Sputtering Deposition of Sn–Mo-Based Composite Anode for Thin-Film Li-Ion Batteries

Abstract

The role of electrochemically inactive molybdenum in alleviating the anomalous volume expansion of tin anode upon charge–discharge cycling has been investigated. Tin–molybdenum thin-film composite anodes for Li-ion batteries were prepared using a direct-current sputtering method from a tin metal target incorporating molybdenum element. Results of structural and compositional analyses confirmed the presence of tin and molybdenum. The elemental ratio obtained from energy-dispersive x-ray spectroscopy confirmed the feasibility of tailoring the thin-film composition by varying the ratio of metallic elements present in the sputtering target. Scanning electron micrographs of the samples revealed the occurrence of flower-like open morphology with Mo inclusion in a Sn matrix. The gravimetric discharge capacity for pure Sn, Sn-rich, and Mo-rich samples was 733 mAh g⁻¹, 572 mAh g⁻¹, and 439 mAh g⁻¹, respectively, with capacity retention after 50 cycles of 22%, 61%, and 74%, respectively. Mo inclusion reduced the surface resistivity of the Sn anode after the initial charge–discharge cycle. The charge-transfer resistance after the first cycle for pure Sn, Sn-rich, and Mo-rich samples was 17.395 Ω, 5.345 Ω, and 2.865 Ω, respectively. The lithium-ion diffusion coefficient also increased from 8.68 × 10⁻⁸ cm²S⁻¹ for the pure Sn sample to 2.98 × 10⁻⁵ cm²S⁻¹ for the Mo-rich sample.