Regulating electric double layer in non-fluorinated ether electrolyte enables high-voltage and low-temperature lithium metal batteries

The poor oxidation stability of ether-based solvents has long been a major challenge limiting their practical application. To enhance the oxidative stability of ether-based electrolytes, the physicochemical properties of various glycol dimethyl ethers are screened, and diglyme (G2) is selected as the sole solvent for the electrolyte. Lithium bis(fluorosulfonyl)imide (LiFSI), a highly dissociative salt, is used as the primary salt; while lithium nitrate (LiNO₃) and lithium difluorophosphate (LiDFP), which have small ionic sizes and strong binding energies, are added as secondary salts. The resulting electrolyte can modulate the electric double layer structure by NO₃⁻ and DFP⁻ on the cathode side, leading to an increased Li⁺ concentration that is originally repelled by the cathode. Additionally, the oxidation stability of the electrolyte is improved and the formed electrode-electrolyte interphase is more uniform and stable, thereby enhancing the electrochemical performance of the cells. As a result, cells assembled with a total of 1 M ternary lithium salts in G2 solvent can operate at high voltage of 4.4 ​V. The Li||NCM811 ​cells maintain 80.2% capacity retention after 270 cycles at room temperature, with an average Coulombic efficiency of 99.5%, and exhibit 88.4% capacity retention after 200 cycles at −30 ​°C.