Organic Cathode Research Articles

Tuning electron delocalization of hydrogen-bonded organic framework cathode for high-performance zinc-organic batteries

Stable cathodes with multiple redox-active centres affording a high energy density, fast redox kinetics and a long life are continuous pursuits for aqueous zinc-organic batteries. Here, we achieve a high-performance zinc-organic battery by tuning the electron delocalization within a designed fully conjugated two-dimensional hydrogen-bonded organic framework as a cathode material. Notably, the intermolecular hydrogen bonds endow this framework with a transverse two-dimensional extended stacking network and structural stability, whereas the multiple C = O and C = N electroactive centres cooperatively trigger multielectron redox chemistry with super delocalization, thereby sharply boosting the redox potential, intrinsic electronic conductivity and redox kinetics. Further mechanistic investigations reveal that the fully conjugated molecular configuration enables reversible Zn2+/H+ synergistic storage accompanied by 10-electron transfer. Benefitting from the above synergistic effects, the elaborately tailored organic cathode delivers a reversible capacity of 498.6 mAh g−1 at 0.2 A g−1, good cyclability and a high energy density (355 Wh kg−1).

Long Cycle-Life Ca Batteries with Poly(anthraquinonylsulfide) Cathodes and Ca-Sn Alloy Anodes.

Calcium (Ca) batteries are attractive post-lithium battery technologies, due to their potential to provide high-voltage and high-energy systems in a sustainable manner. We investigated herein 1,5-poly(anthraquinonylsulfide) (PAQS) for Ca-ion storage with calcium tetrakis(hexafluoroisopropyloxy)borate Ca[B(hfip)4 ]2 [hfip=OCH(CF3 )2 ] electrolytes. It is demonstrated that PAQS could be synthesized in a cost-effective approach and be processed environmentally friendly into the electrodes. The PAQS cathodes could provide 94 mAh g-1 capacity at 2.2 V vs. Ca at 0.5C (1C=225 mAh g-1 ). However, cycling of the cells was severely hindered due to the fast degradation of the metal anode. Replacing the Ca metal anode with a calcium-tin (Ca-Sn) alloy anode, the PAQS cathodes exhibited long cycling performance (45 mAh g-1 at 0.5C after 1000 cycles) and superior rate capability (52 mAh g-1 at 5C). This is mainly ascribed to the flexible structure of PAQS and good compatibility of the alloy anodes with the electrolyte solutions, which allow reversible quinone carbonyl redox chemistry in the Ca battery systems. The promising properties of PAQS indicate that further exploration of the organic cathode materials could be a feasible direction towards green Ca batteries.

A Self‐Healing Chemistry‐Enabled Organic Cathode for Sustainable and Stable Sodium‐Ion Batteries

Sodium‐on batteries (SIBs) are promising alternatives to lithium‐ion batteries (LIBs) because of the low cost, abundance, and high sustainability of sodium resources. Analogous to LIBs, the high‐capacity electrodes in SIBs always suffer from rapid capacity decay upon long‐term cycling due to the particle pulverization induced by a large volume change. Circumventing particle pulverization plays a critical role in developing high‐energy and long‐life SIBs. Herein, tetrahydroxy‐1,4‐benzoquinone disodium salt (TBDS) that can self‐heal the cracks by hydrogen bonding between hydroxyl group and carbonyl group is employed as a cathode for sustainable and stable SIBs. The self‐healing TBDS exhibits long cycle life of 1000 cycles with a high rate capability up to 2 A g−1 due to the fast Na‐ion diffusion reaction in the TBDS cathode. The intermolecular hydrogen bonding has been comprehensively characterized to understand the self‐healing mechanism. The hydrogen bonding‐enabled self‐healing organic materials are promising for developing high‐energy and long‐cycle‐life SIBs.

