Uniquely structured iron hydroxide-carbon nanospheres with yolk-shell and hollow structures and their excellent lithium-ion storage performances

Rationally designed transition metal compound-carbon composites have been widely studied as anode materials for high-efficiency alkali metal-ion batteries. In this study, iron hydroxide-carbon composite nanospheres with yolk-shell and hollow structures were successfully synthesized by a facile in-situ precipitation method using NaOH solution to confirm the effects of morphological control as well as compositing with carbon material on the electrochemical properties for lithium-ion storage. To prepare the yolk-shell and hollow structured iron nitrate-carbon composite precursor nanospheres, “vacuum heat-treatment” and “drop-and-dry” processes were employed, respectively. The graphitic carbon matrix and internal void space provided electronic conductivity and structural durability, respectively, during the repeated discharge and charge processes. Correspondingly, when applied as anodes for lithium-ion batteries, the yolk-shell and hollow structured iron hydroxide-carbon nanospheres delivered extraordinary rate performances and long-term cycle stabilities, revealing reversible discharge capacities of 504 and 442 mA h g⁻¹ for 400 cycles at a current density of 5 A g⁻¹, respectively. In addition, based on the results of various in-situ and ex-situ analyses, the reversible conversion reaction of iron hydroxide with lithium ions could be approximated by the following reaction: Fe(OH)₃ + 3Li⁺ + 3e⁻ ↔ Fe + 3Li(OH).