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Redox-active covalent organic frameworks (COFs) are promising electrode materials for metal-ion batteries owing to their tunable electrochemical properties, adjustable structure, and resource availability. Herein, we report a series of two-dimensional tetrathiafulvalene (TTF)-based COFs incorporating different organic linkers between the electroactive moieties. These COFs were investigated as p-type organic cathode materials for lithium-organic batteries. The electrical conductivity of both neutral and doped TTF-COFs was measured using a van der Pauw setup, and their electronic structures were investigated through quantum-chemical calculations. Binder-free buckypaper TTF-based electrodes were prepared and systematically tested as organic cathodes in lithium half-cells. The results revealed high average discharge potentials (∼3.6 V vs. Li/Li+) and consistent cycling stability (80% capacity retention after 400 cycles at 2C) for the three TTF-COF electrodes. In addition, the specific capacity, rate capability, and kinetics varied depending on the structure of the framework. Our results highlight the potential of TTF-COFs as high-voltage organic cathodes for metal-ion batteries and emphasize the importance of molecular design in optimizing their electrochemical performance. [ABSTRACT FROM AUTHOR]

The development of rechargeable zinc–air batteries requires air cathodes capable of performing both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with high performance and an extended operational lifespan. Here, we present a cost-effective and versatile electrochemical method for the direct assembly of such electrocatalysts, consisting of nitrogen-doped reduced graphene oxide (NrGO) and mixed transition metal sulfides (NiCoMnSx or NCMS). To this end, we use a small electric bias to electro-deposit both NrGO and NCMS directly on conductive graphene foam, resulting in a perfect porous network and two interpenetrated paths for the easy transport of electrons and ions. The NCMS/NrGO composite shows one of the highest limiting currents reported so far for a non-noble metal catalyst. Additionally, it exhibits outstanding bifunctional performance for the ORR/OER, superior to both mixed transition metal compounds and noble metals from previous reports. Thus, it serves as a highly efficient air cathode for practical zinc–air batteries featuring high power densities (124 mW cm−2) and long catalyst durability (1560 cycles, around 260 h). We attribute the excellent performance to the synergistic effect between hetero-structured metallic sites and nitrogen dopants. Our approach can be used for preparing efficient zinc–air cathodes on conductive 3D carbon substrates with arbitrary shapes and good performance. [ABSTRACT FROM AUTHOR]

This document is a compilation of discussions among researchers on various topics related to organic batteries, optoelectric conversion, and polymer electrodes for aluminum-based batteries. The participants delve into the technical aspects of these subjects, including the dielectric constant of the semiconductor layer, performance comparisons between small molecule and polymer semiconductors, film thickness and interface area effects, and the advantages of alternating current output. They also explore the use of insulating and dielectric materials, the molecular design of D-A molecules, and the challenges and potential improvements in battery design. The researchers acknowledge the complexities and limitations of their work, while encouraging further exploration in the field. [Extracted from the article]

One of the possible solutions to circumvent the sluggish kinetics, low capacity, and poor integrity of inorganic cathodes commonly used in rechargeable aluminium batteries (RABs) is the use of redox-active polymers as cathodes. They are not only sustainable materials characterised by their structure tunability, but also exhibit a unique ion coordination redox mechanism that makes them versatile ion hosts suitable for voluminous aluminium cation complexes, as demonstrated by the poly(quinoyl) family. Recently, phenazine-based compounds have been found to have high capacity, reversibility and fast redox kinetics in aqueous electrolytes because of the presence of a C＝N double bond. Here, we present one of the first examples of a phenazine-based hybrid microporous polymer, referred to as IEP-27-SR, utilized as an organic cathode in an aluminium battery with an AlCl3/EMIMCl ionic liquid electrolyte. The preliminary redox and charge storage mechanism of IEP-27-SR was confirmed by ex situ ATR-IR and EDS analyses. The introduction of phenazine active units in a robust microporous framework resulted in a remarkable rate capability (specific capacity of 116 mA h g−1 at 0.5C with 77% capacity retention at 10C) and notable cycling stability, maintaining 75% of its initial capacity after 3440 charge–discharge cycles at 1C (127 days of continuous cycling). This superior performance compared to reported Al//n-type organic cathode RABs is attributed to the stable 3D porous microstructure and the presence of micro/mesoporosity in IEP-27-SR, which facilitates electrolyte permeability and improves kinetics. [ABSTRACT FROM AUTHOR]

