Coordination Polymers-Derived Three-Dimensional Hierarchical CoFeO Hollow Spheres as High-Performance Lithium Ion Storage.

Hierarchical CoFeO (CFO) hollow spheres were successfully synthesized via solvothermal method and calcination treatment. The obtained CFO completely inherited the hollow structure and spherical morphology of its precursor of cobalt-based ferrocenyl coordination polymers (Co-Fc-CPs). The three-dimensional (3D) porous hierarchical hollow structure can not only promote the permeation of electrolyte and shorten the lithium-ion transfer distance but also provide a cushion for the volume change during insertion/extraction of lithium ions. To improve the electrochemical properties, the CFO was combined with two forms of carbonaceous materials to controllably obtain 3D CoFeO@C (CFO@C) and CoFeO@reduced graphene oxide (CFO@rGO) composites. Compared with bare CFO and CFO@C, CFO@rGO exhibited a superior electrochemical performance, achieving a high specific capacity of 933.1 mA h g at a current density of 100 mA g after 100 cycles and showing an outstanding cycling life with a capacity of 615.6 mA h g at 1000 mA g after 600 cycles. In situ X-ray diffraction technique was applied to investigate the lithium storage mechanism during discharge/charge processes. This work provides a new approach to prepare hierarchical hollow bimetallic oxides composites for lithium-ion anode materials.