Bifunctional catalyst directed closed-pore engineering in hard carbon for enhanced sodium storage

Abstract

The plateau capacity of hard carbon is intrinsically linked to the energy density of sodium-ion batteries (SIBs). Given that the closed-pore structure is pivotal for maximizing plateau capacity, precise regulation of the closed-pore architecture in hard carbon is imperative. Herein, we propose a bifunctional “catalysis-self-templating” strategy. This approach employs ammonium acetate to optimize the closed-pore structure of resorcinol–formaldehyde (RF) derived hard carbon. During polymerization, ammonium acetate modulates the cross-linking structure of the precursor. Subsequently, it undergoes in situ decomposition during carbonization to generate micropores. Driven by carbon layer rearrangement, these voids eventually evolve into an abundant closed-pore structure. Consequently, the optimized RF-1100 exhibits a remarkable reversible capacity of 432.3 mA h g⁻¹ with a high plateau capacity of 287.8 mA h g⁻¹ at 20 mA g⁻¹. Moreover, RF-1100 shows 96% capacity retention for 200 cycles at 50 mA g⁻¹. These findings validate the viability of a bifunctional “catalysis-self-templating” strategy to tailor the closed-pore architecture of phenolic resin-derived hard carbons, providing valuable insights for the structural design of advanced SIBs.