Diluent decomposition-assisted formation of LiF-rich solid-electrolyte interfaces enables high-energy Li-metal batteries

Passivation by the inorganic-rich solid electrolyte interphase (SEI), especially the LiF-rich SEI, is highly desirable to guarantee the durable lifespan of Li metal batteries (LMBs). Here, we report a diluent with the capability to facilitate the formation of LiF-rich SEI while avoiding the excess consumption of Li salts. Dissimilar to most of reported inert diluents, heptafluoro-1-methoxypropane (HM) is firstly demonstrated to cooperate with the decomposition of anions to generate LiF-rich SEI via releasing F-containing species near Li surface. The designed electrolyte consisting of 1.8 M LiFSI in the mixture of 1,2-dimethoxyethane (DME)/HM (2:1 by vol.) achieves excellent compatibility with both Li metal anodes (Coulombic efficiency ∼ 99.8%) and high-voltage cathodes (4.4 V LiNi0.8Mn0.1Co0.1O2 (NMC811) and 4.5 V LiCoO2 (LCO) vs Li+/Li). The 4.4 V Li (20 μm)||NMC811 (2.5 mA h cm−2) and 4.5 V Li (20 μm)||LCO (2.5 mA h cm−2) cells achieve capacity retentions of 80% over 560 cycles and 80% over 505 cycles, respectively. Meanwhile, the anode-free pouch cell delivers an energy density of ∼293 W h kg−1 initially and retains 70% of capacity after 100 deep cycles. This work highlights the critical impact of diluent on the SEI formation, and opens up a new direction for designing desirable interfacial chemistries to enable high-performance LMBs.