A Review on the Upgradation of Biomass-derived Hard Carbon Materials

: Sodium-ion battery is a promising alternative to lithium-ion battery because of its abundant raw material resources, low price, and high specific capacity. Amorphous carbon materials (hard carbon) have micropores and impurities, facilitating the intercalation of sodium ions to form "quasi-metallic sodium," resulting in a high sodium storage capacity and a low sodium storage potential. Consequently, hard carbon is one of the most widely studied negative electrode materials. It can be prepared from biomass by thermochemical conversion and has the advantages of large specific capacity, low cost, good cycling stability, and renewability. This review focuses on the recent advances in biomass-based hard carbon materials. Firstly, the preparation methods of hard carbon, including precursor selection, pretreatment, drying methods, and carbonization processes, are summarized. Secondly, the effects of precursor composition and heteroatom doping structure and properties of hard carbon are examined, and the changes in carbon material pores during the activation process, as well as the selection of optimal drying method, pyrolysis temperature, carbonization temperature, activator dosage, and additive, are discussed. Thirdly, the impact of preparation methods on hard carbon's cost, efficiency, and stability is briefly summarized, and the relevant improvement measures and prospects are proposed. Finally, some insights are provided into preparing highperformance biomass-based anode materials for sodium-ion batteries.