Effect of pyrolysis temperature of 3D graphene/carbon nanotubes anode materials on yield of carbon nanotubes and their electrochemical properties for Na-ion batteries

A novel graphene/carbon nanotube (GN-CNT) hybrid was synthesized by thermal pyrolysis of urea on the surface of graphene at 800, 900 and 1000 degrees C. The effects of pyrolysis temperature on yield of carbon nanotubes and electrochemical properties of the GN-CNT hybrid were investigated carefully. The production rate of pyrolysis gas was increased as temperature rising. The GN-CNT hybrid reached the largest surface area and the generation of a mass of pores at the pyrolysis temperature of 900 degrees C due to the carbon nanotubes cracking during pyrolysis at 1000 degrees C. The properties of favorable 3D architecture, the generation of a mass of pores during the release of carbon nitride gases and outstanding mechanical flexibility, showed pronounced effects on the fast and steady transfer of electrons and sodium-ion. Consequently, the GN-CNT hybrid pyrolysized at 900 degrees C exhibit a very high reversible capacity of up to 269.14 mAh g(-1) after 100 cycles at a current density of 300 mA g(-1). Even up to 5 A g(-1), a rate capacity of 19537 mA h g(-1) can be obtained after 700 cycles. (C) 2017 Elsevier B.V. All rights reserved.