Trimming the Degrees of Freedom via a K+ Flux Rectifier for Safe and Long-Life Potassium-Ion Batteries

HighlightsHigh Coulombic efficiency of over 99% for dendrite-free K||Cu cell after 820 cycles.Year-scale-cycling performance of organic PTCDI cathode over 2,100 cycles.Flexible device demonstration such as fibre cell still could operate when cut into three fibre cells.

Toward Full Utilization and Stable Cycling of Polyaniline Cathode for Nonaqueous Rechargeable Batteries

AbstractPolyaniline is the most famous conducting polymer and also a promising organic cathode material for rechargeable batteries, however, it has demonstrated poor utilization of its theoretical capacity (294 mAh g−1) and inferior cycling stability in previous studies. Herein, for the first time, its fully reduced form, i.e., leucoemeraldine base (LB), is studied as an alternative to the commonly used emeraldine salt and base (ES and EB). For the three different forms, the precise structures are carefully determined, and the electrochemical performance are systematically investigated. Within 2.0−4.3 V, LB realizes almost full capacity utilization (92%) that is much superior to those of ES and EB. Within 2.0−4.2 V, it shows both high reversible capacity (277 mAh g−1) and cycling stability (84% capacity retention after 1000 cycles). The combination of electrochemical analysis, density functional theory calculation, and ex situ characterization reveals that the capacity utilization is positively associated with the pristine proportion of ─NH─ groups, and the capacity fading is caused by the irreversible electrochemical deprotonation at high charge potential. This work promotes both the electrochemical performance and mechanistic understanding of polyaniline to a new stage, towards practical application in energy storage devices as a low‐cost, high‐performance, sustainable, and green cathode material.

Designing 3D Porous Organic Polymers for High-Performance Organic Battery Cathodes

Designing 3D Porous Organic Polymers for High-Performance Organic Battery Cathodes

Long‐Life, High‐Rate Rechargeable Lithium Batteries Based on Soluble Bis(2‐pyrimidyl) Disulfide Cathode

AbstractOrganosulfides are promising candidates as cathode materials for the development of electric vehicles and energy storage systems due to their low‐cost and high capacity properties. However, they generally suffer from slow kinetics because of the large rearrangement of S−S bonds and structural degradation upon cycling in batteries. In this paper, we reveal that soluble bis(2‐pyrimidyl) disulfide (Pym2S2) can be a high‐rate cathode material for rechargeable lithium batteries. Benefiting from the superdelocalization of pyrimidyl group, the extra electrons prefer to be localized on the π* (pyrimidyl group) than σ* (S−S bond) molecular orbitals initially, generating the anion‐like intermedia of [Pym2S2]2− and thus decreasing the dissociation energy of the S−S bond. It makes the intrinsic energy barrier of dissociative electron transfer depleted, therefore the lithium half cell exhibits 2000 cycles at 5 C. This study provides a distinct pathway for the design of high‐rate, long‐cycle‐life organic cathode materials.

Long-Life, High-Rate Rechargeable Lithium Batteries Based on Soluble Bis(2-pyrimidyl) Disulfide Cathode.

Organosulfides are promising candidates as cathode materials for the development of electric vehicles and energy storage systems due to their low-cost and high capacity properties. However, they generally suffer from slow kinetics because of the large rearrangement of S-S bonds and structural degradation upon cycling in batteries. In this paper, we reveal that soluble bis(2-pyrimidyl) disulfide (Pym2 S2 ) can be a high-rate cathode material for rechargeable lithium batteries. Benefiting from the superdelocalization of pyrimidyl group, the extra electrons prefer to be localized on the π* (pyrimidyl group) than σ* (S-S bond) molecular orbitals initially, generating the anion-like intermedia of [Pym2 S2 ]2- and thus decreasing the dissociation energy of the S-S bond. It makes the intrinsic energy barrier of dissociative electron transfer depleted, therefore the lithium half cell exhibits 2000 cycles at 5 C. This study provides a distinct pathway for the design of high-rate, long-cycle-life organic cathode materials.

