# Effect of MXene Nanosheet Sticking on Supercapacitor Device Performance
## 2 MXenes as Supercapacitor Electrodes
### Advantages of MXenes in Supercapacitors
#### 2.2.3 MXene-Polymer Composites: A Synergistic Approach to Enhanced Supercapacitors  
While MXenes, in combination with various materials, exhibited extraordinary progress in supercapacitor technology, the stacking of MXene layers and diminishing electrochemical performance with increasing electrode thickness remained concerns. These limitations prompted researchers to explore composite structures of MXenes with polymers, offering flexibility and enhanced electrochemical performance.  
One key consideration was the use of single-layered MXene sheets, which possess higher surface hydrophilicity and superior compatibility with polymers due to their high aspect ratio compared to multilayered MXene sheets [36]. Researchers embarked on a journey to unlock the potential of MXene-polymer composites to overcome these limitations.  
[PERSON] et al. [37] significantly improved the specific capacitance of MXene by electrochemically depositing conducting polypyrrole (PPy) on MXene textile electrodes, resulting in a specific capacitance of 343.20 F g\({}^{-1}\) compared to the pristine MXene electrode with a specific capacitance of 182.70 F g\({}^{-1}\). A solid-state symmetrical supercapacitor fabricated with the MXene-PPy electrode showcased an energy density of 1.30 mWh g\({}^{-1}\). This innovation illustrated the promise of MXene-PPy composite materials in supercapacitor applications [38] with not only improved tensile strength but also resulting in a specific capacitance of 614 F g\({}^{-1}\) at 1 A g\({}^{-1}\). Crucially, this impressive performance retained 100% of its capacitance over 10,000 cycles. PPy nanoparticles and ionic liquid-based microemulsions were incorporated into Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXene layers, acting as dual spacers that elevated the electrochemical performance of supercapacitor electrodes. The PPy particles prevented MXene layer restacking, while the ionic microemulsions improve electrode wettability, enhancing the ion-accessible surface area. A symmetric supercapacitor produced with PPy-MXene-IL-mic composite showed an energy density of 31.2 Wh kg\({}^{-1}\) at room temperature. It maintained a capacitance retention rate of 91% over 2000 cycles and exhibited a coulombic efficiency of 91% over a temperature span of 4 \({}^{\circ}\)C to 50 \({}^{\circ}\)[39].  
[PERSON] et al. [40] took a step further by synthesizing a Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) MXene composite through in situ polymerization of polyaniline (PANI) on the MXene surface. The composite exhibited volumetric and gravimetric capacitances of 1682 F cm\({}^{-3}\) and 503 F g\({}^{-1}\), respectively. Moreover, the specific capacitance reached 336 F g\({}^{-1}\), with 98.3% capacitance retention after 10,000 cycles.  
The scope of MXene-polymer composites extended to asymmetric supercapacitors, exemplified by an asymmetric supercapacitor composed of PANI0.7/MXene as the cathode and MXene as the anode in a 1M H\({}_{2}\)SO\({}_{4}\) electrolyte. This configuration achieved an impressive energy density of 65.6 Wh L\({}^{-1}\)[41]. The performance of MXene/PANI nanoparticle composite symmetric supercapacitors was equally impressive, with an areal and volumetric energy density of 90.3 mWhcm\({}^{-2}\) and 20.9 Wh L\({}^{-1}\), respectively [41]. The heightened capacitance can be attributed to the effect of PANI nanoparticles, which intercalate between the MXene layers, preventing restacking and establishing an interconnected conductive channel that facilitates ion transport. The expansion of interlayer spacing by PANI nanoparticles enhanced the faradic charge storage mechanism, resulting in increased energy density for composite-electrode-based supercapacitors.