RESUMEN
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.
RESUMEN
Redox-active organic molecules are promising candidates for next-generation electrode materials. Nevertheless, finding low-molecular-weight organic materials with a long cycle life remains a crucial challenge. Herein, we demonstrate the application of tetrathiafulvalene and its vinyl analogue bearing triphenylamines as long-cycle-life electrodes for lithium-ion batteries (LIBs). These molecules were successfully synthesized using palladium-catalyzed C-H arylation. Electrochemical analysis revealed that a polymer formed on the electrode. LIBs comprising these molecules exhibited noteworthy charge-discharge properties with a long cycle life (the capacity after 100 cycles was greater than 90% of the discharge capacity in the third cycle) and a high utilization ratio (approximately 100%). "In-cell" polymerization during the first charge process is considered to contribute to the effect. This study indicates new avenues for the creation of organic materials for rechargeable batteries.
RESUMEN
Rare-metal-free and high-performance secondary batteries are necessary for improving the efficiency of renewable energy systems. Organic compounds are attractive candidates for the active material of such batteries. Many studies have reported organic active materials that show high energy density per active material weight. However, organic active materials, most of which exhibit low conductivity and low specific density, typically require a large amount of a conductive additive (>50 wt %) to obtain a high utilization rate. Therefore, organic active materials rarely display high energy density per electrode weight. High energy densities per electrode weight can be obtained using high weight fractions of active materials and low weight fractions of conductive additives. Herein, we report that a low-conductivity organic active material, indigo, showed improved net discharge capacity density when even a small amount of a conductive polymer composite, poly(3,4-ethylenedioxythiophene)/polystyrene sulfonic acid (PEDOT/PSS) with d-sorbitol, was used as both a binder and conductive additive. The cycle life was also improved by coating one side of the separator with the composite, which probably hindered the dissolution of the active material. A discharge capacity of 96% of the theoretical capacity of indigo and an improved cycle life were achieved with an electrode containing 80 wt % indigo and with a PEDOT/PSS-coated separator. The optimal fraction of the conductive binder was examined, and the mechanism of conductivity enhancement was discussed. The present scheme allows us to replace the dispersion solvent of the slurry, N-methylpyrrolidone, with water, which can reduce the environmental load during battery manufacturing processes.
RESUMEN
Organic compounds as electrode materials can contribute to sustainability because they are nontoxic and environmentally abundant. The working mechanism during charge-discharge for reported organic compounds as electrode materials is yet to be completely understood. In this study, the structural behavior of 2,5-dimethoxy-1,4-benzoquinone (DMBQ) during charge-discharge is investigated by using NMR spectroscopy, energy-dispersive X-ray spectroscopy, magnetic measurements, operando Raman spectroscopy, and operando X-ray diffraction. For both lithium and sodium systems, DMBQ works as a cathode accompanied with the insertion and deinsertion of Li and Na ions during charge-discharge processes. The DMBQ sample is found to be in two-phase coexistence state at the higher voltage plateau, and the radical monoanion and dianion phases have no long-distance ordering. These structures reversibly change into the original neutral phase with long-distance ordering. These techniques can show the charge-discharge mechanism and the factors that determine the deterioration of organic batteries, thus guiding the design of future high-performance organic batteries.
RESUMEN
Fused donor-acceptor triads composed of two tetrathiafulvalenes (TTFs) and benzoquinone (BQ; 1) or naphthoquinone (NQ; 2) were successfully synthesized. X-ray structure analysis of the bis(n-butylthio) derivative revealed that the molecules are stacked in a head-to-tail manner. The bis(n-hexylthio)-1 exhibited six-pairs of one-electron transfer waves in the cyclic voltammogram, corresponding to the formation of both reduction and oxidation states from -2 to +4. The unsubstituted and bis(methylthio) derivatives of 1 and 2 were active materials in positive electrodes for rechargeable batteries, several of which displayed energy densities exceeding 800â mWh g-1 . The bis(methylthio)-2 also functions as a positive electrode material for a rechargeable sodium-ion battery.
