M. Jaipal Reddy

Novel composite polymer electrolyte comprising mesoporous structured SiO2 and PEO/Li

Abstract Novel composite polymer electrolytes comprise of hexagonal array of mesoporous structured MCM-41, and poly(ethylene oxide) (PEO)/Li show that the conductivity and mechanical properties are improved simultaneously. The comparison of small angle X-ray diffraction (XRD) of mesoporous MCM-41 and blended films of PEO:Li/MCM-41 shows that the nano-porous SiO 2 channels were not destroyed in PEO/Li. Solid-state 7 Li NMR spectra identified two major lithium species attributed to the Li + ions associated with PEO, and intercalation or penetration of polymer and Li + ions both within and outside the channels of mesoporous MCM-41. The scanning electron microscopy (SEM) photographs indicated that the electrolytes are miscible and homogeneous up to 8 wt.% of MCM-41, and an optimal conductivity is reached at this composition. However, at higher weight ratios (>10 wt.%), the Li/MCM-41-rich domain developed, and the conductivity decreased with increasing mesoporous material. Apart from the fundamental random diffusion within the amorphous PEO, additional conducting mechanism is established by replacing the nearby vacancy (“hole”) with lithium ion on MCM-41 surface, which bears lower activation energy E a . As a result, enhancement of conductivity is observed when the polymer and oxide are well miscible. This additional mechanism is absent in the case of spherical fillers such as TiO 2 , Al 2 O 3 or SiO 2 nano-particles in PEO-based electrolytes.

Effect of Mg2+ on PEO morphology and conductivity

Abstract Morphology, crystallinity and ion conductivity of divalent ionic salt Mg(ClO4)2 in poly (ethylene oxide) (PEO) have been investigated and presented. The X-ray diffraction and differential scanning calorimetry (DSC) studies reveals that the PEO crystallinity is reduced with increasing Mg salt content, which becomes totally amorphous above 25 wt.% of Mg(ClO4)2 (O/Mg ratio ca. 15). Scanning electron microscopy (SEM) micrographs demonstrated improvement of surface morphology from rough to smooth with increasing salt content. The smooth morphology is attributed to the reduction of PEO crystallinity with salt. These results suggested the formation of complex between Mg2+ ionic salt and PEO, similar to that with the lithium salt. The interaction of Mg2+ ion with ether oxygen of PEO facilitated salt dissociation, as well as the disruption of crystallinity of PEO. Unlike that in lithium salt, however, formation of other crystalline complex phases is observed after extensive annealing at 120 °C. The conductivity was optimized at 15 wt.%, (O/Mg ratio=28), which degraded further with increase of salt content where severe ion pairing occurs. The pseudo activation energy derived from variable temperature conductivity measurements is about 0.68 eV, which is larger than that of the mono-valent ionic salt systems and reflecting the heavier Mg2+ ion mass transport in PEO.

PEO:KIO3 Polymer electrolyte system- its application to solid state electrochemical cell

In search of polymer electrolyte based on PEO- salt complexes other than the extensively studied lithium-based polymer electrolytes, we report the new polymer electrolyte based on PEO complexed with KIO3 salt. Several experimental techniques such as differential scanning calorimetry (DSC), composition dependence conductivity, temperature dependence conductivity and transport number measurements have been performed to characterize the polymer electrolyte. DSC study reveals that the melting temperature of pure PEO is shifting towards lower temperatures by complexing with the KIO3 salt. The conductivity-temperature plots show two regions below and above the melting point (Tm). Transport numbers data suggest that the charge transport in this polymer electrolyte system is mainly due to ions. Using the polymer electrolyte films solid-state electrochemical cells have been fabricated and the discharge characteristics studied. The open circuit voltage (OCV) and short circuit current (SCC) are found to be 2.69 V and 346µA respectively.