Lattice Pre-Expansion Facilitates Stable Sodium-Ion Storage in Sn-Based Anodes by High-Throughput Fabrication

The low energy density of sodium-ion batteries (SIBs) remains a major barrier to their large-scale deployment. Alloy-based anodes represent a promising class of materials owing to their high specific capacity and low operating potential for sodium storage. However, their practical application is hindered by severe volume expansion upon cycling. A common strategy to mitigate this issue is the incorporation of inactive components. To systematically explore optimal composite ratios, we developed a high-throughput magnetron sputtering method capable of simultaneously preparing Sn-based anodes with varying types and contents of inactive components. Using this approach, Sn-based anodes doped with Cu and Al were fabricated and screened. Among the compositions tested, Sn₈₇Cu₁₃ showed the best overall performance. It delivered 796.73 mAh g⁻¹ at 0.5 A g⁻¹ while retaining ∼87.49% of its capacity over 200 cycles. Furthermore, this anode exhibited excellent rate capability, sustaining a specific capacity of 577.45 mAh g⁻¹ at 2 A g⁻¹. Further analysis revealed that Cu doping significantly improves both the initial Coulombic efficiency and cyclic stability. These enhancements are attributed to Cu-induced expansion of the (200) lattice plane of Sn, which mitigates volume changes during alloying with Na. Additionally, Cu reduces the Na adsorption energy, enhancing Na capture and overall electrochemical performance.