Significance Lithium (Li) metal battery (LMB) is a very promising candidate for the next-generation high-energy-density batteries. However, its practical applications have been impeded by the instability of metallic Li in the state-of-the-art carbonate electrolytes. Localized high-concentration electrolytes (LHCEs) shed light for practical use of LMBs by generating stable, robust solid electrolyte interphase on Li. Here we investigate various types of fluorinated cosolvents as diluents for LHCEs to understand the correlation between the battery performance and the solvation structure and electrode/electrolyte interfacial chemistry. It clearly reveals that the diluent surrounding the highly concentrated salt-solvating solvent clusters accelerates/decelerates anion decomposition, tunes the properties of interphases, and subsequently influences the battery performance. These results can guide further development of advanced electrolytes for LMBs.