High ionic conductivity, low mass density, and high oxidative stability solid separators are highly desirable for increasing the energy density of Li-ion batteries. In this presentation we show recent results related to a newly developed highly conductive solid separator made from a solid polymer electrolyte (SPE) that is light and compatible with high voltage cathodes. Preliminary results obtained in our laboratory show that the proposed SPE has ionic conductivity of more than 1 mS/cm, a mass density comparable to liquid electrolytes, which is about 4x smaller than ceramics and glasses, and are stable at least up to 5 V vs Li. Efforts are currently being made in our laboratory to successfully scale up the solid separator from a laboratory size material to a cell-size free-standing sheet, which is expected to increase the energy density of current Li metal polymer batteries by more than 50%. Our polymer can operate at temperatures below -20°C and above 100°C, which has the potential to extend the operating temperature limit of Li metal polymer batteries. More details about the physiochemical properties and other characteristics of the developed material will be presented at the conference.