Self-encapsulated nanofibrous ionic skin with superhigh fatigue resistance and broad environmental tolerance.

While skin-inspired ionic conductors are promising soft sensing interfaces for advanced robotics, their practical deployment is often restricted by fatigue crack growth and environment-induced signal drift. Here we present an ultrathin, self-encapsulated nanofibrous ionic skin that integrates superhigh fatigue resistance and broad environmental tolerance via a mechanically interlocked triple-layer architecture. By embedding a high-modulus ionogel nanomesh within a soft adhesive matrix and sealing it with a perfluoroelastomer overlayer, this design mitigates the mechanical mismatch typically observed in conventional post-encapsulated materials. The resulting ionic skin exhibits an ultrahigh fatigue threshold of 12.4 kJ m-2 while preserving skin-mimetic softness, elasticity, strain-stiffening, and conformal self-adhesion. Furthermore, this self-encapsulated structure ensures stable ionic conduction and reproducible sensing under diverse environmental conditions, including vacuum, underwater/saline immersion, organic solvents, and wide temperature fluctuations (-35 to 200 °C). This work offers a robust, iontronic, and environmentally resilient platform for reliable sensing in demanding soft robotic applications.