The Key Role of Molecular Engineering in Developing Hard Carbon Anodes: Precise Regulation and Performance Optimization

Sodium‐ion batteries (SIBs) have demonstrated great potential for energy storage applications due to their unique performance characteristics and the abundant natural reserves of Na in the earth's crust. Hard carbon (HC) is regarded as the most promising anode material for SIBs owing to its high Na storage capacity. However, the highly complex and heterogeneous microstructure of HC poses a significant challenge for performance enhancement. Precise regulation of the HC microstructure at the molecular level is thus crucial for enhancing its performance. Based on the intrinsic structure–performance relationship of HC, this review summarizes recent research progress in molecular engineering strategies for the development of HC. It outlines the principles of controllable design for different precursors at the molecular scale, analyzes in detail the influence of pyrolysis process parameters on the structural evolution of carbon layers. With a focus on crystallites, pores, defects, and interfacial chemistry of HC, various modification approaches are discussed, including molecular coupling, molecular templating, heteroatom doping, metal‐ion catalysis, functional group regulation, and molecular coating modification. This review provides a comprehensive framework for the precise regulation and performance optimization of HC, aiming to offer theoretical guidance for the development of high‐performance HC and to facilitate the commercialization of SIBs.