Uniquely structured quaternary metal oxide polyhedra as efficient anode materials for lithium-ion batteries

Yolk–shell materials have been synthesized by various techniques including the sacrificial carbon template method and spray process, in which the carbon template was formed as an intermediate product. Here, uniquely structured quaternary transition metal oxide (TMO) polyhedra are synthesized by applying a zinc-doped carbon (Zn–C) template derived from a metal-organic framework (ZIF-8). Infiltration of Co, Ni, and Fe salts into the Zn–C template followed by oxidation produces quaternary TMO polyhedra with yolk–shell structures. Yolk–shell (Co_0.5Ni_0.5)Fe₂O₄–ZnO (denoted as YS-qTMOs) polyhedra with and without carbon-coating layer exhibit excellent cycling performances over 300 cycles. The 300th discharge capacity of the carbon-coated YS-qTMOs (denoted as YS-qTMOs/C) at a current density of 0.5 A g⁻¹ is as high as 774 mA h g⁻¹, while their reversible discharge capacity at a high current density of 8 A g⁻¹ is 463 mA h g⁻¹. The thin carbon coating layer improves the capacitive contribution of the YS-qTMOs/C electrode. The high capacitive contribution implies rapid lithium-ion transport kinetics, affording the excellent rate performance of the YS-qTMOs/C electrode. The synergetic effect of the unique structure with the void volume, quaternary composition, and thin carbon coating layer affords high lithium-ion storage performances of YS-qTMOs/C.