## 3 Results
Due to their remarkable thermal stability, membranes are particularly suitable for incorporation into LIBs as they contribute to the overall safety assurance of the battery. To evaluate the thermal stability of the Gel Polymer Electrolytes, Thermogravimetric Analysis (TGA) was performed under a nitrogen atmosphere using a heating rate of 10 \({}^{\circ}\)C min\({}^{-1}\) over a temperature range of 30-600 \({}^{\circ}\)C. Examination of the TGA curves for the PP membranes, as shown in Figure 4a, led to the determination that the onset of degradation occurred at approximately 270 \({}^{\circ}\)C. The apparent weight loss ranging from 4% to 5% for all samples below 200 \({}^{\circ}\)C is attributed to the loss of volatile components incorporated in the polymer matrix. In contrast, PP2 and PP3 membranes containing BMEP exhibit significantly higher decomposition temperatures compared to the PP1 membrane without BMEP. This difference and increased thermal stability are attributed to the highly crosslinked structure provided by BMEP. The evaporation of both bound and unbound water molecules present in the structure is the reason behind the weight reduction in membranes, which approaches 15-18% in the 200-300 \({}^{\circ}\)C temperature range. All these results support the excellent thermal stability of polymer membranes, with significant thermal degradation occurring mainly above 300 \({}^{\circ}\)C. The safety and applicability credentials of these membranes are thus strengthened and they should be considered as reliable and suitable candidates for integration into lithium-ion batteries. Figure 3: SEM images of the membranes: (**a**) PP1; (**b**) PP2; (**c**) PP3. Differential Scanning Calorimetry (DSC) was employed to glass transition temperatures, utilizing a heating rate of 10 \({}^{\circ}\)C min\({}^{-1}\) under a nitrogen (N\({}_{2}\)) atmosphere. The DSC investigations were conducted over two thermal cycles within hermetically sealed aluminum pans, encompassing a temperature range from \(-\)10 \({}^{\circ}\)C to 150 \({}^{\circ}\)C. The glass transition temperature (Tg) was deduced as the midpoint of the gradual transition occurring during the second heating cycle (Figure 4b). In this context, the expected effect of a substantial crosslinked network can lead to high Tg values [39]. The ionic conductivity of gel polymer electrolytes is significantly affected by the glass transition temperature. The claim that polymer electrolytes with certain chemical compositions can achieve high ionic conductivity independent of Tg values is supported by various studies [40]. Consequently, the determined Tg values for the PP1, PP2, and PP3 membranes were observed to be 61 \({}^{\circ}\)C, 59 \({}^{\circ}\)C, and 59 \({}^{\circ}\)C, respectively. The mechanism of the membrane's liquid electrolyte uptake is illustrated graphically in Figure 5a. The lowest absorption values, 279% and 296% for PP1 and PP3 membranes, respectively, demonstrate the way these polymer membranes can absorb electrolytes better than some conventional matrices [41]. An important finding is that the PP2 membrane has the highest electrolyte uptake, with a maximum value of 345%. The membrane's substantial porosity, which promotes effective ion transport and is crucial in increasing the ionic conductivity of gel polymer electrolytes, is responsible for the remarkable electrolyte absorption ability [42]. A battery separator with exceptional dimensional stability can enhance safety and have a positive effect on battery performance by preventing electrode contact [43]. As demonstrated by Figure 1, the PP membranes exhibited good dimensional stability following swelling with liquid electrolyte; no discernible dimensional change, asymmetry, or wrinkles were present. Figure 5b, which depicts the findings of the electrolyte leakage studies, demonstrates that all membranes attain leakage equilibrium within the first 25 min period and that there is no further leaking after that.