Tailoring the pore architecture of cotton stalk-derived hard carbon by oxygen functional groups for enhanced sodium storage plateau capacity

Hard carbon (HC) anodes with a high plateau capacity are crucial to sodium-ion batteries (SIBs). However, controlled construction of HC with a highly closed-pore structure and large plateau capacity remains a challenge. Herein, an oxygen-functional-group mediated strategy is described to tailor the porous architecture cotton stalk activated carbon (CSAC) for high-performance HC. Precise regulation of oxygen-containing functional groups in the porous CSAC precursor is achieved by a pre-oxidation treatment. During subsequent carbonization, these functional groups promote cross-linking and gas evolution, effectively suppressing graphitic domains stacking while generating abundant ultra-micropores. The pre-oxidized CSAC exhibits a larger specific surface area (711.4 m 2 g −1 ) and higher ultra-micropore volume than non‑oxygen-mediated activated carbon. After subsequent pore capping via chemical vapor deposition, the optimized HC (CSHC-Pre200) has a highly closed-pore volume (0.081 cm 3 g −1 ), and a small surface area (13.7 m 2 g −1 ). The resulting CSHC-Pre200 delivers exceptional sodium storage performance, such as a charge capacity of 412.5 mAh g −1 (with plateau capacity of 290.7 mAh g −1 ), initial Coulombic efficiency of 91.3 % and outstanding cycling stability. In situ Raman scattering confirms the pore-filling-dominating sodium storage mechanism. This work presents an innovative strategy of oxygen-mediated microporous reconstruction for developing high-performance hard carbons.