Crown Ether Electrolyte Additive Enables High-Rate and Stable Polyviologen Cathode Material for Chloride Ion Batteries.

A variety of inorganic and inorganic cathode materials for chloride ion storage are reported. However, their application in chloride ion batteries (CIB) is hindered by poor rate capability and cycling stability. Herein, an organic poly(butyl viologen dichloride) (PBVCl2) cathode material with significantly enhanced rate and cycling performance in the CIB is achieved using a crown ether (18-Crown-6) additive in the tributylmethylammonium chloride-based electrolyte. The as-prepared PBVCl2 cathodes exhibit impressive capacity increases from 149.4 to 179.1 mAh g-1 at 0.1 C and from 57.8 to 111.9 mAh g-1 at 10 C, demonstrating the best rate performance with the highest energy density among those of various reported cathodes for CIBs. This impressive performance improvement is a result of the great boosts in charge transfer, ion transport, and interface stability of the battery by the use of 18-Crown-6, which also contributes to a more than twofold increase in capacity retention after 120 cycles. The electrode reaction mechanism of the CIB based on highly reversible chloride ion transfer is revealed by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy.

Synergistic π-Conjugation Organic Cathode for Ultra-Stable Aqueous Aluminum Batteries.

Rechargeable aqueous aluminum batteries (AABs) are promising energy storage technologies owing to their high safety and ultra-high energy-to-price ratio. However, either the strong electrostatic forces between high-charge-density Al3+ and host lattice, or sluggish large carrier-ion diffusion toward the conventional inorganic cathodes generates inferior cycling stability and low rate-capacity. To overcome these inherent confinements, a series of promising redox-active organic materials (ROMs) are investigated and a π-conjugated structure ROMs with synergistic C═O and C═N groups is optimized as the new cathode in AABs. Benefiting from the joint utilization of multi-redox centers and rich π-π intermolecular interactions, the optimized ROMs with unique ion coordination storage mechanism facilely accommodate complex active ions with mitigated coulombic repulsion and robust lattice structure, which is further validated via theoretical simulations. Thus, the cathode achieves enhanced rate performance (153.9 mAh g-1 at 2.0 A g-1) and one of the best long-term stabilities (125.7 mAh g-1 after 4,000 cycles at 1.0 A g-1) in AABs. Via molecular exploitation, this work paves the new direction toward high-performance cathode materials in aqueous multivalent-ion battery systems.

A Small-Molecule Organic Cathode with Extended Conjugation toward Enhancing Na+ Migration Kinetics for Advanced Sodium-Ion Batteries.

Organic cathode materials show excellent prospects for sodium-ion batteries (SIBs) owing to their high theoretical capacity. However, the high solubility and low electrical conductivity of organic compounds result in inferior cycle stability and rate performance. Herein, an extended conjugated organic small molecule is reported that combines electroactive quinone with piperazine by the structural designability of organic materials, 2,3,7,8-tetraamino-5,10-dihydrophenazine-1,4,6,9-tetraone (TDT). Through intermolecular condensation reaction, many redox-active groups C═O and extended conjugated structures are introduced without sacrificing the specific capacity, which ensures the high capacity of the electrode and enhances rate performance. The abundant NH2 groups can form intermolecular hydrogen bonds with the C═O groups to enhance the intermolecular interactions, resulting in lower solubility and higher stability. The TDT cathode delivers a high initial capacity of 293 mAh g-1 at 500 mA g-1 and maintains 90 mAh g-1 at an extremely high current density of 70 A g-1. The TDT || Na-intercalated hard carbon (Na-HC) full cells provide an average capacity of 210 mAh g-1 during 100 cycles at 500 mA g-1 and deliver a capacity of 120 mAh g-1 at 8 A g-1.

Recent Progress of the Cathode Material Design for Aqueous Zn-Organic Batteries.

