Deciphering fundamental mechanism of different-type diluents on manipulating interfacial chemistry toward lithium metal anode

The growth of dendrites on lithium metal anode is troublesome because it induces irreversible capacity loss and safety hazards. Formulating localized high-concentration electrolytes (LHCEs) is an alternative solution to satisfy these challenges. However, the role of diluents in tailoring interfacial chemistry remains to be explicated. Herein, we decipher the direct relationship between different-type diluents and Li-coordinated solvation at the molecular scale. Compare to hydrofluoroethers (HFE), the "active" difluoro ethylene carbonate (DFEC) delivers a pronounced interaction with Li+ and 1, 2-dimethoxyethane (DME) molecule, resulting in a compressed but more accumulated aggregates (AGGs) solvation shell, assisting in the expected chemical nature of SEI with defluorination of DFEC. Consequently, DFEC-based LHCEs (D-LHCEs) realize a record-long lifespan over 3000 h with dendrite-free at 1 mA cm−2 and outstanding dendrite tolerance even under 3 mA cm−2 in symmetric cells. The assembled full cells with D-LHCEs outperform a superior capacity retention of ∼86.83 % with average CE of ∼99.42 % after 500 cycles at 0.5C and the remarkable cycling performance even under harsh conditions (including pouch cells or with controlled N/P of 1.8) in 4.45 V-level Li||LiCoO2 cells. This work highlights the decisive role of diluents in pursuing high-efficiency electrolytes for high-energy Li metal batteries.