Abstract: Hard carbon, a prominent member of carbonaceous materials, shows immense potential as a high-performance anode for energy storage in batteries, attracting significant attention. Its structural diversity offers superior performance and high tunability, making it ideal for use as an anode in lithium-ion batteries, sodium-ion batteries, and potassium-ion batteries. To develop higher-performance hard carbon anode materials, extensive research has been conducted to understand the storage mechanisms of alkali metal ions in hard carbon. Building on this foundation, this paper provides an in-depth review of the relationship between the structure of hard carbon and its electrochemical properties with alkali metal ions. It emphasizes the structural design and characterization of hard carbon, the storage mechanisms of alkali metal ions, and key strategies for structural modulation. Additionally, it offers a forward-looking perspective on the future potential of hard carbon. This review aims to provide a comprehensive overview of the current state of hard carbon anodes in battery research and highlights the promising future of this rapidly evolving field in advancing the development of next-generation alkali metal-ion batteries.

Key words: Hard carbon, Alkali metal ion batteries, Structure design strategy, Electrochemical energy storage, Storage Mechanism