Beyond LiF-Rich SEIs: Multi-Objective Optimization Identifies Li2O-Dominated Stable Interphases for Lithium-Metal Batteries

The prevailing view in lithium-metal batteries (LMBs) regards LiF-rich solid electrolyte interphases (SEIs) as essential for interfacial stability, making fluorinated electrolytes the default choice. This consensus relies mainly on empirical performance rather than quantitative decoupling of individual inorganic components. Here, we isolate LiF, Li 2 CO 3 , and Li 2 O monocomponent SEIs and quantify key descriptors, including exchange current density, ionic/electronic conductivities, activation energies, and mechanical strength. We observe pronounced functional asymmetry: no single component satisfies all demands. Using power-law composition–property mapping and weighted multi-objective optimization, we establish a predictive framework for SEI design. Surprisingly, the model predicts an optimal composition dominated by Li 2 O with a minor Li 2 CO 3 fraction (Li 2 CO 3 /Li 2 O = 0.1428/0.8572), excluding LiF. A symmetric cell with this optimized SEI cycles stably for over 2400 h at 0.5 mA cm −2 . In Li||LFP full cells, 49% of the initial capacity (105 mAh g −1 ) is retained after 900 cycles at 4 C, outperforming all monocomponent SEIs. In LiF-free cells using a non-fluorinated electrolyte, the optimized SEI delivers improved performance. These results show that the “LiF considered a key component for stable SEI” paradigm fails when SEI is deconvoluted into quantifiable physicochemical parameters. Interfacial stability arises from multi-parameter synergy rather than single-component preference.