Interfacial Properties of LiTFSI and LiPF6-Based Electrolytes in Binary and Ternary Mixtures of Alkylcarbonates on Graphite Electrodes and Celgard Separator

For a better understanding of the adsorption behavior of alkylcarbonate-based electrolytes on graphite electrodes and Celgard separator for Li-ion batteries applications, the interface parameters are determined by contact angle and surface tension measurements. The correlation between these parameters and chemical compositions made of alkyl carbonate with a varying nature of lithium salts (LiPF6 and LiTFSI) and volume fractions of binary and ternary mixtures containing propylene carbonate (PC), ethylene carbonate (EC), and dimethyl carbonate (DMC) is investigated. From the obtained contact angle and surface tension (gamma(L)) values for each liquid, the dispersive and polar components of the surface tension (gamma L-d and gamma L-P) of the electrolyte and interfacial free energy between the solid and liquid (gamma(SL)) were then calculated using the Young's equation. The variation of contact angle (theta) and the surface tension, as well as the work of adhesion (W-A) of binary PC/DMC mixtures on PP, PE, and PET model surfaces were also measured and commented as function of volume fraction of PC in DMC. Finally, the Zisman's critical surface tension (gamma(C)) for studied surfaces was then obtained showing positives slopes of cos theta versus gamma(L). This behavior is explained by a relative higher adsorption of alkylcarbonates to the hydrogenated supports or graphite. These results are decisive to understand the performance of electrolyte/electrode material/separator interfaces in lithium-ion battery devices.