Impurity removal strategy enables bamboo-derived hard carbon with abundant closed pores for high-performance sodium-ion batteries

The electrochemical performance of biomass derived hard carbon is strongly influenced by its pore architecture and structural purity, both of which are often limited by naturally occurring mineral species in the raw precursor. To overcome this issue, a sequential preparation route was developed in which bamboo was first precarbonised, then purified through combined acid and alkali washing, and finally subjected to a second heat treatment. Removing the inorganic components at the intermediate stage promotes the formation of numerous open pores, which are subsequently reconstructed into enclosed pore domains during the final carbonisation process. As a result, the obtained hard carbon possesses a more favourable interlayer distance together with a well developed closed pore network, leading to substantially improved sodium storage behaviour. Benefiting from the optimized carbon framework, the bamboo derived anode achieves a reversible capacity of 367.24 mA h g −1 , a discharge capacity of 514.09 mA h g −1 , and a low potential plateau contribution of 247.07 mA h g −1 , together with improved first cycle efficiency, indicating that this economical sequential treatment can effectively raise the energy storage capability of sodium-ion batteries and may be extended to other biomass precursors.