Prospects of organic electrode materials for practical lithium batteries

Organic Electrode Materials for Dual-Ion Batteries

Organic materials are widely used in various energy storage devices due to their renewable, environmental friendliness and adjustable structure. Dual-ion batteries (DIBs), which use organic materials as the electrodes, are an attractive alternative to conventional lithium-ion batteries for sustainable energy storage devices owing to the advantages of low cost, environmental friendliness, and high operating voltage. To date, various organic electrode materials have been applied in DIBs. In this review, we present the development of DIBs with a following brief introduction of characteristics and mechanisms of organic materials. The latest progress in the application of organic materials as anode and cathode materials for DIBs is mainly reviewed. Finally, we also discussed the challenges and prospects of organic electrode materials for DIBs.

Design of Organic Cathode Material Based on Quinone and Pyrazine Motifs for Rechargeable Lithium and Zinc Batteries

Despite the rapid expansion of the organic cathode materials field, we still face a shortage of materials obtained through simple synthesis that have stable cycling and high energy density. Herein, we report a two-step synthesis of a small organic molecule from commercially available precursors that can be used as a cathode material. Oxidized tetraquinoxalinecatechol (OTQC) was derived from tetraquinoxalinecatechol (TQC) by the introduction of additional quinone redox-active centers into the structure. The modification increased the voltage and capacity of the material. The OTQC delivers a high specific capacity of 327 mAh g-1 with an average voltage of 2.63 V vs Li/Li+ in the Li-ion battery. That corresponds to an energy density of 860 Wh kg-1 on the OTQC material level. Furthermore, the material demonstrated excellent cycling stability, having a capacity retention of 82% after 400 cycles. Similarly, the OTQC demonstrates increased average voltage and specific capacity in comparison with TQC in aqueous Zn-organic battery, reaching the specific capacity of 326 mAh g-1 with an average voltage of 0.86 V vs Zn/Zn2+. Apart from good electrochemical performance, this work provides an additional in-depth analysis of the redox mechanism and degradation mechanism related to capacity fading.

Porphyrin-Thiophene Based Conjugated Polymer Cathode with High Capacity for Lithium-Organic Batteries

Organic electrode materials are promising for next-generation energy storage materials due to their environmental friendliness and sustainable renewability. However, problems such as their high solubility in electrolytes and low intrinsic conductivity have always plagued their further application. Polymerization to form conjugated organic polymers can not only inhibit the dissolution of organic electrodes in the electrolyte, but also enhance the intrinsic conductivity of organic molecules. Herein, we synthesized a new conjugated organic polymer (COPs) COP500-CuT2TP (poly [5,10,15,20-tetra(2,2'-bithiophen-5-yl) porphyrinato] copper (II)) by electrochemical polymerization method. Due to the self-exfoliation behavior, the porphyrin cathode exhibited a reversible discharge capacity of 420 mAh g-1, and a high specific energy of 900 Wh Kg-1 with a first coulombic efficiency of 96 % at 100 mA g-1. Excellent cycling stability up to 8000 cycles without capacity loss was achieved even at a high current density of 5 A g-1. This highly conjugated structure promotes COP500-CuT2TP combined high energy density, high power density, and good cycling stability, which would open new opportunity for the designable and versatile organic electrodes for electrochemical energy storage.

Defect-Rich Functional HfO2-x for Highly Reversible Zn Metal Anode

Interface engineering attracted tremendous attention owing to its remarkable ability to impede dendrite growth and side reactions in aqueous zinc-ion batteries. Artificial interface layers composed of crystalline materials have been extensively employed to stabilize the Zn anode. However, the diffusion kinetics of Zn2+ in highly crystalline materials are hindered by steric effects from the lattice, thereby limiting the high-rate performance of the cell. Here, defect-rich HfO2-x polycrystals derived from metal-organic frameworks (MOFs) (D-HfO2-x) are developed to enhance the Zn deposition behavior. The discrepancy of dielectric constants between metallic Zn and HfO2 enables the building of an electrostatic shielding layer for uniform Zn deposition. More importantly, the oxygen vacancies in D-HfO2-x provide abundant active sites for Zn2+ adsorption, accelerating the kinetics of Zn2+ migration, which contributes to the preferential exposure of the Zn (002) plane during plating. Consequently, the D-HfO2-x-modified Zn anode delivers ultrastable durability of over 5000 h at 1 mA cm-2 and a low voltage hysteresis of 30 mV. The constructed defective coating provides a guarantee for the stable operation of Zn anodes, and the innovative approach of defective engineering also offers new ideas for the protection of other energy storage devices.

An Organic Molecular Cathode Composed of Naphthoquinones Bridged by Organodisulfide for Rechargeable Lithium Battery

Organic electrodes that embrace multiple electron transfer and efficient redox reactions are desirable for green energy storage batteries. Here, a novel organic electrode material is synthesized, i.e., 2, 2'-((disulfanediylbis (4, 1-phenylene)) bis(azanediyl)) bis (naphthalene-1, 4-dione) (MNQ), through a simple click reaction between common carbonyl and organosulfur compounds and demonstrate its application potential as a high-performance cathode material in rechargeable lithium batteries. MNQ exhibits the aggregation effect of redox-active functional groups, the advantage of fast reaction kinetics from molecular structure evolution, and the decreased solubility in aprotic electrolytes resulting from intermolecular interactions. As expected, the MNQ electrode exhibits a high initial discharge capacity of 281.2 mA h g-1 at 0.5 C, equivalent to 97.9% of its theoretical capacity, and sustains stable long-term cycling performance of over 1000 cycles at 1 C. This work adds a new member to the family of organic electrode materials, providing performance-efficient organic molecules for the design of rechargeable battery systems, which will undoubtedly spark great interest in their applications.

A Layered Organic Cathode for High-Energy, Fast-Charging, and Long-Lasting Li-Ion Batteries

Eliminating the use of critical metals in cathode materials can accelerate global adoption of rechargeable lithium-ion batteries. Organic cathode materials, derived entirely from earth-abundant elements, are in principle ideal alternatives but have not yet challenged inorganic cathodes due to poor conductivity, low practical storage capacity, or poor cyclability. Here, we describe a layered organic electrode material whose high electrical conductivity, high storage capacity, and complete insolubility enable reversible intercalation of Li+ ions, allowing it to compete at the electrode level, in all relevant metrics, with inorganic-based lithium-ion battery cathodes. Our optimized cathode stores 306 mAh g-1cathode, delivers an energy density of 765 Wh kg-1cathode, higher than most cobalt-based cathodes, and can charge-discharge in as little as 6 min. These results demonstrate the operational competitiveness of sustainable organic electrode materials in practical batteries.

Practical organic batteries: Concepts to realize high mass loading with high performance

Organic electrode materials (OEMs) have been well developed in recent years. However, the practical applications of OEMs have not been paid sufficient attention. The concept here focused on one of the essential aspects for practical applications, i. e., high mass loading of active materials. This paper summarizes the challenges posed by high-mass loading of active materials in organic batteries and discusses the possible solutions in terms of organic electrode materials, conductive additives, electrode structures, and electrolytes or battery systems. We hope this concept can stimulate more attention to practical applications of organic batteries towards industry from lab.

