Optimisation lignin core-shell structures for sodium-ion batteries

Sodium-ion batteries (SIBs) are a sustainable alternative to lithium systems due to the abundance and low cost of sodium. Hard carbon is the most promising SIB anode material. Here, lignin, an abundant aromatic by-product, was used as a renewable carbon precursor to fabricate core–shell nanofibers via coaxial electrospinning. The baseline sample (CS-3.00) exhibited partial shell collapse due to insufficient interfacial consolidation before stabilisation. To address this, a solvent-mediated post-spinning treatment was introduced by immersing the as-spun fibers in hexane for 5–10 min before thermal processing, influencing pore evolution during carbonisation and sodium storage behaviour. The optimised sample showed a 129% increase in specific capacity compared to the standard one.