Butadiene Sulfone Based Binary Deep Eutectic Electrolyte for High Performance Lithium Metal Batteries

Deep eutectic electrolytes (DEEs) have attracted significant interest due to the unique physiochemical properties, yet challenges persist in achieving satisfactory Li anode compatibility through a binary DEE formula. In this study, we introduce a nonflammable binary DEE electrolyte comprising of lithium bis(trifluoro-methane-sulfonyl)imide (LiTFSI) and solid butadiene sulfone (BdS), which demonstrates enhanced Li metal compatibility while exhibiting high Li⁺ ion migration number (0.52), ionic conductivity (1.48 mS ⋅ cm^-1), wide electrochemical window (~4.5 V vs. Li/Li⁺) at room temperature. Experimental and theoretical results indicate that the Li compatibility derives from the formation of a LiF-rich SEI, attributed to the undesirable adsorption and deformation of BdS on Li surface that facilitates the preferential reactions between LiTFSI and Li metal. This stable SEI effectively suppresses dendrites growth and gas evolution reactions, ensuring a long lifespan and high coulombic efficiency in both the Li||Li symmetric cells, Li||LiCoO₂ and Li||LiNi_0.8Co_0.1Mn_0.1O₂ full cells. Moreover, the BdS eutectic strategy exhibit universal applicability to other metal such as Na and Zn by pairing with the corresponding TFSI-based salts.