Li–S batteries are very promising due to high energy density and low cost of sulfur compared to the current commercial Li-ion batteries, but they are yet to be viable in practice due to safety hazard and reliability issues. Here we used lithiated Si anode to couple with S, which are the two of the most appealing due to the high energy density but challenging electrode materials for cycling due to volume expansion and polysulfide shuttle. Our Li x Si–S (LSS) cells showed stable cycling performance with capacity retention up to 80%, which can be attributed to the use of mesoporous structures in the electrodes. More importantly, the LSS cells were found to be safe and reliable even under two common failure modes, internal and external short-circuit. On the contrary, for Li–S cells, Li dendrites formed during charge made the cell internally short-circuited, and external short-circuit made the cathode powdery. This study provides not only crucial information regarding the failure mechanisms, but also safer and more reliable operation of high-capacity and low-cost sulfur batteries, which are crucial for use in practice.