An electrospun three-layer nanofibrous membrane-based in situ gel separator for efficient lithium-organic batteries

An in situ gel separator based on an electrospun three-layer nanofibrous membrane (PSE11-Gel) is developed for high-performance lithium-organic batteries (LOBs). The highly efficient shuttle effect inhibition of organic cathode molecules or lithiated intermediates has been demonstrated for PSE11-Gel to realize high-capacity stable LOBs.

Conductive Metal-Organic Framework with Superior Redox Activity as a Stable High-Capacity Anode for High-Temperature K-Ion Batteries

High-temperature rechargeable batteries are essential for energy storage in elevated-temperature situations. Due to the resource abundance of potassium, high-temperature K-ion batteries are drawing increasing research interest. However, raising the working temperature would aggravate the chemical and mechanical instability of the KIB anode, resulting in very fast capacity fading, especially when high capacity is pursued. Here, we demonstrated that a porous conductive metal-organic framework (MOF), which is constructed by N-rich aromatic molecules and CuO4 units via π-d conjugation, could provide multiple accessible redox-active sites and promised robust structure stability for efficient potassium storage at high temperatures. Even working at 60 °C, this MOF anode could deliver high initial capacity (455 mAh g-1), impressive rate, and extraordinary cyclability (96.7% capacity retention for 1600 cycles), which is much better than those of reported high-temperature KIB anodes. The mechanistic study revealed that C═N groups and CuO4 units contributed abundant redox-active sites; the synergistic effect of π-d conjugated character and reticular porous architecture facilitated the K+/e- transport and ensured an insoluble electrode with small volume deformation, thus achieving stable high-capacity potassium storage.

Reducing undesired solubility of squarephaneic tetraimide for use as an organic battery electrode material

Locally aromatic alkyl-N-substituted squarephaneic tetraimide (SqTI) conjugated macrocycles are four-electron reducible, owing to global aromaticity and presumed global Baird aromaticity of the dianion and tetraanion states, respectively. However, their good solubility inhibits their application as a battery electrode material. By applying sidechain removal as a strategy to reduce SqTI solubility, we report the development of its unsubstituted derivative SqTI-H, which was obtained directly from squarephaneic tetraanhydride by facile treatment with hexamethyldisilazane and MeOH. Compared to alkyl-N-substituted SqTI-Rs, SqTI-H exhibited further improved thermal stability and low neutral state solubility in most common organic solvents, owing to computationally demonstrated hydrogen-bonding capabilities emanating from each imide position on SqTI-H. Reversible solid state electrochemical reduction of SqTI-H to the globally aromatic dianion state was also observed at -1.25 V vs. Fc/Fc+, which could be further reduced in two stages. Preliminary testing of SqTI-H in composite electrodes for lithium-organic half cells uncovered imperfect cycling performance, which may be explained by persistent solubility of reduced states, necessitating further optimisation of electrode fabrication procedures to attain maximum performance.

Chromone-Based Cd(II) Fluorescent Coordination Polymer Fabricated to Study Optoelectronic and Explosive Sensing Properties

Here, electrical conductivity and explosive sensing properties of multifunctional chromone-Cd(II)-based coordination polymers (CPs) (1-4) have been explored. The presence of different pseudohalide linkers, thiocyanate ions, and dicyanamide ions resulted in 1D and 3D architecture in the CPs. Thin film devices developed from CPs 1-4 (complex-based Schottky devices, CSD1, CSD2, CSD3, and CSD4, respectively) showed semiconductor behavior. Their conductivity values increased under photo illumination (1.37 × 10-5, 1.85 × 10-5, 1.61 × 10-5, and 2.01 × 10-5 S m-1 under dark conditions and 5.06 × 10-5, 8.78 × 10-5, 7.26 × 10-5, and 10.21 × 10-5 S m-1 under light). The nature of the I-V plots of these thin film devices under light irradiation and dark are nonlinear rectifying, which has been observed in Schottky barrier diodes (SBDs). All four CPs (1-4) exhibited highly selective fluorescence quenching-based sensing properties toward well-known explosives, 2,4-dinitrophenol (DNP) and 2,4,6-trinitrophenol (TNP). The limit of detection (LOD) values are 55, 28, 27, and 31 μM for TNP and 78, 44, 32, and 41 μM for DNP for complexes 1-4, respectively. A structure property correlation has been established to explain optoelectronic and explosive sensing properties.

Visible-light-induced catalyst-free reductive coupling of aldehydes, ketones and imines with cyanopyridines

This article introduces a reductive coupling driven by visible-light, facilitating the synthesis of pyridine-substituted alcohols and amines through the reaction of aldehydes, ketones and imines with cyanopyridines. Hantzsch esters serve as reductants in this process, eliminating the need for transition-metals or photosensitizers. The method demonstrates extensive compatibility and finds utility in the late-stage functionalization of both natural and pharmaceutical products, offering a sustainable pathway for the diversification of chemical compounds.

Recent Progress in Covalent Organic Frameworks for Cathode Materials

Covalent organic frameworks (COFs) are constructed from small organic molecules through reversible covalent bonds, and are therefore considered a special type of polymer. Small organic molecules are divided into nodes and connectors based on their roles in the COF's structure. The connector generally forms reversible covalent bonds with the node through two reactive end groups. The adjustment of the length of the connector facilitates the adjustment of pore size. Due to the diversity of organic small molecules and reversible covalent bonds, COFs have formed a large family since their synthesis in 2005. Among them, a type of COF containing redox active groups such as -C=O-, -C=N-, and -N=N- has received widespread attention in the field of energy storage. The ordered crystal structure of COFs ensures the ordered arrangement and consistent size of pores, which is conducive to the formation of unobstructed ion channels, giving these COFs a high-rate performance and a long cycle life. The voltage and specific capacity jointly determine the energy density of cathode materials. For the COFs' cathode materials, the voltage plateau of their active sites' VS metallic lithium is mostly between 2 and 3 V, which has great room for improvement. However, there is currently no feasible strategy for this. Therefore, previous studies mainly improved the theoretical specific capacity of the COFs' cathode materials by increasing the number of active sites. We have summarized the progress in the research on these types of COFs in recent years and found that the redox active functional groups of these COFs can be divided into six subcategories. According to the different active functional groups, these COFs are also divided into six subcategories. Here, we summarize the structure, synthesis unit, specific surface area, specific capacity, and voltage range of these cathode COFs.

Precise synthesis of BN embedded perylene diimide oligomers for fast-charging and long-life potassium-organic batteries

Replacing the C[double bond, length as m-dash]C bond with an isoelectronic BN unit is an effective strategy to tune the optoelectronic properties of polycyclic aromatic hydrocarbons (PAHs). However, precise control of the BN orientations in large PAH systems is still a synthetic challenge. Herein, we demonstrate a facile approach for the synthesis of BN embedded perylene diimide (PDI) nanoribbons, and the polarization orientations of the BN unit were precisely regulated in the two PDI trimers. These BN doped PDI oligomers show great potential as organic cathodes for potassium-ion batteries (PIBs). In particular, trans-PTCDI3BN exhibits great improvement in voltage potential, reversible capacities (ca. 130 mA h g-1), superior rate performance (19 s to 69% of the maximum capacity) and ultralong cyclic stability (nearly no capacity decay over 30 000 cycles), which are among those of state-of-the-art organic-based cathodes. Our synthetic approach stands as an effective way to access large PAHs with precisely controlled BN orientations, and the BN doping strategy provides useful insight into the development of organic electrode materials for secondary batteries.

