Regulating closed pore structure enables significantly improved sodium storage for hard carbon pyrolyzing at relatively low temperature

Abstract The closed pore has been considered as the key structure for Na ion storage in hard carbon. However, the traditional view is that closed pores can only be formed by the curling of graphite‐like crystallites in the case of high temperature carbonization. Ingenious designing of closed pore structures at lower temperature is still blank. Herein, for the first time, engineering the wall thickness and number of closed pores in waste rosewood‐derived hard carbon was successfully achieved at a low temperature of 1100°C by removing the lignin and hemicellulose components in wood precursor. When applied as an anode material, the optimum sample exhibits a high capacity of 326 mAh/g at 20 mA/g and a remarkable rate capability of 230 mAh/g at 5000 mA/g, significantly higher than those of the untreated sample (only 33 mAh/g at 5000 mA/g). The significantly improved Na storage performance should be attributed to abundant closed pores that provide sufficient spaces for Na storage and thin pore wall structure that is beneficial to the diffusion of Na + in the bulk phase. This work provides a new idea for the future application of biomass‐based hard carbon for advanced Na ion batteries.