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.