# Development on Solid Polymer Electrolytes for Electrochemical Devices
## 3 Basic Solid Polymer Electrolytes
### Strategies to Improve Ionic Conductivity of SPEs
#### 3.2.5 Plasticized Solid Polymer Electrolytes  
The main idea of plasticized polymer electrolyte is to improve the elasticity by lowering the \(T_{g}\). As stated in the previous section and Equation (3), the segmental movement of the polymer backbone contributes to the conductivity of SPEs. Increasing the segmental \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Electrolyte System**} & **Preparation** & **Conductivity, \(\sigma\)** & **Important Findings** & **Reference** \\  & **Method** & **(S cm\({}^{-1}\))** & & **Reference** \\ \hline \multirow{10}{*}{PVDF-HFF:PEO (4:1)-KI-TBAI-I\({}_{2}\)} & & & \(T_{m}\) = 144.9 \({}^{\circ}\)C; \%X\({}_{C}\) = 18.1\% & \\  & & & \(\text{N3/TiO}_{2}\)/SPE/Pt DSSC (light & \\  & & & intensity of 60 mW cm\({}^{-2}\)): & \\  & & & OCV = 0.674 \(\text{V}\); \(I_{c}\) = 4.39 \(\text{mA cm}^{-2}\); & \\  & & & \(\text{FF}\) = 0.50; \(\eta\) = 2.46\% & \\  & & & \(\sigma\) = 9.99 \(\times\) 10\({}^{-6}\) S cm\({}^{-1}\) (25 \({}^{\circ}\)C) & \\  & & & \(T_{m}\) = 146.5 \({}^{\circ}\)C; \%X\({}_{C}\) = 23.5\% & \\  & & & OCV = 0.648 \(\text{V}\); \(I_{c}\) = 3.78 \(\text{mA cm}^{-2}\); & \\  & & & \(\text{FF}\) = 0.46; \(\eta\) = 1.88\% & \\ \hline \multirow{6}{*}{PVAC:PMMA (70:30)-LiCl} & & \(E_{A}\) = 0.25 eV; \(T_{g}\) = 42.6 \({}^{\circ}\)C; \(t_{\star}\) = 0.97 & \\  & & & \(D_{\star}\) = 6.93 \(\times\) 10\({}^{-11}\) cm\({}^{2}\) s\({}^{-1}\); & \\ \cline{1-1}  & & & \(\mu\) = 2.65 \(\times\) 10\({}^{-9}\) cm\({}^{2}\) V s\({}^{-1}\); & \\ \cline{1-1}  & & & \(n\) = 2.35 \(\times\) 10\({}^{22}\) cm\({}^{-3}\) & \\ \hline \hline \end{tabular}  
* PVP–poly(vinyl pyrrolione); LiNO\({}_{3}\)—lithium nitrate; PPC–propylene carbonate; CMKC–carboremethyl \(\kappa\)-carrageenannan; N719–di-tetrabutylammonium cis-bis(sothiocyanato)bis(2,2’-bipyridyl-4,4’-dicarboxylation) ruthenium(ID; PVC–poly(vinyl chloride); WPU–waterborne polyurethane; TPU—thermoplastic polyurethane; NaIO\({}_{4}\)—sodium periodate; Mg(NO\({}_{3}\))\({}_{2}\)—magnesium nitrate; TBAI—tetrabutylammonium iodide; PVAc—poly(vinyl acetate); LiCl—lithium chloride.  
\end{table} 
Table 5: \(Cont.\)motion will improve the ionic conductivity and can be easily achieved by adding plasticizers into the polymer matrix. There are many types of plasticizers such as EC, PC, PEG, DMSO, diethyl carbonate (DEC), dimethyl carbonate (DMC), glycerol, gBL and DMF to name a few that affect the ionic conductivity of SPEs in different ways. Note that EC, PC, DMSO, gBL and DMF can also serve as a solvent, as listed in Table 3, while PEG of low molecular weight (M\({}_{w}\)) is usually used as a plasticizing agent. Plasticizers with high a dielectric constant, e.g., EC, as mentioned in the previous section, helps in salt dissociation, lowering the formation of ion pairs and ion aggregates leading to conductivity enhancement. Besides high dielectric constant, a good plasticizer should possess low viscosity to increase the mobility of ions. Furthermore, the incorporation of plasticizer in an electrolyte offers additional passage for ion transport. Some plasticized polymer electrolytes in the solid form that have been studied are tabulated in Table 6.