Electromechanical -thermal coupled modeling and optimal design of grease-lubricated triboelectric nanogenerators

In engineering, adding lubricating grease at the friction interface offers a promising strategy to simultaneously enhance the electrical output and durability of triboelectric nanogenerators (TENGs). However, current efforts to optimize the electrification performance of grease-lubricated TENGs remain exploratory, lacking quantitative understanding of how structural parameters influence output and durability. In this manuscript, using a rotary freestanding TENG under grease lubrication, we develop two regression-based models: a charge density-dependent contact model and an electrostatic induction model incorporating interfacial temperature rise.Subsequently, numerical algorithms such as the Augmented Lagrange method and sparse LU decomposition are used to solve the electromechanical-thermal multiphysics coupled model, and the influence of TENG structural parameters on surface temperature rise and electrification performance under grease lubrication is studied. The results show that the electrostatic force in grease-lubricated conditions can reach 20.3 times that under dry friction, significantly affecting electrification performance; Reducing the grating number improves open-circuit voltage but substantially lowers short-circuit current; Increasing the gap ratio enhances short-circuit current, while open-circuit voltage exhibits a non-monotonic trend. Moreover, durability remains unaffected by grating number but declines with increasing gap ratio due to higher interfacial temperature rise and accelerated charge density decay. This study can provide a theoretical basis for the quantitative design of grease-lubricated TENGs with high output and durability.