Dilute Electrolyte with Vehicular Aggregates for Stable High-Energy Lithium-Metal Batteries

Electrolyte design is critical for high-energy lithium-metal batteries (LMBs) because it dictates the aggressive Li-electrolyte interphase that governs cycling stability and Coulombic efficiency (CE). However, traditional high- or locally high-concentration electrolytes, which achieve good Li-metal compatibility by the formation of anion‒solvent‒Li⁺ aggregates (AGG), typically suffer from poor ionic conductivity (e.g., ≈1 mS cm^-1). Therefore, achieving both high ionic conductivity and AGG-dominated solvation structure under dilute conditions still remains a challenge. Herein, a novel dilute electrolyte with vehicular aggregates (DVA) mechanism is proposed by employing pyrrolidine-1-sulfonyl fluoride (PSF) solvent with optimal steric hindrance effect. Based on this DVA electrolyte, the uniquely AGG-dominated solvation structure under dilute conditions achieve high ionic conductivity (4.9 mS cm^-1) featuring its vehicular ion-transport mechanism. It exhibits good Li-metal compatibility with high stripping-plating CE of ≈99.5% with inorganic (LiF, Li₂O)-rich robust solid‒electrolyte interphase. Furthermore, the electrolyte effectively suppresses the stress-corrosion cracking, transition-metal dissolution, gas evolution, and detrimental surface degradation on the cathode side, thus enabling 4.6-V-class LMBs with ultra-high-Ni cathodes to deliver a high discharge capacity of 228.4 mAh g^-1, excellent rate capability up to 2C, and 87% capacity retention after 150 cycles. This work offers a promising approach for designing advanced electrolytes for high-energy LMBs.