Covalent Organic Frameworks as Electrode Materials for Alkali Metal-ion Batteries

Covalent organic frameworks (COFs) are a class of porous crystalline polymeric materials constructed by linking organic small molecules through covalent bonds. COFs have the advantages of strong covalent bond network, adjustable pore structure, large specific surface area and excellent thermal stability, and have broad application prospects in various fields. Based on these advantages, rational COFs design strategies such as the introduction of active sites, construction of conjugated structures, and carbon material composite, etc. can effectively improve the conductivity and stability of the electrode materials in the field of batteries. This paper introduces the latest research results of high-performance COFs electrode materials in alkali metal-ion batteries (LIBs, SIBs, PIBs and LSBs) and other advanced batteries. The current challenges and future design directions of COFs-based electrode are discussed. It provides useful insights for the design of novel COFs structures and the development of high-performance alkali metal-ion batteries.

Design and Synthesis of Viologen-based Copolymers for High Performance Li-Dual-Ion Batteries

Dual-ion batteries based on organic electrodes show great potential to break through the bottlenecks existed in conventional LIBs due to their high specific capacity, lifted working voltage, and environmental benignity. Herein, two innovative viologen-based bipolar copolymers poly(viologen-pyrene-4,5,9,10-tetrone dichloride) (PVPTOCl2 ) and poly(viologen-anthraquinone dichloride) (PVAQCl2 ) were synthesized and applied as high performance cathodes for lithium-dual-ion battery. Bearing the dual-ion storage capability of viologen and carbonyls, as well as the conjugated structure of pyrene-4,5,9,10-tetrone, the synthesized copolymers show remarkable electrochemical performances for LIBs. Compared to PVAQCl2 , PVPTOCl2 shows superior electrochemical performance with high initial specific capacity (235.0 mAh g-1 at 200 mA g-1 ), high reversibility (coulombic efficiency up to 99.96 % at 1 A g-1 ), excellent rate performance (150.3 mAh g-1 at 5 A g-1 ) and outstanding cycling stability (a reversible capacity of 197.5 mAh g-1 at a current density of 1 A g-1 and a low capacity loss per cycle of 0.11‰ during 3000 cycles). Moreover, the charge storage mechanism was systematically investigated by ex-situ FT-IR, ex-situ XPS and DFT calculations. The results clearly reveal the structure-property relationship of the bipolar-molecules, providing a new platform to develop efficient bipolar materials for dual-ion batteries.

Diamino-Substituted Quinones as Cathodes for Lithium-Ion Batteries

This study introduces a sustainable approach to designing organic cathode materials (OCMs) for lithium-ion batteries as a potential replacement for traditional metal-based electrodes. Utilizing green synthetic methodologies, we synthesized and characterized five distinct quinone derivatives and investigated their electrochemical attributes within Li-ion battery architectures. Notably, the observed specific capacities were lower than the theoretical predictions, suggesting limitations in achieving efficient redox reactions in a coin-cell configuration. Among the quinone derivatives studied, one variant derived from natural vanillin showed superior cycle stability, maintaining 58% capacity retention over 95 charge-discharge cycles, and achieving a Coulombic efficiency of 90%. Importantly, we discovered that the commonly used Super-P conductive carbon did not yield any measurable battery performance; instead, these quinones necessitated the incorporation of graphene nanoplatelets as the conductive matrix. Through a facile one-step synthesis in ethanol or water, we have demonstrated a viable synthetic route for producing OCMs, albeit with moderate performances, which have attempted to address common concerns of high solubility and poor redox reactivity of previous OCMs, thereby offering a sustainable pathway for the development of organic-based energy storage devices.

Organoboron-thiophene-based polymer electrodes for high-performance lithium-ion batteries

Polymer electrodes are drawing widespread attention to the future generation of lithium-ion battery materials. However, weak electrochemical performance of organic anode materials still exists, such as low capacity, low rate performance, and low cyclability. Herein, we successfully constructed a donor-acceptor thiophene-based polymer (PBT-1) by introducing an organoboron unit. The charge delocalization and lower LUMO energy level due to the unique structure enabled good performance in electrochemical tests with a reversible capacity of 405 mA h g-1 at 0.5 A g-1 and over 10 000 cycles at 1 A g-1. Moreover, electron paramagnetic resonance (EPR) spectra revealed that the unique stable spin system in the PBT-1 backbone during cycling provides a fundamental explanation for the highly stable electrochemical performance. This work offers a reliable reference for the design of organic anode materials and expands the potential application directions of organoboron chemistry.

Organic Cathodes, a Path toward Future Sustainable Batteries: Mirage or Realistic Future?

Organic active materials are seen as next-generation battery materials that could circumvent the sustainability and cost limitations connected with the current Li-ion battery technology while at the same time enabling novel battery functionalities like a bioderived feedstock, biodegradability, and mechanical flexibility. Many promising research results have recently been published. However, the reproducibility and comparison of the literature results are somehow limited due to highly variable electrode formulations and electrochemical testing conditions. In this Perspective, we provide a critical view of the organic cathode active materials and suggest future guidelines for electrochemical characterization, capacity evaluation, and mechanistic investigation to facilitate reproducibility and benchmarking of literature results, leading to the accelerated development of organic electrode active materials for practical applications.

Spatial Structure Design of Thioether-Linked Naphthoquinone Cathodes for High-Performance Aqueous Zinc-Organic Batteries

Organic electrode materials (OEMs) have gathered extensive attention for aqueous zinc-ion batteries (AZIBs) due to their structural diversity and molecular designability. However, the reported research mainly focuses on the design of the planar configuration of OEMs and does not take into account the important influence of the spatial structure on the electrochemical properties, which seriously hamper the further performance liberation of OEMs. Herein, this work has designed a series of thioether-linked naphthoquinone-derived isomers with tunable spatial structures and applied them as the cathodes in AZIBs. The incomplete conjugated structure of the elaborately engineered isomers can guarantee the independence of the redox reaction of active groups, which contributes to the full utilization of active sites and high redox reversibility. In addition, the position isomerization of naphthoquinones on the benzene rings changes the zincophilic activity and redox kinetics of the isomers, signifying the importance of spatial structure on the electrochemical performance. As a result, the 2,2'-(1,4-phenylenedithio) bis(1,4-naphthoquinone) (p-PNQ) with the smallest steric hindrance and the most independent redox of active sites exhibits a high specific capacity (279 mAh g-1 ), an outstanding rate capability (167 mAh g-1 at 100 A g-1 ), and a long-term cycling lifetime (over 2800 h at 0.05 A g-1 ).

