Sustaining 500,000 Folding Cycles Through Bioinspired Stress Dispersion Design in Sodium-Ion Batteries.

Developing super-foldable electronic materials and devices presents a significant challenge, as intrinsic conductive materials are unable to achieve numerous true-folding operations (super-foldable) due to limitations from short-range forces of chemical bonds. Consequently, super-foldable batteries remain unexplored. This work focused on sodium-ion batteries as a breakthrough point to advance super-foldable devices. By employing a "2+1" bioinspired strategy, we stepwise designed and assembled super-foldable components, from substrates to electrodes, and to ultimately device. This bioinspired approach completely disperses folding stress and thus prevents the breakage of chemical bonds, enabling the successful fabrication of the first super-foldable ion battery. This battery can withstand true-folding at any angle, in any direction, and for an unprecedented number of cycles-far outperforming current foldable phones with hinge structures. Remarkably, after 500,000 true-folding cycles, the battery's microstructure remains intact with no significant degradation of electrochemical performance. Real-time dynamic folding observations reveal an M-shaped folding structure within the bioinspired materials, which effectively disperses stress via bulged layers, dispersed arcs, and slidable microgrooves that work together across different directions and dimensions to achieve super-foldability. Mechanical simulations vividly verify this principle. This work represents a breakthrough in super-foldable devices, offering valuable insights and promoting practical application for future super-foldable devices.