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

Abstract

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.