Sustainable Hard Carbon for Sodium-Ion Batteries: Precursor Design and Scalable Production Roadmaps

Sodium-ion batteries (SIBs) emerge as a sustainable and cost-effective alternative to lithium-ion batteries due to the abundant and widely distributed nature of sodium resources. Hard carbon anodes, characterized by their pseudo-graphitic layered structures and nanoporosity, are key to achieving high-performance SIBs. However, the commercialization of hard carbon is hindered by significant challenges in precursor design, carbonization optimization, and sustainability. This review focuses on the critical role of precursor selection and introduces a classification system based on volatile content. High-volatility biomass precursors, such as bamboo, require pretreatments like acid/alkali leaching or hydrothermal processing to optimize pyrolysis. Medium-volatility resins and plastics benefit from crosslinking strategies, while low-volatility materials such as biochar and petroleum coke rely on nanochannel engineering to improve sodium storage performance. Bamboo-based precursors are highlighted as a promising pathway due to their renewability and environmental advantages, though challenges such as impurity control and structural engineering persist. By integrating precursor design with carbonization strategies, this review provides a comprehensive framework for understanding microstructural regulation and performance enhancement. The insights presented offer valuable guidance for developing scalable and sustainable approaches to produce high-performance hard carbon materials, paving the way for the next generation of SIB technologies.