Deciphering the role of hydrothermal pretreatment in the conversion of biomass waste into hard carbon with superior electrochemical performance in sodium-ion batteries

Abstract

Due to the complex composition of biomass, the microstructure of derived hard carbon (HC) has a large number of defects and pores. This results in a low initial coulombic efficiency (ICE) and poor rate performance of sodium-ion batteries (SIBs), posing significant challenges to their practical application. This article proposes a hydrothermal pretreatment-assisted carbonization method to prepare almond shell-derived HC. Meanwhile, a comprehensive and systematic investigation was conducted to elucidate the impact of hydrothermal conditions (neutral and acidic conditions) on the crystallinity of the precursor and architecture of derived HC, as well as their correlation with sodium-ion storage performance. Hemicellulose in almond shells was selectively removed by the hydrothermal treatment in pure water, which effectively formed HC with high storage sites and regular morphology, thereby improving electrochemical performance. The optimized biomass-derived HC exhibited a remarkable reversible capacity of 317.1 mA h g⁻¹ at 0.1 C, accompanied by an ICE of 85.9%. Even after 600 cycles at 1.0 C, an ultra-high capacity retention rate of 91.1% was achieved. Through in situ and ex situ characterization studies, it was demonstrated that the excellent sodium-ion storage capacity results from the adsorption on the surface and filling in closed pores of HC. This work provides important guidance for the design of biomass-derived HC as an anode material for SIBs.