Organoboron flank-substituted donor-acceptor polymer anode with ultra-long cycling stability for lithium ion batteries

The tunable structure and other properties of organic materials suggest that they can potentially solve the shortcomings of traditional anodes such as graphite. We successfully introduced an organoboron unit into the thiophene-based polymer PBT-2 to construct a donor-acceptor polymer anode. The charge delocalization and LUMO energy level resulting from the unique structure of this material enabled good redox activity and a very stable electrochemical performance in electrochemical tests, with a reversible capacity of 262 mA h g-1 at 0.5 A g-1 and >10 000 cycles at 1 A g-1 with a decay of 0.056‰ per cycle. Accordingly, targeted structural design to overcome the shortcomings of active units such as thiophene can effectively regulate their electrochemical performance, providing a solution for the development of high-performance anode materials for use in lithium ion batteries.

Reliable Organic Carbonyl Electrode Materials Enabled by Electrolyte and Interfacial Chemistry Regulation

ConspectusLithium-ion batteries (LIBs) have achieved great success and dominated the market of portable electronics and electric vehicles owing to their high energy density and long-term cyclability. However, if applying LIBs for large-scale energy storage scenarios, such as regulating the output of electricity generated by sustainable energy in the future age of carbon neutrality, the current electrochemistry of LIBs based on Li-ion interaction/deinteraction between a transition-metal oxide cathode and graphite anode will suffer from problems of scarce natural resources (e.g., Li, Co, and Ni) and high energy consumption/CO2 emission involved in the production of electrodes. Similarly, other commercial batteries such as lead-acid batteries and nickel-metal hydride batteries are also plagued by these issues.In contrast, organic electrode materials, especially carbonyl materials, exhibit advantages of abundant resources, renewability, high capacity, environmental friendliness, and structural designability and have shown great promise for various rechargeable batteries in recent years. However, organic carbonyl electrode materials generally exhibit unsatisfactory cycling stability and rate performance, which are highly dependent on the electrolyte and interfacial chemistry. Appropriate electrolytes and a stable electrode/electrolyte interface would be beneficial for preventing the dissolution of organic carbonyl electrode materials and/or their redox intermediates in electrolytes and promoting fast ion transport between the electrode and electrolyte. In this regard, designing an appropriate electrolyte and constructing a stable electrode/electrolyte interface are the keys to enhancing the comprehensive performance of organic carbonyl electrode materials.In this Account, on the basis of our progress and related works from other groups in the past decade, we afford an overview of understanding the effects of electrolyte and interfacial chemistry on the electrochemical performance of organic carbonyl electrode materials. We will start by briefly introducing the basic properties, working mechanisms, and issues of organic carbonyl electrode materials. Then, the implications of electrolyte and electrode/electrolyte interfacial chemistry on electrochemical performance will be summarized and highlighted through discussing the performance of organic carbonyl electrodes in different types of electrolytes (organic liquid and aqueous and solid-state electrolytes). Meanwhile, the design principles of electrolytes and interfacial chemistry for organic carbonyl electrodes are also discussed. A representative example is that organic carbonyl electrode materials often exhibit better electrochemical performance in ether-based electrolytes than in ester-based electrolytes, which could be mainly attributed to the stable and robust solid electrolyte interphase (SEI) formed on carbonyl electrodes in the ether-based electrolyte. This example demonstrates the importance of investigating the electrode/electrolyte interfacial chemistry of organic carbonyl electrode materials. Finally, future perspectives on designing appropriate electrolytes and understanding electrode/electrolyte interfacial chemistry will also be discussed. It is meaningful to thoroughly reveal the dynamic evolution of the electrode/electrolyte interface during discharge/charge processes and evaluate the compatibility between electrolytes and organic carbonyl electrode materials under practical conditions using limited quantities of electrolytes and high areal-specific-capacity electrodes in the future. This Account could attract more attention to electrolytes and the electrode/electrolyte interfacial chemistry of organic carbonyl electrode materials and finally promote their future commercial applications.

Rational Molecular Design of Redox-Active Carbonyl-Bridged Heterotriangulenes for High-Performance Lithium-Ion Batteries

Carbonyl aromatic compounds are promising cathode candidates for lithium-ion batteries (LIBs) because of their low weight and absence of cobalt and other metals, but they face constraints of limited redox-potential and low stability compared to traditional inorganic cathode materials. Herein, by means of first-principles calculations, a significant improvement of the electrochemical performance for carbonyl-bridged heterotriangulenes (CBHTs) is reported by introducing pyridinic N in their skeletons. Different center atoms (B, N, and P) and different types of functionalization with nitrogen effectively regulate the redox activity, conductivity, and solubility of CBHTs by influencing their electron affinity, energy levels of frontier orbitals and molecular polarity. By incorporating pyridinic N adjacent to the carbonyl groups, the electrochemical performance of N-functionalized CBHTs is significantly improved. Foremost, the estimated energy density reaches 1524 Wh kg-1 for carbonyl-bridged tri (3,5-pyrimidyl) borane, 50% higher than in the inorganic reference material LiCoO2 , rendering N-functionalized CBHTs promising organic cathode materials for LIBs. The investigation reveals the underlying structure-performance relationship of conjugated carbonyl compounds and sheds new lights for the rational design of redox-active organic molecules for high-performance lithium ion batteries (LIBs).

Ni-Co-Mn complexed 3,4,9,10-perylenetetracarboxylic acid complexes as novel organic electrode materials for lithium-ion batteries

Ni-Co-Mn complexed 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA-NiCoMn) is prepared by hydrolysis of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) and complexed reaction with Ni, Co and Mn ions. At the same time, graphene was added to PTCDA-NiCoMnin situ to obtain graphene in situ composited Ni-Co-Mn complexed 3,4,9,10-perylenetetracarboxylic dianhydride composites (PTCDA-NiCoMn-G). The prepared PTCDA-NiCoMn composite exhibited a fibrous structure, and the number of pore units increased with the expansion of the fibrous structure. After the in situ recombination of graphene, shorter PTCDA-NiCoMn tubular fibers were dispersed between the thin layers of graphene, showing a larger surface area with more PTCDA-NiCoMn active components exposed, which is conducive to better electrochemical properties. As a result, the initial charge/discharge capacities of PTCDA-NiCoMn and PTCDA-NiCoMn-G electrodes are 1972.9 and 1806.6 mA h g-1 with initial coulombic efficiencies of 56.3% and 62.52%, respectively, at 100 mA g-1. After 200 cycles, the charge/discharge capacities of PTCDA-NiCoMn and PTCDA-NiCoMn-G are 617.0 and 876.4 mA h g-1 with capacity retention ratios of 51.4% and 73.0% at 100 mA g-1, respectively. Similarly, PTCA-NiCoMn-G electrodes show higher capacities than the PTCA-NiCoMn electrode at different current densities of 0.1, 0.2, 0.5, 1.0, 2.0 and 5 A g-1. The results show that PTCDA-NiCoMn-G electrode displays superior capacity, ICE, cycle and rate behaviors. The complexation of NiCoMn reduces the solubility of the PTCDA active units in the electrolyte, and the in situ recombination of graphene increases the dispersion of the active components, exposes more active sites, and effectively improves the conductive performance, which contributes to the electrochemical properties of the PTCDA-NiCoMn-G electrode.

