Triboelectric Properties of Polyimide Films under Oil Lubrication

The method of introducing lubricant at the friction interface of sliding triboelectric nanogenerators (TENGs) can reduce material wear and charge density attenuation caused by dry friction. However, the triboelectric mechanism of metal-polymer under oil lubrication remains ambiguous, leading to a lack of guidance for the design of high-performance oil-lubricated TENGs. In this paper, squalane, castor oil, and CD-15W-40 are introduced into the polyimide (PI)-copper (Cu) friction interface of a sliding TENG, and the effects of lubricant species on open-circuit voltage, coefficient of friction, and mass loss are investigated. The results show that the conductivity and electron affinity of the lubricant are key factors affecting the electrical output. Compared to the dry condition, the castor oil and CD-15W-40 reduced the electrical output of the sliding-mode TENG due to the charge carrier shielding effect formed at the friction interface caused by their high conductivity. In contrast, squalane has both extremely low conductivity and a higher electron affinity than polyimide, which enhances interfacial charge transfer through oil-solid contact electrification, thereby increasing the electrical output. Compared to the sliding-mode TENGs with castor oil and CD-15W-40, the sliding-mode TENG with squalane has a lower friction coefficient and mass loss, as well as higher output and stability, showing that squalane is more suitable for the TENG. This work can provide guidance for the design of a sliding TENG under lubrication.