Assembly of flexible nanohelix films: stress–exporting insights into the electrochemical performance of lithium–ion batteries

Next-generation electrode materials with high specific capacity, such as transition-metal oxides, show great potential for the increasing developments of electric equipment. However, during the charge–discharge process, periodic volumetric variations of the electrode materials generate enormous mechanical stress, which leads to pulverization and rapid capacity decay of electrodes. Herein, we propose an efficient strategy to release mechanical stress of volumetric variation via free stretching and compressing through design and preparation of nanohelical hierarchical flexible films as a binder-free electrode for lithium–ion batteries. Benefiting from characteristic hierarchical core-sheath nanohelical structure, the binder-free electrode exhibits high rate capability (686.1 mAh/g at 6.7 A/g) and superior cycling stability (retaining 726.7 mAh/g after 500 cycles at 3 A/g). Simulation results indicate that the mechanical stress induced by Co₃O₄ volumetric variation is greatly exported to the nanohelical skeleton, and the free stretching and compressing endow the electrode with a superior cycling stability. Moreover, the nanohelical hierarchical structure performs a promising feature for boosting high capacity for magnesium–ion batteries by means of protecting the transformation from Co₃O₄ to Mg_xCo₃O₄ during the activation process. These results indicate that the nanohelical structure with stress-exporting function holds great potentials in energy storage applications.