Organic Rechargeable Batteries Research Articles

Unlocking the Full Redox Capability of Organic Charge‐Transfer Complex in High‐Loading Electrodes for Organic Rechargeable Batteries

AbstractOrganic charge‐transfer complex (OCTC) comprising redox‐active donor and acceptor molecules is a promising electrode material group, potentially resolving issues of low power and inferior cycle stability of organic electrodes in rechargeable batteries. Strong intermolecular interactions in OCTC such as π–π interaction and hydrogen bonding enable high electronic conductivity and suppress solubility to solvents. However, full redox activities of OCTC have not been achieved yet despite the inherent redox capabilities of respective donor and acceptor molecules. Here, it is revealed that the limited redox activities of OCTC stem from electrolyte‐incorporated complex formation, which weakens the characteristic intermolecular interactions, thereby hindering the redox reaction, particularly in Li‐based electrolytes. It is further shown that tailoring electrolyte types, specifically using Zn‐aqueous electrolytes, can substantially mitigate the complex formation and unlock the four‐electron redox activity of OCTC (phenazine (PNZ)‐7,7,8,8‐tetracyanoquinodimethane (TCNQ), that is, PNZ–TCNQ), with superior cycle stability retaining 88% of maximum capacity over 100 cycles. Surprisingly, the full redox reaction achieves an unprecedentedly high electrode‐level energy density, delivering ≈10 mAh cm−2 of areal capacity (580 µm‐thick electrodes) in Zn‐aqueous batteries. The findings elucidate the complex interplay between organic electrodes and electrolytes in the charge storage mechanism, highlighting the importance of electrolyte design in developing organic electrode materials.

A Porphyrin-Phenylalkynyl-Based Conjugated Organic Polymer as a High-Performance Cathode for Rechargeable Organic Batteries.

Organic electrode materials (OEMs) have attracted much attention for rechargeable batteries due to their low cost, environment friendliness, flexibility, and structural versatility. Despite the above advantages, high solubility in electrolyte and low electronic conductivity remain critical limitations for the application of OEMs. In this work, the conjugated organic polymer (COP) poly([5,10,15,20-tetrakis(4-phenylalkynyl)porphyrin]Cu(II)) (PCuTPEP) is proposed as a cathode for high performance in organic lithium batteries. The polymerization inhibits the dissolution of the organic electrodes in the electrolyte, and the porphyrin and ethynyl-phenyl groups greatly expand the conjugated system and result in a high average discharge plateau at 4.0 V (vs Li+/Li). The PCuTPEP cathode exhibits a reversible discharge capacity of 119 mAh g-1 at a current of 50 mA g-1. Even at a high current density of 2.0 A g-1, excellent cycling stability up to 1000 cycles is achieved with capacity retentions of 88.5 and 90.4% at operating temperatures of 25 and 50 °C in organic lithium batteries, respectively. This study provides the approach for the development of organic cathodes for electrochemical energy storage.

High performance phenothiazine-based battery materials achieved by synergistic steric blocking and extended conjugation

Phenothiazine derivatives, as sustainable cathode materials for batteries, show significant promise for large-scale electrical energy storage applications. However, the irreversibility of the sulfur redox active center severely limits their energy density and discharge voltage in rechargeable organic batteries. This study concentrates on identifying the potential side reactions that contribute to the irreversibility of phenothiazine-based materials. We propose a molecular design strategy that synergistically blocks the active site and extends the conjugation, markedly improving the electrochemical reversibility of these materials. Our findings reveal that phenothiazine derivatives can undergo two successive, one-electron redox reactions without interference from chemical bond rearrangement and reactive radicals. The assembled cells, utilizing lithium (Li) and sodium (Na) as anodes, display two distinct discharge plateaus at 3.3/3.9 V vs. Li+/Li and 3.1/3.7 V vs. Na+/Na, respectively, with nearly identical contributions from the nitrogen (N) and sulfur (S) redox centers. The phenothiazine derivatives designed via this strategy rank among the few phenothiazine-based organic electrode materials capable of achieving highly reversible, two-electron transfer redox reactions in organic batteries.

