Molten salt electrolytic synthesis of silicon-copper composite nanowires with enhanced performances as lithium ion battery anode

Highlights: • Silicon and silicon-copper composite have been electrochemically synthesized in molten salt. • Silicon bending nanowires and Cu-Si straight nanowires have been tested as the anode. • Cu-Si nanocomposite anode shows a higher capacity retention after 500cycles at 500 mA g⁻¹. A facile metallurgical method named molten salt electrolysis was introduced to prepare silicon nanowires (Si NWs) and Cu₉Si/Si composite nanowires that were used as the anode materials for lithium-ion batteries (LIBs). Simply utilizing SiO₂ and Cu/SiO₂ mixture as the raw materials, by tailoring voltage into the molten salt chamber, SiO₂ was constantly deoxidized to form Si flexible nanowires with 1–3 μm in length and 100–200 nm in width. Cu ingredient further catalyzed the growth of silicon nuclei to generate straight wires with longer 10 μm and narrower 60–100 nm. Benefiting from the compositional and structural advantages, the Cu₉Si/Si nanocomposite anode exhibited a better capacity retention that delivered a specific capacity of 601.3 mAh·g⁻¹ at 200 mA g⁻¹ after 200 cycles and 398.8 mAh·g⁻¹ at 500 mA g⁻¹ after 500 cycles. Notably Cu₉Si/Si NWs anode with enhanced rate capability was also obtained, with a specific capacity of 747.6 mAh·g⁻¹, 550.6 mAh·g⁻¹ and 412.2 mAh·g⁻¹ at the current density of 200 mA g⁻¹, 500 mA g⁻¹ and 1000 mA g⁻¹, respectively.