Impact of Solvent Impurities from Upscaled Synthesis and Their Purification in Lithium Metal Batteries
Hao Lyu, Tianyang Chen, Zehao Cui, Chen Liu, Jonathan Miller, Hui Zhou, Fenghua Guo, Elizabeth Zhang, Yangju Lin, Gan Chen, Yuelang Chen, Il Rok Choi, Trevor L. Dzwiniel, Arumugam Manthiram, M. Stanley Whittingham, Zhenan BaoAbstract
Fluorinated ether electrolytes are promising for high-energy-density lithium metal batteries, yet their translation to larger-scale production requires systematic control of solvent impurities generated during synthesis and purification. Using 2-(2-(2,2-difluoroethoxy)ethoxy)–1,1,1-trifluoroethane (F5DEE) as a high-performance model solvent, we compare gram- and kilogram-scale batches to correlate impurity origin, purification, and electrochemistry. Although upscaled F5DEE shows >99% purity by standard techniques, ppm-level moisture and organic impurities reduce Li Coulombic efficiency and increase cell variability. We classify impurities by generation pathway into retained intermediates, starting-material-derived analogues, side-reaction products, and purification-introduced residues. Distillation, adsorption, and reactive purification implicate water, alkoxide-derived byproducts, and amines as key performance-limiting species. However, excessive purification generates secondary impurities that degrade performance, revealing a removal–generation trade-off. Thermal, electrochemical, operando microcalorimetry, and online mass spectrometry analyses reveal impurity-dependent current-collector corrosion, heat release, gas evolution, and full-cell degradation. This route-resolved, source-to-consequence workflow provides a transferable qualification framework for electrolyte solvent scale-up.