Weakening Li+–solvent interaction with dual diluents enabling high-performance lithium metal batteries

Abstract

The practical application of energy-dense lithium (Li) metal batteries is severely hindered by the lack of suitable electrolytes. Weakening solvent coordination to enhance Li⁺ kinetics has become a critical principle in electrolyte design. Here, we propose an electrolyte design strategy that weakens Li⁺–solvent coordination through the synergistic drag effects of dual diluents. Specifically, the –CF₂H group in ethyl 1,1,2,2-tetrafluoroethyl ether (ETE) forms hydrogen bonds with the oxygen atom in 1,2-dimethoxyethane (DME), while the electron-donating –N= and C₂H₅O– groups in ethoxy (pentafluoro) cyclotriphosphazene (PFPN) coordinate synergistically with Li⁺. The combined effects of hydrogen bonding between ETE and DME, along with the coordination of PFPN with Li⁺, weaken the Li⁺–DME interaction and promote anion-enriched solvation structure, thereby facilitating Li⁺ desolvation process and forming an inorganic-rich solid-electrolyte interphase. In a Li metal battery with a 30 μm ultrathin Li anode and high-loading LiNi_0.5Co_0.2Mn_0.3O₂ cathode (23.5 mg cm⁻²), 80% of capacity was achieved after 430 cycles at 4.3 V and 84% after 310 cycles at 4.5 V. Furthermore, a 331 mAh pouch cell achieved 148 cycles with 94.9% of capacity retention.