On the Factors Affecting Aging and Self‐Discharge of Lithium–Sulfur Cells. Effect of Positive Electrode Composition

Fast self‐discharge (reversible capacity loss during storage) and aging (irreversible capacity loss during cycling and storage) are important and difficult problems in the development of lithium–sulfur batteries (LSB). Both problems are caused by the solubility of the active materials of the positive electrode in the electrolyte. Processes at the negative and positive electrodes result in self‐discharge and aging of LSB. Sulfur (S) and lithium polysulfides (Li 2 S n ), dissolved in the electrolyte, interact with the lithium metal electrode, causing the formation of insoluble lithium sulfide (Li 2 S). The main reasons for irreversible capacity loss are the accumulation of Li 2 S on the negative electrode and the binding of S and Li 2 S in the micropores of carbon materials, included in positive electrodes, during prolonged cycling and storage of LSB. Li 2 S does not accumulate on the lithium electrode during storage of LSB for 120 days. The equilibrium content of Li 2 S on the lithium electrode is 0.06 mg cm −2 . The main reason for the irreversible capacity loss is the binding of sulfur in the pore spaces of the carbon particles. The interaction of sulfur and Li 2 S n ( n > 4) with metallic lithium, causing the formation of soluble Li 2 S n ( n ≤ 4), is the reason for a reversible capacity loss.