The Role of Hydrothermal Carbonization in Sustainable Sodium-Ion Battery Anodes

Sodium-ion batteries as a prospective alternative to lithium-ion batteries are facing the challenge of developing high-performance, low-cost and sustainable anode materials. Hard carbons are appropriate to store sodium ions, but major energy and environmental concerns during their fabrication process (i.e., high-temperature carbonization) have not been properly assessed. Furthermore, the rational design of high-performing hard carbon anodes is usually limited by the conventional direct carbonization of organic precursors. Here, the hydrothermal carbonization process is employed as a versatile pre-treatment method of renewable precursors, followed by high-temperature carbonization, for producing advanced hard carbon anodes. The critical role of hydrothermal pre-treatment in regulating the structure for an optimized performance of hard carbon anodes is elucidated, while revealing the sodium-ion storage mechanism using electrochemical kinetic calculations, advanced characterization and multi-scale modeling. Furthermore, the environmental impacts of hydrothermal pre-treatment and subsequent carbonization are evaluated using life cycle assessment compared to direct carbonization. By comparing hard carbon anodes with and without the hydrothermal pre-treatment, it is verified that the additional hydrothermal process is responsible for enhanced electrochemical performance, increased carbon yields and reduced carbon emissions. The work provides a systematic understanding of functions and energy consumptions of hydrothermal systems to achieve next-generation sustainable sodium-ion batteries.