Abstract
Conducting polymer‐based organic electrochemical capacitor materials have attracted attention because of their highly conductive nature and highly reversible redox reactions on the surface of electrodes. However, owing to their poor stabilities in aprotic electrolytes, alternative organic electrochemical capacitive electrodes are being actively sought. Here, fluorine atoms are introduced into contorted hexabenzocoronene (cHBC) to achieve the first small‐molecule‐based organic capacitive energy‐storage cells that operate at high current rates with satisfactory specific capacities of ≈160 mA h g−1 and superior cycle capabilities (>400) without changing significantly. This high capacitive behavior in the P21/c crystal phase of fluorinated cHBC (F—cHBC) is caused mainly by the fluorine atoms at the end of each peripheral aromatic ring. Combined Monte Carlo simulations and density functional theory (DFT) calculations show that the most electronegative fluorine atoms accelerate ion diffusion on the surface to promote fast Li+ ion uptake and release by an applied current. Moreover, F—cHBC has potential applications as the capacitive anode in Na‐ion storage cells. The fast dynamics of its capacitive behavior allow it to deliver a specific capacity of 65 mA h g−1 at a high current of 4000 mA g−1.
Highlights
The decreased highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) energy levels of F contorted hexabenzocoronene (cHBC) were blended with a Super P carbon black conducting agent and a poly(vinylidene fluoride) (PVDF) polymer binder and was subsequently coated onto an 18 μm thick copper current collector and dried overnight at 120 °C in a vacuum oven to expel residual solvent
To examine the crystal phase evolution of the fluorinated cHBC (F cHBC) anode on the current collector, we performed in situ grazing incidence wide-angle X-ray scattering (GIWAXS) measurement on the mixtures of F cHBC/PVDF after the samples had been annealed at temperatures from room temperature to 330 °C
The F cHBC anode with a controlled crystal phase in the Li-ion cell could operate for more than 400 cycles without changes of its performance and provided an adequate specific capacity of 100 mA h g−1 at a high current density of 7000 mA g−1
Summary
To examine the crystal phase evolution of the F cHBC anode on the current collector, we performed in situ grazing incidence wide-angle X-ray scattering (GIWAXS) measurement on the mixtures of F cHBC/PVDF (ratio: 90/10 wt%) after the samples had been annealed at temperatures from room temperature to 330 °C. The results suggest that the crystal phase and crystallinity of F cHBC were affected by the thermal annealing treatment, as the full-width at half-maximum (FWHM) of the peak at q = 0.49 Å−1 for the sample annealed at 330 °C was smaller than that at the q = 0.67 Å−1 in the sample that was only THF-annealed (endothermic peak of F cHBC in differential scanning calorimetry (DSC) analysis; Figure S4, Supporting Information). Enhanced electrochemical performances when the crystals had nanopores in the electrolyte.[32]
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