Co-solvent engineering of weakly solvating electrolytes for stable lithium metal batteries

Abstract

High-energy-density lithium metal batteries are limited by unstable electrode/electrolyte interfaces and severe parasitic reactions at high voltages. Herein, a co-solvent engineering strategy is developed for cyclopentyl methyl ether (CPME)-based weakly solvating electrolytes to regulate Li+ solvation and interphase formation. By introducing co-solvents with different coordination abilities and molecular structures, the relationship among solvation chemistry, ion transport, interfacial evolution, and cell performance was investigated through theoretical calculations, Raman spectroscopy, XPS characterization, and electrochemical evaluation. The CPME/THP dual-weak-solvent electrolyte promotes anion-involved solvation, delivering a wide oxidative stability window of 4.92 V, a discharge capacity of 47.7 mAh g−1 at 10 C, and improved cycling stability at −5°C. In comparison, the CPME/SL strong/weak co-solvent electrolyte exhibits high ionic conductivity (1.58 mS cm−1), oxidative stability (4.99 V), stable Li||LFP cycling for 1500 cycles, and enhanced stability at 45°C. XPS analysis further confirms inorganic-rich interphase formation. This work provides molecular-level guidance for designing weakly solvating electrolytes for stable lithium metal batteries.