From industrial waste to energy storage: Si@C core-shell anodes derived from coal gasification fine slag for lithium-ion batteries

Coal gasification fine slag (CGFS) is a solid waste rich in inorganic components (over 60%, mainly SiO₂, Al₂O₃, and Fe₂O₃). Disposal of CGFS via landfilling and stockpiling leads to resource waste and environmental pollution, making effective valorization of this material a critical necessity. Silicon-based anode materials for lithium-ion batteries are highly attractive for commercial applications but are currently limited by high production costs. In this work, we propose a combined strategy of mechanical activation and chemical modification to convert the silicon fraction of CGFS into high-value silicon‑carbon (Si@C) anode materials, achieving both efficient waste utilization and significant cost reduction. The process begins with the extraction of spherical SiO₂ from the inorganic fraction through an ash-removal treatment; however, the low electronic conductivity and poor initial coulombic efficiency of SiO₂ restrict its practical application. To resolve these issues, pure silicon is synthesized via magnesiothermic reduction. Nevertheless, the severe volumetric expansion of silicon during repeated charge-discharge cycles often causes particle cracking, electrode pulverization, and rapid capacity fade, which compromises the cycle stability and safety of the electrode. To address this challenge, a carbon coating is deposited from sucrose - a hydroxyl-rich carbon source that can form hydrogen bonds with the silicon surface - via an in-situ liquid-phase coating method. The resulting carbon layer not only buffers the volume expansion stress of silicon, but also improves the overall electrical conductivity of the composite electrode. Electrochemical tests show that the Si@C composites deliver outstanding electrochemical performance: the initial discharge capacities of [email protected], Si@C-1, Si@C-2, and Si@C-3 are 904.9, 1147.6, 1111.9, and 1076.1 mAh/g, with corresponding initial coulombic efficiencies of 68.42%, 79.59%, 83.59%, and 79.68%, respectively. After 100 cycles at 0.1 A/g, the Si@C-2 electrode retains 82.1% of its initial capacity, significantly outperforming [email protected] (80.3%), Si@C-1 (76.1%), and Si@C-3 (74.97%). This superior cycling stability, combined with high specific capacity, demonstrates the effectiveness of the carbon coating in mitigating volume changes and enhancing electron transport. Overall, this work offers a sustainable and economically viable pathway for upgrading CGFS into high-performance anode materials, contributing to both industrial waste management and the development of advanced energy storage technologies.