Pomegranate Clusters of N-Doped Carbon-Coated CoO_x Supported on Graphene as a Flexible Lithium-Ion Battery Anode

Due to the large reversible capacities, transition-metal oxides have received a lot of interest as anodes for lithium-ion batteries. However, their poor electrical conductivity and dramatic volume change prevent them from being widely used in lithium-ion batteries. In this study, we present a double protection strategy by fabricating a pomegranate-like N-doped carbon-coated CoOx clusters supported on three-dimensional (3D) graphene framework structure (NC@CoOx@GF) to improve the electrochemical performance of CoOx in lithium storage. The hierarchical structure is constructed by the thermal transformation of Co-MOF to CoOx with N-doped carbon/graphene by using polyaniline-coated metal–organic framework (Co-MOF)/graphene oxide as precursors. The pomegranate clusters coupled with porous CoOx induced by the partial thermal collapse of the MOF with N-doped carbon were derived from polyaniline and 3D high-conductivity graphene frameworks. The confinement of the clusters effectively relieves the volume expansion of CoOx and significantly shortens the transport paths of electrons and ions in the composite. The robust 3D graphene frameworks further offer highly interpenetrated conductive networks. Therefore, the flexible NC@CoOx@GF anode delivered a high capacity (at 0.1 A g–1, 1153 mA h g–1), excellent rate performance (at 8 A g–1, 337 mA h g–1), and superlong cycling stability (66.4% capacity retention after 2500 cycles at 1000 mA g–1).