Tuning the Solvent Alkyl Chain to Tailor Electrolyte Solvation for Stable Li-Metal Batteries

1,2-Dimethoxyethane (DME) has been considered as the most promising electrolyte solvent for Li-metal batteries (LMBs). However, challenges arise from insufficient Li Coulombic efficiency (CE) and poor anodic stability associated with DME-based electrolytes. Here, we proposed a rational molecular design methodology to tailor electrolyte solvation for stable LMBs, where shortening the middle alkyl chain of the solvent could reduce the chelation ability, while increasing the terminal alkyl chain of the solvent could increase the steric hindrance, affording a diethoxymethane (DEM) solvent with ultra-weak solvation ability. When serving as a single solvent for electrolyte, a peculiar solvation structure dominated by contact ion pairs (CIPs) and aggregates (AGGs) was achieved even at a regular salt concentration of 1 m, which gives rise to anion-derived interfacial chemistry. This illustrates an unprecedentedly high LillCu CE of 99.1% for a single-salt single-solvent (non-fluorinated) electrolyte at similar to 1 m. Moreover, this 1 m DEM-based electrolyte also remarkably suppresses the anodic dissolution of Al current collectors and significantly improves the cycling performance of high-voltage cathodes. This work opens up new frontiers in engineering electrolytes toward stable LMBs with high energy densities.

Automated summary

This study proposes a rational molecular design method to achieve stable lithium-metal batteries by adjusting the structure of the electrolyte solvents. By shortening the middle alkyl chain and increasing the terminal alkyl chain, a diethoxymethane (DEM) solvent with ultra-weak solvation ability is obtained. The DEM solvent exhibits high lithium Coulombic efficiency and suppresses anodic dissolution, leading to improved cycling performance of the batteries.