# Development on Solid Polymer Electrolytes for Electrochemical Devices
## 3 Basic Solid Polymer Electrolytes
### Strategies to Improve Ionic Conductivity of SPEs
#### 3.2.3 Treatment of SPEs  
The polymer electrolytes can also be subjected to radiation in order to tune their properties in terms of structural, thermal, electrical and mechanical aspects. Various radiation sources, including gamma rays, X-rays, ultraviolet rays, electron, neutron and ion beams, can be employed. Solution-cast-prepared SPE based on PEO with lithium sulfate (Li\({}_{2}\)SO\({}_{4}\)) salt has been irradiated with low-energy electron beams of 8 MeV by [PERSON] et al. [76]. At 30 \({}^{\circ}\)C, the conductivity was enhanced to the order of 10\({}^{-4}\) S cm\({}^{-1}\) for PEO-Li\({}_{2}\)SO\({}_{4}\) electrolyte after exposure to 30 kGy dose of electron beam from 10\({}^{-5}\) S cm\({}^{-1}\) for non-irradiated electrolyte. Analyses from DSC and X-ray diffraction (XRD) demonstrated that the former have a lower melting temperature (67.6 \({}^{\circ}\)C) and are more amorphous in nature, with reduced crystallinity, than the latter (69.4 \({}^{\circ}\)C melting temperature and more crystalline), while FTIR results indicated that the polymer chain was disrupted and degraded after irradiation [76]. Irradiating of Li\({}^{3+}\) ion at high energy of 60 MeV on two different electrolytes of PEO-NaI and PVP-NaI showed increment in conductivity as compared to unirradiated electrolyte films [77]. Besides conductivity, higher values for number of mobile ions, ionic mobility and dielectric constant have been reported for the solution-cast-prepared SPE after ion-beam irradiation [77]. PAN-based SPE having LiBOB salt also exhibited enhancement in conductivity and transport properties (\(n\), \(\mu\) and \(D\)) after being radiated with a gamma-ray dose of 15 kGy [78]. Ambient conductivity was increased by 58.6 times from 1.74 \(\times\) 10\({}^{-6}\) S cm\({}^{-1}\) to 1.02 \(\times\) 10\({}^{-4}\) S cm\({}^{-1}\), while improvement of 12.2, 4.8 and -4.7 times was obtained in \(n\), \(\mu\) and \(D\), respectively [78]. Likewise, PVDF-LiBOB SPE has attained higher values of conductivity and ionic transport upon gamma-ray radiation as compared to non-irradiated electrolyte [79]. [PERSON] et al. [80] also reported similar observation in PVA-PVDF-LiCF\({}_{3}\)SO\({}_{3}\)-SiO\({}_{2}\) SPEs, where conductivity was boostedto 9.40 \(\times\) 10\({}^{-4}\) S cm\({}^{-1}\) at 30 \({}^{\circ}\)C after gamma-ray exposure (15 Gy dose). The conductivity of such an electrolyte without radiation treatment was 1.70 \(\times\) 10\({}^{-4}\) S cm\({}^{-1}\). Ionic transference number for the irradiated SPE also showed increment (\(t_{ion}\) = 0.99) as compared to that of non-gamma ray treated SPE (\(t_{ion}\) = 0.98) [80]. On the other hand, lower values for the percentage of crystallinity, \(T_{g}\) and melting point were detected in the former than in the latter [80]. In general, it is to be noted that conductivity enhancement has been observed at optimized dosage of radiation irrespective of the sources due to polymer chain scission, whereas too much radiation dose will be detrimental to the properties of SPE, and this is attributed to crosslinking and increase in crystallinity. In another work of [PERSON] et al. [81], a comparison was made between gamma-ray (cobalt-60 source) and electron-beam (energy of 8 MeV) treatments on PEO-based SPEs of cadmium chloride (CdCl\({}_{2}\)) salt. Non-irradiated electrolyte exhibited the lowest conductivity value at 8.63 \(\times\) 10\({}^{-6}\) S cm\({}^{-1}\) at 30 \({}^{\circ}\)C, as compared to gamma-ray-treated (0.115 S cm\({}^{-1}\)) and electron-beam-irradiated (0.175 S cm\({}^{-1}\)) electrolytes. Micrographs from scanning electron microscopy (SEM) showed less PEO spherulites in both irradiated SPEs as compared to that of non-irradiated SPE, indicating that a more amorphous region existed in the former case. In addition, the SEM image for electrolyte after electron-beam exposure displayed a homogenous morphology, while the formation of aggregates was seen in the micrograph of SPE irradiated with gamma radiation [81].