Free-standing and flexible organic cathode based on aromatic carbonyl compound/carbon nanotube composite for lithium and sodium organic batteries

A bipolar organic molecule towards the anion/cation-hosting cathode compatible with polymer electrolytes for quasi-solid-state dual-ion batteries

Ion concentration and mobility are tightly associated with the ionic conductance of polymer electrolytes in solid-state lithium batteries. However, the anions involved in the movement are irrelevant to energy generation and cause uncontrolled dendritic growth and concentration polarization. In the current study, we proposed the strategy of using a bipolar organic molecule as the anion/cation-hosting cathode to expand the active charge carriers of polymer electrolytes. As a proof-of-concept demonstration of the novel strategy, a bipolar phthalocyanine derivative (2,3,9,10,16,17,23,24-octamethoxyphthalocyaninato) Ni(II) (NiPc-(OH)8) that could successively store anions and cations was used as the cathode hosting material in quasi-solid-state dual-ion batteries (QSSDIBs). Interestingly, peripheral polyhydroxyl substituents could build a compatible interface with poly(vinylidene fluoride-hexafluoro propylene-based gel polymer electrolytes (PVDF-HFP). As expected, NiPc-(OH)8 displays a high specific capacity of 248.2 mAh/g (at 50 mA g-1) and improved cyclic stability compared with that in liquid electrolyte. This study provides a solution to the issue of anion migration and could open another way to build high-performance QSSDIBs.

Toward Conductive Additive Free Organic Electrode for Lithium-Ion Battery Using Supramolecular Columnar Organization

With the aim to meet the greatest challenge facing organic batteries, namely the low conductivity of the electrodes, the electrochemical properties of a series of substituted perylene diimides able to form semi-conductive columnar material are investigated. Depending on the substituent group, a strong influence of this group on the reversibility, redox potential but especially on the gravimetric capacity of the electrodes is observed. In the case of substitution by a simple propyl group, the corresponding diimide shows a complete electrochemical activity with only 10% by mass of conductive additive and even shows a half-capacity activity without any additive and without particular electrode engineering. Extensive research has highlighted the intrinsic reactivity of the columnar material but also its perpetual rearrangement during charge/discharge cycles. This study shows that the amount of conductive additive can be significantly reduced by adapting the design of the molecular material and favoring the assembly of redox units in the form of a conductive column.

Discovery of lead quinone cathode materials for Li-ion batteries

Organic cathode materials are attractive candidates for the development of high-performance Li-ion batteries (LIBs). The chemical space of candidate molecules is too vast to be explored solely by experiments; however, it can be systematically explored by a high-throughput computational search that incorporates a spectrum of screening techniques. Here, we present a time- and resource-efficient computational scheme that incorporates machine learning and semi-empirical quantum mechanical methods to study the chemical space of approximately 200 000 quinone-based molecules for use as cathode materials in LIBs. By performing an automated search on a commercial vendor database, computing battery-relevant properties such as redox potential, gravimetric charge capacity, gravimetric energy density, and synthetic complexity score, and evaluating the structural integrity upon the lithiation process, a total of 349 molecules were identified as potentially high-performing cathode materials for LIBs. The chemical space of the screened candidates was visualized using dimensionality reduction methods with the aim of further downselecting the best candidates for experimental validation. One such directly purchasable candidate, 1,4,9,10-anthracenetetraone, was analyzed through cyclic voltammetry experiments. The measured redox potentials of the two lithiation steps, , of 3.3 and 2.4 V, were in good agreement with the predicted redox potentials, , of 3.2 and 2.3 V vs. Li/Li+, respectively. Lastly, to lay out the principles for rational design of quinone-based cathode materials beyond the current work, we constructed and discussed the quantitative structure property relationships of quinones based on the data generated from the calculations.