Pillar[5]arene-supported viologen networks with enhanced rate capability and cycling stability for rechargeable organic batteries

Organic redox-active compounds are promising alternatives to traditional inorganic counterparts because of their sustainable resources and highly tunable properties. However, their solubility in organic electrolyte solvents and the sluggish electrode reactions hinder their further development. Herein, an intrinsically microporous decabromopropyl pillar[5]arene (P5Br) was used to support the methyl viologen (MV) functionality to yield two non-crosslinked and crosslinked organic electrode materials, namely MV-P5Br and CMV-P5Br, respectively. When evaluating against Li metal counter electrode, the MV-P5Br and CMV-P5Br electrodes delivered high discharge capacities of 87.9 and 92.7 mAh g−1 at 0.1 C, respectively, which are close to their theoretical values. After galvanostatic cycling at 0.1 C for 100 cycles, the CMV-P5Br electrode maintained a discharge capacity of 82.3 mAh g−1, much higher than the 43.7 mAh g−1 of the MV-P5Br electrode. When the current rate was increased to 10 C, the CMV-P5Br electrode delivered a discharge capacity of 60.7 mAh g−1, also higher than the 41.3 mAh g−1 of the MV-P5Br electrode. The increased cycling stability and rate performance of the CMV-P5Br electrode were attributed to the diminished solubility and the enhanced ion diffusion coefficient of the active material. When the counter electrode was changed to Na metal, similar results were obtained, suggesting that the CMV-P5Br electrode can also be used in Na-ion systems. This study demonstrates that the combination of crosslinked and microporous structure is highly effective to boost the electrochemical performance of organic redox-active compounds for rechargeable batteries.

Recycling Compatible Organic Electrode Materials Containing Amide Bonds for Use in Rechargeable Batteries.

Organic rechargeable batteries that do not use any scarce heavy metals are candidates for the next generation of rechargeable batteries; although, it is not easy to realize both high capacity and long cycle life. Organic compounds linked by amide bonds are expected to have superior recycling properties after battery degradation, since they will become a single monomer upon hydrolysis. In this study, anthraquinone was chosen as a model redox active unit, and dimeric and trimeric compounds were synthesized, their cycle performances as electrode materials for use in rechargeable batteries were compared, and a trend in which oligomerization improves cycle properties was confirmed. Furthermore, quantum chemistry calculations suggest that oligomerization decreases solubility, which would support a longer life for oligomerized compounds. This methodology will lead to the development of organic rechargeable batteries with further environmental benefits.

Modulation of Radical Intermediates in Rechargeable Organic Batteries.

Organic materials have been considered as promising electrodes for next-generation rechargeable batteries in view of their sustainability, structural flexibility, and potential recyclability. The radical intermediates generated during the redox process of organic electrodes have profound effect on the reversible capacity, operation voltage, rate performance, and cycling stability. However, the radicals are highly reactive and have very short lifetime during the redox of organic materials. Great efforts have been devoted to capturing and investigating the radical intermediates in organic electrodes. Herein, this review summarizes the importance, history, structures, and working principles of organic radicals in rechargeable batteries. More importantly, challenges and strategies to track and regulate the radicals in organic batteries are highlighted. Finally, further perspectives of organic radicals are proposed for the development of next-generation high-performance rechargeable organic batteries.

Two-Dimensional Covalent Organic Framework with Synergistic Active Centers for Efficient Electrochemical Sodium Storage

Benefiting from the adjustable molecule structures, abundant functional units, large specific surface areas, and ordered pores, covalent organic frameworks (COFs) are highly desirable for electrochemical energy storage. Herein, a two-dimensional COF (denoted as HHTP-TABQ) with a fully π-conjugated framework and C═N and C═O dual-active sites has been synthesized and applied as the anode in organic rechargeable sodium-ion batteries (SIBs). During the sodium-storage process, it delivered remarkable rate capability, satisfactory ultra-long cycle stability (84.5% capacity retention ratio after 1000 cycles at 5000 mA g–1), and facile charge exchange kinetics (2.49 × 10–7 cm2 s–1), which is superior among most reported COF-based electrodes. Furthermore, the sodiation mechanism was investigated by density functional theory calculations and ex situ characterizations, which confirms that the electrochemical reaction is dominated by the synergistic reaction of C═N and C═O groups. These results suggest that COFs with stable π-conjugated structures, insoluble characteristics, and abundant active sites would have great potential for practical applications in rechargeable SIBs.

