One-step regulation of pore evolution in hard carbon from open to closed for high rate and high plateau capacity sodium-ion storage

Abstract

The performance of hard carbon (HC) anodes in sodium ion batteries is hampered by slow kinetics at potentials below 0.1 V and the lack of facile approaches to create closed pores. This work proposes a strategy for effectively constructing closed pores through a one-step pyrolysis of white dextrin. The overall capacity was significantly enhanced, attributable to the superior stability of thermodynamic sites for Na⁺ storage enabled by a combination of moderate graphitization and an optimal pore structure. At 10C, it retains high reversible specific capacity (248.4 mAh g⁻¹) and outstanding performance after 9000 cycles, demonstrating an exceptionally low average cycling capacity fade of just 0.0037%, which is primarily attributed to its sufficiently large opening size of closed pores at high rates. Additionally, at 10C, the anode still has 173.38 mAh g⁻¹ plateau capacity, exhibiting nearly 100% retention compared to the low rate plateau capacity. A comprehensive elucidation of the mechanism for closed pore generation reported in this study will significantly advance the approaches for developing HC with high capacity.