Solid polymer electrolytes I, preparation, characterization, and ionic conductivity of gelled polymer electrolytes based on novel crosslinked siloxane/poly(ethylene glycol) polymers

A series of crosslinked siloxane/poly(ethylene glycol) (Si-PEG) copolymers were synthesized from the reactive methoxy-functional silicone resin (Si resin) and PEGs with different molecular weights via two kinds of crosslinking reactions during an in situ curing stage. One of the crosslinking reactions is the self-condensation between two methoxy groups in the Si resin, and another one is an alkoxy-exchange reaction between the methoxy group in the Si resin and the OH group in PEG. The synthesized crosslinked copolymers were characterized by Fourier transform infrared spectroscopy, DSC, and ¹³C NMR. The crosslinked copolymers were stable in a moisture-free environment, but the Si-O-C linkages were hydrolyzed in humid conditions. The gel-like solid polymer electrolytes (SPEs) were prepared by impregnating these crosslinked Si-PEG copolymers in a propylene carbonate (LiClO₄PC) solution. The highest conductivity reached 2.4 × 10^-4 S cm^-1 at 25°C and increased to 8.7 × 10^-4 S cm^-1 at 85 °C. The conductivities of these gel-type SPEs were affected by the content of LiClO₄/PC, the molecular weights of PEGs, and the weight fraction of the Si resin.