Synthesis of Nitrogen-Conjugated 2,4,6-Tris(pyrazinyl)-1,3,5-triazine Molecules and Electrochemical Lithium Storage Mechanism

Organic anode materials for lithium-ion battery have attracted widespread attention due to their diversity in organic linker functional species and the ability to tune their molecular levels. However, the rational design of advanced organic anodes with high reversible capacity and intentional organic molecular design requires a deep understanding of their mechanism for use in small-molecule organic rechargeable batteries. Herein, an optimized small-molecule-based organic anode material containing highly efficient active sites was developed for use in an organic lithium-ion battery. A small-molecule organic compound, 2,4,6-tris(pyrazinyl)-1,3,5-triazine (TPT), was formed by the trimerization of the 2-cyanopyrazine monomer. This molecule was rationally designed and evaluated as a lithium-ion battery organic anode material. TPT has a relatively small structure, but a superior reversible specific capacity was still achieved. Excitingly, TPT2 (liquid-phase synthetic) released a reversible capacity of 622 mAh g–1 at 100 mA g–1. Moreover, impressive long-term cycling performance was obtained, with a storage capacity of 541 mAh g–1 at 800 mA g–1 after 500 cycles. This demonstrated the durable cyclic stability of TPT2, which also achieved excellent rate performance at different current densities from 100 mA g–1 to 1.6 A g–1. The lithium storage mechanism of TPT was studied by theoretical calculations and ex situ Fourier transform infrared spectroscopy (FTIR) combined with X-ray photoelectron spectroscopy (XPS) characterization, which demonstrated that multiple active sites consisting of −C–N and −C═N groups were responsible for its superior lithium storage performance. This study provides a new understanding of the energy storage mechanism in small-molecule organic-based anode electrodes.

Lithium-Conducting Organic Solid Electrolyte for Organic Rechargeable Batteries: Boronated Benzoimidazole-Linked Polymer

Some of the Benzimidazole-linked polymers (BILPs) are a class of porous organic polymers that have high porosities, large specific surface areas, and high thermal and chemical stability. Owing to these properties, BILPs can be used in various applications including solid electrolytes for renewable energy utilization. In this study, we carried out the boran-modification of a kind of BILPs, in order to increase the Li ion conductivity by decreases the interaction between lithium ions and the anion backbone. The resulting B-TFB-HAB-BILP materials have an ionic conductivity of 2.9 × 10−6 S cm−1 at 30 °C, which increases to 1.4 × 10−4 S cm−1 at room temperature with the addition of the ionic liquid, PP13[TFSA]. This can be attributed to the suppression of resistance at the grain boundary. A coin cell with an organic cathode active material, B-TFB-HAB-BILP/PP13[TFSA] as the quasi-solid electrolyte, and Li foil as the anode exhibited an initial discharge capacity of 223 mAh g−1 (76 % of theoretical capacity). Our study can aid in the realization of organic rechargeable batteries with high gravimetric energy density.

Validating the reversible redox of alkali-ion disulfonyl-methanide as organic positive electrode materials

Alkali-ion reservoir organic positive electrode materials with high redox potential emerge as promising candidates for rocking-chair batteries. Despite recent major advances on coordinated Li-enolates and conjugated Li-sulfonamides, alike chemistries remain rare with clearly enormous room to explore and investigate. Herein, we report a new high-voltage redox functionality for alkali-ion storage based on aromatic di-sulfonyl methanide. The versatile paradigm chemistry of di-alkali p-phenylene-bis-diethylsulfonyl methanide (denoted as A2-p-TESO2, where A = Li+, Na+, K+) displays high voltage (3.13 vs Li+/Li), a two-electron reversible redox in both liquid phase and solid phase electrochemistry. A2-p-TESO2 also shows great stability under ambient air conditions in their alkali-ion reservoir states. This work not only suggests a new charge storage mechanism for organic batteries but also highlights the versatility of organic chemistry in designing new redox functionalities for next-generation organic rechargeable batteries.