Aqueous zinc-ion batteries (ZIBs) have emerged as the most promising candidate for large-scale energy storage due to their inherent safety, environmental friendliness, and cost-effectiveness. Simultaneously, the utilization of organic electrode materials with renewable resources, environmental compatibility, and diverse structures has sparked a surge in research and development of aqueous Zn-organic batteries (ZOBs). A comprehensive review is warranted to systematically present recent advancements in design principles, synthesis techniques, energy storage mechanisms, and zinc-ion storage performance of organic cathodes. In this review article, we comprehensively summarize the energy storage mechanisms employed by aqueous ZOBs. Subsequently, we categorize organic cathode materials into small-molecule compounds and high-molecular polymers respectively. Novel polymer materials such as conjugated polymers (CPs), conjugated microporous polymers (CMPs), and covalent organic frameworks (COFs) are highlighted with an overview of molecular design strategies and structural optimization based on organic cathode materials aimed at enhancing the performance of aqueous ZOBs. Finally, we discuss the challenges faced by aqueous ZOBs along with future prospects to offer insights into their practical applications.

Intermolecular Hydrogen Bonding Networks Stabilized Organic Supramolecular Cathode for Ultra-High Capacity and Ultra-Long Cycle Life Rechargeable Aluminum Batteries.

Rechargeable aluminum batteries (RABs) are a promising candidate for large-scale energy storage, attributing to the abundant reserves, low cost, intrinsic safety, and high theoretical capacity of Al. However, the cathode materials reported thus far still face challenges such as limited capacity, sluggish kinetics, and undesirable cycle life. Herein, we propose an organic cathode benzo[i] benzo[6,7] quinoxalino [2,3-a] benzo [6,7] quinoxalino [2,3-c] phenazine-5,8,13,16,21,24-hexaone (BQQPH) for RABs. The six C=O and six C=N redox active sites in each molecule enable BQQPH to deliver a record ultra-high capacity of 413 mAh g-1 at 0.2 A g-1. Encouragingly, the intermolecular hydrogen bonding network and π-π stacking interactions endow BQQPH with robust structural stability and minimal solubility, enabling an ultra-long lifetime of 100,000 cycles. Moreover, the electron-withdrawing carbonyl group induces a reduction in the energy level of the lowest unoccupied molecular orbital and expands the π-conjugated system, which considerably enhances both the discharge voltage and redox kinetics of BQQPH. In situ and ex situ characterizations combined with theoretical calculations unveil that the charge storage mechanism is reversible coordination/dissociation of AlCl2 + with the N and O sites in BQQPH accompanied by 12-electron transfer. This work provides valuable insights into the design of high-performance organic cathode materials for RABs.

A High Capacity p-Type Organic Cathode Material for Aqueous Zinc Batteries.

P-type organic cathode materials typically exhibit high redox potentials and fast redox kinetics, presenting broad application prospects in aqueous zinc batteries (AZBs). However, most of the reported P-type organic cathode materials exhibit limited capacity (< 100 mAh g-1), which is attributable to the low mass content ratio of oxidation-reduction active functional groups in these materials. Herein, we report a high-capacity p-type organic material, 5,12-dihydro-5,6,11,12-tetraazatetracene (DHTAT), for aqueous zinc batteries. Both experiments and calculation indicate the charge storage of DHTAT involves the adsorption/ desorption of ClO4- on the -NH- group. Benefitting from the high mass content ratio of the -NH- group in DHATA molecule, the DHATA electrode demonstrates a remarkable capacity of 224 mAh g-1 at a current density of 50 mA g-1 with a stable voltage of 1.2 V. Notably, after 5000 cycles at a high current density of 5 A g-1, DHTAT retains 73% of its initial capacity, showing a promising cycling stability. In addition, DHTAT also has good low-temperature performance and can stably cycle at -40 °C for 4000 cycles at 1 A g-1, making it a competitive candidates cathode material for low-temperature batteries.

Dynamically Ion-Coordinated Bipolar Organodichalcogenide Cathodes Enabling High-Energy and Durable Aqueous Zn Batteries.

