Efficient Stress Dissipation in Well-Aligned Pyramidal SbSn Alloy Nanoarrays for Robust Sodium Storage

Alloy-type anode materials are promising for sodium-ion batteries owing to their high theoretical specific capacity. However, their practical application is limited by the rapid capacity decay resulted from drastic volume change upon sodium (Na) alloying/dealloying. Here, a facile fabrication of well-aligned antimony tin (SbSn) alloy nanoarrays electrodeposited on copper (Cu) substrates is reported. Such a binary alloy possesses well-defined triangular pyramid-like structure, and the subsequent thermal annealing process develops an "alloy glue" at the root of the nanoarrays which generates a strong connection between the active alloy and the copper substrate. Density functional theory calculation results suggest that the as-fabricated alloy offers an energetically favorable Na diffusion as compared to the individual metals, and the "alloy glue" provides a strong interaction between the substrate and SbSn. More importantly, based on finite-element analysis, such a unique construction of the triangular pyramid-like nanostructure not only creates a small difference in the Na+ concentration gradient, but also builds a uniform stress distribution that promotes both highly efficient Na+ diffusion and effective stress dissipation. Collectively, the optimized composition and geometry give rise to the enhanced high-rate performance and prolonged cycle life of the current SbSn alloy nanoarrays.