Towards Stable Lithium-Sulfur Batteries with a Low Self-Discharge Rate: Ion Diffusion Modulation and Anode Protection

The self-discharge of a lithium-sulfur cell decreases the shelf-life of the battery and is one of the bottlenecks that hinders its practical applications. New insights into both the internal chemical reactions in a lithium-sulfur system and effective routes to retard self-discharge for highly stable batteries are crucial for the design of lithium-sulfur cells. Herein, a lithium-sulfur cell with a carbon nanotube/sulfur cathode and lithium-metal anode in lithium bis(trifluoromethanesulfonyl)imide/1,3-dioxolane/dimethyl ether electrolyte was selected as the model system to investigate the self-discharge behavior. Both lithium anode passivation and polysulfide anion diffusion suppression strategies are applied to reduce self-discharge of the lithium-sulfur cell. When the lithium-metal anode is protected by a high density passivation layer induced by LiNO₃, a very low shuttle constant of 0.017 h^-1 is achieved. The diffusion of the polysulfides is retarded by an ion-selective separator, and the shuttle constants decreased. The cell with LiNO₃ additive maintained a discharge capacity of 97% (961 mAhg^-1) of the initial capacity after 120 days at open circuit, which was around three times higher than the routine cell (32% of initial capacity, corresponding to 320 mAhg^-1). It is expected that lithium-sulfur batteries with ultralow self-discharge rates may be fabricated through a combination of anode passivation and polysulfide shuttle control, as well as optimization of the lithium-sulfur cell configuration.