High-Value Utilization of Residue After Ammonia-Extraction Aluminum from Coal Fly Ash: A Novel Strategy for Preparation of Lithium-Ion Battery Anodes

Silicon suboxide (SiOx) has been extensively investigated as an anode material for lithium-ion batteries. However, its low electrical conductivity and significant volume expansion during cycling have hindered its practical application. Although compounding SiOx with carbon can effectively alleviate these issues, practical challenges such as complex preparation processes and high production costs still remain. In this study, porous SiOx/C anode materials were synthesized in a single step using residue after acid-extraction aluminum from coal fly ash (high silica slag) as the silicon source and calcium carbide as both the reducing agent and carbon source, in a NaCl-CaCl2 molten salt medium. The intimate interface between SiOx and carbon not only enhances the electrical conductivity of the electrode but also buffers volume expansion, while the porous structure inside the SiOx/C particles facilitates rapid ion transport. The SiOx/C anode fabricated from this material exhibits excellent electrochemical performance and cycling stability: the anode material synthesized at 700 °C for 3 h (denoted as SiOx/C-700-3) retains a reversible specific capacity of 1093.58 mAh g−1 after 1000 cycles at a current density of 0.4 A g−1. Moreover, the optimized SiOx/C-700-3 electrode achieves robust long-cycle stability under a high current density of 2 A g−1, sustaining a reversible capacity of 486.22 mAh g−1 after 800 cycles with an average Coulombic efficiency approaching 99.6%. The method proposed in this work provides a new strategy for the preparation of SiOx/C anode materials and holds great significance for the high-value comprehensive utilization of coal fly ash and the protection of the ecological environment.