Lithium batteries are the dominant power source in portable device technology and are poised to play a similar, important role in electrified transportation systems. While significant strides have been made in recent years in evolving the cathode chemistry and electrolyte formulations to meet higher energy storage demands, almost all contemporary LIB designs rely on flammable electrolyte solvents that are fundamentally unsafe. In this thesis, we explore crosslinked polymer networks as safe electrolytes for Lithium based battery systems. We thoroughly investigate the ion conduction mechanisms in these networks and exploit their degrees of freedom to create multifunctional electrolytes. We then report a facile UV cross-linking chemistry that can be used to create ion-conducting polymer networks containing dangling chains that impart specific, desired functionalities to liquid electrolytes. We show in particular that incorporation of monofunctional sulfonate and phosphate species in a photo-/heat-initiated cross-linking reaction of a multifunctional oligomer provides a straightforward route to mechanically robust membranes able to transform both transport properties and flammability of standard liquid electrolytes incorporated in their pores. We evaluate the physical and mechanical properties of the materials and on that basis report that dangling functional groups in the membrane pores can improve electrolyte properties, without compromising performance in electrochemical cells. Such cross-linked membranes with different pendant groups covalently tethered to an ion-conducting framework are argued to provide an important platform for more broadly enhancing lithium battery performance.