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Liquid metals have remarkable heat transport capabilities and are, thus, promising heat transfer fluids in thermal receivers in solar thermal electricity systems with high heat loads, such as central receiver systems. For thermal energy storage, a dual-media storage system with solid filler material is proposed. This configuration increases the storage capacity and decreases the storage material costs compared with a direct two-tank system. It also improves the storage performance, when comparing with a single-tank thermocline system without filler. Theoretical results show that the discharge efficiencies are highest for the largest storage heights and higher for heavy metals (lead and lead-bismuth eutectic) compared with sodium, both due to the decreased axial heat conduction and thus, minimized degradation of the thermocline. At the Karlsruhe Liquid Metal Laboratory (KALLA) at the Karlsruhe Institute of Technology (KIT) a lab-scale prototype of a dual-media storage system with filler material and lead-bismuth eutectic (LBE) as the heat transfer fluid is currently taken into operation. The first results without filler material show a good agreement between the theoretical model and the experimental results. In parallel, the compatibility of filler material candidates with LBE is investigated by storing the material in stagnant LBE for several weeks at 500°C and afterwards examining the filler material with a scanning electron microscope (SEM). The results indicate that ceramics are the most promising candidates.