Design of a bipolar organic small-molecule cathode with mesoporous nanospheres structure for long lifespan and high-rate Li-storage performance

Organic small-molecule compounds have become promising cathode materials for high-performance lithium-ion batteries (LIBs) due to their high theoretical capacity, efficient utilization of active sites, low cost, and sustainability. However, severe dissolution and poor electronic conductivity limit their further practical applications. Herein, we have synthesized an insoluble organic small molecule, ferrocenyl-3-(λ1-azazyl) pyrazinyl [2,3-f] [1,10] phenanthrolino-2-amine (FCPD), by grafting ferrocene onto pyrazino[2,3-f] [1,10] phenanthroline-2,3-diamine (PPD). The combination of ferrocene (p-type Fe2+ moiety) and PPD (n-type C[double bond, length as m-dash]N groups) in a bipolar manner endows the target FCPD cathode with an increased theoretical capacity and a wide voltage window. The highly conjugated π-π aromatic skeleton inside enhances FCPD's electron delocalization and promotes strong interaction between FCPD units. Additionally, the mesoporous structure within the FCPD can provide numerous electroactive sites, contact area, and ion diffusion channels. Benefiting from the bipolar feature, aromatic, and mesoporous structure, the FCPD cathode demonstrates a large capacity of 250 mA h g-1 at 0.1 A g-1, a long lifespan of 1000 cycles and a high-rate capability of 151 mA h g-1 at 5 A g-1 along with a wide voltage window (1.2-3.8 V). Additionally, in situ synchrotron FT-IR and ex situ XPS reveal its dual ion storage mechanism in depth. Our findings provide essential insights into exploring the molecular design of advanced organic small molecules.

Establishing Exceptional Durability in Ultralow-Temperature Organic-Sodium Batteries via Stabilized Multiphase Conversions

Operation of rechargeable batteries at ultralow temperature is a significant practical problem because of poor kinetics of the electrode. Here, we report for the first time stabilized multiphase conversions for fast kinetics and long-term durability in ultralow-temperature, organic-sodium batteries. We establish that disodium rhodizonate organic electrode in conjunction with single-layer graphene oxide obviates consumption of organic radical intermediates, and demonstrate as a result that the newly designed organic electrode exhibits excellent electrochemical performance of a highly significant capacity of 130 mAh g-1 at -50 °C. We evidence that the full-cell configuration coupled with Prussian blue analogues exhibits exceptional cycling stability of >7000 cycles at -40 °C while maintaining a discharge capacity of 101 mAh g-1 at a high current density 300 mA g-1. We show this is among the best reported ultralow-temperature performance for nonaqueous batteries, and importantly, the pouch cell exhibits a continuous power supply despite conditions of -50 °C. This work sheds light on the distinct energy storage characteristics of organic electrode and opens up new avenues for the development of reliable and sustainable ultralow-temperature batteries.

Regulating Electrostatic Interaction between Hydrofluoroethers and Carbonyl Cathodes toward Highly Stable Lithium-Organic Batteries

Organic carbonyl electrode materials have shown great promise for high-performance lithium batteries due to their high capacity, renewability, and environmental friendliness. However, their practical application is hindered by the high solubility of these materials in traditional electrolytes, leading to poor cycling stability and serious shuttle effects. Here, we develop a series of hydrofluoroethers (HFEs) with weak electrostatic interaction toward organic carbonyl cathode materials, aiming to address the dissolution issue and achieve high cycling stability in lithium batteries. Theoretical calculations reveal that the electrostatic interactions between HFEs and pyrene-4,5,9,10-tetraone (PTO) are significantly weaker compared with common solvents such as 1,2-dimethoxyethane. Consequently, the dissolution of PTO in the HFE-based electrolyte is remarkably reduced, as observed by in situ ultraviolet-visible spectra. Notably, when using the electrolyte based on 1,1,1,3,3,3-hexafluoro-2-methoxypropane with a certain coordination ability, PTO exhibits excellent cycling stability with a high capacity retention of 78% after 1000 cycles. This work proposes the regulation of electrostatic interactions to inhibit the dissolution of organic carbonyl cathode materials and significantly enhance their cycle life.

Towards the 4 V-class n-type organic lithium-ion positive electrode materials: the case of conjugated triflimides and cyanamides

Organic electrode materials have garnered a great deal of interest owing to their sustainability, cost-efficiency, and design flexibility metrics. Despite numerous endeavors to fine-tune their redox potential, the pool of organic positive electrode materials with a redox potential above 3 V versus Li+/Li0, and maintaining air stability in the Li-reservoir configuration remains limited. This study expands the chemical landscape of organic Li-ion positive electrode chemistries towards the 4 V-class through molecular design based on electron density depletion within the redox center via the mesomeric effect of electron-withdrawing groups (EWGs). This results in the development of novel families of conjugated triflimides and cyanamides as high-voltage electrode materials for organic lithium-ion batteries. These are found to exhibit ambient air stability and demonstrate reversible electrochemistry with redox potentials spanning the range of 3.1 V to 3.8 V (versus Li+/Li0), marking the highest reported values so far within the realm of n-type organic chemistries. Through comprehensive structural analysis and extensive electrochemical studies, we elucidate the relationship between the molecular structure and the ability to fine-tune the redox potential. These findings offer promising opportunities to customize the redox properties of organic electrodes, bridging the gap with their inorganic counterparts for application in sustainable and eco-friendly electrochemical energy storage devices.

Toward Conductive Additive Free Organic Electrode for Lithium-Ion Battery Using Supramolecular Columnar Organization

With the aim to meet the greatest challenge facing organic batteries, namely the low conductivity of the electrodes, the electrochemical properties of a series of substituted perylene diimides able to form semi-conductive columnar material are investigated. Depending on the substituent group, a strong influence of this group on the reversibility, redox potential but especially on the gravimetric capacity of the electrodes is observed. In the case of substitution by a simple propyl group, the corresponding diimide shows a complete electrochemical activity with only 10% by mass of conductive additive and even shows a half-capacity activity without any additive and without particular electrode engineering. Extensive research has highlighted the intrinsic reactivity of the columnar material but also its perpetual rearrangement during charge/discharge cycles. This study shows that the amount of conductive additive can be significantly reduced by adapting the design of the molecular material and favoring the assembly of redox units in the form of a conductive column.

Design and synthesis of п-conjugated aromatic heterocyclic materials with dual active sites and ultra-high rate performance for aqueous zinc-organic batteries

Acid anhydride cathode materials garner considerable interest for aqueous zinc ion batteries (AZIBs) due to ideal specific capacity and structural diversity, however, serious solubility leads to capacity degradation. Herein, 1,4,5,8-naphthalene tetracarboxylic acid dianhydride - 2,3-diamino phenothiazine (NTDP) featuring multiple active sites (6 with CN and 2 with CO) and large π-conjugated backbone, was designed and synthesized utilizing solid-phase method. The smallest energy gap (ΔE) and the lowest LUMO levels (against monomers) induced by multiple active sites and п-conjugated backbone with high aromaticity, NTDP exhibited excellent specific capacity (307.5 mA h g-1 under 0.05 A/g), ultrahigh rate performance (194.9 mA h g-1 under 20 A/g) and impressive cycling stability (190.0 mA h g-1 over 9000 cycles with a capacity retention of 91.2 % at 15 A/g). The reversible Zn2+ insertion/removal mechanism on multiple active centers (CO and CN) was proposed through XPS, FT-IR, and Raman. The specific capacity of the NTDP//zinc flexible cell was 112.6 mA h g-1 at 3 A/g under various folding angles (45°, 90°, 135°, and 180° bends), suggesting its practical potential for flexible devices. This work will offer opportunities for the rational design of battery structures.

