Abstract
We report a gel polymer electrolyte (GPE) supercapacitor concept with improved pathways for ion transport, thanks to a facile creation of a coherent continuous distribution of the electrolyte throughout the electrode. Poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) was chosen as the polymer framework for organic electrolytes. A permeating distribution of the GPE into the electrodes, acting both as integrated electrolyte and binder, as well as thin separator, promotes ion diffusion and increases the active electrode–electrolyte interface, which leads to improvements both in capacitance and rate capability. An activation process induced during the first charge–discharge cycles was detected, after which, the charge transfer resistance and Warburg impedance decrease. We found that a GPE thickness of 12 μm led to optimal capacitance and rate capability. A novel hybrid nanocomposite material, formed by the tetraethylammonium salt of the 1 nm-sized phosphomolybdate cluster and activated carbon (AC/TEAPMo12), was shown to improve its capacitive performance with this gel electrolyte arrangement. Due to the homogeneous dispersion of PMo12 clusters, its energy storage process is non-diffusion-controlled. In the symmetric capacitors, the hybrid nanocomposite material can perform redox reactions in both the positive and the negative electrodes in an ambipolar mode. The volumetric capacitance of a symmetric supercapacitor made with the hybrid electrodes increased by 40% compared to a cell with parent AC electrodes. Due to the synergy between permeating GPE and the hybrid electrodes, the GPE hybrid symmetric capacitor delivers three times more energy density at higher power densities and equivalent cycle stability compared with conventional AC symmetric capacitors.
Highlights
Portable/wearable electronic devices are flourishing and demanding improved energy storage devices: small, thin, lightweight, flexible, fire-retardant, etc. [1]
We developed a facile way to build coherent pathway throughout the electrodes and the gel polymer electrolyte by applying PVDF-HFP both in electrodes and electrolyte
The active material (AC) symmetric capacitor with gel polymer electrolyte (GPE) show that 4 μm GPE is the threshold as effective separator, and 12 μm GPE is the optimized thickness with regard to the capacitance and rate capability
Summary
Portable/wearable electronic devices (e.g., mobile phones, laptops, cameras, smartwatch, activity trackers, and many more) are flourishing and demanding improved energy storage devices: small, thin, lightweight, flexible, fire-retardant, etc. [1]. Conventional organic electrolytes [19], redox-active electrolytes [20], and ionic liquids [21,22] have already been incorporated with PVDF-HFP matrix to fabricate flexible supercapacitors with high energy density and safety. The coherent PVDF-HFP matrix provides a highway for ion movement throughout the electrodes and the electrolyte This structure enhances the rate capability and the capacitance, which, in turn, allows for both high power densities and energy densities. We fabricate a symmetric supercapacitor with high energy density and power density thanks to the novel activated carbon/polyoxometalates hybrid material coupled with the gel polymer electrolyte. The gel-polymer-contained electrodes were prepared by dispersing the active materials, carbon black and PVDF-HFP (pre-dissolved in NMP), at a weight ratio of 85:5:10. The calculation of capacitance, power densities and energy densities are presented in Supplementary Materials 1, Equation S1–S5
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