Tailoring Electrolyte Solvation for LiF-Rich Solid Electrolyte Interphase toward a Stable Li Anode

A solid electrolyte interphase (SEI) with robust mechanical property and high ionic conductivity is imperative for high-performance lithium metal batteries since it can efficiently impede the growth of notorious lithium dendrites. However, it is difficult to form such a SEI directly from an electrolyte. In this work, a crowding dilutant modified ionic liquid electrolyte (M-ILE) has been developed for this purpose. Simulations and experiments indicate that the 1,2-difluorobenzene (1,2-dfBen) dilutant not only creates a crowded electrolyte environment to promote the interaction of Li⁺-FSI^-, leading to abundant aggregate ion pairs (AGGs), but also participates in the reduction to construct a robust and high ionic-conductive SEI. With this M-ILE, Li/LiFePO₄ cells achieve a capacity retention of 96% over 250 cycles with 9.5 mg cm^-2 mass loading, and Li/LiNi_0.5Co_0.2Mn_0.3O₂ cells also deliver a discharge capacity of 132 mAh g^-1 with a high retention of 88% after 100 cycles. Therefore, the use of a crowding diluent is considered to be an efficient way to construct an advanced SEI for a Li anode.