## 3 Varieties of Epoxide-Based Polymer Electrolyte
### Plasticizers and Gel Electrodes
The ionic conductivity was found to be dependent on both the quantity of LiGPS and LiTFSI-PC that was present. Ionic conductivity increased from 4.8 \(\times\) 10\({}^{-8}\) to 3.4 \(\times\) 10\({}^{-7}\) S/cm when the weight percent of LiGPS was increased from 6.3 to 19 [37]. Swelling the electrolyte in LiTFSI-PC had an even greater impact on the ionic conductivity. Ionic conductivities in the swollen samples were 9.2 \(\times\) 10\({}^{-3}\) and 2.4 \(\times\) 10\({}^{-3}\) S/cm for the samples with 19 and 6.3 wt% LiGPS respectively (Figure 8) [37]. LiTFSI-PC was similarly used by [PERSON] et al. who prepared an epoxy-based polymer electrolyte using DGEPEG and 4,4-methylenebis(cyclohexylamine) (PACM) [6]. This material had a relatively high T\({}_{\text{g}}\), 160 \({}^{\circ}\)C, but still achieved a high room temperature ionic conductivity: 1 \(\times\) 10\({}^{-3}\) S/cm when the LiTFSI-PC loading was 30 wt% [6]. The measured ionic conductivity is anticipated to be high, despite limited polymer mobility, as a result of PC decreasing the affinity between the lithium cations and the polymer phase. The material was thermally stable up to 240 \({}^{\circ}\)C where evaporation of PC was observed. Figure 8: Ambient temperature ionic conductivity of polymer electrolytes comprised of DGEPEG, PEGB and LiGPS with various solvent mixtures as a function of LiGPS weight percent. Made from data presented in Journal of Polymer Science Part A-1: Polymer Chemistry, 2010. [PERSON] et al. prepared plasticizer-containing solid polymer electrolytes via the amine-catalyzed polymerization of an epoxide [38]. N-benzyldimethylamine (BDMA) was used to catalyze the polymerization of DGEBA [38]. The resultant polymer was soaked in a mixture of succinonitrile (SN) and LiTFSI to produce samples with various weight percent of the plasticizer mixture. After the curing process, samples containing 30, 50 and 70 wt% of the plasticizer mixture exhibited sufficient three-dimensional crosslinking to exhibit solid-like behavior. The sample containing 30 wt% of the plasticizer mixture was the most conductive with an ionic conductivity on the order of \(10^{-2}\) S/cm at room temperature [38]. The activation energy for ionic conductivity in the material, determined based on the Arrhenius method, was 1.2 eV [38]. As the Arrhenius method is usually used in polymer electrolytes to describe ionic motion at lower temperatures, where ion mobility is dominated by the motion of ions pairs, it is unclear whether this determination of activation energy accounts for the influence of the plasticizer on ion mobility or is solely related to the motion of ion pairs in the solid polymer [90]. Although the solid polymer electrolytes that have been presented thus far contain amine crosslinking agents, they do not need to be present to produce plasticizer-containing solid polymer electrolytes. [PERSON] and [PERSON] prepared solid polymer electrolytes using LiTFSI dissolved in SN to activate the ring opening polymerization reaction in a bisphenol-A epoxy resin called YD-128 [39]. Ionic conductivity increased with increasing LiTFSI-SN content. Ionic conductivity on the order of \(10^{-4}\) S/cm was recorded at 25 \({}^{\circ}\)C in a sample containing 70 wt% LiTFSI [39]. The ionic conductivity in this system is improved by at least an order of magnitude compared with the other polyether epoxide-based solid polymer electrolytes that are discussed in this work. Like plasticizers, ionic liquids can also be used to enhance ionic conductivity in epoxide-based solid polymer electrolytes. Ionic liquids are fused salts that are comprised of an organic cation and an organic or inorganic anion and have melting points that are lower than 100 \({}^{\circ}\)C [41; 91]. Ionic liquids tend to have low melting points but high boiling points and are non-flammable making them safe options for inclusion in solid electrolyte assemblies [92].