Coal Fly Ash-Derived Hollow-Porous Si@C Anode for High-Performance Lithium-Ion Batteries

Developing high-performance and affordable silicon (Si) anodes to replace graphite for large-scale deployment remains a significant challenge. Advancing silicon anodes requires not only mitigating volume expansion, a commonly encountered issue during lithiation, but also incorporating a durable, conductive, and inert coating to protect silicon from the electrolyte. In this context, a cost-effective, high-performance hollow porous silicon with an in situ carbon coating anode (HPSi@C) for lithium-ion batteries was synthesized from low-cost coal fly ash (CFA), a major industrial waste product. The hollow, porous spherical structure of silicon is inherited from the CFA bead via a simple magnesiothermic reduction. The structure enables the Si anode to expand and contract without collapsing over repeated charge/discharge cycles. In addition, the in situ carbon coating forms a stable solid electrolyte interphase, ensuring that the composite maintains its structural stability. This rational design yields an impressive initial charging capacity of 2493.3 mAh g –1 at 100 mA g –1, along with a first Coulombic efficiency of 82.6%. The composite also delivers a capacity of 1109.4 mAh g –1 at a high current density of 5000 mA g –1, demonstrating an excellent rate performance.