Non-fluorinated Asymmetric Ether Electrolytes with Controlled Solvation Structure for High-voltage Lithium Metal Batteries

Ether-based electrolytes are well-suited for lithium metal anodes but suffer from limited oxidative stability, restricting their use with high-voltage cathodes. Fluorination has been employed to mitigate this challenge; however, their recycling poses environmental challenges. Increasing salt concentration can enable the use of non-fluorinated ethers but often results in larger ion clusters, compromising conductivity and rate capability. Here, we design amphiphilic ether solvents, 1-(2-methoxyethoxy)butane (M4C) and 1-(2-methoxyethoxy)hexane (M6C), to promote preferential contact ion pair (CIP) formation across different LiFSI concentrations, breaking the usual linear cluster size-concentration relationship. Notably, 2 M LiFSI in M4C supports stable cycling of a 20 mu m lithium metal anode paired with an NMC811 cathode at 4.3 V for over 200 cycles under stringent conditions (N/P = 2.5). The electrolyte also delivers robust performance under fast charging (3C) and slow discharging (1C), demonstrating its potential for high-energy, high-rate lithium metal batteries without relying on fluorinated solvents.