In Situ Formation of Coordinated Polymer via Organic–Inorganic Hybridization Engineering Boosting High‐Efficiency Potassium Storage

AbstractOrganic redox‐active molecules with merits of structure diversity and tunable properties are emerging as promising cathodes for the practical usage of potassium‐ion batteries (PIBs). However, the inferior cycle stability and sluggish charge‐carrier mobility are two main drawbacks hindering the practical application of organic cathode materials. Herein, highly conductive inorganic CuS is combined with small molecule‐based redox species (perylene‐3,4,9,10‐tetracarboxylic dianhydride, PTCDA) to form a novel organic–inorganic hybrid cathode (PTCDA/CuS) for PIBs, which could undergo electrochemical‐induced in situ self‐transformation of a sulfur‐linked and Cu2+‐coordinated PTCDA polymer (labeled as Cu@PTCDA‐SP). Benefiting from improved redox sites from activated carbonyl groups, high stability afforded by the sulfur‐bridging, isotropic amorphous nature, and 3D cross‐linked nanosheet morphologies, the resulting Cu@PTCDA‐SP cathode exhibits a high‐rate capacity involving trielectron enolization (vs 2‐electron transformation in PTCDA monomers) and long‐term cycle life (over 2800 cycles at 5 A g−1). This organic–inorganic hybridized cathode is very promising for PIBs. Additionally, the self‐transformation strategy provides new insight into the discovery of more electrochemically induced interaction between organic–inorganic hybrids toward high‐performance secondary batteries.

Spontaneous electrochemical stabilization of nanostructured organic electrodes by field-induced charge-transfer

Organic electrodes are promising candidates for the next-generation energy storage system of rechargeable lithium-ion batteries (LIBs) due to their natural abundance and lightweight. However, they have weaknesses: low electrochemical capacity, low capacity retention, and elution of active electrode materials. In this study, the field-induced charge-transfer route and nanostructuring are developed to resolve the poor electrochemical performance. When the 5,10-Dihydro-5,10-dimethylphenazine (DMPZ) with a nanoporous structure is homogeneously mixed with organic and metal nanoparticles (perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA), perylenetetracarboxylic diimide (PTCDI), Flavanthrone, and Aluminum), the organic nanocomposite cathodes exhibit a remarkable enhancement in electrochemical performance: unprecedented cycling stability with capacity retention over 90% up to 600 redox cycles, a high specific capacity of 215 mA·h·g−1 at the current density of 150 mA·g−1, and an excellent rate-capability for the DMPZ and PTCDA nanocomposite cathode. The excellent specific capacity and retention of the redox reaction are due to the fast charge transport through the nanoporous network of the nanocomposites with a high specific surface area. The charge-transfer between the vicinal organic materials with different ionization energies is induced by the charging potential of the redox reaction, which suppresses the elution during the oxidation process and leads to the remarkable cyclability. The all-organic pouch-type full-cell, composed of a PTCDI anode and the nanocomposite cathode, is realized with excellent cyclability of 76% capacity retention at the 200th cycle. This work provides a promising way of developing stable organic electrodes for electrocatalytic applications as well as LIBs.

In-situ CNT-loaded organic cathodes for sulfide all-solid-state Li metal batteries

Organic cathodes show promising advantages of extensive resources, high theoretical specific capacity, and mild synthesis conditions, etc., but suffer from low density, poor electronic conductivity, and high solubility in liquid electrolytes. Herein, an in-situ coating method is developed to overcome the above issues by realizing high-performance sulfide all-solid-state batteries with organic Li4C8H2O6 cathode. Li4C8H2O6 composite cathodes with carbon nanotubes (CNTs) and vapor grown carbon fiber (VGCF) were systematically studied to reveal that CNTs accelerate the electrochemical decomposition of sulfide electrolyte, despite the effectively improved electronic conductivity, rate capability and active material utilization. Therefore, in-situ coating of Li4C8H2O6 onto CNTs (Li4C8H2O6@CNT) is developed to further improve the contact between Li4C8H2O6 and CNTs, but to reduce the contact of CNTs with sulfide solid electrolyte and its decomposition. As a result, the Li4C8H2O6@CNT electrode demonstrates a high capacity of 200.3 mAh/g, and a high active material utilization rate (83.4% at 0.1C). It also exhibits a specific capacity of 85.9 mAh/g at a high cathode loading of 40 wt% and a high rate of 1C.

