A Bipolar and Self‐Polymerized Phthalocyanine Complex for Fast and Tunable Energy Storage in Dual‐Ion Batteries

Anchoring π-d Conjugated Metal-Organic Frameworks with Dual-Active Centers on Carbon Nanotubes for Advanced Potassium-Ion Batteries

Potassium-ion batteries (PIBs) are gradually gaining attention owing to their natural abundance, excellent security, and high energy density. However, developing excellent organic cathode materials for PIBs to overcome the poor cycling stability and slow kinetics caused by the large radii of K+ ions is challenging. This study demonstrates for the first time the application of a hexaazanonaphthalene (HATN)-based 2D π-d conjugated metal-organic framework (2D c-MOF) with dual-active centers (Cu-HATNH) and integrates Cu-HATNH with carbon nanotubes (Cu-HATNH@CNT) as the cathode material for PIBs. Owing to this systematic module integration and more exposed active sites with high utilization, Cu-HATNH@CNT exhibits a high initial capacity (317.5 mA h g-1 at 0.1 A g-1 ), excellent long-term cycling stability (capacity retention of 96.8% at 5 A g-1 after 2200 cycles), and outstanding rate capacity (147.1 mA h g-1 at 10 A g-1 ). The reaction mechanism and performance are determined by combining experimental characterization and density functional theory calculations. This contribution provides new opportunities for designing high-performance 2D c-MOF cathodes with multiple active sites for PIBs.

Long-Term Cycling Stability of Porphyrin Electrode for Li/Na Charge Storage at High Temperature

Bipolar redox organic compounds have been considered as potential next-generation electrode materials due to their sustainability, low cost and tunable structure. However, their development is still limited by the poor cycling stability and low energy density ascribed to high dissolution during cycling and the low conductivity of organic molecules. Herein, porphyrin-based bipolar organics of [5,10,15,20-tetrathienylporphinato] M^II (M=2 H, Cu (CuTTP)) are proposed as new stable organic electrodes. Enhanced cycling stability is obtained by a temperature-induced in situ polymerization strategy of porphyrin molecules. The resulting polymer exhibits excellent cycling stability up to 10 00 cycles even at a high current density (1000 mA g^-1 ) in organic lithium-/sodium-based charge storage devices at 50 °C. In a symmetrical cell using CuTTP as both cathode and anode material a discharge capacity of 72 mAh g^-1 is achieved after 600 cycles at 1000 mA g^-1 . This strategy would offer a new approach to developing stable energy storage bipolar materials in organic-based devices at high temperature.

Spreading the Landscape of Dual Ion Batteries: from Electrode to Electrolyte

The working mechanism of a dual-ion battery (DIB) differs from that of a lithium-ion battery (LIB) in that the anions in the electrolyte of the former can be intercalated as well. Researchers have been paying close attention to this device because of its high voltage, low price, and environmental friendliness. However, DIBs are still in their early research stages, and numerous issues need to be addressed and investigated further. Initially, this Review explains how DIBs work in principle and discusses the progress of electrode materials for cathode and anode. Furthermore, since the electrolytes used as the active material, as well as anion, solvent, and additives, have a significant impact on the DIB's capacity and voltage, the current status is also presented in terms of electrolytes, followed by an outlook on confronting the challenges. A comprehensive summary from electrode to electrolyte will guide the development of next-generation DIBs.

Anchoring I3- via Charge-Transfer Interaction by a Coordination Supramolecular Network Cathode for a High-Performance Aqueous Dual-Ion Battery

Iodine is considered to have broad application prospects in the field of electrochemical energy storage. However, the high solubility of I₃^- severely hampers its practical application, and the lack of research on the anchoring mechanism of I₃^- has seriously hindered the development of advanced cathode materials for iodine batteries. Herein, based on the molecular orbital theory, we studied the charge-transfer interaction between the acceptor of I₃^- with a σ* empty antibonding orbital and the donor of pyrimidine nitrogen with lone-pair electrons, which is proved by the results of UV-vis absorption spectroscopy, Raman spectroscopy, and density functional theory (DFT) calculations. The prepared dual-ion battery (DIB) exhibits a high voltage platform of 1.2 V, a remarkable discharge-specific capacity of up to 207 mAh g^-1, and an energy density of 233 Wh kg^-1 at a current density of 5 A g^-1, as well as outstanding cycle stability (operating stably for 5000 cycles) with a high Coulombic efficiency of 97%, demonstrating excellent electrochemical performance and a promising prospect in stationary energy storage.

Mesoporous Polyimide-Linked Covalent Organic Framework with Multiple Redox-Active Sites for High-Performance Cathodic Li Storage

Covalent organic frameworks (COFs) are gaining increasing attention as renewable cathode materials for Li-ion batteries. However, COF electrodes reported so far still exhibit unsatisfying capacity due to their limited active site density and insufficient utilization. Herein, a new two-dimensional polyimide-linked COF, HATN-AQ-COF with multiple redox-active sites for storing Li⁺ ions, was designed and fabricated from a new module of 2,3,8,9,14,15-hexacarboxyl hexaazatrinaphthalene trianhydrides with a 2,6-diaminoanthraquinone linker. HATN-AQ-COF possessing excellent stability, good conductivity, and a large pore size of 3.8 nm enables the stable and fast ion transport. This, in combination with the abundant redox active sites, results in a high reversible capacity of 319 mAh g^-1 at 0.5 C (1 C=358 mA g^-1 ) for the HATN-AQ-COF electrode with a high active site utilization of 89 % and good cycle performance, representing one of the best performances among the reported COF electrodes.

