Tailoring the pore structure of hard carbon for enhanced sodium-ion battery anodes

Biomass-derived hard carbons, usually prepared by pyrolysis, are widely considered the most promising anode materials for sodium-ion batteries (SIBs) due to their high capacity, low potential, sustainability, cost-effectiveness, and environmental friendliness. The pyrolysis method affects the microstructure of the material, and ultimately its sodium storage performance. Our previous work has shown that pyrolysis in a sealed graphite vessel improved the sodium storage performance of the carbon, however the changes in its microstructure and the way this influences the sodium storage are still unclear. A series of hard carbon materials derived from corncobs (CCG-T, where T is the pyrolysis temperature) were pyrolyzed in a sealed graphite vessel at different temperatures. As the pyrolysis temperature increased from 1000 to 1400 °C small carbon domains gradually transformed into long and curved domains. At the same time, a greater number of large open pores with uniform apertures, as well as more closed pores, were formed. With the further increase of pyrolysis temperature to 1600 °C, the long and curved domains became longer and straighter, and some closed pores gradually became open. CCG-1400, with abundant closed pores, had a superior SIB performance, with an initial reversible capacity of 320.73 mAh g⁻¹ at a current density of 30 mA g⁻¹, an initial Coulomb efficiency (ICE) of 84.34%, and a capacity retention of 96.70% after 100 cycles. This study provides a method for the precise regulation of the microcrystalline and pore structures of hard carbon materials.

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