N -Heterocycles Extended π-Conjugation Enables Ultrahigh Capacity, Long-Lived, and Fast-Charging Organic Cathodes for Aqueous Zinc Batteries

<i>N</i> -Heterocycles Extended π-Conjugation Enables Ultrahigh Capacity, Long-Lived, and Fast-Charging Organic Cathodes for Aqueous Zinc Batteries

Pyrazine and crown ethers: functional covalent organic polymers for (solar-assisted) high capacity and rate performance lithium-organic battery

Multifunctional two-dimensional (2D) covalent organic polymers (COPs) benefiting from unique features display great potential in lithium-organic batteries yet are rarely reported. In this work, we fabricate a novel conjugated polymer (TQ-COP) functioned with flexible crown ethers and pyrazine redox-active sites, used as an organic rechargeable battery cathode. The Fourier transform infrared spectroscopy (FT-IR) and 13C cross-polarization and magic-angle spinning nuclear magnetic resonance (MAS NMR) verify the chemical identity of redox-active units formed during polymerization. In this structure, pyrazine-redox components exhibit a maximum six-electron transfer per active site, resulting in an initial specific capacity of 162 mA h/g(20 mA/g). Because of macrocyclic cavities and preferential coordination with the alkali metal ions of crown ethers, the rate determining step is changed into a charge transfer process, urging TQ-COP to emerge with a superior rate performance (132 mA h/g at 2 C, 81% vs. 0.1 C). Furthermore, the introduction of crown ethers facilitates photo-excited charge-carriers transfer by narrowing the HOMO-LUMO gap, rendering a photo-assisted lithium-organic battery with significant photovoltage responses and ∼10% improvement of battery round-trip efficiency under illumination, demonstrating its promising capability of solar energy utilization. This work proposes new insights into multifunctional COPs for advanced lithium-organic batteries.

Polypeptide Radical Cathode for Aqueous Zn-Ion Battery with Two-Electron Storage and Faster Charging Rate.

The rapidly growing demand for batteries has led to a lack of global mineral resources and rechargeable organic batteries are paid extensive attention, owing to the abundance resources, light weight, and high flexibility of organic electrodes. However, most organic electrodes that use aliphatic backbones are nondegradable, leading to unsustainability when active sites fail. In this study, a poly(aspartic acid) polypeptide (PASP) with amide links in the backbone and nitroxide radical pendant groups in the side chains is synthesized by modifying the polypeptides with 4-amino-2,2,6,6-tetramethylpiperidine. In combination with a Zn anode, the PASP-TEMPO composite electrode exhibits rapid charge-discharge and superior cycling stability with reversible two-electron redox reaction in aqueous electrolyte. The Zn/PASP-TEMPO organic radical battery delivers a discharge capacity of around 80 mAh g-1 by two-electron reaction and charge-discharge rates of up to 18 A g-1 . Because the redox reaction process of the nitroxyl radical turning into oxoammonium follows a p-type mechanism that interacts with an anion, three electrolytes with different anions are tested in the Zn/PASP-TEMPO organic radical battery. Experimental results indicate that discharge plateau voltage is tunable by choosing different zinc salts as electrolytes. Capacity retention of up to 97.4 % after 500 cycles is realized in 1 m ZnClO4 electrolyte, which can be attributed to the adjacent reaction potentials of the two-step one-electron reaction.

Biredox-Ionic Anthraquinone-Coupled Ethylviologen Composite Enables Reversible Multielectron Redox Chemistry for Li-Organic Batteries.

Organic compounds bearing redox‐active ionic pairs as electrode materials for high‐performance rechargeable batteries have gained growing attention owing to the properties of synthetic tunability, high theoretical capacity, and low solubility. Herein, an innovative biredox‐ionic composite, i.e., ethylviologen dianthraquinone‐2‐sulfonate (EV‐AQ2), affording multiple and reversible active sites as a cathode material in lithium‐organic batteries is reported. EV‐AQ2 exhibits a high initial capacity of 199.2 mAh g−1 at 0.1 C rate, which corresponds to the transfer of two electrons from one redox couple EV2+/EV0 and four electrons from two redox‐active AQ− anions. It is notable that EV‐AQ2 shows remarkably improved cyclability compared to the precursors. The capacity retention is 89% and the Coulombic efficiency approaches 100% over 120 cycles at 0.5 C rate. The results offer evidence that AQ− into the EV2+ scaffold with multiple redox sites are promising in developing high‐energy‐density organic rechargeable batteries.

