Pore structure regulation of hard carbon: Towards fast and high-capacity sodium-ion storage

Hard carbon is regarded as one of the most promising anode material for sodium-ion batteries in virtue of the low cost and stable framework. However, the correlation between pore structures of hard carbon and sodium-ion storage is still ambiguous. In this work, based on precise control of pore-size distribution, the capacity, ion diffusion, and initial Coulombic efficiency were improved. Meanwhile, the relationship between pore structure and capacity was investigated. Our result indicates that the micropores hinder ion diffusion and hardly ever accommodate Na⁺ ions, while mesopores facilitate Na⁺ ion intercalation. Hard carbon with negligible micropores and abundant mesopores delivers a maximum capacity of 283.7 mAh g^-1 at 20 mA g^-1, which is 83% higher than that of micropore-rich one. Even after 320 cycles at 200 mA g^-1, the capacity still remains 189.4 mAh g^-1.