterns,nuclear magnetic resonance spectra,and 1H detected heteronuclear multiple bond correlation spectra.These results suggested the small structural change could lead to a big difference in anion storage,and we hope this work will stimulate more attention to the structural design for boosting the performance of organic batteries.

Advanced Organic Materials for Nonmetallic Charge Carrier-Based Batteries

Organic electrode materials(OEMs),withmerits of structural diversity,molecular-level controllability,resource abundance,and environmental friendliness,have become a promising electrode candidate for low-carbon renewable batteries.Safer,environmentally benign,and sustainable aqueous rechargeable batteries are particularly appealing for large-scale energy storage applications.This review aims to provide an insightful discussion of OEMs in nonmetallic charge carrier-based batteries,especially for the application in aqueous rechargeable systems.The emerging application of OEMs in versatile aqueous batteries will be analyzed emphatically,including aqueous proton batteries,aqueous ammonium-ion batteries,and air self-charging batteries.We expect that this review can serve as a guide for the future development of OEMs in nonmetallic charge carrier-based batteries and provide inspiration for unmet challenges.

“Co-coordination force”assisted rigid-flexible coupling crystalline polymer for high-performance aqueous zinc-organic batteries

Organic electrode materials(OEMs)have attracted substantial attention for aqueous zinc-ion batteries(AZIBs)due to their advantages in relieving resource and environmental anxiety.However,the potential of OEMs is plagued by their low achievable capacity and high solubility.Here,we have proposed a new concept of“co-coordination force”and designed a rigid-flexible coupling crystalline polymer that can overcome the abovementioned limitations.The obtained crystalline polymer(BQSPNs)with multiredox centres makes the BQSPNs exist intermolecular hydrogen bonds(HB)among-C=O,-C=N,and-NH and consequently exhibits transverse two-dimensional arrays and longitudinalπ-πstacking structure.Additionally,in-situ FTIR,Raman,variable temperature FTIR spectra,and 2D nuclear overhauser effect spectroscopy(NOESY)well capture the existence and evolution process of HB during the electrochemistry reaction process of BQSPNs,uncovering the effect of HB in stabilizing the structure and promoting the reaction kinetics.As a result,the BQSPNs with rationally designed“co-coordination force”deliver a high capacity of 459.6 m Ah/g and a stable cycling lifetime for more than 100,000 cycles at 10 A/g in AZIBs.Our results disclose the HB effect and provide a brand-new strategy for high-performance OEMs design.

Unlocking high-performance organic cathodes:tailoring active group densities in covalent frameworks for aqueous zinc ion batteries

Aqueous zinc ion batteries(AZIBs)are a promising energy storage technology due to their cost-effectiveness and safety.Organic materials with sustainable and designable structures are of great interest as AZIBs cath-odes.However,small molecules in organic cathode materials face dissolution problems and suboptimal cycle life,whereas large molecules suffer from a low theoretical capacity due to their inert carbon skeletons.Here,we designed two covalent organic framework(COF)materials(benzoquinoxaline benzoquinone-based COF(BB-COF)and triquinoxalinylene benzoquinone-based COF(TB-COF))with the same structure and number of energy storage groups to investigate the correlation between the densities of active sites and electrochemi-cal performance.We conclude that the electrochemical behavior of organic conjugate-based energy storage materials lacks a linear correlation with active site quantity.Adjusting active site densities is crucial for mate-rial advancement.BB-COF and TB-COF with dual active sites(C=O and C=N)exhibit distinct characteristics.TB-COF,which has dense active groups,shows a high initial capacity(222 mAh g^(-1)).Conversely,BB-COF,which features a large conjugated ring diameter,presents superior rate performance and enduring cycle stability.It even maintains stable cycling for 2000 cycles at-40℃.In-situ electrochemical quartz crystal mic-robalance tests reveal the energy storage mechanism of BB-COF,in which H+storage is followed by Zn2+storage.

