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

Molecular engineering of benzimidazole-linked conjugated microporous polymers as cathodes for air-rechargeable aqueous zinc-organic batteries

Conjugated microporous polymers (CMPs) have become a recent research hotspot as cathodes for aqueous zinc-organic batteries (AZOBs) owing to their stable conjugated structure and abundant accessible redox active sites. Herein, we have designed and synthesized two benzimidazole-linked CMPs (TABQ-BTA and TABQ-H3BTB) and a linear polymer (TABQ-PTA) by a one-pot polymerization reaction. Benefiting from the introduction of CO and newly emerging imidazole groups, each active structural unit can transfer four electrons in the electrochemical reaction. Especially, the optimum TABQ-H3BTB delivers impressive reversible specific capacity (308.8 mAh g-1 at 50 mA g-1) and good cyclability (above 1000 cycles at 5 A g-1). Moreover, TABQ-H3BTB is also capable of exhibiting reversible air self-charging characteristics. In addition, theoretical calculations and experimental evidence support the ions (Zn2+ and H+) co-storage mechanisms in dual redox centers (CO and CN). This work can provide a molecular construction idea for developing high-performance and sustainable organic cathodes of AZOBs.

Electron-Withdrawing Group Functionalized Anthraquinone Polymers for High-Performance Organic Zinc-Ion Batteries

Aqueous zinc ion batteries (AZIBs) stand out among various battery technologies for their advantages, including low cost, high safety, and green credentials. We chemically polymerized anthraquinone and triphenylamine derivatives to prepare the π-conjugated polymers poly 2-((4-(diphenylamine)benzylidene)amino)anthracene-9,10-dione (PDAH) and poly 2-((4-((4-bromophenyl)(phenyl)amino)benzylidene)amino)anthracene-9,10-dione (PDABr), as cathode materials for AZIBs. The anthraquinone-based structure's high charge storage capacity, coupled with the π-conjugated structure's strong charge transfer capability, enabled these electrode materials to exhibit excellent electrochemical performance. Among them, the electron-withdrawing group -introduced in PDABr induces a p-π interaction with the adjacent benzene ring, optimizing electron and ion migration within the battery. This enhancement improves the electrode material's stability and electrochemical activity, leading to superior battery performance, especially in rate performance, cycle life, and stability. Comparative experiments revealed that PDABr//Zn exhibited a higher specific capacity (0.1 A g-1, 210.57 mA h g-1) than PDAH//Zn (0.1 A g-1, 145.7 mA h g-1). At the same current density, PDABr//Zn also showed better cycling stability with a (capacity retention of 93% after 6000 cycles at 5 A g-1). Additionally, PDABr//Zn exhibited exceptional rate capability, maintaining its specific capacity upon returning to the initial current density. By comparing the physical and electrochemical properties of PDAH//Zn and PDABr//Zn, the relationship between the p-π conjugation effect and electrochemical performance is elucidated. This study provides a strategy for the fine-tuned, molecular design of organic electrode materials, specifically aimed at enhancing high-energy organic zinc-ion batteries.

A new polymer with rich carbonyl delocalized π-conjugated structure for high-performance aqueous zinc ion batteries

The development of sustainable and clean energy has become a top priority, driven by global carbon peaking and carbon neutrality targets. Organics are widely used in aqueous zinc ion batteries (AZIBs) due to their environmental friendliness, high structural designability, and safety. However, organic materials often face some challenges, including high solubility, low specific capacity, and unclear mechanism, which hinder its further applications. In this paper, two new conjugated organic polymers were synthesized as cathodes for AZIBs by molecular structure design. Notably, the introduction of new actives (C = O) in (poly-(tetraamino-p-benzoquinone-alt-2,5-dihydroxy-1,4-benzoquinone, DHTA) along with the extension of the π-π conjugated structure to form polymers is conducive to the improvement of the specific capacity and reversibility of AZIBs compared to (poly-(1,2,4,5-tetraaminobenzene-alt-2,5-dihydroxy-1,4-benzoquinone, DHPH). The DHTA cathode delivers high initial specific capacity of 282.5 mAh/g at a current of 0.05 A/g and excellent rate performance (56.8 mAh/g at 5 A/g). The excellent rate performance and long cycle life of the as synthesized DHTA can be attributed to the low solubility, extended π-conjugated structure and enhanced electronic conductivity, which result from the polymerization with the introduction of carbonyl groups into organic skeleton. Moreover, the mechanism of Zn2+ storage in DHTA is also explored by various ex-situ characterization techniques and density-functional theory (DFT) calculations. In each repeating unit, DHTA can store two Zn2+ while transferring four electrons to form a stable O⋯Zn⋯N coordination. This work provides a molecular engineering strategy for organic materials, revealing their potential application in zinc ion batteries.

High-Performance Bipolar Small-Molecule Organic Cathode for Wide-Temperature-Range Aqueous Zinc-Ion Batteries

Organic small-molecules with redox activity are promising cathode candidates for aqueous zinc-ion batteries (AZIBs) due to their low cost, high safety and high theoretical capacity. However, their severe dissolution leads to unsatisfactory electrochemical performance. Here, a dihydro-octaaza-pentacene (DOP) compound is synthesized as a cathode for AZIBs by extending its N heterocyclic molecular structure. The extended N heterocyclic structure provides dual active sites of n-type (C═N) and p-type (-NH-) redox reactions while reducing dissolution through enhanced π-conjugation. Hence, the Zn//DOP battery demonstrates improved performance, e.g., an enhanced capacity of 360 mAh g-1 at 0.05 A g-1. Even under extended temperature conditions of - 50 and 50 °C, the batteries still maintain the capacities of 172 and 312 mAh g-1, respectively. In/ex-situ spectroscopy provide a thorough understanding of the storage mechanisms of cations and anions (Zn2+/H+ and ClO4-) through multielectron transfer process occurring at dual electroactive sites. This strategy offers a promising approach to designing high-performance zinc-organic batteries for sustainable energy storage.

Electropolymerized Bipolar Poly(2,3-diaminophenazine) Cathode for High-Performance Aqueous Al-Ion Batteries with An Extended Temperature Range of -20 to 45 °C

Achieving reversible insertion/extraction in most cathodes for aqueous aluminum ion batteries (AAIBs) is a significant challenge due to the high charge density of Al3+ and strong electrostatic interactions. Organic materials facilitate the hosting of multivalent carriers and rapid ions diffusion through the rearrangement of chemical bonds. Here, a bipolar conjugated poly(2,3-diaminophenazine) (PDAP) on carbon substrates prepared via a straightforward electropolymerization method is introduced as cathode for AAIBs. The integration of n-type and p-type active units endow PDAP with an increased number of sites for ions interaction. The long-range conjugated skeleton enhances electron delocalization and collaborates with carbon to ensure high conductivity. Moreover, the strong intermolecular interactions including π-π interaction and hydrogen bonding significantly enhance its stability. Consequently, the Al//PDAP battery exhibits a large capacity of 338 mAh g-1 with long lifespan and high-rate capability. It consistently demonstrates exceptional electrochemical performances even under extreme conditions with capacities of 155 and 348 mAh g-1 at -20 and 45 °C, respectively. In/ex situ spectroscopy comprehensively elucidates its cation/anion (Al3+/H3O+ and ClO4 -) storage with 3-electron transfer in dual electroactive centers (C═N and -NH-). This study presents a promising strategy for constructing high-performance organic cathode for AAIBs over a wide temperature range.