# Effect of MXene Nanosheet Sticking on Supercapacitor Device Performance
## 2 MXenes as Supercapacitor Electrodes
### Overview of MXenes
Subsequent research led to the synthesis of various MXenes, including Ti\({}_{2}\)CT\({}_{X}\), Zr\({}_{3}\)C\({}_{2}\)T\({}_{X}\), Nb\({}_{2}\)CT\({}_{X}\), Nb\({}_{4}\)C\({}_{3}\)T\({}_{X}\), V\({}_{2}\)CT\({}_{X}\), Ti\({}_{3}\)CNT\({}_{X}\), Mo\({}_{2}\)CT\({}_{X}\), Ti\({}_{4}\)N\({}_{3}\)T\({}_{X}\), Mo\({}_{4}\)VC\({}_{4}\)T\({}_{X}\), Mo\({}_{2}\)ScC\({}_{2}\)T\({}_{X}\), (Ti\({}_{0.5}\), Nb\({}_{0.5}\))\({}_{2}\)CT\({}_{X}\), (Nb\({}_{0.8}\), Ti\({}_{0.2}\))\({}_{4}\)C\({}_{3}\)T\({}_{X}\), and (Nb\({}_{0.8}\), Zr\({}_{0.2}\))\({}_{4}\)C\({}_{3}\)T\({}_{X}\), among others. While over 100 MAX phases have been identified, only more than 30 MXenes have been synthesized and experimentally assessed, fueling ongoing research into the discovery of novel MXenes and their distinctive properties [18]. MXenes have become distinguished for their unique blend of metallic (transition metal atoms) and ceramic (carbon/nitrogen atoms) properties. This distinctive combination has resulted in exceptional attributes: high metallic conductivity reaching up to 6000-8000 S cm\({}^{-1}\), excellent thermal conductivity, remarkable mechanical stability, exceptional optical properties, impressive electric and magnetic properties, outstanding hydrophilicity, customizable surface functional groups, and intercalation capabilities [19; 20]. A 3D VN/MXene composite structure was developed for aqueous zinc-ion batteries, enhancing storage capacity and service life [4]. By encapsulating VN microspheres in MXene nanosheets, the electrode demonstrated high reversible capacity, superior rate performance, and exceptional stability over 2200 cycles. This design strategy offers insights into advanced cathode materials for zinc-ion batteries. These exceptional properties have positioned MXenes as a versatile material suitable for a wide range of practical applications. The tiny lateral size, atomic-scale thickness, and remarkable hydrophilic ability facilitate the creation of flexible, thin MXene layers through processes like vacuum filtration and spraying technology [21]. MXenes' outstanding conductivity enables higher power density compared to metal-oxide semiconductors, ultimately contributing to fast device charging [22]. The tunable surface chemistry, a result of the HF acid etchant, makes MXenes an ideal material for efficient composite electrodes [23]. The swift electron transfer between MXene layers renders them an excellent substrate for catalysis. The characteristics and uses of MXenes demonstrate diversity based on elemental compositions, stoichiometry, synthesis techniques, interlayer distances, layer thickness, and lateral flake dimensions [24]. Traditionally, energy storage devices tend to be rigid and inflexible, limiting their application in emerging domains like wearable electronics, smart garments, and flexible displays [25]. This need has spurred research into devices that provide not just high energy storage capability but also the necessary flexibility and resilience for such uses. In this context, MXene materials have demonstrated significant potential in wearable electrochemical energy storage elements, thanks to their distinctive layered arrangement, abundance of surface terminations, superior electrical conductivity, hydrophilicity, and large specific surface area [26]. The myriad applications of MXenes in electrochemical energy storage devices inspire a comprehensive overview of their synthesis, microstructure, properties, and prospects, factors affecting their electrochemical behavior in supercapacitors, charge storage mechanisms, and state-of-the-art supercapacitors based on MXene composites.