To follow your boulder/hill metaphor, the lithium boulder rolls down the hill (crosses the electrolyte), settles at the bottom of the valley (bonds sulfur)... A

To follow your boulder/hill metaphor, the lithium boulder rolls down the hill (crosses the electrolyte), settles at the bottom of the valley (bonds sulfur)... And then somehow as more lithium rolls down the hill, it continues to pile up at the bottom until it forms another hill, the same size as the first (lithium plates onto the anode). That's what they claim happens- that the sulfur acts as a redox center and sets the voltage for an unlimited amount of lithium. But a redox center cannot just lower the voltage of an arbitrary amount of metal. The metal is an entirely normal bond and can be cut with an energy proportional to mass^(2/3), while the energy stored increases linearly.