Optimizing Hard Carbon Anodes for Sodium‐Ion Batteries: Effects of Pre‐Treatment and Post‐Treatment Techniques

ABSTRACT Hard carbon (HC), an amorphous carbon‐based material, is a promising anode for sodium‐ion batteries (SIBs) due to its sustainability and electrochemical performance. Direct carbonization offers a simple and energy‐efficient synthesis route with relatively high initial coulombic efficiency (ICE), though often at the expense of capacity. To overcome this limitation, both pre‐treatment and post‐treatment strategies have been developed to enhance HC properties. pre‐treatment methods modify structural characteristics during synthesis by increasing structural disorder, surface activity, and defect density. In contrast, post‐treatment methods improve the electrochemical behavior of the final product, yet remain comparatively underexplored. These two approaches serve complementary functions and, when integrated, offer potential for optimizing performance. This review discusses the methodologies, benefits, limitations, and impact of various pre‐ and post‐treatment strategies for HC anodes in SIBs. Advancing understanding in this area is essential for the development of high‐performance and sustainable SIB technologies.