MXene-Based Current Collectors for Advanced Rechargeable Batteries

As an indispensable component of rechargeable batteries, the current collector plays a crucial role in supporting the electrode materials and collecting the accumulated electrical energy. However, some key issues, like uneven resources, high weight percentage, electrolytic corrosion, and high-voltage instability, cannot meet the growing need for rechargeable batteries. In recent years, MXene-based current collectors have achieved considerable achievements due to its unique structure, large surface area, and high conductivity. The related research has increased significantly. Nonetheless, a comprehensive review of this area is seldom. Herein the applications and progress of MXene in current collector are systematically summarized and discussed. Meanwhile, some challenges and future directions are presented.

Nonplanar π-Conjugated Sulfur Heterocyclic Quinone Polymer Cathode for Air-Rechargeable Zinc/Organic Battery with Simultaneously Boosted Output Voltage, Rate Capability, and Cycling Life

π-conjugated organic compounds with a good charge transfer ability and rich redox functional groups are promising cathode candidates for air-rechargeable aqueous Zn-based batteries (AAZBs). However, the output voltage of even the state-of-the-art π-conjugated organic cathodes lies well below 0.8 V, resulting in insufficient energy density. Herein, we design a nonplanar π-conjugated sulfur heterocyclic quinone polymer (SHQP) as an advanced cathode material for AAZBs by polymerization 1,4-Benzoquinone (BQ) and S heteroatoms periodically. The extended π-conjugated plane and enhanced aromaticity endow SHQP with a more sensitive charge transfer ability and robust structure. Furthermore, the delocalized π electrons in the whole system are insufficient as the π orbit of the S heteroatom is not in the same plane with the π orbit of BQ due to its folded configuration, resulting in negligible variation of electron density around C═O after the polymerization. Thus, the output voltage of SHQP shows no significant decrease even though the thioether bond (-S-) functions as electron donor. Consequently, the Zn/SHQP AAZBs can deliver a record high midpoint discharging voltage (0.95 V), rate performance (119 mAh g-1 at 10 A g-1), and durability (98.7% capacity retention after 200 cycles) across a wide temperature range.

Organic electrodes based on redox-active covalent organic frameworks for lithium batteries

Electroactive organic materials have received much attention as alternative electrodes for metal-ion batteries due to their high theoretical capacity, resource availability, and environmental friendliness. In particular, redox-active covalent organic frameworks (COFs) have recently emerged as promising electrodes due to their tunable electrochemical properties, insolubility in electrolytes, and structural versatility. In this Highlight, we review some recent strategies to improve the energy density and power density of COF electrodes for lithium batteries from the perspective of molecular design and electrode optimisation. Some other aspects such as stability and scalability are also discussed. Finally, the main challenges to improve their performance and future prospects for COF-based organic batteries are highlighted.

Stable organic polymer anode for high rate and fast charge sodium based dual-ion battery

Considering the extensive resources, flexible structural designability, and abundant active sites, organic electrodes have been considered as the ideal sodium storage materials. However, organic materials generally face the limitations of unstable and dissolved characteristic, leading to a poor cyclic stability. In this work, we proposed a carbon nanotube (CNT) modified polyimide as the anode for sodium-based dual-ion battery (SDIB). The polyimide remains well the structure and morphology of monomer with a stable conjugated structure and high degree of crystallinity, effectively enhancing the electrochemical performance of the SDIBs. Also, the cooperation with CNT particularly improves the ion conductivity of the anode and advances the rate performance. Combined with an ionic liquid electrolyte, the constructed dual-ion battery exhibits excellent rate capability, high specific discharge capacity and stable cycling performance. It delivers a specific discharge capacity of 119.3 mA h g-1 at 0.2 C (1 C=100 mA g-1 ) and still has a specific discharge capacity of 82.3 mA h g-1 even after 1000 cycles at 10 C. Besides, the system displays a low self-discharge rate and stable fast charging performance, which is expected to be applied in the large-scale electrochemical energy storage devices and inspire the future development of SDIBs.

A donor-acceptor (D-A) conjugated polymer for fast storage of anions

Organic electrode materials have attracted a lot interest in batteries in recent years. However, most of them still suffer from low performance such as low electrode potential, slow reaction kinetics, and short cycle life. In this work, we report a strategy of fabricating donor-acceptor (D-A) conjugated polymers for facilitating the charge transfer and therefore accelerating the reaction kinetics by using the copolymer (p-TTPZ) of dihydrophenazine (PZ) and thianthrene (TT) as a proof-of-concept. The D-A conjugated polymer as p-type cathode could store anions and exhibited high discharge voltages (two plateaus at 3.82 V, 3.16 V respectively), a reversible capacity of 152 mAh g-1 at 0.1 A g-1 , excellent rate performance with a high capacity of 124.2 mAh g-1 at 10 A g-1 (≈50 C) and remarkable cyclability. The performance, especially the rate capability was much higher than that of its counterpart homopolymers without D-A structure. As a result, the p-TTPZ//graphite full cells showed a high output voltage (3.26 V), a discharge specific capacity of 139.1 mAh g-1 at 0.05 A g-1 and excellent rate performance. This work provides a novel strategy for developing high performance organic electrode materials through molecular design and will pave a way towards high energy density organic batteries.

Facile Construction of Advanced 1D Metal-Organic Coordination Polymer for Efficient Lithium Storage

Recently, coordination polymers (CPs) have been frequently reported in the field of energy storage as electrode materials for lithium-ion batteries (LIBs) due to their highly adjustable architectures, which have a variety of active sites and obviously defined lithium transport routes. A well-designed redox-active organic linker with potential active sites for storing lithium ions, pyrazine-2,3-dicarboxylate (H2PDA), was applied for generating CPs by a simple hydrothermal method. When employed as anode materials in LIBs, those two one-dimensional (1D) CPs with an isomorphic composition, [M(PDA)(H2O)2]n (M = Co for Co-PDA and Ni for Ni-PDA), produced outstanding reversible capacities and stable cycling performance. The Co-PDA displays a substantial reversible capacity of 936 mAh g-1 at 200 mA g-1 after 200 cycles, as well as an excellent cycling life at high currents. According to the ex situ characterizations, the high reversible specific capacity of the post-cycled electrodes was found to be a result of both the transition metal ions and the organic ligands, and Co-PDA and Ni-PDA electrode materials show reversible insertion/extraction processes that are accompanied by crystallization to an amorphous state.

