Recycling Waste Al–Si Alloy for Micrometer-Sized Spongy Si with High Areal/Volumetric Capacity and Stability in Lithium-Ion Batteries

People are becoming more conscious of the necessity of sustainable development, and waste recycling is getting increased attention. As for the highly concerned Si in lithium-ion batteries (LIBs), the recycled nanoscale Si displays a small packing density that would impede its industrialization. Moreover, Si recycling commonly shows a lengthy process and specialized device usage, resulting in high energy/cost consumption and pollution. This study employs waste Al–Si alloy as raw materials and proposes a hypothermal chemical corrosion method to recycle and construct micrometer-sized spongy Si. The nanopores/nanoskeletons in the spongy Si and the amorphous carbon coating (Si@C) regulate electron/lithium ion transference, capacitance behavior, and structural stability to achieve high areal/volumetric capacity and cycling performance. The spongy Si@C anode delivers an areal and volumetric capacity of 1.13 mAh cm–2 and 1909 mAh cm–3 (0.05 C), respectively. Increasing mass loading further improves areal capacity to 2.52 mAh cm–2 (0.1 mA cm–2) which retains 0.89 mAh cm–2 after 100 cycles at 1.2 mA cm–2. Furthermore, in the full-cell configuration, the initial energy density is 483 Wh kg–1 at 0.5 C, and the capacity retention is 84% after 150 cycles at 2 C. This study provides novel insights into the efficient and economical fabrication of high-performance LIBs.