In Situ Construction of LiF–Li3N-Rich Interface Contributed to Fast Ion Diffusion in All-Solid-State Lithium–Sulfur Batteries

All-solid-state lithium-sulfur batteries (ASSLSBs) have attracted wide attention due to their ultrahigh theoretical energy density and the ability of completely avoiding the shuttle effect. However, the further development of ASSLSBs is limited by the poor kinetic properties of the solid electrode interface. It remains a great challenge to achieve good kinetic properties, by common strategies to substitute sulfur-transition metal and organosulfur composites for sulfur without reducing the specific capacity of ASSLSBs. In this study, a sulfur-(Ketjen Black)-(bistrifluoromethanesulfonimide lithium salt) (S-KB-LiTFSI) composite is constructed by introducing LiTFSI into the S-KB composite. The initial discharge capacity reaches up to 1483 mA h g^-1, benefited from the improved ionic conductivity and diffusion kinetics of the S-KB-LiTFSI composite, where numerous LiF interphases with a Li₃N component are in situ formed during cycling. Combined with DFT calculations, it is found that the migration barriers of LiF and Li₃N are much smaller than that of the Li₆PS₅Cl solid electrolyte. The fast ionic conductors of LiF and Li₃N not only enhance the Li⁺ transfer efficiency but also improve the interfacial stability. Therefore, the assembled ASSLSBs operate stably for 600 cycles at 200 mA g^-1, and this study provides an effective strategy for the further development of ASSLSBs.