FeCo-Nx encapsulated in 3D interconnected N-doped carbon nanotubes for ultra-high performance lithium-ion batteries and flexible solid-state symmetric supercapacitors

Lithium-ion batteries and supercapacitors represent the predominant electrochemical power sources and energy storage devices. High-capacity and long-life electrode materials are essential for the next-generation lithium-ion batteries (LIBs) and supercapacitors (SCs) with high power density and high energy density. Herein, FeCo-Nx doped hollow shelled polyhedrons excessively covered with a 3D network of carbon nanotubes (FeCo-N-x@CNTs) have been successfully developed and investigated as one of the most promising materials for lithium-ion batteries and supercapacitors. We developed a self-template strategy to synthesize a series of FeCo-Nx@CNTs via one step carbonization process of Fe doped ZIF-67 MOF. Such a FeCo-Nx doped 3D network of carbon nanotubes effectively tolerates the volume strain and prevents the metal nanoparticles aggregation. In the interim, the 3D network of porous N-doped carbon nanotubes agrees fast electron transport to accomplish remarkably excellent rate capability. Consequently, the FeCo-N-x@CNTs-1.5 shows excellent electrochemical activity for Li-ion hopping in LIBs and SCs. Additionally, this effort also unveils the synergistic effect of the iron doping on the Li-ion storage capability.