The latest research progress on closed pore hard carbon for sodium-ion batteries

Hard carbons are promising anode materials for sodium-ion batteries due to their high specific capacity, strong conductivity, low cost, and environmentally friendly nature. The active sites responsible for Na+ storage primarily include pores, interlayers and defects in hard carbon, among which closed pores play a crucial role in enhancing the capacity of hard carbon anode in the low voltage plateau region. This review introduced the structural feature and pores classification of hard carbon, as well as the influencing factors and Na+ storage mechanism of closed pores. The latest strategies employed for constructing closed pores are also discussed. We hope that this review will provide valuable guidance for designing high-performance closed pore hard carbon anode.