Fast-charging and durable all-solid-state lithium-sulfur batteries enabled by pre-embedded solid-solid redox mediator

All-solid-state lithium-sulfur batteries promise high specific energy and low cost. However, they are challenged by poor rate capability and cycling stability owing to the slow solid-solid sulfur redox reactions. Here, we present fast-charging and durable all-solid-state lithium-sulfur batteries enabled by a pre-embedded solid-solid redox mediator using an amorphous sulfur/iodine nano-eutectic positive electrode. The iodine, intimately homogenized with sulfur owing to carbon mesopore encapsulation, undergoes rapid I2/I− redox reaction, mediating solid-solid sulfur reactions by promoting electron transfer across the boundaries. The iodine within the carbon and on its surface reacts in situ with the sulfide catholyte to form a globally distributed I2/I− nano-network throughout the positive electrode, thereby enabling fast charging. The cell exhibits a specific capacity of 851.9 mA h g−1S/I when charged at 10 C, and 474.7 mA h g−1S/I at a charging rate of 24 C (1 C is defined as 945 mA g−1S/I). The high reversibility of the redox-mediated reaction enables durable cycling for 9,000 cycles over 9 months at 2 C and 2,800 cycles over 17 months at 0.5 C. This strategy represents a perspective for developing solid-state conversion electrodes that are plagued by sluggish reactions. All-solid-state lithium sulfur batteries suffer from sluggish solid-solid sulfur redox reactions. Here, the authors report fast charging and durable all-solid-state lithium-sulfur batteries enabled by a pre-embedded solid-solid redox mediator in an amorphous sulfur/iodine nano-eutectic positive electrode.