Minimizing Solvent-Coordination in Ether Electrolytes for Lithium Metal Batteries under Extreme Operating Conditions.

Ether-based electrolytes are considered to be one of the most promising systems for high-performing lithium metal batteries (LMBs). However, the poor oxidation stability (<4.5 V) of ether solvents seriously limit their practical applications. Herein, high-voltage LMBs with LiNiCoMnO (NCM811) cathode operated under extreme conditions by minimizing solvent-coordination in ether electrolytes with fluoroethers, nitrile ethers, and highly fluorinated additives, are demonstrated. It is revealed that ethylene glycol bis(propionitrile) ether (DENE) inhibits the lone-pair electrons loss on ether oxygen through strongly electron-withdrawing cyano groups to increase the electrochemical window to ≥5 V. Heptafluorobutyric anhydride (HFAA) triggers the formation of solid electrolyte interphase rich-in LiF-species, ensuring uniform deposition/stripping and high reversibility of Li. Especially, DENE and HFAA synergistically minimizes the coordination number of ethylene glycol dimethyl ether (DME) and hexafluorophosphate (PF ), thereby promoting the desolvation process of Li and inhibiting the interfacial side reactions. Therefore, the NCM811 cathodes using modified electrolytes exhibit excellent electrochemical performance at ultrahigh voltage (4.7 V), ultrahigh rate (20 C), and ultrawide temperature range (-30 to 120 °C), and achieve stable operation in a high-capacity Li metal pouch cell of 30 Ah and a high-energy density Li metal pouch cell of 502.7 Wh kg, respectively.