Dynamic Balance of Partial Charge for Small Organic Compound in Aqueous Zinc‐Organic Battery

AbstractOrganic cathodes for aqueous zinc‐ion batteries (AZIBs) feature intrinsic flexibility and favorable kinetics, but they suffer from high solubility. Herein, a partial charge regulation strategy is deployed by designing a small organic molecule with extended π‐conjugated plane, namely benzo[i]benzo[6′,7′]quinoxalino[2′,3′:9,10]phenanthro[4,5‐abc]phenazine‐5,10,16,21‐tetraone (PTONQ). The charge equalization of active sites induced by the extended π‐conjugated plane of the PTONQ molecule combined with high aromaticity renders the molecule low solubility, fast charge transfer, and high structural stability. The fabricated Zn//PTONQ battery cycles more than 500 h at 175 mA g−1 with small capacity reduction, fast charged/discharged kinetics, and anti‐freeze performance (below ‐20°C). By a series of ex situ characterizations, it is attested that the capacity originates mainly from Zn2+ insertion/removal of PTONQ without H+ incorporation, which also accounts for the formation of Znx(CF3SO3)y(OH)2x‐y·nH2O by‐products. This result benefits the understanding of the by‐product formation mechanism of organic cathode and paves a new way to advance the aqueous Zn‐organic batteries.

Multimodal investigation of electronic transport in PTMA and its impact on organic radical battery performance

Organic radical batteries (ORBs) represent a viable pathway to a more sustainable energy storage technology compared to conventional Li-ion batteries. For further materials and cell development towards competitive energy and power densities, a deeper understanding of electron transport and conductivity in organic radical polymer cathodes is required. Such electron transport is characterised by electron hopping processes, which depend on the presence of closely spaced hopping sites. Using a combination of electrochemical, electron paramagnetic resonance (EPR) spectroscopic, and theoretical molecular dynamics as well as density functional theory modelling techniques, we explored how compositional characteristics of cross-linked poly(2,2,6,6-tetramethyl-1-piperidinyloxy-4-yl methacrylate) (PTMA) polymers govern electron hopping and rationalise their impact on ORB performance. Electrochemistry and EPR spectroscopy not only show a correlation between capacity and the total number of radicals in an ORB using a PTMA cathode, but also indicates that the state-of-health degrades about twice as fast if the amount of radical is reduced by 15%. The presence of up to 3% free monomer radicals did not improve fast charging capabilities. Pulsed EPR indicated that these radicals readily dissolve into the electrolyte but a direct effect on battery degradation could not be shown. However, a qualitative impact cannot be excluded either. The work further illustrates that nitroxide units have a high affinity to the carbon black conductive additive, indicating the possibility of its participation in electron hopping. At the same time, the polymers attempt to adopt a compact conformation to increase radical–radical contact. Hence, a kinetic competition exists, which might gradually be altered towards a thermodynamically more stable configuration by repeated cycling, yet further investigations are required for its characterisation.

Exploration of Organic Cathode Active Materials with High Energy Densities for Li-Ion Batteries via First-Principles Calculations

Exploration of Organic Cathode Active Materials with High Energy Densities for Li-Ion Batteries via First-Principles Calculations

Double-Dipole Induced by Incorporating Nitrogen-Bromine Hybrid Cathode Interlayers Leads to Suppressed Current Leakage and Enhanced Charge Extraction in Non-Fullerene Organic Solar Cells.

