Sustainable Closed-Pore Engineering of Biomass-Derived Hard Carbon via LPRA Crosslinking for Efficient Sodium Storage

Biomass-derived hard carbon is considered a promising anode material for sodium-ion batteries (SIBs) because of its low cost, sustainability, and tunable microstructure. However, the efficient construction of closed pores for sodium storage remains a major challenge. Herein, a simple and efficient strategy based on lignin-based phenolic resin adhesive (LPRA) crosslinking is proposed to induce open-to-closed pore conversion in biomass-derived hard carbon. During curing and subsequent pyrolysis at 1500 °C, the LPRA-derived crosslinked network promotes pore sealing and pore fusion, leading to the in situ formation of abundant closed pores within activated carbon frameworks and providing sufficient sodium-storage space. Structural characterization demonstrates that open pores with sizes of 1.23 and 1.14 nm are extensively converted into closed pores after LPRA incorporation and high-temperature carbonization. Benefiting from the engineered closed-pore architecture, the optimized sample (ACPC-2) exhibits markedly enhanced electrochemical performance. The capacity reaches 2.32 times that of ACC-2, while the initial coulombic efficiency increases to 89.85%. In addition, a high capacity retention of 93.49% is maintained after 100 cycles at 300 mA g–1. Combined in situ and ex situ characterizations further reveal distinct sodium-storage behaviors in hard carbons with different pore structures. In particular, ACPC-2 predominantly stores sodium through sodium-cluster filling within closed pores, which contributes dominantly to the capacity. This work provides a low-cost and sustainable strategy for converting biomass-derived carbon into high-value closed-pore hard carbon and offers useful insights into pore evolution and sodium-storage behavior for the development of high-performance SIB anodes.