Development of a high-performance lubricant based on halogen-free phosphonium ionic liquid for electrified vehicle transmissions

Electrified vehicle transmissions impose high demands on lubricating oils due to the electrification effects caused by stray currents. Therefore, this study aims to develop a high-performance, low-SAPS lubricant by synthesizing a halogen-free phosphonium-based ionic liquid (P 888P -SP) additive that is added to PAO10 baseline oil at varying concentrations (0.5, 1.0, and 2.0 wt%). The formulated oil is then compared with a fully formulated automatic transmission fluid (ATF-EV). An SRV-IV tribometer was utilized for assessing the tribological performance at different DC levels (0, 3, 6, and 9 A) and sliding parameters. Herein, the main underlying mechanism of antiwear tribofilm formation on the electrified AISI 52100 surfaces is explored. The results demonstrated that the 2.0-P 888P -SP oil achieved a 29% and 43% decline in the coefficient of friction (COF) compared with ATF-EV oil and PAO10 oil, respectively, under triboelectrification conditions at 9 A. Furthermore, the 2.0-P 888P -SP oil decreased the wear volume of the tribosystem by 63% and 79% in comparison to ATF-EV oil and PAO10 oil, respectively. This improvement relates to the synergistic action and adaptability of the P 888P -SP additive with electrification effects. These characteristics resulted in the tribofilm formation, with thickness ranging from 839 nm to 1.41 µm, thereby enhancing the durability of mechanical components. Ultimately, the halogen-free structure of P 888P -SP contributes to its environmental compatibility, making it a promising candidate for use as a lubricant additive in electrified vehicle transmissions. • This study offers a solution to tribological issues in electrified vehicle transmissions. • 2.0-P 888P -SP oil delayed onset decomposition by 56–99 °C vs. ATF-EV commercial oil. • 2.0-P 888P -SP oil improved antiwear properties by 79% under electrification effects. • P 888P -SP oil additive adapts effectively to electrification effects. • 2.0-P 888P -SP oil formed a lubricating tribofilm with thickness reaching up to 1.41 µm.