The cathode interlayer plays a vital role in organic solar cells, which can modify the work function of electrodes, lower the electron extraction barriers, smooth the surface of the active layer, and remove solvent residuals. However, the development of organic cathode interlayer lags behind the rapidly improved organic solar cells because their intrinsic high surface tension can lead to poor contact with the active layers. Herein, a double-dipole strategy is proposed to enhance the properties of organic cathode interlayers, which is induced by incorporating nitrogen- and bromine-containing interlayer materials. To verify this approach, the state-of-the-art active layer composed of PM6:Y6 and two prototypical cathode interlayer materials, PDIN and PFN-Br is selected. Using the cathode interlayer PDIN: PFN-Br (0.9:0.1, in wt.%) in the devices can reduce the electrode work function, suppress the dark current leakage, and improve charge extractions, leading to enhanced short circuit current density and fill factor. The bromine ions tend to break from PFN-Br and form a new chemical bond with the silver electrode, which can adsorb extra dipoles directed from the interlayer to silver. These findings on the double-dipole strategy provide insights into the hybrid cathode interlayers for efficient non-fullerene organic solar cells.

Electro-activation to achieve entropy increase of organic cathode for potassium-ion batteries

Developing highly stable cathode materials is the key to achieving long-life K-ion batteries (KIBs). Considering that cathode with higher entropy can promote the ion adsorption process, we developed a method with heat treatment and synergistic electro-activation of 3,4,9,10-perylene-tetracarboxylic dianhydride (EA-PTCDA) to realize entropy increase in PTCDA, which achieves a stable K-ion storage. From our characterization results, the molecular stacking structure of EA-PTCDA and the C–O and C–H bending vibration at the edge position of PTCDA molecules decreased after electro-activation, indicating the achievement of entropy increase in the EA-PTCDA cathode. After treatment, our EA-PTCDA exhibits a high discharge capacity of 92 mA h g−1 after 100 cycles at 20 mA g−1 for KIBs. Even at a high current density of 200 mA g−1, our EA-PTCDA also maintains a discharge specific capacity of 66 mA h g−1 after 1000 cycles, showing shallow capacity decay. We believe that our method of achieving entropy increase in cathode materials based on electro-activation provides a reference for achieving high-performance KIBs.

Redox-Bipolar Polyimide Two-Dimensional Covalent Organic Framework Cathodes for Durable Aluminium Batteries.

Emerging rechargeable aluminium batteries (RABs) offer a sustainable option for next-generation energy storage technologies with low cost and exemplary safety. However, the development of RABs is restricted by the limited availability of high-performance cathode materials. Herein, we report two polyimide two-dimensional covalent organic frameworks (2D-COFs) cathodes with redox-bipolar capability in RAB. The optimal 2D-COF electrode achieves a high specific capacity of 132 mAh g-1. Notably, the electrode presents long-term cycling stability (with negligible ~0.0007% capacity decay per cycle), outperforming early reported organic RAB cathodes. 2D-COFs integrate n-type imide and p-type triazine active centres into the periodic porous polymer skeleton. With multiple characterizations, we elucidate the unique Faradic reaction of the 2D-COF electrode, which involves AlCl2+ and AlCl4- dual-ions as charge carriers. This work paves the avenue toward novel organic cathodes in RABs.

Redox‐Bipolare Polyimid Zweidimensionale Covalent Organic Framework Kathoden für langlebige Aluminum‐Akkumulatoren

