Highly Stretchable Multilayer Core-Shell Triboelectric Fiber for Tensile Energy Harvesting and Self-Powered Strain Sensing

Harvesting energy from human motion offers a promising route toward battery-free wearable and implantable medical devices. While triboelectric nanogenerators have emerged as a leading solution, most rely on repeated compressive contact between tribolayers, limiting their effectiveness under tensile deformation. Here, we introduce a novel fibre-based TENG architecture comprising two multilayer core-shell fibers helically wound around an elastic core, enabling efficient energy harvesting under cyclic stretching. The negative triboelectric fiber consists of a conductive yarn coated with multilayer dielectric shells, designed to enhance charge storage while suppressing charge leakage to the electrode. The positive triboelectric fiber is formed by helically winding wool yarn around a conductive core. The contact dynamics between the two fibers are tunable via inter-fiber spacing and pre-strain in the elastic core, allowing controlled contact-separation during cyclic stretching. Under stretching, the helical fibers undergo progressive separation and contact, generating triboelectric charge and producing an electrical output approximately proportional to the applied strain. Experimental results demonstrate that the multilayer core-shell design achieves approximately 500% higher open-circuit voltage and 700% higher short-circuit current compared with a single-layer counterpart. In addition, the device functions as a stretchable strain sensor capable of detecting tensile strain up to 20% associated with joint rotation. This twist-amplified, interlayer-engineered fiber-based triboelectric device provides a versatile platform for simultaneous energy harvesting and motion sensing, offering significant potential for next-generation self-powered wearable systems.