Bipolar organic cathode materials (OCMs) implementing cation/anion storage mechanisms are promising for high-energy aqueous Zn batteries (AZBs). However, conventional organic functional group active sites in OCMs usually fail to sufficiently unlock the high-voltage/capacity merits. Herein, we initially report dynamically ion-coordinated bipolar OCMs as cathodes with chalcogen active sites to solve this issue. Unlike conventional organic functional groups, chalcogens bonded with conjugated group undergo multielectron-involved positive-valence oxidation and negative-valence reduction, affording higher redox potentials and reversible capacities. With phenyl diselenide (PhSe-SePh, PDSe) as a proof of concept, it exhibits a conversion pathway from (PhSe)- to (PhSe-SePh)0 and then to (PhSe)+ as unveiled by characterization and theoretical simulation, where the diselenide bonds are periodically broken and healed, dynamically coordinating with ions (Zn2+ and OTF-). When confined into ordered mesoporous carbon (CMK-3), the dissolution of PDSe intermediates is greatly inhibited to obtain an ultralong lifespan without voltage/capacity compromise. The PDSe/CMK-3 || Zn batteries display high reversibility capacity (621.4 mAh gPDSe -1), distinct discharge plateau (up to 1.4 V), high energy density (578.3 Wh kgPDSe -1), and ultralong lifespan (12 000 cycles) at 10 A g-1, far outperforming conventional bipolar OCMs. This work sheds new light on conversion-type active site engineering for high-voltage/capacity bipolar OCMs towards high-energy AZBs.

Anthraquinone-Quinizarin Copolymer as a Promising Electrode Material for High-Performance Lithium and Potassium Batteries.

The growing demand for cheap, safe, recyclable, and environmentally friendly batteries highlights the importance of the development of organic electrode materials. Here, we present a novel redox-active polymer comprising a polyaniline-type conjugated backbone and quinizarin and anthraquinone units. The synthesized polymer was explored as a cathode material for batteries, and it delivered promising performance characteristics in both lithium and potassium cells. Excellent lithiation efficiency enabled high discharge capacity values of >400 mA g-1 in combination with good stability upon charge-discharge cycling. Similarly, the potassium cells with the polymer-based cathodes demonstrated a high discharge capacity of >200 mAh g-1 at 50 mA g-1 and impressive stability: no capacity deterioration was observed for over 3000 cycles at 11 A g-1, which was among the best results reported for K ion battery cathodes to date. The synthetic availability and low projected cost of the designed material paves a way to its practical implementation in scalable and inexpensive organic batteries, which are emerging as a sustainable energy storage technology.

Anion-Dependent Redox Chemistry of p-Type Poly(vinyldimethylphenazine) Cathode Materials.

Metal-free organic electrode materials have attracted vast research attention owing to their designable structures and tunable electrochemical properties. Although n-type cathode materials could be used in various metal-ion batteries, p-type ones with high potential can deliver high energy density. Herein, we report a new p-type polymeric cathode material, poly(2-vinyl-5,10-dimethyl-dihydrophenazine) (PVDMP), with a theoretical capacity of 227 mAh g-1 . PVDMP featuring two-step redox reaction will be doped by two anions to maintain electroneutrality during oxidation, which resulted in an anion-dependent electrochemical behavior of PVDMP-based cathode. The suitable dopant anion for PVDMP was selected and the doping mechanism was confirmed. Under the optimized condition, PVDMP cathode can deliver a high initial capacity of 220 mAh g-1 at 5 C and even remains 150 mAh g-1 after 3900 cycles. This work not only provides a new kind of p-type organic cathode materials but also deepens the understanding of its anion-dependent redox chemistry.

Anion Storage Chemistry of Organic Cathodes for High-Energy and High-Power Density Divalent Metal Batteries.

Multivalent batteries show promising prospects for next-generation sustainable energy storage applications. Herein, we report a polytriphenylamine (PTPAn) composite cathode capable of highly reversible storage of tetrakis(hexafluoroisopropyloxy) borate [B(hfip)4 ] anions in both Magnesium (Mg) and calcium (Ca) battery systems. Spectroscopic and computational studies reveal the redox reaction mechanism of the PTPAn cathode material. The Mg and Ca cells exhibit a cell voltage >3 V, a high-power density of ∼∼3000 W kg-1 and a high-energy density of ∼∼300 Wh kg-1 , respectively. Moreover, the combination of the PTPAn cathode with a calcium-tin (Ca-Sn) alloy anode could enable a long battery-life of 3000 cycles with a capacity retention of 60 %. The anion storage chemistry associated with dual-ion electrochemical concept demonstrates a new feasible pathway towards high-performance divalent ion batteries.

