## 2 Preparation of IL-Based Gel
### Classification of Preparation Methods
#### 2.1.2 Polymerization Method
The TMPTMA monomer and initiator (2,2-Azobis-(2,4-dimethylwateronitrile)) (ABVN) were dissolved into the mixture of plasticizer, N1,4,4, TFSI, LiTFSI, and DMC by ultrasonic stirring for 30 min to obtain the precursor solution. The as-formed precursors were polymerized at 80 \({}^{\circ}\)C for 30 min to obtain transparent IL-based gel electrolytes for lithium-ion battery applications. Photopolymerization has been used extensively for fabricating IL-based gel electrolytes in recent years. This process offers a facile and quick synthesis route. A study published in 2018 reported the preparation of a flexible and highly conductive IL-based gel by in situ UV-initiated free-radical polymerization of thiolacrylate precursors in the presence of EMIMTFSI of various proportions [38]. Another work by [PERSON] and colleagues [39] showed the fabrication of a hydrophobic, robust, and ultrahigh stretchable IL-based gel using an ex situ method that was the photopolymerization of the monomer and subsequent swelling of the polymer in IL. For fabrication of the IL-based gel ethyl acrylate (EA), ethylene glycol dimethacrylate (EGDMA) and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (PBPO) as the monomer, cross-linker, and photoinitiator, respectively, were used. Firstly, the photopolymerization of EA monomer solution in EGDMA and PBPO was conducted to obtain a poly(ethyl acrylate) PEA elastomer. Finally, EMIMTFSI IL was incorporated into the elastomers to obtain a transparent IL-based gel. The as-prepared IL-based gel exhibited outstanding durability while utilized in a skin-like sensor under harsh environmental conditions. Meanwhile, [PERSON]'s team described the preparation of a highly conductive IL-based gel electrolyte via photopolymerization using a mixture of PEGDA polymer and camphorquinone and (4-octyloxyphenyl)phenyliodonium hexafluoroantimonate) as the photoinitiator in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF\({}_{4}\)) containing calcium salt as solvent [40]. Recently, in 2019, [PERSON] et al. synthesized an ultradurabledouble network (DN) IL-based gel composed of densely cross-linked polyvinyl alcohol (C-PVA) as the first network and coarsely cross-linked poly(2-hydroxyethyl methacrylate) (C-pHEMA) as the second network in EMIMBF\({}_{4}\) as solvent and K\({}_{2}\)S\({}_{2}\)O\({}_{8}\) as initiators via a two-step, thermally-initiated, free-radical polymerization [41]. Then, in 2020, [PERSON] and coworkers developed a physically linked DN IL-based gel for a flexible bimodal sensor via interpenetrating a poly- (hydroxyethyl acrylate) (PHEA) into an agarose network in 1-ethyl-3-methylimidazolium chloride (EMIMCI) [42]. The mixture of hydroxyethyl acrylate (HEA) and EMIMCI were heated and magnetically stirred for 5 min to obtain a homogeneous solution. Then, agarose was added to the solution and stirred at 85 \({}^{\circ}\)C and cooled to room temperature to obtain an agarose IL-based gel. The DN IL-based gel was finally produced by the photopolymerization of HEA monomer after irradiating under a 365 nm LED light intensity of 80 mw/cm\({}^{2}\) for 5 min. Similarly, by using in situ photopolymerization, [PERSON]'s group reported the synthesis of a transparent, stretchable, phase-transformable 1,3-dimethyl imidazolium bis(trifluoromethyl  
solution casting technique [50; 51; 52]. The authors concluded that by increasing the LiTFSI and Pyr\({}_{13}\)TFSI content, the ionic conductivity of the IL-based gel increases and reaches a maximum value of 0.693 mS cm\({}^{-1}\) at 25 \({}^{\circ}\)C when the IL-based gel contains 30 wt% LiTFSI and 60 wt% Pyr\({}_{13}\)TFSI. Recently, in 2020, [PERSON] employed the solution casting method to synthesize a polymer gel electrolyte with P(VDF-HFP) and TFSI-based IL containing trihexyltetradoylphosphonium (P\({}_{14,6,6,6}\)) cation at different ratios of polymer to IL [53]. Similarly, [PERSON] et al. fabricated an IL-based gel electrolyte from P(VDF-HFP) and LiTFSI/EMIMTFSI via a simple solution casting method [54].