Influence of Positional Isomerism in Weakly Solvating Ethers on Lithium Metal Deposition

Lithium metal is a promising anode for next-generation high-energy batteries but faces issues like internal short circuits and low Coulombic efficiency (CE), limiting its performance. Although factors like solid-electrolyte interphase (SEI) composition, charge transfer resistance, solvation structure, and solvent symmetry influence Li metal deposition, a unified descriptor remains absent. Here, we systematically investigate three positional isomers of weakly solvating ether solvents-dipropyl ether (DPE), butyl ethyl ether (BEE), and pentyl methyl ether (PME), selected to maintain the same C/O (carbon/oxygen) ratio of 6, allowing isolation of minor structural variations on Li metal deposition. By correlating charge transfer kinetics, solvation structure, SEI composition, and lithium microstructure with electrochemical performance, we identify key factors influencing deposition. The symmetric ether, DPE, with sluggish charge transfer kinetics and the most pronounced ion pairing, achieved the highest CE of 99.26%, followed by BEE (99.24%) and PME (98.89%). Increased ion pairing and enhanced LiF content in the SEI were found to have the strongest linear correlation with interfacial stability as reflected in CE. These findings challenge previous studies that faster charge transfer kinetics led to improved CE and enhance the understanding of designing weakly solvating ethers with optimized oxygen placement for future Li metal batteries.