## 3 Varieties of Epoxide-Based Polymer Electrolyte
### Silicone-Based Reagents  
This section discusses the use of silicone-based reagents such as silanes and siloxanes in epoxide-based polymer electrolytes. Silanes are generally considered to be the silicon-based analogue of methane. However, the hydrogens can be replaced by other various organic functional groups. Siloxanes are functional groups that are comprised of Si-O-Si linkages. Siloxanes can be linear or branched and they are the backbone components of many polymers such as polydimethylsiloxane (PDMS). Silicone-based reagents have features that make them particularly attractive as electrolyte components. Namely, polymer chains in PDMS-containing compounds tend to be very mobile which confers a low T\({}_{\text{g}}\) and a high Coulombic efficiency [76,79]. However, as silicone-based reagents tend to be liquids under ambient conditions and have relatively low ionic conductivity, these must be co-polymerized to produce viable electrolyte materials [76,80]. The real advantage of incorporating silicone-based polymers into solid electrolytes is that they are highly compatible with lithium-based electrodes. The Si-O-Si polymer backbone makes these materials highly flexible and lithophilic which gives them a high affinity for lithium anodes [76,80]. In fact, nano-scale PDMS-based coatings are able to respond to changes in the lithium anode surface that occur during cycling which protects the solid electrolyte interface from damage and improves the Coulombic efficiency of the device [80]. In terms of the cathode, the high oxidative stability of siloxanes means that these materials are compatible with a wide range of cathode materials [76]. In addition, the extremely low toxicity and facile modification of PDMS make it suitable for a variety of co-polymerization reactions rendering it a highly customizable electrolyte component [76]. Silicon-containing reagents are also compatible with the cationic ring opening polymerization reaction. Both silanes and siloxanes offer significant advantages to the resultant polymer electrolytes as they confer the stability of inorganic materials as well as the film-forming ability that has been traditionally attributed to organic polymers [17]. Preparing polymer electrolytes with Si-O centers also has the potential to increase the conductivity of the polymer electrolyte as the low rotational energy barrier of the Si-O bond can result in increased chain mobility [23]. Under acidic conditions, silanes react to form silanol (S-OH) groups [17]. As acidic conditions also cause ring opening in epoxides, the resultant OH groups can interact to form C-O-C bonds [17]. This mechanism, a combination of polycondensation and organic crosslinking, causes polymerization between these two types of monomers (Scheme 2) [21]. [PERSON] et al. prepared a relatively conductive electrolyte via this method using 3-glycidyloxypropyltrimethoxysilane (GLYMO), LiClO\({}_{4}\) and DGEPEG. When the weight percent of the lithium salt was 8.8%, the resultant film had an ionic conductivity of 1.2 \(\times\) 10\({}^{-4}\) S/cm at 25 \({}^{\circ}\)C, an activation energy of 0.057 eV and a T\({}_{\text{g}}\) of \(-60\)\({}^{\circ}\)C [21]. These characteristics make this silane-containing polymer electrolyte a better ion conductor than most of the polyether-based electrolytes that were discussed in the previous section. It is anticipated that these improvements are a result of the inorganic silane domains functioning similarly to inorganic inert nanoparticles in hybrid electrolytes: they reduce crystallinity as a result of contact between organic and inorganic domains [22]. This produces higher ionic conductivity and higher thermochemical stability than traditional PEO and other polyether-based electrolytes. It is predicted that the effects of incorporating silicone-based monomers into polymer electrolytes may be even more pronounced than those of silica nanoparticles as the connectivity between the organic and inorganic domains is maximized. [PERSON] et al. also used GLYMO to produce polymer electrolytes [22].