AbstractNeuartige Aluminium‐Akkumulatoren (AlAKs) stellen eine nachhaltige Option für Energiespeichertechnologien der nächsten Generation mit niedrigen Kosten und beispielhafter Sicherheit dar. Die Entwicklung von AlAKs wird jedoch durch die begrenzte Verfügbarkeit von Hochleistungs‐Kathodenmaterialien eingeschränkt. In diesem Artikel beschreiben wir zwei Polyimid‐ basierte zweidimensionale Covalent‐Organic‐Framework‐ (2D COF) Elektrodenmaterialien mit redox‐bipolarer Fähigkeit in AlAKs. Die optimierte 2D‐COF‐Elektrode erreicht eine hohe spezifische Kapazität von 132 mAh g−1. Die Elektrode weist eine langfristige Zyklenstabilität auf (mit einem vernachlässigbaren Kapazitätsabfall von ≈0.0007 % pro Zyklus) und übertrifft damit frühere Ergebnisse organischer AlAK‐Kathoden. Unsere 2D‐COFs beinhalten n‐Type‐Imide und p‐Type‐Triazine als aktive Zentren im periodisch‐porösen Polymerskelett. Anhand umfänglicher Charakterisierungen erklären wir die ungewöhnliche Faradische Reaktion der 2D‐COF‐Elektrode, bei der AlCl2+‐ und AlCl4− Dualionen als Ladungsträger beteiligt sind. Diese Arbeit ebnet den Weg zu neuartigen organischen Kathodenmaterialien in AlAKs.

Small-Molecule Organic Cathodes with Carbon Coating for Highly Efficient Potassium-ion Batteries.

Small-molecule organic cathodes face dissolution in potassium-ion batteries (PIBs). For the first time, an interesting and effective strategy is unveiled to resolve this issue by designing a new soluble small-molecule organic compound namely [N,N'-bis(2-anthraquinone)]-1,4,5,8-naphthalenetetracarboxdiimide (NTCDI-DAQ, 237 mAh g-1 ): Through the precise manipulation of carbonization temperature and time, the molecules on the surface of NTCDI-DAQ particles can be transformed into amorphous carbon with controllable thickness. This strategy called surface self-carbonization can form a carbon protective layer on organic cathodes and significantly increase their insolubility against liquid electrolytes without affecting the electrochemical behavior of bulk particles. As a result, the as-obtained NTCDI-DAQ@C sample displays significantly improved cathode performance in PIBs. In half cells, NTCDI-DAQ@C shows superior capacity stability of 84 % compared to 35 % of NTCDI-DAQ during 30 cycles under the same conditions. In full cells with a KC8 anode, NTCDI-DAQ@C delivers a peak discharge capacity of 236 mAh g-1 cathode and a high energy density of 255 Wh kg-1 cathode in 0.1-2.8 V, with 40 % capacity retention during 3000 cycles at 1 A g-1 . To the best of our knowledge, the integrated performance of NTCDI-DAQ@C is among the best of soluble organic cathodes reported in PIBs.

Stable quasi-solid-state lithium-organic battery based on composite gel polymer electrolyte and compatible organic cathode material

High-performance organic small-molecule electrode materials are troubled with their high solubility in liquid electrolytes. The construction of quasi-solid-state lithium organic batteries (LOBs) using gel polymer electrolytes with high mechanical properties, compromised ionic conductivity, high safety, and eco-friendly is an effective way to inhibit the dissolution of active materials. Herein, two hexaazatriphenylene (HATN)-based organic cathode materials (HATNA-6OCH3 and HATNA-6OH) are synthesized and then matched with polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP)-based gel polymer electrolytes to construct quasi-solid-state LOBs. Thanks to the enhanced interfacial compatibility between organic cathode material and gel polymer electrolyte, HATNA-6OH with compatible hydroxyl group shows the enhanced electrochemical properties compared with HATNA-6OCH3. Further, the electrochemical performance is improved when HATNA-6OH is combined with a gel polymer electrolyte modified with a succinonitrile (SN) plasticizer (GPE-0.4SN), including a high specific capacity of 153.3 mAh g−1 at 50 mA g−1 and a good reversible capacity of 88 mAh g−1 after 100 cycles at 200 mA g−1. In addition, the good electrochemical properties and lithium-ion storage mechanism of HATNA-6OH have been elucidated using density functional theory (DFT) and spectral characterizations.