Abstract: Carbonaceous materials for lithium (Li)/sodium (Na)-ion batteries have attracted significant attention because of their widespread availability, renewable nature, and low cost. During the past decades, although great efforts have been devoted to developing high-performance carbonaceous materials with high capacity, long life span, and excellent rate capability, the low initial Coulombic efficiency (ICE) of high-capacity carbonaceous materials seriously limits their practical applications. Various methods have been successfully exploited, and a revolutionary impact has been achieved through the utilization of different techniques. Different carbonaceous materials possess different ion storage mechanisms, which means that the initial capacity loss may vary. However, there has rarely been a special review about the origins of and progress in the ICE for carbonaceous materials from the angle of the crystal structure. Hence, in this review, the structural differences between and ion storage mechanisms of various carbonaceous materials are first introduced. Then, we deduce the correlative factors of low ICE and thereafter summarize the proposed strategies to address these issues. Finally, some challenges, perspectives, and future directions on the ICE of carbonaceous materials are given. This review will provide deep insights into the challenges of improving the ICE of carbonaceous anodes for high-energy Li/Na-ion batteries, which will greatly contribute to their commercialization process.Carbonaceous materials for lithium (Li)/sodium (Na)-ion batteries have attracted significant attention because of their widespread availability, renewable nature, and low cost. During the past decades, although great efforts have been devoted to developing high-performance carbonaceous materials with high capacity, long life span, and excellent rate capability, nevertheless the low initial Coulombic efficiency (ICE) of high capacity carbonaceous materials seriously limits their practical applications. Various methods have been successfully exploited and a revolutionary impact has been achieved through the utilization of different techniques. It is well known that different carbonaceous materials possess different ion storage mechanisms, which means the initial capacity loss may vary. However, there has rarely been a special review about the origins and progress of ICE for carbonaceous materials from the angle of crystal structure. Hence, in this review, the structural differences and ion storage mechanisms between various carbonaceous materials are particularly introduced firstly. And then, we conclude the correlative factors of low ICE, and thereafter summarize the proposed strategies to address these issues. Finally, some challenges, perspectives, and future directions on the ICE of carbonaceous materials have been given. This review will provide deep insights into the challenges of improving the ICE of carbonaceous anodes for high-energy Li/Na-ion batteries, which will greatly contribute to their commercialization process.

Key words: Lithium/sodium-ion batteries, Initial Coulombic efficiency, Carbonaceous materials, Energy storage