Superimposed effect of hollow carbon polyhedron and interconnected graphene network to achieve CoTe₂ anode for fast and ultralong sodium storage

Owing to the high trap density, large ionic radius, and unique crystal structure, CoTe₂ shows great potential as anodes for sodium storage. However, the intrinsic poor electronic conductivity and large volume variation of CoTe₂ during the charge-discharge process result in inferior electrochemical performance. Herein, three-dimensional hollow porous carbon dodecahedron composed of CoTe₂ microparticles on reduced graphene oxide (rGO) nanosheets (denoted as CoTe₂@3DG) is prepared by coordination regulation between rGO and Co-MOF (ZIF-67) and subsequent tellurization reaction. The CoTe₂@3DG hybrids combine the synergistic advantages of the double-carbon skeleton and provide efficient volume expansion space of CoTe₂ nanoparticles throughout cycling to realize excellent electrochemical capability. The electrochemical analysis and in-situ X-ray diffraction measurement reveal the fast electrons/sodium-ions transfer kinetics and phase evolution mechanism for sodium storage. Thus, the CoTe₂@3DG hybrids display an excellent cycling stability (∼103 mAh g⁻¹ is maintained after 4500 cycles at 1.0 A g⁻¹) as well as excellent rate capability (135 mAh g⁻¹ at 5.0 A g⁻¹). This work proposes a simple and facile double-carbon-encapsulation technique for improving sodium storage performance in anode materials with conversion mechanisms.