Change in the content of lithium sulfide is quantitatively studied through the methods of precipitation and back iodometric titration in lithium-sulfur cells during charge-discharge cycling for 100 cycles. It is shown that in the initial cycles (25 cycles) of charge-discharge cycling, electrochemically inactive lithium sulfide accumulates. The predominantly inactive lithium sulfide accumulates in the sulfur electrode. It is likely that lithium sulfide is deposited in the pores of the carbon material, blocks the pores and loses the ability to participate in the electrochemical reactions. On the surface of the lithium electrode, a surface layer containing lithium sulfide is formed during the cycling of the lithium-sulfur cells and is in equilibrium with the electrolyte system. It is found that lithium sulfide does not accumulate on the lithium electrode for at least 100 charge-discharge cycles.