Carboxyl-Guided Ultrafine Zinc-Acetate Templating Enables Closed-Pore Engineering in Coal-Derived Hard Carbon Anodes for High-Performance Sodium-Ion Batteries.

Coal‑derived hard carbon (HC) is an appealing anode for sodium‑ion batteries (SIBs) thanks to its abundance and cost‑effectiveness, yet its practical deployment is hampered by modest capacity and a low initial coulombic efficiency (ICE) stemming from uncontrolled porosity. Here, carboxyl‑mediated chelation chemistry is combined with an ultrafine zinc acetate (ZA) templating (≈2 nm) approach and phenolic‑resin interfacial encapsulation to deliver deterministic closed‑pore engineering in bituminous‑coal HC. NaOH activation generates a carboxyl‑rich surface that homogeneously anchors ZA nanodomains. Resin coating locks these templates at the coal/resin interface, and a sequence of mild oxidation, gradient carbonization, and acid leaching yields a dense network of closed nanocavities. The optimized HC delivers 370.9 mAh g-1 at 20 mA g-1, retains 92.5% ICE, and sustains 80.4% of its capacity over 3000 cycles at 1 A g-1, surpassing state‑of‑the‑art coal‑based HCs. These findings illustrate a scalable, molecular‑level strategy that reconciles low‑cost feedstocks with high‑performance SIB anodes.