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

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.

High-Performance Poly(1-naphthylamine)/Mesoporous Carbon Cathode for Lithium-Ion Batteries with Ultralong Cycle Life of 45000 Cycles at -15 °C

Organic electrode materials for lithium-ion batteries have attracted significant attention in recent years. Polymer electrode materials, as compared to small-molecule electrode materials, have the advantage of poor solubility, which is beneficial for achieving high cycling stability. However, the severe entanglement of polymer chains often leads to difficulties in preparing nanostructured polymer electrodes, which is vital for achieving fast reaction kinetics and high utilization of active sites. This study demonstrates that these problems can be solved by the in situ electropolymerization of electrochemically active monomers in nanopores of ordered mesoporous carbon (CMK-3), combining the advantages of the nano-dispersion and nano-confinement effects of CMK-3 and the insolubility of the polymer materials. The as-prepared nanostructured poly(1-naphthylamine)/CMK-3 cathode exhibits a high active site utilization of 93.7%, ultrafast rate capability of 60 A g-1 (≈320 C), and an ultralong cycle life of 10000 cycles at room temperature and 45000 cycles at -15 °C. The study herein provides a facile and effective method that can simultaneously solve both the dissolution problem of small-molecule electrode materials and the inhomogeneous dispersion issue of polymer electrode materials.

Advanced 1D Metal-Organic Coordination Polymer for Lithium-Ion Batteries: Designing, Synthesis, and Working Mechanism

Anthraquinone (AQ) and its derivatives have been attracting more attention as promising electrode materials for lithium storage because of their high specific capacity, structural diversity, and environmental friendliness. The dissolution and poor electrical conductivity of AQ, however, limit its practical application. Here, a novel metal-organic coordination polymer with a one-dimensional (1D) chain ([C₁₄H₆O₄Cu]_n denoted as Cu-DHAQ; DHAQ, 1,5-dihydroxyl anthraquinone) and its composite with graphene (Cu-DHAQ/G; G, graphene) are developed by the introduction of graphene and copper ion into DHAQ. The fabricated polymer with a 1D chain not only well inhibits the dissolution of DHAQ in organic electrolytes but also facilitates lithium-ion insertion/extraction on carbonyl groups and shortens the migration path of lithium ions. Furthermore, the addition of the conductive network of graphene provides fast transfer rates of electrons. As a result, Cu-DHAQ/G delivers a high discharge capacity, long cycle life, and excellent rate capability. The lithium storage mechanism shows lithium ion insertion/extraction on two carbonyl groups of Cu-DHAQ in the range of 1.6-2.0 V and the redox reaction of Cu⁺/Cu²⁺ between 2.8 and 3.0 V, and Cu²⁺ and Cu⁺ coexist in the Cu-DHAQ/G electrode during the charge/discharge process. This study provides meaningful guidance to develop metal-organic coordination polymer electrodes for high-performance Li-ion batteries.

Molecular and Morphological Engineering of Organic Electrode Materials for Electrochemical Energy Storage

Organic electrode materials (OEMs) can deliver remarkable battery performance for metal-ion batteries (MIBs) due to their unique molecular versatility, high flexibility, versatile structures, sustainable organic resources, and low environmental costs. Therefore, OEMs are promising, green alternatives to the traditional inorganic electrode materials used in state-of-the-art lithium-ion batteries. Before OEMs can be widely applied, some inherent issues, such as their low intrinsic electronic conductivity, significant solubility in electrolytes, and large volume change, must be addressed. In this review, the potential roles, energy storage mechanisms, existing challenges, and possible solutions to address these challenges by using molecular and morphological engineering are thoroughly summarized and discussed. Molecular engineering, such as grafting electron-withdrawing or electron-donating functional groups, increasing various redox-active sites, extending conductive networks, and increasing the degree of polymerization, can enhance the electrochemical performance, including its specific capacity (such as the voltage output and the charge transfer number), rate capability, and cycling stability. Morphological engineering facilitates the preparation of different dimensional OEMs (including 0D, 1D, 2D, and 3D OEMs) via bottom-up and top-down methods to enhance their electron/ion diffusion kinetics and stabilize their electrode structure. In summary, molecular and morphological engineering can offer practical paths for developing advanced OEMs that can be applied in next-generation rechargeable MIBs.

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Soluble Organic Cathodes Enable Long Cycle Life, High Rate, and Wide-Temperature Lithium-Ion Batteries

Organic electrode materials free of rare transition metal elements are promising for sustainable, cost-effective, and environmentally benign battery chemistries. However, severe shuttling effect caused by the dissolution of active materials in liquid electrolytes results in fast capacity decay, limiting their practical applications. Here, using a gel polymer electrolyte (GPE) that is in situ formed on Nafion-coated separators, the shuttle reaction of organic electrodes is eliminated while maintaining the electrochemical performance. The synergy of physical confinement by GPE with tunable polymer structure and charge repulsion of the Nafion-coated separator substantially prevents the soluble organic electrode materials with different molecular sizes from shuttling. A soluble small-molecule organic electrode material of 1,3,5-tri(9,10-anthraquinonyl)benzene demonstrates exceptional electrochemical performance with an ultra-long cycle life of 10 000 cycles, excellent rate capability of 203 mAh g^-1 at 100 C, and a wide working temperature range from -70 to 100 °C based on the solid-liquid conversion chemistry, which outperforms all previously reported organic cathode materials. The shielding capability of GPE can be designed and tailored toward organic electrodes with different molecular sizes, thus providing a universal resolution to the shuttling effect that all soluble electrode materials suffer.

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

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

Performance Enhancement of Polymer Electrode Materials for Lithium-Ion Batteries: From a Rigid Homopolymer to Soft Copolymers

Synthesizing redox-active units containing polymers is a promising route for improving the cycling stability of organic electrode materials. However, constructing uniform electrode architectures with good polymer dispersion is a big challenge in the case of polymer electrode materials. In this work, we design and synthesize two anthraquinone-containing copolymers and compare their electrochemical performance with that of the corresponding homopolymer. It is uncovered that the copolymers with soft units in the main chain display increased chain flexibility, thus leading to a slightly increased solubility. Because of this, the soft copolymers are less likely to precipitate during solvent volatilization of electrode preparation and thus can form more uniform electrode architectures. The cyclic voltammogram and electrochemical impedance spectroscopy measurements indicate that copolymer electrodes display decreased polarization and improved kinetics compared with the homopolymer electrode. The copolymers exhibit significantly enhanced cycling stability and improved rate performance. After 100 cycles, both copolymers reveal very high capacity retention of above 98%, while the homopolymer retains only 71% of its highest capacity. Moreover, the copolymer can discharge/charge at 1C for over 2000 cycles with almost no capacity fading, indicating excellent long-term cycling performance. This work further demonstrates the importance of molecular structure and electrode architecture in determining the electrochemical performance of polymer electrode materials.