Fabrication of β-CoV₃O₈ nanorods embedded in graphene sheets and their application for electrochemical charge storage...

The fabrication of β-CoV₃O₈ nanorods embedded in graphene sheets and their application as electrochemical charge storage electrodes is reported. From the surfactant treatment of raw graphite, graphene was directly prepared and its nanocomposite with β-CoV₃O₈ nanorods distributed between graphene layers (β-CoV₃O₈-G) was synthesized by a hydrothermal method. When applied as an anode in lithium-ion batteries, the β-CoV₃O₈-G anode exhibits greatly improved charge and discharge capacities of 790 and 627 mAh · g^-1, respectively, with unexpectedly high initial efficiency of 82%. The observed discharge capacity reflected that at least 3.7 mol of Li⁺ is selectively accumulated within the β-CoV₃O₈ phase (Li_xCoV₃O₈, x > 3.7), indicative of significantly improved Li⁺ uptake when compared with aggregated β-CoV₃O₈ nanorods. Moreover, very distinct peak plateaus and greatly advanced cycling performance are observed, showing more improved Li⁺ storage within the β-CoV₃O₈ phase. As a supercapacitor electrode, moreover, our composite electrode exhibits very high peak pseudocapacitances of 2.71 F · cm^-2 and 433.65 F · g^-1 in the β-CoV₃O₈ phase with extremely stable cycling performance. This remarkably enhanced performance in the individual electrochemical charge storage electrodes is attributed to the novel phase formation of β-CoV₃O₈ and its optimized nanocomposite structure with graphene, which yield fast electrical conduction through graphene, easy accessibility of ions through the open multilayer nanosheet structure, and a relaxation space between the β-CoV₃O₈-G.