Aqueous all-polymer batteries (AqPBs) are foreseen as promising solutions for safe, sustainable, and high-performance energy storage applications. Nevertheless, their development is still challenging as it demands precise optimization of both electrodes and the electrolyte composition to be able to sustain a stable redox activity, while delivering an optimal voltage output. Herein, we report AqPBs based on a poly(imide) (PI) anode and poly(catechol) (PC) cathode that exhibit tunable cell voltage depending on the salt used in the aqueous electrolyte, i.e., 0.58, 0.74, 0.89, and 0.95 V, respectively, when Li+, Zn2+, Al3+, and Li+/H+ were utilized as charge carriers. The PI–PC full-cell delivers the best rate performance (a sub-second charge/discharge) and cycling stability (80% capacity retention over 1000 cycles at 5 A g−1) in Li+. Furthermore, a maximum energy/power density of 80.6 W h kganode+cathode−1/348 kW kganode+cathode−1 is achieved in Li+/H+, superior to most of the previously reported AqPBs. [ABSTRACT FROM AUTHOR]

High-performance anodes for rechargeable Li-ion batteries are produced by nanostructuring of transition metal oxides on a conductive support. Here, we demonstrate a hybrid material of MnO2 directly grown onto fabrics of carbon nanotube fibres, which exhibits notable specific capacities over 1100 and 500 mA h g−1 at discharge current densities of 25 mA g−1 and 5 A g−1, respectively, with a coulombic efficiency of 97.5%. Combined with 97% capacity retention after 1500 cycles at a current density of 5 A g−1, both capacity and stability are significantly above literature data. Detailed investigations involving electrochemical and in situ synchrotron X-ray scattering studies reveal that during galvanostatic cycling, MnO2 undergoes an irreversible phase transition to LiMnO2, which stores lithium through an intercalation process, followed by a conversion mechanism and pseudocapacitive processes. This mechanism is further confirmed by Raman spectroscopy and X-ray photoelectron spectroscopy. The fraction of pseudocapacitive charge storage ranges from 27% to 83%, for current densities from 25 mA g−1 to 5 A g−1. The firm attachment of the active material to the built-in current collector makes the electrodes flexible and mechanically robust, and ensures that the low charge transfer resistance and the high electrode surface area remain after irreversible phase transition of the active material and extensive cycling. [ABSTRACT FROM AUTHOR]

Mixed metal sulfides have recently attracted great attention for energy storage applications due to their low cost and enhanced electrical/electrochemical performance compared to oxide/hydroxide analogues. Despite of being demonstrated as high performance energy storage electrode materials, a profound understanding of their electrochemical signal is vital to unravel their charge storage mechanism and achieve a roadmap for rational design and engineering of high-performance electrode materials. Herein, energy storage properties of directly grown Ni1.80Co0.50Mn0.50S1.52 (NCMS) nano-needles on nickel foam were evaluated as novel binder/additive-free high-performance electrodes in alkaline media and their electro-activation process and charge storage mechanism were tracked through ex situ XRD and operando Raman spectroscopy. Accordingly, NCMS nano-needles exhibited a high specific capacity of 138 mA h g−1 (0.71 mA h cm−2), excellent rate capability and exceptional cycling stability demonstrating a peculiar electro-activation over cycling (the specific capacity increased by almost 2 times ∼220 mA h g−1). STEM, ex situ XRD and Raman spectroscopy at different states of charge and after cycling suggested the growth of amorphous hydroxide phases at the surface, resulting in the formation of a core–shell structure during cycling. To further confirm this hypothesis charging/discharging process using operando Raman spectroscopy was conducted in the mixed metal sulfide electrode. Based on the obtained results, a charge storage mechanism was proposed. In addition, when integrated with rGO electrodes in an asymmetric device, NCMS nano-needles exhibited a maximum energy density of 36.2 W h kg−1 and power density of 16.5 kW kg−1, with evidenced long-term cycling and rate performance. Therefore, the present work not only sketches electrochemical behavior of NCMS but also helps to achieve a better understanding of the electro-activation process and charge storage origin of mixed metal sulfides in alkaline media. [ABSTRACT FROM AUTHOR]

