Correlation between Potassium-Ion Storage Mechanism and Local Structural Evolution in Hard Carbon Materials

Hard carbons (HCs) are the most promising anode materials for potassium-ion batteries (PIBs) due to their low cost, diverse precursors, easy-to-design nature, and excellent electrochemical performance. However, the relationships between the structure and K+ storage mechanism of HCs have not been clearly and systematically investigated, while the principles of hard carbon structure design remain unclear. Here, a series of hard carbon materials with a continuously adjustable structure are synthesized at 800–2900 °C to study the structure–mechanism relationships. With the increase in temperature, the evolution of the structural domain unit of hard carbon is amorphous domain → pseudographite domain → graphitelike domain, which is confirmed by transmission electron microscopy, X-ray powder diffraction, pair distribution function, near-edge X-ray absorption fine structure, etc. The amorphous domain contributes to surface-controlled absorption behavior, while pseudographite and graphitelike domains show diffusion-controlled insertion behavior. The corresponding carbonization temperature stages of the relevant structure–mechanism relationship were proposed as amorphous domain–absorption (800 °C), amorphous and pseudographite domain–absorption–insertion (1000–1500 °C), and pseudographite and graphitelike domain–insertion (1800–2900 °C). The hybrid amorphous and pseudographite domain structure exhibits the best electrochemical performance. Furthermore, the desired K+ storage performance could be obtained by modulating the structure of hard carbon. This achievement will certainly promote the development of hard carbon anodes for PIBs.