Refining Chemical Evolution of Resin Toward High-Performance Hard-Carbon Anodes

Hard carbon (HC) anodes are pivotal for advancing sodium-ion battery technology, yet their performance is fundamentally limited by the sluggish ion-insertion kinetics into closed pores during the low-voltage plateau. Prevailing improvement approaches, relying on extrinsic templates or graphitic carbon additives, typically compromise structural precision or scalability. Here, we demonstrate a molecular engineering strategy by tailoring the pre-condensation of a resorcinol-formaldehyde resin. This modification simultaneously modulates the evolution of light volatiles and guides the ordered alignment of polycyclic aromatic hydrocarbons during pyrolysis, yielding an HC architecture with increased accessible closed pores and expanded pseudo-graphitic domains. The optimized HC anode delivers a significantly enhanced low-voltage plateau capacity (from 183 to 255.5 mAh g^{- 1}) and a total reversible capacity of 349.8 mAh g^{- 1} at 60 mA g^{- 1} with an initial Coulombic efficiency (ICE) of 86.69%. The anode also sustains 260.8 mAh g^{- 1} at a high rate of 200 mA g^{- 1} in a standard ester-based electrolyte. The strategy's generality is confirmed using a resorcinol-amine resin, achieving a comparable capacity of 360.8 mAh g^{- 1} and an ICE of 83.17%. This work establishes a scalable, template-free synthesis pathway for high-performance HCs via molecular precursor regulation.