Rejuvenation of Mechanical Fatigue Resistance in 2D Ferroelectric CuInP₂S₆ by Reversing Ionic Motion

Fatigue degradation remains an intrinsic reliability bottleneck for conventional ferroelectric oxides, where irreversible ionic defect accumulation leads to progressive failure. In contrast, 2D van der Waals (vdW) ferroelectrics feature inherently defect-suppressed interfaces and weak interlayer coupling, mitigating charge trapping and defect accumulation. These attributes make them promising candidates for flexible and reconfigurable electronics, yet their long-term mechanical endurance remains largely unexplored. Here, using atomic-force-microscopy-based cyclic loading, we reveal that the ionic vdW ferroelectric CuInP₂S₆ (CIPS) sustains stresses approaching 7 GPa for over 10⁷ cycles -exceeding all known ferroelectric counterparts. The fatigue process is dominated by stress-induced flexoelectric fields that drive Cu⁺ ions migration and local lattice disorder, which can be completely reversed by an external electric field to restore the crystal integrity. This field-activated ionic rejuvenation extends the lifetime by an order of magnitude and introduces a new paradigm of fatigue engineering in ferroionic systems. Beyond revealing a self-recoverable fatigue mechanism, our results establish design principles for durable, self-healing, and reconfigurable 2D electromechanical and memory devices.