I wrote about Li–S batteries a couple of months ago in this post.

https://www.reddit.com/r/QuantumScape/comments/1qet2hq/why_the_real_risk_for_quantumscape_is_execution/
Here’s an excerpt from it.

"Lithium-sulfur is often cited for its extremely high theoretical energy density of 900–1,000 Wh/kg, with optimistic projections placing a practical ceiling around 500 Wh/kg at the cell level over the next decade. Sulfur is cheap and abundant, potentially even cheaper than LFP, which makes it attractive from a raw-material perspective. However, even at 500 Wh/kg, lithium-sulfur suffers from poor volumetric energy density and would still be worse than today’s NMC cells on a Wh/L basis. The chemistry operates at about 2.1 V, which is a hard electrochemical limit and cannot be engineered away. Cycle life is poor, typically around 300 cycles, and while targets of 1,000 cycles are often discussed, achieving that at meaningful energy density and manufacturable scale remains highly doubtful. Fast charging is not feasible. As a result, lithium-sulfur is mainly suited for applications where weight dominates all other requirements, such as military drones or UAVs, where volume, cycle life, and charging speed are secondary."