An amorphous co-network consisting of poly(ethylene glycol) diacrylate (PEGDA) and thiosiloxane was prepared by means of thiol-ene "click" reaction to impart high ion conduction via enhanced segmental mobility of the co-network. By varying PEGDA-thiosiloxane ratios, several polymer electrolyte membranes (PEM) have been fabricated to control the glass transition temperature (T-g), while keeping the equal molar ratio of succinonitrile (SCN) plasticizer and bis(trifluoromethane sulfonyl)imide (LiTFSI) salt for solid-state lithium ion batteries. It was found that the addition of thiosiloxane into the PEM network not only results in improved thermal stability and greater extensibility, but also reduces T-g leading to higher ionic conductivity that reaches the level of superionic conductor at room temperature, which further increases to 10(-2) Scm(-1) at high battery operating temperatures (60-70 degrees C). To evaluate their electrochemical performance, half-cells comprising of LiFePO4/PEM/Li foil were tested by means of cyclic voltammetry. An initial discharge capacity of 148 mAhg(-1) was obtained at a current rate of 0.2 degrees C with capacity retention of about 89%.