Molecular Tailoring of p-type Organics for Zinc Batteries with High Energy Density.

P-type organic electrode materials are known for their high redox voltages and fast kinetics. However, single-electron p-type organic materials generally exhibit low capacity despite high operating voltage and stability, while some multi-electron p-type organic materials have high theoretical capacity but low stability. To address this challenge, we explore the possibility of combining single-electron and multi-electron units to create high-capacity and stable p-type organic electrodes. We demonstrate the design of a new molecule, 4,4'-(10H-phenothiazine-3,7-diyl) bis (N,N-diphenylaniline) (PTZAN), which is created by coupling the triphenylamine molecule and the phenothiazine molecule. The resulting PTZAN||Zn battery shows excellent stability (2000 cycles), high voltage (1.3 V), high capacity (145 mAh g-1 ), and energy density of 187.2 Wh kg-1 . Theoretical calculations and in/ex situ analysis reveal that the charge storage of the PTZAN electrode is mainly driven by the redox of phenothiazine heterocycles and triphenylamine unit, accompanied by the combination/release of anions and Zn2+ .

Orthoquinone-Based Covalent Organic Frameworks with Ordered Channel Structures for Ultrahigh Performance Aqueous Zinc-Organic Batteries.

Elaborate molecular design on cathodes is of great importance for rechargeable aqueous zinc-organic batteries' performance elevation. Herein, we design a novel orthoquinone-based covalent organic framework with an ordered channel structures (BT-PTO COF) cathode for an ultrahigh performance aqueous zinc-organic battery. The ordered channel structure facilitates ions transfer and makes the COF follow a redox pseudocapacitance mechanism. Thus, it delivers a high reversible capacity of 225 mAh g-1 at 0.1 A g-1 and an exceptional long-term cyclability (retention rate 98.0 % at 5 A g-1 (≈18 C) after 10 000 cycles). Moreover, a co-insertion mechanism with Zn2+ first followed by two H+ is uncovered for the first time. Significantly, this co-insertion behaviour evolves to more H+ insertion routes at high current density and gives the COF ultra-fast kinetics thus it achieves unprecedented specific power of 184 kW kg-1 (COF) and a high energy density of 92.4 Wh kg-1 (COF) . Our work reports a superior organic material for zinc batteries and provides a design idea for future high-performance organic cathodes.

Organic Positive Materials for Magnesium Batteries: A Review.

Magnesium batteries, like lithium-ion batteries, with higher abundance and similar efficiency, have drawn great interest for large-scale applications such as electric vehicles, grid energy storage and many more. On the other hand, the use of organic electrode materials allows high energy-performance, metal-free, environmentally friendly, versatile, lightweight, and economically efficient magnesium storage devices. In particular, the structural diversity and the simple activity of organic molecules make redox properties, and hence battery efficiency, easy to monitor. While organic magnesium batteries still in their infancy, this field becomes more and more promising because significant results were reported. To summarize the achievements in studies on organic cathodes for magnesium systems, their synthesis is discussed, combined with electrode design to provide the basis for controlling the electrochemical properties. Moreover, the techniques to synthesize organic materials with high-yield are mentioned. Finally, potential problems and prospects are explored to further improve organic cathodes.

Rechargeable Aqueous Aluminum Organic Batteries.

Aqueous aluminum-ion batteries (AABs) are regarded as promising next-generation energy storage devices, and the current reported cathodes for AABs mainly focused on inorganic materials which usually implement a typical Al3+ ions (de)insertion mechanism. However, the strong electrostatic forces between Al3+ and the host materials usually lead to sluggish kinetics, poor reversibility and inferior cycling stability. Herein, we employ an organic compound with redox-active moieties, phenazine (PZ), as the cathode material in AABs. Different from conventional inorganic materials confined by limited lattice spacing and rigid structure, the flexible organic molecules allow a large-size Al-complex co-intercalation through reversible redox active centers (-C=N-) of PZ. This co-intercalation behavior can effectively reduce desolvation penalty, and substantially lower the Coulombic repulsion during the ion (de)insertion process. Consequently, this organic cathode exhibits a high capacity and excellent cyclability, which exceeds those of most reported electrode materials for AABs. This work highlights the anion co-intercalation chemistry of redox-active organic materials, which is expected to boost the development of high-performance multivalent-ion battery systems.

