Sustainable approach in the production of carbon coated nanostructured silicon-based anodes: Selective leaching of Al from hypoeutectic AlSi9Cu4 casting scrap

A green, practical and environmentally friendly approach has been utilized to synthesize carbon coated silicon-based powders from AlSi9Cu4 casting alloy's process scraps. In the experiments, oxalic acid is chosen to remove metallic Al selectively and keep Si and Cu in the residue. The Central Composite Design allows to optimize the factors (leaching time, temperature, solid-to-liquid ratio) and identifies that the highest Al leaching efficiency (85 %) is achieved when 1 M oxalic acid is utilized, with a solid-to-liquid ratio of 1:50, at 80°C for 6 h. Then, three control experiments are carried out. The findings are in good agreement with each other (a standard variation of 1 %) and with the predicted theoretical efficiency value (a yield of 99 %). These facts confirms the validity of the experimental setup and the reliability of the results. Furthermore, a kinetic analysis is performed. It reveals that the leaching follows a mixed kinetic control model, and the activation energy is 25.77 kJ/mol. Then, to allow its use as an anode active material in lithium-ion batteries a porous carbon layer is deposited over the composite by pyrolysis of sucrose. The existence of crystalline Si, Cu and porous C layer is verified by advanced characterizations. The galvanostatic tests reveal that this electrode demonstrates a higher capacity than graphite and successfully achieves cycle tests without delamination even at high current loads. Finally, testing with different cut-off voltages provides an understanding behind this composite's reaction mechanism with Li which highlights the strengths of material selection and process design in the fabrication of anode active material.