Research progress on coal-based hard carbon anode materials for sodium-ion batteries

Sodium-ion batteries (SIBs) are considered an effective alternative to lithium-ion batteries due to their abundant resources and extensive industrialization potential. However, the synthesis and preparation of anode materials directly affect the industrialization process of SIBs. Carbon materials are favored for their stable structure, abundant resources, and practical applications. In this paper, the most abundant coal is selected as the hard carbon precursor. Yet, the internal structure of coal is complex, and there is a lack of systematic discussion on the various structural configurations of coal-based hard carbon materials. Therefore, the four mechanisms of sodium storage are discussed in depth, and the latest research progress on effectively improving the electrochemical performance of coal-based hard carbon anodes is comprehensively introduced. The above include coal selection, heteroatom incorporation, pore adjustment, soft and hard carbon compounding. Additionally, personal insights are provided on the challenges and issues faced by coal-based hard carbon materials in this review,thereby offering useful guidance for the development of high-end advanced energy storage electrode materials and the formulation of design rules to promote the industrialization of SIBs.