A Pyridine Mediator Enables High-Efficiency, Long-Cycling Anode-Less/Free Lithium-Sulfur Batteries With Li₂S Cathodes

Lithium sulfide (Li₂S) is a promising high-capacity cathode material. Importantly, it can provide lithium source, enabling lithium batteries with an anode-less/free configuration. However, Li₂S suffers from poor conductivity, high polarization, low material utilization, as well as the shuttle effect, severely restricting the long cycling performance of batteries. Herein, lithium pyridine-2-thiolate (PySLi) is proposed as a multifunctional mediator for Li₂S-based anode-less/free batteries. It is revealed that PySLi can modify the reaction pathway of Li₂S, comprehensively enhancing its electrochemical redox kinetics and stability. Results show that the energy efficiency of the Li||Li₂S cell with PySLi stabilizes at ∼80% in the full-scale range from 0.1 C to 3 C rate, which is much higher than that without PySLi (49% at 0.1 C and 22% at 3 C). The stability of the lithium metal anode is also improved, maintaining a high coulombic efficiency of >98% for 200 cycles and stable lithium stripping/plating behavior for 1000 h. Moreover, an anode-free battery based on Li₂S cathode works normally for 150 cycles, and an anode-less pouch cell retains steady performance for 200 cycles. This multifunctional mediator provides a new strategy for the application of Li₂S and stable anode-less/free batteries with high energy density.