Lithium-sulfur (Li-S) batteries promise improved capacities over lithium ion batteries. While currently mostly metallic lithium anodes are used, the use of silicon-anodes might offer better safety and durability. However, in a lithium-sulfur-Silicon (Li-S-Si) battery, lithium must be introduced either on the anode or on the cathode in form of Li 2 S. In this study, we have prepared Li 2 S cathodes in combination with Si anodes (i.e., Si/Li 2 S full-cells) to investigate both the processes during initial charging/activation of Li 2 S cathodes and the effect of Li 2 S cathode activation on the cycling performance of Si/Li 2 S full-cells. We observed that the initial activation requires a substantially higher charging potential than for the subsequent cycles. In situ XRD analysis of the cathode during the first cycle clearly indicates the gradual transformation of Li 2 S to polysulfides and finally to crystalline sulfur, i.e., even large Li 2 S particles (≈20 μm) can be charged completely. The result is further confirmed by ex-situ SEM/EDS analysis, which revealed the formation of large sheets of sulfur at the cathode/separator interface. Similar cycling performance of Si/Li 2 S full-cells is observed at both 0.1 C and 1 C rates, a clear advantage over Li/Li 2 S cells, which suffer from severe dendrite formation at 1 C in the case of high Li 2 S loadings. High capacity energy storage systems are needed for various applications ranging from portable electronic devices to automotive applications. For the latter, a safe onboard energy storage system that can provide sufficient driving range is needed. However, the specific energy of current intercalation based lithium ion batteries (≈250-280 Wh/kg cell ) substantially limits the driving range compared to that of conventional fuel vehicles 1,2 so that batteries offering higher specific energy are required.Lithium-air (Li-O 2 ) 3 and lithium-sulfur (Li-S) 4,5 batteries are among the most widely explored so-called post-lithium ion technologies, for which the lithium ions in the cathode react with either oxygen or sulfur during discharge, resulting in Li 2 O 2 or Li 2 S discharge product, respectively. Considering the high theoretical specific energy of these post-lithium ion cathodes on the active materials level (viz., ≈3.5 kWh/kg Li2O2 for Li-O 2 and ≈2.5 kWh/kg Li2S for Li-S 1 ), they are very promising for use in electric vehicles, even though the specific energy gains over lithium ion batteries if compared on the battery system level are substantially lower. 6 However, there are still several major issues to be resolved. In the case of Li-O 2 batteries, these include the poor charge/discharge reversibility 7,8 as well as the poor stability of electrolytes 9-11 and of the catalyst support. 12 Similarly, Li-S batteries are still plagued by an irreversible loss of active sulfur species, by polysulfide shuttling, and by the continuous electrolyte consumption at the lithium electrode.13,14 Nevertheless, Li-S battery performance/durability has improved significantly over ...