Anode Materials of Sodium‐ion Batteries

Anodes, as the primary member of capacity contributions, have captured numerous attentions. Series of materials have been regarded as promising candidates. Up to now, carbon and metal-based samples have been successfully applied in energy-storage systems. Based on their redox mechanisms, they could be divided into four kinds: (i) insertion-type materials, (ii) conversion-type materials, (iii) alloying-type materials, and (iv) mixing-type materials. Among them, insertion-type materials could induce the stable storage of energy through the insertion behaviors of ions, accompanied by stable structure. And, it could be found that numerous layer materials and space-type samples have been applied due to the larger storage accommodation region, such as carbon, TiO 2 , and MoO 3 . Meanwhile, metal-based samples have been always deemed as conversion-type samples, such as metal-oxides, metal-sulfides, metal-selenides, and other metal-based samples. And the anions serve as the energy-storage elements, mainly contributing to the ion-storage capacity. Of course, similar to conversion-type materials, alloying materials displayed enormous potential, mainly ascribed to the relatively high capacity (like Sn, Sb, and so on). Thus, the illustration of advanced anodes was necessary for further exploring about sodium-ion batteries (SIBs).