Investigating sodium storage behavior in hard carbon directly fabricated from industrial biochar precursors

Abstract

As a key component enabling the commercialization of SIBs, hard carbon anodes have attracted extensive interest. The promise of SIBs is anchored in their cost advantage, which necessitates the development of electrode materials through cost-effective routes. Biomass is abundant and low-cost, serve as ideal precursors for hard carbon anodes. In this work, commercial walnut shell biochar was used as the starting material to synthesize hard carbon through simple acid washing and thermal treatment. Structural analysis shows that the obtained hard carbon possesses a relatively large interlayer spacing and well-developed closed pore structure with a diameter of 2.22 nm. The material HHC1300 exhibits a reversible sodium storage capacity of 287.41 mAh g⁻¹ and an ICE of 89.38%. Notably, the low-voltage plateau region contributes about 70% of the total capacity. These performance metrics exceed those of commercial hard carbon and most laboratory-reported hard carbons derived from lignocellulosic biomass. Furthermore, due to the intrinsically low ash content of the precursor, samples carbonized directly without acid washing can still achieve an ICE of 88.91%. This study demonstrates that incorporating mature industrial carbonization processes into hard carbon fabrication is an effective strategy, paving a practical route toward low-cost, high-performance electrode materials for scalable SIB production.