Designing bifunctional cosolvent-based electrolyte to optimize anion- cation associations for a stable electrode-electrolyte interphase in high-nickel li-metal batteries

JB Park and T Lee and S Chae and AR Choi and Y Park and S Jo and P Oh and SH Kwon and JH Baik and BG Kim and JH Lee, CHEMICAL ENGINEERING JOURNAL, 506, 160012 (2025).

DOI: 10.1016/j.cej.2025.160012

Electrolytes are a key determinant of the performance and stability of Li-metal batteries (LMBs), particularly in regulating the electrode- electrolyte interfacial chemistry. Herein, we propose a novel electrolyte system incorporating methyl 1,1,2,2-tetrafluoroethyl ether (MTFEE) as a bifunctional cosolvent, aimed at enhancing highvoltage cycling of Li||LiNi83Co11Mn6O2 (NCM83) cells. MTFEE refines the solvation structure in electrolyte through its fluorinated alkyl chain (- CF2CF2H), which provides enhanced oxidative stability, and weak interactions between the methoxy group (-OCH3) and Li+, allowing more anions to enter the first solvation shell of Li+. These properties suppress interfacial side reactions, including solvent decomposition, and promote more compact anion-cation associations, facilitating the formation of robust solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI) layers. As a result, the Li||NCM83 cells with MTFEE-based electrolyte show excellent cycling stability (165.9 mAh g- 1 after 200cycles at 4.5 V) and rate capability (173.0 mAh g- 1 at 2.0C). Spectroscopic measurements and theoretical calculations demonstrate that MTFEE functions as a critical bifunctional cosolvent, enabling more anions to enter the first solvation shell of Li+, thereby promoting the stable formation of SEI and CEI layers. This work provides an invaluable lesson that electrolyte design is crucial for achieving high-voltage and stable LMBs with high-nickel cathodes.

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