Optimization of Monomer Molecular Structure for Polymer Electrodes Fabricated through in-situ Electro-Polymerization Strategy

In-situ electro-polymerization of redox-active monomers has been proved to be a novel and facile strategy to prepare polymer electrodes with superior electrochemical performance. The monomer molecular structure would have a profound impact on electro-polymerization behavior and thus electrochemical performance. However, this impact is poorly understood and has barely been investigated yet. Herein, three carbazole-based monomers, 9-phenylcarbazole (CB), 1,4-bis(carbazol-9-yl)benzene (DCB), and 2,6-bis(carbazol-9-yl)naphthalene (DCN), were applied to study the above issue systematically and achieve excellent long cycle performance. The monomers were rationally designed with different polymerizable sites and solubilities. It was found that a monomer with increased polymerizable sites and decreased solubility brought about enhanced electrochemical performance. This is because poor solubility could enhance utilization of the monomer for polymerization and more polymerizable sites could lead to a stable crosslinked polymer network after electro-polymerization. DCN with four polymerizable sites and the poorest solubility displayed the best electrochemical performance, which showed stable cycling up to 5000 cycles with high capacity retention of 76.2 % (among the best cycle in the literature). Our work for the first time reveals the relationship between monomer structure and in-situ electro-polymerization behavior. This work could shed light on the structure design/optimization of monomers for high-performance polymer electrodes prepared through in-situ electro-polymerization.

Molecular Tailoring of an n/p-type Phenothiazine Organic Scaffold for Zinc Batteries

The p-type or n-type redox reactions of organics are being used as the reversible electrodes to build the next-generation rechargeable batteries with sustainable and tunable characteristics. However, the n-type organics that store cations generally exhibit low potential (<0.8 V vs. Zn/Zn²⁺ ), while the p-type organics that store anions suffer from limited capacity (<100 mAh g^-1 ). Herein, we demonstrate that bis(phenylamino)phenothiazin-5-ium iodide (PTD-1) containing both n-type and p-type redox moieties exhibits a hybrid charge storage mechanism (n/p-type at low potential, p-type at high potential). Such a hybrid mechanism combines the advantages of n- and p-type reactions and compensates for the associated drawbacks of each. Accordingly, the aqueous Zn//PTD-1 full cell shows a high voltage (1.8 V_maximum or 1.1 V_average ), a high capacity 188.24 mAh g_PTD-1 ^-1 (achieved at 40 mA g^-1 ), a long-life and a supercapacitor-like high power. These results shed new light on the design of advanced organic electrodes.

A Self-Conditioned Metalloporphyrin as a Highly Stable Cathode for Fast Rechargeable Magnesium Batteries

Development of practical rechargeable Mg batteries (RMBs) is impeded by their limited cycle life and rate performance of cathodes. As demonstrated herein, a copper-porphyrin with meso-functionalized ethynyl groups is capable of reversible two- and four-electron storage at an extremely fast rate (tested up to 53 C). The reversible four-electron redox process with cationic-anionic contributions resulted in a specific discharge capacity of 155 mAh g-1 at the high current density of 1000 mA g-1 . Even at 4000 mA g-1 , it still delivered >70 mAh g-1 after 500 cycles, corresponding to an energy density of >92 Wh kg-1 at a high power of >5100 W kg-1 . The ability to provide such high-rate performance and long-life opens the way to the development of practical cathodes for multivalent metal batteries.

Pre-Polymerization Enables Controllable Synthesis of Nanosheet-Based Porphyrin Polymers towards High-Performance Li-Ion Batteries

The precise regulation of nucleation growth and assembly of polymers is still an intriguing goal but an enormous challenge. In this study, we proposed a pre-polymerization strategy to regulate the assembly and growth of polymers by facilely controlling the concentration of polymerization initiator, and thus obtained two kinds of different nanosheet-based porphyrin polymer materials using tetrakis-5,10,15,20-(4-aminophenyl) porphyrin (TAPP) as the precursor. Notably, due to the π-π stacking and doping of TAPP during the preparation process, the obtained PTAPP-nanocube material exhibits a high intrinsic bulk conductivity reaching 1.49×10^-4  S m^-1 . Profiting from the large π-conjugated structure of porphyrin units, closely stacked layer structure and excellent conductivity, the resultant porphyrin polymers, as electrode materials for lithium ion batteries, deliver high specific capacity (≈650 mAh g^-1 at the current density of 100 mA g^-1 ), excellent rate performance and long-cycle stability, which are among the best reports of porphyrin polymer-based electrode materials for lithium-ion batteries, to the best of our knowledge. Therefore, such a pre-polymerization approach would provide a new insight for the controllable synthesis of polymers towards custom-made architecture and function.

A Self-Polymerized Nitro-Substituted Conjugated Carbonyl Compound as High-Performance Cathode for Lithium-Organic Batteries

Conjugated carbonyl compounds have received much attention as cathode materials for developing green lithium-ion batteries (LIBs). However, their high dissolution and poor electronic conductivity in organic electrolyte restrict their further application. Herein, a self-polymerized nitro-substituted conjugated carbonyl compound (2,7-dinitropyrene-4,5,9,10-tetraone, PT-2 NO₂ ) is applied as a high-performance cathode material for LIBs. PT-2 NO₂ exhibits a high reversible capacity of 153.9 mAh g^-1 at 50 mA g^-1 after 120 cycles, which is higher than that of other substituted compounds. Detailed characterization and theoretical calculations have testified that PT-2 NO₂ is transformed into an azo polymer through an irreversible reductive coupling reaction in the first discharge process, and then carbonyl and azo groups reversibly react with Li ions in subsequent cycles. In addition, this azo polymer is also synthesized and applied as the electrode material, which shows similar electrochemical performance to PT-2 NO₂ but with higher initial coulombic efficiency. Thus, this work provides a simple but effectively way to construct organic cathode materials with multiple redox sites for green and high-performance LIBs.