The chemistry underlying the storage phenomena in batteries and supercapacitors has been known to mankind for quite some time now. Nonetheless, a holistic apprehension of their rudimentary characteristics throughout their lifetime and beyond is imperative to accentuate their maximum potential. Although numerous reviews have addressed many of the facts individually, a consolidated report on the associated history, challenges, and environmental aspects considering the cutting‐edge advancements in this field is missing. This review gives a comprehensive insight into the two technologies by drawing a detailed comparison between their governing attributes and potential challenges. First, a brief history of batteries and supercapacitors along with their classifications based on materials and corresponding working mechanisms are delineated. Thereafter, some of the inexorable losses restricting the performance of these systems from reaching their theoretical limits are outlined. A picture of the significance of theoretical modeling of batteries and supercapacitors highlighting the associated challenges in the same is drawn. Furthermore, their fates after retirement as well as their scopes in the future based on their current trends are reported in the ensuing sections. Alongside detailed tutorial background of energy storage literature, this review compares different energy storage devices and the latest developments in this field.

Supercapacitors store electrical energy on the basis of electrostatic attraction between opposite charges as a result of the formation of an electric double layer (EDL) at the electrolyte/electrode interface. Carbon-derived materials are commonly used to fabricate supercapacitor electrodes owing to their high electrical conductivity, high capacitance, excellent porosity, good electrochemical stability, and large specific surface area. [131-136] Predominantly, these materials include carbon nanotubes (CNTs), graphene, carbon spheres, hollow carbon spheres, carbon nanoparticles (CNPs), etc. [62,137-145] Nevertheless, they fail to demonstrate the desirable performance in practical applications after a certain threshold owing to their short durability and low energy density. Although, metal-organic frameworks (MOFs) have proven to be better electrode candidates in certain aspects, [142,143,146-148] however, these materials incur high cost, low yield of porous carbon, high consumption of metallic nitrate, [62] and hence higher waste generation. Due to the rising concerns of waste production and its management and hence the need for sustainable and cheap resources, reusing and/or converting waste from various sources such as industrial, agricultural, food, and spent electronic devices efficiently into usable carbon has attracted much interest since recently.

With countries and regions setting strict targets for adopting renewable and sustainable technologies, worldwide demand for energy storage has surged dramatically. Novel materials and new storage chemistry solutions are being explored to realize storage technologies for the next generation. This step-change includes fundamental research in the design of new electrolytes. Ionogels are gaining popularity in electrochemical applications because of their ability to overcome the drawbacks of their liquid counterparts while retaining certain beneficial qualities of the latter. The present study reports the preparation of a novel quasi-solid ionogel through the confinement of the ionic liquid (IL) trihexyltetradecylphosphonium bis(trifluoromethylsulfonyl)imide ([P 66614 ][TFSI]) into a matrix of titania (TiO 2 ) by a simple one-pot sol−gel process. The properties of the ionogel have been studied via field emission scanning electron microscopy (FESEM), rheology, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and cyclic voltammetry (CV). The ionogel manifests shear-thinning viscoelastic behavior. The integrity of the IL remains unaffected after its confinement in TiO 2 . Thermal stability analysis shows little mass loss of the ionogel up to a temperature of ∼93 °C, favoring its utilization in hightemperature applications. The ionogel demonstrates a double-layer capacitive behavior with an impressive operating potential window (OPW) of 4 V (−4 to +4 V), substantiating its applicability and excellent stability in the electrochemical domain. The formation of the weakly coordinating ionogel is analyzed using density functional theory (DFT). The electronic structures of the precursors and the ionogel are elucidated at the B3LYP/LANL2DZ level of theory. The quantum chemical (QC) calculations reveal that the interaction of the IL with the cross-linker results in some dimensional changes due to alterations in the vibrational frequencies of the respective groups present in the ionogel system.

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