Electrolytes were evaluated for their potential use as a pure solvent or additive in lithium-ion battery applications. Ionic conductivities, VTF parameters, and ion dissociation values were determined using Electrochemical Impedance Spectroscopy (EIS) for organosilyl nitrile solvents with varying degrees of fluorination and the salts LiPF6 or LiTFSI. Silyl compounds have been shown to improve the thermal and electrochemical stability of electrolyte solutions. Each solvent contained either the salt LiPF6 or LiTFSI at a molar ratio of either 5 or 20 solvent/Li+. Impedance was measured over a temperature range of -5°C to 50°C. By comparing the molar conductivity from the impedance measurements with the molar conductivities based on NMR diffusion measurements, ion dissociation values (a) for the electrolytes over the same temperature range were calculated. Increasing fluorination of the solvents improves conductivity and ion dissociation. More fluorinated electrolytes resulted in higher activation energies and higher values of ion dissociation. Solvents containing LiPF6 demonstrated higher conductivities and higher ion dissociation than the same solvents with the LiTFSI salt. All electrolytes reached the commercial viability benchmark of 1 mS/cm at 298 K. For both LiPF6 and LiTFSI electrolytes, the trifluoro solvent at 20 molar salt ratio had the highest conductivity at 298 K, 2.38 and 2.07 mS/cm respectively, and the highest ion dissociation, 0.46 and 0.37. These electrolytes were synthesized by Silatronix® Inc.

Ionic conductivities and ion dissociation in silyl nitrile electrolytes with LiPF6 and LiTFSI salts for applications in lithium-ion batteries

255th National Meeting (2018)

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