Modern Li-Ion batteries are multicomponent systems involving advanced materials and technologies. One part highly influencing performance and safety of the arrangement is the separator. Separators can be divided into three groups: (i) macroporous polymers, (ii) non-woven fabric mats and (iii) inorganic composite membranes. In any case the manufacturing of these separators has to be done in a multistep process, often involving the use of compounds harmful or toxic to the environment and being energy intensive overall. Polymerized high internal phase emulsions (polyHIPEs) are porous emulsion-templated polymers synthesized within high internal phase emulsions (HIPEs). HIPEs are highly viscous, paste-like emulsions in which the major, “internal” phase, usually defined as constituting more than 74% of the volume, is dispersed as discrete droplets within the continuous, minor, “external” phase. Recently they have attracted attention due to their possible application as in situ electrolyte filled separators for Lithium ion batteries. Using RT-IL based electrolytes, stable HIPEs have been synthesized and successfully casted as thin films with thicknesses lower 100μm. UV polymerized material shows an open porous structure and thermal stabilities up to at least 200°C. Conductivity measurements resulted in McMullin numbers below a value of 2 that increases with increasing temperature, suggesting some possible thermal shutdown mechanism. Based on these results, the most promising formulations were chosen and directly casted and polymerized onto commercial Li-electrodes followed by long term stability tests. As energy storage nowadays becomes more and more important in situ electrolyte filled polyHIPEs are of interest as they could provide a possible way in preparing highly advanced materials for economic manufacturing of Lithium ion batteries.