Metal-organic frameworks derived porous core/shellCoP@C polyhedrons anchored on 3D reduced graphene oxide networks as anode for sodium- ion battery

A novel strategy is developed to synthesize metal-organic framework (MOF) derived core/shell structured CoP@ C polyhedrons anchored on 3D reduced grapheme oxide (RGO) on nickel foam (NF) as binder-free anode for high performance sodium-ion battery, through an in-situ low-temperature phosphidation process from ZIF-67 derived core/shell Co@C polyhedral structures. The unique CoP@C-RGO-NF binder-free anode exhibits a remarkable electrochemical performance with outstanding cycling stability and high rate capability, delivering a specific capacity of 473.1 mA h g(-1) at a current density of 100 mA g-1 after 100 cycles. The excellent properties can be attributed to synergistic effects between core/shell CoP@C polyhedrons and RGO networks. The unique core/shell CoP@C polyhedrons can offer more electrode/electrolyte contact area and reduce the diffusion distance of Na+, while carbon layer shell can enhance electronic conductivity and buffer volume change, and prevent CoP from pulverization and aggregation. Furthermore, 3D RGO networks can provide adequate surface areas for a high loading content of CoP and enhance charge transfer kinetics. Meanwhile, RGO/NF can efficiently act as a binder and electrical conductor to interconnect the separate CoP@C polyhedrons. The present strategy for CoP@C-RGO-NF architectures can be extended to other novel electrodes for high performance energy storage devices.