RESUMEN
Many types of batteries have been proposed as next-generation energy-storage systems. One candidate is a rocking-chair-type "molecular ion battery" in which a molecular ion, instead of Li+ , works as a charge carrier. Previously, we reported a viologen-type derivative as a negative electrode material that releases and receives PF6 - anions during the charge-discharge process; however, its redox potential was not satisfactorily low. Further, the two potential plateaus of this material (difference=0.5â V) should be reduced. In this study, PF6 - salts of viologen (bipyridinium) derivatives extended by aromatic rings were synthesized to obtain a negative electrode material with a lower redox potential and small potential change during the charge and discharge processes. Some of the synthesized viologen derivatives were fluorescent even in solid-state electrodes. In the half-cell configuration, the prepared negative electrode materials showed average voltages of approximately 2â V (vs. Li+ /Li), which is lower than that of conventional viologen derivatives.
RESUMEN
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 200â mAh g-1 with an average voltage of 2.2-2.3â 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.
RESUMEN
To analyse the electrocatalytic oxidation of carbon monoxide by Rh porphyrins, we isolated a CO-adduct of Rh octaethylporphyrin, and examined its properties and reactivity by IR, NMR, and X-ray crystallographic analyses. The results indicate that the CO adduct of Rh octaethylporphyrin is vulnerable to nucleophilic attack by H2O. The CO-adduct was easily oxidized by an electron acceptor (1,4-naphthoquinone) to generate CO2. This indicates that CO is sufficiently activated in the CO complex of Rh octaethylporphyrin to reduce an electron acceptor. This mechanism is in contrast to that for the CO oxidation by Pt-based electrocatalysts.
RESUMEN
Is it possible to exceed the lithium redox potential in electrochemical systems? It seems impossible to exceed the lithium potential because the redox potential of the elemental lithium is the lowest among all the elements, which contributes to the high voltage characteristics of the widely used lithium ion battery. However, it should be possible when we use a molecule-based ion which is not reduced even at the lithium potential in principle. Here we propose a new model system using a molecular electrolyte salt with polymer-based active materials in order to verify whether a molecular ion species serves as a charge carrier. Although the potential of the negative-electrode is not yet lower than that of lithium at present, this study reveals that a molecular ion can work as a charge carrier in a battery and the system is certainly a molecular ion-based "rocking chair" type battery.
RESUMEN
Using sodium, instead of lithium, in rechargeable batteries is a way to circumvent the lithium's resource problem. The challenge is to find an electrode material that can reversibly undergo redox reactions in a sodium-electrolyte at the desired electrochemical potential. We proved that indigo carmine (IC, 5,5'-indigodisulfonic acid sodium salt) can work as a positive-electrode material in not only a lithium-, but also a sodium-electrolyte. The discharge capacity of the IC-electrode was ~100 mAh g(-1) with a good cycle stability in either the Na or Li electrolyte, in which the average voltage was 1.8 V vs. Na(+)/Na and 2.2 V vs. Li(+)/Li, respectively. Two Na ions per IC are stored in the electrode during the discharge, testifying to the two-electron redox reaction. An X-ray diffraction analysis revealed a layer structure for the IC powder and the DFT calculation suggested the formation of a band-like structure in the crystal.
RESUMEN
A Rh porphyrin on carbon black was shown to catalyze the electro-oxidation of several aliphatic alcohols (ethanol, 1-propanol, and 2-propanol) and benzyl alcohols. The overpotentials for alcohol oxidation were very low. The reaction mechanism and substrate specificity are discussed.
RESUMEN
Five amphiphilic meso-disubstituted porphyrins bearing one polar group were synthesized, and their monolayer films were prepared. Their limiting molecular areas obtained from pi-A isotherms were 0.5-0.6 nm2, which were smaller than those of the corresponding meso-tetrasubstituted porphyrins. At the air-water interface, the disubstituted porphyrins showed a broad band in visible absorption spectra compared with the solution state, and the red shift of the Soret band exhibited a significant dependence on the kind of hydrophilic groups at the meso positions. Interestingly, the monolayer of the disubstituted porphyrin bearing a carboxyphenyl group (1-CO2H) showed a blue shift of the Soret band by adding cadmium chloride to the subphase, and the spectra varied upon multilayer deposition. The observed phenomena were interpreted by using the exciton theory. The effect of hydrophilic substituents on the absorption spectra of disubstituted porphyrin monolayers is discussed.