Anthraquinone-Based Oligomer as a Long Cycle-Life Organic Electrode Material for Use in Rechargeable Batteries.

An anthraquinone (AQ)-based dimer and trimer linked by a triple bond (-C≡C-) were newly synthesized as active materials for the positive electrode of rechargeable lithium batteries. These synthesized oligomers exhibited an initial discharge capacity of about 200 mAh g-1 with an average voltage of 2.2-2.3 V versus Li(C.E.) . These capacity values are similar to that of the AQ-monomer, reflecting the two-electron transfer redox per AQ unit. Regarding their cycling stability, the capacity of the monomer electrode quickly decreased; however, the electrodes of the prepared oligomers showed an improved cycling performance. In particular, the discharge capacities of the trimer remained almost constant for 100 cycles. A theoretical calculation revealed that the intermolecular binding energy can be increased to the level of a weak covalent bonding by oligomerization, which would be beneficial to suppress the dissolution of the organic active materials into the electrolyte solutions. These results show that the cycle-life of organic active materials can be extended without lowering the discharge capacity by the oligomerization of the redox active molecule unit.

Facile Synthesis of Diazaanthraquinone Dimers as High-Capacity Organic Cathode Materials for Rechargeable Lithium Batteries.

Organic cathode materials (OCMs) have tremendous potential to construct sustainable and highly efficient batteries beyond conventional Li-ion batteries. Thereinto, quinone/pyrazine hybrids show significant advantages in material availability, energy density, and cycling stability. Herein, we propose a facile method to synthesize quinone/pyrazine hybrids, i.e., the condensation reaction between ortho-diamine and bromoacetyl groups. Based on it, we have successfully synthesized three 1,4-diazaanthraquinone (DAAQ) dimers, including 2,2'-bi(1,4-diazaanthraquinone) (BDAAQ) with an exceptional theoretical capacity of 512 mAh g-1 based on the eight-electron reaction. It can be fully utilized in Li batteries in a wide voltage range of 0.8-3.8 V, at the cost of inferior cycling stability. In an optimal voltage range of 1.4-3.8 V, BDAAQ exhibits one of the best comprehensive electrochemical performances for small-molecule OCMs, including a high specific capacity of 366 mAh g-1, an average discharge voltage of 2.26 V, as well as a respectable capacity retention of 59% after 500 cycles. Moreover, the in-depth investigations reveal the redox reaction mechanisms based on C═O and C═N groups as well as the capacity fading mechanisms based on dissolution-redeposition behaviors. In brief, this work provides an instructive synthesis method and mechanism understanding of high-performance OCMs based on a quinone/pyrazine hybrid structure.

Cost-Effective Rechargeable Magnesium Battery Based on a Fluorinated Alkoxyaluminate Electrolyte and a Carbonyl Polymer Cathode.

Rechargeable magnesium batteries (RMBs) are one of the most promising "post-lithium" battery technologies, but the electrochemical performance is still far from expectation due to the sluggish reaction kinetics of divalent Mg2+ ions. Herein, we report a low-cost, high-performance Mg-organic battery based on the combination of a fluorinated alkoxyaluminate electrolyte and a carbonyl polymer cathode material. First, the one-pot synthesized Mg[Al(HFIP)4]2 (HFIP = hexafluoro-2-propanol) is proved superior to the Mg[B(HFIP)4]2 analogue in both Mg anode compatibility and electrochemical window, as the electrolyte salt in the G2-DME (G2 = diethylene glycol dimethyl ether; DME = 1,2-dimethoxyethane) mixture solvent. Second, a simple wet grinding method is proposed to effectively improve the dispersion uniformity of the poly(benzoquinone-pyrrole) (PBQPy) active material in the cathode. Third, the elaborate Mg-PBQPy battery exhibits superior electrochemical performance within 0.4-3.0 V, including a high reversible capacity of 197 mA h g-1, a high average discharge voltage of 1.6 V, and a high capacity retention of 71% after 500 cycles. Finally, based on various electrochemical analysis and ex situ characterization results, we propose a general microscopic structure evolution model to reveal the electrochemical behaviors of carbonyl polymer cathode in RMBs, including the swelling of polymer active material, trapping of Mg2+ ions, and reversible redox reaction.

