Influence of Electrical Stimulation on the Friction Performance of LiPF₆-Based Ionic Liquids

This work studied the influence of the voltage parameters on the friction and superlubricity performances of LiPF₆-based ionic liquids (ILs). The results show that the voltage direction and magnitude greatly affected the friction performances of ILs and that macroscale superlubricity can be achieved with a stimulation of −0.1 V. The surface analysis and experiment results indicate that the voltage magnitude influences the coefficient of friction (COF) by determining the types of substances in the tribochemical film formed on the ball, while the voltage direction influences the COF by affecting the adsorption behavior of Li(PEG)⁺ ions on the ball. At −0.1 V, the cation group Li(PEG)⁺ adsorption film and FeOOH-containing tribochemical film contribute to friction reduction. The formation of Fe_xO_y within the tribochemical film results in an increase in friction at −0.8 V. The limited adsorption of Li(PEG)⁺ ions and the formation of Fe_xO_y contribute to the elevated COF at +0.1 V. This work proves that the friction performances of LiPF₆-based ILs could be affected by voltage parameters. A lubrication model was proposed hoping to provide a basic understanding of the lubrication mechanisms of ILs in the electric environment.