Superlubricity of graphite sliding against graphene can be easily attained at the nanoscale when it forms the incommensurate contact under a low normal load. However, the achievement of superlubricity under ultrahigh contact pressure or at the macroscale, which has more applications in the lubrication, remains unclear. In this work, we first obtain the robust superlubricity of graphite under ultrahigh contact pressures of up to 2.52 GPa by the formation of transferred graphene nanoflakes on an AFM tip. The friction coefficient becomes as low as 0.0003, a state that is attributed to the extremely low shear strength of graphene/graphite interface in the incommensurate contact. We find out a threshold of pressure, at which the superlubricity state disappears, and the friction coefficient increases approximately 10 times. The failure of superlubricity originates from the delamination of the topmost graphene layers on graphite under ultrahigh contact pressure. According to these results, we extend the superlubricity of graphite sliding against graphene nanoflake to the macroscale, showing that the friction coefficient was reduced to 0.001, but randomly being attained as the test progressed, with a maximal sliding distance of 131 μm. The macroscale superlubricity was derived from the statistical frictional forces of multiple transferred multilayer graphene nanoflakes (in the contact zone) sliding on the graphite in the presence of atomic steps at the nanoscale. To solve this instability, we take advantage of the synergy effect of graphene-oxide nanoflakes and ethanediol at Si₃N₄–SiO₂ interfaces, and achieve a robust macroscale superlubricity state (μ = 0.0037). Such macroscale superlubricity provides a new approach towards realization of extremely low friction in graphene through the synergy effect with liquids.

Jinjin Li received the BS degree in mechanical engineering from University of Science and Technology of China, Hefei, China, in 2009, and the PhD degree in mechanical engineering from Tsinghua University, Beijing, China in 2014. He is currently an associate professor at Tsinghua University, Beijing, China. His major research area includes surface and interface, nanotribology and friction theory at the nanoscale. He has published more than 40 papers (SCI index) on the international journals (36 papers as the first and corresponding author). He has been awarded the China youth talents lifting project, Hiwin award for outstanding doctoral dissertation, first prize for outstanding doctoral dissertation, and outstanding postdoctor in Tsinghua University.