Foldable high‐strength electrode enabled by nanosheet subunits for advanced sodium‐ion batteries

Power sources with strong mechanical properties and high‐energy density are highly desirable for the next‐generation flexible electronics. However, the challenge arises from the current electrode structure design, which is unable to bring both satisfactory mechanical and electrochemical properties with high active materials content and mass. Herein, we reported novel flexible, high‐strength, and mechanically stable TiO 2 ‐based film electrodes for advanced sodium‐ion batteries, achieving an ultrahigh strength (up to ≈60 MPa) and commercial‐level areal capacity (4.5 mAh cm −2 ). Highly‐dispersed TiO 2 and interlaced carbon nanotube (CNT) networks are embedded in the sheet‐liked cellulose to form porous, high‐conductive, and high‐active TiO 2 ‐C nanosheets that is basic building subunits of TiO 2 ‐C films, allowing the films with structural robustness and origami‐level flexibility. This strategy reconciles the contradiction between mechanical properties and active material content in flexible electrodes, and the fabricated electrode with a high TiO 2 content of >65% can be bent more than 11 000 times without breaking. Meanwhile, good capacity and excellent cycle stability (0.02‰ capacity‐decay rate over 9000 cycles) of TiO 2 ‐C film under a higher active content (75%) has well satisfied the demands of flexible energy storage devices for electrochemical performances. This TiO 2 ‐C subunit assembly methodology demonstrates enormous potential in high‐strength/toughness flexible electrode construction for flexible electronics.