## 3 Applications of IL-Based Gels
### Ca-Ion Batteries  
Ca-ion batteries are a prospect for a broad field of research, and there is much scope for the development of electrodes and electrolytes that enable stable long-term battery operation [99]. Due to this promising alternative to post-Li batteries that are more cost-effective and can be applied on a large scale, various designs of Ca batteries have been devised to facilitate research [100,101]. For the first time, liquid GPEs were used as electrolytes and separators in Ca-ion batteries at room temperature. [PERSON] et al. [40] prepared an electrolytle solution of Ca perchlorate salt (Ca(ClO\({}_{4}\))\({}_{2}\)), Ca-tetrafluoroborate (Ca(BF\({}_{4}\))\({}_{2}\)), and Ca bis-(trifluoromethylsulfonyl)imide (Ca(TFSI)\({}_{2}\)) dissolved in 1-ethyl-3-methylimidazolium trifluorethanesulfonate (EMIMTFMS) to mix with 2.5% poly(ethylene glycol) diacrylate-photoinitiator camphorquinone (PEGDA-CQ) and 1.5% 4-octyloxyphenyl)phenyliodonium hexafluoroantimonate (4 OPP-HFA) as a photoinitiator system, and then injected them into a Teflon ring cell and exposed them to a light emitting diode (LED) to form a gel. They reported ionic conductivity at room temperature between 10\({}^{-4}\) and 10\({}^{-3}\) S cm\({}^{-1}\), stability of up to 4 V, a cationic transfer rate of 0.17, high thermal stability up to 300 \({}^{\circ}\)C, and an initial discharge capacity of 140 mAh g\({}^{-1}\). They further constructed a full cell battery consisting of a vanadium oxide (V\({}_{2}\)O\({}_{5}\)) anode and a calcium cobalt oxide (Ca\({}_{3}\)Co\({}_{4}\)O\({}_{9}\)) cathode, particularly for the case of Ca(TFSI)  
Figure 5: Proportion regulation and optimization of components in Na-IL/P(VDF–HFP)@SBA-15: (**a**) ternary phase diagram of Na-IL/PVDF–HFP@SBA-15 with different X and Y values; X, mass ratios of Na-IL/SBA-15; Y, mass ratios of PVDF–HFP/SBA-15; (**b**) digital photographs of Na-IL/PVDF–HFP@SBA-15 with X = 2.3, 2.7, 3.0 (fixed Y = 0) and Y = 0.1, 0.2, 0.3 (fixed X = 2.7); (**c,d**) ionic conductivity of Na-IL/P(VDF–HFP)@SBA-15 corresponding to different ratios of Na-IL/SBA-15 and different ratios of PVDF–HFP/SBA-15 at room temperature, with fixed Y = 0 and X = 2.7, respectively; (**e**) cycle performance of Na! Na-IL/PVDF–HFP@SBA-15! NVP at 0.1 C (30 \({}^{\circ}\)C). Reprinted with permission from ref. [69]. salt. The battery offered first cycle charge and discharge capacities above 120 mAh/g and an open-circuit voltage of 1.2 V (Figure 6a). In addition, the battery was charged and discharged at operating cell voltages from 3 V (cutoff) to 5 V for 25 operational cycles (Figure 6b). Organic batteries are proclaimed to be the lifestyle of the future because they are environmentally friendly, simple, inexpensive, and can be charged and emptied multiple times at high faradaic efficiencies with no signs of degradation [102]. The trends and developments in organic batteries have been summarized by [PERSON] et al. [103]. Roll-to-roll printable GPE was also developed for all-organic batteries. [PERSON] et al. [46], placed IL-based gel in the form of 370 GPE microfilms of BMIMTFSI and a polymer matrix of poly(ethylene glycol) methylether methacrylate (mPEG-MA) directly onto a solid-state battery electrode, and then polymerized using UV-polymerization to create a stable film. The advantage of this process is that it does not require a solvent. They tested with a poly(2,2,6,6-tetramethyl-4-piperidinyl-N-oxyl methacrylate) (PTMA) cathode and a poly(2-vinyl-11,11,12,12-tetracyano-9,10-anthraquinondimethene) (poly(TCAQ)) anode and found positive reports when this IL-based gel was applied as an electrolyte and separator in organic solid-state batteries. To make it easier to compare the applications of various IL-based gels on various batteries, the reports are arranged in Table 2. Formulating IL-based gel electrolytes with a large electrochemical window and ionic conductivity is an important research orientation for obtaining high-performance batteries.