## 3 Applications of IL-Based Gels
### Li-Ion Batteries  
Li batteries are still the most widely developed and commercialized. The nano approach involving cathode and anode materials, e.g., CNT anodes, silicon anode, and cathode nanoparticles, was revealed by [PERSON] et al. as the most promising for the development of Li-ion batteries [78]. The development of IL-based gel in this type of battery also varies according to the trend of the Li battery itself [24; 79]. For example, IL-based gels, in order with most inventions, are found in Li-ion batteries, Li-metal batteries, Li-oxygen batteries, and Li polymer batteries. In 2017, [PERSON] et al. [20] reported the development of two IL-based gel capabilities in two different cases. In the first case, the electrolyte was prepared as thin film, gel 1, by mixing and stirring TMOS/VTEOS and formic acid catalyst in IL, as shown in Figure 4a. The authors then made a Li iron phosphate (LiFePO\({}_{4}\))/IL-based gel film/Li electrochemical device that operated at a capacity of 145 mAh g\({}^{-1}\) at C/10 rate to ensure the ability of the sol to penetrate the LiFePO\({}_{4}\) electrode; therefore, the resulting power density (203.15 W kg\({}^{-1}\)) and energy density (406.3 Wh kg\({}^{-1}\)) were higher compared to previously reported solid-state Li batteries [80]. Moreover, at increased C/2 rate, the device retains 96% of its initial capacity after 150 cycles (Figure 4b). In the second case, they examined the versatility of the IL-based gel for a new fabrication utilizing UV cross-linking synthesis by mixing TMOS, methanol, and BMIMTFSI IL containing 0.5 M LiTFSI (gel 2). The Li battery with LiFePO\({}_{4}\) cathode, Li anode, and gel 2 electrolyte delivered a capacity of 124 mAh g\({}^{-1}\) with an energy density of 403 Wh kg\({}^{-1}\) and a power density of 201.5 W kg\({}^{-1}\) at C/2 rate and impressive reversibility (80 cycles) with no virtual loss of capacity (Figure 4b). [PERSON] et al. again carried out an investigation in 2019 [27] and found the inhibitors of the reaction that they called 'chemical attack' and their solutions. In addition, this year, [PERSON] et al. [81] also experimented with electron beam irradiation (EBI) to create stretchable cross-linked GPE (C-GPE). Poly(vinylidene fluoride-co-hexafluoropropylene) polymer film (P(VDF-HFP))/trially1 isocyanurate (TAIC) combined IL EMIMTFSI exhibited a tensile strength of 10.6 MPa, with almost full recovery after 100% stretching. Contributing to the development of IL-based gels in Li-ion batteries, [PERSON] et al. [82] revealed an increase in the ionic conductivity of a battery to 1.19 mS cm\({}^{-1}\) that was assembled with a GPE membrane with 45.5% IL N-methyl-N-butyl-piperidine-bis(trifluoromethylsulfonyl)imide (NNBI). With cast, the membrane of GPE polyvinylidene fluoride (PVDF)/polyvinyl alcohol (PVA)/NNBI had a tensile strength of 24.11 MPa compared to PVDF/PVA with only 17.95 MPa. The capacities of 118 mAh g\({}^{-1}\) and 136 mAh g\({}^{-1}\) were achieved in the first and second discharge cycles. A new, porous, cross-linked membrane GPE, used as a rechargeable Li-ion battery separator, was introduced in 2018 and contained ZnONP as pore-forming and filler materials [83]. The membrane is made from a mixture of P(VDF-HFP) and a cross-linked polymer of poly(ethylene glycol methyl ether methacrylate) (PEGMEMA), methyl methacrylate (MMA), and octavinyl-T8-silesquisoxane (OVPOSS), which were swelled by propylene carbonate (PC) and 18% 30 nm ZnONP before being eluted by hydrochloric acid, resulting in micropores. The ionic conductivity of a Li-ion battery using this membrane is 1.4 mS cm\({}^{-1}\) and the mechanical strength is 11.5 MPa. \begin{table}
\begin{tabular}{l l} \hline \hline
**GPE** & **OIG** \\ \hline + solid or semisolid phase & + solid-like phase \\ + high mechanical strength & + higher conductivity \\ + wide temperature range & - medium temperature range \\ - complicated manufacturing process & + easy manufacturing process \\ - non-recyclable & + recyclable \\ & + eco-friendly \\ \hline \hline \end{tabular}
\end{table}