Lithium-Difluoro(oxalato)borate Concentration Effects on Anion-Enhanced Solvation Structure and Low-Temperature...

The formation of anion-derived, inorganic-rich electrode/electrolyte interphases (EEIs) on the both electrodes is essential for achieving long-cycle-life lithium batteries. The properties of these EEIs are largely governed by the solvation structure of Li⁺, which can be precisely modulated through interactions between solvents and lithium salts. Our previous work demonstrated that an ultralow concentration electrolyte (2 wt %, 0.16 mol L^-1 (M)) lithium difluoro(oxalato)borate (LiDFOB) in standard carbonate solvents is compatible with commercial Li-ion materials, facilitating the formation of stable, inorganic-rich interphases. Nevertheless, the underlying mechanisms─why such a low concentration of LiDFOB promotes anion-driven interphase formation, and how LiDFOB concentration influences the solvation structure─remain unclear. To address these issues, we systematically prepared LiDFOB/ethylene carbonate (EC)-dimethyl carbonate (DMC) electrolytes with concentrations ranging from 0.2 to 10 wt % and then evaluated their electrochemical performance, particularly under low-temperature conditions. Combining Raman, Fourier Transform Infrared (FTIR), and Nuclear Magnetic Resonance spectroscopy (NMR), we deciphered the evolution of solvation structures across these concentrations. The results identify 2 wt % as a critical threshold for inducing a well-defined solvation configuration conducive to anion participation, thereby promoting the formation of a robust, inorganic-rich passivation layer. This study provides new insights into the role of lithium salt concentration in modulating solvation chemistry and offers a fresh perspective on electrolyte design for next-generation lithium batteries.