In the past decade, MXenes, a new class of advanced functional 2D nanomaterials, have emerged among numerous types of electrode materials for electrochemical energy storage devices. MXene and their composites have opened up an interesting new opportunity in the field of functional materials, owing to their transition metal nitrides/carbides/carbonitride-based unique layered structures, higher electrical and thermal conductivity, higher charge carrier mobility, high negative zeta-potential, high mechanical properties, tunable bandgap, superior hydrophilicity, metallic nature and rich surface chemistry, which enhance the number of metal active redox sites on the surface and short ion diffusion path. However, in the case of electrochemical energy storage applications, the unavoidable problem of aggregation and nanosheet restacking significantly reduces the accessibility of the active surface sites of MXene materials for electrolyte ions. Currently, there is a number of research efforts devoted to solutions in order to avoid these deficits. This Review complies extensively with the recent advances in the application of MXene-based materials in the energy storage devices such as batteries and supercapacitors. Particular attention is paid to the understanding of the relation of MXenes chemical composition, and morphology with their electrochemical performances. Moreover, the challenges of MXenes and MXene-based composited for the commercial application are considered and the ways to overcome their drawbacks are provided. Finally, opportunities given with MXenes for future research on novel energy storage materials are highlighted.

Nowadays, the rapid development and demand of high-performance, lightweight, low cost, portable/wearable electronic devices in electrical vehicles, aerospace, medical systems, etc., strongly motivates researchers towards advanced electrochemical energy storage (EES) devices and technologies. The electrolyte is also one of the most significant components of EES devices, such as batteries and supercapacitors. In addition to rapid ion transport and the stable electrochemical performance of electrolytes, great efforts are required to overcome safety issues due to flammability, leakage and thermal instability. A lot of research has already been completed on solid polymer electrolytes, but they are still lagging for practical application. Over the past few decades, ionic liquids (ILs) as electrolytes have been of considerable interest in Li-ion batteries and supercapacitor applications and could be an important way to make breakthroughs for the next-generation EES systems. The high ionic conductivity, low melting point (lower than 100 °C), wide electrochemical potential window (up to 5–6 V vs. Li⁺/Li), good thermal stability, non-flammability, low volatility due to cation–anion combinations and the promising self-healing ability of ILs make them superior as “green” solvents for industrial EES applications. In this short review, we try to provide an overview of the recent research on ILs electrolytes, their advantages and challenges for next-generation Li-ion battery and supercapacitor applications.