# Development on Solid Polymer Electrolytes for Electrochemical Devices
## 3 Basic Solid Polymer Electrolytes
### Strategies to Improve Ionic Conductivity of SPEs
#### 3.2.7 SPEs Containing Other Kind of Additives
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Electrolyte System**} & **Preparation** & **Conductivity, \(\sigma\)** & **Important Findings** & **Reference** \\  & **Method** & **(S cm\({}^{-1}\))** & **Invert** & **Invert** \\ \hline \multirow{9}{*}{\begin{tabular}{c} PVAc:PMMA \\ (70:30)-LiCl-TiO\({}_{2}\) \\ \end{tabular} } & \multirow{3}{*}{Solution casting} & \multirow{3}{*}{4.45 \(\times\) 10\({}^{-4}\) (30 \({}^{\circ}\)C)} & \multirow{3}{*}{\begin{tabular}{c} \(T_{g}\) = 28.1 \({}^{\circ}\)C; \(t_{+}\) = 0.99 \\ \(D_{+}\) = 7.07 \(\times\) 10\({}^{-11}\) cm\({}^{2}\) s\({}^{-1}\); \\ \(\mu\) = 2.71 \(\times\) 10\({}^{-9}\) cm\({}^{2}\) V\({}^{-1}\) s\({}^{-1}\); \\ \(n\) = 2.35 \(\times\) 10\({}^{2}\) cm\({}^{-3}\) \\ \(n\) = 2.35 \(\times\) 10\({}^{2}\) cm\({}^{-3}\) \\ \(n\) = 2.35 \(\times\) 10\({}^{2}\) cm\({}^{-3}\) \\ \(\text{Electrochemical stability}\) \\ \(\text{window 1.69}\) V \\ \hline \multirow{2}{*}{\
\begin{tabular}{c} PEO-LiTESI-Ni\({}_{3}\)- \\ (BTC)\({}_{2}\) \\ \end{tabular} } & \multirow{2}{*}{
\begin{tabular}{c} Hot pressing \\ (2-chloro-3,5,6-trisulfide-1,4-benzoquinone); \(\alpha\)CNT—amorphous carbon nanotubes; CuI—copper sulfate; CA—cellulose acetate; OMMT—organic modified montmorillonite; MMT—montmorillonite; Al\({}_{2}\)O\({}_{3}\)—nano alumina; NaClO\({}_{4}\)—sodium peripadote; GO—graphene oxide; PMA—poly(methacrylate); \(g\)C\({}_{3}\)N\({}_{4}\)—polymeric graphitic carbon nitride; Ni\({}_{3}\)(BTC)\({}_{2}\)—nickel-13,5-benzene terarboxylate metal organic framework.} \\ \hline \hline \end{tabular}
\end{table} 
Table 7: \(Cont.\)anion of the salt [194]. Usually, this will lead to reduce the anionic mobility and unwittingly decrease the ionic conductivity, as stated in preceding paragraph. Nevertheless, there are some controversial reports that showed otherwise. [PERSON] and co-workers [195] observed that the SPE containing PVC doped with lithium chloride (LiCl) salt and calix[4]pyrrole exhibited higher ionic conductivity, at around 10\({}^{-3}\) S cm\({}^{-1}\) at 25 \({}^{\circ}\)C, compared to that calix-free SPE (10\({}^{-5}\) S cm\({}^{-1}\)). Using density functional theory, they obtained that the dissociation energies for LiCl-calix and PVC-LiCl-calix complexes were 110.8 and \(-\)18.1 kcal mol\({}^{-1}\), whereas, for LiCl salt, the dissociation energy value was 145.6 kcal mol\({}^{-1}\)[195]. A lower dissociation energy value implies that the cation of salt is more free to move, while its anion has complexed with calix [195]. Plastic crystal SN has also been employed as a polymer matrix in electrolyte, besides serving as a plasticizer and ionizer for both Li- and Na-based salts [131; 196]. In order to improve the transference number of Na\({}^{+}\), [PERSON] et al. [196] synthesized boron-containing 2-hydroxyethyl methacrylate (B-HEMA) before incorporating it into SN-based polymer electrolyte that had non-woven polypropylene-cellulose composite framework and NaClO\({}_{4}\) salt. This electrolyte having B- (boron anion) acceptor was prepared via a UV-assisted curing method, using 2-hydroxy-2-methyl-1-phenyl-1-propanone as photo-initiator. This electrolyte demonstrated superior properties in terms of ambient conductivity (3.60 \(\times\) 10\({}^{-4}\) S cm\({}^{-1}\)), tensile strength (28.2 MPa) and Na\({}^{+}\) transference number of (\(t_{Na+}\) = 0.62) [196]. Promising results were also obtained after applying the electrolyte in Na-ion batteries (initial capacity of \(\sim\)10 mAh g\({}^{-1}\) at 0.1 C and retaining 80% capacity after 120 cycles) [196]. The boron moiety is said to complex with ClO\({}_{4}\)- ion of the salt, thus lowering the anionic mobility and subsequently enhancing the Na\({}^{+}\) ion transference number. Meanwhile, the authors have stated that the polypropylene-cellulose structure did not contribute in ionic conduction, but instead improved the mechanical property of the plastic crystal polymer electrolyte [196].