Perylene diimide growth on both sides of carbon nanotubes for remarkably boosted photocatalytic degradation of diclofenac

Perylene diimide and its derivatives are promising photocatalysts for clean and efficient production, but their practical application in the field of photocatalysis is still limited by the rapid photogenerated charge recombination. In this work, the confined photocatalysts were synthesized by using a gas-phase self-assembly method and comparing the morphology and photocatalytic properties of different photocatalysts after the confinement of carbon nanotubes. The confinement effect of carbon nanotubes acts to stabilize perylene diimide. Electrostatic interaction formed by a wide range of dispersion forces is dominant in the process of stabilization. Benefitting from the three-dimensional electron transfer pathway formed by the conjugation of perylene diimide with a large number of π electrons to the carbon nanotubes plane, the confined photocatalyst shows the pseudo-first-order kinetic constant k of 1.106 h^-1 for the photocatalytic degradation of diclofenac under light, which is 6.11 times higher than that of perylene diimide. The electron transfer created an internal electric field at the interface from carbon nanotubes to perylene diimide, which greatly accelerated the separation of photogenerated electron-hole pairs and improved the photocatalytic activity. This study further expands the applicability of perylene diimide in the field of photocatalysis and provides a new approach for water environment treatment.

A 1.9-V all-organic battery-supercapacitor hybrid device with high rate capability and wide temperature tolerance in a metal-free water-in-saltelectrolyte

Developing battery-supercapacitor hybrid devices (BSHs) is viewed as an efficient route to shorten the gap between supercapacitors and batteries. In this study, a composite hydrogel consisting of perylene tetracarboxylic diimide (PTCDI) and reduced graphene oxide (rGO) is tested as the anode for BSHs in the electrolyte of ammonium acetate (NH₄Ac) with a record concentration of 32 molality (m). This water-in-salt electrolyte exhibits a wide electrochemical stability window of 2.13 V and high conductivity of 23.3 mS cm^-1 even at -12 °C. Molecular dynamics calculations and spectroscopic measurements reveal that a favorable water-acetate interaction occurs in a high concentration NH₄Ac electrolyte. On the other hand, the study of electrode kinetics in 32 m NH₄Ac demonstrates a high capacitive contribution to charge storage in PTCDI-rGO although an electrode redox reaction involves reversible enolization of carbonyl groups in PTCDI. This result suggests fast NH₄⁺-ion intercalation kinetics in charge-discharge processes. Furthermore, the electrode performance is improved by optimizing the loading amount of rGO in composites. The best-performing composite electrode delivers the maximum capacity of 165 mAh g^-1 at 0.5 A g^-1 and sustains a great capacity retention of 66% at 8 A g^-1. Finally, an all-organic BSH device is tested in a broad temperature window from -20 to 50 °C and is well operated at 1.9 V regardless of operating temperatures. Due to the synergetic effect of splendid electrolyte properties and high anode capacities, BSH devices possess the maximum energy density of 12.9 Wh kg^-1 at the power density of 827 W kg^-1 and retain 74 % of the initial capacity after 3000 cycles at 1 A g^-1. Our study paves a novel route towards designing inexpensive and environmentally friendly BSH devices with high performances.

A review of π-conjugated polymer-based nanocomposites for metal-ion batteries and supercapacitors

Owing to their extraordinary properties of π-conjugated polymers (π-CPs), such as light weight, structural versatility, ease of synthesis and environmentally friendly nature, they have attracted considerable attention as electrode material for metal-ion batteries (MIBs) and supercapacitors (SCPs). Recently, researchers have focused on developing nanostructured π-CPs and their composites with metal oxides and carbon-based materials to enhance the energy density and capacitive performance of MIBs and SCPs. Also, the researchers recently demonstrated various novel strategies to combine high electrical conductivity and high redox activity of different π-CPs. To reflect this fact, the present review investigates the current advancements in the synthesis of nanostructured π-CPs and their composites. Further, this review explores the recent development in different methods for the fabrication and design of π-CPs electrodes for MIBs and SCPs. In review, finally, the future prospects and challenges of π-CPs as an electrode materials for strategies for MIBs and SCPs are also presented.