High-Energy Aqueous/Organic Hybrid Batteries Enabled by Cu2+ Redox Charge Carriers

Lithium||sulfur (Li||S) batteries are considered as one of the promising next-generation batteries due to the high theoretical capacity and low cost of S cathodes, as well as the low redox potential of Li metal anodes (-3.04 V vs. standard hydrogen electrode). However, the S reduction reaction from S to Li2 S leads to limited discharge voltage and capacity, largely hindering the energy density of Li||S batteries. Herein, high-energy Li||S hybrid batteries were designed via an electrolyte decoupling strategy. In cathodes, S electrodes undergo the solid-solid conversion reaction from S to Cu2 S with four-electron transfer in a Cu2+ -based aqueous electrolyte. Such an energy storage mechanism contributes to enhanced electrochemical performance of S electrodes, including high discharge potential and capacity, superior rate performance and stable cycling behavior. As a result, the assembled Li||S hybrid batteries exhibit a high discharge voltage of 3.4 V and satisfactory capacity of 2.3 Ah g-1 , contributing to incredible energy density. This work provides an opportunity for the construction of high-energy Li||S batteries.

Toward Sustainable All Solid-State Li-Metal Batteries: Perspectives on Battery Technology and Recycling Processes

Lithium (Li)-based batteries are gradually evolving from the liquid to the solid state in terms of safety and energy density, where all solid-state Li-metal batteries (ASSLMBs) are considered the most promising candidates. This is demonstrated by the Bluecar electric vehicle produced by the Bolloré Group, which is utilized in car-sharing services in several cities worldwide. Despite impressive progress in the development of ASSLMBs, their avenues for recycling them remain underexplored, and combined with the current explosion of spent Li-ion batteries, they should attract widespread interest from academia and industry. Here, the potential challenges of recycling ASSLMBs as compared to Li-ion batteries are analyzed and the current progress and prospects for recycling ASSLMBs are summarized and analyzed. Drawing on the lessons learned from Li-ion battery recycling, it is important to design sustainable recycling technologies before ASSLMBs gain widespread market adoption. A battery-recycling-oriented design is also highlighted for ASSLMBs to promote the recycling rate and maximize profitability. Finally, future research directions, challenges, and prospects are outlined to provide strategies for achieving sustainable development of ASSLMBs.

Refreshing the Legacy of Rudolf Nietzki: Benzene-1,2,4,5-tetramine and Related Compounds

Like hydroquinones and quinones, aromatic compounds with multiple NH2 groups and the corresponding quinonediimines have the potential to serve as components of useful redox-active organic materials. Benzene-1,2,4,5-tetramine (BTA) and its oxidized form BTA-H2 offer a promising redox pair of this type, and the compounds have proven to be useful in many areas of chemistry. However, key aspects of their behavior have remained poorly studied, such as the nature of their protonated forms, their preferred molecular structures, their reactivity, and their organization in condensed phases. In the present work, we have used a combination of improved methods of synthesis, computation, spectroscopic studies, and structural analyses to develop a deeper understanding of BTA, BTA-H2, their salts, and related compounds. The new knowledge is expected to accelerate exploitation of the compounds in areas of materials science where desirable properties can only be attained by properly controlling the organization of molecular components.

Application of triphenylphosphine organic compounds constructed with O, S, and Se in aluminum ion batteries

Due to their high reactivity and theoretical capacity, chalcogen elements have been favored and applied in many battery studies. However, the high surface charge density and high solubility of these elements as electrode materials have hindered their deeper exploration due to the shuttle effect. In this article, organic structural triphenylphosphine is used as a molecular main chain structure, and chalcogen elements O, S, and Se are introduced to combine with P as active sites. This approach not only takes advantage of the beneficial effects of the aromatic ring on the physical and chemical properties of the chalcogen element but also allows for the optimization of its advantages. By utilizing Triphenylphosphine selenide (TP-Se) as the cathode material in aluminum-ion batteries(AIBs), a high-performance Al-organic battery was fabricated, which exhibited a high initial capacity of 180.6 mAh g-1 and stable cycling for up to 1000 cycles. Based on density functional theory (DFT) calculations, TP-Se exhibits a smaller energy gap, which renders it favorable for chemical reactions. Moreover, the calculated results suggest that TP-Se tends to undergo redox reactions with AlCl2+. The molecular structure of triphenylphosphine and its combination with Se offers an enticing pathway for designing cathode materials in aluminum-organic batteries.

Activating Organic Electrode via Trace Dissolved Organic Molecules

Organic electrode materials have gained attention for their tunable structures and sustainability, but their low electronic conductivity requires the use of large amounts of carbon additives (30 wt %) and low mass loadings (<2 mg cm-2) in electrodes. Here, we synthesize dibenzo[b,i]phenazine-5,7,12,14-tetrone (DPT) as a cathode active material for an aqueous Zn battery and find that Zn2+ storage dominates the cathode reaction. This battery demonstrates high capacity (367 mAh g-1), high-rate performance, and superlong life (12000 cycles). Remarkably, despite DPT's insulative nature, even with a high mass loading (10 mg cm-2) and only 10 wt % carbon additives, the DPT-based cathode exhibits promising performance due to trace dissolved discharge product (DPTx-). During discharge, the DPT is reduced to trace amounts of dissolved DPTx- at the cathode surface, which in turn reduces the remaining solid DPT as a redox mediator. Furthermore, dissolution-redeposition results in the reduction of DPT size and the formation of pores, further activating the electrode.

Charge Transfer in Spatially Defined Organic Radical Polymers

Charge transfer in nonconjugated redox-active polymers is influenced by redox site proximity and polymer flexibility, but it is challenging to observe these effects independently. In this work, spatially defined radical-containing polymers are synthesized by using acyclic diene metathesis (ADMET) polymerization of α,ω-dienes bearing a central activated ester. Postpolymerization functionalization with 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) introduces TEMPO radical groups onto the polymer backbone through amide linkages to yield spatially defined polymers with radical units every 9, 11, 15, and 21 carbons. Increased radical spacing leads to reduced spin-spin coupling and increased chain flexibility. The glass transition temperatures (Tg) range from 47.6 to -13.8 °C, depending on the radical spacing. The spatially defined TEMPO-substituted polymer with a spacing length of 15 carbons displays the lowest Tg and the shortest hopping distance, as shown through molecular dynamics simulations. Also, this polymer displays kinetics 1000 times faster than the commonly studied TEMPO-containing polymer poly(2,2,6,6-tetramethylpiperidinyloxy-4-ylacrylamide) (PTAm). Remarkably, comparison of the diffusion and kinetics attributed to the redox reaction reveals that both the apparent diffusion coefficient and the self-exchange reaction rate constant are correlated to the polymer's Tg as log[Dapp] and log[kex,app] ∼ Tg, respectively. Critically, these data demonstrate that controlling the spacing of redox-active groups along a polymer backbone strongly influences backbone flexibility and radical packing, which leads to synergetic improvements in the charge transfer kinetics of nonconjugated redox-active polymers.

