Solid-state graphene-based supercapacitor with high-density energy storage using ionic liquid gel electrolyte: electrochemical properties and performance in storing solar electricity

One-step hydrothermal synthesis of porous Ti3C2Tz MXene/rGO gels for supercapacitor applications

Titanium carbide/reduced graphene oxide (Ti₃C₂T_z/rGO) gels were prepared by a one-step hydrothermal process. The gels show a highly porous structure with a surface area of ∼224 m² g^-1 and average pore diameter of ∼3.6 nm. The content of GO and Ti₃C₂T_z nanosheets in the reaction precursor was varied to yield different microstructures. The supercapacitor performance of Ti₃C₂T_z/rGO gels varied significantly with composition. Specific capacitance initially increased with increasing Ti₃C₂T_z content, but at high Ti₃C₂T_z content gels cannot be formed. Also, the retention of capacitance decreased with increasing Ti₃C₂T_z content. Ti₃C₂T_z/rGO gel electrodes exhibit enhanced supercapacitor properties with high potential window (1.5 V) and large specific capacitance (920 F g^-1) in comparison to pure rGO and Ti₃C₂T_z. The synergistic effect of EDLC from rGO and redox capacitance from Ti₃C₂T_z was the reason for the enhanced supercapacitor performance. A symmetric two-electrode supercapacitor cell was constructed with Ti₃C₂T_z/rGO, which showed very high areal capacitance (158 mF cm^-2), large energy density (∼31.5 μW h cm^-2 corresponding to a power density of ∼370 μW cm^-2), and long stability (∼93% retention) after 10 000 cycles.

Structural, electrical and electrochemical studies of ionic liquid-based polymer gel electrolyte using magnesium salt for supercapacitor application

In the present studies, the effect of ionic liquid 1-Ethyl-2,3-dimethylimidazoliumtetrafluoroborate (EDiMIM)(BF4) on ionic conductivity of gel polymer electrolyte using poly(vinylidene fluoride-co-hexafluoropropylene) [PVdF(HFP)] and magnesium perchlorate [Mg(ClO4)2] as salt was investigated. The maximum room temperature ionic conductivity for the optimized system was found to be of the order of 8.4 × 10–3 S cm−1. The optimized composition reflects Vogel-Tammann-Fulcher (VTF) behavior in the temperature range of 25 °C to 100 °C. The X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy studies confirm the uniform blending of ionic liquid, polymer, and salts along with the enhanced amorphous nature of the optimized system. Dielectric and modulus spectra studies provide the information of electrode polarization as well as dipole relaxation properties of polymeric materials. The optimized electrolyte system possesses a sufficiently large electrochemical window of the order of 6.0 V with stainless steel electrodes.

Two-Dimensional Tungsten Oxide/Selenium Nanocomposite Fabricated for Flexible Supercapacitors with Higher Operational Voltage and Their Charge Storage Mechanism

The present work elaborates the high-energy-density, stable, and flexible supercapacitor devices (full-cell configuration with asymmetric setup) based on a two-dimensional tungsten oxide/selenium (2D WO₃/Se) nanocomposite. For this, the 2D WO₃/Se nanocomposite synthesized by a hydrothermal method followed by air annealing was coated on a flexible carbon cloth current collector and combined separately with both 0.1 M H₂SO₄ and 1-butyl-3-methyl imidazolium tetrafluoroborate room temperature ionic liquid (BmimBF₄ RTIL) as electrolyte. Different physicochemical characterization techniques, viz., transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy, are utilized for phase confirmation and morphology identification of the obtained samples. The electrochemical analysis was used to evaluate charge storage mechanism. The half-cell configuration (three electrode system) in 0.1 M H₂SO₄ shows a specific capacitance of 564 F g^-1 at 6 A g^-1 current density, whereas with ionic liquid as electrolyte, a higher specific capacitance of 1650 F g^-1 was obtained at a higher current of 40 mA and working potential of 4 V. Importantly, the asymmetric flexible supercapacitor device with PVA-H₂SO₄ electrolyte shows a working voltage of 1.7 V. A specific capacitance of 858 mF g^-1 is obtained for the asymmetric electrode system with an energy density of 47 mWh kg^-1 and a power density of 345 mW kg^-1 at a current density of 0.2 A g^-1.

Roadmap on Ionic Liquid Electrolytes for Energy Storage Devices

Ionic liquids are considered to be promising electrolyte solvents or additives for rechargeable batteries (i. e., lithium-ion batteries, sodium-ion batteries, lithium-sulfur batteries, aluminum-ion batteries, etc.) and supercapacitors. This is related with the superior physical and electrochemical properties of ionic liquids, which can influence the performance of rechargeable batteries. Therefore, it is necessary to write a roadmap on ionic liquids for rechargeable batteries. In this roadmap, some progress, critical techniques, opportunities and challenges of ionic liquid electrolytes for various batteries and supercapacitors are pointed out. Especially, properties and roles of ionic liquids should be considered in energy storage. Ionic liquids can be used as electrolyte salts, electrolyte additives, and solvents. For optimizing ionic liquid-based electrolytes for energy storage, their applications in various energy storage devices should be considered by combing native chemical/physical properties and their roles. We expect that this roadmap will give a useful guidance in directing future research in ionic liquid electrolytes for rechargeable batteries and supercapacitors.