Synthesis and Properties of Fused Extended Tetrathiafulvalene Donors with Dithienylmethylene Spacer and Application to Organic Rechargeable Batteries

Abstract Several derivatives of 1,3-dithiole[3]dendralene derivatives with two thiophene spacers (2) were synthesized. The results of an X-ray structure analysis of an analog without fused TTF units and a DFT calculation of the unsubstituted-2 (2Aa) suggested that 2Aa had a structure significantly distorted between the central 1,3-dithiole (DT) ring and one of the thiophene rings. Cyclic voltammograms of tetrakis(n-hexylsulfanyl) derivatives (2Be and 2Ce) consisted of one pair of two-electron redox waves and five pairs of one-electron redox waves in correspondence with the presence of seven redox-active DT rings. The tetrakis(methylsulfanyl) or bis(ethylenedithio) derivative (2Bc or 2Bd) worked as a positive electrode material for lithium-ion batteries, and the 2Bc/Li and 2Bd/Li cells exhibited the first discharge capacities of 133–138 mAh g−1.

The synthesis of the D-A-type polymers containing benzo[1,2-b:6,5-b′]dithiophene-4,5-dione unit, their composites with carbon, and the lithium storage performances as electrode materials

Two novel donor-acceptor (D-A)-conjugated polymers, poly[(thiophene-2,5-yl)-((benzo[1,2-b:6,5-b′]dithiophene-4,5-dione)-2,7-yl)] (PTDT) and poly[((2,3-dihydrothieno[3,4-b] [1, 2]dioxine)-5,7-diyl)-((benzo[1,2-b:6,5-b′]dithiophene-4,5-dione)-2,7-diyl)] (PTDO), have been synthesized with the same acceptor unit of benzo[1,2-b:6,5-b′]dithiophene-4,5-dione and different donor units of thiophene (Th) and 3,4-ethylenedioxothiphene (EDOT), respectively. And then, two composites (PTDT@C and PTDO@C) are made by coating the polymers on the surface of active carbon with an in situ method, which are used as the electrode materials of lithium-ion battery. The reversible capacities of PTDT@C and PTDO@C are 246.9 and 322.3 mAh g−1 at 0.1 A g−1 after 300 cycles running, respectively. By deducing the capability contribution of pure carbon, the theoretical capacities of the pure polymers are calculated to be 596 and 991 mAh g−1, respectively, for PTDT and PTDO, which correspond to the lithium storage number of 6.7 and 13.3, respectively, for the least repeating unit of the polymers. With the help of theoretical calculations, the underlying mechanisms for the different electrochemical performances of the polymers are discussed and revealed. The structure-activity relationship discussed in this work may provide the design principle for the construction of the D-A-type polymers used as high-capacity electrode materials for organic rechargeable batteries.

Functional separator with a lightweight carbon-coating for stable, high-capacity organic lithium batteries

• A C@PP separator is proposed to suppress the shuttle of quinone electrodes. • Inhibitory shuttle correlates with the physical barrier and excellent adsorption. • The separator increases the utilization of PT cathode for high capacities. • The other three quinone cathodes also exhibit greatly improved performances. A major challenge facing organic rechargeable batteries is the problem of the dissolution and shuttle effect of organic cathodes in aprotic electrolytes, resulting in limited capacity, low cyclability and poor rate performance. Herein, a functional polypropylene separator coated with Ketjen black (C@PP) was introduced to tackle the shuttle issue. The inhibitory effect on quinone shuttle correlates with physical barrier and excellent adsorption of Ketjen black (KB), as proved by a series of spectroscopy studies. With the C@PP separator, quinone cathodes including pentacene-5,7,12,14-tetrone (PT), Calix[4] quinone (C4Q), 9,10-anthraquinone (AQ) and 9,10-phenanthrenequinone (PQ) demonstrated high reversible capacity and excellent cyclic stability in Li storage. Specially, PT exhibited high capacity (>300 mAh g −1 ), long-term cyclability (~0.06% decay per cycle over 400 cycles at 0.5 C) and fast kinetic (5 C). C4Q delivered high energy density (782 Wh kg −1 ) and respectable cyclability (~60% after 500 cycles). This facile and versatile separator modifying strategy opens a new avenue for solving quinone electrode issues to achieve high-performance OLBs.

