In-situ growth of V-shaped CoSe2 nanorods on graphene with C-Co bonding for high-rate and long-life sodium-ion batteries

A new V-shaped CoSe2 nanorods @ Graphene (GR) nanocomposite has been prepared by using a simple one-step hydrothermal method. The V-shaped CoSe2@GR shows the enhanced electrochemical properties compared to pure hierarchical urchin-like CoSe2 microspheres. When acting as an anode material of sodium-ion battery (SIBs), the CoSe2@GR electrode delivers an initial capacity of 549.4 mAh g(-1) with a high coulomb efficiency of 91.5% at 0.1 A g(-1), and high capacity retention of 93.1% (about 327.7 mAh g(-1)) after 1500 cycles at 2 A g(-1). Strong coupling in the hybrid interface through the C-Co bond between CoSe2 and GR can increase the mechanical strength of CoSe2@GR and buffer the volume expansion caused by sodiation-desodiation process. Moreover, a kinetic analysis demonstrated the high rate of pseudocapacitance contributions support its excellent rate performance. And a series of systematic ex-situ characterizations and detailed analysis confirm a mixed intercalation-conversion reaction mechanism of CoSe2 + 2Na(+) + 2e(-) <-> Na2CoSe2 and Na2CoSe2 + 2Na(+) + 2e(-) <-> Co + 2Na(2)Se. (C) 2019 Elsevier B.V. All rights reserved.