The synthesis of alternating donor-acceptor polymers based on pyrene-4,5,9,10-tetraone and thiophene derivatives, their composites with carbon, and their lithium storage performances as anode materials

Two conjugated polymer@activated carbon composites were synthesized by the in situ polymerization of two donor-acceptor type polymers including poly[(thiophene-2,5-yl)-((pyrene-4,5,9,10-tetraone)-2,7-yl)] (PTPT) and poly[((2,3-dihydrothieno[3,4-b][1,4]dioxine)-5,7-yl)-((pyrene-4,5,9,10-tetraone)-2,7-yl)] (POTPT) on activated carbon (AC) by one-step cross-coupling reaction catalyzed by an organometallic catalyst. Cyclic voltammetry showed that both polymers exhibited ambipolar properties, low bandgaps, and low electrode potentials, which could be useful for their application as anodes in lithium-ion battery cells (LIBs). For PTPT@AC and POTPT@AC anodes, they showed a high capacity of 253.9 and 370.5 mA h g-1 at 100 mA g-1. Besides, the capacities of pure polymers were calculated to be 693.5 and 1276.5 mA h g-1 for PTPT and POTPT, respectively, at 100 mA g-1. Compared with PTPT, the introduction of the 3,4-ethylenedioxy unit into the side chain of the thiophene unit leads to substantially improved performance of POTPT due to the lowered LUMO energy levels of POTPT and the electron-rich feature of the EDOT unit. It is suggested that the structure-tuning strategy might be an effective method to prepare the new polymer-based anode for next generation LIBs with high performance and high safety.

High Capacity and Energy Density Organic Lithium-Ion Battery Based on Buckypaper with Stable π-Radical

Owing to an increasing demand on high performance and rare-metal free energy storage systems, organic rechargeable battery has attracted much attention. To increase the capacity of the whole battery, we have fabricated coin-type buckypaper cells composed of a trioxotriangulene neutral radical derivative (H₃ TOT) and single-walled carbon nanotubes as a cathode and lithium metal plate as an anode without current collector. The cells exhibited a stable charge-discharge behavior even at a 90 wt % H₃ TOT content with a high-rate performance of 10 C originating from high electrical conductivity of H₃ TOT. Furthermore, based on the four-stage redox ability of H₃ TOT, the H₃ TOT 90 wt % cathode showed a high capacity of approximately 260 mAh g^-1 and a high energy density of 546 Wh g^-1 . In view of the simple fabrication of the cathode and excellent performance, TOT-based buckypaper will open a new strategy for the flexible cells for next-generation energy storages.

Three-Dimensional Monolithic Organic Battery Electrodes

Design of freestanding electrodes incorporated with redox-active organic materials has been limited by the poor intrinsic electrical conductivity and lack of methodology driving the feasible integration of conductive substrate and the organic molecules. Single-walled carbon nanotube (SWCNT) aerogels, which possess continuous network structure and high surface area, offer a three-dimensional electrically conducting scaffold. Here, we fabricate monolithic organic electrodes by coating a nanometer-scale imide-based network (IBN) that possesses abundant redox-active sites on the 3D SWCNT scaffold. The substantially integrated 3D monolithic organic electrodes sustain high electrical conductance through a 3D electronic pathway in their compressed form (∼21 μm). A thin and controllable layer (<8 nm) of IBN organic materials has a strong adhesion onto the ultra-lightweight and conductive substrate and facilitates multielectron redox reactions to deliver a specific capacity of up to 1550 mA h g^-1 (corresponding to the areal capacity of ∼2.8 mA h cm^-2). The redox-active IBN in synergy with the 3D SWCNT scaffold can enable superior electrochemical performances compared to the previously reported organic-based electrode architectures and inorganic-based electrodes.

CNT-Intertwined Polymer Electrode toward the Practical Application of Wearable Devices

One of the greatest challenges for wearable electronics is the lack of virtually flexible electrodes with satisfactory electrochemical performance, and there is always a "softness vs effective capacity" dilemma. Herein, a polymer electrode is proposed. The carefully chosen and partially conjugated polyimide realizes the dual function of a flexible agent and an active agent. The softness of the electrode is rendered by the polymer, while the carbon nanotube ensures electron transfer (ET) within the polymer. A modified electrospinning method has been used in the preparation of a carbon nanotube (CNT)-intertwined polyimide (PI) film. The binder-free and current collector-free polymer electrode has as high as 80% active phase and releases near-theoretical capacity accompanied by very stable cycling up to 200 cycles. Owing to the dual role of the polymer component, the softness vs effective capacity dilemma has been well addressed. Aiming at the practical application, a fatigue test has been first conducted in a practical mode and the well-reserved electrochemical activity under extreme stress change as well as in plenty of electrolyte has been revealed. The work realizes that the flexible electrode well fulfills the requirement and sheds more light on the application of the polymer electrode materials.

