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.