Tailored electrolyte salt anion chemistry for enhanced high-nickel lithium-ion batteries.

Abstract

The instability of lithium salts within the electrolyte has consistently posed a significant challenge to next-generation lithium-ion batteries. The most commercialized lithium hexafluorophosphate (LiPF₆) suffers from ligand abstraction, causing excessive formation of erosive HF at elevated temperatures. Another promising salt of lithium difluoro(oxalato)borate (LiDFOB), featuring hydrophilic/lithiophilic carbonyl groups, possesses high moisture sensitivity and insufficient dissociation in electrolytes. Herein, we propose an anion-skeleton editing strategy that increases the fluoride ion affinity of the parent Lewis acid while reducing its interaction with H⁺/Li⁺ by replacing the carbonyl groups in DFOB^- anion with hydrophobic/lithiophobic -CF₃ groups. The lithium salt alternative, lithium 2,2-difluoro-4,4,5,5-tetrakis(trifluoromethyl)-1,3,2-dioxaborolan-2-uide (LiDFTFB), has been successfully synthesized and serves as a well-balanced salt in terms of moisture stability, thermal stability, electrochemical stability, ionic conductivity, solubility, and aluminum foil passivation, outperforming LiPF₆ and LiDFOB. Even at an elevated temperature of 50 °C, LiDFTFB endows 1 Ah graphite | |LiNi_0.8Mn_0.1Co_0.1O₂ pouch cells with enhanced cycling stability (81.7% retention after 650 cycles, 0.5 C charge and 0.5 C discharge, 1 C = 200 mA g^-1). This work emphasizes the critical importance of strategically modulating anion chemistries to promote the development of the next-generation lithium-ion batteries.