Sustainable Energy Storage: Recent Trends and Developments toward Fully Organic Batteries

In times of spreading mobile devices, organic batteries represent a promising approach to replace the well-established lithium-ion technology to fulfill the growing demand for small, flexible, safe, as well as sustainable energy storage solutions. In the last years, large efforts have been made regarding the investigation and development of batteries that use organic active materials since they feature superior properties compared to metal-based, in particular lithium-based, energy-storage systems in terms of flexibility and safety as well as with regard to resource availability and disposal. This Review compiles an overview over the most recent studies on the topic. It focuses on the different types of applied active materials, covering both known systems that are optimized and novel structures that aim at being established.

Conjugated Carbonyl Polymer-Based Flexible Cathode for Superior Lithium-Organic Batteries

Conjugated carbonyl compounds are deemed as high theoretical capacity and green electrode materials for lithium-ion batteries (LIBs) but are limited by their high dissolution and poor electronic conductivity. In this paper, we have successfully synthesized a series of multicarbonyl conjugated polymers using the coupling polymerization reaction and then constructed carbonyl-conjugated polymer/carbon nanotube hybrid films by a vacuum-filtration method. Importantly, the hybrid films could serve as a flexible, binder-free, and free-standing organic cathode for LIBs, which could deliver a high reversible discharge capacity of 142.3 mAh g^-1 at 50 mA g^-1, good cycling stability with a capacity retention of 74.6% at 500 mA g^-1 after 300 cycles, and excellent rate capability of 120.6 mAh g^-1 at 1000 mA g^-1. In addition, the theoretical calculation has proved that the symmetrical conjugated structure can well accommodate four Li⁺ ions during the electrochemical reaction. Interestingly, the assembled full cell and flexible battery can power the small devices, suggesting its potential to use in bendable or wearable energy-storages devices.

Recent Progress on Organic Electrodes Materials for Rechargeable Batteries and Supercapacitors

Rechargeable batteries are essential elements for many applications, ranging from portable use up to electric vehicles. Among them, lithium-ion batteries have taken an increasing importance in the day life. However, they suffer of several limitations: safety concerns and risks of thermal runaway, cost, and high carbon footprint, starting with the extraction of the transition metals in ores with low metal content. These limitations were the motivation for an intensive research to replace the inorganic electrodes by organic electrodes. Subsequently, the disadvantages that are mentioned above are overcome, but are replaced by new ones, including the solubility of the organic molecules in the electrolytes and lower operational voltage. However, recent progress has been made. The lower voltage, even though it is partly compensated by a larger capacity density, may preclude the use of organic electrodes for electric vehicles, but the very long cycling lives and the fast kinetics reached recently suggest their use in grid storage and regulation, and possibly in hybrid electric vehicles (HEVs). The purpose of this work is to review the different results and strategies that are currently being used to obtain organic electrodes that make them competitive with lithium-ion batteries for such applications.

Organic Carbonyl Compounds for Sodium-Ion Batteries: Recent Progress and Future Perspectives

Sodium-organic batteries, which use organic materials as the electrodes in sodium-ion batteries, are an attractive alternative to conventional lithium-ion batteries for next-generation sustainable and versatile energy storage devices owing to the abundant sodium resources and environmental friendly features. However, organics used in sodium-ion batteries also encounter some issues such as low redox potential, high solubility in the electrolyte, and low conductivity. In response, altering the aromatic system/attaching electron-withdrawing groups, constructing polymers, and incorporating a conductive matrix are effective strategies. This review summarizes and briefly discusses recent organic carbonyl compounds for sodium-organic batteries from the viewpoint of function-oriented design, including function evolution from small-molecule compounds to polymers, then composites, and finally flexible electrodes. In particular, as a timely overview, carbonyl-based organic flexible electrodes for sodium-organic batteries are also highlighted for the first time.