Unraveling the mechanism of sodium storage in low potential region of hard carbons with different microstructures

The exploration of sodium storage mechanism is of great significance to the development of high-performance hard carbon materials. However, the complex and diverse structure makes the exploration process pretty difficult. Hence, hard carbons with different microstructures were prepared, and the relationship between different microstructures and sodium storage properties was investigated. The results show that "insertion" and "pore-filling" are both effective mechanisms for sodium storage in low potential region. The "pore-filling" mechanism plays an absolutely dominant role in rich-micropores carbons, and pseudo-graphitic layers are the "transport channel" for Na-ions to enter into internal micropores. The density functional theory (DFT) results further confirmed the stronger binding effect of the micropores structure on Na-ions. NMG (magnesium gluconate-derived hard carbons) with abundant micropores can provide a capacity of 346 mAh g−1 at 50 mA g−1. Besides, the capacity maintains 227.7 mAh g−1 after 1000 cycles at a high current density of 1 A g−1. The excellent performance of the full-cells also reflects the great practical application value of NMG.