## 2 Preparation of IL-Based Gel
### Classification of Preparation Methods
#### 2.1.2 Polymerization Method  
There have been a number of reviews on the preparation of IL-based gels by in situ polymerization or cross-linking of monomers dissolved in IL [13; 14; 16; 17; 18]. Generally, the in situ polymerization process involves dissolving a polymerizable monomer in ILs with or without the use of a cosolvent and followed by the removal of the cosolvent. Free radical, chain, step, thermal, and photopolymerization are the common techniques employed to synthesize IL-based polymeric gels [13; 14; 23]. Another route is the soaking method, which involves the swelling of a polymer in IL or by preparing polymer film in multistep procedures and then soaking the as-prepared film with IL [33]. The IL-based polymer-IL  
Figure 1: (**a**) FESEM image of the surface of IE-T electrolyte; (**b**) FESEM image of the cross-section of IE-T electrolyte; (**c,d**) FESEM images of the IE-T electrolyte sample after ionic liquid has been extracted; (**e**) FESEM image of the surface of IE-B electrolyte; (**f**) FESEM image of the IE-B sample after ionic liquid has been extracted; (**g**) photograph of IE-T electrolyte and schematic of internal microscopic three-dimensional structure of ionogel. Reprinted with permission from ref. [30]. -based gels can also be obtained via the solution casting method, which typically includes the dissolution of polymer and IL in a volatile solvent followed by the casting and drying of the homogenous mixture to remove the solvent. [PERSON] et al. [34] summarized the design and preparation of polymer/inorganic hybrid electrode (HE), as well as the enhancement of its electrochemical characteristics. Recently, [PERSON] et al. [35] reported the preparation of robust IL gel electrolytes for a supercapacitor by dissolving Poly(vinylidene fluoride-co-hexafluoropropylene) polymer (P(VDF-HFP)) in two promising ILs, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIMTFSI) and 1-butyl-1-methylpyrrolidininium tris(pentafluoroethyl)trifluorophosphate [C4 mpyrr][eFAP], respectively, with stirring at 70 \({}^{\circ}\)C for 12 h and drying at 50 \({}^{\circ}\)C. Finally, the samples were stirred vigorously for 0.5 h above their sol-gel temperature and followed by cooling again to 50\({}^{\circ}\)C. The minimum concentration of P(VDF-HFP) polymer needed to form an IL-based gel was reported to be 4 wt% for these, EMIMTFSI and [C4 mpyrr][eFAP]. The ionic conductivities of EMIMTFSI-based and [C4 mpyrr][eFAP]-based IL-based gels were estimated to be 8.6 and 1.0 mS cm\({}^{-1}\) at 25 \({}^{\circ}\)C, respectively, with a very minor loss of conductivities compared to those of pure ILs, EMIMTFSI (9.5 mS cm\({}^{-1}\)) and [C4 mpyrr][eFAP] (1.2 mS cm\({}^{-1}\)). In 2019, [PERSON] and coworkers [23] prepared a 3D IL-based gel by mixing thiol, acrylate monomers, trimethylolpropane tris(3-mercaptoethanol), and polyethylene glycol diacrylate (PEGDA) in triethylamine (TEA) catalyst in the presence of EMIMTFSI using the Michael addition polymerization process. The resulting IL-based gel with 50% wt of IL showed remarkable ionic conductivity in the range of 0.1 mS cm\({}^{-1}\), and the prepared IL-based gels were suggested as advantageous for fabricating soft robotics, soft actuators, flexible and stretchable electronics, and medical devices. Recently, in 2021, [PERSON]'s group designed an IL-based gel electrolyte for sodium battery applications by mixing N-ethyl-N-methylpyrrolidinium bis(fluorosulfonyl)imide (C2 mpyrrFSI) IL with NaFSI supported on a mat of electrospun poly (vinylidene fluoride) (PVDF) nanofibers [36]. Meanwhile, [PERSON] and his team developed a novel trimethylolpropane trimethylacrylate (TMPTMA)-based IL-based gel electrolyte via in situ thermal polymerization using lithium bis(trifluoromethane)sulfonamide (LiTFSI), dimethylcarbonate (DMC), and IL (IL)-tributylmethylammonium bis(trifluoromethane)imide (N1,4,4, TFSI) [37].