| dc.description.abstract | The thesis divided into two parts. First, we are interested that the effect of addition of Mesoporous silica MCM-41 with surface modification of (3-glycidyloxypropyl)trimethoxysilane (GLYMO) to poly(ethylene oxide) (PEO) complexed with LiClO4 has been explored by alternating current (AC) impedance, powder X-ray diffraction (XRD) , differential scanning calorimeter (DSC), and multinuclear solid-state NMR measurements.
The presence of small quantity of GLYMO modified MCM-41 enhances the ionic conductivity of the resulting composite electrolyte as compared to present PEO/LiClO4 electrolyte. The enhancement in conductivity is directly correlated with the improved compatibility between PEO and surface modified MCM-41 as a result of blending PEO with GLYMO group.
Addition of high concentration of surface modified MCM-41 leads to a decrease in the conductivity of the composite electrolyte, mainly because MCM-41 filler acts an insulator that impedes the lithium ion transport. DSC results show that both the polymer segmental motion and the proportion of amorphous PEO phase are affected by addition of MCM-41 filler. The change of portion of crystalline PEO phase can be explained by Lewis acid-base interactions between PEO chain, MCM-41 surface, and lithium cation.
Solid-state 7Li NMR measurements show that the 7Li linethwidth narrowing begins at temperature much lower than the glass transition temperature of PEO chains, indicative of the presence of an additional conduction mechanism with lithium ions moving along (both interior and exterior) the mesoporous channels of MCM-41.The additional mechanism is unique for the composite electrolytes doped with mesoporous silica MCM-41, and is absent in the case of other spherical fillers such as Al2O3 and SiO2 particles in PEO-based electrolytes. Variable temperature proton decoupled 7Li MAS (magic angle spinning) NMR spectra reveal that at least two different lithium environments are present in the composite electrolyte, serving as an evidence for the existence of interaction between lithium cation and MCM-41 surface.
In the second part of my thesis, the effect of addition of uncalcined or calcined mesoporous silica MCM-41 to poly(ethylene oxide) (PEO) complexed with LiClO4 has been explored by alternating current (AC) impedance, powder X-ray diffraction (XRD) , differential scanning calorimeter (DSC), and multinuclear solid-state NMR measurements.
The present of small quantity of uncalcined MCM-41 do not enhance the ionic conductivity of the resulting composite electrolyte as compared to present PEO/LiClO4 electrolyte. However, the present of small quantity of calcined MCM-41 enhances the ionic conductivity of the resulting composite electrolyte as compared to present PEO/LiClO4 electrolyte. The enhancement in conductivity is directly correlated with Lewis acid-base interactions between PEO chain, MCM-41 surface, and lithium cation.
Addition of high concentration of uncalcined or calcined MCM-41 leads to a decrease in the conductivity of the composite electrolyte, mainly because uncalcined or calcined MCM-41 filler acts an insulator that impedes the lithium ion transport. Variable temperature proton decoupled 7Li MAS (magic angle spinning) NMR spectra reveal that at least two different lithium environments are present in the composite electrolyte, serving as an evidence for the existence of interaction between lithium cation and MCM-41 surface. | en_US |