The development of rechargeable aluminum-ion batteries (AIBs) has recently attracted much scientific attention due to the low cost and high specific capacity of Al. Most efforts are being concentrated on enhancing the specific charge capacity of active materials for the positive electrode, while other important issues for commercial deployment of this technology have often been overlooked. The aim of this frontier article is not to systematically review the recent advances in the literature, but to bring under the spotlight the critical aspects requiring intensive research activity for paving the way toward the commercialization of AIBs. After a brief revision of the fundaments of an Al-ion battery, the discussion is classified into 5 sections: energy density, specific power, cost, cycle life and safety. Finally, a performance comparison among Al-ion, Li-ion and lead-acid battery technologies on the basis of these 5 primary parameters summarizes the strengths and limitations of Al-ion batteries. [ABSTRACT FROM AUTHOR]

Macroscopic ensembles of nanocarbons, such as fibres of carbon nanotubes (CNT), are characterised by a complex hierarchical structure combining coherent crystalline regions with a large porosity arising from imperfect packing of the large rigid building blocks. Such structure is at the centre of a wide range of charge storage and transfer processes when CNT fibres are used as electrodes and/or current collectors. This work introduces a method based on wide and small-angle X-ray scattering (WAXS/SAXS) to obtain structural descriptors of CNT fibres and which enables in situ characterisation during electrochemical processes. It enables accurate determination of parameters such as specific surface area, average pore size and average bundle size from SAXS data after correction for scattering from density fluctuations arising from imperfect packing of graphitic planes. In situ and ex situ WAXS/SAXS measurements during electrochemical swelling of CNT fibre electrodes in ionic liquid provide continuous monitoring of the increase in effective surface area caused by electrostatic separation of CNT bundles in remarkable agreement with capacitance changes measured independently. Relative contributions from quantum and Helmholtz capacitance to total capacitance remaining fairly constant. The WAXS/SAXS analysis is demonstrated for fibres of either multi- and single-walled CNTs, and is expected to be generally applicable to operando studies on nanocarbon-based electrodes used in batteries, actuators and other applications. [ABSTRACT FROM AUTHOR]

Functional porous carbon nanospheres with tunable textural properties and nitrogen functionalities were synthesized from a cheap and sustainable phenolic carbon precursor (tannic acid) and nitrogen precursor (urea) using a facile one-step salt-templating method. The diverse functional carbons were obtained by calcination of mixtures of different molar ratios of urea to tannic acid (0 : 1, 5 : 1, 9 : 1, 13 : 1 and 17 : 1) with a eutectic salt (NaCl/ZnCl2) that was used as the porogen. The physico-chemical characterization of the obtained microporous carbons demonstrated that the textural properties, morphology, surface functionalities, and conductivity were strongly influenced by the molar ratio of urea to tannic acid. The nitrogen content in the carbons increased with the molar ratio of urea, reaching a maximum of 8.83% N at the highest molar ratio while the specific surface area (SBET) of the microporous carbons varied from 890 m2 g−1 to 1570 m2 g−1 depending on the synthesis conditions. The electrochemical performance of the carbon nanospheres in the ionic liquid 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14FSI) was also significantly influenced by the synthesis conditions due to the combined effect of textural properties, morphology, nitrogen functionalities and electrical conductivity. Supercapacitors based on the functional porous carbon synthesized with a molar ratio of urea to tannic acid of 9 : 1 exhibited the best performance, with a specific capacitance as high as 110 F g−1 and a real energy density of 33 W h kg−1, when charged–discharged at 3.5 V in PYR14FSI. [ABSTRACT FROM AUTHOR]

Cholinium-based bio-ion gels were prepared by photopolymerization of poly(cholinium lactate methacrylate) network within cholinium lactate ionic liquid. The rheological and thermal properties as well as ionic conductivity of ion gels of different compositions were measured. As indicated by rheological measurements, the ion gels show the properties of gel materials which become soft by increasing the amount of free ionic liquid. Cholinium ion gels with various composition of free ionic liquid vs. methacrylic network show glass transitions between −40° and −70 °C and thermal stability up to 200 °C. The ionic conductivity of these gels increases from 10−8 to 10−3 S cm−1 at 20 °C by varying the amount of free ionic liquid between 0 and 60 wt%, respectively. Low glass transition temperature and enhanced ionic conductivity make the cholinium-based ion gels good candidates to be used as a solid electrolytic interface between the skin and an electrode. The ion gels decrease the impedance with the human skin to levels that are similar to commercial Ag/AgCl electrodes. Accurate physiologic signals such as electrocardiography (ECG) were recorded with ion gels assisted electrodes for a long period of time (up to 72 h) with a remarkable stability. The low toxicity and superior ambient stability of cholinium ionic liquids and ion gels make these materials highly attractive for long-term cutaneous electrophysiology and other biomedical applications. [ABSTRACT FROM AUTHOR]

