Molecular-Scale Templating to Regulate Active-Rich Closed-Pore Structures in Polycyclic Aromatic Hydrocarbon-Based Hard Carbon for High-Plateau-Capacity Sodium Storage

Hard carbon (HC) is considered as the most promising anode for sodium-ion batteries (SIBs), and the preparation of high-plateau-capacity HC anodes starting from porous carbon is an existing efficient strategy. However, the complex open-pore distributions in porous carbon hinder the understanding of how to create active-rich closed-pore structures (ACPs), and HC anodes based on polycyclic aromatic hydrocarbons still have lower plateau capacity. Herein, the molecular-scale template, polyhedral oligomeric silsesquioxane (POSS), serves as the building block to generate richer closed-pore structures. These structures are formed by the conversion of open pores featuring small sizes and narrow distributions, inhibiting π-π interactions in POSS-modified anthracene-derived hard carbon (PAHC). This allows the optimized PAHC to exhibit excellent sodium storage (499 mA h g^-1) and a superhigh plateau capacity (392 mA h g^-1) representing 78.5% of the total capacity. Furthermore, the corrected closed-pore volumes resulting from the shrinkage of open pores smaller than 1.6 nm present the strongest linear relationship (R₂ = 0.90) with the plateau capacities of PAHC. These closed-pore structures are identified as ACPs. Capacity discharge curves demonstrate that the large-sized pores may promote sodium clusters to metallic sodium, producing inactive pore structures rather than ACPs.