Abstract
Recent critical issues regarding next-generation energy storage systems concern the cost-effective production of lightweight, safe and flexible supercapacitors yielding high performances, such as high energy and power densities as well as a long cycle life. Thus, current research efforts are concentrated on the development of high-performance advance electrode materials with high capacitance and excellent stability and solid electrolytes that confer flexibility and safety features. In this work, emphasis is placed on the binder-free, needle-like nanostructured Mn/MnOx layers grown onto graphite-foil deposited by reactive sputtering technique and to the polymer gel embedded ionic electrolytes, which are to be employed as new flexible pseudocapacitive supercapacitor components. Microstructural, morphological and compositional analysis of the layers has been investigated by X-ray diffractometer (XRD), Field Emission Scanning Electron Microscope (FE–SEM) and X-ray photoelectron spectroscopy (XPS). A flexible lightweight symmetric pouch-cell solid-state supercapacitor device is fabricated by sandwiching a PPC-embedded ionic liquid ethyl-methylimidazolium bis (trifluoromethylsulfonyl) imide (EMIM)(TFSI) polymer gel electrolyte (PGE) between two Mn/MnOx@Graphite-foil electrodes and tested to exhibit promising supercapacitive behaviour with a wide stable electrochemical potential window (up to 2.2 V) and long-cycle stability. This pouch-cell supercapacitor device offers a maximum areal capacitance of 11.71 mF/cm2@ 0.03 mA/cm2 with maximum areal energy density (Ea) of 7.87 mWh/cm2 and areal power density (Pa) of 1099.64 mW/cm2, as well as low resistance, flexibility and good cycling stability. This supercapacitor device is also environmentally safe and could be operated under a relatively wide potential window without significant degradation of capacitance performance compared to other reported values. Overall, these rationally designed flexible symmetric all-solid-state supercapacitors signify a new promising and emerging candidate for component integrated storage of renewable energy harvested current.
Highlights
The growing demand for modern flexible portable electronics increases the need for lightweight, low-cost, high-performance compact power sources [1,2,3]
The phase analysis of sputter-grown Mn/manganese oxide (MnOx)@Graphite-foil electrodes and bare graphite foil was performed by X-ray diffraction (XRD) analysis
The X-ray diffractometer (XRD) analysis (Figure 1a) exhibits that in the as-coated case, Mn/MnOx coatings deposited on graphite foils are amorphous
Summary
The growing demand for modern flexible portable electronics increases the need for lightweight, low-cost, high-performance compact power sources [1,2,3]. The commercially available supercapacitors (SCs) can provide a reasonably high capacitance value, fast charge–discharge rate (~0.3 to 30 s), long cycling stability (~105) and high energy density and power density compared to conventional capacitor and batteries [11,12]. There is a focus on alternative TMOs electrode materials, especially abundant manganese oxide (MnOx) and its composites, due to its eco-friendliness, low cost and high charge storage capabilities, but the increase in the stable potential window to enhance the energy density of the SC is still under debate. It is crucial to design advance flexible binder-free electrodes to improve the stable potential window as well as enhancing the overall conductivity of the active electrode materials [19,25,28]
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