The demand for more efficient energy storage systems stimulates research efforts to seek and develop new energy materials with promising properties. In this regard, binary metal oxides have attracted great attention due to their better electrochemical performance as compared to their single oxide analogues. Herein, nanostructured porous wires of FeCo2O4 were grown on nickel foam via a facile hydrothermal route and employed as binder/additive-free electrodes to investigate the electrochemical behavior of FeCo2O4 as electrode materials for supercapacitors. The FeCo2O4 sample exhibits a high specific capacitance of 407 F g−1 at a scan rate of 10 mV s−1 in the initial cycling. After cycling for 2000 cycles, electro-activation of the material results in subsequent increase in capacitance up to 610 F g−1, showing promising characteristics of this material for energy storage. The performance of the prepared FeCo2O4 sample is found to be much better than that of the corresponding single oxides. Furthermore, porous nanostructured FeCo2O4//AC asymmetric supercapacitors were assembled and could achieve a high energy density of 23 W h kg−1 and a maximum power density of 3780 W kg−1. [ABSTRACT FROM AUTHOR]

The influence of the Zn2+concentration and temperature on the electrochemical reduction of O2in a solution of zinc bis(trifluoromethanesulfonyl)imide (Zn(TFSI)2) salt in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) ionic liquid is presented. ZnO nanocrystalline films were then electrodeposited, under enhanced O2reduction, at temperatures in the 75–150 °C range. Their morphology, chemical composition, structural and optical properties were analyzed. In contrast to the polar-oriented ZnO usually obtained from aqueous and conventional solvent based electrolytes, nanocrystalline films oriented along non-polar directions, (1110) and (1120), were obtained from this ionic liquid electrolyte. A significant content of carbon was detected in the films, pointing to the active participation and crucial effect of pyrrolidinium cation (and/or byproducts) during the electrodeposition. The films showed semiconducting behavior with an optical gap between 3.43 and 3.53 eV as measured by optical transmittance. Their room temperature photoluminescence spectra exhibited two different bands centered at ∼3.4 and ∼2.2 eV. The intensity ratio between both bands was found to depend on the deposition temperature. This work demonstrates the great potential of ionic liquids based electrolytes for the electrodeposition of ZnO nanocrystalline thin films with innovative microstructural and optoelectronic properties. [ABSTRACT FROM AUTHOR]

The influence of the Zn(2+) concentration and temperature on the electrochemical reduction of O(2) in a solution of zinc bis(trifluoromethanesulfonyl)imide (Zn(TFSI)(2)) salt in 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR(14)TFSI) ionic liquid is presented. ZnO nanocrystalline films were then electrodeposited, under enhanced O(2) reduction, at temperatures in the 75-150 °C range. Their morphology, chemical composition, structural and optical properties were analyzed. In contrast to the polar-oriented ZnO usually obtained from aqueous and conventional solvent based electrolytes, nanocrystalline films oriented along non-polar directions, (11 ̅10) and (11 ̅20), were obtained from this ionic liquid electrolyte. A significant content of carbon was detected in the films, pointing to the active participation and crucial effect of pyrrolidinium cation (and/or byproducts) during the electrodeposition. The films showed semiconducting behavior with an optical gap between 3.43 and 3.53 eV as measured by optical transmittance. Their room temperature photoluminescence spectra exhibited two different bands centered at ∼3.4 and ∼2.2 eV. The intensity ratio between both bands was found to depend on the deposition temperature. This work demonstrates the great potential of ionic liquids based electrolytes for the electrodeposition of ZnO nanocrystalline thin films with innovative microstructural and optoelectronic properties., (This journal is © the Owner Societies 2011)