Switchable Design of Redox-Enhanced Nonaromatic Quinones Enabled by Conjugation Recovery.

An innovative switchable design strategy for modulating the electronic structures of quinones is proposed herein, leading to remarkably enhanced intrinsic redox potentials by restoring conjugated but nonaromatic backbone architectures. Computational validation of two fundamental hypotheses confirms the recovery of backbone conjugation and optimal utilization of the inductive effect in switched quinones, which affords significantly improved redox chemistry and overall performance compared to reference quinones. Geometric and electronic analyses provide strong evidence for the restored backbone conjugation and nonaromaticity in the switched quinones, while highlighting the reinforcement of the inductive effect and suppression of the resonance effect. This strategic approach facilitates the development of an exceptional quinone, viz. 2,6-naphthoquinone, with outstanding performance parameters (338.9 mAh g-1 and 912.9 mWh g-1). Furthermore, 2,6-anthraquinone with superior cyclic stability, demonstrates comparable performance (257.4 mAh g-1 and 702.8 mWh g-1). These findings offer valuable insights into the design of organic cathode materials with favorable redox chemistry in secondary batteries.

Revisit of Polyaniline as a High-Capacity Organic Cathode Material for Li-Ion Batteries.

Polyaniline (PANI) has long been explored as a promising organic cathode for Li-ion batteries. However, its poor electrochemical utilization and cycling instability cast doubt on its potential for practical applications. In this work, we revisit the electrochemical performance of PANI in nonaqueous electrolytes, and reveal an unprecedented reversible capacity of 197.2 mAh g-1 (244.8 F g-1) when cycled in a wide potential range of 1.5 to 4.4 V vs. Li+/Li. This ultra-high capacity derives from 70% -NH- transformed to =NH+- during deep charging/discharging process. This material also demonstrates a high average coulombic efficiency of 98%, an excellent rate performance with 73.5 mAh g-1 at 1800 mA g-1, and retains 76% of initial value after 100 cycles, which are among the best reported values for PANI electrodes in battery applications.

Long Cycle Life for Rechargeable Lithium Battery using Organic Small Molecule Dihydrodibenzo[c,h][2,6]naphthyridine-5,11-dione as a Cathode after Isoindigo Pigment Isomerization.

Sustainability and adaptability in structural design of the organic cathodes present promises for applications in alkali metal ion batteries. Nevertheless, a formidable challenge lies in their high solubility in organic electrolytes, particularly for small molecular materials, impeding cycling stability and high capacity. This study focuses on the design and synthesis of organic small molecules, the isomers of (E)-5,5'-difluoro-[3,3'-biindolinylidene]-2,2'-dione (EFID) and 3,9-difluoro-6,12-dihydrodibenzo [c, h][2,6]naphthyridine-5,11-dione (FBND). While EFID, characterized by a less π-conjugated structure, exhibits subpar cycling stability in lithium-ion batteries (LIBs), intriguingly, another isomer, FBND, demonstrates exceptional capacity and cycling stability in LIBs. FBND delivers a remarkable capacity of 175 mAh g-1 at a current density of 0.05 A g-1 and maintains excellent cycling stability over 2000 cycles, retaining 90% of its initial capacity. Furthermore, an in-depth examination of redox reactions and storage mechanisms of FBND are conducted. The potential of FBND is also explored as an anode in lithium-ion batteries (LIBs) and as a cathode in sodium-ion batteries (SIBs). The FBND framework, featuring extended π-conjugated molecules with an imide structure compared to EFID, proves to be an excellent material template to develop advanced organic small molecular cathode materials for sustainable batteries.