# Development on Solid Polymer Electrolytes for Electrochemical Devices
## 3 Basic Solid Polymer Electrolytes
### Strategies to Improve Ionic Conductivity of SPEs
#### 3.2.4 Blended Solid Polymer Electrolytes  
Polymer blending can be regarded as the most convenient and simplest way to prepare SPEs that are highly conducting, flexible and thermally stable and that have good mechanical strength without additional employment of materials such as initiator, linker agent, radiation sources, etc., thus indirectly making this approach more cost-effective as compared to other techniques aforementioned. In this technique, two or more polymers which are miscible in the appropriate solvent form a homogenous solution before addition of the conducting salt. The blending of polymer approach is able to (i) reduce the glass transition temperature, (ii) decrease the degree of crystallinity, (iii) increase the ionic conductivity, (iv) improve the thermal stability, (v) enhance the mechanical strength and (vi) boost the performance of electrochemical devices. There are many studies on blended SPEs available in the literature. Table 5 lists some of the systems under this category. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Electrolyte System** & **Preparation** & **Conductivity, \(\sigma\)** & **Important Findings** & **Reference** \\  & **Method** & **(S cm\({}^{-1}\))** & & **Temperature** \\ \hline  & & & & \(E_{A}=0.27\) eV; \(T_{g}=80\)\({}^{\circ}\)C & \\ PVA:PVP (  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Electrolyte System** & \begin{tabular}{c} **Preparation** \\ **Method** \\ \end{tabular}  & \begin{tabular}{c} **Conductivity, \(\sigma\)** \\ **(S cm\({}^{-1}\))** \\ \end{tabular}  & **Important Findings** & **Reference** \\ \hline CMC:PVA:NH\({}_{4}\)NO\({}_{3}\) (56:14:30 wt.\%) & Solution casting & \(1.70\times 10^{-3}\) & \begin{tabular}{c} \(T_{g}\) = 88.7 \({}^{\circ}\)C; \(t_{\rm H+}\) = 0.42 \\ 340 \({}^{\circ}\)C \\ \end{tabular}  & [91] \\ \hline MG49:PMMA (70:30)-25 wt.\% LiBF\({}_{4}\) [O]/[Li] = 5:1 & Solution casting & \(8.60\times 10^{-6}\) (30 \({}^{\circ}\)C) & \begin{tabular}{c} MG49-PMMA film: \\ \(\sigma=1.10\times 10^{-12}\) S cm\({}^{-1}\) (30 \({}^{\circ}\)C) \\ \end{tabular}  & [73] \\ \hline MG49:PMMA (70:30)-25 wt.\% LiClO\({}_{4}\) [O]/[Li] = 6:1 & Solution casting & \(1.50\times 10^{-8}\) (30 \({}^{\circ}\)C) & \begin{tabular}{c} MG49-PMMA film: \\ \(\sigma=1.10\times 10^{-12}\) S cm\({}^{-1}\) (30 \({}^{\circ}\)C) \\ \end{tabular}  & [73] \\ \hline CMKC:CMC (60:40)-LiI & Solution casting & \(3.89\times 10^{-3}\) (27 \({}^{\circ}\)C) & \ \begin{tabular}{c} \(T_{g}\) = \(-43.0\) \({}^{\circ}\)C \\ N719/TiO\({}_{2}\)/SPE/Pt DSSC (light \\ intensity of 100 mW cm\({}^{-2}\)): \\ OCV = 0.492 V; \(J_{sc}\) = 0.40 mA cm\({}^{-2}\); \\ _FF_ = 0.57; \(\eta\) = 0.11\% \\ \end{tabular}  & [92] \\ \hline HCh:PVC (90:10)-NaI & Solution casting & \(1.50\times 10^{-5}\) (RT) &
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[PERSON] et al. [100] have investigated the effect of SPE preparation method on conductivity. The SPE comprising PEO blended with PMMA at a ratio of 1:1 and LiCF\({}_{3}\)SO\({}_{3}\) salt has been prepared in four ways: (i) conventional solution cast coupled with hot melt-pressing; (ii) ultrasonication followed by solution casting and hot melt press; (iii) irradiation of microwave before solution-cast and hot-melt-press techniques; and (iv) ultrasonication followed by microwave exposure, solution casting and hot melt press. The authors have observed that conductivity decrement of the similar SPE in the following order: \(\sigma_{\text{(route iii)}}\) (1.99 \(\times\) 10\({}^{-6}\) S cm\({}^{-1}\)) \(>\sigma_{\text{(route iv)}}\) (1.56 \(\times\) 10\({}^{-6}\) S cm\({}^{-1}\)) \(>\sigma_{\text{(route ii)}}\) (0.11 \(\times\) 10\({}^{-6}\) S cm\({}^{-1}\)) [100]. They have speculated that the electrolyte made from microwave-assisted solution-cast/hot-melt-press procedure has produced more of a pathway for ionic conduction as compared to other methods [100].