Laser-carbonized anodes for sodium-ion batteries: A sustainable fabrication route toward spatially resolved and practical energy storage

Laser-induced carbonization of polymer films offers a rapid, scalable, and additive-free route to functional carbon materials. Here, a hierarchically structured hard carbon anode is developed by laser carbonizing 5-hydroxyme- thylfurfural (HMF)-based films under ambient conditions. Optimizing laser power yields a vertically graded architecture with a graphitic-like surface and a disordered, microporous core. The resulting binder- and additive- free anode exhibits high electronic conductivity, ion-accessible porosity, and mechanical stability. Despite high areal mass loading (>4 mg cm⁻²), the anode delivers high reversible capacity, excellent rate capability, and >85 % capacity retention over 300 cycles. Operando Raman spectroscopy reveals phase-specific sodium storage mechanisms: surface-confined interactions in graphitic regions and highly reversible pore-filling in disordered domains. These insights clarify the roles of local structure and porosity in charge storage. This work demonstrates laser carbonization as a powerful platform for producing performance-tuned carbon electrodes for practical sodium-ion battery applications.