Stabilization of Organic Cathodes by a Temperature-Induced Effect Enabling Higher Energy and Excellent Cyclability.

To face the challenge of all-climate application, organic rechargeable batteries must hold the capability of efficiently operating both at high temperatures (>50 °C) and low temperatures (-20 °C). However, the low electronic conductivity and high solubility of organic molecules significantly impede the development in electrochemical energy storage. This issue can be effectively diminished using functionalized porphyrin complex-based organic cathodes by the in-situ electropolymerization of electrodes at elevating temperatures during electrochemical cycling. [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP)- and 5,15-bis(ethynyl)-10,20-diphenylporphinato (DEPP)-based cathodes are proposed as models, and it is proved that a largely improved electrochemical performance is observed in both cathodes at a high operating temperature. Reversible capacities of 249 and 105 mA h g-1 are obtained for the CuDEPP and DEPP cathodes after 1000 cycles at 50 °C, respectively. The result indicates that the temperature-induced in situ electropolymerization strategy responds to the enhanced electrochemical performance. This study would open new opportunities for developing highly stable organic cathodes for electrochemical energy storage even at high temperatures.

Permselective metal-organic framework gel membrane enables long-life cycling of rechargeable organic batteries.

Rechargeable organic batteries show great potential as a low-cost, sustainable and mass-producible alternatives to current transition-metal-based cells; however, serious electrode dissolution issues and solubilization of organic redox intermediates (shuttle effect) have plagued the capacity retention and cyclability of these cells. Here we report on the use of a metal-organic framework (MOF) gel membrane as a separator for organic batteries. The homogeneous micropores, intrinsic of the MOF-gel separator, act as permselective channels for targeted organic intermediates, thereby mitigating the shuttling problem without sacrificing power. A battery using a MOF-gel separator and 5,5'-dimethyl-2,2'-bis-p-benzoquinone (Me2BBQ) as the electrode displays high cycle stability with capacity retention of 82.9% after 2,000 cycles, corresponding to a capacity decay of ~0.008% per cycle, with a discharge capacity of ~171 mA h g-1 at a current density of 300 mA g-1. The molecular and ionic sieving capabilities of MOF-gel separators promise general applicability, as pore size can be tuned to specific organic electrode materials. The use of MOF-gel separators to prevent side reactions of soluble organic redox intermediates could lead to the development of rechargeable organic batteries with high energy density and long cycling life.

Redox chemistry of nitrogen-doped CNT-encapsulated nitroxide radical polymers for high energy density and rate-capability organic batteries

To enhance the electrochemical performance and identify the redox reaction of a nitroxide radical-based organic battery, poly(2,2,6,6-tetramethylpiperidinyloxy-4-vinylmethacrylate) (PTMA) as nitroxide radical polymer is synthesized and used to fill the central pore of nitrogen-doped carbon nanotubes (NCNTs). The PTMA-filled NCNTs demonstrate high rate capability, stable cycling, and high electrode stability, owing to their high charge transfer and ion diffusion; further, they prevent the dissolution of organic active material. The nitrogen doping on CNTs improves the electrochemical properties by created defects. The PTMA-filled NCNT cells have a high reversible capacity of 199.8 mAh g−1 and high energy density of 489.4 Wh kg−1 on electrode level at 0.2C with a two-step redox couple. Moreover, the cells with the two-step redox couple exhibit excellent stable cycle performance with high capacity retention and Coulombic efficiency for 3000 cycles. The nitroxide radical of PTMA can be converted to either an oxoammonium cation or an aminoxy anion; further, the redox reaction of each step exhibits different performance. The nitroxide radical–oxoammonium cation redox step in NCNTs shows a high rate capability owing to the high charge transfer rate and ion diffusion coefficient. The unusual results will help further improve the properties and commercialization of rechargeable organic batteries.