Proton storage chemistry in aqueous zinc-organic batteries:A review

Benefiting from the advantageous features of structural diversity and resource renewability,organic electroactive compounds are considered as attractive cathode materials for aqueous Zn-ion batteries(ZIBs).In this review,we discuss the recent developments of organic electrode materials for aqueous ZIBs.Although the proton(H^(+))storage chemistry in aqueous Zn-organic batteries has triggered an overwhelming literature surge in recent years,this topic remains controversial.Therefore,our review focuses on this significant issue and summarizes the reported electrochemical mechanisms,including pure Zn^(2+)intercalation,pure H^(+)storage,and H^(+)/Zn^(2+)co-storage.Moreover,the impact of H^(+)storage on the electrochemical performance of aqueous ZIBs is discussed systematically.Given the significance of H^(+)storage,we also highlight the relevant characterization methods employed.Finally,perspectives and directions on further understanding the charge storage mechanisms of organic materials are outlined.We hope that this review will stimulate more attention on the H^(+)storage chemistry of organic electrode materials to advance our understanding and further its application.

Carbonyl polymeric electrode materials for metal-ion batteries

Benefiting from the diversity and subjective design feasibility of molecular structure, flexibility,lightweight, molecular level controllability, resource renewability and relatively low cost, polymeric electrode materials are promising candidates for the next generation of sustainable energy resources and have attracted extensive attention for the foreseeable large scale applications. The conductive polymers have been utilized as electrode materials in the pioneer reports, which, however, have the disadvantages of low stability, low reversibility and slope voltage due to the delocalization of charges in the whole conjugated systems. The discovery of carbonyl materials aroused the interest of organic and polymeric materials for batteries again. This review presents the recent progress in carbonyl polymeric electrode materials for lithium-ion batteries, sodium-ion batteries and magnesium-ion batteries. This comprehensive review is expected to be helpful forarousing more interest of organic materials for met

Iterative design of polymer fabric cathode for metal-ion batteries

Organic electrode materials(OEMs)have attracted significant attention for use in aqueous zinc-ion batteries(AZIBs)because of their abundant resources and flexible designability.However,the development of high-performance OEMs is strongly hindered by their high solubility,poor conductivity,sluggish ion diffusion kinetics,and difficult coordination toward Zn^(2+).Herein,inspired by fabric crafts,we have designed a robust polymer fabric through the iterative evolution of the building blocks from point to line and plane.The evolution from point to line could not only improve the structural stability and electrical conductivity but also adjust the active site arrangement to enable the storage of Zn^(2+).In addition to further boosting the aforementioned properties,the evolution from line to plane could also facilitate the construction of noninterference channels for ion migration.Accordingly,the poly(1,4,5,8-naphthalenete tracarboxylic dianhydride/2,3,5,6-tetraaminocyclohexa-2,5-diene-1,4-dione)(PNT)polymer fabric has the most enhanced structural stability,optimized active site arrangement,improved electrical conductivity,and suitable ion channels,resulting in a record-high capacity retention of 96%at a high mass loading of 56.9 mg cm-2and a stable cycle life of more than 20,000 cycles at 150 C(1 C=200 mA g^(-1))in AZIBs.In addition,PNT exhibits universality for a wide range of ions in organic electrolyte systems,such as Li/Na/K-ion batteries.Our iterative design of polymer fabric cathode has laid the foundation for the development of advanced OEMs to promote the performance of metal-ion batteries.

Thiourea-based polyimide/RGO composite cathode:A comprehensive study of storage mechanism with alkali metal ions

Although organic electrode materials have merits of abundant resources,diverse structures and environmental friendliness,their performance for electrochemical energy storage is far insufficient.In this work,a thiourea-based polyimide/reduced graphene oxide(PNTCSA/RGO)composite was synthesized via a condensation polymerization method.As a cathode material in lithium-ion batteries,excellent performance is demonstrated with high reversible capacity(144.2 mA h g^−1),high discharge voltage(∼2.5 V),and long cycling life(over 2000 cycles at 500 mA g^−1),which are comparable to those of other well documented in organic electrodes.Encouraging electrochemical performance is also demonstrated for sodium ion batteries(a cycling life of 800 cycles at 500 mA g^−1),while poor performance is delivered in potassium ion batteries.Theoretical studies reveal that the active sites are carbonyl groups for all alkali ions but one inserted alkali metal ion is shared by two carbonyl groups from the two neighbor units.More importantly,K ions have stronger interaction with S atoms than Li/Na ions,which may lead to poor structure reversibility and account for the poor cycling performance.Our findings provide a fundamental understanding of polyimide based polymer electrodes and help to design and develop high performance organic electrode materials for alkali metal ion batteries.