Construction of Naphthalene Diimide Derived Nanostructured Cathodes through Self-Assembly for High-Performance Sodium-Organic Batteries

Organic nanostructured electrodes are very attractive for next-generation sodium-ion batteries. Their great advantages in improved electron and ion transport and more exposed redox-active sites would lead to a higher actual capacity and enhanced rate performance. However, facile and cost-effective methods for the fabrication of nanostructured organic electrodes are still highly challenging and very rare. In this work, we utilize a bioinspired self-assembly strategy to fabricate nanostructured cathodes based on a rationally designed N-hydroxy naphthalene imide sodium salt (NDI-ONa) for high-performance sodium-organic batteries. Such a well-organized nanostructure can greatly enhance both ion and electron transport. When used as cathode for sodium-organic batteries, it provides among the best battery performances, such as high capacity (171 mA h g-1 at 0.05 A g-1), excellent rate performance (153 mA h g-1 at 5.0 A g-1), and ultralong cycling life (93% capacity retention after 20000 cycles at 3.0 A g-1). Even at low temperature or without a conductive additive, it can also perform well. It is believed that self-assembly is a very powerful strategy to construct high-performance nanostructured electrodes.

Mobile energy storage technologies for boosting carbon neutrality

Carbon neutrality calls for renewable energies, and the efficient use of renewable energies requires energy storage mediums that enable the storage of excess energy and reuse after spatiotemporal reallocation. Compared with traditional energy storage technologies, mobile energy storage technologies have the merits of low cost and high energy conversion efficiency, can be flexibly located, and cover a large range from miniature to large systems and from high energy density to high power density, although most of them still face challenges or technical bottlenecks. In this review, we provide an overview of the opportunities and challenges of these emerging energy storage technologies (including rechargeable batteries, fuel cells, and electrochemical and dielectric capacitors). Innovative materials, strategies, and technologies are highlighted. Finally, the future directions are envisioned. We hope this review will advance the development of mobile energy storage technologies and boost carbon neutrality.

Bio-Based Polyhydroxyanthraquinones as High-Voltage Organic Electrode Materials for Batteries

Organic materials have gained much attention as sustainable electrode materials for batteries. Especially bio-based organic electrode materials (OEMs) are very interesting due to their geographical independency and low environmental impact. However, bio-based OEMs for high-voltage batteries remain scarce. Therefore, in this work, a family of bio-based polyhydroxyanthraquinones (PHAQs)-namely 1,2,3,4,5,6,7,8-octahydroxyanthraquinone (OHAQ), 1,2,3,5,6,7-hexahydroxyanthraquinone (HHAQ), and 2,3,6,7-tetrahydroxyanthraquinone (THAQ)-and their redox polymers were synthesized. These PHAQs were synthesized from plant-based precursors and exhibit both a high-potential polyphenolic redox couple (3.5-4.0 V vs Li/Li+) and an anthraquinone redox moiety (2.2-2.8 V vs Li/Li+), while also showing initial charging capacities of up to 381 mAh g-1. To counteract the rapid fading caused by dissolution into the electrolyte, a facile polymerization method was established to synthesize PHAQ polymers. For this, the polymerization of HHAQ served as a model reaction where formaldehyde, glyoxal, and glutaraldehyde were tested as linkers. The resulting polymers were investigated as cathode materials in lithium metal batteries. PHAQ polymer composites synthesized using formaldehyde as linker and 10 wt % multiwalled carbon nanotubes (MWCNTs), namely poly(THAQ-formaldehyde)-10 wt % MWCNTs and poly(HHAQ-formaldehyde)-10 wt % MWCNTs, exhibited the best cycling performance in the lithium metal cells, displaying a high-voltage discharge starting at 4.0 V (vs Li/Li+) and retaining 81.6 and 77.3 mAh g-1, respectively, after 100 cycles.

All-Graphene Quantum Dot-Derived Battery: Regulating Redox Activity Through Localized Subdomains

In the quest for materials sustainability for grid-scale applications, graphene quantum dot (GQD), prepared via eco-efficient processes, is one of the promising graphitic-organic matters that have the potential to provide greener solutions for replacing metal-based battery electrodes. However, the utilization of GQDs as electroactive materials has been limited; their redox behaviors associated with the electronic bandgap property from the sp2 carbon subdomains, surrounded by functional groups, are yet to be understood. Here, the experimental realization of a subdomained GQD-based anode with stable cyclability over 1000 cycles, combined with theoretical calculations, enables a better understanding of the decisive impact of controlled redox site distributions on battery performance. The GQDs are further employed in cathode as a platform for full utilization of inherent electrochemical activity of bio-inspired redox-active organic motifs, phenoxazine. Using the GQD-derived anode and cathode, an all-GQD battery achieves a high energy density of 290 Wh kgcathode -1 (160 Wh kgcathode+anode -1 ), demonstrating an effective way to improve reaction reversibility and energy density of sustainable, metal-free batteries.

Solid-Solution or Intermetallic Compounds: Phase Dependence of the Li-Alloying Reactions for Li-Metal Batteries

Electrochemical Li-alloying reactions with Li-rich alloy phases render a much higher theoretical capacity that is critical for high-energy batteries, and the accompanying phase transition determines the alloying/dealloying reversibility and cycling stability. However, the influence of phase-transition characteristics upon the thermodynamic properties and diffusion kinetic mechanisms among the two categories of alloys, solid-solutions and intermetallic compounds, remains incomplete. Here we investigated three representative Li-alloys: Li-Ag alloy of extended solid-solution regions; Li-Zn alloy of an intermetallic compound with a solid-solution phase of a very narrow window in Li atom concentration; and Li-Al alloy of an intermetallic compound. Solid-solution phases undertake a much lower phase-transition energy barrier than the intermetallic compounds, leading to a considerably higher Li-alloying/dealloying reversibility and cycling stability, which is due to the subtle structural change and chemical potential gradient built up inside of the solid-solution phases. These two effects enable the Li atoms to enter the bulk of the Li-Ag alloy to form a homogeneous alloy phase. The pouch cell of the Li-rich Li20Ag alloy pairs with a LiNi0.8Co0.1Mn0.1O2 cathode under an areal capacity of 3.5 mAh cm-2 can retain 87% of its initial capacity after 250 cycles with an enhanced Coulombic efficiency of 99.8 ± 0.1%. While Li-alloying reactions and the alloy phase transitions have always been tightly linked in past studies, our findings provide important guidelines for the intelligent design of components for secondary metal batteries.

Recent Progress in Design Principles of Covalent Organic Frameworks for Rechargeable Metal-Ion Batteries

Covalent organic frameworks (COFs) are acknowledged as a new generation of crystalline organic materials and have garnered tremendous attention owing to their unique advantages of structural tunability, frameworks diversity, functional versatility, and diverse applications in drug delivery, adsorption/separation, catalysis, optoelectronics, and sensing, etc. Recently, COFs is proven to be promising candidates for electrochemical energy storage materials. Their chemical compositions and structures can be precisely tuned and functionalized at the molecular level, allowing a comprehensive understanding of COFs that helps to make full use of their features and addresses the inherent drawback based on the components and functions of the devices. In this review, the working mechanisms and the distinguishing advantages of COFs as electrodes for rechargeable Li-ion batteries are discussed in detail. Especially, principles and strategies for the rational design of COFs as advanced electrode materials in Li-ion batteries are systematically summarized. Finally, this review is structured to cover recent explorations and applications of COF electrode materials in other rechargeable metal-ion 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.